US3864970A

US3864970A - Methods and apparatus for testing earth formations composed of particles of various sizes

Info

Publication number: US3864970A
Application number: US407690A
Authority: US
Inventors: William T Bell
Original assignee: Schlumberger Technology Corp
Current assignee: Schlumberger Technology Corp
Priority date: 1973-10-18
Filing date: 1973-10-18
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11
Also published as: CA1009570A

Abstract

In the representative embodiments of the new and improved methods and apparatus disclosed herein for testing earth formations of differing compositions, fluid-admitting means carrying a selectively-sized filter of a unique design are selectively extended into sealing engagement with a potentiallyproducible earth formation and operated so as to establish communication with the isolated formation without the fluidadmitting means being plugged with mudcake from the formation wall. Should, however, loose formation materials enter the fluidadmitting means as the testing is conducted, the filter is uniquely arranged to collect these loose materials and halt the further erosion of such materials from the formation wall so as to assure continued communication with the isolated formation.

Description

United States Patent [1 1 Bell [451 Feb. 11, 1975 METHODS AND APPARATUS FOR TESTING EARTH FORMATIONS COMPOSED OF PARTICLES OF VARIOUS SIZES William T. Bell, Houston, Tex.

Schlumberger Technology Corporation, New York, NY.

Oct. 18, 1973 Inventor:

Assignee:

Filed:

App]. No.:

[52] US. Cl 73/155, 73/421 R, 166/264 [58] Field of Search 73/155, ll, 421 R;

References Cited UNITED STATES PATENTS 6/1965 Briggs, Jr. 73/155 7/l972 Hallmark 73/155 Primary Examiner- -Jerry W. Myracle Attorney, Agent, or Firm-Ernest R. Archambeau, Jr.; William R. ShermamStewart F. :Moore Int. Cl E2lb 49/04 [57] ABSTRACT lect these loose materials and halt the further erosion of such materials from the formation wall so as to assure continued communication with the isolated formation. v

34 Claims, 11 Drawing Figures 54 LI I 55 7 55 PATENIEU E U S M 3.864.970

sum nor 7 METHODS AND APPARATUS FOR TESTING EARTH FORMATIONS COMPOSED OF PARTICLES OF VARIOUS SIZES Until very recently, the so-called wireline formation testers, which have been most successful in commercial service have, for the large part, been limited to attempting only a single test or, at best, two tests of selected earth formations. Generally, the success of these tests has depended to some extent upon knowing in advance the general character of the particular formations which were to be tested so that the tester could be equipped as required to test a formation of a given nature.

For example, where the formations to be tested were considered to be fairly competent and, therefore, not easily eroded, testers such as that shown in US. Pat. No. 3,01 1,554 have been highly effective. On the other hand, in those situations where tests were to be conducted in fairly incompetent or unconsolidated formations, it has usually been the practice to use new and improved testers such as those shown in US. Pat. No. 3,352,361, US. Pat. No. 3,530,933, US. Pat. No. 3,565,169 or US. Pat. No. 3,653,435. As fully described in these last-mentioned patents, each of those testing tools employs a tubular sampling member which is cooperatively associated with a filtering medium having fluid openings of a selected, but uniform, size for preventing the unwanted entrance of unconsolidated formation materials into the testing tool. Thus, except for dual-purpose tools such as that shown in U.S. Pat.

No. 3,261,402, these typical formation testing tools have been most successful in making tests in formations which are known in advance either to be fairly competent or to be relatively unconsolidated. Moreover, since all of these prior-art testers are operated only once during a single trip into a well bore, it has been customary to simply select in advance the particular size of filter medium believed to be best suited for a given testing operation.

One of the most'significant advances in the formation-testing art has been the recent introduction into commercial service of the new and improved repetitively-operable testers such as fully described in US. Pat. No. 3,780,575. As disclosed there, these tools are capable of repetitively taking any number of pressure measurements from various formations as well as collecting at least two fluid samples during a single trip in a given well bore.

Although these new and improved testers have been quite successful, there are situations where the performance of these testers is significantly affected since no one filtering medium is capable of operating efficiently with every type of earth formation. For instance, if the tester is equipped with a particular filter which is best suited for stopping exceptionally-fine formation materials, the flow rate for this tester will be materially limited where a fairly-competent formation is being tested. More importantly, in situations like this, it is not at all uncommon for the filter to be quickly plugged by the mudcake which usually lines the borehole wall adjacent to a potentially-producible formation. Thus, a test under these conditions will often be inconclusive, if not misleading, since it will not be known for sure whether the formation is truly unproductive or if the filter was simply plugged at the outset of the test. On the other hand, if the tester is then using a filter designed for filtering out only fairly-large loose formation materials, there will often be an excessive induction of very-fine formation materials into the tool where the tool is testing a highly-unconsolidated formation. This will, of course, frequently result in a continued erosion of the formation wall around the sealing pad so that communication with the formation is quickly lost. This also causes an incomplete or inconclusive test.

It will be recognized, of course, that is wholly impractical to change the filter in a repetitively-operable tool of this type between tests of different types of formations in a given borehole. Moreover, there is no assurance that the character of various formations traversed by a given borehole can be reliably determined in advance.

Accordingly, it is an object of the present invention to provide new and improved formation-testing methods and apparatus for reliably obtaining multiple measurements of one or more fluid or formation characteristics as well as for selectively collecting one or more samples of connate fluids, if desired, from different earth formations of any character even where these formations vary in their compositions and competency.

This and other objects of the present invention are attained by providing formation-testing apparatus having fluid-admitting means adapted for selective movement into sealing engagement with a potentiallyproducible earth formation to isolate a portion thereof from the borehole fluids. ln practicing the methods of the present invention for testing a formation, mudcake is first inducted into the fluid-admitting means by way of a first filtering passage selectively sized to readily pass such plugging materials. Then, should incompetent formation materials be drawn into the fluidadmitting means, these materials are collected so as to halt their further erosion from the borehole wall by quickly blocking at least substantial flow through this first passage as well as thereafter directing the flow of connate fluids through a second filter passage selectively sized to be smaller than the formation materials. In the new and improved apparatus of the present invention, the fluid-admitting means are provided with filtering means having one or more enlarged filter passages sized to easily pass large plugging materials such as mudcake particles and one or more reduced filter passages which are sized to screen or retain formation particles of a selected size. In this manner, when the fluid-admitting means are initially placed into communication with an isolated earth formation, mudcake lining the formation wall will be passed through the enlarged filter passages thereby leaving the inlet face of the filtering means free of such plugging materials. Thereafter, should loose formation materials be inducted into the fluid-admitting means, they will be collected in a compact mass along the inlet face of the filtering means so as to effectively block at least significant flow through the enlarged filter passages and direct the flow of producible connate fluids through the reduced filter passages.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following descriptions of the new and improved methods of the present invention as well as various embodiments of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

Flg. 1 depicts the surface and downhole portions of one embodiment of formation-testing apparatus including new and improved fluid-admitting means incorporating the principles of the present invention;

FIG. 2 is an enlarged view ofa preferred embodiment of the new and improved fluid-admitting means shown in FIG. 1;

FIGs. 3A and 3B together show a somewhatschematic representation of the formation-testing tool illustrated in FIG. 1 as the tool will appear in its initial operating position in readiness for practicing the new and improved methods of the invention;

FIGS. 4, 5, 6A and 68 respectively depict the successive positions of various components of the testing tool shown in FIGS. 3A and 38 during the course of a typical testing and sampling operation to illustrate the methods as well as the operation of the new and improved fluid-admitting means of the present invention; and

FIGS. 7-9 schematically illustrate the practice of the methods of the present invention by the new and improved fluid-admitting means with different types of earth formations as well as depict alternative embodiments of filter members which may be employed therewith to achieve the objects of the present invention.

Turning now to FIG. 1 a preferred embodiment of new and improved fluid-admitting means 10 incorporating the principles of the present invention is shown on a formation-testing tool 11 as this tool will appear during the course of a typical measuring and sampling operation in a well bore such as a borehole 12 penetrating one or more earth formations as at 13 and 14. As illustrated, the tool 11 is suspended in the borehole 12 from the lower end of a typical multiconductor cable 15 that is spooled in the usual fashion on a suitable winch (not shown) at the surface and coupled to the surface portion of a tool-control system 16 as well as typical recording-and-indicating apparatus 17 and a power supply 18. In its preferred embodiment, the tool 11 includes an elongated body 19 which encloses the downhole portion of the tool-control system 16 and carries a selectively-extendible tool-anchoring member 20 arranged on one or more piston actuators, as at 21, for movement from the opposite side of the body from the new and improved fluid-admitting means 10 as well as one or more fluid-collecting

chambers

22 and 23 which are tandemly coupled to the lower end of the tool body 19.

As is explained in greater detail in U.S. Pat. No. 3,780,575 which is incorporated by reference herein, the depicted formation-testing tool 11 and its control system 16 are cooperatively arranged so that, upon command from the surface, the tool can be selectively placed in any one or more of five selected operating positions. As will be subsequently described briefly, the control system 16 will function either to successively place the tool 11 in one or more of these positions or else to selectively cycle the tool between various ones of these operating positions. These five operating positions are simply achieved by selectively moving suitable control switches, as schematically represented at 24 and 25, included in the surface portion of the control system 16 to various switching positions, as at 26-31, so as to selectively apply power to different conductors 32-38 in the cable l5.

The new and improved fluid-admitting means 10 of the present invention are cooperatively arranged for selectively sealing-off or isolating selected portions of the wall of the borehole l2; and, once a selected portion of the borehole wall is packed-off or isolated from the borehole fluids, establishing pressure or fluid communication with the adjacent earth formation, as at 13. In the preferred embodiment depicted in FIG. 2, the fluid-admitting means 10 include an elastomeric annular sealing pad 39 mounted on the forward face of an upright support member or plate 40 that is coupled to a longitudinally-spaced pair of laterally-movable piston actuators, as at 41, which are similar to the actuators 21 and are arranged transversely on the tool body 19 for moving the sealing pad back and forth in relation to the forward side of the tool body. Accordingly, as the control system 16 selectively supplies a pressured hydraulic fluid to the piston actuators 4], the sealing pad 39 will be moved laterally between a retracted position adjacent to the forward side of the tool body 19 and an advanced or forwardly-extended position.

By arranging the annular sealing member 39 on the opposite side of the tool body 19 from the toolanchoring member 20 (FIG. 1), the simultaneous extension of these two wall-engaging members will, of course, be effective for urging the sealing pad into sealing engagement with the adjacent wall of the borehole 12 as well as for anchoring the tool 11. It should. however, be appreciated that the tool-anchoring member 20 would not be needed if the effective stroke of the piston actuators 41 is sufflcient for assuring that the sealing pad 39 can be extended into firm sealing engagement with one wall of the borehole 12 with the rear of the tool body 19 securely anchored against the opposite wall of the borehole. Conversely, the piston actuators 21 could be similarly omitted where the extension of the tool-anchoring member 20 alone would be effective for moving the front side of the tool body 19 forwardly toward one wall of the borehole 12 so as to place the sealing pad 39 into firm sealing engagement therewith. However, in the preferred embodiment of the formation-testing tool 11, both the toolanchoring member 20 and the fluid-admitting means 10 are arranged to be simultaneously extended to enable the tool to be operated in boreholes of substantial diameter. This preferred design of the tool 11, of course, keeps the overall stroke of the

piston actuators

21 and 41 to a minimum so as to reduce the overall diameter of the tool body 19.

To conduct connate fluids into the testing tool 11, the fluid-admitting means 10 of the present invention further include an enlarged tubular member 42 having an open forward portion coaxially disposed within the annular sealing pad 39 and a closed rear portion which is slidably mounted within a larger tubular member 43 secured to the rear face of the plate 40 and extended rearwardly therefrom. By arranging the nose of the tubular fluid-admitting member 42 to normally protrude a short distance ahead of the forward face ofthe sealing pad 39, extension of the fluid-admitting means 10 will engage the forward end of the fluid-admitting member with the adjacent surface of the wall of the borehole 12 just before the annular sealing pad is also forced thereagainst for isolating that portion of the borehole wall as well as the nose of the fluid-admitting member from the borehole fluids. The significance of this sequence of engagement will be subsequently explained. To selectively move the tubular fluid-admitting member 42 in relation to the enlarged outer member 43, the smaller tubular member is slidably disposed within the outer tubular member and fluidly sealed in relation thereto as by sealing

members

44 and 45 on inwardly-

enlarged end portions

46 and 47 of the outer member and a sealing member 48 on the enlarged-diameter intermediate portion 49 of the inner member.

Accordingly, it will be appreciated that by virtue of the sealing

members

44, 45 and 48,

enclosed piston chambers

50 and 51 are defined within the outer tubular member 43 and on opposite sides of the outwardlyenlarged portion 49 of the inner tubular member 42 which, of course, functions as a piston member. Thus, by applying an increased hydraulic pressure in the rearward chamber 50, the fluid-admitting member 42 will be moved forwardly in relation to the outer tubular member 43 as well as to the sealing pad 39. Conversely, upon the application of an increased hydraulic pressure to the forward piston chamber 51, the fluid-admitting member 42 will be retracted in relation to the outer member 43 and the sealing pad 39.

Pressure or fluid communication with the new and improved fluid-admitting means of the present invention is preferably controlled by means such as a generally-cylindrical valve member 52 which is coaxially disposed within the fluid-admitting member 42 and cooperatively arranged for axial movement therein between a retracted or open position and the illustrated advanced or closed position where the enlarged forward end 53 of the valve member is substantially, if not altogether, sealingly engaged with the forwardmost interior portion of the fluid-admitting member. To support the valve member 52, the rearward portion of the valve member is axially hollowed, as at 54, and coaxially disposed over a tubular member 55 projecting forwardly from the transverse wall 56 closing the rear end of the fluid-admitting member 42. The axial bore 54 is reduced and extended forwardly along the valve member 52 to a termination with one or more transverse fluid passages 57 in the forward portion of the valve member just behind its enlarged head 53.

To provide actuating means for selectively moving the valve member 52 in relation to the fluid-admitting member 42, the rearward portion of the valve member is enlarged, as at. 58, and outer and inner sealing members 59 and 60 are coaxially disposed thereon and respectively sealingly engaged with the interior of the fluid-admitting member and the exteriorof the forwardly-extending tubular member 55. A sealing member 61 mounted around the intermediate portion of the valve member 52 and sealingly engaged with the interior wall of the adjacent portion of the fluid-admitting member 42 fluidly seals the valve member in relation to the fluid-admitting member. Accordingly, it will be appreciated that by increasing the hydraulic pressure in the enlarged piston chamber 62 defined to the rear of the enlarged valve portion 58 which serves as a piston member, the valve member 52 will be moved forwardly in relation to the fluid-admitting member 42. Conversely, upon application of an increased hydraulic pressure to the forward piston chamber 63 defined between the sealing

members

59 and 61, the valve member 52 will be moved rearwardly along the forwardlyprojecting tubular member 55 so as to retract the valve member in relation to the fluid-admitting member 42.

As previously discussed, it will, of course, be appreciated that many earth formations, as at 13, are relatively unconsolidated and are, therefore, readily eroded by the withdrawal of connate fluids. Thus, to prevent any significant erosion of such unconsolidated formation materials, the fluid-admitting member 42 is arranged to define an internal annular space 64 and a flow passage 65 in the forward portion of the fluid-admitting member. As will subsequently be described in greater detail by reference to FIGS. 7-9, the objects of the present invention are preferably attained by coaxially mounting a tubular filter member 66 (or 66) with slits or apertures therein ofa unique arrangement in the nose of the fluid-admitting member 42 so as to cover the annular space 64. In this manner, when the valve member 52 is retracted from its extended position inside of the filter. formation fluids will be compelled to pass through the now-exposed filter member 66 ahead of the enlarged head 53, into the annular space 64, and then through the fluid passage 65 into the fluid passage 57 and the tubular member 55. Thus, as the valve member 52 is retracted, should loose or unconsolidated formation materials be eroded from a formation as connate fluids are withdrawn therefrom, the materials will be stopped by the uniquely-arranged filter 66 ahead of the en- I larged head 53 of the valve member thereby quickly forming a permeable barrier to prevent the continued erosion of loose formation materials once the valve member halts.

Turning now to FIGS. 3A and 3B, the new and improved fluid-admitting means 10 as well as the entire downhole portion of the control system 16, the toolanchoring member 20, and the fluid-collecting

chambers

22 and 23 are schematically illustrated with their several elements or components depicted as they will respectively be arranged when the tool 11 is fully retracted and the control switches 24 and 25 are in their first or off operating positions 26 (FIG. 1). Since the aforementioned U.S. Pat. No. 3,780,575 fully describes the control system 16 and various components of the tool 11, it is believed adequate to simply cover only the major aspects of this system.

A sample or flow line 67 is cooperatively arranged in the formation-testing tool 11 and has one end coupled, as by a flexible conduit 68, to the fluid-admitting means 10 and its other end terminated in a pair of

branch conduits

69 and 70 respectively coupled to the fluidcollecting chambers'22 and 23. To control fluid communication between the new and improved fluidadmitting means 10 and the fluid-collecting

chambers

22 and 23, normally-closed flow-control valves 71-73 of a similar or identical design are arranged respectively in the flow line 67 and in the

branch conduits

69 and 70 leading to the sample chambers. For reasons which will subsequently be described, a normally-open control valve 74 which is preferably similar to the normally-closed control valves 71-73 is cooperatively arranged in a branch conduit 75 for selectively controlling communication between the borehole fluids exterior of the tool 11 and the upper portion of the flow line 67 and the flexible conduit 68 extending between the flow-line control valve 71 and the new and improved fluid-admitting means 10.

As illustrated, the normally-open control valve 74, for example, is operated by a typical pressureresponsive actuator 76 which is arranged to close the valve in response to an actuating pressure of at least a predetermined magnitude. As fully described in the aforementioned U.S. Pat. No. 3,780,575, a spring biasing the control valve 74 to its open position is cooperatively arranged to establish the magnitude of the pressure required to close the valve. Furthermore, the normally-closed control valves 71-73 are preferably similar to the control valve 74 except that they are respectively operated by pressure-responsive actuators 77-79 selectively arranged to open these valves in response to pressures of different predetermined magnitudes.

in the particular embodiment of the testing tool 11 shown in FIGS. 3A and 38, a branch conduit 80 is coupled to the flow line 67 at a convenient location between the sample-

chamber control valves

72 and 73 and the flow-line control valve 71, with this branch conduit being terminated at an expansion chamber 81 of a predetermined volume. A reduced-diameter displacement piston 82 is operatively mounted in the chamber 81 and arranged to be moved between selected upper and lower positions therein by a typical piston actuator shown generally at 83. Accordingly, it will be appreciated that upon movement of the displacement piston 82 from its lower position as illustrated in FIG. 3A to an elevated or upper position, the combined volume of whatever fluids that are then contained in the branch conduit 80 as well as in that portion of the flow line 67 between the flow-line control valve 71 and the sample-

chamber control valves

72 and 73 will be correspondingly increased.

As best seen in FIG. 3A, the control system 16 further includes a pump 84 that is coupled to a driving motor 85 and cooperatively arranged for pumping a suitable hydraulic fluid such as oil or the like from a reservoir 86 into a discharge or outlet line 87. Since the tool 11 is to be operated at extreme depths in boreholes, as at 12, which typically contain dirty and usually corrosive fluids, the reservoir 86 is preferably arranged to totally immerse the pump 84 and the motor 85 in the clean hydraulic fluid. The reservoir 86 is also provided with a spring-biased isolating piston 88 for maintaining the hydraulic fluid at a pressure about equal to the hydrostatic pressure at whatever depth the tool is then situated as well as accommodating volumetric changes in the hydraulic fluid which may occur under different borehole conditions. one or more inlets, as at 89 and 90, are provided for returning hydraulic fluid from the control system 16 to the reservoir 86 during the operation of the tool 11.

The fluid outlet line 87 is divided into two major branch lines which are respectively designated as the set line 91 and the retract line 92. To control the admission of hydraulic fluid to the set and retract

lines

91 and 92, a pair of normally-

closed solenoidactuated valves

93 and 94 are cooperatively arranged to selectively admit hydraulic fluid to the two lines as the control switch 24 at the surface is selectively positioned; and a typical check valve 95 is arranged in the set line 91 downstream of the control valve 93 for preventing the reverse flow of the hydraulic fluid whenever the pressure in the set line is greater than that then existing in the fluid outlet line 87. Typical pressure switches 96-98 are cooperatively arranged in the set and retract

lines

91 and 92 for selectively starting and stopping the pump 84 as required to maintain the line pressure within a selected operating range. Since the pump 84 is preferably a positive-displacement type to achieve a rapid predictable rise in the operating pressures in the set and retract

lines

91 and 92, each time the pump is to be started the control system 16 also functions to temporarily open the control valve 94 (if it is not already open) as well as a third normally-closed solenoid-actuated valve 99 for bypassing hydraulic fluid directly from the output line 87 to the reservoir 86 by way of the return line 89. Once the motor has reached operating speed, the bypass valve 99 will, of course, be reclosed and either the set line control valve 93 or the retract line control valve 94 will be selectively opened as required for that particular operational phase of the tool".

Accordingly, it will be appreciated that the control system 16 cooperates for selectively supplying pressured hydraulic fluid to the set and retract

lines

91 and 92. Since the pressure switches 96 and 97 respectively function only to limit the pressures in the set and retract lines to a selected maximum pressure range commensurate with the rating of the pump 84, the control system 16 is further arranged to cooperatively regulate the pressure of the hydraulic fluid which is being supplied at various times to selected portions of the system. Although this regulation can be accomplished in different manners, it is preferred to employ a number of pressure-actuated control valves such as those shown schematically at 100-103 in FIGS. 3A and 3B for controlling the hydraulic fluid in the control system 16. As shown in FlG. 3A, the hydraulic control valve 100, for example, includes a valve body 104 having an enlarged upper portion carrying a downwardly-biased actuating piston 105 which is cooperatively coupled to a valve member 106 as by an upright stem 107 thereon which is slidably disposed in an axial bore 108 in the piston. A spring 109 of selected strength is disposed in the axial bore 108 for normally urging the valve member 106 into seating engagement.

In its non-actuated position depicted in FIG. 3A, the control valve 100 (as well as the valve 101) will, therefore, simply function as a normally-closed check valve. That is to say, in this operating position, hydraulic fluid can flow only in a reverse direction whenever the pressure at the valve outlet is sufficiently greater than the inlet pressure to unseat the valve member 106 against the predetermined closing force imposed by the spring 109. On the other hand, whenever the actuating piston 105 is elevated by the application of hydraulic pressure thereto, opposed shoulders, as at 110, on the stem 107 and the piston 105 will engage for unseating the valve member 106. As shown in FIGS. 3A and 38, it will be appreciated that the control valve 102 (as well as the valve 103) is similar to the control valve 100 except that in these first-mentioned control valves, the valve member, as at 111, is preferably rigidly coupled to its associated actuating piston, as at 112. Thus, the control valve 102 (as well as the valve 103) has no alternate checking action allowing reverse flow but is simply a normally-closed pressure-actuated valve for selectively controlling fluid communication between its inlet and outlet ports.

The set line 91 downstream of the check valve 95 is comprised of a low-pressure section 113 having one branch 114 coupled to the fluid inlet of the control valve 102 and another branch 115 which is coupled to the fluid inlet of the hydraulic control valve 100 to selectively supply hydraulic fluid to a high-pressure section 116 of the set line which is itself terminated at the fluid inlet of the hydraulic control valve 103. To regulate the supply of hydraulic fluid from the low-pressure section 113 to the high-pressure section 116 of the set line 91, a pressure-communicating line 117 is coupled between the low-pressure section and the control port of the hydraulic control valve 100. Accordingly, so long as the pressure of the hydraulic fluid in the lowpressure section of the set line 91 remains below the predetermined actuating pressure required to open the hydraulic control valve 100, the high-pressure section 116 will be isolated from the low-pressure section 113. Conversely, once the hydraulic pressure in the lowpressure line 113 reaches the predetermined actuating pressure of the valve 100, the hydraulic control valve will open to admit the hydraulic fluid into the highpressure line 116.

The

hydraulic control valves

102 and 103 are respectively arranged to selectively communicate the lowpressure and high-

pressure sections

113 and 116 of the set line 91 with the fluid reservoir 86. To accomplish this, the control ports of the two

hydraulic control valves

102 and 103 are each connected to the retract line 92 by suitable pressure-communicating

lines

118 and 119. Thus, whenever the pressure in the retract line 92 reaches their respective predetermined actuating levels, the

hydraulic control valves

102 and 103 will be respectively opened to selectively communicate the two

sections

113 and 116 of the set line 91 with the reservoir 86 by way of the return line 89 coupled to the respective outlets of the two control valves.

As previously mentioned, in FIGS. 3A and 3B the tool 11 and the sub-surface portion of the control system 16 are depicted as their several components will appear when the tool is retracted. At this point, the tool-anchoring member 20 and the sealing pad 39 are respectively retracted against the tool body 19 to facilitate passage of the tool 11 into the borehole 12. To prepare the tool 11 for lowering into the borehole 12, the

switches

24 and 25 are moved from their first or off positions 26 to their second or initialization positions 27. At this point, the hydraulic pump 84 is started to raise the pressure in the retract line 92 to a selected maximum to be certain that the pad 39 and the toolanchoring member 20 are fully retracted. At this time, the pressure-equalizing valve 74 is open and that portion of the flow line 67 between the closed flow-line control valve 71 and the fluid-admitting means will be filled with borehole fluids as the tool 11 is being lowered into the borehole 12.

When the tool 11 is at a selected operating depth, the

switches

24 and 25 are advanced to their third positions 28. Then, once the pump 84 has reached its rated operating speed, the hydraulic pressure in the output line 87 will rapidly rise to its selected maximum operating pressure as determined by the maximum or off setting of the pressure switch 96. As the pressure progressively rises, the control system 16 will successively function at selected intermediate pressure levels for sequentially operating the several control valves 71-74 and 100-103 in an operating cycle such as the one described fully in the aforementioned US. Pat. No. 3,780,575. It must, however, be recognized that the forthcoming particular operational sequence of the tool 11 as illustrated is not essential to either the practice of the methods of the present invention or the successful operation of the new and improved fluidadmitting means 10. Those skilled in the art will, therefore, understand that the present invention can be practiced either with different types of formationtesting tools or with different arrangements of the tool 11 and the control system 16.

Turning now to FIG. 4, selected portions of the control system 16 and various components of the tool 11 are schematically represented to illustrate the operation of the illustrated embodiment of the tool at about the time that the pressure in the hydraulic output line 87 reaches its lowermost intermediate pressure level. To facilitate an understanding of the operation of the tool 11 and the control system 16 at this point in the operating cycle illustrated in the several drawings, only those components which are then operating are shown in FIG. 4.

At this time, since the control switch 24 (FIG. 1) is in its third position 28, the

solenoid valves

93 and 99 will be open; and, since the hydraulic pressure in the set line 91 has not yet reached the upper pressure limit as determined by the pressure switch 96, the pump motor will still be operating. Since the hydraulic control valve 100 (not shown in FIG. 4) is closed, the highpressure section 116 of the set line 91 will still be isolated from the low-pressure section 113. Simultaneously, the hydraulic fluid contained in the forward pressure chambers of the

piston actuators

21 and 41 will be displaced (as shown by the arrows as at 120) to the retract line 92 and returned to the reservoir 86 by way of the open solenoid valve 99. These actions will, of course, cause the tool-anchoring member 20 as well as the sealing pad 39 to be respectively extended in opposite lateral directions until each has moved into firm engagement with the opposite sides of the borehole 12.

It will be noticed in FIG. 4 that hydraulic fluid will be admitted by way of branch

hydraulic lines

121 and 122 to the enclosed annular chamber 50 to the rear of the enlarged-diameter portion 49 of the fluid-admitting member 42. At the same time, hydraulic fluid from the piston chamber 51 ahead of the enlarged-diameter portion 49 will be discharged by way of branch

hydraulic lines

123 and 124 to the retract line 92 for progressively moving the fluid-admitting member 42 forwardly in relation to the sealing member 39 until the nose of the fluid-admitting member engages the wall of the borehole 12 and then halts. The sealing pad 39 is then urged forwardly in relation to the now-halted tubular member 42 until the pad sealingly engages the borehole wall for packing-off or isolating the isolated wall portion from the borehole fluids. In this manner, mudcake immediately ahead of the fluid-admitting member 42 will be displaced radially away from the nose of the fluid-admitting member so as to minimize the quantity of unwanted mudcake which will subsequently be admitted into the fluid-admitting means 10. Those skilled in the art will appreciate the significance of this unique arrangement.

It should also be noted that although the pressured hydraulic fluid is also admitted at this time into the forward piston chamber 63 between the sealing

members

59 and 61 on the valve member 52, the valve member is temporarily prevented from moving rearwardly in relation to the inner and outer

tubular members

42 and 55 inasmuch as the hydraulic control valve 101 (not shown in FIG. 4) is preferably still closed thereby temporarily trapping the hydraulic fluid in the rearward piston chamber 62 to the rear of the valve member. The purpose of this delay in the retraction of the valve member 52 will be subsequently explained.

As also illustrated in FIG. 4, the hydraulic fluid in the low-pressure section 113 of the set line 91 will also be directed by way of a branch hydraulic line 125 to the piston actuator 83. This will, of course, result in the displacement piston 82 being elevated as the hydraulic fluid from the piston actuator 83 is returned to the retract line 92 by way of a branch hydraulic conduit 126. As will be appreciated, elevation of the displacement piston 82 in the expansion chamber 81 will be effective for significantly decreasing the pressure initially existing in the isolated portions of the branch line 80 and the flow line 67 between the still-closed flow-line control valve 71 and the still-closed chamber control valves 72 and 73 (not shown in FIG. 4). The purpose of this pressure reduction will be subsequently explained.

Once the tool-anchoring member 20, the sealing pad 39 and the fluid-admitting member 42 have respectively reached their extended positions as illustrated in FIG. 4, it will be appreciated that the hydraulic pressure delivered by the pump 84 will again rise. Then, once the pressure in the output line 87 has reached its second intermediate level of operating pressure, the hydraulic control valve 101 will open in response to this pressure level to now discharge the hydraulic fluid previously trapped in the piston chamber 62 to the rear of the valve member 52 back to the reservoir 86.

As illustrated in FIG. 5, once the hydraulic control valve 101 opens, the hydraulic fluid will be displaced from the rearward piston chamber 62 by way of branch

hydraulic lines

127, 128 and 124 to the retract line 92 as pressured hydraulic fluid from the set line 91 surges into the piston chamber 63 ahead of the enlargeddiameter portion 58 of the valve member 52. This will, of course, cooperate to rapidly drive the valve member 52 rearwardly in relation to the now-halted fluidadmitting member 42 for establishing fluid or pressure communication between the isolated portion of the earth formation 13 and the

flow passages

54 and 57 in the valve member by way of the filter member 66.

Although this is not fully illustrated in FIG. 5, it will be recalled from FIGS. 3A and 38 that the control valves 71-73 are initially closed to isolate the lower portion of the flow line 67 between these valves as well as the branch line 80 leading to the pressure-reduction chamber 81. However, the flow-line pressureequalizing control valve 74 will still be open at the time the hydraulic control valve 101 opens to retract the valve member 52 as depicted in FIG. 5. Thus, as the valve member 52 progressively uncovers the new and improved filtering member 66, borehole fluids at a pressure greater than that of any connate fluids which may be present in the isolated earth formation 13 will be introduced into the upper portion of the flow line 67 and, by way of the flexible conduit member 68, into the rearward end of the tubular member 55. As these highpressure borehole fluids pass into the annular space 64 around the filtering member 66, they will be forcibly discharged (as shown by the arrows 129) from the forward end of the fluid-admitting member 42 for washing away any plugging materials such as mudcake or the like which may have become deposited on the internal surface of the filtering member when it is first uncovered by the retraction of the valve member 52. Thus, the particular embodiment of the control system 16 illustrated in the drawings is operative for providing a momentary outward surge or reverse flow of borehole fluids for cleansing the filtering member 66 of unwanted debris or the like before a sampling or testing operation is commenced. This is, however, not essential to the successful operation of the new and improved fluid-admitting means 10.

It will be appreciated that once the several components of the formation-testing tool 11 and the control system 16 have reached their respective positions as depicted in FIG. 5, the hydraulic pressure in the output line 87 will again quickly increase to its next intermediate pressure level. Once the pump 84 has increased the hydraulic pressure in the output line 87 to this next predetermined intermediate pressure level, the hydraulic control valve will selectively open as depicted in FIG. 6A. As seen there, opening of the hydraulic control valve 100 will be effective for now supplying hydraulic fluid to the high-pressure section 116 of the set line 91 and two branch conduits and 131 connected thereto for successively closing the pressureequalizing valve 74 and then opening the flow-line control valve 71.

In this manner, as respectively depicted by the several arrows at 132 and 133, hydraulic fluid at a pressure representative of the intermediate operating level will be supplied by way of a typical check valve 134 to the upper portion of the actuator 76 of the normally-open pressure-equalizing valve 74 as fluid is exhausted from the lower portion of the actuator by way of a conduit 135 coupled to the retract line 92. This will, of course, be effective for closing the pressure-equalizing valve 74 so as to now block further communication between the flow line 67 and the borehole fluids exterior of the tool 11. Simultaneously, the hydraulic fluid will also be admitted to the lower portion of the actuator 77 of the flow-line control valve 71. By arranging the actuator 76 for the normally-open pressure-equalizing valve 74 to operate somewhat quicker than the actuator 77 for the normally-closed flow-line control valve 71, the second valve will be momentarily retained in its closed position until the first valve has had time to close. Then, once the pressure-equalizing valve 74 closes, as the hydraulic fluid enters the lower portion of the actuator 77 of the flow-line control valve 71, the latter valve will be opened as hydraulic fluid is exhausted from the upper portion of its actuator through a typical check valve 136 and a branch return line 137 coupled to the retract line 92.

It will be appreciated, therefore, that with the tool 11 in the position depicted in FIGS. 6A and 6B, the flow line 67 is now isolated from the borehole fluids and is in communication with the isolated portion of the earth formation 13 by way of the flexible conduit 68. It will be recalled from the preceding discussion of FIG. 4 that the fluid volumes in the branch flow line 80 as well as the portion of the main flow line 67 between the flowline control valve 71 and the sample-

chamber control valves

72 and 73 were previously expanded by the upward movement of the displacement piston 82 in the reduced-volume chamber 81. Thus, upon opening of the flow-line control valve 71, the isolated portion of the earth formation 13 will be communicated with the reduced-pressure space represented by the previouslyisolated portions of the flow line 67 and the branch conduit 80.

Of particular interest to the present invention, it should be further noted that should the formation 13 be relatively unconsolidated, the rearward movement of the valve member 52 in cooperation with the forward movement of the fluid-admitting member 42 will allow only those loose formation materials displaced by the advancement of the fluid-admitting member into the formation to enter the fluid-admitting member. This is to say, the fluid-admitting member 42 can advance into the formation 13 only by displacing loose formation materials; and, since the space opened within the forward end of the fluid-admitting member by the rearward displacement of the valve member 52 is the only place into which the loose formation materials can enter, further erosion of the formation materials will be halted once the fluid-admitting member has been filled with loose materials as shown at 138 in FIG. 63. On the other hand, should a formation interval which is being tested be relatively well-compacted, the advancement of the fluid-admitting member 42 will be relatively slight with its nose making little or no penetration into the isolated earth formation. It will, of course, be appreciated that the nose of the fluid-admitting member 42 will be urged outwardly with sufficient force to at least penetrate the mudcake which typically lines the borehole walls adjacent to permeable earth formations. In this situation, however, the forward movement of the fluid-admitting member 42 will be unrelated to the rearward movement of the valve member 52 as it progressively uncovers the filtering member 66. In either case, the sudden opening of the valve 52 will cause the plug of mudcake in the nose of the fluid-admitting member 42 to be pulled to the rear of the filter 66. The significance of these actions will be subsequently explained.

As best seen in FIGS. 6A and 68, therefore, should there be any producible connate fluids in the isolated earth formation 13, the formation pressure will be effective for displacing these connate fluids by way ofthe new and improved fluid-admitting means 10 into the flow line until such time that the lower portion of the flow line 67 and the branch conduit 80 are filled and pressure equilibrium is established in the entire flow line. By arranging a typical pressure-measuring transducer, as at 140 (or, if desired, one or more other suitable types of property-measuring transducers) in the flow line 67, one or more measurements representative of the characteristics of the connate fluids and the formation 13 may be transmitted to the surface by a conductor 141 and either indicated or, if desired, recorded on the recording apparatus 17 (FIG. 1). In any event, the pressure measurements provided by the transducer 140 will, of course, permit the operator at the surface to readily determine the formation pressure as well as to obtain one or more indications representative of the potential producing capability of the formation 13. The various techniques for analyzing formation pressures are well known in the art and are, therefore, of no significance to understanding the present invention.

The measurements provided by the pressure transducer 140 at this time will indicate whether the sealing pad 39 has, in fact, established complete sealing engagement with the earth formation 13 inasmuch as the expected formation pressures will be recognizably lower than the hydrostatic pressure of the borehole fluids at the particular depth which the tool 11 is then situated. This ability to determine the effectiveness of the sealing engagement will, of course, allow the operator to retract the tool-anchoring member 20 and the sealing pad 39 without having to unwittingly or needlessly continue the remainder of the complete operating sequence.

Assuming, however, that the pressure measurements provided by the pressure transducer show that the sealing pad 39 is firmly seated, the operator may leave the formation-testing tool 11 in the position shown in FIGS. 6A and 63 as long as it is desired to observe as well as to record the pressure measurements. As a result, the operator can determine such things as the time required for the formation pressure to reach equilibrium as well as the rate of any pressure increase and thereby obtain valuable information indicative of various characteristics of the earth formation 13 such as permeability and porosity. Moreover, with the illustrated embodiment of the tool 11, the operator can readily determine if collection of a fluid sample is warranted.

Before'eontinuing with a description of a complete testing operation it is believed appropriate to now consider the details of the present invention. The significance of the present invention will be best understood with the performance of the new and improved fluidadmitting means 10 while obtaining a pressure measurement or fluid sample is compared to the performance of prior-art formation testers with conventional filtering members. Typically, these prior-art filter members have been an elongated tubular member having. only a plurality of narrow slits ofa uniform width which are disposed either longitudinally along the tubular member or circumferentially around the member. U.S. Pat. No. 3,352,361 is an example of this previous practice. Alternatively, either porous members or finelymeshed screens of a conventional design have often been employed as described, for example, in U.S. Pat. No. 3,653,436. In any case, these prior-art tools have employed conventional filters having only uniformly sized filter openings which are customarily sized as dictated by the particular size of loose formation particles which were expected to be encountered during a given operation.

It has been found, however, that when these prior-art filters are used in soft formations, the pressure drop across the filtering element and the accumulated formation particles will often become so excessive that a fluid sample simply cannot be obtained in a reasonable period of time. This is easily understood when a priorart testing tool such as shown in U.S. Pat. No. 3,653,436 is considered. As shown in FIG. 5 of that pa tent, fluids entering the nose of the sampling tube will be divided into a number of fluid paths, with the shortest path being through the first opening in the filter screen at the forward end of the sampling tube and the longest path theoretically being through the sampling tube and out the rearwardmost opening in the screen. In actuality, however, it has been found that by virtue of the additional flow resistance imposed by the tightlypacked column of finely-divided sand particles which will be trapped in the sampling tube, most, if not all, of the flow will be through the forwardmost openings in the filter screen. Thus, since, at best, little or none of the flow will be through the rearward portions of the screen, the overall flow rate will be drastically curtailed. It should be noted in passing, however, that in this situation, it is unlikely that the filter screen will be entirely plugged by, mudcake since any mudcake initially entering the sampling tube is typically concentrated at the rearward end of the tube and held there by the column of sand since the mudcake particles are too large to pass through filter openings small enough to retain the sand particles. Experience has shown, however, that if the screen openings are slightly oversized so that some sand grains will pass through the front openings, it is not at all uncommon for the sand to gradually erode the filter screen to the point that the screen is no longer effective. Thus, enlargement of the openings to improve the flow rate will often result in rapid failure of the filter.

A more-serious problem is encountered, however, when a prior-art testing tool equipped with a conventional filter having very narrow slits is used to test a fairly competent or hard formation. In this situation, the usual result will be that the mudcake entering the sampling tube will swirl around inside of the tube so that the internal or inlet face of the filter screen will be quickly coated with the mudcake particles thereby plugging the narrow filter openings. Heretofore, the only practical solution to this problem has been to use a screen with the largest-possible openings that will hopefully still trap any loose formation materials which might be encountered. This obviously poses a problem where formations composed of different degrees of hardness or competency are expected to be encountered during a multi-formation testing operation such as is capable of being performed by the tool 11. Thus, if the filter openings are too large, sand will easily pass through the filter screen when unconsolidated formations are tested. On the other hand, if the screen openings are too small, they will be easily plugged by mudcake when hard formations are tested.

The practice of the methods of the present invention as well as the new and improved fluid-admitting means 10 avoids these several problems, however. Accordingly, as best seen in FIGS. 7 and 8, somewhatsimplified enlarged views are respectively shown of the new and improved fluid-admitting means 10 at successive moments during the initiation of a test of an incompetent earth formation, as at 13, which is primarily composed of extremely-fine particles of sand and the like. At the time illustrated in FIG. 7, the various elements of the tool 11 have just been placed in their re spective positions as previously described by reference to FIGS. 6A and 6B. Thus, as previously discussed, upon advancement of the fluid-admitting member 42 into the formation 13, the plug of mudcake 142 in the nose of the fluid-admitting member will be impelled from the wall of the borehole 12 into the tubular member and its interior will be quickly filled with the loose formation materials 138 that are correspondingly displaced into the fluid-admitting member as it penetrates the formation.

As illustrated in FIG. 7, since the plug of mudcake 142 from the wall of the borehole 12 enters the fluidadmitting member 42 ahead of the inrushing formation materials 138, the mudcake will, of course, be carried to the rear of the tubular member as the valve member 52 is moved to the rear of the filter member 66. However, instead of the mudcake plug 142 coming to rest at the rear of the fluid-admitting member 42 as has been the case with prior-art testing tools, the mudcake will be capable of passing through the rearward slits 143 in the screen 66. As will be subsequently described, however, the uniquely-arranged filter member 66 will trap the incoming sand particles so as to quickly form a compacted column of these particles, as at 138.

To accomplish this, the filtering member 66 of the new and improved fluid-admitting means 10 is selectively arranged so that at least the rearwardmost filter openings or slits 143 are individually wider than the forwardmost openings or slits I44. If desired, the intermediately-located slits, as at 145, in the filtering member 66 also can be selectively sized to have a width somewhat less than the width of the rear slits I43 but slightly greater than the width of the forward slits 144. This can, of course, be accomplished in different manners. For example, as shown by the preferred embodiment in FIGS. 7 and 8, the several filter openings are respectively arranged as circumferentially-oriented elongated slits which are disposed in multiple sets of two or three slits around the filter member 66, with the several sets being distributed along almost the full length of the filter member and respectively sized or incrementally graduated so that the rearwardmost slits, as at 143, are selectively wider than the forwardmost slits, as at 144. Alternatively, as shown in somewhat of an exaggerated form in FIG. 9, the filter member 66' could also be arranged with a plurality of elongated longitudinally-oriented slits spaced uniformly around the circumference of the filter member and tapered or progressively graduated so as to have relatively-wide rear portions, as at 143, and relatively-narrow forward portions, as at 144*.

In either manner, during the practice of the methods of the present invention with the tool 11, mudcake, as at 142, which enters the fluid-admitting member 42 at the very outset of the testing operation is capable of freely passing through the enlarged rearward slits 143 (or the rear slit portions 143') and on into the flow line 67. Therefore, as shown in both FIGS. 7 and 9, by virtue of the new and improved methods and apparatus of the present invention mudcake, as at 142, is effectively purged from the interiors of the fluid-admitting member 42 and the filtering member 66 so as to eliminate this mudcake as a source of possibly-plugging materials such as frequently occurs during the testing of fairlycompetent formations, as at 14, in FIG. 9.

It must be recognized, however, that the presence of the enlarged filter openings 143 (or the rearward slit portions 143) presents a potentially-serious problem where the formation, as at 13, is substantially composed of unconsolidated fine materials such as the sand particles 138. As previously discussed, unless the flow of such fine particles into the fluid-admitting member 42 is quickly halted, the isolated wall portion of the unconsolidated formation, as at 13, will be rapidly eroded away to the extent that the sealing pad 39 will no longer be in sealing engagement with the wall of the borehole 12.

Accordingly, as a further significant aspect of the inventive concept of the new and improved methods and apparatus disclosed here, the rear filter openings 143 (or the rearward slit portions 143') are selectively sized so that once a significant number of the rapidlyinrushing sand particles, as at 138, have entered the fluid-admitting member 42, these fine particles will be capable of quickly and reliably bridging the rear openings. This bridging action should, of course, occur by the time the fluid-admitting member 42 is fully extended. Once this bridging occurs, the compacted column of collected sand grains 138 will thereafter serve as an auxiliary filtering medium which will at least significantly reduce, if not completely block, further fluid flow through at least the rearwardmost filter slits 143 (as well as the rearward slit portions 143). It will, of course, be appreciated that the narrower forward slits 144 (as well as the forward slit portions 144) must be selectively sized to positively retain sand particles of a given size under even relatively-high flow rates. On the other hand, although the wider rearward slits 143 (as well as the rear slit portions 143) are sufficiently larger than the forward slits 144 (as well as the front slit portions 144') so as to easily pass mudcake particles at high flow rates, these rearward slits and slit portions cannot exceed a particular width which will reliably create rapid bridging of the entrapped sand particles 138 once the increasing pressure drop across the column of sand particles has effected a significant reduction in the flow rate of fluids passing through these rear slits and slit portions.

To understand the operation of the new and improved fluid-admitting means of the present invention, a description of fluid theory as it relates to the fluid-admitting means is believed in order. With the new and improved fluid-admitting means 10 in the position illustrated in FIG. 7, for example, it will be recognized that if the formation 13 contains producible connate fluids, these fluids can enter the flow line only as fast as these fluids can pass through the fluid-admitting member 42 and the filtering member 66. The total flow rate of these fluids will, as a matter of course, be directly governed by the degree of flow restriction presented by the column of entrapped formation particles I38 and the filtering member 66.

It will be recognized, of course, that the pressure differential between any arbitrary point, as at 146, in the nose of the tubular member 42 and the annular space 64 will be a constant for a given flow situation; and that this overall pressure differential will be a function of the total flow rate, the total restriction presented by the filter member 66, and the total restriction of the column of entrapped formation particles 138. Fluids entering the fluid-admitting member 42 must, of course, divide into a number of flow paths, as at 147-149, in order to pass through the various openings 143-145 along the full length of the filtering member 66 before the fluids recombine in the annular space 64. Thus, for there to be any fluid flow along the rearwardmost flow path 147, for example, the total pressure drop of fluids flowing along that path between the point 146 and the chamber 64 cannot exceed the overall available pressure differential then existing between these two locations.

The total pressure along any one of the several flow paths 147-149 is, of course, the total of each of the partial pressure drops along that path. Thus, for the longest flow path 147, the total pressure drop will be the summation of the pressure drop through the entire columnar length of the entrapped particles 138 and the pressure drop through the rearwardmost openings or slits 143 in the filter member 66. On the other hand, the pressure drop along the shortest path 149 will be the total of the drop through only. the first few of the trapped particles 138 and the drop through the forwardmost openings or slits 144 in the filter member 66. This, of course, means that for any given testing situation with an unconsolidated formation, the entering fluids will be inherently divided proportionally along the several flow paths 147-149, with the flow rate along any one of these flow paths being a function of the combined incremental pressure drops at that flow rate along the length of the path through the column ofsand grains 138 and whichever one of the several slits 143-145 that portion passes through. Since the overall pressure drop along each of these paths 147-149 will be the same for that particular situation, the net result will be that a major percentage of the total flow will be through the forward slits 144, a significant percentage of the flow will perhaps be through the intermediate slits 145, and, at best. only a minor percentage of the flow will be through the enlarged rearward slits 143.

This division of the flow along the several flow paths 147-149 is, therefore, a critical aspect of the present invention. As previously mentioned, the rearward slits 143 must, on the one hand, be large enough to reliably pass particles of mudcake at least when a competent formation is being tested and, on the other hand, be small enough to reliably effect a quick bridging of sand grains across these slits when an unconsolidated form ation is instead being tested. This critical limitation is best achieved by sizing the rearward slits 143 so that, with whatever overall pressure differentials that may be reasonably experienced during the testing of an unconsolidated formation, the compacted column' of sand grains 138 will present such a substantial flow restriction that only minimal flows can pass along the flow path 147 and pass through the enlarged slits without disrupting the bridge of sand grains formed across those slits.

Thus, by deliberately restricting the flow path 147 through these rearward slits 143 (or the enlarged rear slit portions 143') in this manner, it can be reliably assured that the flow of fluids therethrough will be well below the critical flow rate which would-preclude either the formation or the maintenance of bridges of the sand grains in the compacted column 138 across the rearward slits. In other words, for a given width of the rearward slits 143 and for a given overall available pressure differential between the point 146 and the annular space 64, adetermination can be easily made (either by empirical testing or calculations) of the maximum allowable flow rate of fluids which can be passed safely through these enlarged slits before sand grains of a size ordinarily retained by the forward slits 144 will no longer bridge across the rearward slits. Knowing this, it is, of course, simple to then determine length of the column of sand grains 138 required to provide a flow restriction sufficient to keep the flow rate along the long flow path 147 well below the maximum allowable flow rate which will be reliably supported by the sand particles bridging the rearward slits 143.

It will, of course, be appreciated that the same criteria can be applied to designing intermediately-located slits, as at 145, to have an intermediate width if this is desired. There will naturally be a proportional reduction in the restriction provided by the compacted column of sand grains 138 since the flow path 148 goes through a proportionately-shorter length of the column. Thus, since this lesser restriction will result in a proportionately-greater flow rate along the intermediate flow path 148 for a given overall pressure differential, the intermediate slits must be somewhat narrower than the rearward slits 143 to maintain a bridge of sand particles across the intermediate slits. This degree of refinement is believed unnecessary, however. By way of example, with the filter member 66 arranged generally as depicted in FIG. 7, it has been found that three rows of the rear slits 143 each with a width of 0.0l8-inch and eight rows of slits each with a width of 0.0l-inch for the intermediate and

forward slits

145 and 144, respectively, will enable the sample-admitting means 10 to effectively function in most, if not all, testing situations and still provide much-greater flow rates in finely-divided formation materials than were possible with prior-art filters.

Although FIG. 9 depicts an alternative embodiment of apparatus arranged in accordance with the principles of the present invention, it will be noted that in the illustrated situation, the formation, as at 14, is more competent than the formation 13. As a result, the fluidadmitting member 42 has not been able to move forwardly to its furtherest-possible extended position. This has, therefore, resulted in substantially fewer sand particles entering the flud-admitting member so that a much-higher overall flow rate is possible than would have occurred if the fluid-admitting member 42 had been filled with such particles. In this situation, it is, of course, quite possible that some, if not all, of any entering sand particles will simply flow on through the rear portions 143 of the tapered slits. The same thing would, of course, occur with the filter member 66. Thus, should there be only a short column of the sand particles (or none at all) captured in the filter member 66', the larger available flow area defined by the rear slit portions 143 (or the rear slits 143) will simply result in greater flow rates than would otherwise be possible with conventional filters. The important thing to note here is that in the testing ofa relatively-competent formation, the unique design of the filter 66' (as well as the filter 66) with the enlarged rear slit portions 143' (or the rear slits 143) will assure the passage of most, if not all, of the mudcake which typically lines the wall of the borehole 12 where it traverses a permeable formation, as at 14. Thus, regardless of which one of the

filters

66 or 66 is being employed with the new and improved fluid-admitting means 10, there will be little or no mudcake retained in the filter member which would otherwise be capable of plugging the filter. By virtue of the enlarged filter openings 143 (or 143), the mudcake will instead be free to quickly pass on into the flow line 67 so that the interior of the filter 66 (or 66') will remain fully open. It will, of course, be recognized that since few if any formation particles will be dislodged from the wall of the borehole 12 in this situation, there will be no occasion requiring bridging of the particles over the rearward openings 143 (or 143) to prevent continued erosion of the isolated portion of the formation 14.

Now that the methods and apparatus of the present invention have been fully set out, it is believed necessary only to quickly summarize the balance of the complete operating cycle of the tool 10. Accordingly, referring again to FIGS. 6A and 68, it will be appreciated that once the several components of the tool 11 and the control system 16 have moved to their respective positions shown in these figures, the hydraulic pressure will again rise until such time that the set line pressure switch 96 operates to halt the hydraulic pump 84. Inasmuch as the pressure switch 96 has a selected operating range, in the typical situation the pump 84 will be halted shortly after the pressure-equalizing valve 74 closes and the flow-line control valve 71 opens. At this point in the operating cycle of the tool 11, once a sufficient number of pressure measurements have been obtained as previously described, a decision can be made whether it is advisable to obtain one or more samples of the producible connate fluids present in the earth formation 13. If such samples are not desired, the operator can simply operate the control switches 24 and 25 for retracting the tool-anchoring member 20 as well as the sealing pad 39 without further ado. This freedom of action is, of course, made possible by virtue of the flexibility of operation of the new and improved fluidadmitting means 10 and the assurance that connate fluids can reliably pass through the filter member 66.

On the other hand, should a fluid sample be desired. the control switches 24 and 25 (FIG. 1) are advanced to their next or so-called sample positions 29 to open, for example, a solenoid valve 150 (FIG, 3B) for coupling pressured hydraulic fluid from the highpressure section 116 of the set line 91 to the piston actuator 78 of the sample-chamber control valve 72. This will, of course, be effective for opening the control valve 72 to admit connate fluids through the flow line 67 and the branch conduit 69 into the sample chamber 22. If desired, a chamber selection" switch 151 (FIG. 1) in the surface portion of the control system 16 could also be moved from its first sample position 152 to its so-called second sample" position 153 (FIG. 1) to energize a solenoid valve 154 (FIG. 3B) for opening the sample-chamber control valve 73 to also admit connate fluids into the other sample chamber 23. In either case, one or more samples of the connate fluids which are present in the isolated earth formation 13 can be selectively obtained by the testing tool 11.

Upon moving the control switches 24 and 25 to their so-called sample-trapping positions 30, the pump 84 will again be restarted. Once the pump 84 has reached operating speed, it will commence to operate much in the same manner as previously described and the hydraulic pressure in the output line 87 will again begin rising with momentary halts at various intermediate pressure levels.

Accordingly, when the control switches 24 and 25 have been placed in their sample trapping positions 30 (FIG. 1 the solenoid valve 94 (FIGS. 3A and 38) will open to admit hydraulic fluid into the retract line 92. By means of the electrical conductor 98a, however, the pressure switch 98 is enabled and the pressure switch 97 is disabled so that in this position of the control switches 24 and 25 the maximum operating pressure which the pump 84 can initially reach is limited to the pressure at the operating pressure level determined by the pressure switch 98. Thus, by arranging the hydraulic control valve 103 to open in response to a hydraulic pressure corresponding to this predetermined pressure level, hydraulic fluid in the high-pressure section 116 of the set line 91 will be returned to the reservoir 86 by means of the return line 89. As the hydraulic fluid in the high-pressure section 116 returns to the reservoir 86, the pressure in this portion of the set line 9l will be rapidly decreased to close the hydraulic control valve once the pressure in the line is insufficient to hold the valve open. Once the hydraulic control valve 100 closes, the pressure remaining in the low-pressure section 113 ofthe set line 91 will remain at a reduced pressure which is nevertheless effective for retaining the tool-anchoring member 20 and the sealing pad 39 fully extended.

As hydraulic fluid is discharged from the lower portion of the piston actuator 78 by way of the still-open solenoid valve 150 and fluid from the retract line 92 enters the upper portion of the actuator by way of a branch line 155, the sample-chamber control valve 72 will close to trap the sample of connate fluids which is then present in the sample chamber 22. Similarly, should a fluid sample have also been collected in the other sample chamber 23. the sample-chamber control valve 73 can also be readily closed by operating the switch 151 (FIG. 1) to reopen the solenoid valve 154. Closure of the sample-chamber control valve 72 (as well as the valve 73) will, of course, be effective for trapping any fluid samples collected in one or the other or both of the

sample chambers

22 and 23.

Once the sample-chamber control valve 72 (and, if

necessary, the control valve 73) has been reclosed, the

control switches 24 and 25 are moved to their next or so-called retreat" switching positions 31 for initiating the simultaneous retraction of thetool-anchoring member and the sealing pad 39. In this final position of the control switch 25, the pressure switch 98 is again rendered inoperative and the pressure switch 97 is enabled so as to now permit the hydraulic pump 84 to be operated at full rated capacity for attaining hydraulic pressures greater than the first intermediate operating level in the retract cycle. Once the pressure switch 98 has again been disabled, the pressure switch 97 will now function to operate the pump 84 so that the pressure will now quickly rise until it reaches the next operating level.

At this point, hydraulic fluid will'be supplied through the retract line 92 and the branch hydraulic line 135 for reopening the pressure-equalizing control valve 74 to readmit borehole fluids into the flow line 67. Opening of the pressure-equalizing valve 74 will admit borehole fluids into the isolated space defined by the sealing pad 39 so as to equalize the pressure differential existing across the pad before it is retracted. Hydraulic fluiddisplaced from the upper portion of the piston actuator 76 of the pressure-equalizing valve 74 will be discharged through a typical relief valve 156 which is arranged to open only in response to pressures equal or greater than that of this present operating level. The hydraulic fluid displaced from the piston actuator 76 through the relief valve 156 will be returned to the reservoir 86 by way of the branch hydraulic line 130, the high-pressure section 116 of the set line 91, the still-open hydraulic control valve 103, and the return line 89.

When the hydraulic pressure in the output line 87 has either reached the next operating level or, if desired, a still-higher level, pressured hydraulic fluid in the retract line 92 will reopen the hydraulic control valve 102 to communicate the low-pressure section 113 of the set line 91 with the reservoir 86. When this occurs, hydraulic fluid in the retract line will be admitted to the retract sides of the

several piston actuators

21 and 41. Similarly, the pressured hydraulic fluid will also be admitted into the annular space 51 in front of the enlargeddiameter piston portion 49 for retracting the fluidadmitting member 42 as well as into the annular space 62 for returning the valve member 52 to its forward position. The hydraulic fluid exhausted from the

several piston actuators

21 and 41 as well as the

piston chambers

50 and 63 will be returned directly to the reservoir 86 by way of the low-pressure section 113 of the set line 91 and the hydraulic control valve 102. This action will, of course, retract the tool-anchoring member 20 as well as the sealing pad 39 against the tool body 19 to permit the tool 11 either to be repositioned in the borehole 12 or to be returned to the surface if no further testing is desired.

It should be noted that although there is an operating pressure applied to the upper portion of the piston actuator 77 for the flow-line control valve 71 at the time that the pressure-equalizing valve 74 is reopened, a normally-closed relief valve 157 which is paralleled with the check valve 136 is held in a closed position until the increasing hydraulic pressure developed by the pump 84 exceeds the operating level used to retract the tool-anchoring member 20 and the sealing pad 39. At this point in the operating sequence of the new and improved tool 11, the flow-line control valve 71 will be reclosed.

The pump 84 will, of course, continue to operate until such time that the hydraulic pressure in the output line 87 reaches the upper limit determined by the setting of the pressure switch 97. At some convenient time thereafter, the control switches 24 and 25 are again returned to their initial or off positions 26 for halting further operation of the pump motor as well as reopening the solenoid valve 99 to again communicate the retract line 92 with the fluid reservoir 86. This completes the operating cycle of the illustrated embodiment of the tool 1 1.

Accordingly, it will be appreciated that the new and improved fluid-admitting means 10 of the present in vention enable the formation-testing tool, such as that shown herein at 11, to be operated for testing any type of formation which may be reasonably expected to be encountered during a formation-testing operation. By providing a filter member with selectively-larger filter openings at the rear of the member, it is assured that a buildup of formation particles in the sample member will not block the flow of connate fluids through at least the rear portion of the fluid-admitting member into the portions of the fluid-admitting means. Thus, with the new and improved fluid-admitting means described herein, tests may now be conducted in various types of formations without experiencing either unduly-reduced flow rates where a given formation is composed of exceptionally-fine, unconsolidated sand particles or plugging of the filtering means with mudcake or the like where a relatively-complete formation is encountered.

While only one method and particular embodiments of apparatus of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What is claimed is:

l. A method for obtaining samples of connate fluids from earth formations traversed by a borehole and having mudcake lining the boreholes wall adjacent thereto and comprising the steps of:

packing-off a portion of said borehole wall adjacent to earth formations therebeyond for isolating said wall portion and said earth formations from fluids in said borehole;

inducting connate fluids from said formations through filtering means having paralleled filter passages with at least a'first one of said filter passages being of an enlarged size sufficient to pass particles of mudcake and at least a second one of said filter passages being of a reduced size sufficient to retain loose formation materials for initially drawing mudcake removed from said isolated wall portion on through said first filter passage; and, thereafter, inducting additional connate fluids from said earth formations through said filtering means for depositing loosened formation particles in a permeable bridge over at least said first filter passage so as to at least reduce the continued flow of connate fluids therethrough and increase the continued flow of connate fluids through said second filter passage.

2. The method of claim 1 wherein said first and second filter passages are respectively arranged as separated elongated slits in said filtering means.

3. The method of claim 1 wherein said first and second filter passages are arranged as a single elongated slit in said filtering means having an enlarged portion defining said first filter passage and a reduced portion defining said second filter passage.

4. A method for obtaining samples of connate fluids from earth formations traversed by a borehole and having mudcake lining the borehole wall adjacent thereto and comprising the steps of:

packing-off a borehole wall adjacent to earth formations therebeyond for isolating a portion of said wall and said earth formations from fluids in said borehole;

inducting connate fluids from said isolated wall portion and earth formations through filtering means having at least one enlarged filter passage sized to pass particles of said mudcake and in parallel flow relationship with at least one reduced filter passage sized to retain loose formation particles for initially directing at least a substantial portion of said mudcake particles on through said enlarged filter passage; and

whenever loose formation particles are eroded from said isolated wall portion, collecting such loosened particles with said filtering means for reducing the flow of connate fluids through said enlarged filter passage sufficiently to build a bridge of such loosened particles across said enlarged filter passage and directing at least a major portion of the flow of connate fluids through said reduced filter passage to retain any subsequently-loosened formation particles.

5. The method of claim 4 further including the step of:

measuring at least one property of connate fluids passing through said filtering means for determining one or more characteristics of said earth formations.

6. The method of claim 4 further including the step of:

collecting at least one sample of connate fluids passing through said filtering means.

7. The method of claim 4 further including the steps of:

obtaining at least one measurement of the pressure of connate fluids passing through said filtering means for determining one or more characteristics of said earth formations; and, thereafter,

8. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising:

a body having a fluid passage adapted to receive connate fluids;

fluid-admitting means on said body including a fluid entry coupled to said fluid passage and adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids;

means selectively operable for positioning said fluid admitting means against a borehole wall to place said fluid entry in communication with earth formations beyond the isolated wall surface of said borehole wall; and

fluid-filtering means cooperatively arranged between said fluid passage and said fluid entry for initially passing mudcake particles displaced from said isolated wall surface on through said filtering means into said fluid passage and operable thereafter whenever loose formation particles of a size smaller than such mudcake particles are eroded from said isolated wall surface for collecting such loosened smaller formation particles as connate fluids pass on through said filtering means into said fluid passage.

9. The formation-testing apparatus of claim 8 wherein said fluid-filtering means include:

a filter member having at least one reduced filter passage sized to retain loose formation particles, and at least one enlarged filter passage in parallel flow relationship with said reduced filter passage sized to pass mudcake particles and cooperatively arranged for collecting loosened formation particles in a bridge across said enlarged filter passage for reducing the flow of connate fluids therethrough so that at least a major portion of connate fluids will then be directed through said reduced filter passage.

l0. The formation-testing apparatus of claim 9 wherein said filter passages are arranged as a single elongated slit having an enlarged end portion for defining said enlarged filter passage and a reduced end portion for defining said reduced filter passage.

11. The formation-testing apparatus of claim 9 further including:

means selectively. operable after disengagement of said fluid-admitting meansfrom said borehole wall for displacing from said flud entry any loosened formation materials previously collected as a bridge across said enlarged filter passage.

12. The formation-testing apparatus of claim 9 further including:

pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage.

13. The formation-testing apparatus of claim 9 further including:

sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.

14. The formation-testing apparatus of claim 9 further including:

pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage; and

Claims

1. A method for obtaining samples of connate fluids from earth formations traversed by a borehole and having mudcake lining the boreholes wall adjacent thereto and comprising the steps of: packing-off a portion of said borehole wall adjacent to earth formations therebeyond for isolating said wall portion and said earth formations from fluids in said borehole; inducting connate fluids from said formations through filtering means having paralleled filter passages with at least a first one of said filter passages being of an enlarged size sufficient to pass particles of mudcake and at least a second one of said filter passages being of a reduced size sufficient to retain loose formation materials for initially drawing mudcake removed from said isolated wall portion on through said first filter passage; and, thereafter, inducting additional connate fluids from said earth formations through said filtering means for depositing loosened formation particles in a permeable bridge over at least said first filter passage so as to at least reduce the continued flow of connate fluids therethrough and increase the continued flow of connate fluids through said second filter passage.

4. A method for obtaining samples of connate fluids from earth formations traversed by a borehole and having mudcake lining the borehole wall adjacent thereto and comprising the steps of: packing-off a borehole wall adjacent to earth formations therebeyond for isolating a portion of said wall and said earth formations from fluids in said borehole; inducting connate fluids from said isolated wall portion and earth formations through filtering means having at least one enlarged filter passage sized to pass particles of said mudcake and in parallel flow relationship with at least one reduced filter passage sized to retain loose formation particles for initially directing at least a substantial portion of said mudcake particles on through said enlarged filter passage; and whenever loose formation particles are eroded from said isolated wall portion, collecting such loosened particles with said filtering means for reducing the flow of connate fluids through said enlarged filter passage sufficiently to build a bridge of such loosened particles across said enlarged filter passage and directing at least a major portion of the flow of connate fluids through said reduced filter passage to retain any subsequently-loosened formation particles.

5. The method of claim 4 further including the step of: measuring at least one property of connate fluids passing through said filtering means for determining one or more characteristics of said earth formations.

6. The method of claim 4 further including the step of: collecting at least one sample of connate fluids passing through said filtering means.

7. The method of claim 4 further including the steps of: obtaining at least one measurement of the pressure of connate fluids passing through said filtering means for determining one or more characteristics of said earth formations; and, thereafter, collecting at least one sample of connate fluids passing through said filtering means.

8. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising: a body having a fluid passage adapted to receive connate fluids; fluid-admitting means on said body including a fluid entry coupled to said fluid passage and adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids; means selectively operable for positioning said fluid-admitting means against a borehole wall to place said fluid entry in communication with earth formations beyond the isolated wall surface of said borehole wall; and fluid-filtering means cooperatively arranged between said fluid passage and said fluid entry for initially passing mudcake particles displaced from said isolated wall surface on through said filtering means into said fluid passage and operable thereafter whenever loose formation particles of a size smaller than such mudcake particles are eroded from said isolated wall surface for collecting such loosened smaller formation particles as connate fluids pass on through said filtering means into said fluid passage.

9. The formation-testing apparatus of claim 8 wherein said fluid-filtering means include: a filter member having at least one reduced filter passage sized to retain loose formation particles, and at least one enlarged filter passage in parallel flow relationship with said reduced filter passage sized to pass mudcake particles and cooperatively arranged for collecting loosened formation particles in a bridge across said enlarged filter passage for reducing the flow of connate fluids therethrough so that at least a major portion of connate fluids will then be directed through said reduced filter passage.

10. The formation-testing apparatus of claim 9 wherein said filter passages are arrangEd as a single elongated slit having an enlarged end portion for defining said enlarged filter passage and a reduced end portion for defining said reduced filter passage.

11. The formation-testing apparatus of claim 9 further including: means selectively operable after disengagement of said fluid-admitting means from said borehole wall for displacing from said flud entry any loosened formation materials previously collected as a bridge across said enlarged filter passage.

12. The formation-testing apparatus of claim 9 further including: pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage.

13. The formation-testing apparatus of claim 9 further including: sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.

14. The formation-testing apparatus of claim 9 further including: pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage; and sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.

15. The formation-testing apparatus of claim 14 further including: means selectively operable after disengagement of said fluid-admitting means from said borehole wall for displacing from said fluid entry any loosened formation materials previously collected as a bridge across said enlarged filter passage.

16. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising: a body having a fluid passage adapted to receive connate fluids; fluid-admitting means on said body and including a fluid-sampling member having an inlet passage adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids and an outlet passage downstream of said inlet passage and coupled to said fluid passage; means selectively operable for positioning said fluid-sampling member against a borehole wall to place said inlet passage into communication with earth formations beyond the isolated wall surface of said borehole; and filtering means cooperatively arranged on said fluid-sampling member for intercommunicating said inlet and outlet passages and including means defining a chamber adapted for collecting loose formation particles entering said inlet passage, means defining at least one enlarged filter passage between said chamber and said outlet passage and selectively sized to initially pass mudcake particles entering said particle-collecting chamber into said outlet passage as well as to subsequently develop a bridge of loosened formation particles across said enlarged filter passage whenever such entering formation particles are collected in said particle-collecting chamber, and means defining at least one reduced filter passage upstream of said enlarged filter passage and selectively sized to retain such loosened formation particles without halting the flow of connate fluids between said inlet and outlet passages.

17. The formation-testing apparatus of claim 16 wherein said fluid-sampling member is tubular with a forward portion thereof defining said inlet passage, said outlet passage includes an inwardly-opening fluid chamber formed in an intermediate portion of said fluid-sampling member, and said filtering means include a filter member covering the entrance of said inwardly-opening fluid chamber and having a forward portion with said reduced filter passage therein and a rearward portion with said enlarged filter passage therein and defining at least part of a side wall of said particle-collecting chamber.

18. The formation-testing apparatus of claim 17 wherein said filter passages are separated from oNe another.

19. The formation-testing apparatus of claim 17 wherein said filter passage are joined to one another by an intermediate filter passage having a width less than that of said enlarged filter passage.

20. The formation-testing apparatus of claim 17 wherein said filter passages are joined to one another by an intermediate filter passage having a width less than that of said enlarged filter passage and greater than that of said reduced filter passage.

21. The formation-testing apparatus of claim 17 further including: a piston member coaxially arranged in said fluid-sampling chamber for movement between a retracted position in the rearward portion thereof to define the rear wall of said particle-collecting chamber and a normal extended position in said forward portion of said fluid-sampling member to block said inlet passage; and means coupled to said piston member and selectively operable for moving said piston member to its retracted position following engagement of said fluid-sampling member with a borehole wall to admit connate fluids into said inlet passage and for returning said piston member to its extended position following disengagement of said fluid-sampling member from a borehole wall to expel any lossened formation materials previously collected as a bridge across said enlarged filter passage from said fluid-sampling member.

22. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising: a body having a first fluid passage adapted to receive connate fluids; fluid-admitting means on said body and including a fluid-sampling member having a tubular forward portion adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids; means selectively operable for positioning said fluid-sampling member against a borehole wall to establish communication with earth formations therebeyond; first means adapted for limiting the entrance of loose formation particles into said first fluid passage including a second fluid passage in said fluid-sampling member and coupled to said first fluid passage, and filtering means cooperatively arranged on a wall of said fluid-sampling member for controllably communicating said second fluid passage with said tubular forward portion and including enlarged filter passage means selectively sized to initially pass mudcake particles entering said fluid-sampling member as well as to subsequently develop a bridge of loosened formation particles across said enlarged filter passage means whenever such formation particles enter said fluid-sampling member and reduced filter passage means upstream of said enlarged filter passage means and selectively sized for retaining loosened formation particles within said fluid-sampling member as filtered connate fliuds pass through said filtering means into said second fluid passage; second means adapted for controlling the entrance of particles into said fluid-sampling member and including a piston member coaxially arranged in said fluid-sampling member for movement past said filtering means between an advanced position within said tubular forward portion ahead of said reduced filter passage means blocking communication into said fluid-sampling member and a retracted position to the rear of said enlarged filter passage means for uncovering said filtering means and defining a space adjacent to said enlarged filter passage means for collecting loosened formation particles entering said tubular forward portion; and piston-control cooperatively arranged for selectively moving said piston member back and forth between its said advanced and retracted positions.

23. The formation-testing apparatus of claim 22 wherein said second fluid passage includes an annular chamber formed around an intermediate interior wall portion of said fluid-sampling member between said advanced and retracted positionS of said piston member; and said filtering means include a tubular filter member coaxially mounted in said fluid-sampling member around said annular chamber and sized for passage of said piston member as it moves between its said positions.

24. The formation-testing apparatus of claim 23 wherein said filter passage means are comprised of a plurality of longitudinally-oriented slits circumferentially spaced around said filter member and respectively having enlarged rearward portions defining said enlarged filter passage means and reduced forward portions defining said reduced filter passage means.

25. The formation-testing apparatus of claim 24 wherein said longitudinally-oriented slits are symmetrically tapered between said enlarged rearward portions and said reduced forward portions.

26. The formation-testing apparatus of claim 23 wherein said filter passage means are comprised of a plurality of circumferentially-oriented slits spaced longitudinally along said filter member with at least the rearwardmost ones of said slits being wider than at least the forwardmost ones of said slits for respectively defining said enlarged filter passage means and said reduced filter passage means.

27. The formation-testing apparatus of claim 26 wherein all of said slits ahead of said wider rearwardmost slits are of an equal width which is narrower than the width of said wider rearwardmost slits.

28. The formation-testing apparatus of claim 22 further including: sealing means cooperatively arranged on said fluid-admitting means around said tubular forward portion and adapted for packing-off a borehole wall around said tubular forward portion.

29. The formation-testing apparatus of claim 22 further including: means cooperatively mounting said fluid-sampling member on said body for movement relative thereto between a laterally-extended position and a retracted position; and control means cooperatively arranged for selectively moving said fluid-sampling member back and forth between its said extended and retracted positions.

30. The formation-testing apparatus of claim 22 further including: sample-receiving means on said body and adapted for receiving filtered connate fluids entering said first fluid passage; and control means cooperatively arranged for selectively coupling said sample-receiving means to said first fluid passage.

31. The formation-testing apparatus of claim 22 further including: pressure-monitoring means for providing indications at the surface indicative of the pressure of connate fluids in said first fluid passage.

32. The formation-testing apparatus of claim 22 further including: a wall-engaging member movably mounted on said body on the opposite side thereof from said forward portion of said fluid-sampling member; and piston means cooperatively coupled to said wall-engaging member for moving said wall-engaging member between an extended wall-engaging position and a retracted position against said opposite body side to respectively engage and disengage said fluid-admitting means with and from a borehole wall.

33. The formation-testing apparatus of claim 22 further including: means cooperatively coupling said fluid-sampling member to said body for movement relative to one side thereof between a laterally-extended position and a retracted position; and piston means cooperatively coupled to said fluid-sampling member for moving said fluid-sampling member between its said laterally-extended position and its said retracted position to respectively engage and disengage said fluid-sampling member with and from a borehole wall.

34. The formation-testing apparatus of claim 33 further including: a wall-engaging member movably mounted on said body on the opposite side thereof; and piston means cooperatively coupled to said wall-engaging position and a retracted position against said opposite body side upon movement of said fluid-sampling member between its said positions.