GB2044322A

GB2044322A - Apparatus for well logging while drilling

Info

Publication number: GB2044322A
Application number: GB8007872A
Authority: GB
Original assignee: Exploration Logging Inc
Current assignee: Baker Hughes Oilfield Operations LLC
Priority date: 1979-03-19
Filing date: 1980-03-07
Publication date: 1980-10-15
Also published as: EP0026188A1; GB2044322B; WO1980002051A1; CA1156341A; AU5597080A; AU547865B2

Abstract

A monostable, solenoid-operated valve in a passage which bypasses the drilling fluid pressure drop across a drill bit (34) at the lower end of a drill string (30) in a well opens and closes in response to downhole conditions to create pressure pulses in the drilling fluid. The valve (166) is urged toward a closed position by drilling fluid pumped through the drill string. A larger force is required to open the valve than to hold it open. Current supplied to the solenoid (67, 70) is thereafter reduced to a value sufficient to hold the valve open. The solenoid is deenergized to close the valve.

Description

SPECIFICATION Apparatus for Well Logging While Drilling This invention relates to the logging of wells during drilling, and more particularly to the wireless telemetry of data relating to down hole conditions.

It has long been the practice to log wells, that is, to sense various downhole conditions within a well and transmit the acquired data to the surface through wire line or cabletype equipment. To conduct such logging operations, drilling is stopped, and the drill string is removed from the well. Since it is costly to stop drilling operations, the advantages of logging while drilling have long been recognized. However, the lack of an acceptable telemetering system has been a major obstacle to successful logging while drilling.

Various systems have been suggested for logging while drilling. For example, it has been proposed to transmit data to the surface electrically. Such methods have been impractical because of the need to provide the drill pipe sections with a special insulated conductor and appropriate connections for the conductor at the drill pipe joints. Other proposed techniques include the transmission of accoustical signals through the drill pipe. Examples of such telemetering systems are shown in U.S. Pat.

Nos. 3,015,801 and 3,205,477. In those systems, an accoustical signal is sent up the drill pipe and frequency modulated in accordance with a sensed downhole condition.

Wireless systems have also been proposed using low-frequency electromagnetic radiation through the drill string, borehole casing, and the earth's lithosphere to the surface of the earth.

Other telemetering procedures proposed for logging while drilling use the drilling fluid within the well as the transmission medium. U.S. Pat.

Nos. 2,925,251 and 3,964,556 disclose systems in which the flow of drilling fluid through the drill string is periodically restricted to cause positive pressure pulses to be transmitted up the column of drilling fluid to indicate a downhole condition. U.S. Pat. Nos. 2,887,298 and 4,078,620 discloses systems which periodically vent drilling fluid from the drill string interior to the annular space between the drill string and the borehole of the well to send negative pulses to the surface in a coded sequence corresponding to a sensed downhole condition. A similar system is described in The Oil and Gas Journal, June 12, 1978 at page 71.

Of the various wireless transmission systems considered to date, the most promising creates negative pressure pulses in the drilling fluid circulated through the drill string, drill bit, and borehole annulus. Negative pressure pulses are generated by intermittently bypassing a relatively small proportion of the total drilling fluid flow around the drill bit by opening and closing a valve in a passageway connecting the drill string interior with the borehole annulus.

A general problem with using pressure pulses in the drilling fluid to send information is that the pulse generators to date have been bulky and, therefore, impose a wasteful pressure drop in the drilling fluid flowing through the drill string. This invention provides a "slim" pulse generator which minimizes energy losses due to pressure drop in the drill string.

A specific problem with previous negative pulse generating systems is that if the valve in the bypass passage fails in the open position, energy of the drilling fluid is wasted, because part of the drilling fluid continuously bypasses the drill bit.

Moreover, with the valve stuck in the open position, the abrasive nature of the drilling fluid may rapidly enlarge the bypass passage, with further waste of drilling fluid energy. Even more serious, a continuous, uncontrolled high-speed jet of drilling fluid out the side of the drill string may wash out a cavity in the well bore, leading to a possible cave-in and sticking of the drill string.

Uncontrolled bypassing of drilling fluid also makes it difficult to place lost circulation material, or the like, in a desired position in the well bore, when the volume of fluid displaced through the drill bit must be accurately known.

Because of the disadvantages just referred to, bypass valves have not generally been trusted in oil well drilling operations. This invention provides a "fail-safe" bypass valve for generating negative pressure pulses in a manner which is safe, efficient, and reliable.

The present invention is apparatus for sending information through a drilling fluid in a borehole drilled in the earth with a drill bit on the lower end of a drill string in the borehole and through which the drilling fluid is circulated with a pump to flow through the interior of the drill string, past the drill bit, and into an annulus between the drill string and the borehole wall, the apparatus including means defining a passage for drilling fluid between the drill string interior and the annulus, a valve disposed in the passage to be held in a normally closed position by the difference in drilling fluid pressure across the valve, means for applying an opening force to open the valve so drilling fluid flows through it, means urging the valve from an open position toward a closed position as drilling fluid flows through it, means for removing the force on the valve so it moves to the closed position, the opening and the closing of the valve generating a pressure pulse in the drilling fluid, and means for detecting the pulse.

Means are provided to urge the valve from an open to a closed position, preferably by pressure of the drilling fluid pumped through the drill string. A larger force is required to open the valve than to hold it open.

Preferably, the valve is actuated by a solenoid, which is first supplied enough current to open the valve. Thereafter, the current to the solenoid is reduced to a value just sufficient to hold the valve open to minimize power consumption. The solenoid is de-energized to close the valve. The opening and closing of the valve generates a nagative pressure pulse in the drilling fluid to indicate a down hole condition.

In the preferred embodiment of the invention, the valve is urged to a closed position by a fluid catcher secured to a valve disk, which opens and closes the valve by moving away from or resting on a valve seat. Preferably, the fluid catcher is disposed on the low pressure side of the valve seat.

In another embodiment of the invention, a spring urges the valve disk toward the valve seat.

Thus, when the flow of drilling fluid is stopped, or is relatively slow, the valve automatically closes, thereby preventing the bypass of drilling fluid around the drill bit during slow pumping operations, such as when lost circulation material is being "spotted" in a desired position.

In the preferred embodiment, the surface of the valve seat slopes inwardly in the direction of fluid flow at an angle of between about 50 and 40 to where the disk rests in a sealing position. The valve disk is undercut on the low-pressure side to provide rapid opening of the valve in response to slight movement of the disk away from the seat.

The valve also includes a valve guide chamber on the high-pressure side of the seat. A piston connected to the disk makes a sliding seal in the chamber, and a pressure-balancing bore connects the interior of the valve guide chamber to the lowpressure side of the valve. The effective area of the piston acted on by the drilling fluid on the high-pressure side when the valve is closed is slightly less than that of the valve disk so a positive closing force is kept on the disk while the valve is closed. Preferably, the pressure-balancing bore extends through a valve stem which connedts the piston to the valve disk to simplify construction and minimize the size of the pulse generator.

The valve is preferably operated by a solenoid shaft mounted to engage and lift the valve disk from the valve seat. A circuit supplies a relatively high current to the solenoid to generate enough force to open the valve. The force required to hold the valve open is substantially less than that required to open it. After the valve opens, the current to the solenoid is reduced to a value which generates a force just sufficient to overcome the closing force generated by the flow of fluid through the valve. The solenoid is subsequently de-energised so that the fluid flow through the valve (and the spring, if used) urges the valve to a closed position.

The solenoid is ordinarily surrounded by a liquid, such as oil or drilling fluid. To accelerate the action of the solenoid, the face plate of the solenoid is provided with shallow channels to facilitate the movement of fluid as the face plate moves toward and away from the solenoid core.

Preferably, longitudinal bores extend through the face plate to further facilitate the surge of liquid as the solenoid is actuated.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a system for simultaneously drilling and logging a well; Fig. 2 is a schematic longitudinal cross-section of a presently-preferred embodiment of the pulse generator mounted in a drill string; Fig. 3 is a perspective view of a solenoid face plate modified in accordamce with this invention; and Fig. 4 is schematic diagram of a circuit used to control current through one or more solenoids for operating the pulse generator.

In the preferred embodiments of the invention, as described in detail below, pressure pulses are transmitted through a drilling fluid to send information from the vicinity of a drill bit on the lower end of a drill string in a well to the surface of the earth as the well is drilled. At least one downhole condition within the well is sensed, and a signal, usually analog, is generated to represent the sensed condition. The signal is used to control the bypass of the flow of drilling fluid around the drill bit such as to cause pressure pulses at the surface in a coded sequence, representing the downhole condition.

Referring to Fig. 1, a well 10 is drilled in the earth with a rotary drilling rig 12, which includes the usual derrick 14, derrick floor 16, draw works 18, hook 20, swivel 22, kelly joint 24, rotary table 26, and a drill string 28 made up of drill pipe 30 secured to the lower end of the kelly joint 24 and to the upper end of a section of drill collars 32, which carry a drill bit 34. Drilling fluid (commonly called drilling mud in the field) circulates from a mud pit 36 through a mud pump 38, a desurger 40, a mud supply line 41, and into the swivel 22.

The drilling mud flows down through the kelly joint, drill string and drill collars, and through jets (not shown) in the lower face of the drill bit.

The drilling mud flows back up through an annular space 42 between the outer diameter of the drill string and the well bore to the surface, where it is returned to the mud pit through a mud return line 43.

The usual shaker screen for separating formation cuttings from the drilling mud before it returns to the mud pit is not shown.

A transducer 44 in the mud supply line 41 detects variations in drilling mud pressure at the surface. The transducer generates electrical signals responsive to drilling mud pressure variations. These signals are transmitted by an electrical conductor 46 to a surface electronic processing system 48, such as that described in U.S. Patent No. 4,078,620.

Referring to Fig. 2, an elongated vertical, cylindrical pulser housing 50 includes a pair of outwardly extending fins or spiders 52 on diametrically opposite sides of the pulser housing.

The spiders centralize the pulser housing within the drill collar and rest at their lower ends on inwardly extending shoulders 54, formed on the interior of the drill collar. Drilling fluid flows down an annular space 55, formed between the pulser housing and the drill collar, past the spiders, and out the drill bit, where it experiences a pressure drop of 1,000 to 3,000 p.s.i. in a typical drilling operation.

A central bore 56 extends longitudinally through the pulser housing. An externallythreaded plug 58, screwed into an internallythreaded section 59 at the lower end of the central bore, closes the bottom of the pulser housing. The plug seals against an O-ring gasket 60 in a downwardly opening annular groove 61 in the lower face of an inwardly extending annular shoulder 62 in the central bore 56 just above threaded portion 59.

A first, or lower, solenoid 67 rests on the upper end of a cylindrical lower solenoid spacer 68, which makes a snug fit within the lower end of a solenoid housing 69, which makes a snug fit within the pulser housing. The lower end of the solenoid spacer and the solenoid housing rest on the upper face of annular shoulder 62 at the lower end of the pulser housing. A second, or upper, solenoid 70 rests on the upper end of a cylindrical upper solenoid spacer 72, which has an inwardly extending annular flange 74 that rests on the upper surface of the lower solenoid. A pair of upwardly extending aligning pins 76 on the upper surface of the lower solenoid fit into respective vertical bores 78 in the inwardly extending flange 74.Upwardly extending aligning pins 110 on the upper face of the upper solenoid extends into aligning holes 112 in the bottom of a cylindrical valve assembly housing 113, which makes a snug fit within the pulser housing. The bottom of the valve assembly housing rests on the upper end of the solenoid housing and the top face of the upper solenoid.

The two solenoids are identical, and may be conventional. Only the lower solenoid is shown in cross-section. Each solenoid includes an annular solenoid winding or coil 11 6, through which electrical current is passed to create a strong magnetic field in an annular core 118 which has a relatively small central vertical bore 120 extending from its upper face to about the center of the core. The bore is then stepped outwardly to an enlarged diameter at 122 to form a downwardly facing internal shoulder 1 24. A cylindrical solenoid armature or face plate 126 includes a central cylindrical core 127, which makes a close, sliding fit within the enlarged portion 122 of bore 120.Radially extending channels 128 (Fig. 3) in the upper surface of an outwardly extending annular flange 129 on the lower end of the core of each face plate, and longitudinally extending bores 1 32 through each core permits the face plate to move freely in a body of oil (not shown) which surrounds the two solenoids. Each face plate carries a longitudinally extending central shaft 133, which projects above and below the face plate. The upper end of the solenoid shaft of the lower solenoid bears against the lower end of the solenoid shaft of the upper solenoid. The solenoids are energized simultaneously so that the solenoid face plates are driven upwardly together when the valve of this invention is to be opened.The two solenoids connected in tandem provide a strong force with a relatively small diameter required by the solenoids, thus permitting the pulser housing to be relatively small in diameter to minimize restriction of flow of drilling fluid past it. When the solenoids are de-energized, the outwardly extending annular flange 129 on the lower end of the core of the face plate of the lower solenoid rests on an inwardly extending limit switch 1 36 at the upper portion of the lower solenoid support sleeve 68. The limit switch is held open when the flange rests on it. The switch and its operation are described in more detail below with respect to Fig. 4.

The upper end of the shaft of the upper solenoid makes a sliding fit through an O-ring seal 1 38 in a central bore 144 in a floating piston 146, which has an outwardly extending annular flange 148 within an annular O-ring seal 1 50 that makes a sliding seal against the inside of a reduced bore section 1 52 of a central bore 1 53 through the valve assembly housing. An inwardly extending C-ring 1 54 in an inwardly opening annular groove 1 56 just above the floating piston limits the upper travel of that piston, which forms the upper end of a solenoid chamber 1 57 filled with oil (not shown).

The lower end of a vertical valve stem 160 bears against the upper end of the upper solenoid shaft. The valve stem extends up through a bore 1 62 in a transverse partition 1 64 which extends across the central bore of the valve assembly housing. A vent 1 65 through the partition equalizes fluid pressure on opposite sides of the partition. The intermediate portion of the valve stem is enlarged to form an annular valve disk 1 66, which normally rests on an annular valve seat 167, formed integrally with the interior wall of the valve housing assembly. The valve seat includes an upwardly and outwardly sloping conical wall inclined at an angle between about 200 and about 300 from the centerline of the valve stem.

The valve disk includes a downwardly and outwardly sloping upper conical surface 168, the lower edge of which rests on the valve seat. The valve disk extends inwardly and horizontally for a short distance from the line of contact the valve disk makes with the valve seat, and then extends downwardly and inwardly along a second conical surface 1 69. This provides a sharp and rapidly opening orifice as the valve disk is'lifted slightly off the valve seat, and thereby facilitates movement of drilling fluid around the edge of the valve disk once it has moved marginally off the seat. This action minimizes the force required to open the valve.

A valve stem piston 1 70 on the upper end of the valve stem makes a close sliding fit within a downwardly opening cylindrical valve guide chamber 172 in the lower face of a cylindrical upper guide 174 for the valve stem. The upper portion of the valve guide chamber 1 72 is stepped down to a reduced diameter section 1 76 to receive the upper end of a compression spring 1 78, the lower end of which bears down against the top surface of the valve stem piston.

A main-lock ring 180, threaded into the upper end of the valve assembly housing central bore, holds an outwardly extending flange 1 81 on the upper valve guide in compression against the upper end of the valve assembly housing. An annular O-ring seal 1 84 around the exterior of the upper valve guide makes a fluid-tight seal against the interior of the valve assembly housing. An annular O-ring seal 185 at the upper end of the valve assembly housing makes a fluid-tight seal against the interior of the pulse housing.

An annular O-ring seal 186 on the valve stem piston makes a fluid-tight sliding seal within the wall of the valve guide chamber. A pressureequalizing bore 1 88 extends longitudinally through the piston and upper portion of the valve stem down to a point just below the valve disk 166.

The lower end of bore 1 88 branches out into two lateral bores 190, which open into the central bore of the valve assembly housing just below the valve seat so that pressure on the low-pressure side of the valve disk when the valve is closed is transmitted to the upper surface of the valve stem piston. The effective area of the valve stem piston acted on by the pressure of the drilling fluid in the valve is slightly less than that of the valve disk to balance the pressure across the disk to a relatively small, but steady, force which tends to hold the disk down on the valve seat. That force is equal to the differential pressure multiplied by the difference in the effective cross-sectional areas of the piston and the valve disk.By using the internal bore in the valve stem, instead of passages through the pulser housing or valve assembly housing, the diameter of the pulser housing is set by the diameters of the solenoids, which may be relatively small because the two solenoids work together.

A lateral bore 192 through the wall of the valve assembly housing is aligned with a bore 1 94 through the wall of the pulser housing to form a valve inlet 196 for drilling fluid from the annular space 55 between the pulser housing exterior and the drill collar interior. A screen 198 over the valve inlet prevents the entry of large solid particles into the valve. A plurality of upwardly and inwardly inclined bores 200 in the screen minimize the entry of solid particles into the valve.

An inner exhaust nozzle 202 is press-fitted in colinear matching bores 204 and 206 in the pulser housing wall and valve assembly housing wall, respectively. The inner end of the inner nozzle bears against an annular shoulder 209 formed where bore 206 is reduced In diameter.

Preferably, the inner nozzle is of reduced diameter in an outwardly extending direction. An outer exhaust nozzle 208 is press-fitted in a bore 210 through the wall of the drill collar and colinear with a bore 211 through the spider on the left (as viewed in Fig.2) side of the pulser housing. Bores 210 and 211 are colinear with, and slightly larger than, bores 204 and 206 so the inner end of the outer nozzle bears against a shoulder 21 2 at the juncture of bores 204 and 211. Preferably, the outlet exhaust nozzle Increases in diameter In an outward direction. A retaining ring 213 in an annular groove 214 at the outer end of bore 210 holds the exhaust nozzles in place. The exhaust nozzles 202 and 208 form a valve outlet 216 for fluid when the valve is open.A check valve 217 in nozzle 202 prevents the flow of fluid from the well bore annulus into the valve, such as when reverse circulation may be imposed on the drilling fluid.

An outwardly extending fluid catcher 220, in the form of an annular ring with an inwardly and upwardly sloping surface 222, is secured to the valve stem by a set screw 224 at about the same level as the upper portion of the valve outlet.

Alternatively, the fluid catcher may be formed integrally with the valve stem.

An annular O-ring seal 230 in the bore 204 makes a fluid-tight seal around the inner exhaust nozzle, and an annular O-ring seal 232 in the bore 210 makes a fluid-tight seal around the outer exhaust nozzle.

An O-ring 233 in an annular groove 234 in the outer face of the valve housing wall makes a fluidtight seal against the interior surface of the pulser housing exterior 66 above the upper end of the solenoid housing. An O-ring 235 in an annular groove. 236 in the outer face of the valve assembly housing makes a fluid-tight seal against the interior surface of the pulser housing exterior between the valve inlet and outlet.

The upper end of the pulser housing is sealed by a cap 240 threaded into the pulser housing. An annular O-ring seal 242 in the lower face of the cap seats against the upper end of the pulser housing to awake a fluid-tight seal.

Upwardly opening recesses 246 in the upper surface of the main lock-ring for the valve assembly housing permit the main lock-ring to be screwed tightly into place or removed, as required. Similar recesses 248 in the upper surface of the cap 240 permit it to be installed or removed, as required.

Thus, with the pulser housing mounted in the drill collar as shown in Fig. 2, drilling fluid flows as indicated by the arrows down the annular space between the pulser housing and the drill collars, into the valve inlet, and, when the valve is open, out the valve outlet, thereby bypassing some of the fluid flow around the drill bit at the lower end of the drill string. The drilling fluid which does not pass through the valve continues to flow down past the pulser housing and out through the drill bit.

Although Fig. 2 shows the valve inlet and valve outlet in the same vertical plane, more than one inlet or outlet can be provided, and they need not be in the same vertical plane. For example, the valve assembly housing may include two inlets (not shown) on opposite sides of the valve assembly housing, with a single valve outlet centered between the two inlets.

A power source (not shown In Fig. 2), such as a battery or generator (not shown) driven by a turbine (not shown) through which drilling fluid flows, may be mounted in the pulser housing.

The valve opens and closes in response to electrical signals developed by the circuit shown in Fig. 4. The circuit may be in a sealed chamber (not shown) within the pulser housing. For clarity, the electrical leads between the power source, the electronic circuitry, and the solenoids are not shown in Fig. 2.

Referring to Fig. 4, a power supply 300 supplies current through a first conductor 301 to the solenoid coils 11 6 connected in series, and across which is connected a diode rectifier 302.

The solenoid coils 116 are connected to ground 304 through a rheostat 306 and a first transistor 310, the base of which is connected by conductor 312 to the output of a pulse generator 314. The input of a one-shot vibrator 31 6 is connected to the output of the pulse generator, and the output of the one-shot vibrator is connected to the base of a second transistor 318, the collector of which is connected to the end of the solenoid coils remote from the power source. The emitter of the second transistor is grounded to provide a low resistance path for current through the solenoid windings.

The R-C components (not shown) in the oneshot vibrator are connected by a line 31 9 to a contact of switch 136, which is open when the valve is closed. A compression spring 320 closes the switch when the valve opens, thereby grounding the R-C components to stop the pulse from the one-shot vibrator.

A sensor 322 (normally mounted in the drill collar near the drill bit) detects a downhole condition, such as, formation electrical resistivity, mud temperature, mud pressure, weight on drill bit, natural radioactivity of the formation, inclination of the borehole, or the like. The pulse generator delivers a coded sequence of pressure pulses in response to signals received from the sensor.

When the valve is to be opened and closed to generate a negative pulse in the drilling fluid, the pulse generator applies a long, say, 500 milliseconds, pulse to the input of the one-shot vibrator and to the base of the first transistor. The one-shot vibrator applies a short pulse to the base of the second transistor, causing it to conduct d.c.

electrical power from the power supply, through the solenoid coil windings, arid to ground.

The pulse from the one-shot vibrator lasts until the valve opens. At that time the lower solenoid flange moves away from switch 136, which closes and turns off the one-shot vibrator, causing the second transistor to stop conducting. The switch may be of any suitable type, such as a limit switch, proximity detector, magnetic switch, or the like. Alternatively, the switch may be omitted, and the vibrator set to provide a pulse of fixed duration, say, 40 milliseconds, which is ordinarily sufficient time for the valve to open. The duration of the short pulse is substantially less than that of the long pulse. For example, the short pulse duration is between about 1% and about 50% of that of the long pulse.

The resistance of the circuit through the second transistor is low so that a relatively large current of 4 to 5 amps flows through the solenoid coil windings, generating a sufficiently large force on the solenoid armatures that the solenoid shafts are driven upwardly to lift the valve disk off its seat, thereby permitting drilling fluid to flow from the annular space between the pulser housing and drill collar, through the valve, and into the annular space between the drill collar and well bore.

The diode connected across the solenoid coils permits "free wheel" current to flow through them as the large current drops to the lower value. This provides additional force without drawing energy from the power source, and helps hold the valve open, if it should tend to "bounce" closed.

After the second transistor stops conducting, current continues to flow through the rheostat 306 and the first transistor 310 until the long pulse from the pulse generator terminates. The variable resistor is set so that the current flowing through the solenoid coil windings after the pulse from the one-shot vibrator has ended is just sufficient to hold the valve open against the pressure exerted by drilling fluid flowing through it against the fluid catcher. Once the solenoid is de-energized, the force exerted by the drilling fluid on the fluid catcher forces the valve stem down so that the valve disk comes to rest on the valve seat, thereby preventing further bypass of drilling fluid around the drilling bit, and completing a negative pressure pulse, which may be detected at the surface.

Since the area of the valve stem piston is slightly less than that of the valve disk, a relatively small, but steady, force is applied on the upper side of the valve disk when the valve is closed.

Ordinarily, the pressure drop across the drill bit is between about 1000 and about 3000 pounds per square inch, but with the pressure-balancing bore in the valve stem, the force on the valve disk in the closed position is only 30 to 50 pounds, thereby permitting the valve to be opened with a relatively small force. It is held open with an even smaller force. For example, the current through the solenoid windings-after the second transistor stops conducting is substantially less than, and usually only about ten percent of, that required to open the valve. Ordinarily, the holding current is between about 1% and about 50% of the opening current The amount of current required to hold" the valve in the open position depends on the shape, size. and location of the fluid catcher. In a valve in which the diameter of the valve seat is about i inch, and the maximum diameter of the catcher is about 0.6 inch, the minimum holding current is produced when the catcher is between about i and about i inch below the line where the valve disk contacts the valve seat.

The two solenoids acting in tandem and simultaneously in the same direction provide a large lifting force, and yet are smaller in diameter than a single solenoid which would supply the same force with the same current. Accordingly, the pulser housing can be made relatively slim to minimize pressure drop in the drilling fluid as it flows down the drill string.

Another advantage of the two solenoids working together is that the solenoid shafts and valve stem work together by simple abutment without requiring any complicated linkages which could break, jam, or permit misalignment, during operation.

Moreover, the monostable valve cannot be bounced into a permanently open position, as can happen with a bistable valve. Therefore, the balanced force keeping the valve closed can be lower, resulting in a lower opening force. This, of course, permits the use of smaller solenoids and requires less power for operation.

The spring 1 78 urging the valve disk into the closed position is not essential to the operation of the valve, although it is useful in those situations where the valve might tend to remain open under low flow conditions. For example, if cement is being placed in the well by displacing it downwardly during slow operation of the drilling pump, the accuracy of the placement is improved if the valve is closed so that no drilling fluid can bypass the drill bit. In such a situation, the spring would ensure that the valve is closed.

If used, the spring is chosen so that it does not substantially affect the force required to open the valve. The spring is not intended to supplement the force produced by the fluid catcher on the valve stem. It is present only to provide a steady minimum closing force under slow or no-flow conditions for the drilling fluid.

The fluid catcher can be omitted, if the valve disk is shaped and located so the flow of drilling fluid through the open valve produces the desired closing force after the solenoids are de-energized.

Venting bore 1 65 permits the application of drilling fluid pressure against the top of the floating piston 146 so that the oil in the solenoid chamber remains fully pressurized to reduce any tendency for drilling fluid to leak into the solenoid chamber.

The radial channels 130 and the bores 132 in the solenoid face plates facilitate surging of the oil and free movement of the solenoid face plates as the solenoids are energized and de-energized.

Those surfaces of the valve which are exposed to the abrasive action of flowing drilling fluid are preferably made of an abrasion-resistant material, such as tungsten carbide or titanium carbide, to ensure long life.

Claims

1. Apparatus for sending information through a drilling fluid in a borehole drilled in the earth with a drill bit on the lower end of a drill string in the borehole and through which the drilling fluid is circulated with a pump to flow through the interior of the drill string, past the drill bit, and into an annulus between the drill string and the borehole wall, the apparatus including means defining a passage for drilling fluid between the drill string interior and the annulus, a valve disposed in the passage to be held in a normally closed position by the difference in drilling fluid pressure across the valve, means for applying an opening force to open the valve so drilling fluid flows through it, means urging the valve from an open toward a closed position as drilling fluid flows through it, means for removing the force on the valve so it moves to the closed position, the opening and the closing of the valve generating a pressure pulse in the drilling fluid, and means for detecting the pulse.

2. Apparatus as claimed in claim 1, which includes means responsive to the flow of drilling fluid through the valve to urge it from an open toward a closed position.

3. Apparatus as claimed in claim 1, which includes means for reducing the opening force to a holding force great enough to hold the valve open against the means urging the valve closed as drilling fluid flows through it.

4. Apparatus as claimed in any preceding claim, in which the valve includes a valve housing with an inlet and an outlet, a valve seat in the housing between the inlet and the outlet, a valve disk disposed in the housing on the inlet side of the seat so the disk is urged against the seat by fluid pressure difference between the valve inlet and outlet, the disk being shaped to rest on the seat and close the valve by sealing the valve inlet from the outlet, a valve guide chamber in the housing on the inlet side of the seat, a piston secured to move with the disk and disposed to slide in the chamber, means connecting the chamber interior with the fluid on the outlet side of the seat when the valve is closed, and means on the valve disk for urging the valve toward a closed position when fluid passes through it so the fluid exerts a net force on the valve disk in the direction of the seat.

5. Apparatus as claimed in claim 4, in which the valve seat includes a generally conical surface which extends inwardly in the direction of fluid flow through the valve to where the valve seat is contacted by the valve disk when the valve is closed.

6. Apparatus as claimed in claim 5, in which the valve seat surface is inclined at an angle of between about 5 and about 40O with respect to direction of travel of the disk as the valve is operated.

7. Apparatus as claimed in claim 5, in which the valve disk includes a generally conical surface extending outwardly in the direction of fluid flow to where the valve disk contacts the valve seat.

8. Apparatus as claimed in claim 7, in which the valve disk includes a generally annular surface which extends substantially perpendicular to the direction of travel of the valve disk from where the valve disk contacts the valve seat when the valve is closed.

9. Apparatus as claimed in claim 4, which includes a fluid catcher secured to the valve disk and disposed within the valve housing on the downstream side of the valve seat.

10. Apparatus as claimed in claim 9, in which a valve stem is secured to the valve disk and extends through the valve seat when the valve is open, the fluid catcher being secured to the valve stem.

11. Apparatus as claimed in claim 9, in which the fluid catcher includes a generally conical surface extending outwardly in the direction of fluid flow through the valve.

12. Apparatus as claimed in claim 10, which includes means for adjusting the position of the fluid catcher on the valve stem relative to the valve seat.

13. Apparatus as claimed in claim 4, which includes means for applying pressure from fluid on the downstream side of the valve seat to the interior of the valve guide chamber.

14. Apparatus as claimed in claim 13, which includes a valve stem connecting the piston to the valve disk, the piston and valve stem having an opening through it to connect the interior of the valve guide chamber with fluid pressure on the downstream side of the valve seat to reduce the force on the valve disk when the valve is closed.

1 5. Apparatus as claimed in claim 4, which includes a solenoid winding, a solenoid armature, a solenoid shaft secured to the armature and arranged to engage the valve disk to move the disk from the valve seat to an open position, means for applying a first large current to the solenoid winding to develop a relatively large force to open the valve, means for reducing the current to the solenoid winding to produce a smaller force which holds the valve disk in the open position, and means for de-energizing the solenoid so the valve disk returns to the valve seat and closes the valve.

1 6. Apparatus as claimed in claim 15, which includes a second solenoid winding, armature and shaft, the solenoid windings being connected to receive current simultaneously, and the solenoid shafts being aligned to exert a force simultaneously in the same direction.

17. Apparatus as claimed in claim 15, in which the solenoid winding and armature are disposed in a chamber adapted to be filled with fluid, the armature having bores extending through it in the direction in which the armature moves to facilitate travel of the armature in the fluid.

1 8. Apparatus as claimed in claim 17, in which a face of the armature contains outwardly extending grooves to facilitate fluid flow past the armature when the solenoid winding is energized.

19. Apparatus as claimed in claim 18, in which the armature includes bores extending through it in the direction of armature travel.

20. Apparatus as claimed in claim 3, which includes a spring urging the valve disk into the closed position when there is no flow of drilling fluid through the drill string.

21. Apparatus as claimed in claim 15, in which the duration of the opening current is substantially less than that of the holding current.

22. Apparatus as claimed in claim 21, in which the duration of the opening current is between about 1% and about 50% of the holding current.

23. Apparatus as claimed in claim 15, in which the holding current is substantially less than the opening current.

24. Apparatus as claimed in claim 23, in which the value of the holding current is between about 1% and about 50% of the opening current.

25. Apparatus as claimed in claim 1, and substantially as hereinbefore described with reference to; and as shown in, the accompanying drawings.