DE1548363A1 - Seismic investigation method and device - Google Patents

Description

DR. F. ZUMSTEIN - OR. E. ASSMANN DR. R. KOENIQSBERQER - DIPL-PHYS. R. HOLZBAUER

TELEPHONE: 22 3-4 7 «and 221911

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BANK ACCOUNT: BANKHAUS H, AufHÄU8ER

8 MUNICH 2,

BRÄUHAUS8TRAS8E 4 / l »

(2/2/1) 87 487

She Atlantic Refining Company, Philadelphia, Penn. USA

Seismic. Investigation procedure and gate direction

The present invention relates generally to a method and a gate direction with a better ratio of the signal to the house in seismic signals. In particular, the invention relates to methods for processing seismic data, those according to the common reflection point method (common reflection point method). .

Seismic surveys relate to a method of obtaining information relating to subterranean earth formations thereby getting that energy from a first point down into the formations at or near the surface of the earth is sent, and that the reflected and / or diffracted energy is measured at one or more second points. It is common to an explosive iaduög-odeEveiiJLe other source of energy; -to

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use to generate seismic energy. Multiple seismometers are in a previously "determined geometric series or Order set up at a distance from the "shot" point. the Energy that hits the seismometers is converted into corresponding electrical signals that are amplified and recorded will. By taking the time for the enemas of the selected Vibrations can provide usable information about the depth and properties of the underground earth formations are preserved. However, external energy forums are usually present whereby the recognition of the desired signals can be made more difficult or prevented.

For several years, the geophysicists have therefore been continuously working on it Aimed at improving the signal-to-noise ratio in seismic signals. There were different systems described which by means of multiple element rows an itauscJad attenuation Achieve a variety of school points and Detectors is increased, however, the underground area that is averaged also increases accordingly. Lies can in the Eat has the effect of obscuring the very details that are being sought.

The multiple occupancy common reflection point method, as described in U.S. Patent 2,732,906 designed to be practical means of increasing diversity to have. According to this U.S. patent it is proposed that

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that the information that comes with a given point of reflection related, but with a variety of weft point and Geophone positions are recorded, combined algebraically after appropriate time corrections have been applied. · So, if the reflected signals received on multiple paths are aligned on ifoincidence, their resultant is Sum proportional to the number of signals. Faults that run on other than the required energy paths, n ± Coincident and are therefore relative to the keflections of interest weakened, iiies is analogous to the model implementation (pattern performanee). YES but the source and itapfangpunkts like this are chosen that seismic energy from each shot of the same small subterranean surface is reflected, so is that discussed above adhering to conventional modeling techniques Restriction no longer applicable. Yes procedure of the "common Sprungpunlct'es "(" common bounce point ") has the further advantage that multiple reflections are attenuated. This technique can too for carrying out land surveys applied to outside operations on the coast, or for surveying shallow inland canals, lakes, etc. .

Although the data layer technology has a common point of reflection the signal-to-noise ratios far exceed practical ones The limits of the most common pattern methods increased there is still a lot of room for improvement. The main problem was that the horizontal, distance or "AuSdeli-

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“Spread spacing” between the various “shot points and receivers through exit or exit points”. Stepout distances are limited, the k ^ a in must be kept with respect to the reflection period. Since in generally an area near the surface of interest is so

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the maximum installation distance or receiver distribution is considerable limited. Likewise, the type and shape of the energy that is reflected from the selected jump points changes, with the angle of reflection. This prevents coincidence matching with the required accuracy as soon as the source-receiver distance is relatively large.

The present invention relates to a method of the art of the common jump point, which eliminates these difficulties.

According to the invention, a method is provided for combining seismic traces which represent seismic signals which have been reflected from a common point in a subterranean .Formation which contains the stages in which the traces are adjusted by introducing static and dynamic corrections to match the seismic signals on the various tracks in which a part of at least one of the corrected tracks is selectively suppressed and in which the corrected tracks that have not been suppressed and the remaining part of each suppressed track are added by one generate summed track. ^; '-? - ·' ■ -'- "' ^%

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According to the invention, a device is also provided, to combine seismic traces that represent seismic signals, those of a common point in an underground Formation have been reflected, which is provided among other things with converter means to convert the seismic information contained in these traces into electrical signals, a delay system to differentiate these electrical signals To give time delays, a suppressor unit, In order to suppress unwanted parts of these electrical signals, an adding circuit to suppress the undiminished parts of these electrical signals Signals to add up, and transducers to add up to bring electrical signal into the desired recording form.

For a better understanding, the invention is based on the following of preferred embodiments and with reference to the drawing explained in the

I ¹ Ig. 1 shows a schematic representation of the setup or arrangement of the shot points and seismometers using the common reflection point method.

ff ± g. Figure 2 shows the application of a point of the present invention to the angle of reflection from a subterranean formation.

Pig. 3 shows a representation of the frequency differences that between an uncorrected seismic signal and the same Signal with additional time delays can be obtained. , ■ iig. 4 is a block diagram showing the basic equipment;

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as they are used in the implementation of the present invention will.

Fig. 5 is a circuit diagram of the suppressor unit according to the invention.

In order to facilitate the understanding of the invention, several are now intended Terms have been defined according to their intended use.

The term. "Seismic trace" or "seismic channel" is intended a seimic information from a particular geophone position mean that are printed on a suitable recording medium or is recorded. Each trace is of course a record of the time, size and phase of the seismic received Energy. It should be noted at this point that most seismic records have compositions of 20 or more Are signal trains from as many geophone positions. Every Geophone position hinwiaäerum can consist of several geophones, which are connected together to form an output signal.

"Static corrections" compensate for the elevation of each separate geophone position in relation to an assumed reference plane, the elevation of the energy source or shot points in relation to the reference plane, the speed of seismic waves through a layer of low velocity immediately on the surface of the earth, etc. These taken together or combined Weathering and elevation corrections are throughout the length

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der.Track not variable, but can possibly be from Spur to trace in every related group of Tracks differ.

"Dynamic" or "variable corrections" include the spread, Movement out or exit correction (spread, moveout, or stepout correction), which is a puncture of the distance of a geophone division from a point of fire, and they include every Corr door created by changing seismic speed with the depth is caused. The magnitude of the danymic correction changes over time for the signals received by any given geophone. The main factor in the Determination of a dynamic correction is the amount of the stepout involved. The exit correction is always the largest at the beginning of each track and takes on one Minimum value (which ITuIl can approach)., While the track is played ". A different changeable ■■ correction of this Type is given on every trace, which depends on how the postures, of the receiving geophones ... in relation to the point of focus.

"Time delays" are used to get each lane through

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ϊΐ of suitable static and / or dynamic corrections to put them in relation to each other, i.e., if the originally recorded tracks are rewritten, so will be on each individual track given up a selected time delay. if they are recorded again, then events stand up every trace in the same relation with respect to time, so that

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Corresponding seismic information in one line with one another lie. The delay that the static correction introduces is usually placed in the initial part of each track while this is rewritten; The dynamic correction can be carried out continuously during the rewriting or through a series of discrete Time delays of equal or unequal length in advance

determined points in time along the track that is currently being processed will be introduced.

"Reflection angle" is used to denote the angle formed by the straight lines going from the common point of reflection to the weft point position under consideration or seismometer position are drawn. The angle of reflection is greater, the further away the observing geophone is from Shot point is removed. The reflection angle also increases (for the same shot and observation point) when the jump point is closer to the surface.

Hit "frequency of the signal" becomes the periodic puncture one seismic signal with reference to time, i.e. the number of repetitions of the seismic signal per unit of time (usually referred to as vibrations per second). Therefore poses the frequency of a signal represents the number of seismic waves, that pass the seismometer position every second.

In Fig. 1 is a schematic illustration of the technique of the common Reflection point shown. The lobsters 10, 11, 12 and

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15 represent shot point divisions. Geophone setups, the equipped with seismometer devices are marked with 14, 15,

16 and 17. At 18, 19 and 20 are, underground formations "denotes those below the surface of the earth and parallel lie at different depths to the earth's surface. The common Reflection points in these underground camps are marked A, B and G respectively. Seismic waves generated at the firing points and reflected from the underground storages are represented by the lines marked "with arrows".

As shown, the vibrations generated are partially due the underground camps 18, 19 and 20 at the designated points A, B and G reflected. The geophone positions 14 » 15, 16 and 1? selected beforehand to move from jump points A, B and G receive reflected vibrations. Electric lines 21, 22, 23 and 24 carry the incoming seismic Signals converter means 25 to where the signals from each Geophone breakdown as separate tracks on a field record 26 can be recorded.

For the sake of explanation it should be assumed that an explosive Charge is detonated at the firing point 10. Then seismic energy spreads in all directions ". Part This energy is reflected from the underground storage 18, at point A, up to the seismometer device 14. Other Parts of the energy are from the camps 19, in point B, and 20, in point C, reflected and also in the geophone division 14

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receive. It is then assumed that an explosive charge is made to explode at the firing point i1. So be seismic Vibrations received at the geophone division 15, the reflections from jump points A, B and G. JPaIls further Charges are detonated at firing points 12 and 13, are reflections from the jump points A, B and G at the G ^ ophone positions 16 and 17 recorded. Of course, additional seismic shots are fired from positions other than positions 10, 11, 12 and 13, and the reflections from the jump points A, B and G are recorded with approximately set up receiver devices.

Because the angle of reflection of sound waves from underground i'ormations is equal to the angle of incidence, the appropriate geophone setup will be determined for a given shot point in that (1) the angle of incidence is determined and that (2) is determined where the seismic energy of interest arrives at the surface by using an equal reflection ratio accepts. For this reason each sciiuiapoint and the corresponding Geophone set up such a horizontal distance from each other that they are equidistant from a line perpendicular to the formation to be examined in the selected reflection point (jump point; is earned. The reference line for the appropriate set-up of the oeismometer equipment relative to the selected weft points is indicated by the "dashed" line oC in Pig. 1 shown. the Line QC runs through jump points A, B and G and is vertical

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right to formations 18, 19 and 20.

It has already been mentioned that the distance between a shot point and the associated geophone installation something in practice is limited. For example, if we consider the shot point 12 and the associated receiving device 16 in Pig.1. When a shot is fired at 12, the vibrations hit the Formations 18, 19 and 20. Reflections from points A, B and ~ ü meet the geophone position 16. If one now looks at the Formations and assumes that 18 is relatively close to the surface, 19 at a medium distance and 20 very far away from the surface. Under these conditions, if the track that has been recorded on the Field Recorder * 26 has been compensated for by static and dynamic corrections is, the resulting track is of quite poor quality ν because of the frequency distortion caused by large dynamic corrections originates, own. Because of this, the common jump point technique may fail and will not be improved Recording received as the final accumulation track Contains tracks that contain ΐ-rush on which are drastic dynamic Corrections have been made.

If one further assumes, with reference to FIG. 1, that a seismic shot has been fired at the point division 11, then vibrations from the points A, B and 0 are reflected to the receiving device 15 and recorded as a track on the field recorder 26 in this case the delayed track (ie the corrected track) is likely to become significantly less

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Have distortion than the track in the previous one Example. This "is based on the fact that the spread distance in this example with reference to the average The depths of the formations are smaller and that is why they are dynamic Corrections are smaller.

From these examples it should be clear that the best overall track is obtained when a shot is in position 10 is emitted, and the reflected vibration-in the position 14 is recorded. Here the scattering distance is very small, and therefore only minimal corrections need to be made for the exit to become. Accordingly, if the recorded track is time-delayed, only minimal frequency distortion occurs.

Deterioration on.

To do this, however, use the common point of flexion method To be able to do this, at least two separate tracks must be "stacked", and preferably more than two tracks will be combined with each other. In addition, these traces are intended to represent seismic data obtained from shooting points that have significant distances from each other. Seismologists then became prefer to add the traces created by the shots in positions 10, 11 and 12, but this would bring no real advantage in the present Pail. Parts of the combined trail would show improvement while other parts would be made illegible. The distortion or deterioration would be increased if even more

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distant tracks, such as the channel that will be recorded when a shot is fired at 13 while layering the final recording would be used.

In summary, you should then have records or traces showing reflections from a common point in every underground! formation, to be added up to reasonable proportions to get from signal to noise. Especially in the addition of several such traces are the strength of the technique of the common point of reflection for seismic prospecting. From the above discussion, however, it follows that, in general, the diversity desired cannot be realized because of the frequency distortion that arises if the length of the stiBi or the spreading increases a significant number of dynamic corrections are introduced.

According to the present invention, the common "reflection point technique" can be used and good results are obtained regardless of the spread distance. Accordingly , any number of seismic shots can be used in recording an area, and one "usable" Information can be taken from each track. Likewise, the corrected tracks obtained according to the method according to the invention can be added to form a summed track in which all parts of the recorded section are reliable, since the final recording section does not reproduce any tracks which, with the introduced time delays, are caused by extreme changes.

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portions have been grossly distorted.

The basic concept of the present invention relates to a technique in which the addition of seismic signals reflected from a common point of a subterranean formation are improved by the fact that signals recorded on certain tracks are optionally suppressed, while others are combined. Traces of seismic energy moving along the most perpendicular paths beneath the earth's surface run /? "" "are corrected and in their entirety at the Making the-stacked track related. Traces, the signals which have run on less vertical paths, are, after they have been corrected, over time segments, which begin with the end of time Hull of each track, suppressed tracks that represent signals that travel over even more distant paths that have run, i.e. less vertical paths, are suppressed before they are added over even longer tent sections.

The suppression generally takes place during a predetermined length of the recording time, such as 0.10 seconds, 0.20 seconds, 0.30 seconds, etc. instead. Generally exceeds the maximum suppression seldom 1.5 seconds, and usually the suppression time is less than during playback 1.0 seconds. The extent of the suppression varies, always depending on the person on the scattering or spreading distance, i.e. the greater the scattering distance, the greater the length of the suppression .

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I) a the unwanted signal part of each track is suppressed, can put shot holes and receivers at any suitable distance can be set up, and any number of separate seismic shots can be performed in relation to predetermined jump points. The seismic energy generated by each energy output is generated and is reflected by the selected jump points, is received by suitably arranged receiving devices, displayed. The seismic information thus obtained is recorded as separate tracks on a field - i.e. a magnetic tape .. or other suitable device. Static and dynamic corrections are made to each lane through an appropriate system of time delays. Now, according to previous practice, all of these traces have been merged together or some would be excluded and the rest merged. The 'fatsacne According to the invention, that at least one rope of each recorded track is used when the overturning track is brought together is used, "therefore means a considerable technical Progress.

Furthermore, the invention is aimed at specifying a method, which determines when a part of a track should be suppressed. This has been found to be in to a certain extent, from the angle of reflection of the particular considered Jump point depends.

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This embodiment according to the invention is explained in FIG. 2. Vibrations are emitted from the shot point 27, which is located on the surface of the earth ". The jump point D is shown on a sloping underground camp 28. Vibrations reflected from point D are in the geophone position 29 received on the surface. The "dashed line" O ('is perpendicular to the formation 28 in

Lines point D. The "arrows" XaUeH show the path of the Wavefront from the shot point 27 to the point D and to the reception pitch 29. The angle whose apex is at D and the legs of which are the "arrows" lines are labeled Y. Thus the angle Y. is that defined above Reflection angle.

The rule for determining when the beginning part of a track should now be suppressed depends on the size of the angle Y. If Y is greater than '5b ° for the particular shot point, jump point and geophone position, then the part of the track that represents the reflections from this jump point should be suppressed. If Y is an angle between approximately 20 and 35 °, the decision as to whether the initial part of the respective track should be suppressed or not is optional. Usually the trace is suppressed, but to a lesser extent. If a track is recorded in which Y is less than about 20 °, it is generally more slowly included in the accumulation process Liit.

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It should be clear that for any given shot and geophone position the angle Y is greatest when reflections are recorded from formations relatively close to the surface of the earth lie. For energy that is reflected from deeper formations, the angle Y has a smaller value. If the reflective formations as lying in an infinite range can be assumed, the angle Y approaches the value O. ! It follows that reflections from very deep beds are likely be used when piling up the final track, however large the scattering distance on the surface is. Reflections from formations near the surface, are usually suppressed, if not naturally, by relatively close positions generated and received so that Y is quite small.

The rule of suppression given above is easy to be used, however, it is not error-free in all situations. E.g. it assumes that the only dynamic corrections are exit corrections. Likewise, the range of the angle is determined by the frequency of the seismic Energy, reflection coefficient, etc. influences. Fig. 3 explains the much preferred method designed to determine when a particular part of a seismic Track should be suppressed. The method according to the invention takes into account both exit corrections and corrections based on changes in speed as of course other considerations.

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Pig. 3 shows a curve f representing the frequency of a seismic signal on a part of an unchanged track, and the curve f having the same seismic signal applied to it Represents time delays. It can be seen that the frequency f · of the corrected track is smaller than the frequency f is the original track. This change (decrease) in frequency is a direct result of the time delays attached to it and is proportioned to the same extent. A similar change in the fundamental or original frequency results itself if the time delays are continuous instead can be applied in discrete steps.

This is the basis for the preferred Y ^ experience for determination the track sections to be suppressed. It It is suggested that if the frequency of the seismic signal on the corrected track is more than 10 $ or more im If compared to the unchanged signal changes, then the part of the track should be suppressed. Where the frequency drop between 5 and 10? & Lies, the choice is free or the track is in suppressed to a lesser extent. Where is the proportional frequency change is about $ 5 or less, you want to use toe-out not be applied. Accordingly, one can see visual records of the original seismic by comparison The data and the corrected composite data conveniently determined whether or not a portion of the track was to be used in making the final roll-up record the different tracks should be suppressed.

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In Pig. 4 is a block diagram of the apparatus shown in FIG is necessary to carry out the inventive method. A converter device 30 converts the seismic information, the Bind recorded on the field record 26, the has been obtained according to the method shown in Fig. 1, into electrical signals. The converter device 30 can individually rewrite each separate track on the field record 26. The electrical signals representing each track are applied to a delay system 31, the appropriate static one and / or apply dynamic corrections. Systems of this kind are well known, ϋίίη an example of one of these systems, 'das is preferably used is in U.S. application Serial Ho. 761 044. The corrected electrical signals are then sent to a suppressor unit 32, which acts so that designated parts of the signals by suppressing the initial part of the signals during selected time lengths turned off. The suppressed 32 are corrected Signals that have not been suppressed and the unsuppressed parts of the signals affected by suppressions to a conventional addition circuit 35. A summation signal is recorded as a single track on a visible record 35 by a writer j4.

Lu Pig. A circuit of a suppressor unit according to the invention is indicated. Electrical signals, which represent a corrected track, are applied to the input line 36. Jas Σίιι ran.r-jsignal wire, amplified by the Tricae i 7 and

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Given via the output line 38 to the adding circuit 33 of the FIG. B +, in Pig. 5, can represent any suitable voltage source, e.g. +300 V. The level to which the capacitor 41 is charged depends "on the voltage drop across the voltage division, which consists of the rotary resistor 40 and the resistor 47, which are connected in series pi B +. The tap 39 is used to apply the voltage which is applied to the capacitance 41. When the signal that is to be treated is applied to the input line 36, the synchronous switch device 42 is switched to the contacts 43 and. The capacitor 41 is then connected to the resistors 45 and 46 While capacitor 41 is discharging, a negative bias voltage suppresses the output from tube 37. Therefore, the charge accumulated on capacitor 41 determines the length of time that the signal is suppressed can be used to achieve the same results.

While in the above description only a limited number of embodiments of the system according to the invention are described are, it is possible to produce still other embodiments without departing from the scope of the present invention.

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Claims (1)

Patent claims 1. Method of merging seismic traces, the seismic Represent signals reflected from a common point in a subterranean hormone, including of the step of adapting the tracks through introduction static and dynamic corrections to adapt the seismic signals on the different tracks, characterized by that optionally a part of at least one of the corrected tracks is suppressed, and that the corrected ones Tracks that have not been suppressed and the remaining part of each track affected by suppressions are added, to create a summed track. 2. The method according to claim 1, characterized in that each track to be suppressed, starting at time zero, is suppressed. 3. The method according to claim 1 or 2, characterized in that the traces representing seismic signals that are less perpendicular to the subterranean formation are suppressed to a greater extent than the tracks that represent signals that have run on more perpendicular paths, 4. The method of claim 1, wherein the static corrections 009816/0596 - ZL- on appropriate tracks by fixed time delays, and with the dynamic corrections on appropriate Tracks through a predetermined system of time delays , characterized in that optionally at least the initial part of the corrected opures is suppressed which shows the more distant propagation paths of the seismic signals. 5. The method according to any one of the preceding claims, characterized in, that every suppressed track starting with the beginning of the track is suppressed, and that the suppression without interruption for a predetermined period of time is continued. 6. The method according to claim 5, characterized in that the aass maximum time for suppression of any given trace does not exceed 1.5 seconds. 7. The method of claim 1, wherein a first and second seismic Track is obtained with a single geophone device and a first and second explosion, respectively, the technique of the common equilibrium point is used, and the first seismic trace is obtained when the first explosion has a smaller horizontal distance from the geophone device as the distance between the second explosion and the geophone device when the second seismic trace is obtained, characterized in that the second track during a previous 009816/0596 The selected time period, starting at the beginning of the track, is suppressed becomes that the first trace and the one not suppressed Part of the second track can be added algebraically, and that the result of the addition is recorded as this summed track will. ö. The method according to claim 1, wherein several shooting points and observation stations according to the common point of reflection method can be used to obtain multiple seismic traces, the first of these traces passing through the first Observation station is obtained along an extending straight line at a horizontal distance in is arranged with respect to the closest weft point, characterized in that with the exception of this first track each of these tracks is suppressed for a predetermined period of time, starting with the beginning of the tracks the first track and the unsuppressed parts of the suppressed tracks are added algebraically, and that the Addition product is recorded as this summed track. 3. Method according to claim 8, characterized in that the time taken to suppress any given track is in direct proportion to the distance separating the particular shot point and the recording station associated with that track. 0C9816 / O596 10. The method of claim 1, wherein multiple seismic traces according to the technique of the common point of reflection -be obtained, characterized in that the angle of reflection the seismic energy from the common reflection point for each trace is determined that the early parts of each Track at which this reflection angle exceeds about 35 ° can be suppressed that the early part of each track, at that this reflection angle is between approximately 20 and 35 °, is optionally suppressed, and that the not suppressed Tracks and the unsuppressed parts of the suppressed tracks are added to this summation track form. 11. The method of claim 1, wherein multiple seismic traces obtained according to the common point of reflection technique, characterized in that the one associated with each track Is determined by the straight lines which are drawn from the common reflection point and extend to the shooting point or to the seismometer graduation that the track is included in the summing step that has the smallest angle in the (totality that the tracks are included in the summing step at which this angle is smaller than about 20 °, a small part of the early recording section is left out of each trace, with this angle between about 20 and 3 ° long, and the reading is less Traces in the- 009816/0596 _{; :;} , _{BATHROOM 0RIGINAL} sen summation step that a main part is involved of the early recording portion of each track is omitted at which this angle is greater than about 35 ° and the remainder is included in this summing step, and that the tracks and parts of the tracks selected above are alike braisch must be added to get this summation trace. 12. The method according to claim 1, in which a plurality of seismic traces according to the technique, the common reflection point is obtained and corrected for the exit by applying a system of time delays to it, characterized in, that the frequency of the seismic signal of each corrected track is equal to the frequency of the corresponding uncorrected one seismic signal is compared that the part of each corrected track is suppressed in which the frequency change is greater than about 10/6, and that the not suppressed Parts of all tracks are added to this summation track to obtain. 15. The method according to claim 12, characterized in that parts of tracks whose frequency change between approximately $ 5 and $ 10 and is also over $ 10, can be suppressed. 14. Device for carrying out the method according to one or several of the preceding claims, characterized by a converter device to convert the seismic information contained in 0098 16/0596 these spilren are to be converted into electrical signals, through a delay system to apply various time delays to these electrical signals, through an overpressure unit to remove unwanted parts of it suppress electrical signals through an aadibion circuit, to add the unsuppressed parts of these electrical signals, and by a converter, uru the summed electrical signal into the desired recording to convert ox'iü. Device according to Aiispracn 14 »thereby ^ e ^ ennzeiciinei; that this suppressing unit contains: an enexgiequexx, a Triode, whose anoae are connected to this energy neej-le Cathode is grounded, a signal input line connected to aem Grid of this triode and connected to earth is a changeable one Ϋ / resistance associated with this energy source a synchronous switch device with a capacitor connected to this variable resistor and to this input line is connected, and a Signax output exercise, which is connected to the anode of this triode. BATH ORIGINAL 009816/05 96