# Патент USA US3075617

код для вставки`Ian. 29, 1963 A. R. ArrKEN ETAL 3,075,607 SEISMIC EXPLORATION Filed Dec. 51, 1958 2 Shee‘lzs‘Sheeìl 1 BY ¿MM Jan. 29, 1963 A. R. A11-KEN E-r AL 3,075,607 s ISMIC EXPLORATION 2 Sheets-Sheet 2 . «ej Ã îìîìì? ' , i@ (_ ~ INVENTORS TTORNEYS United States Íl; arent ddee îßiïäßd? Patented dan. 29, i953 l 2 3,075,637 The l2 seismic signais produced by the geophones 5l through 62 are applied through connecting leads 7l~ä§2 to SEiSMifC EXPLÜRATEÜN Alexander R. Aitken, .lohn A. E. Gerrard, and George l’. ilarratian, Bailes, and Hal Si. iones, Houston, Tex., as signors to Texas instruments incorporated, Dalias, Tex., a corporation of Delaware >different channels of a multichannel preamplifier l5. After being ampliiied by the preampliher l5 the analogue seismic signals are applied through connecting leads 83 Sie to a multiplexer 16, which samples the amplitude of cach seismic signal at regular time intervals and then transmits the samples through connecting lead 95 in a single channel sequentially to analogue-to~digital con Prior to the present invention, the process of seismic exploration has been carried «out by making seismic rec 10 verter 17. ords in the held. These seismic records are then physically According to Shannon’s sampling theorem, an analogue signal containing no frequencies f cycles per second or we shall refere to as channels l through l2, respectively. higher may be completely represented by a sot of samples transported back to a data processing location Where the records are analyzed mentally, or with the aid of analyti cal apparatus such as that disclosed in the Patent No. 15 2,794,965, issued June 4, 1957, to William l. Yost. This procedure necessarily takes a lot of time. The iinal re seconds apart in time. For example, an analogue signal sults of any test are often not available until days after containing no frequencies 250 cycles per second or higher the test is performed. can >be completely represented by samples taken two 20 According to the system of the present invention, the milliseconds apart. It should be pointed out, however, seismic signals produced by the geophones are sequen that frequencies 250 cycles per second or above may not tially sampled and the sequentially sampled amplitudes be iiltered out from .an analogue signal by sampling the are converted into digital data. The digital data is then analogue signal at two millisecond intervals. Neverthe transmitted over a radio link to a computer, such as dis less, a faithful representation of an ordinary seismic sig« closed in British 1?atent 749,836, issued June 6, 1956, at 25 nal may be made for the purposes of digital analysis by the data processing center which processes the seismic samples taken not impractically close to one another. data and makes the results available after a matter of For most seismic signals, the samplinfy at intervals of two minutes instead of days. milliseconds will be satisfactory. ‘Erior to the present invention there was no known The multiplexer, since it samples the amplitudes of all method which gave satisfactory results of operating a 30 twelve channels, will transmit l2 sampled amplitudes for digital computer to process seismic data. This lack was each sampling interval to the analogue to digital con~ due to the fact that the mental process of analyzing the verter 1'7. The analogue to digital converter ll'î converts analog seismic records was for a large part subjective each sampled amplitude to a binary number. The ana and hence could not be programmed into a digital com 35 logue to digital converter also identities each group of puter` sampled amplitudes for each sampling interval and as The present invention comprises a method of program signs a binary number to each group to identify the time ming a digital computer to process the seismic data to of »the sampling for that group. The binary number as give results superior to those obtained by the subjective signed to each group of sampled amplitudes equals the mental or analog methods of the prior art. interval between the time of the shot and the time An additional object is to provide an improved method 40 time of sampling of such group of sampled amplitudes. These of seismic exploration which lends itself to an improved time intervals are expressed in sampling intervals rather quality, or as it is sometimes identilied, a more sophisti than seconds to facilitate the operation of the assigning cated data reduction procedure. of these time intervals to each group. A simple counter Further objects and advantages of the present inven may be used to determine the time interval assigned to tion can be understood when taken in conjunction with each group of sampled intervals. If the count registere the following drawings in which: FIG. l is a bloeit diagram illustrating the ovenall method and system of seismic surveying; and in the counter is increased by one for each succeeding group, the count registered in the counter will always EEG. 2 is an analog representation of a typical set oi 50 be the time interval, expressed in sampling intervals, be tween the time of the sampling and the time of the shot. seismic signals that may be obtained in a method of seis The binaryidata including the sampled amplitudes land mic surveying or that may be obtained when monitoring the assigned time intervals may be delivered through con the system of the present invention. necting lead 95 to and recorded by magnetic tape recorder ln a seismic surveying operation an explosion is set 22 to provide a record of the data in the tield. rl`he data oil below the ground to send shock waves traveling is also delivered through lead 97 to transmitter 18 and through the earth. This explosion is referred to in the then transmitted by transmitter 1S over a radio link to art as a shot. ln FIG. l the point of the explosion is receiver i9 in the data processing center. The data re designated by the reference number 3i. The shock ceived by receiver i9 is delivered through connection 99 waves travel in the direction indicated by the arrows and to tape transport 20 and recorded in binary digital form are reilected by the rock strata 32 and 33. After being 60 on a magnetic tape loop on tape transport itl. The data reflected by the rocl; strata, the shock waves travel up to is then fed from the magnetic tape loop to computer 2l gcophones Si through 62 which are spaced laterally through connection ltlll where it is processed. In the across the earth’s surface. The geophones 5l through 62 computer the data is digitally filtered, corrected for time transduce the waves into eletcrical energy to produce l2 displacement, the reilection zones determined which is analogue electrical signals in l2 separate channels which 65 called reflection picking, and then the depth and dip in we shall refer to as channels ll throuhg l2, respectively. formation computed. These signals are referred to as seismic signals. The re If O( t) is a time function vwith :a value of Zero outside iiected shock waves in the seismic signals are referred to »some ñnite time interval and if X(t) is another time as reiiection zones. A typical series of seismic signals that function, then the function would be obtained by monitoring such a process is shown 70 in FIG. 2. From these signals the depth and dip of the strata 32 and 33 can be determined. 3,075,6o7 3 4 . through @1_30 would be partially completed. Next, the seismic signal amplitude Xt+1 would be multiplied times constitutes a time function with certain frequencies re duced and/or eliminated from X(t). In other words, O1 through O32. The resulting product O1X1+1 would <I>(1-) is what is obtained after XU) has been filtered. The frequency transfer function Y(w) of vsuch filtering is the frequency spectrum G00) of the function O(t). Thus, by a proper choice of the filter operator 0(1‘) any filter start a new summation @t+1 and resulting products O2X1+1 through O32X1+1 would be added to the partially computed sums dit through @1_30. This process will go on until all of the ifs have been computed for the seismic signal.» As is well known in the seismic surveying art, the times by conventional L-C circuits. This kind of filtering is of the seismic signals must be corrected for normal move called cross-correlation (or convolution where the sign is minus) filtering. In the case of a signal existing in gaus 10 out, and incremental shock wave velocity increases with depth. Also, a static time correction must be added to sian noise,> the optimum cross-correlation filter procedure each signal. Because of the incremental average velocity involves the cross-correlation between a representation of increase with depth, the time correction is less for that part the 'signal and the signal plus noise function. AlthoughA of the seismic signal which occurs later. Thus, if t the noise in a seismic signal is not actually gaussian, quite favorable results can be obtained by using a typical shock 15 designates the time interval from the shot to the amplitude'y sampling, the time correction will vary with t and mustv wave reflection in the seismic signal as the filter operator be determined for each t. The time correction for each t" 0(1). is often determined from the formula AT=ATS+A in To carry out this operation digitally, the operator O(`t) which ATS is the known static time correction and is sampled at 32 points at sampling intervals equal to the sampling interval used in obtaining the digitalized seismic 20 signals. 'I‘he amplitude of the operator at each of these 32 points is converted to the binary system to give 32 binary numbers O1 through O32. Letting the binary num In the formula for A, d equals the lateral distance between ers equalling the sampled amplitudes of the seismic sig the geophone producing the seismic signal and the shot, nal for a single channel be designated by X1, X2, X3, . . . 25 V0 is the average initial velocity, and V1 is the incremental XI1 . . . in which the subscript indicates the time of the increase in the average velocity with depth. sampling, the computer is programmed to solve for each By rearranging the terms of the formula for A, the may be simulated including many which are not realizable sampled amplitude of the seismi-s signal the equation equation 30 in which X(t) is any one of the sampled amplitudes of the seismic signal. The «P’s obtained then will represent the amplitudes of the seismic signal after it has been filtered. For every `<I>, an X is determined. Thus, @tris deter mined for X(t). Together all of the «ifs for one seismic signal comprise sampled amplitudes of the ñltered seismic signal. These <I>’s are spaced at Vthe same intervals or the sampling intervals of the X’s. l is obtained. If an arbitrary value is assumed for A, for example 50 sample intervals, then the expression on the left side of the equation will have a negative value for all 35 t less than the t for which the assumed value of A is core rect. Therefore, if the expression 21/’12t3-l-2V0V1t2-l-2V02t-íiÃ 40 is evaluated for increasing values of t with A equal to the assumed value, the value of t at the time the expres sion turns positive will be the t for which the assumed operation on the seismic signals of each of the 12 channels. value of A is correct. This operation will produce twelve series of binary num 1 By evaluating Ythe expression for increasing t and de bers, „one series for each channel, each of which is the sequentially sampled amplitudes of a seismic signal of a 45 creasing the value of A by one increment each time the expression becomes positive, the A’s for each t after the different one of the signal channels after such seismic t for which the arbitrarily assumed value of A is correct signal has been filtered. These filtered seismic signals may be determined. The computer is programmed to of channels 1 through 12 shall be designated <I>‘1(t) carry out these operations and thus the AT’s are deter through <ï>12(zf), respectively. The series of binary nurn bers which make up the sequentially sampled amplitudes 50 mined. In this yprogramming the value of A is initially chosen large enough that the AT at which the value of of the functions lï>(z‘) shall be designed as follows: The computer is programmed to carry out this filtering the expression goes positive occurs in the seismic signals prior to the useful part of the seismic signals. ’ It is convenient to program the computer to determine 55 the time correction AT for each <I> along with the deter In each binary number of the above series of binary numbers, the superscript designates the channel of the ñltered function of which such binary number is a sam# mination of such <I>. To carry out the operation of reiiection picking, each one of the filtered seismic signals is operated on to form a -function p(t) and aU) from each seismic signal. The tween the shot .and the sampling of the filtered function 60 function p(t) is formed from a seismic signal by identify ing the peaks and troughs of the seismic signal. The func. to produce such binary number. The unit'of the time in tion 1;(1?) is made to equal l at the time of each of the tervals expressed .bythe subscripts is sampling intervals. pled amplitude, `and the subscript is the time interval be~ peaks and made to equal zero at each of the troughs.. `In carrying out the filtering operation for one of the Numerical representation of straight lines are then con seismic signals it is convenient `to perform the summation for several lIfs at once. To do this, partially completed 65 nected between the peaks and the troughs thus forming the new function p(t). The function rr(t) is derived summations for @1_1 through @1_31 will be stored in the from a seismic signal by identifying the peaks and troughs computer at sequential adresses in the computer. Then ofthe seismic signal. The function a(t) is then made to XU) is multiplied in sequence by the Values O1 through equal the absolute value of the peaks and troughs at the O32. The product X101 will be stored to start a new summation. -The product X102 will be added to the 70 times of the respective peaks and troughs. Straight lines are then connected between the adjacent absolute values partially computed snmfor @1_1. Likewise, each of the and thus the function :1(1‘) is derived from the seismic sig products X103 through XtOgZ Vwill be added to the par nal. The functions a‘l-(t) through a12(t) are derived from tially completed summations @1__2 through <I>1_31, respec the filtered seismic signals of channels 1 through 12, re tively, to further compute these summations. The summa tion @1_31 would then be completed and the summations @t 75 spectively. TheV functions p1(t) through P120) are ¿finil4 3,075,607' 5 derived from the ñltered seismic signals of channels 1 obtained from the formula S(9, t) :K0P(0, t)[A(0, l) through l2, respectively. -l-Ks] in which K0 and Ks are constants. After all of the combined search functions Sw, t) are obtained they From the functions a1(t) through ¿112(1‘), a plurality of search functions A(0, t) are computed at each sampling from the following formula: are examined to determine whether they exceed an arbi trary selection level L1. if one of the S(0, t)’s for -any given time t is found to be above the arbitrary selection value, the highest S(0, t) for that time t is selected as in dicating the existence of a rellection Zone. Once the existence of a reflection zone is determined, This formula for A(0, t) perhaps may be better under 10 the criteria selection level is changed from L1 to L2, which is slightly less than L1 for all the SU), 2)’s of that stood graphically. If the functions a1(t) through ¿112(1?) reflection zone. Thus, the reilection Zones are identiîicd. were plotted on the same time coordinates with each func The depth and dip of the rock stratum or strata causing tion placed in order according to its superscript, then the each reilecticn zone can then be determined. values of the function (11(1‘) through ttl-2U) used in the The computer is programmed to carry out this reflec summation in the formula for computing A(0, t) will be 15 tion picking operation. Of course, the computer oper found at the intersection of a straight line with the zero ates on the e’s, the binary numbers which represent the amplitude ordinate of each of the functions ¿11(t) through sequentially sampled seismic signals after they have been @12(1‘). The straight line is referred to as a search line. lîltered and time corrected. The search line will intersect the zero amplitude ordinate To identify the peaks and troughs, the series of e’s of ¿11(2) at time t and the zero ordinate of the function 20 representing each seismic signal are taken in time se ¿112(1) at the time t+0. The search factors A(0, t) corn quence and each preceding e is subtracted from each puted at each sampling interval will have different H’s rang succeeding <î>. Whenever the sign of the result of this ing from plus 4 to minus 4 sampling intervals. series of subtractions changes from positive to negative, From the functions p1(t) through p12(t) a plurality of search functions P(9, t) are computed from the following 25 a peak is identiiied at this point'. Whenever the results from the series of subtractions change from negative to formula: v-i l n HM) positive a trough is identified 4at this time. To compute the function p(t) from a seismic l.signal the computer is programmed to assign the binary nun»l 30 ber l to the time of the identified peaks and O to the time of the identiiied troughs. At the standard sampling intervals between the peaks zuid the troughs, the com puter is programmed to assign values interpolated be~ In this formula P1' is a constant equal to 0.25 which is the average coherence coeiiicient for a set of random time functions, and S is an integer selected so that 2S is the tween 0 and l. Thus, a series of binary numbers are computed assigned to times at the standard sampling intervals. rthis series of numbers will represent sequen approximate length of a single cycle of one of the central tially sampled amplitudes of a p(1). The computer is frequencies in the spectrum of a shock wave reflection. programmed to make this computation for each filtered seismic signal to produce a series of binary numbers for each seismic signal. These series of binary numbers 4.0 p12(t) are plotted on the same time coordinates with their shall be identified as follows. Zero amplitude ordinates equally spaced and each func~ tio-n placed in sequence- accorcling to its superscript, then The formula for P(0, t) may be better understod if explained graphically. if the functions p10) through the summation 1 12 L L~1 45 12?;1'113 (H‘ 11 9) P12(f)=p112, @12,11312 - » ~ P1112 equals the average value of the values of the functions n10) through [1120) at the intersection of the zero ordi 50 Here again, the superscripts designate the channel and the subscripts designate the time t. nates of the functions with a search line intersecting To compute the function 0(1) for `a seismic trace the 1:1(1‘) at time t and intersecting a12(t) at time z‘-}-0. The computer is programmed to assign the absolute value of summation the amplitudes of the filtered and time corrected seismic signal to the times of the peaks and troughs. The com puter is programmed to assign at the standard sampling intervals between the times of the peaks and troughs, A values interpolated between the values assigned at the peaks and troughs. rthus, a series of binary numbers of numbers obtained by taking the value of each func are computed and assigned to times at the standard satu~ tion at the intersection with the said search line and sub tracting from each value the average value of the func 60 pling interval. This series 0f numbers will represent the sequentially sampled function @(1‘) derived from the ñl tions at all the intersections. The average of the abso~ then equals the average of the absolute values of a series lute values of the series of numbers is obtained as de scribed above for each of a` series of parallel search lines spaced at intervals of one sampling interval. If each of these averages is subtracted from Pr and the results of tered signal. the subtraction added together, then the summation The computer is programmed to make this computa tion for each filtered seismic signal to produce a series o-f binary numbers for each seismic signal. These series of numbers shall be identified as follows. will be obtained, The subscript of the cz’s of each of these series desig For each 0 and t a combined search factor S(6, t) is nates the time t and the superscript designates the chan amaca? d» 7 and scope of the invention which is to be limited only `as defined in the appended claims. What is claimed is: '1. A method of seismic exploration comprising the 5 steps of: nel. The computer is programmed to compute A(0, t) for each t and 6 according to the formula: l 12 .4(0, wzïêzaœwm N=1 in which DN equals a set of digital delays such that D12=0, D1=O and the other DN's are chosen such that DN 11 5 is equal to a minimum. The computer is programmed to compute P(6, t) according to the formula a. creating a seismic disturbance at a field test site -where reilectionzones of interest may be present, b. detecting the -seismic Waves resulting from said seismic disturbance and converting the detected Waves into a series of electrical signals from spaced points in the vicinity of said seismic disturbance, 9 amplifying said series of electrical signals in an analog'preampliiier and d. Vdelivering said series to multiplexing means and e. therein mixing and combining said series into a l2 PtL+D+M 121751 single channel of analog signal, f. delivering said single channel of analog signal to an analog-to-digital converter and ‘ in which DN is determined in the same manner it is de 20 termined in the formula for determining A(0, t). The computer is programmed to then compute S(6, t) g. converting said single channel of analog signal into ' a single channel of digital signal, l. delivering said single channel of digital signal to a zones in the following manner. radio transmitter, í. transmitting said -digital signal to a remotely lo cated radio receiver, j. delivering said received digital signal to a computer, `and S(0, t). The selected S(0, t) indicates the existence of . analyzing said received signal for detecting reflec tion zones whereby an immediate result is obtained at said remote location while said seismic explora tion operation is in progress. 2. A method of seismic exploration as in claim 1, for each 6 and t according to formula The computer is programmed to select the reflection All of the SU?, t)’s are compared in time sequence With L1 to determine which S(0, t)’s are greater than L1. When one of the S(6, t)’s is found to be greater than L1, the S(0, t) at the same time t having the highest value is selected and recorded 30 along with the 0 and t used to compute the selected a reflection zone. Once the existence of a reflection zone has been indicated, all the succeeding S(0, t)’s in the same reilection zone are compared with L2, which is slightly less than L1, to minimize -lluctuations at the be~ ginning and end of the reflection zone. The computer is programmed to determine accurately k. unscrambling said previously mixed signal, and wherein said step Iof unscrambling said mixed signal comprises digitally filtering and separating said signal into a plurality of digital signals for computation pur poses. v'3. A method of seismic exploration as in claim 2, wherein said step of analyzing said received signal com prises: generating a set of first functions based on the the times and responses from the reflection zones using the data obtained from the operation of selecting reflec 40 absolute values of the peaks of said plurality of digital signals; generating a set of second functions based on tion Zones. The computer carries out this operation by the positive and negative peaks of said digital signals; examining the reflection zone information with increas generating a set of third functions based on said first ing t until a picked zone is encountered. The computer functions; generating a set of fourth functions based on then examines the values of <I>1(t) occurring after the time of the start of thepicked reflection Zone to locate 45 said second functions; generating a set of ñfth functions based on the combined third and fourth functions to pro the first trough occurring in <ID1(t)‘ after the start of the vide a set of search functions for indicating the existence picked reflection zone. The computer next examines the of a reflection zone. value of @120) to find the nearest trough in the func 4. A method of seismic exploration as in claim 3, tion @120) to a time occurring the time 0 after the time of the trough determined in @10). The times of the two 50 wherein said search functions are generated in accord ance with the formula: located troughs then are recorded. The computer is programmed to carry out the above operation for each picked reflection. i The computer may be programmed to make these re corded times of these troughs available to the operator, 55 or the computer may be programmed to convert this information into dips and depths for the strata causing the reflections. In the above description the number of seismic signal channels is twelve. The invention, of course, may be 60 used with a different number of channels. This and other modifications are deemed to come Within the spirit References Cited in the tile of this patent UNITED STATES PATENTS Re. 23,686 2,265,513 Heising ______________ __ July 14, 1953 Burg ________________ __ Dec. 9, 1941 ’ 2,794,965 Yost ________________ __ June 4, 1957 2,836,356 Forrest et al ......... __ May 27, i958 ` 2,845,597 Perkins _____________ __ July 29, 1958 2,874,356 'Peterson _____________ __ Feb. 17, 1959

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