UIllted States Patent [19]
`Silverman
`
`Patent Number:
`[11
`[45] Date of Patent:
`
`4 497 044
`9
`,
`Jan. 29, 1985
`
`[54] SEISMIC WAVE GENERATOR
`
`[76] Inventor:
`
`Daniel Silverman, 5969 5-
`Blrmmgham St., Tulsa, Okla. 74105
`-
`
`[21] APPI- N°~= 337,678
`[22] Filed:
`Jan- 71 1982
`[51] Int. c1.3 ........................ .. (101v 1/02;GO1V 1/28
`[52] US. Cl. .............................. .1 .... .. 367/41; 181/107;
`181/111; 181/116; 367/40; 367/57
`[58] Field of Search ............. .. 181/103 104 106 107
`181/108 111 116 367/40 56 ’57 1145 4,1 42:
`’
`’
`’
`’
`’
`’
`5640728’
`
`[56]
`
`References Cited
`Us. PATENT DOCUMENTS
`
`1,998,412 2/1935 Prescott ............................ .. 18é/127
`l
`gala??? "
`“1313403
`2’922’484 V1960 Kesney :t al"
`181/107
`
`2,953,214 9/1960 Merten . . . . . . . . . . . .
`. . . .. 181/107 _
`2,992,694 7/1961 Musgrave et a1. ................ .. 181/107
`3,012,625 12/1961 Piety ................................... .. 367/57
`
`3,048,235 8/1962 Itria ................................... .. 181/103
`3,050,148 8/1962 Lee ....... ..
`181/103
`3,050,149 8/1962 Itria et a1. ..
`.. 181/107
`3,195,676 7/1965 Eisler et a1.
`367/40
`3,365,020 1/1968 Walker, Jr.
`181/103
`3,687,228 8/1972 Morris ............................... .. 181/116
`Primary Examiner—Maynard R. Wilbur
`Assistant Examiner-19 R- Kaiser
`[57]
`ABSTRACI‘
`
`.
`.
`.
`_
`_
`A selsmlc Wave genera“ and method °f “Smg 1" Whlch
`comprisesavertical array of sources at known spacings,
`for detonation in a seismic wave propagating medium of
`known seismic velocity; means to initiate the sources in
`time sequence in a selected series of known different
`time intervals and recording the seismic waves at a
`distant location to provide a ?rst electrical signal; and
`Correlating the ?rst electrical signal with a Second e1ec_
`trical signal derived from the pattern of initiation, as
`modi?ed by the travel times of the waves between the
`
`Several Separate charges‘
`
`34 Claims, 14 Drawing Figures
`
`PGS Exhibit 1013
`PGS v. WG
`
`

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`30
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`26A 268
`‘Ii
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`FIG. I. (PRIOR ART )
`
`US. Patent Jan. 29, 1985
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`\Sheet 1 of 4
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`4,497,044
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`24
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`PGS Exhibit 1013
`PGS v. WG
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`PGS Exhibit 1013
`PGS v. WG
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`

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`PGS Exhibit 1013
`PGS v. WG
`
`

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`US. Patent Jan. 29, 1985
`
`, Sheet4of4
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`4,497,044
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`ll6A
`use
`use
`II6D
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`I 6A I268
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`FIG. 9.
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`PGS Exhibit 1013
`PGS v. WG
`
`

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`1
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`4,497,044
`
`2
`
`SEISMIC WAVE GENERATOR
`
`CROSS-REFERENCES TO RELATED ART
`Reference is made to the following patents and publi
`cations:
`U.S. Pat. No. 2,609,885, issued Sept. 9, 1952 in the
`name of D. Silverman.
`US. Pat. No. 2,808,894, issued Oct. 8, 1957 in the
`names of J. D. Eisler and D. Silverman.
`US. Pat. No. 2,779,428, issued Jan. 29, 1957 in the
`name of D. Silverman.
`S. T. Martner and D. Silverman, 1962, Broomstick
`Distributed Charge. GEOPHYSICS, vol. XXVII #6,
`Part II.
`M. E. Arnold and J. W. Haylett, 1981, Delaystick: A
`New Distributed Charge. GEOPHYSICS, vol. 46 #9,
`September 1981.
`
`SUMMARY OF THE INVENTION
`It is a primary object of this invention to provide a
`method of generating seismic waves in the earth by an
`improved arrangement of impulsive sources and differ
`ent initiation times.
`It is a further object of this invention to provide an
`improvement in seismic wave generation by an array of
`impulsive sources so that the resulting seismic waves
`can be detected, recorded and processed to provide a
`higher signal-to-noise ratio (S/NR) record.
`It is a further object of this invention to provide a
`seismic wave generator which will produce seismic
`records in a way to minimize ghost signals and con
`verted shear waves.
`It is a still further objective to provide a system of
`constructing and initiating a seismic wave generator in
`a borehole on land, or in a body of water, in such a way
`as to get an improved signal, processed to a higher
`S/NR, and also to provide a separate record of the
`up-traveling signal which produces ghosts and shear
`waves.
`While this method is applicable to the use of explo
`sive charges, it is equally applicable to arrays of other
`types of impulsive sources, such as water guns, air guns,
`gas guns, etc. For purposes of illustration, but without
`limitation, it will be described mainly in terms of explo
`sive sources.
`These and other objects are realized and the limita
`tions of the prior art are overcome in this invention by
`using a distributed charge, or a linear charge, of spaced
`explosive units (EUs), and processing the resulting elec
`trical signals in a speci?c manner, quite different from
`the prior art.
`The seismic sources intended for use in a borehole are
`constructed in a manner somewhat similar to that uti
`lized in the prior art for constant velocity charges. In
`the constant velocity charges or “convel” charges, they
`are generally spaced at equal vertical distances and are
`detonated by a timing fuse or cord, so as to provide
`equal time intervals between the detonation of succes~
`sive charges in the array. These arrays are always deto
`nated from the top charge downwardly, and the timing
`between successive detonation is made equal to the time
`of travel of seismic waves in the surrounding wave
`propagating medium, over a distance equal to the spac
`ing between the successive charges. In this way the
`seismic wave from the detonation of the ?rst charge
`reaches the second charge at the same instant that the
`second charge detonates, so the two seismic waves
`reinforce each other, and so on, down through the se
`quence of charges. Thus at the bottom of the array a
`very strong seismic wave will be generated, to travel
`downwardly through the earth.
`All of these conditions are utilized in the present
`invention except that in the present invention the spac
`ings between charges can be equal or they can be differ
`ent. Also, the time intervals between the detonations of
`adjacent pairs of charges are preferably not equal, but
`are preferably arranged in a random sequence or in a
`sequence of time intervals which increase from the ?rst
`to the last one, or conversely, which decrease from the
`?rst one to the last one.
`When a vertical sequence of charges are detonated at
`unequal time intervals, which time intervals are prefera
`bly greater than the time of travel of seismic waves
`between adjacent charges, a downgoing seismic signal
`in the earth will be in the form of a time series of pulses,
`
`65
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`20
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`25
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`55
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`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention lies in the ?eld of seismic geophysical
`prospecting, and is directed particularly to improve
`ments in the generation of seismic waves and in their
`processing.
`It concerns a seismic wave generator which com
`prises a vertical array of separate sources at known
`spacings which are initiated at an arbitrary selected
`known time sequence, different from that normally
`provided in a constant velocity type distributed charge.
`Still more particularly, it concerns the reception of
`the series of timed seismic waves after travel through
`out the earth, to form a ?rst electrical signal, and corre
`lating this signal with another signal which represents a
`series of pulses at the known time separations derived
`from the time sequence of initiations, as modi?ed by the
`travel times between vertical source positions, of seis
`mic waves in the surrounding medium.
`2. Description of the Prior Art
`There is considerable prior art both in publications
`and patents, of the use of long vertical arrays of spaced
`charges for use in boreholes. However, all of these
`without exception provide equally spaced charges, in a
`region of constant known rock velocity, and the equal
`time intervals chosen for successive detonations is equal
`to the travel time of seismic waves in the rocks over a
`distance equal to the spacing between successive
`charges in the array.
`Furthermore, all of these so-called constant velocity,
`convel, and broomstick charges are detonated from the
`top downward, in order to concentrate the successive
`pulses into a single additive pulse which is directed
`downwardly.
`The main basis for this use of separately spaced
`charges detonated in sequence with the travel time of
`the seismic wave in the rocks is based upon the principle
`that the downgoing waves from each of the charges
`reinforce each other, to provide a seismic pulse, or
`wave, which is the sum of the separate pulses from each
`of the charges. The ongoing waves comprise a series of
`spaced pulses, equal in number to the pulses generated
`by individual charges, which do not add in any way, but
`do provide down-going reflections from each of the
`separate charges which are reflected from reflectors
`above the array. These re?ections complicate the seis
`mic record.
`
`PGS Exhibit 1013
`PGS v. WG
`
`

`
`4,497,044
`4
`ghost signals. These two records when provided at each
`shotpoint, and carried out over a prospect, will provide
`two maps which should be in agreement, provided the
`difference in timing of the two sources, that is, the
`downgoing source, and the upgoing source, are prop
`erly taken care of.
`One way of determining the time interval between
`the two records, that is, the one generated by the down
`going pulse stream in a conventional manner, and the
`other generated by the upgoing pulse stream in this
`invention, is by correlating the ?rst correlogram with
`the second correlogram, in a well-known manner.
`Summarizing some of the details of what has been
`described, the number of series charges in the array is
`preferably comparable to those in prior art constant
`velocity charges. The spacing between charges can be
`any desired value. Furthermore, the two time series,
`provided by the downgoing pulses and upgoing pulses
`from the charge array, differ in timing from each other
`by twice the time of travel of seismic waves over a
`distance equal to the spacing between charges. Since
`these two time patterns are going to be separately corre
`lated with the received record, the larger this spacing,
`the more perfectly will the two sets of signals be sepa
`rated by the correlation process. Also, the larger the
`number of charges, the better the separation.
`The arrays can be detonated from the top down, or
`from the bottom up, with equal bene?t in the records.
`This indicates that this process is quite different from
`that of constant velocity charges which must be deto
`nated from the top only.
`
`25
`
`20
`
`3
`which are in the time sequence of the detonations but
`modi?ed by the times of travel of the seismic waves
`between adjacent pairs of charges. Since the spacings of
`the charges, the velocity in the adjacent medium, and
`the sequence of time intervals between detonations are
`known, a time series can be calculated which is pre
`cisely equal to the time series represented by the se
`quence of seismic wave pulses traveling downwardly,
`and similar to the signal that would be provided by a
`geophone positioned below the array.
`These seismic waves follow identical paths one be
`hind the other and at a re?ecting horizon will be re
`?ected upwardly, in the same time pattern to the surface
`and will be recorded on one or more seismic sensors, or
`geophones, converted to electrical signals, and tempo
`rarily stored or recorded.
`Knowing the precise time intervals between these
`seismic waves as they leave the bottom of the array, it is
`possible to correlate the received electrical signals from
`the geophones with this time pattern, to provide a ?rst
`correlogram. This ?rst correlogram then provides a
`record which is more or less similar to that provided by
`the vibroseis type of operations currently in use.
`Referring to the vibroseis operations of the prior art,
`it is well known that given a series of seismic impulses
`such as a plurality of timed detonations of small
`charges, it will provide a higher signal-to-noise ratio
`(S/NR) record if the received record is correlated with
`the time sequence of pulses, rather than if successive
`pulses are delayed and stacked. On this basis, detonating
`an array of separate spaced charges in a borehole in a
`known time pattern, and correlating the received re
`cord with this time pattern, will provide a seismic re
`cord of higher S/NR than would be provided by the
`prior art system of adding, or stacking, the separate
`seismic signals from the detonations of the separate
`charges.
`It will be clear that from the preceding description,
`the resulting record will have improved quality over
`that which would be produced by a conventional con
`stant velocity charge. Furthermore, this process just
`described will be fully as useful as the constant velocity
`charge, in delaying the upgoing pulse from the series of
`detonations, so that the effect of re?ections from hori
`zontal re?ectors above the charge will be minimized.
`Another way of saying this is that ghost re?ections will
`be minimized by this method as they are with the con
`stant velocity charge method, but to a greater degree.
`However, there is a further important advantage of
`this present invention over that of the constant velocity
`charge. This involves the capability of detecting, by
`means of a surface geophone at the shot point, the se
`quence of up-going pulses from the downward detona
`tion of the charges. This second sequence of pulses
`represents a seismic wave pattern which travels up
`wardly and is re?ected downwardly from horizontal
`re?ectors above the source, and produces ghost re?ec
`tions, precisely as does the pattern of waves going up
`wardly from a constant velocity charge. However, in
`this case, the precise timing, as indicated on the uphole
`geophone, is known, and can be correlated with the
`received record. The resulting correlogram will pro
`vide a record which is based upon the downgoing re
`?ections from the upper re?ectors being the source for
`the record.
`This procedure provides an improved record over
`the conventional constant velocity charges, and also
`provides a second record which indicates clearly the
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`These and other objects and advantages of this inven
`tion and a better understanding of the principles and
`details of the invention will be evident from the follow
`ing description taken in conjunction with the appended
`drawings, in which:
`FIG. 1 is a representation of a prior art constant ve
`locity type distributed charge for use in a borehole in
`the earth.
`FIG. 2 is an illustration of this invention which uti
`lizes an array of separate spaced explosive units, illus
`trating the various paths of seismic waves which are
`involved.
`FIG. 3 illustrates an array according to the principles
`of this invention using timing fuses arranged for uphole
`shooting.
`FIG. 4 illustrates a similar array of explosive units
`arranged for uphole shooting by means of a sequencing
`blaster at the surface.
`FIG. 5 illustrates another embodiment of this inven
`tion utilizing an array of explosive units and designed
`for downward sequencing of detonation by means of a
`bottom hole sequencing blaster.
`FIG. 6 is a more detailed illustration of the system of
`FIG. 5 in which the details of one embodiment of a
`sequencing blaster are illustrated.
`FIG. 7 illustrates the time functions and seismic wave
`trains that are produced by initiating vertical arrays of
`sources in timed sequence.
`FIGS. 8 and 9 illustrate horizontal and vertical arrays
`of impulsive sources in offshore seismic operations initi
`ated in time sequence.
`FIGS. 10A, 10B, 10C, 10D and 10B illustrate various
`arrangements of explosive units in land seismic opera
`tions detonated in time sequence.
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`PGS Exhibit 1013
`PGS v. WG
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`

`
`5
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Referring now to the drawings and in particular to
`FIG. 1, there is shown a‘prior art drawing of the normal
`type of constant velocity (convel) distributed charge for
`use in a deep shothole. The purpose of this ?gure is to
`illustrate the status of the present-day prior art, so that
`the differences between this prior art and the present
`invention, which will be described in conjunction with
`the following ?gures, can be better understood.
`There is a borehole 12 drilled to a selected depth D in
`the earth 14, having a surface 16. The charge array is
`indicated generally by the numeral 10, and comprises a
`series of a selected number of separate small charges, or
`explosive units (EU). These separate charges 18A, 18B,
`18C, 18D, etc. are attached to a strength member 23,
`which may be a cable, or it may be a sequence of
`wooden poles or plastic cases, which together form a
`substantially rigid long linear object. In the prior art the
`most common method of detonation of the charges is by
`means of fuse-type timers will known in the industry.
`This is indicated generally by the numerals 20A, 20B,
`20C, etc. An example of this type of timing cord would
`be primacord, as in the conventional “broomstick”
`charges, and Primeline, and Nonel cord, well known in
`the industry. These are manufactured by the Ensign
`Bickford Co.
`The detonation of the sequence of separate explosive
`units is by means of a cap 25 in the top unit, connected
`by wires 24 to a blaster 22 of conventional design. When
`the blaster is operated, the cap 25 in the top unit 18A
`will detonate the succeeding explosive units. Generally
`the spacing between separate charges 18A, 18B, etc. are
`equal and the entire array of explosive units is posi
`tioned opposite a rock or other wave transmitting me
`dium of constant known velocity. The overall length of
`the array is generally of the order of 100 feet, this is an
`arbitrary length but it permits the use of eleven charges
`with 10 foot spacings between them, which appears to
`give satisfactory operation, as a distributed charge.
`Keeping the same overall length, the operation of the
`distributed charge is improved by having a greater
`number of individual explosive units correspondingly
`closer spaced, until a continuous explosive unit is con
`?gured, “broomstick charge”, so as to have the desired
`velocity of detonation of explosive cord equal to the
`velocity of seismic waves in the surrounding seismic
`wave transmitting medium. In all cases for distributed
`charge operation, the direction of detonation is from the
`top unit 18A downward to the bottom unit 18D, in
`accordance with arrow 17. The time between the sepa
`rate detonations of charges 18A and 18B, for example, is
`designed to be equal to the time of travel of the seismic
`wave generated in the earth 14 by the ?rst charge 18A
`to arrive at the position of the second charge 18B. By
`this means, each of the seismic waves generated by the
`charges will be in-phase with the passage of the seismic
`wave from the preceding units and they will all be
`summed or stacked to provide a total seismic wave
`moving downwardly below bottom unit 18D, and hav
`ing an energy equal to the sum of the energy of the
`individual separate explosive pulses from each of the
`unlts.
`In FIG. 2 is illustrated one embodiment of the present
`invention. It still utilizes a borehole, or shothole, in the
`earth 14, having a surface 16. It can also be used in a
`body of water. Also shown is a geologic interface 40
`
`4,497,044
`6
`which separates the weathered layer 15 from the sub
`weathered layer 14. Energy moving upwardly from
`below the interface 40 will be partly re?ected down
`wardly at that interface 40, and the energy which does
`not re?ect will move upwardly to the surface 16 and
`will be downwardly re?ected there, as will be further
`explained.
`An array of explosive units 52A, 52B, 52C, etc. is
`illustrated, positioned below the interface 40 so that the
`entire unit will be in a rock body 14 of known constant
`velocity. While only three such explosive units are
`shown, there can be any number, but preferably there
`should be at least of the order of ?ve to ten separate
`explosive units, stretching over an interval of the order
`of at least 100 feet.
`The listing of the preferred value of the number of the
`explosive units as ten or more, and the spacings of 10
`feet and of total length of 100 feet, are only for purposes
`of illustration, and are not to be taken as a limitation,
`since the explosive units can be positioned closer or
`farther apart, and the length of charge can be much less
`or much greater, and so on.
`The separate explosive units 52 are supported by a
`tension means 23 which can be a tension cable, or tube
`or rod, of paper, wood or plastic, as has been used in the
`conventional convel units as shown in FIG. 1. The
`purpose of the tension member 23 is to lower the
`charge, and support it at a selected depth in the bore
`hole 12 until it is detonated.
`The explosive charge illustrated in FIG. 2 is also of
`the type as indicated in FIG. 1. It uses timing fuse 54A,
`54B, etc. to provide the delayed detonation of succeed
`ing explosive units. This illustration indicates a series of
`explosive units detonated from the top. This is taken
`care of by providing a conventional blaster 22 with
`leads 24 going to a cap 25 in the top explosive unit 52A.
`Once the blaster is operated the top unit will detonate
`and the successive units will detonate in accordance
`with the delay introduced into the fuse or delay ele
`ments 54A, 54B, etc.
`There is one important difference between the explo
`sive array in FIG. 2 as compared to FIG. 1. In FIG. 1
`all of the explosive units are equally spaced and the
`timing fuse provides a delay equal to the travel time of
`seismic waves in the rock wall, over a distance equal to
`the spacing of the explosive units.
`In FIG. 2 while the delay units are used, they provide
`a much greater delay than that which would be equal to
`the travel time of a seismic wave in the wall. This will
`be illustrated further in connection with FIG. 7. While
`the individual charges create their own seismic waves, I
`have shown only a single seismic wave 58A going
`downward from the top unit 52A. However, since the
`distance from the charge down to the re?ection inter
`face 42 is so large compared to the overall length of the
`explosive assembly that the ray 58 can be assumed to be
`the pattern of seismic pulses, constituting the signal
`going downward from the array to the re?ecting inter
`face 42, and moving upwardly according to ray 58B to
`a sensor or geophone 26A. There will, in general, be a
`large number of sensors 26A, 26B, etc. although only
`two are shown, and the rays to one of them are shown,
`in the interest of keeping the diagram simple. This sur
`face instrumentation is all conventional.
`Each of the individual explosive units creates its own
`seismic wave; and as just explained, ray 58 represents
`the series of separate impulses from the separate explo
`sive units that go downwardly. These separate units
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`PGS Exhibit 1013
`PGS v. WG
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`

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`0
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`7
`each create spherical seismic waves, so there is another
`series of seismic impulses 56 that goes upwardly, as well
`as others which go sideways, which are of no interest at
`the moment. The up-going series of pulses 56 will par
`tially re?ect at the interface 40, the bottom surface of
`the weathered layer, and will then move downwardly
`in accordance with ray 56A; and part of the energy in
`ray 56 will reach the surface as 56’ and be re?ected
`downwardly, as before, as ray 56B. Consequently, as a
`result of this explosive array there could be at least two
`sets of seismic pulses 58A and 58B, from the down
`travelling aeries of pulses, and 56A, 56A’, 56B, and 56B’
`from the up-going series of pulses.
`One of the advantages of the constant velocity dis
`tributed charge illustrated in FIG. 1, put up by its pro
`ponents, is that the sum of the detonation waves from
`each of the plurality of explosive units are summed by
`the process of timing the detonations in accordance
`with the downward movement of the seismic wave.
`Thus more energy goes downwardly than goes up
`wardly. This is not quite correct because the same
`amount of energy would go in each direction. How
`ever, the power con?guration of the seismic waves will
`certainly be different, and the power represented by
`energy per unit of time in the downgoing signal 58A
`will certainly be greater than the power represented by
`the upgoing signal 56. I point this out because there is
`no way of eliminating the upgoing energy. But while it
`is reflected downward in the form of ghost waves, be
`- cause of their distribution over a period of time, the low
`energy of each individual pulse makes them less promi
`nent, and therefore, they constitute simply a noise
`through which the record must be interpreted.
`FIG. 2 illustrates that the total energy that goes up as
`ray 56 is of the same order of magnitude as the ray 58A
`going down, but it is broken up into one or more pack
`ages, each of which occur at still later times. Thus, the
`result is a large number of separate small pulses which
`come in a time pattern.
`In this invention, neither of the rays 58A or 56 are
`summed in the ground. They are both time series, each
`having a plurality of pulses, one for each of the separate
`explosive units. However, the time pattern of the down
`going series 58A will be different from that of the upgo
`ing series 56. While the detonation times are ?xed for
`each of the units, the way they combine into a time
`series depends upon their physical position and the
`velocity of seismic waves in the rock. This will be dis
`cussed fully in connection with FIG. 7, but I point out
`here that the various rays which I have described in
`connection with FIG. 2 are substantially the same as
`would occur in FIG. 1, except that the delay times
`introduced by the means 54 are quite different in FIG.
`2 than they are in FIG. 1.
`In this invention, instead of summing the separate
`waves from each of the explosive units, a single record
`is formed which includes each of the separate waves or
`pulses in a known time pattern. The pattern of pulses in
`the record is then correlated with a known pattern of
`pulses. This provides a higher signal/noise ratio ?nal
`processed record, than would be the case where the
`waves are summed.
`Since control of timing of the detonations of each of
`the units 52 is under control of the operator, if the spac
`65
`ing between charges is known and the velocity of seis
`mic waves in the rock is known, the actual timing of
`pulses in the downgoing direction is known. Thus, the
`
`4,497,044
`8
`record can be correlated with this known pattern to
`provide a correlogram, which is a ?nal record.
`Shown in FIG. 2 is a geophone 44 placed on the
`surface 16 near to the borehole 12. This geophone is
`connected to a signal processing box 50 by lead 45, as
`are the signals from the geophones 26A and 26B, etc. by
`leads 47, 48, etc. Also, the firing time of the top charge
`52A as a time break, is carried by lead 46 to the process
`ing box 50. Here the signals are ampli?ed and stored and
`correlations made, etc. providing permanent records
`with a recorder 30. This is all conventional.
`The signal on line 45 from the geophone 44 will con
`sist of a series of electrical pulses timed according to the
`uptraveling pattern of seismic waves. In other words,
`the output of geophone 44 represents a time function of
`time spaced pulses, which when correlated with the
`record taken from geophones 26A, 26B, etc., will then
`provide a correlogram which will show the uptraveling
`waves in the rays 56 subsequently re?ected down
`wardly as rays 56A and 56B, for example. Thus, having
`the timing of the upgoing pulses as read by the geo
`phone 44, the record can be correlated with this pattern
`of pulses to provide a picture of the energy in the ghost
`re?ections.
`This can be very useful since it represents a body of
`energy, which has heretofore been wasted. Thus the
`correlogram provided by the process described, that is,
`correlating the received record from the geophones 26
`by the signal on line 45, will provide a second correlo
`gram similar to the ?rst correlogram, which will be a
`record showing only the once re?ected energy as the
`source of seismic waves.
`By correlating these two correlograms there will be
`evident a time difference between the patterns in the
`record which is a function of the time of travel from the
`top explosive unit 52A upwardly to the base of the
`weathered layer, and to the surface, and back down to
`the level of the top explosive unit. It will be clear there
`fore that this invention permits not only obtaining an
`improved seismic record resulting from the detonation
`of the distributed charge shown in FIG. 2, but it also
`provides a second record which is a record comprising
`a different source; namely, the uptraveling waves 56
`from the explosive array, and these two records to
`gether will provide more information for the geophysi
`cist than the ?rst one alone.
`Referring now to FIGS. 3 and 4, there are shown
`similar explosive arrays in the borehole 12 correspond
`ing to that of FIGS. 1 and 2. In the process of FIG. 1,
`it is only possible to get a summed explosive effect by
`detonating the set of explosive units downwardly start
`ing from the top.
`In this invention the time intervals between the deto
`nations of successive explosive units have been in
`creased. It is no longer of interest to sum these effects in
`the earth. Therefore, by choosing proper time intervals
`relative to the time of travel of the seismic waves in the
`earth, it is possible to detonate the charges upwardly or
`downwardly.
`FIG. 2 shows how this can be done by detonating
`downwardly. FIG. 3 shows the same explosive array as
`in FIG. 2, but turned upside down, and detonated at the
`bottom. It will be clear by comparing them precisely,
`that ray 56 will move downwardly, and the ray 58 will
`move upwardly. So far as the ?nal results are con
`cerned, there would not be any substantial difference.
`FIGS. 3 and 4 show two methods by which upwardly
`directed detonations can be provided. Referring now to
`
`45
`
`55
`
`PGS Exhibit 1013
`PGS v. WG
`
`

`
`4,497,044
`
`45
`
`50
`
`25
`
`FIG. 3, there is shown the same borehole 12 in the earth
`14 and surface 16 with a blaster 22 and cap leads 24
`attached to the cap 25 in the bottom unit 60A, and
`having other explosive units 60B, 60C, 60D, etc., for
`example. All of these are tied to a tension member 23.
`The timing is by means of the fuse cords 62A, 62B, 62C,
`etc., such as was used in FIG. 2.
`One of the features of the array of FIG. 1 is that it
`takes a considerable amount of effort and material to
`provide the selected time interval between detonation.
`Once they are built into the explosive units they cannot
`easily be changed. Consequently, I illustrate in FIG. 4
`how a sequencing blaster 68 can be used to detonate a
`sequence of explosive units 60A, 60B, 60C, 60D starting
`at the bottom end, by placing caps in each of the
`charges, and using cap leads 66A, 66B, 66C, 66D, etc.
`from each one to the blaster 68. The caps are detonated
`electronically, in a well-known manner, such as will be
`shown, for example, in FIG. 6. Thus, the simplicity of
`FIG. 4 is provided to produce an upwardly detonating
`20
`charge in the earth which is equally useful to the down
`ward detonating charge as shown in FIG. 5.
`In FIG. 5 is shown how a sequencing blaster 68 can
`be attached to the bottom end of the array 23, and by
`using a simple blaster 70 at the surface, the array can be
`?red by providing electrical power from the surface,
`?ring ?rst charge 72A, then 72B, then 72C, 72D, etc.
`While the explosion of the topmost explosive unit will
`cut the cap leads 82, this will not prevent the full opera
`tion of the cycle since that has been taken care of in the
`blaster 68.
`Referring now to FIG. 6, there is an illustration of
`one embodiment of a sequencing blaster, which when
`mounted at the bottom of the hole can provide a se
`quence of detonations in a downward direction as illus
`trated by the arrow 87. The blaster 70 at the surface
`shown in dashed outline contains a battery 80 and the
`switch 81 and provides two conductor wires 82 to the
`sequencing blaster shown in the box 68.
`It is, of course, of great interest to provide the safety
`of having no electric power in the blaster 68 while it is
`connected to capped charges and being lowered into
`the hole. Thus, all of the electrical power is supplied
`down the two conductors 82 to the blaster 68 after the
`charge is in position in th