FR1464403A - Apparatus and method for geophysical seismic exploration - Google Patents

Description

Apparatus and method for geophysical seismic exploration.

The present invention relates, as a whole, to geophysical prospecting in which seismic techniques are used and, more particularly, to the exploration of a zone of the underlying surface of the ground, in which exploration is carried out a technique. seismic.

The general method of geophysical exploration in which seismic waves produced in the ground are used is well known. In short, in this process, a seismic pulse is created at or near the surface of the ground and signals generated by geophones are recorded, signals which result from the movement of the ground at one or more points more or less distant from the point of origin of the seismic pulse. The recording must make it possible to measure the lapse of time between the moment when the impulse was generated and the moment when the signals resulting from the following ground movement are generated. The original impulse gives rise to elastic waves which are transmitted through the ground. Any discontinuity or variation in structure within the ground reflects and / or retracts part of the energy contained in said waves, so that a recording of the signals coming from the point of reception includes a number of incident waves. each derived from the original pulse and each being different from the others by its time of arrival, by its amplitude, by its waveform or by its three parameters at the same time. The common type of seismogram produced by the technique described above includes several traces varying in amplitude along an axis representing time, plotted through. shot from a common point of reference which is the instant when the impulse was generated. The traces are recorded side by side, so that the phenomena or actions exerted on them and resulting from the reflections from a given discontinuity can be identified by the way in which they align with the recording. It is obvious that very many traces are necessary to make it possible to distinguish between wave reflections and noise.

According to the current techniques practiced until now, there is either a linear row of detectors spaced apart from one another and arranged on either side of a point of seismic pulses, or a single detector or an arrangement of seismic detectors. at a fixed location and repeatedly impulses or shocks are communicated to the ground along a straight line passing through the location where the detection is performed. In the first technique, a seismogram is obtained by simultaneously recording the output signals of the geophones which are produced by a single seismic pulse; in the second technique, the signals from the geophones resulting from the pulses are recorded successively, in the form of several traces arranged side by side on a common time axis. In yet another technique which has been proposed, seismic wave detectors are disseminated over a certain area of the ground and pulses are communicated to the ground at certain points within or in the vicinity of this area. The electrical signals generated by the geophones are recorded individually and simultaneously in a reproducible manner and in the form of a series of traces and, some time after, the signals produced by the seismogram are modulated on a plan display at two dimensions corresponding to the arrangement or row of detectors, such that the signal from any given detector modulates part, and only part, of the display surface. This way of proceeding, as described in the prior art, has not been practiced due to the high price of the seismic equipment capable of simultaneously amplifying the number of seismic signals that one would have to use to obtain measurements. valid results according to this technique. In addition, the display apparatus available in the prior art has proved imprecise, difficult to construct and limited in operating flexibility.

According to one of the characteristics of the present invention, a fixed location of the detector and several locations where a seismic pulse is generated are used, this location and these locations being disposed on the surface in the vicinity of the location where the detection is carried out. , this in accordance with a predetermined arrangement. The location where the detection is performed is preferably located within a zone delimited by the locations where the transmission is performed. The ground receives seismic pulses successively at each seismic pulse production location and a separate seismic recording is obtained from the seismic waves detected at the location reserved for detection. The seismic wave recordings thus obtained are combined into a seismogram comprising several traces carried on a common time axis. A display of a surface plane having the configuration of the area of the ground surface which was previously pulsed is made and the seismogram traces are used to simultaneously vary the light projected on various segments of the display. on the face, the segment of the display on which the intensity of the light is varied by a particular trace corresponding to the location of the seismic pulse on the surface of the ground where the seismic waves corresponding to said trace.

According to another feature of the present invention, a seismogram is produced by a surface seismic survey in which the seismic waves are transmitted between at least one and, preferably, several points of production of seismic wave pulses in a zone and at least one single point of detection which may or may not lie in said zone, whereby the points of reflection on a given reflection horizon, lying below the zone, are distributed on the surface in an arrangement which can be determined. The traces obtained are used to modulate or to vary the intensity of light beams projected on the first ends of a linear row of light conduits, the other ends of which are arranged so as to constitute a surface, each fiber which lies in said surface being arranged along X coordinates and y having a linear relationship with respect to the points located on the ground surface covering the area on which the seismic survey is carried out. The light beam is projected from said other end of the light pipes to a display medium on which the time variations of the light from the light pipes allow reproduction of the seismogram as a presentation three-dimensional, the dimensions being made up, on the one hand, by the two dimensions of the zone on which the seismic survey was carried out and, on the other hand, by time (which corresponds to the depth).

Other characteristics and advantages of the present invention will appear in the description which follows, for which reference is made to the appended drawing in which:
Figure 1 is a schematic representation of an apparatus for performing seismic observations in accordance with one of the features of the present invention
Fig. 2 is a plan view of an area of the ground showing the locations of a seismic detector and the points where the seismic pulses are produced, in accordance with one of the features of the present invention, as well as the area of the earth. underlying ground surface plotted based on multiple seismic observations of horizontal flat layers; in this figure, the abbreviations
TDG, SC and PSS mean respectively, radiation path, grid layout for pulse source, pulse source location points;
Figure 2A is an enlarged part of Figure 2; in this figure, the abbreviation PC means drop point;
Fig. 3 is a block diagram illustrating a technique for obtaining and reproducing or processing seismic records, in accordance with the present invention; in this figure, the abbreviations DF and PSE mean respectively: displacement of the film and projection on the screen;
Figure 4 is a top cutaway view illustrating certain component parts of said light transducer apparatus illustrated in Figure 3; in this figure, the abbreviations BFO,
EL and B. mean respectively: fiber optic strips, line-shaped end and box;
Figure 5 is a front view of the light transducer illustrated in Figures 3 and 4;
Figure 6 is a rear view of part of the light transducer;
Figure 7 is an enlarged view of the end of the optical fiber arrangement shown in Figure 6; in this figure 7, the abbreviation BE means stacked optical fiber strips;
Figure 8 is a view on a larger scale
one of the optical fiber strips shown
in Figures 6 and 7; in this figure, the abbreviation
BFO stands for: optical fiber tapes;
Figure 9 is a partial view and on a larger scale
scale of the large end of the structure illus
trée in Figure 5; in this figure 9, the abbreviation
tion EL means: end in the form of a line;
Fig. 10 is a side view of the apparatus for recording and processing seismograms, in accordance with one of the features of the present invention; in this figure,
The abbreviation VE means: towards the screen;
Figure 11 is a sectional view of the apparatus of Figure 10, taken along 11-11; in this figure 11, the abbreviations BSL and T. signify respectively: housing of the light source and transformer;
Figures 12 and 13 are light ray path diagrams for flat layers which illustrate a technique for rapidly delineating the underlying surface, in accordance with a feature of the present invention; in FIG. 12, the abbreviations SC and G. signify respectively: underlying surface covered and grid arrangement;
Fig. 14 shows part of the ground seen in plan and in section at various times after a seismic pulse has been generated; in this fi gure: OS means surface wave; ROS stands for reflection of surface waves; RS signifies reflection only Vs signifies, for T1, transverse velocity and, for T2, surface velocity; means apparent speed of reflection; S means surface;
Figure 15 is an electrical circuit diagram of the electrical control devices for the apparatus illustrated in Figures 10 and 11; in this figure, the initials AV and AR mean respectively: front and rear;
Fig. 16 illustrates a preferred technique for performing the part of the geophysical survey operations in place, in accordance with the present invention; in this figure. the abbreviation TSSsigni. fie: path of the source of sound pulses.

For the purposes of the present invention, the terms light conduits or waveguides denote one or more rods or fibers preferably having a high refractive index and arranged so as to transmit with a high efficiency the light of one of their ends to the other. The term optical fibers denotes bundles or rows of rods or fibers intended to transmit light of a vitreous or resinous nature preferably having a high refractive index and which can be embedded in a resinous or vitreous substance. transparent
(or coated with this substance). having a lower refractive index. so as to isolate opti
only said fibers or rods of the part thereof
turning.

Although optical fibers can include
a single filament or fiber, they are more commonly made up of several filaments connected together in bundles. The individual filaments of each bundle used in the present apparatus are ordinarily about 0.06mm in diameter and thirty-six separate filaments are tied together in each bundle. The filaments can be arranged methodically in the bundle, so that an image detected at one of their ends can be faithfully transmitted to their other end.

If we now return more generally to Figures 1, 2 and 2A, it can be seen that said figures have illustrated a preferred technique for performing a seismic observation on site, in accordance with the present invention. . A seismic or geophone detector 111 is placed on the surface of the ground 101 at a fixed point of detection.

Pulses are then communicated to several locations arranged on the surface around the point of detection. These places are designated in Figure 2 by the references 1, 2, 4, 11, 16, 46, 50 and so on. It can be seen from the references that pulses are communicated to the ground at 2,500 distinct places in the example shown in fibure 2. It is obvious that a different number can be used in practice. places where pulses are communicated to the ground. Preferably, the grid of the pulse locations is drawn symmetrically around the geophone 111, forming a rectangle. As will be explained below, this arrangement is not necessary for the present invention and, in many cases, there are definite advantages to using several geophones arranged in a different way on the surface of the ground.

This will become more evident in the description which will follow with regard to Figures 12 and 13.

In a very practical technique for imparting impulses to the ground, in accordance with the present invention, equipment called a drop-weight truck is used in which a very heavy weight is dropped onto the surface of the ground. so as to produce seismic waves, the instant of the fall being coordinated with the operation of a recording apparatus on a truck reserved for recording and placed at a certain distance from the point of drop.

As illustrated, a truck 103 is used to transport the very heavy weight 105 and to bring it to the various locations. An assembly 109, intended to raise the weight and to control the fall of the latter, is transported by a truck whose role is to raise the weight and to control the instant of its fall. Preferably the instant at which the fall occurs is determined by a switch on the recording unit of the truck 115 and an electrical pulse is transmitted by a radio link from the antenna 117 to the receiving antenna. 107 and by means of associated radio transmitting and receiving equipment on the trucks, from the recording apparatus to the weight drop control apparatus.

Apparatus of this nature is conventional in the art and has been used for many years by seismic exploration companies.

Other sources of seismic pulses which can be used in practice are: dynamite, gas explosion devices, and other controllable seismic pulse sources well known in the art.

Although ron has shown a single geophone in Figures 1 and 2, it is obvious that one can advantageously use a group or conventional arrangement of geophones connected together so as to produce a single electrical signal on the conductor 13, in view of the recording of said signal by the recorder located on the truck 115. This arrangement may be in the form of a star or any other configuration well known in the art. The seismic waves generated by the fall of the weight 105 on the ground little. wind follow a number of different radiation paths before being detected by the geophone sensor 111, the reference 119 designating one of these paths which is followed by seismic waves reflected by a ground interface or reflector 121.

Assuming that the places where the weight drop takes place are 30.50 m apart from each other as shown in Figure 2A, the area of the ground included within the grid covering the area where the he weight drop device communicates impulses to the ground, is a square 1493.50 m square.

However, a smaller area of the underlying soil surface can be explored since the reflected seismic waves do not travel in an absolutely vertical direction. If we further assume that the space separating the drop points is 30.50 m and that the geophone is placed in the center of the grid delimited by the drop points, the area of the underlying surface of the ground is noted at any level (assuming a reflection horizon that does not include any difference in level or inclination) is a square of approximately 746.80 m on a side, in the center of which is the geophone 111.

The ground is pulsed at each of the drop locations designated in Figure 2 and a separate trace is plotted on a reproducible recording medium as a result of each pulse. The tracks are recorded side by side in the order of numbering of the drop locations. In other words, the traces corresponding to the falls along a given linear row are recorded side by side in the order of position of the falls and the groups of traces are recorded side by side in the order of the positions of the traces, for example going downwards, as shown in FIG. 2. The final result is a conventional seismogram comprising a series of traces along a common time axis from a common starting point on the seismogram. This seismogram can be thought of as a composite seismogram comprising several individual seismograms, the traces present in each individual seismogram corresponding to the places of seismic disturbance along a particular linear row.

If we now examine Figure 3, we see that we have shown in this figure, in the form of a general diagram, the way in which one can obtain seismograms and according to which one can carry out their subsequent processing, in accordance with the present invention. The seismic signals detected by the geophone 111 and recorded by the magnetic recording apparatus 116 by means of a magnetic recording head 114 are reproduced by a read head 118. The magnetic recording apparatus 116 can be selected from conventional type devices such as, for example, those manufactured by the Allipex Company of Los Angeles, California. Alternatively, recording devices can be used. another type, arranged so as to make it possible to obtain reproducible seismograms (that is to say seismograms where the electrical signals which constitute them can be faithfully reproduced in the form of secondary electrical signals, of light signals and others), for example recording devices where photographic techniques are employed. The electrical signals produced at the read head 118 are transmitted to a processing zone 123 where they are converted into a form which makes it possible to modulate light beams passing through or reflected by it. The seismograms thus obtained can, for example, be of the variable density type, of the variable area type or of any type well known in the art, such as for example the seismograms with parallel lines and variable spacing. Assuming that a variable density seismogram has been obtained on a photographic film, so that the light passing through the film varies in intensity as a function of the density of the traces of the seismogram, then the negative film is slowly advanced. between a light source 129 and a light transducer 131 arranged to detect the variations in intensity of the light projected through the film 125 as it is moved upwards, as shown, between the light source and the line-shaped end 133 of the transducer, so that the light is projected through the film 125 to an end 135 in the form of a grid where a corresponding plan view is reproduced in the plane of the zone on which the ground has been subjected to pulses in order to obtain the traces of the seismogram and where the variations of the light intensity on the points of the zone represented in plan, vary according to the sig seismic values resulting from the ground impulse operation at the corresponding points on the ground surface. In other words, at the grid-shaped end of the transducer, one obtains a visual display of an essentially two-dimensional plan view corresponding to the places where pulses are produced on the area of the ground surface. and a given seismic trace is used to modulate the light intensity of the part of the display surface corresponding to the place of origin of the pulses on the ground surface corresponding to the given seismic trace.

Light from the grid-shaped end 135 of transducer 131 is directed onto a viewing screen 139 by means of an objective 137.

As a result, the display appearing on the grid-shaped end 135 is greatly enlarged. Obviously, the image coming from the end grid 135 of the transducer 131 is inverted by the objective 137 when it appears on the screen 139. In FIG. 3, the rear face of the screen has been shown. 139 for the sake of convenience of representation, but it is understood that ordinarily it is the front face which is examined.

The details of the transducer 131 are shown in Figures 4 to 9. Basically, the transducer comprises a plurality of strips 1A to 50A of optical fibers arranged in line at one end of the transducer and arranged to form a surface at the end of the transducer. other end of said transducer. Each of the optical fiber strips has a width equal to the width of the portion of film 125 of the seismogram which is necessary for the presentation of fifty traces (i.e. the number of traces corresponding to the number of seismic pulses in one of the rows of the area on which the seismic observations are made). Since fifty rows were used each comprising fifty pulse points in the example of FIG. 2, there is shown in FIGS. 4 and 5, fifty bands of optical fibers arranged in line in the slots 133A and glued or fixed inside the slots so as to be permanently attached to them. The optical fiber strips are arranged so as to form a grid-like surface at the end 135 of said optical fiber strips, with the optical fiber strip 1A at the top and the optical fiber strip 50A at the end. . lower tie of a layered structure, the other bands of optical fibers being arranged between the band 1A and the band 50A in the order of their numbering, as shown in Figures 5 and 9. The constitution of the structure formed by the Layers of optical fiber tapes is shown more clearly in Figure 7 which is an enlarged view of the layered structure as shown in Figure 6.

Each of the optical fiber bands comprises a large number of optical fiber strands, each of which itself comprises a number of optical fiber filaments connected together, so as to constitute a single strand. As noted above, a typical strand of optical fibers which can be found commercially comprises thirty-six optical fiber filaments with a diameter of 1/10 of a mm, bonded together in a regular arrangement. having six filaments on one side. It may also be noted that the filaments typically comprise a core or central core surrounded by two sheaths each made up of different types of glass, so as to present to the light transmitted via the central core an appropriate refractive index.

It is desirable that the number of filaments constituting a given optical fiber strip is at least equal to the number of depth points in a given row of the zone to be surveyed. A larger number of filaments can advantageously be used. It is not necessary for the individual filaments to be exactly aligned with the traces at their ends grouped in line for the luminous image of a trace to be transmitted by a single filament; in fact, the luminous image of one of the traces is usually transmitted through several filaments.

As shown, the light-tight housing of the fiber optic transducer is extremely wide at one end and extremely narrow at the other end. At the wide end, the optical fiber strips are attached side by side and are arranged in a group forming a surface in the hollow central part of the transducer which decreases in section to the narrow width block 138 at the end. grid-shaped of said transducer. The block 138 can be formed by two parts, so that the optical fiber strips are fixed therebetween in a central and rectangular bore therein. In a variant, the block 138 can be made from a single piece.

Although optical fibers are the preferred form of the transducer elements, other light conductive materials can be used, provided that the efficiency of the transmission is very high and the light losses are little or no light during transmission. is transmitted from one end to the other.

There is shown in Figures 10 and 11 a preferred embodiment of the apparatus in which the transducer described above is used and whose housing contains optical fibers to advance a movable film slide 139 between a light source 129 and the line-shaped end of the transducer as well as for directing light emanating from the surface-shaped end of the transducer onto a viewing screen. The apparatus is mounted on a frame comprising horizontal members 143A and 143B, vertical members 144A and 144B as well as other members not shown. A movable film slide mechanism 139 is mounted on the horizontal member 143A and is arranged to hold in place the negative film obtained as described above and on which is recorded a large number of seismic traces.

The film slide can be moved horizontally in either direction, as shown by the double headed arrow, and it includes an open frame so that light can pass through the film it supports and can be detected by the end. line-shaped fiber optic transducer 131.

Raised above the level of the movable film slide and placed immediately above the latter is a high intensity light source 129 which may be a conventionally designed Ozalide assembly. The light coming from the source 129 is concentrated by a lens 128 constituted by a Pyrex rod a. The lens 128 is disposed transversely to the longitudinal axis of the film strip and is held on the light source housing by a retainer 126. The distance of the lens 128 above the film strip is adjustable at the same time. means of bolts 145 which extend through the flanges 130A and 130B projecting out of the light source housing 129 at each end thereof. The bolts 145A and 145B bear against the horizontal part of the frame member 147A. The Ozalide light source> is cooled by the lamp 223 is connected to terminals 198 via a switch 215, a set 221 of capacitor and resistor connected in parallel, an auto-transformer 219 and a shock choke 217. The motor 177A of the blower which is intended for cooling the lamp 223 is started by closing the switch 215 at the same time as the aforementioned lamp is energized.

The operation of the apparatus which has just been described with reference to FIGS. 10, 11 and 15 is as follows. Initially, switch 215 is closed to ignite the lamp and start the blower motor 177A. After about 5 minutes (the time required for the Oxalide lamp to assume its normal operating light intensity), switch 213 is moved to its drive position in front of motor 161.

The motor drives the film slider and guides it under the lens 128 formed by a Pyrex rod so that the light from the lamp 223 and reaching the line-shaped end of the optical fiber assembly varies from intensity or modulated according to the density of the film.

Light is transmitted from the line-shaped end of the fiber optic transducer by the optical fibers themselves from the grid-shaped end of said transducer and is projected onto the screen through mirror 171 and lens 165. If it is desired to stop the film in order to examine the presentation for an extended period of time, the switch 205 is opened momentarily. When the end of the film strip has been reached, the position of the switch 213 is reversed so that the drive motor returns the film strip to its initial position.

We will now examine the general operation of the apparatus described above. As already mentioned, the ground is subjected to pulses on a rectilinear grid in several places arranged symmetrically on the surface of the ground. The pulses are not communicated to the surface of the ground simultaneously but successively, the ground being subjected to the pulses at only one place at a time. With each pulse of the ground, the resulting seismic waves are detected at a single fixed location and are recorded in a reproducible form. Each record or trace is on a common time axis so that the end result is presented as a seismogram of a series of traces starting at a common time reference point. With regard to the seismic waves produced directly by the seismic pulses, the seismogram contains all the phenomena that can occur when the ground is subjected to pulses in
right where the detector is located and the resulting seismic waves detected at the pulse points. All direct reflections, all phenomena of surface parasitic waves, all phenomena of air waves as well as all phenomena originating from localized reflecting elements such as, for example, large blocks in the ground, refracted waves and others appear in the seismogram obtained as it has just been described, in the same way as in a seismogram obtained using a single impurity point and a large number of detection stations, this because of the law of reciprocity . When the seismogram is reproduced on film and processed in the apparatus shown in Figures 10 and 11, the seismic phenomena appearing on the display, particularly those arising from direct reflections on reflection horizons of underlying surfaces, are highlighted under gradually increasing diameter rings. The phenomena of surface parasitic waves and certain other phenomena are highlighted in the same way. This case is particularly well represented in FIG. 14. At the instant T1, a transverse wave or distortion wave S moving outwards is the only phenomenon which is particularly identifiable, the instant T1 being immediately afterwards usually considered as being what one can suppose to be the instant of the seismic impulse. At time T2, the transverse wave component appears at a greater distance from the center of the presentation and the first reflections from the H horizon of reflection of underlying layers appear on the recording as d 'an R band near the center of the presentation. At time T2, the phenomena produced by the transverse wave cease to appear on the presentation and the phenomena produced by reflections coming from the horizon of reflection H appear in the form of a band of very large diameter . The visual effect is the same as looking at the seismic waves appearing on the ground surface as a result of a seismic pulse at the location of the geophone.

This is true although what is actually presented is a record of the times of movement of seismic waves between several pulse locations and a location or locations of detection and not the waves themselves. However, the effect is such that the observer has the illusion
to actually see seismic waves arriving from the underlying surface of the ground or moving in line with the surface of the ground. The relative outward propagation speeds of various types of seismic waves (reflections, multiple reflections, transverse or distortion waves, and others) make it easy to identify the various types of seismic waves and determine their time of arrival at various points on the ground surface. The horizontal speed of transverse waves, for example, is extremely low while the apparent horizontal speed of reflections is relatively high.

Figures 12 and 13 show one way of performing seismic prospecting on a large scale in accordance with the present invention. Figure 12 is a simplified representation similar to Figure 2 and illustrating a grid array of two thousand five hundred seismic pulse points comprising fifty rows of fifty pulse points each, arranged side by side, each of the pulse points being 30.50 m apart, from each other. As described above, the region of any particular level of the underlying ground surface that is explored when using this grid arrangement, is a square of approximately 746.80 m on a side. flat layers. This is the case when the location of the seismic detection
PU is located exactly in the center of the grid. However, we will now assume that we use the grid network of seismic pulse points shown in Figure 13 but that we use three seismic detection locations referenced
PU-1, PU-2, PU-3 respectively. The location
PU-1 is in the center of the square delimited by the grid, while PU-2 is 1493.50 m to the left of PU-1 and PU-3 is 1493.50 m to the right of PIJ-1. In other words, PU-2 and PU-3 are on either side of PU-1, at a distance which is equal to the distance between the seismic rows and are arranged on a line parallel to the seismic rows . The square referenced A, B, C and
D denotes the area of the underlying soil surface which is surveyed using the pulse point grid in combination with PU-1. From the radiation paths plotted between the pulse points at the corners of the grid and from the detection locations PU-2 and PU-3, it is evident that the rectangle A'AD'C delimits the area of the underlying ground surface at any given level which is surveyed using the aforementioned pulse location grid and PU-2, and further can be seen by using the detection location PU-3 in combination with the pulse location grid, the rectangle BB'DC 'delimits the area of the underlying ground surface, at any given level that is raised, assuming that we are dealing with a diaper or flat bed. Consequently, if three detection locations are used on a line parallel to the row lines used, it is possible to seismically detect three very large areas of the underlying surface of the ground at any level by. particular.

There is shown in Figure 16 a preferred technique for performing the part of the operations to be performed on site, in accordance with the present invention. A section 300 of the ground including the surface 301 of the ground is shown as lying
above a reflection horizon 305 of the underlying horizontal and planar surface which can be
considered to be the top surface of soil layer 303. We designate several locations reserved for geophones and referenced G1, G2,
G3, G4, G5, G6 and C7, along a line substantially perpendicular to a line of pulse points located on the surface of the soI and referenced respectively from S1 to S9. Preferably, the line or row of geophones is substantially perpendicular to the line of pulse points although this is not absolutely necessary.

However, it is desirable to keep the two lines substantially perpendicular, within 10 or 150. We will now assume that a perturba. seismic tion is generated at the momentum point
S1, for example by detonating a charge of dynamite or by dropping a very heavy weight or even by vibrating the ground in said place.

It is obvious that the seismic waves will propagate in all directions from the place S1 and we have referenced Sl-Gl and S1-G7 respectively the radiation paths followed by the seismic waves reflected from the place SI to the horizon reflection 305 and returned to the geophones G1 to G7. The reflection points of the seismic waves detected by the geophones G1 to G7 as a result of a seismic disturbance produced at the location SI, are referenced respectively, 1-1, 1-2, 1-3, 1-4, 1- 5, 1-6 and 1-7. Likewise, the seismic waves reflected by the reflection horizon 305 as a result of a disturbance produced at the location S9 detected by a row of aux geophones. indicated, will be reflected at points between reflection points 9-1 and 9-7. Reflection points on the 305 reflection horizon for seismic waves produced at all locations
If at S9, will form the grid bounded by locations 1-1, 9-1, 9-7 and 1-7 at the corners. The reflection points can be easily determined from par. firing from any particular pulse location to any particular geophone location; for example, the point of reflection of seismic waves produced at the pulse location S7 and detected at the geophone location S2 is referenced 7-2 in the drawing.

In practice, a long strip of the underlying surface of the ground can thus be delimited by arranging a line of geophones, as shown, intersecting the line of pulse points at S5, communicating pulses to the ground at the locations Si to
S4, by arranging another row of geophones along a line intersecting the line of pulse points at S9, sequentially producing seismic disturbances at pulse points S5 through
S8, detecting the seismic waves using the two rows of geophones and individually recording the signals from the geophones, then moving the first row of geophones to the other side of the second row of geophones, then producing seismic disturbances at a third series of locations along a line indicated by the arrow which begins at location S9 and, while detecting and recording the seismic waves with the two rows of geophones then continuing the same process, for as long as you want. Thus, with two rows of geophones, one can seismically prospect a large strip of the underlying surface of the ground. It is obvious that the seismic waves will be detected simultaneously by the two rows of geophones after the first series of pulses (such as for example those produced at the pulse locations 51 to S4) has been completed.

When the recording equipment is limited to one row of geophones and two corresponding recording channels, the following on-site procedure can be used. After completing the seismic observations made by producing seismic disturbances at locations S1 to S9, the row of geophones is moved in the direction of the line on which this row is placed. For example, assuming the row is moved north, as shown in Figure 16, the row of geophones is transferred as a whole until the geophone that was previously at location G7 is at l 'location G4, that is to say at a distance equal to half the length of the row of geophones.

Seismic observations can then be made by producing seismic disturbances along
a line which passes through location G1 and which
is parallel to the line passing through the locations
ment S1 to S9. This method of transferring the ran
age of geophones over half its length and
seismic disturbance production is repeated successively, in order to delimit a band
of the underlying soil surface along a ran
north-south transverse gée, as shown on the fi
gure 16.

Obviously, it is not necessary for the
distance between adjacent geophones is the same
that the distance separating places of disturbance
adjacent seismic conditions, just as it is not
necessary as the length of a row of geopho
nes is equal to the distance between the locations
end points of a particular group of places
seismic disturbances. However, it is preferred
rable as the distance between adjacent geophones
as well as the distance between the places of disturbance
adjacent seismic bations is kept sensitive
constantly.

When seismic prospecting is carried out on
lakes or at sea, it is possible to have a
seismic source as well as a united seismic detector
than at substantially the same location on a boat and it is possible to produce seismic pulses at each of several locations on a grid such as that shown in Figures 2 and 2A, by detecting the seismic waves with the detector and recording the signals from output from said detector, in the form of a single trace after each pulse. The traces will be formed on a composite seismogram, the individual traces being aligned side by side in the order of numbering of the positions of the seismic disturbance locations on the grid, such as, for example, those shown in Figures 2 and 2A. We can then process the composite seismogram, as described above, with reference to Figures 3 to 11.

When the seismograms thus obtained are to be processed by the apparatus described here previously, a composite seismogram is produced from each of the individual seismograms obtained as a result of a single seismic disturbance, the individual seismograms being recorded side by side in order locations of corresponding seismic disturbances. The composite seismogram can then be reproduced as described above in connection with Figures 4 to 11. The resulting display is the equivalent of the entire surface of the ground subjected to simultaneous pulses at the various pulse points.

As already mentioned, the seismic source used to make the seismic observations can include any number of sources such as dynamite, a very heavy weight that is dropped on the surface of the ground, or a device communicating vibrations. on the ground.

When using a vibrator to perform the operation known as continuous wave prospecting, it is common to produce a seismogram by correlating a detected signal with a signal corresponding to the seismic signal transmitted to the ground and that this can be obtained by means of a geophone at or near the location of the vibrator or by using the electrical signal whose waveform corresponds to the signal used to drive the vibrator. This particular type of seismogram, which is often called a correlogram> in the petroleum technique, is obtained in a conventional manner according to techniques well known to those skilled in the art and it is not necessary to describe it.

It is understood that the foregoing description has been given for purely illustrative and non-limitative purposes and that any variants or modifications can be made to it without thereby departing from the general scope of the present invention.

RESULT
The object of the present invention is

** ATTENTION ** end of DESC field can contain start of CLMS **.

Claims (4)

** ATTENTION ** start of field CLMS can contain end of DESC **. placing the first row of geophones to the other side of the second row of geophones, then producing seismic disturbances at a third series of locations along a line indicated by the arrow that begins at location S9 and, while detecting and recording the seismic waves with the two rows of geophones then continuing the same process, for as long as desired. Thus, with two rows of geophones, one can seismically prospect a large strip of the underlying surface of the ground. It is obvious that the seismic waves will be detected simultaneously by the two rows of geophones after the first series of pulses (such as for example those produced at the pulse locations 51 to S4) has been completed. When the recording equipment is limited to one row of geophones and two corresponding recording channels, the following on-site procedure can be used. After completing the seismic observations made by producing seismic disturbances at locations S1 to S9, the row of geophones is moved in the direction of the line on which this row is placed. For example, assuming the row is moved north, as shown in Figure 16, the row of geophones is transferred as a whole until the geophone that was previously at location G7 is at l 'location G4, that is to say at a distance equal to half the length of the row of geophones. Seismic observations can then be made by producing seismic disturbances along a line which passes through location G1 and which is parallel to the line passing through locations S1 to S9. This process of transferring the geophone row over half its length and producing seismic disturbances is repeated successively, in order to delimit a strip of the underlying surface of the soil along a north-south transverse row. , as shown in Figure 16. Obviously, the distance between adjacent geophones need not be the same as the distance between adjacent seismic disturbance locations, just as it is not necessary. The length of a row of geophons need not be equal to the distance between the end locations of a particular group of seismic disturbance locations. However, it is preferred that the distance between adjacent geophones as well as the distance between adjacent seismic disturbance locations be kept substantially constant. When seismic prospecting is carried out on lakes or at sea, it is possible to have a seismic source as well as a united seismic detector that in substantially the same place on a boat and it is possible to produce seismic pulses at each of several places. on a grid such as that shown in FIGS. 2 and 2A, by detecting the seismic waves with the detector and by recording the output signals of said detector, in the form of a single trace after each pulse. The traces will be formed on a composite seismogram, the individual traces being aligned side by side in the order of numbering of the positions of the seismic disturbance locations on the grid, such as, for example, those shown in Figures 2 and 2A. The composite seismogram can then be processed, as described above, with reference to Figures 3 to 11. When the seismograms thus obtained are to be processed by the apparatus described here previously, a composite seismogram is produced from of each of the individual seismograms obtained as a result of a single seismic disturbance, the individual seismograms being recorded side by side in the order of the corresponding seismic disturbance locations. The composite seismogram can then be reproduced as described above in connection with Figures 4 to 11. The resulting display is the equivalent of the entire surface of the ground subjected to simultaneous pulses at the various pulse points. As already mentioned, the seismic source used to make the seismic observations can include any number of sources such as dynamite, a very heavy weight that is dropped on the surface of the ground, or a device communicating vibrations. on the ground. When using a vibrator to perform the operation known as continuous wave prospecting, it is common to produce a seismogram by correlating a detected signal with a signal corresponding to the seismic signal transmitted to the ground and that this can be obtained by means of a geophone at or near the location of the vibrator or by using the electrical signal whose waveform corresponds to the signal used to drive the vibrator. This particular type of seismogram, which is often called a correlogram> in the petroleum technique, is obtained in a conventional manner according to techniques well known to those skilled in the art and it is not necessary to describe it. It is understood that the foregoing description has been given for purely illustrative and non-limitative purposes and that any variants or modifications can be made to it without thereby departing from the general scope of the present invention. SUMMARY The present invention relates to A. An apparatus intended to present in a visual form traces constituting data of a reproducible seismogram, the above-mentioned apparatus comprising: a device intended for the production of the traces of the seismogram in the form of light rays the intensity of which varies as a function of the variations in amplitude of a characteristic of said traces; A row of elongated light transmitting elements arranged so as to intercept said light rays at one of their ends and arranged at their opposite end in a predetermined surface arrangement; 30 a display medium sensitive to light; 40 a device intended to direct, on this light sensitive display medium, light emerging from said opposite end of said ran aged; the aforementioned device also having the following characteristics taken individually - or in combination: I. When the apparatus is intended to convert data traces from a series of reproducible multi-linear-trace seismogram sections into a surface-shaped seismogram in which the amplitudes of the traces are displayed in multanelty si as a function of time, it comprises: a device intended to reproduce the traces of each seismogram in the form of light beams the intensity of which varies as a function of the variations in amplitude of a characteristic of said traces; 20 a row of light transmitting elements, of elongated shape, arranged so as to intercept the aforementioned light beams at one of their end and arranged at their opposite end in several parallel rows each corresponding to one of the sections of the seismogram; He. When the apparatus is intended to convert the data traces of a series of sections of a reproducible seismogram with multiple linear traces, each of said traces having a certain amplitude and time axes, into a surface-shaped seismogram and wherein the amplitudes of the traces are displayed simultaneously as a function of time; it comprises: a light source; 2'1 a series of light waveguides arranged in line at one of its ends and arranged at its other end in a series of parallel rows each corresponding to one of said seismogram sections; A device for moving said seismogram sections relative to the light source as well as to the first end of the light waveguides, so as to simultaneously modulate the light moving from the light source to said first end light waveguides according to variations of a characteristic of each trace of the said seismogram; III. A device measures the relative displacement between the seismogram sections and the light source die and gives a digital indication of the die aforementioned placement; IV. The device further includes a vision and a device for directing light from said other end of the guides light waves to this viewing screen; V, A device directs the light from from said other end of the light waveguides neuses to the viewing screen; VI. When the device is intended to convert traces constituting the data present on a sis composite mogram including a big name reproducible linear seismogram sections with multiple traces in a pre felt in the form of a surface in which the trace amplitudes are displayed simultaneously as a function of time, it includes 10 a source bright; 20 a large number of waveguides lights arranged in a line at one of their ends mothballed and arranged at their other end in several parallel rows, each of which corresponds to one the aforementioned seismogram sections; 30 a châs sis intended to maintain said sections of earthquake gram in position relative to the light source aforementioned neuse and relative to said first end the light waveguides so as to simultaneously modulate the light directing from said light source to said first ex end of the light waveguides as and when as the frame is moved; 40 a rack- 1st connected to the aforementioned frame; 5 a high motor cudgel; 60 a device comprising a spur gear connecting the electric motor to the pre rack cited for the purpose of moving the latter as well than of the aforementioned frame in the direction of the axis times of the seismogram; - 70 an electric circuit that intended to control the direction of rotation of the aforementioned engine; VII. A device is connected to the motor and to the rack to give a numerical indication than the value of the displacement of the chassis by compared to the light source. B. A method of obtaining a seismic bearing that intended to use the apparatus referred to under A and consisting in carrying out a large number of ob seismic servations at several places where seismic waves, XIthesaid places being on an area of the ground surface; to be produced, at par. from the aforementioned seismic observations, an earthquake composite reproducible gram comprising a large number of sections with a large number of linear traces, each of said sections corresponding to a line of reflection points on an underlying surface reflection horizon substantially horizontal and flat, and lying below said area of the ground surface; to do varying, by means of said seismogram, the intensity of the light projected onto a first end of a row of elongated light transmission waveguide elements, each trace of said seismogram modulating the light projected onto at minus one of the given elements of said row; directing light from the other end of the row of light transmitting elements onto a two-dimensional display so that the light from each given element of the row of waveguides illuminates part of the surface of the display, the part the location of which corresponds on this display to the location of a point of reflection on said substantially flat and horizontal reflection horizon lying below said area; the aforementioned process also having the characteristics according to your taken singly or in combination VIII. It comprises the following phases: a seismic disturbance is produced successively at each location of a series of locations spaced apart from each other along a first line on the ground surface; the ground movements due to each of the aforementioned seismic disturbances are detected at each location of a series of detection locations spaced apart from each other along a second line intersecting said first line almost perpendicularly; a composite seismogram is produced comprising a series of seismograms with several linear traces, each of which corresponds to the seismic waves detected due to one of the aforementioned seismic disturbances; by means of the aforementioned composite seismogram, a projection of light is varied on one of the ends of a row of a series of light waveguide elements, of elongated shape, intended for the transmission of light and, finally, the light from the other end of the row of light transmitting elements is directed onto a two-dimensional display so that the light from each of the given elements of the above arrangement illuminates a part of the surface. of the display, which part corresponds by its location on said display to the location of the point of reflection lying on a substantially flat and horizontal reflection horizon lying below the area of the ground surface which is bounded by the ends of the first and second aforementioned lines; IX. The aforementioned process also consists of: producing a seismic disturbance successively at each of a series of locations spaced from the ground over an area of the ground surface; in detecting at a given location of this zone the ground movements resulting from each of the seismic disturbances and in creating electrical signals in response to this detection; producing from the aforementioned electrical signals a composite seismogram reproducible by means of the individual traces of said said signals, traces which correspond to the individual seismic disturbances arranged side by side; reproducing said traces and forming a two-dimensional plane visual display which is the counterpart of the seismic locations and disturbances in that area and using the signal from a given seismic trace to light modulate the surface portion of the display corresponding to the location of seismic disturbances which corresponds to the given seismic trace; X. The aforementioned method makes it possible to obtain a seismic survey of a surface in which a multiple-trace seismogram is produced, the individual traces of which contain reflection phenomena indicative of the travel time of the seismic waves to the various scattered reflection locations. surface on a substantially flat and horizontal underlying surface reflection horizon and a two-dimensional display is formed which is the counterpart of the reflection spots, each individual trace of the seismogram being used to modulate the surface portion of the display which corresponds to the point of reflection where the phenomenon of reflection takes place on each of the aforementioned traces coming from the horizon of reflection and it consists in: producing seismic disturbances in several places arranged linearly on the surface of the ground; detecting seismic waves produced by each of the aforementioned seismic disturbances at a large number of detection locations arranged on a line substantially perpendicular to the line connecting the points of seismic disturbance; producing from the detected seismics individual seismograms corresponding to each of the aforementioned seismic disturbances; finally, in producing the above-mentioned multiple-trace seismogram by recording said individual seismograms, side by side, in the order of the above-mentioned seismic disturbances; XI. The above-mentioned seismic survey method also consists of: producing seismic disturbances successively at a large number of seismic disturbance locations along a first line on the ground surface; in detecting seismic waves produced by the aforementioned disturbances at detection locations arranged along a second line intersecting said first line almost perpendicularly; producing a large number of multiple trace seismograms each corresponding to one of said disturbances; forming a two-dimensional display comprising a large number of parallel linear elements; finally, in modulating a light projected onto each of the linear parallel elements by means of the multiple-trace seismogram, the light projected onto each element being modulated by a particular seismogram, said elements corresponding to the particular seismograms being arranged in the order of the locations of corresponding seismic disturbances; XII. The method allows seismic prospecting and, in this case, seismic pulses are generated successively at each location of a series of spaced locations on the ground and on an area of the ground surface; the displacements of the ground resulting from each of said seismic pulses are detected at a point in said zone and electrical signals are created in response to this detection; a composite seismogram with individual traces corresponding to the individual seismic pulses and arranged side by side is formed from said electrical signals; the projection of light on one of the ends of a light transmission arrangement comprising several light transmission waveguide elements is varied with the aid of said composite seismogram, each trace of said seismogram modulating a given element of said arrangement; finally, light is directed from the other end of the light transmitting arrangement onto a two-dimensional display which is homologous to the pulse locations on said area, so that light from the element aforementioned given of said arrangement illuminates a portion of the display surface, said portion corresponding, by its location, to the pulse location on said zone of the trace which modulates the projection of light on one end of the element given above.