FR2544869A1 - METHOD FOR IMPROVING THE RESOLUTION OF SEISMIC COLLECTED DATA - Google Patents

Abstract

THE INVENTION RELATES TO A METHOD FOR INCREASING THE RESOLUTION OF HIGH INTENSITY AMPLITUDE EVENTS IN SEISMIC RECORDINGS CARRIED OUT BY COMMON MEDIUM POINTS (CMP) COLLECTION METHODS. IN ACCORDANCE WITH THE INVENTION, THE CONVERTED PHASES OF A CLASSIC SEISMIC WAVE ARE TREATED IN A WAY TO DEFINE A SERIES OF COORDINATES OF COMMON REFLECTION POINTS CRP EACH ASSOCIATED WITH A GROUP OF CONVERTED TRACKS. THE SOURCE OCCUPIES POSITIONS SP1, SP2, SP3, ETC. RESPECTIVELY, AND THE DETECTORS OCCUPY POSITIONS D1, D2, D3, ETC., PROGRESSING FOLLOWING A LINE OF SURVEY 13. FIELD OF APPLICATION: SEISMIC PROSPECTION.

Description

The invention relates to geophysical exploration and more particularly to

  simultaneously collecting converted conventional primary or secondary wave data, followed by a resulting trace processing in which the lengths of the non-symmetric paths of the incident primary waves and the reflected converted waves are taken into account before summation of the traces to transform a resulting finite offset section into a real zero offset section regardless of the depth or inclination of the reflector The use of receivers

  multicomponents for collection purposes is foreseen.

  The conventional collection and processing of seismic reflection data begins with the separate generation of conventional (P-wave or P-wave) or conventional (secondary wave or S-wave) pressure waves, followed by their recording.

  separated on single-component receivers, that is,

  receptors that contain active elements reacting to movements of waves reflected in a single direction. If a vertically oriented seismic source is assumed, classical P waves descend into the earth and are reflected by one or more geological layers beneath them. P waveform A device

  receptors, the active elements of which react only

  to a movement of elastic waves oriented vertically

  similarly, in the case of cross-wave exploration or

  shear, S waves produced by a source

  horizontally oriented are reflected by

  similar reflectors in the form of S waves and are

  registered by the receiver device in a similar manner, except that the active elements of the receivers react exclusively to the movement of horizontally oriented waves. The processing of the P-wave and / or S-wave data is further complicated by the fact that the collection is generally carried out by means of

  common midpoint "progress" (CMP processes).

  Such methods use stacked receiver devices in combination with "forward-moving" sources along a survey line to generate

  substantial numbers of "redundant" smear traces.

  In other words, these traces are redundant by the fact that a certain number of traces can be associated with the

  same central point midway between

  the respective source-receiver pairs that produce

  traces in the first location After the application

  In the event of time offsets to these traces (called static and dynamic corrections), a common midpoint group (CMP) is created. Then the associated traces of this group are summed to give a signal / noise characteristic. improved, (tem account of the importance of understanding the relationship between collection coordinates, in which traces are identified either by source-position (s) and location-receiver (g) coordinates along the line survey, or by coordinates

  associated with the offset distance (f) of the source stations

  to-receiver, and the position of the midpoint (y) between the source and the receiver of the respective pairs, one can refer, in detail, to the work of John F Claerbout

  "FUNDAMENTALS OF GEOPHYSICAL DATA PROCESSING-, McGraw-

  Hill, 1976, pages 228 and following).

  Even though summation-derived clustering is improved (due to summation), interpretations can still be made difficult by the fact that at the boundaries between different types of rocks, a partial conversion occurs between a type wave and another, if it is assumed that the angle of incidence-of the wave is greater than zero For example, an incident wave P can be partially converted into a reflected wave Sv Alternatively, an incident wave Sv can be partially converted into a P-wave reflected signal. Although Zoeppritz's equations determine the amplitudes of reflected and converted waves, they have rarely been used by geophysical data decoders despite the fact that modern collection methods in seismic reflection, such as CMP processes, use long distances and use a high angle of incidence The reason is that in the case of reflector At greater depth, the angles of incidence are relatively small and the contrasts in speed and density between the layers are assumed to be low. See, for example, pp. 21 et seq., from Kenneth H Waters, entitled " TOOL FOR ENERGY RESOURCE EXPLORATION, John Wiley and

Sounds, 1978.

  Moreover, the complexity of applying these equations to the many different energy levels associated with the various waves reflected at all angles of incidence and the different contrasts of the materials present in the field can be at the root of a problem. enough data to simply overwhelm the interpreter or decipherer The latter may find it too difficult

  to apply the Zoeppritz equations consistently

  especially when field data are collected by modern common midpoint (CMP) methods In this respect, even though the center points / points of reflection may not be vertically aligned, the performer usually ignores the fact that that is, it ignores the differences in the length of the P wave paths converted to Sv waves on vertical projections through central points

  mid-distance between the respective source-pairs

receptors.

  In other words, with incident waves and

  reflective classics, reflection points of reflec-

  flat and horizontal are located directly

  below the vertical projections of the middle points of the respective sour-receptor pairs associated with the interesting traces Consequently, the traces associated with the common points of reflection (or points of depth)

  on flat reflectors, although coming from different

  Even source-receiver pairs can be summed (processed by summation), after appropriate corrections to align the traces. However, with waves converted under the same conditions, the reflection points are not located below the projections starting from the midpoints. respective source-receiver pairs, but they are shifted a certain distance

compared to these projections.

  The closest prior art describes the problem of non-symmetrical path lengths and can be found in the book "DIGITAL PROCESSING OF TRANSFORMED REF I ECTED XAVES", SOVIET GEOLOGY AND GOEPHYSICS, V 21,

No. 4, pages 51-59.

  TT Nefedkina et al. Describe the use of P waves converted to Sv waves in regions of Siberia and other similar regions with permafrost. A summation process for these converted waves gives the advantage of varying the summation point of groupings in accordance with a series of normalization values associated with a special Soviet digital processing code called "Kondakova alpha-language" But, since the process uses a particular processing terminology, groups

  inferior data and simplistic models, a use of

  classical work of this work in the context of modern exploration methods, especially

  to use immersion reflectors, is impossible.

  According to the invention, the non-symmetrical path lengths of incident primary waves and reflected reflected waves, whether or not the incident wave is a P wave or a Sv wave, are taken into account so that traces of the converted Sv or P wave can be properly collected in groups in

  which traces associated with each sample group

  essentially the same point of reflection on a common target reflector. In other words, converted Sv or P waveforms can be identified by common reflection point (CRP) coordinates that have been correctly transformed from coordinates of a source point (SP) and a detection station (D) to take into account the lengths of the

  non-symmetric paths of incident and converted waves.

  The present invention is based in part on the fact that unsymmetrical path lengths are a function of the type of the source, the ratio of

  the speed of the P waves at the speed of the S waves, that is to say

  the ratio Vp / Vs of the coverage areas above the target reflector, as well as the angle of inclination and the depth of the reflector. In order to relate the aforementioned variables, the present invention provides for the simultaneous collection of wave data. P or S classical and converted, on the spot, by the implementation of methods

  conventional collection points common areas (CMP).

  These techniques involve sequentially actuating a conventional seismic source placed in a series of source-point (SP) positions along a survey-raising line and redundantly collecting reflections from both conventional waves and their phases. These detectors are positioned along the prospecting line in several detectors stations (D). Consequently, each of the conventional and converted traces may be associated with a sourcepoint / detector station pair of which the coordinates of the location are known (SP with respect to D). Then, the classical traces undergo a transformation of coordinates and an increase or an amplification in order to take into account (a) the different paths of course of the classical wave in the roof area above

  the target reflector, and (b) the depth and

  of each target reflector.

  and the slope of the target reflector were thus determined, the invention adjusts the slope of imaginary straight lines of clustering on a coordinate summation diagram (SP as a function of D) which identifies common converted traces. differences in path lengths and angles of incidence and reflection of the incident and reflected waves, as well as the inclination and depth of the target reflectors The summation of the tracks reordered takes place then to form a section of actual zero offset of converted traces.

  In the case of flat reflectors, the coordinates

  of the common reflection point (CRP) for a grouping of conventional traces projected on a horizontal reference plane, are related to the coordinates of the source-point (SP) and the detector station (D) in accordance with:

CRP = (D + SP) / 2.

  The above transformation may be considered

  as a process for determining the coordi-

  born from a point of reflection of the target, which have been projected on the reference plane by multiplication of a constant (k) which also takes into account the velocity ratio (incident waves and reflected waves

  in the coverage area), multiplied by the coordinates

  (SP) and (D) of the respective common

  receptors constituting the grouping of traces, in accordance

  to a shape transformation equation

  CRP = k D + (1-k> SP, where k is 0.5.

  According to the present invention, the coordinates of the common reflection point (CRP) for a grouping of converted traces can be of the same

  way related to the coordinates of the source-

  point (SP) and detector station (D), ie

  say in accordance with similar equations of transformation

  mation, of the form: P-Sv conversion: CRP k D + (1-k) SP Sv-P conversion: CRP (1-k) D + KSP o SP and D are source and detector coordinates respectively and k is a constant that takes into account the ratio of the coverage ground velocities (Vp / Vs), the tilt angle a and the depth (h) of the target reflector, as well as the source-receiver departure distance X Vp and Vs are the velocities of the waves

  P and Sv, respectively, of the coverage area.

  An approximate formula for k, which encompasses all these effects, is: k (Vp / Vs) k = pl (Vp / Vs) + {l ± (X / h) sin x} (l + f) -1/2 lof = s) l + X / h) 2 cos 2 x lV / Vs) + 1 Vp, Vs refer to the speed ratio

  the ground of coverage; the angle dp (a) and the depth

  deur (h), as well as the X source-receiver offset are as previously defined. This formula proved to be accurate for inclinations reaching a = 30, and offsets as large as twice the depth of the reflector. that is 2 hours, and it can also

  be applied to conventional P-P waves (long wave

  tudinal) if Vp / Vs is equal to one.

  In many offset applications (where the offset X is much smaller than the depth h and the inclination a is zero) k is given approximately by the simpler expression: k = (V / Vs) (Vp / Vs) + 1 In this case, with flat target reflectors placed below a coverage for which Vp / vs = 2.4, the evaluation of k using the equations above is reduced to:

P-Sv: CRP = 0.73 D + 0.27 SP -

Sv-P: CRP = 0.27D + 0.73 MS

DEFINITIONS

  In the present invention, certain basic terms relating to the collection and processing of multi-point seismic data will be used and are defined below. It is assumed that each trace collected CMP

  is described by the function W (SP, D) and that the coordinates

  source position (SP) and coordinates

  of the receiver position (D) -are inde-

pending.

  In reality, the source position (SP) and receiver location (D) do not have a continuous distribution along the defined survey line (or axis)

  by x coordinates, but they are usually enough

  close together so that it is possible, by simple interpolation, to find W for all coordinates (SP)

  and (D) Moreover, along the x-axis are the coordinates

  the distance from the source to the receiver and the coordinates (CMP) of the locations of the common midpoints, which are orthogonal to each other, but

  intersecting the plan (SP, D) from a given angle

  If the incremental "progress" distance is ASP = AD, then the intersection angle is 450 and the coordinates of

  offset and the middle point are in relation to the coordon-

  source and receiver according to f = D SP

CMP = (D + SP) / 2.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limitative examples and in which FIG. 1 is a plan view of a common environment dot collection system (CMP) illustrating how CMP data is conventionally collected on site, using, for example, a line of detectors

  Dl Dm associated with sources located in

  points SP 1 SP, the activation of the source in SP,

  setting the data record by the detectors D 1 Dm and the activation of the source in SP 2 allowing the recording of data in the positions D 2 Dm + 1

  FIGS. 2A to 2D are vertical sections

  of a field formation surveyed using the CMP collection system of Figure 1, these sections illustrating in detail how conventional reflections are recorded for a source, and also showing the fact that that in the absence of mode conversion to the reflector concerned, the lengths of the paths of the incident wave and the reflected wave are symmetrical with respect to associated reflection points on a flat reflector so that the traces associated with of the

  central points of common midpoints between posi-

  The source and receiver locations coincide, whether or not the wave generated by the source is (i) a P wave (Figure 2A), (ii) a Sh wave (Figure 2B) or (iii) a Sv wave (Figure 2 C), provided that the associated receiver has a component response matching capability (Figure 2 D); FIGS. 3 and 4 are vertical sections of a surveyed field formation using the CMP collection system shown in FIG. 1, these views illustrating in detail the change in location of the reflection point as a function of of the initial elastic wave propagation mode (that is to say that it is a P wave or a Sv wave), where the inclination of the target is equal to 0 and the depth, the coordinates Dl Dn of the detector station and the coordinates S P1 of the location of the source-point remain constant; FIGS. 5 and 6 are sections of a field formation showing in detail that traces associated with a group of common midpoints

  coincide (or do not co Incident) with a deep point

  associated common deur on a flat reflector, according to whether a wave conversion or not has occurred; FIG. 7 is a summation diagram in which the source-receiver coordinates associated with traces produced by CMP collection steps are superimposed on a common midpoint coordinate system as a function of the offset, to better illustrate the processes associated with method of the present invention; Figures 8 to 11 are sections of a field formation illustrating in detail ray tracing modeling techniques used in accordance with the invention for determining the degree of variation of reflection points along flat reflectors (Figure 8). ) and along inclined reflectors (Figures 9 to 11)

  depending on the offset, when an elastic wave conversion

  tick occurs; FIG. 12 is a flowchart of a process implementing the method of the invention using a suitably programmed digital computer, in which converted traces can be grouped along appropriate grouping lines to take into account non-svm path paths. triers of incident rays

  and reflect using a chosen equation of transformation

  mation of coordinates; Fig. 13 is an enlarged scale detail view of the summation diagram of Fig. 7, in which the lines of common reflection points (CRPs) along which converted traces may be

  grouped, are established by a selected equation of trans-

  coordinate formation; FIGS. 14 and 15 are flowcharts for conventional and converted trace processing, collected simultaneously, for carrying out the method of the invention, FIGS.

  and sections of sections illustrating the ability to diagnose

  the method of the invention to solve complex structures in real-world examples; and FIGS. 19 and 20 are summation velocity curves Vp, Vs, and their geometric means, depending on the location of the firing point, of separate events in the film slices of FIGS.

Figures 16 to 18.

  Before describing in detail different

  embodiments of the invention, a brief

  to a description of the concepts allowing better

understand the invention.

  In the case of conventional seismic waves

  received and received, such as P waves produced by a P-wave source and recorded on vertically oriented receivers, the reflective reflection points (CRPs) of flat reflectors are vertical projections

  common environmental points between the

  sources-receptors associated with the recorded traces

  This assumption is valid in zones of structure or inclination or limited dip exploration, and it allows those responsible for the exploration

  to group seismic data conveniently and efficiently

  However, in the case of conversion waves, the angles of incidence and reflection on reflectors located below the surface are unequal. The result is that the reflection points are not vertical projections of the midpoints. between the source / receiver pairs. Figure 1 is a plan view of a seismic collection system illustrating how are established

  the interesting expressions of this memoir.

  For example, the expressions "central point"

  and "midpoint" correspond to a geographical location

  phiqu halfway between a source coordinate, for example the source position S P1 of a series of source positions SP 1 SP 4 of an on-site collection system, and a series of receiver positions , for example D1 of a series of D1 Dm receptor positions, at a reference horizon close to the earth's surface, coinciding with the survey or survey line 11 The central points are designated Cl C 4 and each central point appears to be addressably associated with a pair

  source-detector chosen that produces a given trace.

  In a common midpoint collection (CMP), different sets of detector devices "progress" forward, in the direction of an arrow 12, in association with the similar, forward, incremental positioning of a source in new positions along the line of survey 13 Excitations in the positions of the series can then be carried out in a sequence In other words, the source is excited by

  sequentially in source positions SP 2 * SSP 4.

  The result is that traces recorded at the locations of the different receivers can be put in relation with selected midpoints, located in the subterranean zone prospected. For example, if the reflection interface is a flat horizon, the point of reflection or a reflection occurs occurs defines vertical lines

  which do not pass the central points C 1 C 4 interesting.

  The application of static and dynamic corrections to a trace obtained on site is equivalent (under the conditions indicated above) to placing the source at the central point, to activate this source, then to the rem

  placed by a detector at the same location and recorded

  trace If all traces associated with a common midpoint are recomposed on a side by side basis,

  the resulting set of traces is called a CMP grouping.

  If the traces are added, the resulting trace is

  a CMP consortium of summation Therefore, the

  Seismic interpretation requires conventional CMP processing at least two criteria: (i) the improvement of the signal-to-noise ratio (SNR) of the reflections on the resulting summation group, by summation of the traces associated with a common subterranean point; (ii) the projections of the underground reflection points pass through the midpoints of the source-detector pairs (SP, D) of known coordinate locations; therefore, the locations of the structural reflections are known if the lengths of the paths

  incidence and reflection are substantially equal.

  FIGS. 2A to 2C illustrate reflection phenomena of a typical three-layer model of a shallow, young geological section 20 made up of a sandstone 21 between layers 22 and 23, such as found in the Gulf of Mexico, showing that even if separate sources of energy 28, 29 or 30, producing P waves, Sh waves or Sv waves are placed in positions SP 1, SP 2, SP 3, 2 A, 2 B and 2 C, respectively, and then the lengths of the incidence and

  reflection of the energy associated with each source pair-

  Receivers are substantially equal This assumes that the receivers 31, 32 and 33 in the positions D1, D2 and D3 are prepared so as to receive only the dominant energy of the wave produced Vertical projections 34, 35 and 36 conventional common reflection points CMP 1, CMP 2 or CMP 3 intersect the center points (midpoints) C 1, C 2, C 3 of the coordinates of the respective pairs

  source-position position of receiver, as shown.

  In this respect, the term "conventional" is used to describe the energy received by the receivers 31, 32 and 33, energy in which the dominant movement of the particles corresponds to that of the wave produced, that the source produces the energy in the form of a P wave, a Sh wave or a Sv wave in its main mode of activation. It should be noted in Figure 2A that the source 28, located at the point location SP 1, produces an incident wave that moves outward from the location of this source, in the form of a series of wave fronts Each wavefront defines a surface

  spherical joint that joins points of the subterranean zone

  o raine a move is about to start Si

  the propagation medium has independent properties

  hanging from the position and direction of the course,

  the wavefronts form a group of concentric spheres

  It is convenient to "follow" such fronts using conventional ray tracing methods in the art, wherein the energy of the fronts is shifted downwardly. in the earth following a great number of pyramids of infinitesimal section, and the central line of any one of these pyramids, in a directicnchoisie, is considered as a ray which traces paths 37, 38, 39 These paths pass through

  the strata 21 and 22 of the geological section 20.

  It should be noted that at reflector 23, the angle of incidence of the incident wave is equal to the reflection angle of the reflected wave. Therefore, the incremental length of the incident wave path and

  of the reflected wave in the ground, that is,

  say in strata 21 and 22, is the same.

  The wave source P in FIG. 2A is generally a buried dynamite charge or a vibrator mounted on trucks and vibrating vertically on the ground surface. Most common sources of shear (S wave of FIGS. 2B and 2 C) comprise a vibrator which transmits side-wise rather than top-down shaking to the ground. In Fig. 2B, the vibrator Sh 29 produces horizontal shaking perpendicular to the direction of the CMP collection boom 12. If the vibrator is turned horizontally of 90 so that the movement follows the direction of the arrow 12, as shown in Figure 2 C, the source

  is called a source of shear movement or motion

  cross-section, type Sv There is another difference

  between the energy of the Sh waves and that of the Sv waves. In FIGS. 2A, 2B and 2C, we also note in the stratum 21 that the direction of movement of the particles of the incident energy and the energy reflected, as indigated by pairs of arrows 40a, 40b; 41a, 41b; and 42a and 42b, may or may not change when a

  reflection occurs on the reflective stratum 23.

  In FIG. 2A, for example, the arrow 40 associated with the incident wave is directed downward along the path 37, while the reflected wave associated with the arrow 40b is directed upwards. FIG. 2C, the arrow 42 associated with the incident wave

  is directed upwards and away from the path 39

  pendicular to him), while the reflected wave

  is directed downward relative to the ray path.

  On the other hand, in FIG. 2B, the arrow 41a of the incident wave defines the motions of particles and is perpendicular to the plane of the drawing.

  movement of the particles is parallel to the reflecting surface

  The Sh waves are not affected by reflective or refractive mode conversion on the target reflector. In other words, the wave source 29 produces energy rays which, as a result of reflection on beds dishes, only give Sh waves which, when recorded by the receiver 32,

  only require that receiver 32 be oriented

  pendicular to arrow 12 indicating the direction

  prospecting according to which the collection takes place.

  Moreover, P waves and Sv waves arriving on a reflector do not only give

  classical waves, of similar type, but also producing

  When the two types of waves arrive at the surface, Sv reflections are recorded on the horizontal radial motion segment of the receivers 31 and 33, while P waves are recorded mainly on the response segment.

vertical detectors.

  FIG. 2D illustrates how the dominant response directions of the receivers 31, 32 and 33 can be tuned to react to a movement of particles of the incident wave energy P or S. As shown, if the direction of the response of the receivers 31, 32 and 33 is vertical relative to the earth's gravity field, namely according to the arrow 43, the energy of any incoming P wave is detected if the response of the receiver is horizontal, in the direction of the arrow 44, energy of any incoming Sh wave is detected; similarly, if the direction of the response is horizontal, in the direction of the arrow 45, the energy of any arriving Sv wave

  is similarly detected.

  Figures 3 and 4 show that the point of

  reflection on a flat reflector (for classical waves)

  is not a vertical projection of the midpoint

  between respective source-receiver pairs.

  In FIG. 3, the source 49 situated in a source-point S P 1 produces a wave Sv having fronts which follow incident radiating paths 50, 51 and reflection paths 52, 53, respectively, in the cover 54. reflector 55 occur at points CRP 1, CRP 2 CRP'n Due to the production of conversion P-wave reflections on reflector 55, the angle of reflection (r) of the wave

  P of conversion seems to be greater than the inci-

  dence (i) It should also be noted that at significant angles of incidence, not only does the amplitude of the conversion P wave increase, but, in addition, the reflection point CRP 'on the reflector 55 n' is not aligned n with a vertical projection passing through the midpoint of the respective source-receiver pair, i.e., the mid-point between the S-point source

and the position Dn of the receiver.

  Figure 4 illustrates the same principle, but

in a reciprocal way.

  As shown, a P-wave source 60, located at a source-point SP 1, appears to produce P-waves whose edges follow incident radiating paths 61, 62 and reflection paths 63, 64 in a cover ground. 65 However, the slopes of these paths appear to be inversed relative to

  to those shown in Figure 3 Because of the

  converting Sv wave production to CE thinking points? 1,1 CRP 'and CRP'n, the angles of reflection (r) are less than the angles of incidence (i) But it should also be noted that the degree of inequality (between the angles of incidence and reflection) increases with offset The amplitude of the conversion wave increases by

similar way.

  Returning to Figure 1, it should now be remembered that the detectors located in

  stations Dl, D 2 Dm and sources at sources

  points SP 1, SP 2 SP 4 are used redundantly, so that the coordinates of sources and similar receivers are linked to a certain number of traces produced Starting from the activation of the source located

  at point source SP 1, energy is detected at the

  Dl Dm receivers o a movement of the ground is recorded for a specific period of time, often 6 seconds Such a period allows enough time for the energy to go down and be reflected upwards on reflectors, up to the detector placed in the stations D 1 Dm Then the source is 'advanced' to the source point SP 2 and activated At the same time, the detectors are positioned in the stations D 2, D 3 Dm + 1 to record the reflections When the sequence described above is repeated in the direction indicated by the arrow 12 along the prospecting line 13, we obtain, as a result, a series of overlapping traces of traces, which can be identified with redundant coordinates of sources and receivers

  and reflection points similarly sampled

  as described previously.

  Figure 5 illustrates how unconverted classical traces associated with different groups of source-receiver pairs sample

  the same point of reflection on a target reflector.

  As shown, it can be noted that a reflection common point 68 is located on a flat reflector 69, in vertical alignment with an imaginary projection 70 which passes through the central point Co between all possible pairs of detector-sources. The common point 68

  reflection of the illustrated group of source-pairs

  detectors is obviously obtained by tracing the radius

  of the wave from its source-point SPI, S Pl-1, SP 1-2 o.

  downwards, to the reflector 69, then up to the particular detector station DJ, Dj + 1, Dj + 2 Thus, the coordinates of the common midpoint are equal to all the possible coordinates of the pairs of positions of sourceset of detectors, with the same average value In other words: CM Pi, j = CM Pi-1, j + l = CM Pi-2, j + 2 (I) for as many pairs that sample the same point of reflection 68 Others observations can be

shown in Figure 5.

  For example, it may be noted that, even though the lengths of the ray paths associated with the different source-receiver pairs are substantially different, the lengths of the incident wave paths

  and reflection of any pair are identical.

  Moreover, for this same pair, the angle of incidence

  is equal to the angle of reflection on the reflector 69.

  When the traces associated with these source-detector pairs are transformed into groups of common background points, the summation-resulting traces are said to sample the same point of reflection on any flat target reflector, the relationship of the coordinates of the reflection with the coordinates of the reflection. source-point (SP) and station

  detector (D) conforming to a transformation equation

  mation of coordinates of the form: -

  CM Pi, j = l (SP) i + (D) j1 / 2 (II) Figure 6 shows the fact that waves of

  conversion, recorded in Dj, Dj + i stations -

  do not give points of reflection which are vertically aligned with the midpoint coordinates of the respective pairs of sources and sensors from which

the traces are derived.

44869

  As shown, the reflection points 72, 73, 74, 75, 76 and 77 on the flat reflector 78 can not be aligned with the vertical projection 79 which passes through the center point Co of all the source-detector pairs at Earth's surface. The reasons why this is so will be described

briefly below.

  In the case of conversion waves P to Sv, the angle of reflection r of the conversion radius Sv is not equal to the angle of incidence i of the radius P, as a result of the application of the law of Snell, which applies to optical, acoustical, and

  case of the propagation of elastic waves in the earth.

  Snell's law states that the angles (i) and (r) are related by the speed of propagation of the incident and reflected waves. In this case, the relation is Sin (r) / sin (i) = Vs / Vp (III). ) Vp and Vs are the velocities of the compression waves and

  shear, respectively, in the ground of cover

  ture above the point of reflection.

  In solids such as sedimentary rocks, the velocity of the P wave, Vp, is always greater than the shear wave velocity Vs, often by a factor of about 2. This has the effect that the angle (r) is always smaller than the angle of incidence (i) Therefore, the real points of reflection 73-77 can not be aligned vertically with the coordinates of the midpoint between

source-receptor pairs.

  In other words: the real reflection points of the conversion wave P to Sv tend to be distant from the position of the common midpoint CMP 1, on the reflector 78, the distance corresponding to values

  chosen in the direction of the locations of the detectors.

  If the conversion wave data recorded by these pairs of sources and detectors are classically shifted in the time S to be brought into alignment with the projection 79, a loss of lateral resolution appears due to a spreading of these sources. points

on the target reflector.

  In accordance with the invention, the asymmetry of the incident and reflected ray paths is compensated so that the common reflection points (CRPs) of the target reflectors correspond exactly to known sources-point (SP) coordinates and detector stations. (D) CMP collection system along

of the prospecting line.

  Briefly described, the method of the invention comprises the following two basic steps: The first step is a calculation of ray tracing in the case of conventional (unconverted) waves passing through a laminated structure to provide an offset section From classical zero By numerical iteration, a series of target reflectors is positioned for example at certain inclinations and depths and constitutes events along the time axis.

  of each trace The points of reflection of classical waves

  are computed by steps of transformation of coordinates of midpoints, the values obtained being

  increased to take into account the depth and

  Reflector bending Thanks to a geometrical artifice, the path of the starting radius of the iteration is estimated by means of the effective speed of the hybbolic motion formula.

  The second step is to use the information

* Reflection tilt and depth of the first step, described above, then choose the appropriate combination of source coordinates and detectors so that trace groups sample the same point of reflection in the ground surface for This turns out to be, happily, an inclined straight line of clusters on the summation diagram (SP as a function of D) of FIG. 13, rotated with respect to the conventional phase summation lines. of this group of

  data requires a relative coordinate transformation

  This is a direct relocation of the program that sorts the data through common reflection points (CRPs) rather than midpoint coordinates.

  Before the detailed description of the process

  of the invention, a brief description of two sets

  different from site coordinate systems, used with the present invention, is advantageous for understanding certain aspects of the invention and is

  given below with reference to Figure 7.

  The top of FIG. 7 is a plan view of a CMP collection system similar to that illustrated in FIG. 1, except that the positions of the source-points SP 1, SP 2 precede the advance of the detector device D1. D 2 Dm, instead of following the device as shown above The direction of progression is in the direction indicated by the arrow 90 along the line of survey or prospection 91 As a result of similar incremental advances between the device and the positions of the sources ,

  that is, each is advanced by an incremental position

  by collection cycle, so that ASP = AD,

  traces may be associated not only with the posi-

  respective source (SP) and receiver (D) ratios by orthogonal axes 92 and 93, respectively,

  on the summation diagram 94, but they can also

  be identified with the common midpoint (CMP) and offset (f) coordinates that extend along orthogonal axes 96, 97, in accordance with the coordinate transformation equations given above, namely

CMP = (D + SP) />,

f = D-SP.

  Since the coordinate transformation

  born for conversion waves varies substantially

  compared to these formulas, a brief description of the

  theoretical basis for performing coordinate transformation

  from conversion traces according to the invention

will now be given.

  Briefly described in this regard, the transformation equations involving flat reflectors will be

  initially developed, followed by a de-

  cut from the derivation of transformation equations

  in relation to the inclination of the reflectors.

  The tracing of conversion waves

  in the case of flat reflectors will now be described.

  In the case of conventional phases such as the P-wave generated and then recorded on vertically-reacting receivers, the common reflection points (CRPs) are assumed to be the common mid-points (CMP) between the associated source-receiver pairs. given offset, for example for a given offset along the axis 97 of Figure 7, the traces associated with a given midpoint and the coordinate 96 can be grouped simultaneously In other words, in areas without structure or inclination,

  CMP data, can be conveniently grouped according to

  attached to midpoint coordinates of each pair

  source-receiver, then processed by correction of

  time due to the distance from the relevant markpoint (NMO correction), by static and by

  summation to give precise final cut-films.

  However, in the case of conversion waves, since the angles of incidence and reflection are unequal, the reflection points associated with each target can not be aligned with the positions of the aforementioned midpoints. But they can be determined with accuracy and then eliminated in accordance with the

the present invention.

  Figure 8 illustrates aspects of the conversion ray tracing of the present invention for

establishing an alignment.

  This figure represents a stack of layers generally designated 100, namely layers

  1, 2, 3, n, part of which represents the cover.

  The line ioi in solid lines indicates the path of the rays of an incident P wave produced by a source at coordinates SP on the surface 102 of the earth, and a conversion wave P in Sv which is reflected on the interface 103 d The reflection is recorded by a receiver placed in the D position. For a given distance-X distance between the coordinates of the source (SP) and the coordinates of the receiver (D), the radius coordinates must be determined and the reflection offset distance Xr can be determined The conversion problem Sv-P is a reflected image of that shown in Figure 8, but the general solution is the same for the angles

incidence in each layer.

  In short, to find the angles of incidence in order to draw the ray map, the invention transforms ray tracing from the resolution of a ray.

  problem of reflection to that of a transmission problem.

  This can be done, as shown in FIG. 8, by constructing an image corresponding to the symmetry of the Sv rays reflected with respect to an interface 103. In this way, the total ray path appears to be equivalent to the transmission to the down through two groups of layers, i.e. the layers 1, N and the layers n + 1, n + 2, 2 N before a reflection occurs at the point of reflection 105, i.e. say along the descending segments of line 101 in solid lines and line 106 in lines

dotted, as shown.

  It should be noted that the upper layer group is associated only with P wave velocities in the coverage, while the lower group of

  layers is only associated with Sv wave velocities.

  If the layers are numbered from top to bottom, as shown, and are assigned the correct values of velocities, angles and thicknesses, the total distance X of offset and the time T of the radius are 2544 a 69 2 n X = E hi tg O ii = l 2 N -l T = Z hccos ei / vi (2) i = 1 To find the angles of incidence 81, e 2 i in the layers, the time is minimized T of course of travel by constraining to a fixed offset X This determines the parameter p of the rays from which all angles

  can be calculated by Snell's law.

  In this respect, Taner and Koehler (1966) describe

  a technique to trace only classical reflections

  However, this technique is interesting ("VELOCITY SPECTRA-DIGITAL", but it is not suitable for conversion waves and does not use transmission paths).

  COMPUTER DERIVATION AND APPLICATIONS OF VELOCITY FUNCTIONS ",

Geophysics, Vol 34, pp 859-881).

  The function (F) will now be defined.

  F = T p X (3) 2 n F = Z (hivi l {(% tg 2 Oi + 1) 1/2 p vit 4 i} (4) i = l

  o p is a variational parameter.

  To minimize T with a fixed offset X, we consider the differential of F and we give it a value equal to 0, that is to say: 2 N 2 & F = Z (hi / vi) {etg ei / (tg 28 i + 1) 12 p vi} 6 tg oi i = l

  This is possible for arbitrary angle differentials.

  only if P = 1 i (1 + cos 2 Oi) / 2 = sin i (5) that is, Snell's law applies, op is the radius parameter, with units of apparent horizontal inertia This can also be written as sin ai = p Vi = Vi / C (6) oc is the unknown horizontal velocity of the radius By substituting this for the angles in equation 1, we obtain a simple equation for c 2 n X = E h 1 vi / (c 2 V) / i = l 1 i V (7) This equation has no algebraic solution for c, but it can be solved numerically by iteration, requiring an initial evaluation of the path In accordance with the invention, the hyperbolic curvature formula gives surprisingly good starting values for c, as described below. Referring again to FIG. 8, it can be seen that the total transmission path through the two groups of layers is simply equal to half a conventional bidirectional reflection path.

  down to the 2 N interface and back to the

  face The ascending reflection arrives with a 2 X offset. The standard formulas for the increase of the time due to the distance from the point of the shooting mark considered make it possible to estimate the times of the arrivals and the inertia

  in terms of effective speeds downhill

  terface 2 n Unidirectional times up to the 2 N interface with an X offset are obtained from the same curve formula by simply dividing by two the

variables of distance and time.

  Thus, in the considered problem of converts, the approximate formula is: T 2 = T 2 + (X / Vp) 2 ps s reflection (8) where T is the time 'e bidirectional zero offset for converted reflections, equal to 2 ## EQU1 ## where V is the effective speed equal to (10) In expression (10), the terms ti are the unidirectional layer times given by: the unidirectional layer times given by ti = hi / Vi (11) where the times P are obtained for i of 1

  Sv are obtained for i from n + 1 to 2 n.

  From equation (8), initial of co can be given for the apparent radius Let: at N and the times a horizontal velocity evaluation co = d X / d T = Vps lT 2 + (X / Vps) 2 l / 2 / (X / Vps) ps (12) It should be noted that co is infinite at a zero offset and decreases asymptotically towards Vps

when X goes to infinity.

  To find the exact value of c for the stratification model, c O is substituted for c in equation (7) and iterations are performed to

  a solution having the required precision.

  c being determined, the offset Xr of the reflection point can be calculated using equation (7), but by summation of i only 4, smu Ct to n, we obtain n Xr = E hi vi / (c 2-v 2 y / 2 f 138 The effective speed of the conversion wave can be related to the effective rates of the separated P and Sv waves measured on the unconverted separate reflections If Tp and Ts are the zero offset times , bidirectional, for unconverted events, the effective rate of the conversion wave in equation (10) can be written as V Ps = <Tp V 2 + Ts V 2) / (T + Ts) / 2 (14> Ps = ps where Vs and Vs are the effective velocities of the P and p Sv waves, respectively, down to interface n, obtained from adjacent well cores or

by other conventional means.

  Expression (14) shows that Vps is a weighted mean Ps 2 2 of the mean squared velocities V and V so that, in principle, correlations between the classical P and Sv phases and the conversion rates and times are identification can be done. It should also be noted that the problem of conversion waves has now been replaced by

  an equivalent classical curvature problem.

  speeds are quite extreme because the

  P and Sv speeds are a composite function.

  It is interesting to note that in the case of a single layer, equation (14) can be further reduced Since the effective velocities for small offsets are equal to the actual velocities P and Sv, we have ah 1 = Tp V = T Vs By introducing these realities pp SS in equation (14) Vps varies according to: ps

V = (V {1 / 2A 15)

  ps p S / for the effective speed of the conversion wave to be used in equation (12). The coordinates of the points of reflection can now be estimated. Lateral translation from the midpoint is preferably used for a layer

  unique using Snell's law.

  If the horizontal offset X of the coordinates of the source (D) to the position of the detector (SP) is defined as:

X = D -SP (16)

  the real offset Xr of the reflection point can then be defined as a ratio of these two quantities: R = Xr / (X / 2) = 2 tg ep / (tg ep + tg e SV) (17) o ep is the angle of incidence and e Sv is the angle of reflection The multiplication of the upper and lower limbs by cos ep and the use of Snell's law give: R = 2 (Vp / Vs) / (Vp / Vs + cos Op / cos esv) (18) By a development in series of power for each term cosine, by the use of the law of Snell and by simplification, one obtains: R = 2 (Vp / Vs) / {( Vp / Vs + 1 (ap 2/2) (1 (Vp / Vs 2)} (19)

  where ep is the angle of incidence, in radians.

  P The approximate ratio of the offset Xr of the point

  reflection X / 2 from the middle point is of

  where ep = / 4 = 45 degrees For PX offsets smaller than the depth of the reflector, the term ep can be ignored, so that: R = 2 (Vp / Vs) / (Vp / Vs + 1 ) (20) It should be noted that the ratio R only depends on the ratio (VP / Vs) for all the reflectors

  whose depth is greater than the offset distance.

  Expression (20) can therefore be used to group traces associated with selected pairs

  source-receptors presenting events, which

  Till the same point on an interface, as follows. It should be remembered that, in classical waves, the angles ρ p and esv are equal, so that the reflection point is: CR Pi, = S Pl + 0, 5 (Dj S Pi) (21) = 0 , 5 (Dj + S Pi) For P to Sv conversion reflections, the reflection point offset is: CR Pi, j = S Pl + 0.5 R (Dj SP i) The transformation above can be considered as a process for determining projected point coordinates on the horizontal reference plane by multiplying a constant (k) which

  takes into account the speed ratio of the multi-

  folded by the coordinates (SP) and (D) of the source-pairs

  respective receivers, according to: = k Dj + (1-k) S Pi (22) ok = R / 2 = (Vp / Vs) / (Vp / Vs + 1) (23) It follows from equation (22) ) that the actual reflection points for conversion waves are equal to a weighted average of the coordinates of the positions of the sources and the detectors, the weights adding up to unity For conventional reflections, the

  Weights are each 0.5 and their sum reaches 1.

  Due to expressions (22) and (23), traces that are associated with source and detector coordinate pairs can be grouped for a known position.

CRP of a point of reflection.

  It should be noted on expressions (22) and (23) that k is only a function of the ratio Vp / Vs for the terrain above the reflector, ie the ratio Vp / Vs for the cover, if the reflector is flat However, if the reflector is inclined at an angle to a horizontal line perpendicular to the earth's gravity field (instead of being flat), the formulas corresponding to the coordinates CRP i's point of reflection are more complex.

  Tracing of conventional wave rays and converted with inclined reflectors will now be described. FIG. 9 shows the geometric relationship of the CRP reflection points for conversion waves originating from an inclined layer 110.

  in this case, two factors, namely the angle of inclination

  naison a and the ratio of the offset to the depth X / h An exact formula for k is the following: k = 1/2 l 1 + (X / 2 h) sin (24) the previous expression (24) being developed of the following way.

  A source has position coordinates

  (SP) and pulls down, under a certain inclination

  in a receiver placed in a position (D).

  Whereas for classical reflections, the angles of incidence and reflection of the inclined interface 110 are equal, they are not equal in the case of conversion waves. The purpose of the following expressions is to find a relation between the offset real Xr 'of the reflection point along the interface 110 and the offset X' / 2 of the middle point along the same interface, as measured from coordinates s' and of which are, on this interface 110 , the points of the projected images of

  surface points SP and d, respectively.

  R can be defined as the ratio of the reflection point offset to the offset from the midpoint to the

  surface of the earth, indicated in 112, actually recorded.

  By geometry, it is determined that the ratio of the inclination coordinates along the interface 110 is equal to: R = Xr / (X / 2) = Xr '/ (X' / 2) (25) If the tilt angle a was zero, Xr '

  X '/ 2 and R would be 1, as expected According to the geo-

  Figure 9, given that Xr '= h tg ap X' = (2h + X sin) tg p (26) a substitution of these expressions gives k, as follows: k = R / 2 = 1 / 211 + (X / 2 h) sin'al (27)

  as previously stated in equation (24).

  For a zero inclination, the expression in equation (27) is reduced to k = 1/2, which means that the real point of reflexion corresponds to the position of the midpoint between the source and the receiver. null, this equation is convenient to use for estimating the position of the real point of reflection, as a combined function of

  inclination, offset and depth.

  Thus, since k = R / 2, according to expression (22), the actual reflection points CR Pij for conventional waves can be set as: CR Pi, j = k D + (1-k) Sp ; However, the expression (27) only deals with conventional reflections at the interface 110 and it

  do not apply conversion reflections.

  Figure 10 illustrates the geometric relationship of the conversion ray paths with respect to a

inclined interface.

  In this case, the parameter k depends on three factors, namely the ratio Vp / Vs, the angle of inclination a and the ratio of the offset to the depth X / h. An exact formula for k is therefore: Vs) {(VK / Vs) + l 1 + (X / h) sin el 1 + fl-1/2} (28) ol <j Ir 1 1 </) 2 f = (X / h 2) cos 2 (29) l (vp / vs) + there the total expression (28), above, being developed

as follows.

  It should first be noted in Figure 10 that the angle of incidence (ep) and the angle of reflection (esv) are no longer equal. Therefore: Xr '= h tg op (30) and X = h tg op + (h + X sin) tg Osv (31) X '= h tg Op (1 + (1 + (X / h) sin a) tg Osv / tg Op) Substituting them in the equation (25), we obtain: R = 2 / tl + li + (X / k) sinr al tcr sv / tg api (32) Except for the ratio of tangents, this formula is similar to that established for classical reflections . Equation (32) is exact, but the ratio of tangents can not be determined accurately without iterative ray tracing. However, a simple approximation can be made and gives answers

very close.

  If the reflection point is shifted from CRP 'to CRP' as shown in Fig. 11, the angles of incidence and reflection both increase from ep P to ep ,, and from e Sv to esv, respectively. angles of the tangents change very slightly, so that a good approximation is obtained: tg asv / tg ap tg) Sv "/ tg p (33) When the depth of the reflector increases, this approximation becomes more precise Thus, according to Figure 11, we have:

(34)

  cos 8 p "= h / (h 2 + Xr" 2) 1/2 sin op "= Xr" / (h 2 + y 2) 1/2 (35) o (for deep layers) Xr "= (Vp / Vs) X cos a / (Vp / Vs + 1) (36)

  Snell's law indicates that the angles of

  and reflection are in the relation: sin e 5 sv "= (Vs / Vp) sin 3 p" (37) Using Snell's law twice, we can calculate the ratio of the tangents for the disturbed angles, according to : tg esv "/ tg ep" = (Vs / Vp) cos Op "/ cos S Osv '(Vs / Vp) cos Op" l 1- (V 5 / Vp) 2 sin 2 opl 11/2 (38) In substituent (34) and (35) in this equation for cos ep "and sin e", after algebraic simplification,

P P

  we obtain: tg sv "/ tg vp = (Vs / Vp) l 1 + fl-1/2 (39) of = (Xr- / h) 2 (1- (Vs / Vp) 2) (40) To express f by the terms of the distances

  X of surface offset, substitute (36) in this equation

  This gives: = s (vp S j X / h) 2 cos 2 al (Vp / Vs) + 1 l (X / h) 2 cs 2 (41) Finally, the parameter k = R / 2 is obtained by substituting the ratio of tangents of (39) in (32), thereby giving (Vp / Vs) {(Vp / Vs) + 1 + (X / h) sin alIll + f1-11/2} (42) As can be seen from this

  calculation, that equations (41) and (42) verify the

  mules initially established in equations (29) and

(28).

  Although the formula giving k is complex, it is also quite general and is reduced to simpler forms for both conversion waves and for classical waves, with and without

inclined reflectors.

  By giving (Vp / Vs) a value equal to 1, we obtain the formula of classical waves for k in the case of inclined couchies (because the incidence and reflection waves are of the same type) We can see, from after equation (41), that f tends to O and that, therefore, k, in (42), reduces to: k = 1/2 l 11 + (X / 2 h) sin al (43) ce which is in accordance with (24), previously calculated

for classical waves.

  In the case of conversion waves, in

  At the angle of inclination a = 0, we reduce the parameter k to the formula: (vp / vs) {(Vp / Vs) + 1 + f 11 //} (44) ol (vp / vs) 1 lf = (X / h) 2 (45) I (Vp / V 5) + il The effect of f in this expression is

  correct the offset variations affecting X, which becomes

  are important when X reaches a value as large as the depth of the reflector h. If the user is only interested in near offset conditions, where the X / h ratio is much less than 1, f can then be set to zero, resulting in further simplification of k, as follows: = Vp / Vs / (Vp / Vs + 1) (46) which is the least complex approximation in the method of the invention, the aproximation being useful for small offsets in zones with zero inclination This expression for ka been developed previously for

the equation (234.

  It is also apparent from the previous development

  that the parameter k can be calculated for classical waves

  and conversion waves, including the effects of the ratio of offset to depth (X / h), angle of inclination a, and velocity ratio Vp / Vs. Thus, k is a general function of these three. Parameters: k = k (X / h, Vp / Vs, a) (47) which can be calculated for any interesting case As previously described, k is necessary for the calculation of the common points of reflection (CRP) for each type of wave. The present invention will now be described in detail On the solid theoretical basis indicated above, it is possible to describe the operations implementing the method of the invention, with reference to FIGS. 12, 13 and 14.

and 15.

  Figure 12 shows how the

  transformation of a series of traces of land conforming

  In addition to the invention, it represents a point of view

global.

  As shown, flow chart 199 determines

  the desired sequence of steps controlling the functioning

  a numerical computer, such as the IBM model 3033, performing at least the transformation and the return to ordrc of converted traces associated with source-detector pairs whose coordinate positions (SP, D) of the source stations detector-points are known, by the use of a transformation equation for associated common reflection points (CRPs) selected from the group consisting of: CRP = k D + (1-k) SP: for conversions of P waves in Sv waves to the target; CRP = (1-k) D + k SP: for wave conversions Sv to P waves to the target ok (VP / V 5) l (Vp / Vs) + {l + (X / h) sin a} (1 + fr 1/2 lf = 1 (VP / V) (X / h) 2 cos 2 a; 1 (Vp / VS) + 1 l Vp and Vs are the velocities of the P waves and Sv waves, respectively, in the coverage area, X is the distance of the source-receiver offset h is the depth of the target reflector, a is the angle of inclination of the target reflector, and SP and D are the coordinates of the source and detector, respectively , following the line

of survey or prospection.

  As a result of an evaluation centered on the determination of the "k" constant given above as a function of the coverage velocity ratios, the angle of inclination and the depth (h) of the target reflector and the X source-receiver offset distance, it easily appears a transformation by which are

  then produce signals of greater intelligi-

  flexibility and clarity for interpretation

  geophysical It should be noted that although the

  In a general manner, a programmer normally experienced in conventional CMP collection and processing techniques, in addition to the aforementioned transformation equations, can program most conventional computers in relatively a short time to achieve the goals and objectives of the invention A typical language

  programming that can be used is the FORTRAN language.

  Although instruction 200 is the key to transforming source coordinates (SP) and

  receiver (D) in CRP coordinates by evaluation of the equa-

  above, it is assumed that the data has been

  collected as indicated in step 201, previously

  by common medium-point processes (CMP).

  In other words, it is considered an established fact that the data collected in step 201 were produced sequentially by a conventional seismic source placed in a series of source-point (SP) positions and then redundantly collected. in the form of conversion traces by a series of detectors placed in known positions of detectors (D) along the line of survey or prospection Since the traces

  converts are each associated with a source-

  detector whose position coordinates of the source-point detector station (SP, D) are known, a subsequent processing, performed in accordance with step 200, causes their easy transformation in the form of real coordinates of a common reflection point Otherwise said step 200 establishes the OEP coordinates for a grouping of converted traces in order to correct over time each converted trace, the correction relating to (i) any differences in elevation that may have existed between its coordinates of the source station -point-detector at the time of trace determination (static corrections), and (iil differences in curvature associated with the paths

  of course of energy (dynamic corrections) Le-

  As a result, the final traces represent an imaginary collection sequence, as if a source associated with a given trace was placed in each CRP and activated, this operation being followed immediately by a change of position of a detector at the CRP and

  of the phase conversion reception of the produced wave.

  In this way, the CRPs associated with each group of converted traces (in the form of positions (SP, D) of each sourcedetector pair and a constant "k"

  evaluated) take into account non-symmetrical

  of the incident and reflected rays, as well as the inclination and the depth of the target reflector. Then, the converted waves are summed by an instruction 202, in the form of CRP coordinates, then the groups are displayed in accordance with instruction 203-, as an offset seismic section

zero converted traces.

  FIG. 13 is also of interest for the explanation of instruction 200, on which is shown a simplified summation diagram 204 which will be described in association with the collection system

of Figure 7.

  As shown, each point of the diagram 204 has a source coordinate (SP) along the axis 205 corresponding to the position of the source that gives rise to the trace corresponding to that point. The same point also has a coordinate (D) following the the axis 206 corresponding to the position of the receiver whose output signal is also associated with traces in the same way. In other words, the diagram 204 is a curve of the coordinates SP and D of all the

  traces comprising a CMP seismic collection sequence.

  The position of the origin of the seismic line is at the intersection 207 of axes 205 and 206, that is to say at D = SP = 0. The example shown in FIG. 13 is a seismic line consisting of six 13-trace seismograms that have been recorded with end of run geometry, in which the incremental spacing of

  points as shown in diagram 204, namely -

  ASP and AD, is established at a constant value.

  For a given offset, such as along the axis

  208, common grouping-common lines, gen-

  normally indicated at 209, intersect axis 208 perpendicularly

  therefore, the coordinates (ie

  ie "addresses") of groupable traces (aligned along such grouping lines 209) are easily evaluated using the equation: CMP = k D + (1-k) SP

  o k is determined to be 0.5.

  In other words, for conventional flat reflectors without mode conversion, the reflection points of the reflector are vertical projections of the midpoints between the positions of associated receiver-source pairs, producing the trace. Therefore, a common point of reflection on a target reflector is vertically associated with a pair of known coordinates (SP) and (D) For example, in the case of coordinates (SP) and (D) equal to 6, (in association with the offset axis 208), the

  corresponding traces for an appropriate grouping of

  should be aligned along the line of groupings

  209 in phantom, perpendicular to the axis 208.

  In addition, within the defined trace grouping shown on line 209a, the offset distance of

  the source to the receiver, associated with any trace of the

  can also be determined due to the fact that the coordinates of the longest offset trace

  are a direct function of the coordinates of its source-

  point (SP) and the station of its receiver (D) In the example above (on the grouping line 209 a), this obviously appears at coordinates (SP) = 2

and (D) = 10.

  In the case of conversion waves arriving on flat reflectors, the grouping lines are no longer oriented along the 45 degree diagonals indicated in 209 in FIG. 13, but they are modified according to FIG.

  sets of grouping lines in relation to the evaluation of

  of the constant "k" on the basis of the type of elastic wave conversion that occurs and as a function of a chosen Vp / Vs ratio in the coverage, above the target reflector, i.e. (i) along lines 211 a, 211 b in solid lines, associated with the conversion of the wave P into a wave Sv, or (ii) along lines 212 a, 212 b, in solid lines, associated with the conversion of the wave Sv in P wave. The slopes of the lines 211a, 211b and 212a, 212b for a chosen ratio Vp / Vs, for example Vp / Vs = 24, are identified by evaluations "k" in which this last value is equal to 0.73; and 1 = k is found to be 0.24 Therefore, the coordinates for common points of reflection on a flat target are found by the evaluation of: CRP = 0.73 D + 0.27 SP and

CRP = 0.27 D- + 0.73 SP

  for conversions from P to Sv and Sv to P respectively, to give the sets of lines 211a, 211b and 212a, 212b

of Figure 13.

  It should be noted that the resulting sets of grouping lines 211a, 211b and 212a, 212b, although not coinciding with conventional midpoint grouping lines, can nevertheless be summed at using a summation algorithm defined by the equations mentioned above, improved for finding coordinates (SP as a function of D) concerning each of the defined grouping lines,

  for example following a two-dimensional path "passage".

  In this regard, the following two-dimensional tolerance for limiting the search area to include only the transformed traces whose addresses place them in a selected "box" of each defined path of passage,

proved to be suitable.

  Inclusion = <11/2 AD, X 1/2 ASP Therefore, for a grouping around a common reflection point, for example having coordinates (SP) and (D) equal to 6, (tolerance range AD = ASP = 5-1 / 2 to 6-1 / 2) traces associated with line 211a joining the above inclusion tolerance have source-receiver coordinates such as

  data in Table I below.

TABLE I

SP = 7, D = 6

SP = 6, D = 6

SP = 5, D = 6

SP = 4, D = 7

SP = 3, D = 7

SP = 2, D = 8.

  A process, described above, of "boxing" is also useful for data processing

  because of the fact that irregularities

  in the field as a result of interference of roads, rivers and

  the desired positions of shooting and recording

  The former prevent the development of the exact sequence of firing positions and detectors, shown in FIG. 13, i.e. the sequence in which common clustering lines can be

  established in lines 209 of Figure 13.

  In the case of inclined reflectors, several additional variables associated with the evaluation of the constant "k" are determined in the manner described

  previously, ie the angle of inclination of the

  flector and the depth of the point of this reflector, by

  evaluation of classical traces collected simultaneously.

  Figures 14 and 15 illustrate how the present invention can be directly associated with conventional CMP seismic data to account for

tilt reflectors.

  We can now return to the description

  of the transformation of the coordinate equations for an inclined reflector It emerges from FIGS. 14 and 15 that events appearing in the recorded classical traces, as a function of the coordinates of the source (SP) and the receiver (D), are first evaluated Then the determined inclination and depth of the target reflectors are used in the processing of the interesting converted traces. The evaluation of inclination and depth of interesting events is the subject of a

  It is important for these determinations

  maximize the signal response when the angle

  tilt of the event is changed systematically.

  With reference to FIG. 13, the grouping and the summation of the classical traces originating from targets

  flat are made along the diagonal lines 209.

  Therefore, the actual inclination of any reflector

  in a manner previously described with reference to the equa-

  theoretical considerations forming the basis of the present invention,

  only the lines corresponding to the event

  In particular, it should be noted that, since the normal projections of the reflection points are themselves coded and stored,

* in accordance with treatment instructions, the

  and the inclination of these events can similarly be easily incorporated into codes

  stored for later use in the processing of

the converted traces.

  Now, in more detail, as shown in FIG. 14, the terrain traces are first stored in memory. An instruction 300 then assumes the command and sorts the classical traces as a function of the coordinates of the source-receiver pairs. From which the respective traces are determined In other words, the traces are stored to form the trace function W (SP, D), but the address coordinates of the midpoints and offset of these traces are also recorded. Next, an instruction 301 transforms the previously sorted traces in terms of reflection points which are vertical projections of the midpoints of particular source-receiver pairs associated with the interesting traces, over a series of particular time windows. Thus, each trace is initially transformed as a function of a mid-point coordinate value to form the trace function W (y, t) for a fixed offset coordinate (X) The set of trace windows identified with the same fixed offset {X) is then dynamically and statically corrected by an instruction 302, after which the traces are summed initially according to

  common environment points (CMPs) of the source-pairs

  respective receivers via an instruction 303. At the negative response to a decision step 304 as a function of individual sampling points

  along the trace window, an inclination estimate

  is provided by an instruction 306 Using a

  speed function, the depth is also estimated.

  Then, at an instruction 308, the coordinates of the reflections of the trace are again estimated according to

  <i) the inclination of the target reflector lii) coordinates

  born SP and D of the perpendicular projection of the point of reflection on a previously chosen horizon; and

  (iii) the depth h of the Simultaneous Point of Reflection

  It is possible to note the operations carried out by the

  truction 309 which is actuated to memorize the aforementioned coordinates SP and D of the projection, the angle of inclination a and the depth h of the target reflector, while the search for the maximum response of the

signal continues.

  An iteration following the loop 310 occurs until an affirmative response is given to the decision step 304 based on whether or not the response to the signal has been maximized. During this iteration, the instruction 309 simply place in buffer temporary tilt, depth, and surface coordinate data, until step 304 releases loop 310 from active operations. At that time, the last buffered data is released simultaneously to a tape recorder 307 to assist in further processing of the converted data, as described below When the last data is recorded at 307, the buffer is cleared. An instruction 311 then supports the command The instruction 311 determines whether the time window w wl is the last window for the evaluation

  If a negative answer is given to the

  truction 311, the instruction 312 increments the time window by one unit, and the process traverses the loop 313 so as to be repeated. If an affirmative answer is given to the instruction 311, the instruction 313 takes control of the process Instruction 313 increments the operations by advancing the process to the next grouping coordinates. If the previous offset coordinate was (X), then the next fixed offset coordinate in time would be the coordinate

X + 1 offset.

  Returning to loop 312 The operations performed by instructions 301-312, as previously described, are sequentially triggered to account for tilt, depth, and projection data for the new trace group on windows w wl In this way, the process

  can be repeated and can come back several times

  even to generate a series of groupings at different

  offset coordinates, with desired data from

  bending, depth and projection.

  At the same time as Instruction 313

  increments the process to generate new groups-

  to progressively increasing offset coordinates.

  In addition, instructions 314 and 315 are also sequentially processed to (i) store the groups as a function of the offset and (ii) then produce a summation of these groups as conventional seismic sections. The process is complete.

  with an affirmative answer at decision stage 316.

  Now, with reference to Fig. 15, it should be noted that the production method of the converted zero offset section is similar to that shown in Fig. 14. However, there are some differences. For example, after the converted traces present on a band 320 have been introduced and sorted by an instruction 321, the interpreter pre-sets the source to code, by means of an instruction 322, the selection of the coordinate transformation equation, during operations 323 or As previously indicated, these equations are selected from the group consisting of CRP = k D + (1-k) SP: (for wave P conversions to Sv wave); and CRP = (1-k) D + k SP: (for Sv wave conversions in

P wave).

  In more detail, while the operation

  321 sorts the conversion traces according to the coordinates

  source-receptor pairs, ie SP and D coordinates, it should be noted that

  of these traces are also recorded Other-

  that is, when the traces are sorted to form the trace function W (SP, D), offset coordinates for a series of particular time windows w w

  also an integral part of each trace address.

  The instructions 323, 324 transform the previously sorted traces of coordinates of common reflection points (CRPs) which are projections

  surfaces associated with traces of source pairs-

  particular receivers, on the series of windows of t Laps

  w *, * w and offset X X address coordinates.

  After the trace segments identified with the following ones (ie the same fixed offset X, the same time window W and the same CRP coordinates) have been statically corrected, these trace segments make the summation to an instruction 325 This summation obviously takes into account

  tilt information of the reflector, deep

  reflector and reflector offset coordinates, these data being provided by the 307

  operations 323 and 324 as shown in FIG.

  With respect to Instruction 325, it should be noted that the transformed traces are summed according to grouping lines that have been modified by an evaluation of the factor "k", augmented by a search principle of "case" which searches in two dimensions, according to the chosen path of evaluation passage groups "k", as indicated previously In this way, transformed traces, which have been determined by an evaluation of the factor "k" and whose addresses place these traces in the " box "examined, are added These

  summation steps have been described previously.

  A decision instruction 326 then supports the command to decide whether to continue the processing of the data by an iteration block 327, or to allow an instruction 329 to take the command. In other words, the iteration of the process by

  loop 327 continues until an answer is

  mative is given in the decision step 326, which asks whether the data associated with the last window wl have been processed or not In other words, the instruction 326 determines whether the processed data are associated with the last window wl If this is the case, an instruction

  329 takes the order; otherwise, that is

  say in case of a negative response to the instruction 326, an instruction 328 increments the time window by one unit, and the loop 327 is traversed so that the process is repeated. When the instruction 329 takes control, it increments the time. operations by advancing the process to the following clustering coordinates If the previous offset coordinate is (X), then the fixed offset coordinate, which follows in time, should be an offset coordinate X + 1 The loop 327 is

new traveled.

  The operations performed by instructions 322-326, as described above, are therefore performed sequentially to produce data.

  converted from summation, appropriately transformed.

  In other words, the process is repeated several times to generate a series of summed groups at different offset coordinates along with desired coordinate data.

  tilt, depth and CRP projection.

  At the same time as an instruction 329 increments the process to produce new groupings by

  summation, to progressively increasing offset coordinates

  In addition, instructions 330 and 321 are also sequentially executed for (i) memorizing the groups by summation, as a function of the offset and (ii) generating

  a section of these groupings as a section

  Converted process The process ends with an answer

  affirmative at decision stage 333.

EXAMPLE

  A field trial was undertaken in the Sacramento Valley, California.

  vibrators, receivers and recording

  are given below in Table I Io

TABLE II

  Wave source P: Mertz vibrators, model 9 A Diagram: sweeping: 3 vibrations x 20 sweeps over 69 m B Vibrator spacing: 16.5 m C Movement: 1.8 m D Sweeping frequencies: 6-56 Hz , reading E Scan time: 16 S + 8 S listening Recording setup A Coverage: 2400% B Device: VP -288 m-1980 m C Group Interval: 36 m D Geophone Intervals: 3 m E Row of Geophones: Truck Alignment Recording Instrumentation A Gain: Binary B Sampling interval: 4 ms C Recording length: 24 s D Pre-amp gain: 2 ** 7 E Filters: 1 Lower cut: unused 2 Cutoff Upper: 83.5 Hz 3 Band Eliminator: In Service, 60 Hz F Number of Channels: 4 x (48 Data + 4 Aux) Wave Source S: Mertz Vibrators Model 13/609 A Scanning Chart: 3 Vibrations x 20 sweeps over 69 m B Vibrator spacing: 16.5 m C Movement: 1.8 m D Sweep frequencies: 6-28 Hz, reading E Sweep time : 16 S + 8 S of listening Figure 16 represents a section of offset

  classical zero derived from the field data of this test.

  From this section, it can be noted initially that the production consists of gaseous hydrocarbons from Winters sandstone, as indicated generally in box 403 Further interpretations indicate that the sandstone is covered with delta schists that form an impenetrable closure. 404, 405 (inside frame 403) indicate the position

retained gas.

  Interesting additional events are identified in 400,401 and 402, Event 400 is

  situated in a tertiary sedimentary complex.

  401 is located at the base of this complex Event 402 extends from a low-speed shale just above

Winters sandstone interesting.

  Figures 17 and 18 are sections by zero offset summation of the converted data; in Figure 17, the sound of a P wave is used; in Figure 18, a wave source Sv is used.

  resulting conversion of the P-Sv and Sv-P waves,

  are processed in accordance with the process

  the invention shown in FIG.

  In summary, it is apparent from these figures that the low-speed shale just above the Winters sandstone, i.e. the event indicated at 402 in Figure 16, has been significantly extended in the lateral direction of sections, that is to say in the region framed by a solid line 410 It is even more remarkable to note

  that the events 400, 401 At 402 of Figure 18 pre-

  Note that the amplitude level of Sv-P wave conversion is theoretically much lower than that of wave conversion.

P-Sv shown in Figure 17.

  The improved resolution of events in the sections given in Figures 17 and 18 is

  a direct function of the Vp / Vs ratio of the coverage.

  Therefore, a correct determination of P and Sv wave velocities is necessary to obtain sections

accurate to zero real offset.

  Even with such data, assessments

  the horizontal speed of summation, necessary when

  That the coordinate transformation equations according to the invention are used require a good initial estimate of this value. In this respect, the use of the geometric mean of known wave velocities P and Sv has proved very useful. namely Vps = The agreement between the geometric mean of the P and S wave velocities and the final summation rates for the events 401 and 402 of Figures 16 to 18 is good In Figure 19, in the case of the event 401, only a small difference of a few hundred meters per second appears Similarly, in FIG. 20, in the case of event 402, similar good results are evident. It should also be noted that the deviations seem to decrease by Figure 19 in Figure 20 This is predictable since the ratio of the offset to the depth of the reflectors

  concerned, namely event 401 in relation to the event

  402, decreases as a function of the offset.

  It goes without saying that many modifications can be made to the described apparatus and method

  and shown without departing from the scope of the invention.

Z 544869

Claims (13)

  A method for improving zonation resolution is provided by conventional methods of collecting common media points (CMP), sequentially actuating a conventional seismic source (28, 29) in a series of locations. point sources (SP) along a survey line (13) and to collect   redundant way of reflections of both classical waves   and resulting waves by conversion, by means of a series of multicomponent detectors (31, 32, 33) placed in several stations (D) along the survey line, each of the resulting conventional and conversion traces being associated with a known source-points / coordinate-detector station pair (SP, D), the method, which deals with the processing of both conventional traces and converted in a systematic manner so that conventional and converted groups resulting each of these traces each samples a reflection point on a target reflector (23) placed in the basement and common to each grouping, regardless of the inclination and the depth of said target reflector, being characterized in that it consists of (i) to generate seismic records   in the field and including at least recordings   conventional and converted seismic trunks, by positioning and using a set of multicomponent sources and detectors, such as coordinates   of individual source-points / detector stations   can be redundantly associated with a selected number of classical traces and converted from said recordings, the classical and converted traces being the simultaneous output signals of the detectors, (ii) to establish, for said conventional and converted traces, a series of separate points (CRP), each point (CRP) being associated with the grouping traces that are common to it, as if a source associated with a given trace of a common grouping was placed at each point (CRP) and actuated, followed immediately by a change of position of a detector at each   the point (CRP) and the reception of conventional or conver-   constituting said classical or converted trace; i-i each ICRP point) associated with the common grouping of conventional traces being constituted to take account of different paths of travel of the wave due to the depth and inclination of each target reflector; (iv) each point (CRP) associated with said common grouping of converted traces undergoing a dynamic transformation of coordinates of the source-point and the detector station to take account of the path paths   non-symmetrical incident and reflected rays,   and the depth of the target reflectors, wherein the coordinate transformation equation is selected from the group consisting of: CRP = k D + (1-k) SP: for converting P waves into Sv waves to said target; CRP = (1-k) D + k SP: for wave conversions Sv to P waves to said target; vv k = (Vp / Vs) k = Ps l (Vp / Vs) + {1 + {X / h) sin a} (1 + f) -1 / 2 1; o l {(Vp / vs) 11 f = P (X / h) cos a; l (Vp / Vs) + 1 l Vp and Vs are the velocities of the P wave and the Sv wave, respectively, in the coverage area; X is the source-receiver offset distance h is the depth of the target reflector; a is the angle of inclination of the target reflector; and SP and D are the coordinates of the source and the detector, respectively, along the survey line 2 Method for improving the resolution of data Lsmiquas collected by the process of collecting common-point-points (CMP) consisting of sequentially actuating a conventional seismic source (28, 29) into a series of source-point locations (SP) along a survey line (13) and to collect   redundant way of the reflections of both classical waves and   and of their conversion phases, by means of a series of multicomponent detectors (31, 32, 33) placed in several detector stations (D) along said survey line, so that conventional and converted groups resulting from these traces each systematically sample a reflection point of a target reflector (23) placed in the basement and common to each group, regardless of the inclination and the depth of the target reflector, the method being characterized in that it consists of (i) generating field seismic records including at least seismic records   classical and converted, by position and use   a set of multicomponent sources and detectors   such as the individual coordinates of sources-   detector points / stations (SP, D) can be redundantly associated with a selected number of conventional traces and converted from said recordings, these converted and conventional traces constituting the simultaneous output signals of the detectors, (ii) to be separately established, for said conventional and converted traces, a series of common reflection point (CRP) coordinates each associated with a trace group as if a source associated with a given trace was placed at each point (CRP) and activated followed immediately by a change of position of a detector at each point (CRP) and by the reception of waves   classical or converted constituting the said classi-   or (iii) converting each point (CRP) associated with the classical traces to take into account the different path paths of the wave, as a result of the depth and inclination of each target reflector; (iv) each point (CRP) associated with the converted traces undergoing at least one dynamic transformation of source-point coordinates and detector stations to account for non-route paths   symmetry of incident and reflected rays, inclination   naison as well as the depth of the target reflectors, using a coordinate transformation equation selected from: CRP = k D + (1k) SP: for P wave conversions to Sv waves at the target; CRP = (1-k) D + XSP: for Sv-to-P wave conversions to the target; k (Vp / Vs) = = 1 (Vp / Vs) + {1 + (X / h) sin x} (1 + f) -1 / 2 1; ofl (Vp / Vs) 1 (/ h 2 Cs 2 fp (X / h) 2 CO 52 al (Vp / VS) + 1 l Vp and Vs are the velocities of P waves and Sv waves, respectively, in the field X is the source-receiver offset distance, h is the depth of the target reflector, a is the angle of inclination of the target reflector, and SP and D are the coordinates of the source and detector, respectively, following the line of survey   3 Method according to one of claims 1   and 2, characterized in that the inclination and depth values used by said selected equation   coordinate transformation are established as sub-   processing and amplification processing products classic traces.   4. Process according to claim 3, characterized   rised that processing and amplification   The application of classical traces consists in establishing common midpoint coordinates for said conventional traces in the form of a function of the coordinates of the source-point and of the detector station (SP, D) of each trace, to group said traces. following established signs of grouping the common midpoints, summing the grouped traces to form finite offset sections, then estimating the depth and inclination from said event sections and then again estimating the points (CRP) from the tilt and depth data, to group said conventional traces again according to modified grouping lines, in particular to establish their real points (CRP), and to summed the grouped traces again a real zero offset section is formed, the final estimates   depth and inclination of events being   subsequently used in said transformation equation coordinates of step (iv).   Process according to claim 4, characterized in that it also consists of   (v) to carry out a summation of the convergent traces   associated with each point (CRP) established, in sequence,   to form a real zero converted section   as an insignificant horizontal spread of events   in high intensity occurring along this section.   The process according to claim 4, characterized   in that the step of grouping again and re-summing the conventional traces until a real zero offset section is formed is an iteration operation that ends when the signal produced in response to said interesting event is maximum.   Method according to one of claims 1 and   2, characterized in that said step (ii) consists in statically correcting the classical and converted traces in order to normalize the coordinates of the source-points and   detector stations on a horizontal elevation plan   common tal, extending along the creeping liana   8 Process according to one of claims 1   and 7, characterized in that the target reflector is sensi-   parallel to the reference horizontal plane, a coordinate transformation equation for the classical traces being of the form: CR Classical = 0.5 SP + 0.5 D o Vp / Vs of the coverage is equal to unity, and SP, D are the source-point coordinates   and detector stations, respectively.   Process according to claim 8, characterized   in that the constant (k) of the chosen coordinate transformation equation for said converted traces satisfies the following equality: k = (Vp / Vs) (Vp / Vs + 1) o Vp / Vs of the coverage can especially be   determined experimentally or by empirical data.   Method according to one of claims 2   and 3, characterized in that the tilt and depth values of the target reflector are in mutual relationship   such as the constant (k) of the chosen equation of   Dynamic formation of converted traces can take the approximate form: k = (YV / VS) l (Vp / Vs) + (1 + (X / h sin a) l   11 Method for increasing event resolution   amplitude measurements in seismic recordings made by collecting methods (CMP), consisting of generating conventional waves using a conventional seismic source (28, 29) in a series of source-point positions (s). ), and to collect from phase-to-phase converted phases of the conventional waveforms in the form of traces converted into a series of detectors (31, 32, 33) positioned in known locations (d) along a survey line (13), the method, which relates to the processing of converted traces in an efficient manner so that non-symmetrical path paths of incident and reflected rays of said generated conventional waves are taken into account before the summation of the traces, characterized by: (i) sequentially activating said conventional source at said series of source-point locations (ii) to redundantly collect at least converted phases of conventional waves in said known detector stations (d) through said series of detectors to produce a series of   converted traces each associated with a source-pair   detector occupying positions whose coordinates of sourcepoints / detector stations are known (s, d) (iii) to process said converted traces in order to define a series of common reflection point (CRP) coordinates each associated with a grouping of traces converted, as if a source associated with a given trace was placed in each of those points (CRP)   activated, followed immediately by a change of posi-   detection of a detector at each point (CRP) and the reception of converted phases of the generated wave, constituting said   each point (CRP) undergoing at least one trans-   dynamic formation of source-point and detector station coordinates to account for non-symmetrical path paths of incident and reflected rays, tilt and depth of the target reflector, coordinate transformation equation being chosen from the following: CRP = kd + (1-k) s: for P-wave conversions to Sv waves at said target; CRP = (1-k) + ks: for Sv wave conversions to P waves at said target; o (vp, / v) k = k = _V V 5 k = 1 (Vp / Vs) + {1 + (X / h) sin a} (1 + f) 1-1/2; (Vp / Vs) + 1 f (Vp / Vs) + 1+ (X / h) 2 cos 2 a; (Vp / Vs) 1 Vp and Vs are the velocities of the P waves and Sv waves, respectively, in the coverage; X is the source-receiver offset distance; h is the depth of the target reflector; a is the angle of inclination of the target reflector; and S and d are the coordinates of the source and the detector, respectively, along the lifting line.   The process according to claim 11, characterized   in that the inclination and the depth of the target reflector are in mutual relation such that the constant "k" of said selected dynamic transformation equation has the following approximate form: k = (Vp / vs) t (Vp / Vs) + (l + X / h sin a) 2 l   Method according to claim 11, characterized   characterized in that the target reflector is substantially parallel to the horizontal reference plane, said constant "k" of the selected transformation equation being of the form: k (VP / VS) U (Vp / V 5) + 1 l   The method of claim 11, wherein:   rised in that it also consists -   (a) establishing a series of imaginary common group crossing paths on a   classic summation which identifies traces by coordinate   orthogonal sources-points / detector states, each path having a substantially   defined by said coordinate transformation equation   born; and (b) sequentially grouping, along each path, said statically corrected traces, whose source-point coordinates and detector stations place them on that path to establish a series of   Converted and corrected trace groupings.   The process according to claim 14, characterized   in that it further consists in summing the traces of each of said sets of groups to form a seismic section with summation, real zero offset of converted traces.   16 Method for increasing the event resolution   of amplitude in seismic recordings produced by collecting processes (CMP), consisting of   to produce conventional waves with the help of a source   conventional method (28, 29) in a series of source point locations, and redundantly collecting converted phases of said conventional trace waves converted into a series of detectors (31, 32, 33) positioned in known locations (d) along a survey line (13) so that paths   unsymmetrical paths of incident and reflected rays.   of the generated conventional waves are taken into account before summation of the traces, the method being characterized in that it consists in: (i) sequentially activating said source   classic in said series of source locations-   points; (ii) redundantly collecting at least converted phases of said conventional waves in the   said stations (d) known to the detectors via   diary of said series of detectors to produce a series of converted traces each associated with a source-detector pair in positions having known source-point (s, d) coordinates and detector stations;   (iii) to establish for each of the convergent traces   These are the coordinates of a common reflection point (CRP) so that a grouping of converted traces can be associated in the same way at this point, as if a source indexed on a given converted trace was placed at that point (CPR). and activated, followed immediately by a change of position of a detector at said point (CRP) and by the reception of converted phases of said generated wave comprising the trace, each point (CRP) undergoing at least one dynamic transformation of the coordinates of the source -point and the detector station to account for non-symmetrical path paths of the incident and reflected rays, the inclination as well as the depth of the target reflector, the equation of the coordinate transformation being selected from the following: CRP = kd + (1-k) s: for P wave conversions to Sv waves at said target; CRP = (1-k) + ks: for Sv wave conversions to P waves at said target; o (Vp / Vs) k = 1 (Vp / vs) + {1 + (X / h) sin a} (1 + f) 1-1/2; (Vp / Vs) + 1 f p S + (X / h) 2 cos 2; (V / Vs) 1 p 'Vp and Vs are the velocities of the P waves and Sv waves, respectively, in the coverage X is the source-receiver offset distance h is the depth of the target reflector a is the angle of tilt of the target reflector; and s and d are the coordinates of the source and the detector, respectively, along the survey line