Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
  • G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
  • G01V1/30—Analysis
  • G01V1/301—Analysis for determining seismic cross-sections or geostructures
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
  • G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V2210/00—Details of seismic processing or analysis
  • G01V2210/50—Corrections or adjustments related to wave propagation
  • G01V2210/51—Migration

Definitions

• An important objective of seismic reflection is to produce a seismic section which corresponds as closely as possible to an image of the elastic reflectivity of the subsoil which is being explored.
• the elastic reflectivity of a subsoil can be used either to reposition in space the geometry of horizons or seismic reflectors, i.e. events which have spatial continuity and which are characteristic of significant geological events , and then we obtain information on the structure of the explored subsoil, either to quantitatively measure the reflectivity or the reflection coefficient and we then obtain information, on the one hand, on the contrasts of petro-elastic parameters of a given geological event and, on the other hand, on the quality of the rocks that caused the measured reflectivity.
• GREEN function The weighting specific to each trace is called "GREEN function" which essentially comprises two terms:
• the object of the present invention is to propose a method of imaging or representing a subsoil to be explored which is efficient enough to be exploited while reducing the processing costs linked to the calculation of the weights of the GREEN function.
• An object of the present invention is a method of the type consisting in:
• An advantage of the present invention is to limit the calculation of the weights to a reduced number of traces or more exactly of specular rays, compared to the number of traces which is necessary in all the prior methods.
• Another advantage of the present invention lies in the fact that it can be applied to very fine analyzes of the AVO type.
• Another advantage of the present invention is to be able to split the various stages and to carry them out separately in different entities.
• FIG. 2 is a schematic representation of a collection of classified tracks with constant offset
• - Figure 3 is a schematic representation of a depth migration of the traces of the collection shown in Figure 2;
• FIG. 4 is a schematic representation of a grouping of traces constituting an iso-X M collection ;
• FIG. 5 is a schematic representation of a path of specular rays in the propagation velocity model.
• a basement 2 for which an image of the reflectivity is desired there are one or more transmitters S and receivers R, at R n , the distance h ; separating the transmitter S ; an R receptor ; being called offset (offset in English).
• waves are emitted which propagate in the subsoil 2 and which, after reflection on reflectors or H horizons, horizontal or parallel, reach the receivers R ⁇ to R n in which they are recorded in the form of traces.
• the traces are, in a first step, classified according to a determined criterion, for example in common firing point, in common midpoint, in common receiver, in common offset, etc.
• An example of collection of traces is represented very schematically on FIG.
• a time or depth migration is carried out for each collection of traces such as that of FIG. 2, for example a depth migration using in particular the migration before sum of KIRCHHOFF but in a simplified and rapid version, in order to obtain a series of intermediate migrated images, which corresponds to an image by offset or by firing point or by any other common parameter X.
• a model of propagation speeds in x, z which is established or, preferably, which has already been established for the said zone concerned.
• Migrated images can be produced in 2-D (two dimensions) or in 3-D (three dimensions) in the time or depth domain, like that shown very diagrammatically in 2-D in FIG. 3.
• a grouping of the traces of each of the intermediate migrations corresponding to the same position X on the surface of a point M is called iso-value collection (iso-X M ) or "image gather”.
• a first specular radius at point M for example by setting a source point S, »a travel time t t along the radius S MR,> R, being the point of measurement at the surface , as well as the parameters relating to the evolution of the amplitudes of the waves along said path ("dynamic ray-tracing").
• This step is repeated for different couples S, R , which makes it possible to obtain a set of specular rays at point M for a given range of offsets.
• the GREEN function associated with it is calculated, which makes it possible to determine the weight to be applied to the sample of each specific intermediate migration with the constant parameter, for example h i? to have a good representation of the reflectivity at point M for this parameter h ;.
• each intermediate migration image we have for the same point M with coordinates X M , Z M , a set of samples from the iso-X or "image-gather" collection, each sample corresponding to a given offset or a point given firing range chosen for the calculation of specular rays.
• each sample of each trace in the iso-X collection corresponds to a specular radius of the velocity model, it then becomes possible to apply to this sample the weight of the GREEN function associated with the specular radius.
• the present invention constitutes an important improvement to the techniques usually used since, on the one hand, the calculation of a reflection angle is avoided by triple summation of KIRCHHOFF by substituting for it a direct measurement on a pre-established image and a ray tracing which are easier to perform and much less costly, and on the other hand, the corrective weights to be applied for measuring the reflectivity are calculated only for the specular rays specific to said angle of reflection and no not for all angles of reflection corresponding to all the collections of original traces and constituted by all the recordings of the receivers.
• the various stages of the method according to the invention can be divided into several parts, each of said parts being able to be carried out in a separate entity.
• the calculation of simplified intermediate images without calculating the weights of the GREEN functions can be entrusted to a specialized entity, such as a contractor.
• the weight of the Green's function associated with the specular ray can be a scalar or a complex number.

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• Engineering & Computer Science (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Acoustics & Sound (AREA)
• Environmental & Geological Engineering (AREA)
• Geology (AREA)
• General Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• Geophysics (AREA)
• Analysing Materials By The Use Of Radiation (AREA)
• Holo Graphy (AREA)

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• 1996
  • 1996-10-30 FR FR9613253A patent/FR2755243B1/fr not_active Expired - Fee Related
• 1997
  • 1997-10-29 US US09/091,995 patent/US6094621A/en not_active Expired - Fee Related
  • 1997-10-29 WO PCT/FR1997/001944 patent/WO1998019180A1/fr not_active Application Discontinuation
  • 1997-10-29 CA CA002240998A patent/CA2240998A1/en not_active Abandoned
  • 1997-10-29 EP EP97912284A patent/EP0879428A1/de not_active Withdrawn
• 1998
  • 1998-06-19 NO NO982834A patent/NO982834L/no not_active Application Discontinuation
  • 1998-06-30 OA OA9800095A patent/OA10802A/en unknown

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