Abstract: A method of imaging a target area of the subsoil from “walkaway” data having application to development of oil reservoirs or monitoring of geologic storage sites is disclosed. After acquisition of seismic data of walkaway type and estimation of the rate of propagation of the seismic waves in the subsoil, p illumination angles are selected. The seismic measurements are then converted to data Dp by illumination angle. The distribution of acoustic impedances best explaining data Dp is determined within the target by using a non-linear inversion which minimizes a difference between the data Dp obtained from measurements and data by illumination angle resulting from an estimation. This estimation is performed by solving a wave propagation equation from the velocity field, an acoustic impedance distribution and a pressure distribution at the level of the top of the target for each illumination angle.

Abstract: A method of imaging a target area of the subsoil from “walkaway” data having application to development of oil reservoirs or monitoring of geologic storage sites is disclosed. After acquisition of seismic data of walkaway type and estimation of the rate of propagation of the seismic waves in the subsoil, p illumination angles are selected. The seismic measurements are then converted to data Dp by illumination angle. The distribution of acoustic impedances best explaining data Dp is determined within the target by using a non-linear inversion which minimizes a difference between the data Dp obtained from measurements and data by illumination angle resulting from an estimation. This estimation is performed by solving a wave propagation equation from the velocity field, an acoustic impedance distribution and a pressure distribution at the level of the top of the target for each illumination angle.

Abstract: A method of imaging in an underground formation one or more steep-sloping geologic interfaces, which are not necessarily in a plane, by forming with primary reflectors, which are not necessarily in a plane, dihedra giving rise to prismatic seismic reflections (double reflections). The geometry of the steep-sloping interface is determined from choosing seismic records of one or more events corresponding to prismatic reflections for different source-pickup pairs of an acquisition device. A new reflection tomography technique is used, wherein introduction of specific constraints guarantees the convergence of the algorithm. The velocity distribution in the geologic formation and/or the geometry of the interface(s) between the sedimentary layers can be known otherwise or determined by means of the method. The method can apply to a formation comprising several different sloping interfaces.

Abstract: The invention is a method of estimating, from data obtained by exploration of a zone of a heterogeneous medium, a model representative of a distribution, in the zone, of at least one physical quantity, the model being free of a presence of correlated noises that may be contained in the data which has application to determining the distribution in an underground zone of acoustic impedance, propagation velocities and permeabilities, etc.

Abstract: A method intended to obtain reflection travel times from an interpretation of seismic data in migrated cylindrical waves, for a given value of the parameter defining the slope of these waves, or the superposition of such data associated with various substantially parallel acquisition lines, this parameter possibly taking successively several values. The method comprises the steps: a) defining a slowness vector ({right arrow over (p)}) b) for a given position of a seismic receiver of abscissa (XR) on an acquisition line, seeking, the abscissa (?) of the source; c) determining a travel time (te(XR)) d) repeating steps (b and c) for all the positions of the receivers for which demigration result is wanted; and e) repeating steps (a to d) for all the acquisition lines for which a demigration result is wanted and for all the values taken by parameter (px).

Abstract: Method of imaging in an underground formation one or more steep-sloping geologic interfaces, not necessarily plane, forming with primary reflectors, not necessarily plane, dihedra giving rise to prismatic seismic reflections (double reflections). The geometry of the steep-sloping interface is determined from a pick on seismic records of one or more events corresponding to prismatic reflections for different source-pickup pairs of an acquisition device. A new reflection tomography technique is used, wherein introduction of specific constraints allows to guarantee the convergence of the algorithm. The velocity distribution in the geologic formation and/or the geometry of the interface(s) between the sedimentary layers can be known otherwise or determined by means of the method. The method can apply to a formation comprising several different sloping interfaces.

Abstract: A method of forming, from data obtained by exploration of a zone of a heterogeneous medium, a model representative of the distribution in the zone of at least one physical quantity amply free of the presence of correlated noises that may be contained in the data is disclosed. The method essentially comprises the following stages any acquisition of data giving information about certain characteristics of the zone, specification of a modelling operator which associates the response of the model with a model (synthetic data), modelling of each correlated noise by applying a specific modelling operator to a noise-generating function (n.g.f.), specification of a semi-norm in the data space, specification, in each n.g.f. space, of a norm for which each noise modelling operator constitutes an isometry, and seeking, the model and the n.g.f.

Abstract: A prestack migration method allowing imaging of an underground zone, for a given velocity model of arbitrary complexity. The method allows obtaining elementary migrated images associated with the values assumed by a parameter and the sum of the images obtained for the different values of the parameter (post-migration stacking), in the depth domain as well as in the time domain. This migration is independent of the volume of the results calculated and of the number of seismic traces recorded. Volume images are obtained by taking account of all the seismic traces. Azimuth movout correction is applied to the received data to compensate for drift.

Abstract: Method intended to obtain reflection travel times from an interpretation of seismic data in migrated cylindrical waves, for a given value of the parameter defining the slope of these waves, or the superposition of such data associated with various substantially parallel acquisition lines, this parameter possibly taking successively several values.

Abstract: A prestack migration method allowing imaging of an underground zone, for a given velocity model of arbitrary complexity. The method allows obtaining elementary migrated images associated with the values assumed by a parameter and the sum of the images obtained for the different values of the parameter (post-migration stacking), in the depth domain as well as in the time domain. This migration is independent of the volume of the results calculated and of the number of seismic traces recorded. Volume images are obtained by taking account of all the seismic traces. Azimuth movout correction is applied to the received data to compensate for drift.

Abstract: A prestack migration method allowing imaging of an underground zone, for a given velocity model of arbitrary complexity. By means of conventional wave propagation and retropropagation modelling tools, the method allows to obtain elementary migrated images associated with the values assumed by a parameter and the sum of the images obtained for the different values of the parameter (post-migration stacking), in the depth domain as well as in the time domain. This migration is obtained at an attractive price (calculation cost) because it is independent of the volume of the results calculated and of the number of seismic traces recorded. Only the volume of the zone in which the waves are propagated, the complexity of the events to be imaged and the desired accuracy have an effect on the calculation cost. Volume images are thus obtained by taking account of all the seismic traces.

Abstract: The object of the method according to the invention is to synthesize zero-offset seismic data from data acquired within the scope of three-dimensional (or possibly two-dimensional) multiple-offset seismic reflection prospecting operations in a subsurface environment. It mainly comprises selection of a distribution model of the velocities in the environment, seismic data prestack migration (stacking of the multiple-offset seismic events is achieved in the depth domain), and synthesis of zero-offset seismic data in the time domain by applying to the results obtained with this depth domain stacking a known modelling technique, for example that referred to as explosive reflector technique.

Abstract: A method for providing an optimum model having at least two dimensions of a heterogeneous medium, representing the variations of at least one physical parameter, for example the acoustic impedance of underground formations, and satisfying as well as possible the data measured in situ, for example well-logging in wells in studying the sub-soil as well as other data relative to the medium studied, for example geological information and seismic surface recordings. The method includes the construction of a reference model and the definition of covariance operators which model the uncertainties not only in the medium studied but also in the recordings obtained from outside the medium, for example seismic sections. Comparison between the effective recordings and others which are formed on the basis of the constructed model, makes it possible to check the validity thereof.