Abstract: A method of seismic prospecting offshore by means of at least one pair of hydrophone-geophone sensors disposed at the water bottom, in which a sound source at the surface of the water emits a sound signal and the sensors at the water bottom take hydrophone and geophone recordings H and G, the method comprising the following various steps:a filtered signal is determined such that:M=H.sub..DELTA. -G.sub..SIGMA.withH.sub..DELTA. =1/2(H-H.sub.R)andG.sub..SIGMA. =1/2(G+G.sub.R)where H.sub.R and G.sub.R correspond respectively to the recordings H and G propagated over a go-and-return path through the layer of water; andthe data obtained in this way is processed to deduce therefrom information about the geology of the subsoil.

Abstract: The invention relates to a seismic prospection method in which a seismic disturbance is generated in the sub-soil and sensors are used to pick up seismic data, the seismic data being processed to deduce useful information concerning the geology of the sub-soil, the seismic data containing a signal y.sub.0 that is to be isolated, said signal y.sub.0 being present in the seismic data embedded in an additive signal. The method comprises the steps consisting in: 1) for .alpha. given integer p, computing a prediction error filter a having p coefficients and providing best cancellation of the signal y.sub.0 ; 2) applying the self-deconvoluted prediction error filter to the seismic data to obtain filtered data in which the signal y.sub.0 is absent; and 3) subtracting the filtered data from the initial data to obtain processed data containing the signal y.sub.0 without the additive signal.

Abstract: The transducer comprises for example a block (1) of sensitive elements such as piled piezoelectric disks held up by a stud bolt between two ferrules and a shell (8) all in one piece, that is arranged around the piling with a concave central part (8A) extended on either side by a solid cylindrical part (8 B, 8 C). Two sleeves are arranged at the two opposite ends of the transducer and elastic elements (14) for decoupling them in relation to the vibrating block (1) are interposed. A flexible housing (18) can be placed around the shell (8) so as to insulate from the outside environment the inner volume of the transducer that can be filled with a fluid such as oil. Connecting means allow the vibrating block to be connected to an exciting voltage source. The transducer can be used for the emission of vibrations at sea or in wells and notably petroleum or gas wells for example.

Abstract: The present invention relates to a method of extrapolating a set of traces recorded by means of an array of sensors, in the context of a geophysical prospecting process, the method comprising the steps consisting in: i) approximating a minus Laplacian L.sub.0 (k.sub.x,k.sub.y)=k.sub.x.sup.2 +k.sub.y.sup.2 by the sum of two one-dimensional filters; and ii) approximating an extrapolation operator F.sub.0 by a polynomial of the minus Laplacian L.sub.0. The invention also provides a system for geophysical prospecting.

Abstract: The invention relates to a method of processing seismic data in which a volume of raw focusing data is constituted by downwards extrapolation of seismic data obtained by means of at least one seismic source and of sensors disposed at the surface at regular abscissas along a prospecting section. For a subset of said volume corresponding to a given extrapolation depth and for a contiguous set of abscissas along the prospecting section, zero offset downwards migration is performed to a first set of depths greater than said extrapolation depth in order to constitute a first block of focusing analysis migrated data, and similarly inverse zero offset migration is performed upwards to a second set of depths less than said extrapolation depth in order to constitute a second block of focusing analysis migrated data.

Abstract: A method and the apparatus for in situ analysis of a rock formation that already contains fluid in its interstices an excitation device is provided for imparting motion to the fluid relative to the rock formation and the magnetic fields created by the relative motion of the fluid in the rock formation measured. The permeability of the rock formation are deduced from the measurement. The measurement system is particularly applicable to in situ measurement of the permeability of rocks, e.g. down an oil well.

Abstract: A string of sondes is designed to be lowered down a borehole by means of a cable in order to detect the arrival of seismic waves therein, the sondes including retractable anchor means that are hydraulically actuateable and that are connected by a hydraulic circuit to a common source of hydraulic pressure. The string includes means for putting said hydraulic circuit to ambient pressure, said means being connected to said cable and being adapted to act on said hydraulic circuit in order to cause said anchor means to be retracted when a traction force exceeding a selected value is exerted on said cable.

Abstract: A method for obtaining a model of a surface including the steps of obtaining measurements of geometrical data concerning specific points on the surface, making a grid of the surface, with the grid passing through said points, memorizing, at an address which is specific to each node of the grid, the coordinates of the node, the number of satellites of the node, information for access to the addresses of said satellites and thereafter to information which relates to them, and geometrical data which may be associated with said node; for each node, defining a local roughness index obtained from a weighted sum of the current coordinates of the node and its satellites, defining the sum of an overall roughness index representing the sum of all the local roughness indices, and of an overall index of the infringement of said geometrical data, iteratively adjusting the coordinates of indefinite nodes, by using at each adjustment the sum of a weighted combination of current node neighbor coordinates and of a combination

Abstract: A method of acquiring and processing seismic data for repetitive monitoring of displacement of fluids impregnating a reservoir deep in the sub-surface below the surface weathered zone comprises the steps of: making at each point of a predetermined grid on the surface a vertical axis shallow borehole in the earth above the reservoir passing through the surface weathered zone; positioning in each borehole along its vertical axis a plurality of fixed receivers adapted to be connected separately to a seismic recorder on the surface; emitting near each borehole seismic waves into the earth by means of an emitter on the surface or close to the surface near the vertical axis of the borehole; recording for each borehole by means of receivers placed in the borehole the direct incident seismic waves and the seismic waves reflected at the interfaces of deep strata of the sub-surface, each receiver providing a separate record of an incident wave and a plurality of reflected waves; and carrying out the following processin

Abstract: An off-shore seismic prospecting method for enabling at least two ships to prospect over a single site simultaneously, in which each of the ships generates disturbances in the off-shore environment and uses sensors to record seismic traces containing useful information concerning the geology of the subsoil. A ship is liable to constitute a point source of noise for another ship, which noise gives rise to an undesirable signal that masks said useful information. According to the invention said point source of noise is localized in three dimensions and the space-time coordinates thereof [(X'(t), Y'(t), Z(t)] during the recording is stored in terms of a frame of reference in which the space-time coordinates [(X.sub.r (t), Y.sub.r (t), Z.sub.r (t)] of the sensors are also recorded, after which the recorded seismic traces are processed as a function of the space-time coordinates of the point source of noise in order to eliminate said undesirable signal.

Abstract: The method of the invention consists in measuring remanent magnetization along a borehole drilled through a geological bed, in detecting the set of reversals in the remanent magnetization, in measuring the induced magnetization at the various levels in said bed, in detecting maxima in the induced magnetization, and in correlating these measurements with known dates, firstly of reversals in the earth's magnetic field and secondly of terrestrial phenomena that have given rise to concentrations of highly magnetic substances, thus making it possible to give dates to the various levels of the bed. The method is particularly applicable to oil prospecting.

Abstract: The invention concerns an apparatus for the acquisition of a seismic signal transmitted by a drill bit, placed at the end of a drill pipe rotating about an axis of rotation.

Abstract: A method for determining a far-field signature FF(t) of a plurality of N seismic sources Si (i=1, . . . , N) comprises a stage of measuring a near-field signature NFi(t) of each seismic source Si. In a preliminary stage an initial near-field signature NFio(t) of each seismic source Si and an initial far-field signature FFo(t) of the plurality of N seismic sources are measured simultaneously. An operator G is determined, defined by the convolution integral ##EQU1## The near-field signature NFi(t) measuring stage is carried out on each firing of the N seismic sources Si.

Abstract: The invention relates to a method and apparatus for acquiring borehole seismic data in two opposite directions in a borehole. Acquisition consists in emitting a pressure wave (R, R') at a point (E) in the borehole (PU), and, at a point (R) in the borehole (PU) that is offset relative to the pressure wave emission point (E), in detecting the echoes reflected and refracted by the adjacent geological formations (Ci) in such a manner as to discriminate between pressure waves reflected and refracted by the above-mentioned geological formations in a longitudinal plane of symmetry (P) of the borehole (PU). The discrimination is performed on the basis of detecting the sum and the difference of echo signals coming from opposite directions. The invention is applicable to determining horizons above and below an inclined borehole.

Abstract: In a multisource array of seismic sources, each source is associated with one or more sensors (Ci) for picking up the impulses (TB or signature) emitted by the associated source when triggered. The apparatus essentially includes one or more acquisition arrays (Ai), each one associated with a storage unit (Mi) for all the signals emitted by the pickups (Ci) under the control of a computer (10). Each memory unit includes a comparison module (19, 21, 22) for comparing the digitized samples with a threshold value. The number of each one of the channels where a threshold overrun has occurred is recorded in a reference register (24) which is systematically read by the computer. This monitoring of the level of the picked up signals is carried out outside the normal period where the sources are triggered.

Abstract: A system to control sea navigation or traffic of a plurality of ships or moving bodies is disclosed. The system comprises a radio navigation reference system comprising at least two reference beacon sources and a navigation central station M. Said central station M, the reference beacon sources and the ships or moving bodies are provided with a first intercommunication means from said central station M to each reference beacon source, said first intercommunication means being synchronized by said central station M, and a second intercommunication means from said central station and each reference beacon source to each ship or moving body.

Abstract: Each source of an array of seismic signal sources is associated with one or several sensors (Ci) which pick up the impulses the associated source emits at the time of triggering. The device essentially includes an apparatus (6) for the acquisition and the storage of all the signals emitted by the sensors (Ci) and a shooting control apparatus (7), having memories for reference data, for triggering the seismic sources according to these reference data. A computer (10) is programmed to determine the reference data used for the triggering, preferable according to the signals from the sensors (Ci) acquired during the previous emission cycles and validated in order to check whether their form and/or arrival times are within fixed limits. This arrangement makes it possible to take into account the real working conditions of the emission array. The invention can be utilized in marine seismic prospecting.

Abstract: For seismic monitoring of a petroleum deposit at least one signal receiving unit is fixed to an outside of a casing pipe before the casing plate is cemented in a borehole passing through the monitored zone.At least one housing, defined by projecting elements, (longitudinal members, stops), is provided along an outer surface of the casing pipe, with the where the reception unit being embedded and fixed therein so as to protect the reception unit from shocks or compressive forces which may occur during lowering of the pipe into the well. Each reception unit comprises a support assembly with cavities for sensors, electronic cards for amplifying the signals delivered by the sensors and a sealed external case which is easy to position and which is held firmly in position by embedment in the housing. A multiconductor cable is used, for example, for connecting the reception unit to the surface.

Abstract: The invention relates to a down-hole seismic source with containment. The seismic source comprises a source body (1) supporting an explosive test charge (SE). The source body (1) is constituted by a hollow cylinder and the outside surface of the cylinder includes a containment housing (2) in which the explosive source (SE) is received. The invention is applicable to down-hole seismic sources.

Abstract: In a method of acquiring seismic data in a prospecting area, an array of excitation vibration receivers is placed on or over the terrestrial surface. A plurality of excitation vibration sources is disposed in the vicinity of the array, each source emitting excitation vibrations with a frequency spectrum in a specific frequency band. These bands are adjacent and together cover the frequency band of usable seismic data signals. When the excitation vibrations are emitted by the plurality of sources, the excitation vibration echoes reflected from strata beneath the terrestrial surface are registered by the receivers. The above steps are repeated for a plurality of successive trace increment displacements to produce an emission figure and to cover the prospecting area. The method and the device implementing it can be used for acquisition of terrestrial or marine seismic data.