Abstract: A method and a device for detecting and correcting a saturated current profile of a current transformer in a particularly simple and reliable way, initially uses a number of logic inquiries derived from sampled values of the present current signal profile to detect a start of saturation on the basis of a pattern recognition. An end of saturation is subsequently determined, likewise with the aid of a number of logic inquiries. A saturation signal is then formed from a combination of the logic inquiries. In the case of the detection of saturation, the current sampled values are discarded, and an image of the unsaturated current signal profile is reconstructed from a number of sampled values determined ahead of the time of detection of saturation.

Abstract: The invention pertains to transmission to a remote station, by means of transmission channels (generally radio transmission channels), of seismic data acquired by a data collection equipment comprising a plurality of acquisition units, each being suited to acquire, to store and preferably to compress the data to be transmitted.

Abstract: A seismic lead-in for a seismic streamer cable has been invented which, in certain aspects, has at least one stress member, the at least one stress member having an interior surface, a first sealing member adjacent the interior surface of the at least one stress member, at least one transmission element positioned within the at least one stress member, the at least one transmission element having an outer surface, a second sealing member adjacent the outer surface of the at least one transmission element, and a fluid in a space, the space defined by and between the first sealing member and the second sealing member. In one aspect the lead-in also includes a housing enclosing one or both ends of the lead-in. In one aspect the lead-in has a port through an end housing extending to the space for introducing fluid into the space and for removing it therefrom.

Abstract: A method for using S-waves recorded at sea floor to determine anellipticity relating to at least one rock substrate is provided. In particular the method comprises identifying an S-wave event in recorded pre-stack seismic data and then determining at least one anisotropy parameter by adjusting moveout of a corresponding modeled S-wave event to agree with moveout of the identified S-wave event. The method is particularly applicable to mode converted S-waves in seismic signals.

Abstract: A non-destructive method of measuring physical characteristics of a medium, such as uncemented sediment, sandstone, or limestone. A pseudo-random code is generated and is used to generate a pseudo-random acoustic signal. This signal is transmitted into the medium to be measured through the use of a transducer, such as a piezoelectric element, and is received by a plurality of hydrophones. The received signal is then processed to obtain an image of its velocity and attenuation. A universal geoacoustic model of the medium for a given set of measured data is determined, and the model is solved to obtain a pair of permeability-porosity results for the medium. The one of this pair of permeability-porosity results which is correctly indicative of the physical characteristics of the medium is then determined.

Abstract: Methods and systems are provided for orientation of multicomponent geophones, for rotating traces, and for correcting polarity differences between traces. According to an example embodiment, a receiver orientation angle is assigned, based on a determination of an angle between one or more horizontal components and one or more sources.

Abstract: A method and system for correcting seismic survey signals for separating and correcting for the effects of azimuthal anisotropy caused by the overburden, rather than the subsurface reflectivity, is disclosed. Following an initial estimate and normal moveout correction of the traces in a common midpoint gather, analytical traces are generated for coefficient series corresponding to zero-offset travel time response and to the azimuthal anisotropy, over the corrected gather. The quadrature-phase component of the azimuthal anisotropy coefficient series relative to the zero-offset travel time coefficient series indicates the effects of overburden azimuthal anisotropy, while the in-phase component indicates the effects of azimuthal anisotropy from subsurface reflective interfaces. Additional normal moveout correction to correct for the overburden azimuthal anisotropy may then be performed.

Abstract: A system and method are disclosed for reducing flow-induced noise in an urwater towed system. The system includes at least one neutrally buoyant towed array, a tow platform for defining a towed direction of the at least one towed array, a neutrally buoyant tow cable connected to the at least one towed array and the tow platform, and a deploy and retrieve apparatus for deploying and retrieving the tow cable. The deploy and retrieve apparatus is connected to both the tow cable and the tow platform. Deployment of the tow cable from the deploy and retrieve apparatus correspondingly deploys the at least one towed array, and retrieval of the tow cable with the deploy and retrieve apparatus correspondingly retrieves the at least one towed array. The speed of deployment of the tow cable can be varied to decrease the velocity of the towed array relative to the surrounding water thus reducing flow-induced noise.

Abstract: A computer-implemented method, and system implementing the method, of performing impedance inversion of seismic survey data are disclosed. Sonic and density well logs are used to generate an elastic impedance model, at selected angles of incidence or offset range, using an expression for elastic impedance that depends upon the measured or estimated compressional velocity, shear velocity, and density of the subsurface layers in the survey region. The elastic impedance expression also includes a reference density value, and is dependent upon the ray parameter (or angle of incidence). This elastic impedance model is used, for example by way of a pseudo-density log, in estimating the input wavelet, and in carrying out an impedance inversion of the seismic survey over the entire survey region, for at least two angles of incidence.

Abstract: A computer system and method of operating the same to apply overburden corrections to seismic signals prior to amplitude-versus-offset (AVO) analysis is disclosed. The system and method retrieve common midpoint gathers of the seismic signals, and generate analytical, or complex, AVO intercept and AVO slope traces therefrom, effectively stacking the traces in each gather. Over a sliding time window of the stacks, the computer system generates p-measure standard deviation and correlation statistics, preferably using a p-measure value less than one. The AVO intercept and AVO slope traces are then modified, at each depth point of interest corresponding to a time window placement, according to the relationship between the p-measure statistics and the desired statistics for the background distribution.

Abstract: A method of determining the acoustic impedance of a fluid in a borehole, by gating a reflected acoustic signal into a plurality of time slots, and comparing received energies of the signal for the time slots to obtain a value indicative of the acoustic impedance of the fluid. The value may be normalized to yield the acoustic impedance of the fluid using the acoustic impedance of, e.g., water as a calibration point. The comparison is performed by comparing a ratio of an integration of a first ring down time slot and a second ring down time slot, to an integration of an internal reflection time slot. The acoustic pulse may be generated using a transducer immersed in an intermediate fluid contained within a chamber defined in part by a plate in contact with the borehole fluid and having a thickness such that a mechanical resonance frequency of the plate in a thickness mode is substantially equal to a resonance frequency of the transducer.

Abstract: The invention is a method for facilitating discrimination and identification of seismic or microseismic events by means of permanent pickups in an underground zone under development. The method comprises permanent installation of, in one or more wells, elastic wave receivers, geophones and hydrophones leaving the wells clear for development of the zone, at least one reference pickup with direct acoustic coupling with the technical zone development equipment (pickup pressed against a production string for example) for detection of events directly connected with the operation of the wells (valve opening and closure, etc.

Abstract: An apparatus and method for removing the distortion in marine seismic data resulting from the motion of the ship. The ship trails one or more seismic sources and receivers and moves forward at a known velocity. The seismic sources emit seismic waves that travel through the water and reflect off interfaces between rock formations below the ocean floor. The motion of the sources and receivers introduces distortion in the recorded seismic data that can be modeled using Doppler theory. The data preferably is corrected for source motion independently from the correction for receiver motion. The seismic data is first corrected for receiver motion and then for source motion. The technique for correcting for source motion includes correlating the receiver-corrected data with a reference sweep signal, performing an F-K transform, performing an inverse F-K transform on a selected subset of the F-K transformed data, and computing appropriate correction filters for the data resulting from the inverse F-K transform.

Abstract: A plurality of seismic traces are arranged in order of increasing of feet and features therein are analyzed so as to identify corresponding features in each of the curves. The travel time to each of the features is derived in order to extract an actual travel time curve as a function of offset.

Abstract: A method of acquiring seismic data locates a central position above a peaked stratigraphic subsurface. The method then positions receiver lines radially out from the central position, angularly displaced relative to one another, at equal intervals, throughout an entire circle. The method then positions shot lines between and transverse to the receiver lines. The method can also change the circle to the shape of an ellipse. For an ellipse, the receiver lines radiate from a point at the intersection of the major and minor axes of the ellipse. The receiver lines are more closely spaced about the end points of the major axis than about the end points of the minor axis. The shot lines are more closely spaced adjacent the end points of the major axis than adjacent the end points of the minor axis.

Abstract: A marine seismic cable system for marine surveying comprises an electrical conductor within a tubing for conveying compressed air and electricity between a seismic vessel and equipment such as air guns. The tubing resists elongation caused by water drag forces acting against the tubing exterior surface and provides a protective shield to the enclosed electrical conductor or conductor bundle. This combination uniquely conveys compressed air and electricity while significantly reducing the outside cable diameter to reduce the weight and drag forces acting on the cable system. The combination also permits repair and replacement of the tubing or electrical conductor independent of the other component.

Abstract: A geophysical attribute migration method for a medium is disclosed. The method comprises forming at least one collection of seismic traces associated with an area of the medium and classified according to a predetermined criterion, and a stack section is produced on the basis of said seismic trace collection using a stacking speed field related to said area.

Abstract: The present invention relates to a time-lapse or 4-D seismic data processing method in which cross-correlation of trace information in a series of time-lapse seismic images is used to distinguish one source of noise from another source of noise. After a source of noise has been identified, an appropriate filter is constructed to provide a correction to the noise produced by this particular source of noise. The data from one of the time-lapse seismic images is then applied to the filter to produce a corrected image. Differences between the corrected image and an uncorrected image are then used to determine time-lapse changes in the underlying geological structure. By being able to provide filters specifically tailored to correct each of the different types of noise present in a series of time-lapse seismic images, an accurate image of the time-lapse changes in the underlying geological structure is attained.

Abstract: A method of producing images of the limits of a geologic reservoir from measurements of fluid pressure in a well controlled to produce from the reservoir at a constant flow rate. The measurements are taken over a period of time, which includes initiation of well flow and recorded in a plot of well pressure v. time. The method includes detecting abrupt changes in slope of the pressure v. time function, where each abrupt change signifies the arrival of a primary shock wave at a discrete section of a boundary limit of the reservoir; and calculating the minimum radial distance to the discrete section from the well bore as a function of wave travel time. The changes in the slope of the pressure v. time function are used to calculate the curvature of the boundary at the minimum radial distance.

Abstract: A method for inverting a seismic signal, wherein an input seismic signal is represented as an input vector i(t) of length m+n-1, an output seismic signal is represented as an output vector o(t) of length m, and a finite impulse response filter is represented as a solution vector u(t) of length n, satisfying a convolutional equation i(t)Xu(t)=o(t). An m.times.n Toeplitz matrix T(t,.tau.) corresponding to i(t) is calculated, satisfying a matrix equation T(t,.tau.).multidot.u(t)=o(t). Both sides of the matrix equation are transformed to the frequency domain, to generate a transformed equation. Both sides of the transformed equation are spectrally pruned, to generate a pruned equation. The pruned equation is then solved.