Abstract: Method for efficient computation of wave equation migration angle gathers by using multiple imaging conditions. Common reflection angle or common azimuth gathers or gathers including both common reflection angles and common azimuth angles are produced as the data are migrated. In the course of either wave equation migration or reverse time migration, the pressures and particle motion velocities that need to be computed are sufficient to also compute the Poynting vector pointing in the direction of source-side (35) or receiver-side (37) wavefield propagation. From that, the reflection and azimuth angles can be computed (38). The seismic images can then be stored in the appropriate angle bins, from which common reflection angle or azimuth data volumes can be assembled (39).

Abstract: A stable method for using fat-ray tomography to determine a high-resolution velocity model of the subsurface from seismic data (71). The velocity model (72) may be used in migrating the seismic data (76) to image the subsurface. Rays are traced from a subsurface reflection point to surface source and receiver locations (73), using Fresnel zone construction methods (74) that honor correct initial conditions, with the Fresnel radius being a function of velocity.

Abstract: Techniques are disclosed for performing time-lapse seismic monitor surveys with sparsely sampled monitor data sets. A more accurate 3D representation (e.g., image) of a target area (e.g., a hydrocarbon bearing subsurface reservoir) is constructed using the sparsely sampled monitor data set (11). The sparsely sampled monitor data set may be so limited that it alone is insufficient to generate an accurate 3D representation of the target area, but accuracy is achieved through use of certain external information (14). The external information may include information accurately identifying a shape of the seismic reflector(s) present in the target area. The shape may be predetermined from a fully sampled base survey, and used to enable an accurate 3D representation (12) of the target area to be later generated for a monitor survey using a sparsely sampled monitor data set.

Abstract: Method for separating different seismic energy modes in the acquisition (65) of seismic survey data by using sensors that preferentially record a single mode (63), optionally combined with a source that preferentially transmits that mode.

Abstract: Method for efficient computation of wave equation migration angle gathers by using multiple imaging conditions. Common reflection angle or common azimuth gathers or gathers including both common reflection angles and common azimuth angles are produced as the data are migrated. In the course of either wave equation migration or reverse time migration, the pressures and particle motion velocities that need to be computed are sufficient to also compute the Poynting vector pointing in the direction of source-side (35) or receiver-side (37) wavefield propagation. From that, the reflection and azimuth angles can be computed (38). The seismic images can then be stored in the appropriate angle bins, from which common reflection angle or azimuth data volumes can be assembled (39).

Abstract: Method for migration of seismic data into datasets having common azimuth angle at the reflection point. A velocity model is selected that prescribes subsurface P and/or S wave velocities including any required anisotropy parameters. (41) For shot locations on a surface grid, rays are traced on to a 3D grid of points in a target region of the subsurface. (42) At least the travel times of the rays and their dip angles at each subsurface point are stored in computer memory as they are computed. (43) Using the stored ray maps, the seismic data are migrated into seismic image volumes, each volume being characterized by at least an azimuthal angle bin, the azimuthal angles being computed from said ray dip angle information (44).

Abstract: A stable method for using fat-ray tomography to determine a high-resolution velocity model of the subsurface from seismic data (71). The velocity model (72) may be used in migrating the seismic data (76) to image the subsurface. Rays are traced from a subsurface reflection point to surface source and receiver locations (73), using Fresnel zone construction methods (74) that honor correct initial conditions, with the Fresnel radius being a function of velocity.

Abstract: Techniques are disclosed for performing time-lapse seismic monitor surveys with sparsely sampled monitor data sets. A more accurate 3D representation (e.g., image) of a target area (e.g., a hydrocarbon bearing subsurface reservoir) is constructed using the sparsely sampled monitor data set (11). The sparsely sampled monitor data set may be so limited that it alone is insufficient to generate an accurate 3D representation of the target area, but accuracy is achieved through use of certain external information (14). The external information may include information accurately identifying a shape of the seismic reflector(s) present in the target area. The shape may be predetermined from a fully sampled base survey, and used to enable an accurate 3D representation (12) of the target area to be later generated for a monitor survey using a sparsely sampled monitor data set.

Abstract: Method for migration of seismic data into datasets having common azimuth angle at the reflection point. A velocity model is selected that prescribes subsurface P and/or S wave velocities including any required anisotropy parameters. (41) For shot locations on a surface grid, rays are traced on to a 3D grid of points in a target region of the subsurface. (42) At least the travel times of the rays and their dip angles at each subsurface point are stored in computer memory as they are computed. (43) Using the stored ray maps, the seismic data are migrated into seismic image volumes, each volume being characterized by at least an azimuthal angle bin, the azimuthal angles being computed from said ray dip angle information.

Abstract: A method for multipath imaging of three-dimensional volumes of seismic data, given the subsurface velocity distribution. Ray tracing is used to generate the volumes of information needed for migration, but using coarse-scaled grids for computational efficiency. Interpolation methods are disclosed that address the specific shot points and receiver locations and that enable a final image on a grid with the desired resolution. Data storage and retrieval techniques are also disclosed.

Abstract: A method for multipath imaging of three-dimensional volumes of seismic data, given the subsurface velocity distribution. Ray tracing is used to generate the volumes of information needed for migration, but using coarse-scaled grids for computational efficiency. Interpolation methods are disclosed that address the specific shot points and receiver locations and that enable a final image on a grid with the desired resolution. Data storage and retrieval techniques are also disclosed.

Abstract: A model seismic image of a subsurface seismic reflector is constructed, wherein a set of source and receiver pairs is located, and a subsurface velocity function is determined. Specular reflection points are determined on the subsurface seismic reflector for each of the source and receiver pairs. A Fresnel zone is determined on the subsurface seismic reflector for each of the specular reflection points, using the subsurface velocity function. One or more seismic wavelets are selected and a set of image points is defined containing the subsurface seismic reflector. A synthetic seismic amplitude is determined for each of the image points by summing the Fresnel zone synthetic seismic amplitude for all of the Fresnel zones that contain the image point, using the seismic wavelets. The model seismic image of the subsurface seismic reflector is constructed, using the synthetic seismic amplitudes at the image points.

Abstract: A method for controlled-amplitude prestack time migration of seismic data traces. According to the inventive method, common-offset gathers of the prestack seismic data traces are 3-D Fourier transformed from the space-time domain to a preselected alternate data domain, such as the frequency-wavenumber domain, the wavenumber-time domain, or the slant-stack domain. A migration operator that substantially preserves the seismic amplitudes of the original data traces is computed in the {right arrow over (p)}−z domain. This migration operator is applied to the transformed data traces in the alternate data domain, an imaging condition is applied, and the resulting migrated data traces are then transformed back to the space domain.

Abstract: A method for correcting seismic amplitudes for geometrical artifacts resulting in non-uniform illumination of reflector surfaces. The illumination is calculated for each offset as a function of spatial position. The amplitudes are scaled by a scale factor which may be the reciprocal of the illumination. Data considered to be poor quality due to low illumination may be discarded, and the amplitudes scaled further to compensate for the discarded data.

Abstract: The current invention is an apparatus useful for generating seismic waves with an enhanced signal to noise ratio. The enhanced signal is produced at a fundamental resonant frequency, and multiples thereof, by producing a near zero acoustic pressure condition around and beyond each end of the apparatus having an intermediate acoustic source. Such a near zero acoustic pressure condition is established preferably by either (1) using two end acoustic sources to produce a destructive interference effect with the acoustic output of a third acoustic source postioned therebetween, or (2) using two active or passive end acoustic capacitors or resonators to produce a near zero impedance condition at each end of the apparatus. The enhanced signal may be produced over a range of frequencies, including both resonant and nonresonant frequencies, by creating a high impedance condition experienced by the intermediate source and hence a high acoustic pressure around the intermediate region of the apparatus.

Abstract: The current invention is an apparatus useful for generating seismic waves with an enhanced signal to noise ratio. The enhanced signal is produced at a fundamental resonant frequency, and multiples thereof, by producing a near zero acoustic pressure condition around and beyond each end of the apparatus having an intermediate acoustic source. Such a near zero acoustic pressure condition is established preferably by either (1) using two end acoustic sources to produce a destructive interference effect with the acoustic output of a third acoustic source postioned therebetween, or (2) using two end acoustic capacitors or resonators to produce a near zero impedance condition at each end of the apparatus. The enhanced signal may be produced over a range of frequencies, including both resonant and nonresonant frequencies, by creating a high impedance condition experienced by the intermediate source and hence a high acoustic pressure around the intermediate region of the apparatus.

Abstract: The current invention is an improved method for preventing annular fluid flow following primary cementing of a casing string in a wellbore. The method involves injecting high pressure pulses of a working fluid into a liquid-filled casing string to produce tube waves that will propagate through the casing liquid until they encounter a casing restriction or barrier. This encounter vibrates the casing string. Vibration of the casing string helps to maintain the pressure of the cement slurry at or above the pressure of fluids in the surrounding formations, thereby preventing or reducing annular fluid flow.

Abstract: Method and apparatus for generating resonant broad band pressure waves in a fluid-filled wellbore for seismic exploration. In the preferred embodiment, a device is provided in a borehole; the device comprises a cylindrical choke body and a means at each end of the choke body for partially or completely blocking off the borehole and creating a fluid-filled borehole cavity. The fluid inside the cavity is oscillated to establish a standing pressure wave of a desired bandwidth in the fluid. The standing wave is radiated through the wellbore into the earth formation and is received by seismic detectors. The fluid is oscillated over a range of frequencies to generate more information about the earth formation.

Abstract: A downhole seismic source for producing seismic waves in the 0.2-5 KHz frequency with a bandwidth of between 5 and 50 Hz is formed from a magnetostrictive bar with undamped end weights.

Abstract: A seismic source for downhole use is disclosed which is formed by an outer tubular member having weighted ends which carries within a coaxially mounted tubularly shaped piezoelectric element. The piezoelectric element is cyclically driven to produce a standing wave having a frequency in the range of 0.25 to 5 kHz and a narrow bandwidth in the range of 5-50 Hz.