A computer-implemented method for seismic event localization includes: generating, with at least one processor, a vectorized snapshot matrix representing wave propagation data at a series of snapshots in time for a subterranean formation; computing a reduced orthonormal column basis matrix based on the vectorized snapshot matrix; constructing a reduced order wave propagation model based on the reduced orthonormal column basis matrix; receiving seismic data collected from a plurality of receivers at the subterranean formation; generating a time-domain coefficient matrix based on back propagation of the received seismic data and the reduced order wave propagation model; reconstructing time-reversed wavefield data based on the time-domain coefficient vector; and generating signals for outputting wavefield or seismic event location information based on the time-reversed wavefield data.

Systems, methods, and apparatuses directed to determining a long wavelength velocity model using acquired seismic data lacking low-frequency data is disclosed. Determination of the long wavelength velocity model may include generating a time-delayed signal from the acquired seismic data to produce low-frequency information and reducing a residual energy between the time-delayed signal from the acquired seismic data and a time-delayed signal of modeled data using an objective function to produce an optimized initial velocity model using full waveform inversion. Moreover, a full waveform inversion on the optimized initial velocity model using acquired data can be used to produce a velocity model more accurately representing subterranean formations.

A system for seismic imaging of a subterranean geological formation uses a two-way imaging condition. A seismic signal is emitted into a subterranean formation and recorded at receiver(s). Source and receiver wavefields are decomposed into respective right-down/left-up and left-down/right-up propagating waves. The right-down/left-up and left-down/right-up direction can be defined along the direction emitted from the source or receiver to corresponding direction in two dimensional (2D) case. An imaging condition for generating both a positive-dip structure image and a negative-dip structure image is the inner product of the wavefields. Applying the sample-by-sample multiplication imaging condition to the opposite dip images, the diffraction energy is retained while the reflection energy is significantly attenuated. The diffraction image can be used to detect faults and fractures in subsurface regions.

A method of generating target-oriented acquisition-imprint-free prestack angle gathers using common focus point (CFP) operators includes receiving a plurality of seismic traces associated with a target point in a reservoir. A first angle domain common image gather (ADCIG) is generated based on the received plurality of seismic traces. A plurality of synthetic traces associated with the target point is generated. A second ADCIG is generated based on the synthetic traces. An enhanced ADCIG is generated using the first ADCIG and the second ADCIG.

A long-offset acquisition system includes a source vessel; a signal source coupled to the source vessel; and a long-offset streamer coupled to a survey vessel and including an aft-most receiver, an offset of the aft-most receiver being at least 12 km. A long-offset acquisition method includes towing a signal source with a source vessel; towing a first long-offset streamer with a survey vessel; and acquiring data with receivers of the first long-offset streamer. A long-offset acquisition method includes towing a signal source with a first survey vessel; towing a long-offset streamer with a second survey vessel, the long-offset streamer having a plurality of receivers; actuating the signal source while an offset between the signal source and at least one of the plurality of receivers is at least 15 km; and acquiring data with receivers of the long-offset streamer.

Methods and systems described herein are directed to determining properties of a subterranean formation using an acoustic wave-equation with a novel formulation in terms of a velocity model and a reflectivity model of the subterranean formation. The acoustic wave equation may be used with full-waveform inversion to build high-resolution velocity and reflectivity models of a subterranean formation. The acoustic wave equation may be also used with least-squares reverse time migration in the image and space domains, to build a reflectivity model of the subterranean formation with enhanced resolution and amplitude fidelity. The velocity and reflectivity models of materials that form the subterranean formation reveal the structure and lithology of features of the subterranean formation and may reveal the presence of oil and natural gas reservoirs.

Active source surface wave prospecting method which is applicable to technical field of geological prospecting, comprising: collecting, by detector at preset station, surface wave data transmitted from seismic source; calculating to obtain dispersion energy graph on basis of vector wave-number transformational algorithm and according to surface wave data; extracting dispersion curve from dispersion energy graph, dispersion comprising base-order surface wave dispersion curve and high-order surface wave dispersion curve; establishing initial stratigraphic model according to base-order surface wave dispersion curve and high-order surface wave dispersion curve, performing, according to initial stratigraphic model, joint inversion on base-order surface wave dispersion curve and high-order surface wave dispersion curve to obtain inverting data of stratigraphic texture. Accuracy of surface wave prospecting result is effectively improved. Further provided are surface wave exploration device and terminal device.

A method for partial differential equation inversion, the method including receiving measured data do; selecting an objective function having first and second measures N.sub.1 and N.sub.2, wherein the objective function depends on three independent variables V, u, and f, V being a perturbation of a wave equation operator L from a background operator L.sub.0, u being a wavefield that satisfies the wave equation operator L, and f being a source function that describes the source of the waves; optimizing with a processor the objective function by finding a minimum or a maximum using the inversion; calculating with the processor solutions V*, u*, and f* of the three independent variables V, u, and f; and generating with the processor an image of an object based on the solutions V*, u*, and f*.

The present disclosure describes methods and systems, including computer-implemented methods, computer program products, and computer systems, for generating geophysical images. One computer-implemented method includes receiving a set of seismic data associated with a subsurface region; generating source analytic wavefields and receiver analytic wavefields based on the set of seismic data; decomposing the source analytic wavefields and receiver analytic wavefields; computing directions of propagations for the source analytic wavefields and receiver analytic wavefields; computing, for a plurality of subsurface points, an azimuth angle and a reflection angle for a respective subsurface point based on the directions of propagations; generating for each of the plurality of subsurface points, a weighting function for a respective subsurface point based on the azimuth angle and the reflection angle of the respective subsurface point; and generating a subsurface image using the weighting functions of the plurality of subsurface points.

A method is described for seismic imaging including generating extended image gathers by extended reverse time migration of a seismic dataset using an earth model; processing the extended image gathers to generate processed image gathers; performing extended modeling based on the processed image gathers to generate a modeled seismic dataset; enhancing the processed image gathers to generate an enhanced image; performing extended modeling based on the enhanced image gathers to generate a modeled enhanced dataset; differencing the modeled enhanced dataset and the modeled seismic dataset to determine a data residual; inverting the data residual to generate a model residual; updating the earth model based on the model residual to create an updated earth model; performing seismic imaging of the seismic dataset using the updated earth model to create an improved seismic image. The method may be executed by a computer system.