Systems and methods for improving or generating an image of a surveyed subsurface based on seismic interferometry. A method includes actuating interferometry-based sources over an area to be surveyed to generate seismic waves; recording seismic signals due to the interferometry-based sources, with seismic receivers; selecting traces corresponding to a pair of seismic receivers and an interferometry-based source such that ray paths between the interferometry-based source and the pair of seismic receivers contribute to a Green's function between the two receivers of the pair; cross-correlating the traces for calculating an earth's response associated with a ray propagating from a first seismic receiver of the pair to a second receiver of the pair; and generating an image based on the calculated earth's response.

A method is described for seismic imaging including receiving a pre-stack seismic dataset and an earth model at one or more computer processors; performing least-squares reverse time migration of the pre-stack seismic dataset using the earth model to create a digital seismic image, wherein the least-squares reverse time migration includes wave-equation forward modeling based on an asymptotic expression for reflection in a subsurface Kirchhoff integral; and generating a display of the digital seismic image on a graphical user interface.

A method of performing measurements of an earth formation includes disposing at least a first receiver and a second receiver in one or more monitoring boreholes in a formation, and injecting fluid into the formation from an injection borehole, wherein injecting includes operating a fluid control device to generate seismic and/or acoustic noise having an identifiable characteristic. The method also includes detecting seismic and/or acoustic signals at the first receiver and detecting seismic and/or acoustic signals at a second receiver, the seismic and/or acoustic signals corresponding to the seismic and/or acoustic noise, calculating an estimate of a Green's function between the first receiver and the second receiver by processing seismic and/or acoustic waves detected by the first receiver and the second receiver to at least partially reconstruct the Green's function, and estimating variations in a velocity of a region of the formation by determining variations in the reconstructed Green's function.

Synthetic survey data is generated using a two-way or one-way wave propagator based on a current model of a target structure. The current model is modified to reduce a difference between the synthetic survey data and observed survey data, while maintaining unchanged a velocity component of the current model, where the modifying of the current model produces a modified model. The modified model is used to reduce an adverse effect of multiples in the target structure, or to promote a favorable effect of multiples in the target structure.

This disclosure describes processes and systems for generating a high-resolution velocity model of a subterranean formation from recorded seismic data gathers obtained in a marine seismic survey of the subterranean formation. A velocity model is computed by iterative FWI using reflections, resolving the velocity field of deep subterranean targets without requiring ultralong offsets. The processes and systems use of an impedance sensitivity kernel to characterize reflections in a modeled wavefield, and then use the reflections to compute a velocity sensitivity kernel that is used to produce low-wavenumber updates to the velocity model. The iterative process is applied in a cascade such that position of reflectors and background velocity are simultaneously updated. Once the low-wavenumber components of the velocity model are updated, the velocity model is used as an input of conventional FWI to introduce missing velocity components (i.e., high-wavenumber) to increase the resolution of the velocity model.

A method, including: obtaining, with a computer, an initial geophysical model; modeling, with a computer, a forward wavefield based on the initial geophysical model with wave equations including a second order z-derivative in a rotated coordinate system that accounts for a tilted transverse isotropic (TTI) medium; modeling, with a computer, an adjoint wavefield with adjoint wave equations including a second order z-derivative in a rotated coordinate system that accounts for a tilted transverse isotropic (TTI) medium, wherein the wave equations and the adjoint wave equations include relaxation terms accounting for anelasticity of earth in an update of a primary variable and an evolution relationship for the relaxation terms; and obtaining, with a computer, a gradient of a cost function based on a combination of a model of the forward wavefield and a model of the adjoint wavefield.

A method of redatuming geophysical data, wherein there is provided multi-component geophysical data, and the method includes obtaining at least one focussing function and/or at least one Green's function from the multi-component geophysical data.

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 and methods for generating seismic images of a subsurface formation include obtaining seismic data representing the subsurface formation. Velocity models are generated for the subsurface formation based on the seismic data. Green's functions for the subsurface formation are predicted using a neural network, where the inputs to the neural network include the velocity models, and seismic images of the subsurface formation are generated based on the seismic data and the predicted Green's functions.

To generate dispersion curves for acoustic waves in a radially layered system, a matrix M containing solutions to the wave equation subject to the boundary conditions of the system is constructed. The reciprocal condition number (RCN) of the matrix M is determined as a function of acoustic wave frequency and slowness. The local minima of the RCN in the frequency-slowness plane produces the dispersion curves corresponding to allowable acoustic modes in the system. A sensitivity analysis which identifies the dispersion curves dependent on a selected parameter. The dispersion curves independent of the perturbed parameters are eliminated by perturbing the modeling parameters and generating the RCN of the perturbed matrix M and then subtracting the RCN values of the unperturbed matrix M, leaving the dispersion curves that exhibit dependence on the selected parameter.