Disclosed is a method and associated computer program and apparatus for characterising changes within a subsurface volume between a first time and a second time. The method comprises obtaining first seismic data corresponding to the first time and processing this data to obtain a seismic image of the subsurface volume. This processing is reversed for relevant portions of the seismic image to obtain relevant portions of first seismic data. Changes within the subsurface volume between the first time and the second time are characterised by estimating the changes between second seismic data corresponding to the second time and the relevant portions of first seismic data.

A method of imaging an object includes generating a plurality of mono-frequency waveforms and applying the plurality of mono-frequency waveforms to the object to be modeled. In addition, sparse mono-frequency data is recorded in response to the plurality of mono-frequency waveforms applied to the object to be modeled. The sparse mono-frequency data is cross-correlated with one or more source functions each having a frequency approximately equal to each of the plurality of mono-frequency waveforms to obtain monochromatic frequency data. The monochromatic frequency data is utilized in an inversion to converge a model to a minimum value.

An acoustic signal is transmitted from a downhole tool positioned within a wellbore. Amplitudes and travel times of the acoustic signal received at different azimuthal locations of the downhole tool are measured. Correction factors, each corresponding to a different one of the measured amplitudes, are determined based on the travel times measured at each of the different azimuthal locations. Corrected amplitudes are each determined based on the corresponding measured amplitude and the corresponding correction factor.

A system for near-surface subsurface imaging for detecting and characterizing subsurface heterogeneities comprises a non-contact acoustic source that senses a plurality of acoustic waves that travel through a surface; an instrument that outputs probing electromagnetic signals through the surface that interact and are affected by scattered signals of the acoustic waves and further senses vibrational modes of a subsurface below the surface; an imaging device that dynamically generates a time sequence of images of properties of the acoustic waves and maps elastic wave fields of the acoustic waves; and a processor that analyzes dynamic multi-wave data of the images to quantify spatial variations in the mechanical and viscoelastic properties of the subsurface.

A method and apparatus for generating an image of a subsurface region including obtaining geophysical data/properties for the subsurface region; resampling the geophysical data/properties to generate a resampled data set; iteratively (a) inverting the resampled data set with an initial prior model to generate a new model; and (b) updating the new model based on learned information to generate an updated prior model; substituting the initial prior model in each iteration with the updated prior model from an immediately-preceding iteration; and determining an end point for the iteration. A final updated model may thereby be obtained, which may be used in managing hydrocarbons. Inversion may be based upon linear physics for the first one or more iterations, while subsequent iterations may be based upon non-linear physics.

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.

A method to estimate a depth profile of a weathering layer in a subterranean formation of a field is disclosed. The method includes obtaining gravity survey data of the field, generating an equivalent source density profile based on the gravity survey data, wherein the equivalent source density profile describes a set of equivalent gravitational sources to substitute rock layers of the subterranean formation, generating an equivalent source gravity response based on the equivalent source density profile, wherein the equivalent source gravity response excludes a gravity contribution from the weathering layer, calculating a separated weathering layer gravity response based on a difference between the gravity survey data and the equivalent source gravity response, wherein the separated weathering layer gravity response corresponds to the gravity contribution from the weathering layer, and generating a modeled weathering layer depth profile based on the separated weathering layer gravity response.

The present disclosure provides a TOC prediction method for shale gas reservoirs, including: determining by well-seismic calibration a top interface T.sub.top and a bottom interface T.sub.bottom of the shale gas reservoirs, and performing layer tracking in the entire area; converting the pre-stack CRP gather into angle gather seismic data; performing spectral shaping processing on the pre-stack migration pure wave seismic data; establishing an initial model, and then performing pre-stack simultaneous inversion to obtain P-wave impedance, S-wave impedance, primary-to-shear wave velocity ratio and density data volume; obtaining a TOC inversion volume A through a post-stack inversion; obtaining a TOC inversion volume B by calculation; then adding the well data for correction, and finally determining a planar distribution law of TOC content. The method can eliminate the multiple solutions of pre-stack inversion and improve the accuracy of TOC content prediction of shale.

Systems and methods are disclosed. The method includes obtaining vertical seismic profiling (VSP) data and surface seismic (SS) data for a subterranean region of interest. The VSP data includes a corrupt section and a valid section. The method further includes determining a VSP attribute and a VSP spectrum using the VSP data, determining an SS attribute using the SS data, and determining a corrected VSP attribute for the corrupt section. The method still further includes training a neural network using the VSP attribute, the SS attribute, and the VSP spectrum for the valid section, predicting a corrected VSP spectrum for the corrupt section by inputting the corrected VSP attribute and the SS attribute for the corrupt section into the trained neural network, and determining corrected VSP data for the corrupt section using the corrected VSP attribute and the corrected VSP spectrum.

A method for applying separated wave-field imaging onshore (1) by artificially creating up-going and down-going fields and (2) by using these fields in a migration algorithm. If there are any surface multiples in the data, the resulting image created using the migration algorithm will be distorted by the unknown free-surface reflection coefficient. In fact, the surface multiples may be generated with a complex series of reflection coefficients. The distortions found in the resulting image created using the migration algorithm are then removed.