A method for inversion of 4D seismic data, including: determining time shift between baseline and monitor geophysical datasets; determining time strain from the time shift; iteratively repeating until a stopping criteria is satisfied, performing an iterative elastic AVO inversion with a 4D difference providing an update, from an initial model including the time strain, to generate an updated time strain and an updated physical property model, wherein the stopping criteria is a misfit between synthetic data generated from the updated physical property model and the 4D difference being within a predetermined noise level generating final values for the physical property model; and converting, with a rock physics model or a reservoir simulation model, the final values to saturation and/or pressure changes for a subsurface region.

A computer-implemented method, and system implementing the method, are disclosed for computing a final model of elastic properties, using nonlinear direct prestack seismic inversion for Poisson impedance. User inputs and earth-model data is obtained over points of incidence of a survey region, at various angles of incidence. Various models are then computed that serve for lithology identification and fluid discrimination and take part in preliminary seismic exploration and reservoir characterization. Therefore, further refinement of these models is required due to changes in burial depths, compaction and overburden pressure, as they provide limitations for reservoirs on porous media. The further refinement using nonlinear direct prestack seismic model is performed on a system computer, which produces a final model of elastic properties. This model can then be applied for lithology prediction and fluid detection to identify potential targets of oil and gas exploration and estimating spots in unconventional shale gas applications.

Methods for seismic exploration of an underground formation including at least one anisotropic layer perform a joint velocity-variation-with-azimuth, VVAz, and amplitude-variation-with-azimuth, AVAz, inversion using the azimuthal angle stacks to obtain a structural representation of the underground formation. The structural representation is used to generate scenarios for exploiting resources in at least one layer of the underground formation.

A method is described for calibrating seismic data based on statistical properties of shale derived from either well logs in a volume of interest or a global database of statistical properties of shale. The method may be executed by a computer system.

A method is described for a manner of geologic analysis using seismic data. The method includes steps to produce improved amplitude versus angle (AVA) information that may be used for analysis of geologic features of interest including estimation of pore fluid content. The method assesses the probability of hydrocarbons in a subterranean reservoir based on seismic amplitude variations along offsets or angles for portions of a seismic horizon. The method may be executed by a computer system.

A method of geophysical exploration in a seismic survey includes acquiring a set of seismic traces based on seismic data obtained by a seismic receiver, responsive to seismic energy reflected from a subsurface geology. Additional steps include performing reverse time migration on the seismic traces using a velocity model that represents velocity of the seismic energy propagating through the seismic medium. The migrated gathers have an amplitude based at least in part on the migration, which can be corrected by computing synthetic seismograms to provide compensated gathers. Amplitude versus offset and/or amplitude versus angle analysis can be performed on the compensated gathers, in order to generate a seismic image of subsurface structures in the survey area.

Systems and methods for training a model that uses probabilities of lithologies as prior information in an inversion are disclosed. Exemplary implementations may: obtain training data, the training data including (i) subsurface map data sets, and (ii) known lithologies; obtain an initial seismic mapping model; generate a conditioned seismic mapping model by training the initial seismic mapping model; store the conditioned seismic mapping model; obtain a target subsurface map data set; apply the conditioned seismic mapping model to generate a classified lithology map data set; apply an inversion to the classified lithology map data set to generate volumes of lithologies; generate an image that represents the volumes of lithologies; display the image.

A method can include receiving values of an inversion based at least in part on seismic amplitude variation with azimuth (AVAz) data for a region of a geologic environment; based at least in part on the received values, computing values that depend on components of a second-rank tensor a.sub.ij; selecting a fracture height for fractures in the geologic environment; selecting an azimuth for a first fracture set of the fractures; based at least in part on the values for the second-rank tensor a.sub.ij, the fracture height and the selected azimuth, determining an azimuth for a second fracture set of the fractures; and generating a discrete fracture network (DFN) for at least a portion of the region of the geologic environment where the discrete fracture network (DFN) includes fractures of the first fracture set and fractures of the second fracture set.

In a general implementation, systems, apparatus, and methods for AVO of imaging condition in ERTM include the described system provides for an efficient and accurate vector wavefield decomposition with a corresponding modified dot-product imaging condition of ERTM by employing a modified AVO algorithm. In some implementations, the phases of source wavelet and multicomponent records are modified using a 1/2 filter and the amplitudes of the extrapolated wavefields are scaled using 2 and 2, where , and are the angular frequency, local P- and S-wave velocities, respectively. The results yield correct phases, amplitudes, and physical units for separated P- and S-mode wavefields. Divergence and curl operators may then be applied to the phase-corrected and amplitude-scaled elastic wavefields to extract vector P- and S-wavefields. With the separated vector wavefields, a modified dot-product imaging condition can be employed to produce PP and PS reflectivity images.

A computer-implemented method is described for a manner of geologic analysis using time-lapse seismic data. The method includes steps of receiving a first seismic attribute volume inverted from a seismic dataset recorded at a first time, a second digital seismic attribute volume inverted from a seismic dataset recorded at a second time, and a range of geological and geophysical parameters possible in the subsurface volume of interest; identifying a layer and area of interest; computing an attribute difference volume from the seismic attribute volumes; performing probabilistic attribute analysis of at least two of the first digital seismic attribute volume, the second digital seismic attribute volume, and the attribute difference volume using the range of geological and geophysical parameters; estimating time-lapse reservoir properties based on the probabilistic attribute analysis; and outputting visual information depicting the time-lapse reservoir properties via a user interface.