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 are disclosed for evaluating a material on a remote side of a partition separating first and second domains wherein flexural waves within the partition are received by spaced-apart ultrasonic receivers and processed to determine the velocity of the waves propagating into the second domain from a first receiver to a second receiver located more remote from the transmitter than the first receiver and whose separation from the first receiver is known. Comparison of a theoretical phase velocity with the measured phase velocity of the recorded waves allows determination as to whether the flexural wave is propagating through solid. This may be based on a measurable deviation between the two curves occurring at a critical frequency, which may be identified by a perturbation in a group velocity plot. Discrimination may also be based on the gradient of a straight line that best-fits the attention dispersion of the frequency spectrum.

A method for determining grid cell size in geomechanical modeling of fractured reservoirs including a variation range of mechanical parameters of the reservoir is determined. A three-dimensional fracture discrete network model is established. Mechanical parameters of fracture surface are determined on the basis of fracture surface mechanical test. Equivalent mechanical parameters of models with different sizes are researched by three-cycle method, and size effect and the anisotropy of the mechanical parameters of the fractured reservoir are calculated respectively, and an optimal grid cell size in geomechanical modeling is determined.

Methods and systems are presented in this disclosure for semblance-based anisotropy parameter estimation using isotropic depth-migrated common image gathers. Far-offset image gathers can be generated from seismic data associated with a subterranean formation migrated based on an isotropic depth migration that uses an isotropic velocity model. Based on the far-offset image gathers, a plurality of semblance values can be calculated as a function of an anisotropy parameter of the subterranean formation for the different depths and the surface locations. Effective values of the anisotropy parameter of the subterranean formation can be then chosen that result in maxima of the plurality of semblance values for the different depths and the surface locations. Anisotropy model of the subterranean formation can be obtained based on the effective values of the anisotropy parameter.

A procedure that integrates petrophysics and rock typing taken from vertical well measurements, 3D seismic elastic properties and seismic attributes, and geostatistical modeling to build a 3D reservoir model is provided. The 3D reservoir model may be directly incorporated into horizontal fracture model designs. The developed 3D reservoir model for a subsurface volume may be used in a fracture model to optimize fracturing designs and maximize well performance.

Mapping is performed of chemostratigraphic signatures of hydrocarbon reservoirs in three dimensions. Up-scaled chemostratigraphic data from well cuttings and well cores are tied with high-resolution elastic wireline data at well locations in the reservoir. The wireline data is used to determine suitable seismic attributes for mapping the desired chemostratigraphic property, and are obtained by performing pre- and/or post-stack inversions. A multi-attribute template, derived from the well data, is developed to characterize the reservoir in terms of its chemostratigraphic properties. The seismic data is then inverted to map the chemostratigraphic signatures of reservoir in three dimensions.

A method and system for modeling a subsurface region include applying a trained machine learning network to an initial petrophysical parameter estimate to predict a geologic prior model; and performing a petrophysical inversion with the geologic prior model, geophysical data, and geophysical parameters to generate a rock type probability model and an updated petrophysical parameter estimate. Embodiments include managing hydrocarbons with the rock type probability model. Embodiments include checking for convergence of the updated petrophysical parameter estimate; and iteratively: applying the trained machine learning network to the updated petrophysical parameter estimate of a preceding iteration to predict an updated rock type probability model and another geologic prior model; performing a petrophysical inversion with the updated geologic prior model, geophysical seismic data, and geophysical elastic parameters to generate another rock type probability model and another updated petrophysical parameter estimate; and checking for convergence of the updated petrophysical parameter estimate.

Methods and devices for seismic exploration of an underground formation including an orthorhombic anisotropic medium or a tilted transverse isotropic medium are provided. Isotropic-type processing techniques use effective elastic parameter values calculated based on elastic parameter values, anisotropy parameter values and azimuth angle values for the orthorhombic anisotropic medium. For the tilted transverse isotropic medium, the effective elastic parameter values depend also on the tilt angle thereof.

Described embodiments generally relate to a method of determining parameters of VTI anisotropy of a subsurface shale formation. The method comprises receiving wireline log data relating to the subsurface formation, the data comprising density and a clay content indicator; identifying at least one layer of shale in the subsurface formation based on the wireline log data; calculating porosity, clay fraction and silt fraction based on the wireline log data; calculating an orientation distribution function (ODF) of clay platelets within the at least one layer of shale based on the clay fraction and porosity data; estimating at least three independent anisotropy parameters based on the ODF, porosity and silt fraction, the at least three anisotropic parameters comprising a shear wave anisotropy parameter; comparing the estimated shear wave anisotropy parameter with a measured shear wave anisotropy parameter determined based on the sonic log data; upon determining that the estimated shear wave anisotropy parameter is different from the measured shear wave anisotropy parameter by more than a threshold amount, determining parameters of best fit to minimise the difference between the estimated shear wave anisotropy parameter and the measured shear wave anisotropy parameter; adjusting the estimated anisotropy parameters based on the parameters of best fit; and outputting the adjusted anisotropy parameters.

The present disclosure describes methods and systems, including computer-implemented methods, computer program products, and computer systems, for determining a mudweight of drilling fluids in a hydrocarbon reservoir. One computer-implemented method includes: receiving pore pressure data of a rock formation in the hydrocarbon reservoir; determining permeability data of fractures of the hydrocarbon reservoir; determining Hoek-Brown failure criterion data; and determining a safe mudweight window based on the pore pressure data of the rock formation, the permeability data of the fractures, and the Hoek-Brown failure criterion data.