2 - Geophysical characterization of fracture-vug carbonate reservoirs

Abstract

The main geological tasks and objectives for the geophysical description of fracture-vug carbonate reservoirs include reservoir identification and prediction, understanding of reservoir distribution, and detection of reservoir fillings and fluids. Tahe fracture-vug carbonate reservoir is buried deep (generally below 5600m), and shows multitype, multiscale, heterogeneous and irregular features, making it difficult to get an accurate geological image, resolve complex seismic responses, and distinguish geometric and parametric properties of fracture-vug reservoirs. A high-precision seismic physical simulation device and equal-proportion fracture and vug materials and modeling processes have been created, based on which physical simulation experiments have been carried out on multitype fracture-vug systems and multiscale fractured systems; the results have revealed the seismic response mechanisms and recognition patterns of different types of fracture-vug systems. The separation and imaging technology of diffraction based on a combination of dip filtering in plane wave domain and predictive inversion, and the anisotropic modeling and reverse-time migration technology of fracture-vug reservoirs have been developed to enhance seismic amplitude and to improve the imaging quality of fracture-vug systems. The multiscale seismic classification and detection and multiattribute comprehensive and possibilistic description technology have been improved for comprehensive geometrical delineation of fracture-vug units. The petrophysical modeling method of complex pore structures of karst reservoirs, and the prestack AVO inversion based on viscoelastic medium, and Bayesian probability parameter inversion based on petrophysical statistics, have been proposed for quantitative characterization of voidage, argillaceous fillings content, and fluid composition in fracture-vug reservoirs.