Prestack P-wave Seismic Anisotropy Analysis for Fractures Detection and Characterization in Carbonate Reservoirs

Abstract

Dynamic well data indicated a communication between two hydrocarbon producing Carbonate Jurassic reservoirs: Arab D and Hanifa, in an oil field in Saudi Arabia. Detecting and characterizing the existing fracture system(s) using 3D P-wave prestack seismic data is the main objective of this study. The azimuthal variations of the normal moveout (NMO) velocities and amplitude-variation-with-offset-and-azimuth (AVOA) have been analyzed for Arab D and Hanifa reservoirs, in addition to the upper Fadhili formation. The azimuthal NMO velocity anisotropy suggests the existence of two dominant populations of fracture systems orthogonal to each other: NE (~50-70 deg from N) and SE (~140-160 deg from N). AVOA anisotropy in particular further suggests that the NE trending anisotropy (~65-70 deg from N) is the most dominant fractures orientation among the two. These conclusions are consistent with dynamic data, and with the information obtained from image logs which indicates the dominance of a fracture system oriented ~N70E. The NMO velocity and AVOA ellipticity maps highlight the fractures induced anisotropy network and their intensities allowing more optimized well planning and reservoir development. This is the first successful application of 3D P-wave prestack seismic azimuthal anisotropy analysis for fractures detection and characterization in carbonate reservoirs in Saudi Aramco.