Fracture characterization of deep tight gas sands using azimuthal velocity and AVO seismic data in Saudi Arabia

摘要

Fracture analysis using azimuthal velocity and AVOA data has been carried out over a gas field in Saudi Arabia. Our results showed a slight azimuthal variation in P-wave velocity and significant variation in AVOA at the reservoir, which were interpreted as being caused by aligned vertical fractures. The estimated fracture azimuth computed either from velocity or AVOA data is generally E-W, in agreement with the regional tectonic trend, borehole break-out analysis, and the results of an azimuthal offset VSP conducted at a vertical well. The calculated P-wave anisotropy estimated from velocity analysis is as large as 4% at the reservoir. AVOA analysis showed a more consistent estimate of fracture orientation than velocity analysis. It also displayed a larger amplitude ellipticity magnitude. The results indicate that the azimuthal AVO analysis using 3D P-wave data with reliable amplitude information is more robust than velocity analysis for these reservoirs.