Seismic Anisotropy of the Organic-Rich Shale in Southeast of Sichuan Basin

Abstract

Summary Shales show strongly intrinsic VTI (vertically transverse isotropy) property due to its unique mineral component and microstrue. The factors that cause the shale anisotropy have been extensively investigated. The organic-rich marine shale in the southeast margin of Sichuan Basin is one of the main targets of shale gas exploration in China. However, the rock properties that cause the anisotropy of this shale are still ambigous, and thus need to be intensively investigated. In this paper, we performed unltrosonic velocities measurement, X-ray diffraction mineralogy analysis, Rock Eval pyrolysis and scanning electron microscope observation on 20 shale cores (each is in three directions) from the study area. We found that anisotropy parameters (Thomsen’s □ and □) have good correlation with clay content, but this relationship can be greatly affected by the clay lamination degree. Organic matter content is found have little influence in seismic anisotropy. Organic matters in investied shales show extremly high level of thermal maturity (HI=0∼20), and kerogens in investied shales have different distribution pattern from those in Bakken shale and Bazhenov shale.