A new rock physics model for organic-rich shale and its application

As the lithological properties of organic-rich shale are complicated, no efficacious rock physics model has been developed so far. Based on Berryman's 3D special pore geometry, this paper proposes a new rock physics model for organic-rich shale with the combination of Self Consistent Approximation (SCA) and Differential Effective Medium (DEM). Forward modeling analysis is performed to discuss the critical porosity of SCA and seismic velocity aimed at different pore geometry. According to the results, we find that even with the assumption that regards the composite rock as the background rock, the solid phase and the fluid phase is not symmetric. Pore geometry has a significant effect on the critical porosity and seismic velocity. Then, the new rock physics model is used to simulate the effect of the total organic matter (TOC) on geophysical properties with different pore geometry. At last, a shale-gas well from southern China is taken as a case study to predict the P-wave velocity and S-wave velocity. Compared with those measured from well logging, the prediction results are consistent well, proving the practicality of the new rock physics model for organic-rich shale.