An investigation of a new rock physics model for shale

Due to the complicated lithological properties of organic-rich shale, an effective rock physics model has not been developed so far. Based on Berryman's 3D special pore geometry, this paper proposes a new rock physics model for organic-rich shale by combining Self Consistent Approximation (SCA) with Differential Effective Medium (DEM). Forward modeling analysis is then performed to discuss the critical porosity of SCA and seismic velocity for 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 are not symmetric due to the introduction of DEM. As a result, the critical porosity is not necessary to fall into the interval range from 0.4 to 0.6. Pore geometry has a significant effect on the critical porosity and seismic velocity. Then, with the help of solid substitution using Brown-Korringa equation, it is used to simulate the effect of the total organic matter (TOC) on geophysical properties with different pore geometry. At last, a shale well is taken as a case study to predict the P-wave and S-wave velocities. It is found that the prediction results are well consistent with those measured from well logging. This proves the practicality of the new rock physics model for organic-rich shale.