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Summary
Shale reservoirs with complex pore systems perform a significant volume response to dynamic stress variations during gas depletion/injection. The determination of matrix compressibility is important to reveal the effect of pore structure on gas flow behavior. In this study, various fluid intrusion measurements were applied to determine the multiscale pore structure of shale samples. Moreover, a theoretical method is proposed to estimate matrix compressibility, and the geological controls on matrix compressibility are also discussed. Results showed that the tested shale samples were characterized by diverse components and multiscale pore structures with significant reservoir heterogeneity. High injection pressure could trigger matrix compression during high mercury intrusion porosimetry measurements, which, in turn, resulted in a redistribution of the pore system and enhanced the pore structure heterogeneity. Shale matrix compressibility was influenced significantly by pore structures and matrix mechanical properties. Large matrix compressibility was found in a shale sample with high percentage of micropores and considerable pore structural heterogeneity. Moreover, the types and distributions of the main components with different mechanical properties had significant impacts on matrix compressibility. Additionally, the effects of matrix volumetric change on gas flow behaviors under in situ stress conditions were discussed accordingly. The findings of this study can contribute to target reservoir optimization for long-term shale gas recovery and enhanced recovery/CO2 sequestration in deep shale reservoirs.
