Effects of Cyclic Confining Pressure and Temperature on Static and Dynamic Bulk Compressibility of Reservoir Sandstones

Bulk compressibility of reservoir rocks can be characterized dynamically or statically, and both vary with burial depth due to increasing temperature and pressure. To quantify these effects, cyclic hydrostatic compression tests are conducted on two reservoir sandstones under confining pressure up to 50 MPa at three temperatures (30 °C, 70 °C, and 110 °C). Experimental results show that static bulk compressibility is consistently larger than dynamic values across all tested conditions. As confining pressure increases, static compressibility decreases more sharply than dynamic compressibility, leading to a gradual reduction in their discrepancy. In contrast, temperature exerts a weaker yet more complex influence. Elevated temperature increases dynamic bulk compressibility, but has opposite effects on static compressibility upon loading versus unloading: it reduces static compressibility upon hydrostatic loading but enhances it upon unloading. This complex temperature dependence is attributed to thermally induced stress, which resists hydrostatic compression during loading but assists decompression during unloading. The influence of thermal stress is more pronounced at low confining pressures. These findings highlight that temperature not only alters the magnitude of static compressibility but also introduces path-dependent asymmetry between loading and unloading, which has important implications for reservoir geomechanics, subsidence prediction, and production-induced compaction in high-temperature environments.