Prediction method of pore pressure of carbonate rock and shale considering regional differences - a case study of the Luzhou block in southern Sichuan

Luzhou, in the southern Sichuan Basin, is one of China’s major shale-gas production areas; however, its extensive Permian carbonate formations frequently exhibit gas-logging anomalies and minor gas intrusion during drilling—both in carbonate and shale strata—severely impairing drilling efficiency. In this study, a two-pronged modeling strategy is introduced. First, based on porous–elastic coupling theory, a pore-pressure prediction model for carbonate and shale formations is established, subdividing the reservoir into high- and low-pressure zones to enhance precision. Second, the conventional Eaton model is applied across the full well section. Model performance is assessed against measured pressure data from the B and C wells. In the carbonate interval, the porous–elastic model achieved an average error of 6.02%, compared with 39.06% for the Eaton model. In the shale interval, the two approaches produced comparable errors of 8.75% for the fluid–solid coupling method and 3.30% for the Eaton method. The novel incorporation of stress-dependent zonal partitioning into the porous-elastic framework represents a significant advance beyond single-model approaches reported in previous literature. These findings demonstrate that the coupled model markedly improves pressure estimates in carbonate strata, while the Eaton model remains appropriate for shale. This hybrid methodology offers robust, quantitative support for guiding drilling design and risk mitigation in complex geological settings.