A new pore pressure model for pre-drilling prediction in carbonate rocks considering the abnormal pressure

The pore pressure prediction methods for clastic rocks are well-established and highly accurate but are not directly applicable to carbonate formations. Existing carbonate pore pressure prediction models fail to fully account for the mechanisms of abnormal high pressure during diagenesis, leading to poor adaptability and significant errors. This results in flawed mud density designs and frequent drilling issues such as leakage and overflow. This study proposes a new one-dimensional pore pressure prediction method that incorporates both pressurization and depressurization mechanisms in carbonate diagenesis. Additionally, using well-seismic correlation, a three-dimensional pore pressure prediction model is developed based on sequential gaussian co-kriging interpolation. This model accounts for the influence of fracture-cavity systems, enabling more accurate pre-drilling pore pressure estimation. The results demonstrate that the new one-dimensional prediction method closely aligns with measured pore pressure values, with an error range of −7.35 %∼ 5.87 %. The sequential gaussian co-kriging interpolation overcomes the limitations of single interpolation methods by balancing the randomness of fractured fault zones with the continuity of non-fractured regions. The 3D pore pressure model's pre-drilling predictions show strong agreement with numerical results, with errors within ±10 %. By considering the formation mechanisms of abnormal pressure, this approach enhances the accuracy of carbonate pore pressure predictions, supporting effective risk assessment and the analysis of complex drilling conditions.