An Integrated Pore Pressure Estimation Model Using Sonic and Density Logs: Accounting for Multioverpressure Mechanisms

Summary

Accurate pore pressure (PP) prediction is critical for safe and efficient drilling in petroleum engineering. Under complex geological conditions, the PP estimation needs to account for multiple overpressure generation mechanisms. However, only a few studies have considered the combined effects of these mechanisms in PP prediction. Therefore, there is still a need for a more systematic and integrated approach to improve PP prediction accuracy under complex geological conditions.

A systematic survey was conducted incorporating the different categories of overpressure mechanisms on the effective stress perspectives, which reveals a relationship between the overpressure and density change with depth. Moreover, density log information can be equated with the contribution of abnormally high PP generation from multimechanisms except for undercompaction. Therefore, based on the effective stress/sonic transit time/density compaction theory, an integrated novel model for predicting PP generated by multimechanisms was presented successfully. In addition, dimensionless sonic velocity and density trend lines were used as important indicators to distinguish loading and unloading conditions, which are helpful to calculate the effective stress change due to different overpressure mechanisms. Finally, two cases in the Yinggehai Basin of the South China Sea were examined. Comparisons with the typical Bowers’ model show that the novel model better agrees with PP measurements, indicating its effectiveness and superiority. This study can provide the theoretical guidance for PP prediction under complex geological conditions.