Rock physics and basin modeling nexus for predicting pore pressure

Abstract

Improving accuracy in pre-drill pore pressure predictions is a fundamental starting point for well design including setting boundaries for casing points and mud weights. Although rock physics modeling is used routinely in pore pressure estimates, existing rock physics modeling approaches have been largely empirical and face challenges to predict pore pressure accurately, especially for deeper drilling targets where rock matrix properties deviate from normal compaction trends, due to chemical alterations of the rocks. Moreover, existing rock physics models require petrophysical inversion for porosity and volume of shale. It is well-known that petrophysical inversion has non-uniqueness issues and creates additional uncertainty and inaccuracy in pore pressure prediction. Therefore, we developed an integrated modeling approach that involves rock physics modeling and physics-based basin modeling. Through fundamental rock physics modeling and in-depth understanding of the process of clay diagenesis, we recognize that the acoustic impedance from seismic inversions and level of organic metamorphism (LOM, as a proxy for thermal stress) estimated from basin modeling are critical for pore pressure prediction in mudrocks. Based on extensive post-drill data validation, we demonstrate that our modeling approach improves accuracy in pore pressure prediction for depth zones undergoing clay-diagenesis. In addition, we demonstrate that the integrated rock physics modeling greatly reduces the number of calibration parameters as needed in existing models. Blind tests of our method on well data in two different basins with drastically different burial history demonstrates the validity and generalizability of our approach.