Effect of Overpressure on Porosity of Deep Reservoirs in a Compressive Setting based on Numerical Simulations: A Case Study of the Lower Cretaceous Bashijiqike Formation in the Kuqa Foreland Basin, Tarim Basin, NW China

Abstract Deep burial and intense tectonic compression in the Kuqa Foreland Basin, NW China, have paradoxically allowed for the preservation of primary pores in deep clastic reservoirs. This study investigates this mechanism through numerical simulation, quantitatively restoring the porosity and pore pressure evolution in the Lower Cretaceous Bashijiqike Formation. The analysis reveals the evolution of overpressure has played a significant inhibitory and preservative role in the reduction of porosity in these reservoirs. Overall, the process exhibits similarities across these areas. In the early and middle stages of overpressure formation, it suppressed and slowed the porosity reduction caused by both vertical loading and lateral tectonic compression. In the late stage, overpressure preserved the remaining reservoir porosity. However, the magnitude of porosity preservation and inhibition by overpressure varies in different structural locations. In the southern and northern parts of the Keshen area, the values show little variation, ranging from 1.95% to 1.98%. In contrast, the values are significantly higher in the southern parts of the Dabei and Bozi areas compared to their northern counterparts, with ranges of 2.35% to 3.67% and 1.03% to 1.65%, respectively. These findings provide a new framework for understanding deep reservoir preservation and guide future hydrocarbon exploration.