Modelling of pore pressure evolution in a compressional tectonic setting: The Kuqa Depression, Tarim Basin, northwestern China

Abstract

The Kuqa Depression is part of a Mesozoic-Cenozoic foreland basin located at the northern margin of the Tarim Basin. High fluid overpressures were reported in the Mesozoic section related to both the complex tectonic evolution and the sealing by the salt-bearing sequence within the Paleogene Kumugeliemu Group. The role of structural evolution and compressional shortening in the generation of overpressures is poorly understood and requires a model-based understanding of the basin structure for different time steps. Structurally restored geometries based on a present-day geological section interpreted from a 2D seismic line, has been used as input for a basin and petroleum system model to simulate pore pressure history through geological time. In this simulation, we demonstrate structural dependencies of pore pressure development, and examine the impact of disequilibrium compaction, tectonic compression, opening and closing of faults over time, as well as folding on overpressure evolution. The poroelastic model is used to quantitatively evaluate the contribution of horizontal shortening due to tectonic compression on overpressure. We found that the pressure increase caused by 12.5% shortening can account for a maximum of more than 60% of overpressure, depending on lithology and deformation strength. We also simulated the effect of salt content within the seal layer on overpressure and found that the increase in salt has promoted the onset time and magnitude of overpressure in the underlying strata, which favors porosity preservation. A heat flow sensitivity analysis was performed, suggesting that the pressure increase caused by extremely high heat flow is rather low.