Origin and evolution of overpressure in the Lower Jurassic succession in the Kuqa Depression, western China

摘要

The Kuqa Depression in the Tarim Basin is a prolific tight-sand gas-producing province in China. Over-pressure is common in the Lower Jurassic with pressure gradient up to 1.18. Thus, it is of great importance to study the origin and evolution history of overpressure for deeply understanding hydrocarbon migration and accumulation history. To identify and distinguish abnormal pressure with various mechanisms, this paper constructed numerical models to quantify the timing, duration and magnitude of overpressure development. 2D basin modeling techniques was performed to identify the development of excess pore pressure derived from gas generation through time. The excess pore pressure generated by tectonic compression was determined with numerical model. The results show that the origin and evolution of overpressure in the Lower Jurassic can be attributed mainly to gas generation and tectonic compression. Comparison between excess pressure derived from tectonic compression and gas generation indicates that tectonic compression was the predominant source for overpressure before gas generation, whilegas generation was regarded as the main source from 5Ma to 3Ma when gas generation reached its peak. The overpressure evolution trend suggests that under the general control of the gas generation and tectonic compression, the magnitude of overpressure varied through time, increasing dramatically for 5Ma to 3Ma, with the maximum magnitude of 79.56 MPa. (C) 2015 Elsevier B.V. All rights reserved.