Multimethod Prediction of Pore Pressure in the Deep Jurassic System of the Central Junggar Basin

Abstract

Drilling has shown that there is significant overpressure throughout the Jurassic in the central Junggar Basin and that the maximum pressure coefficient exceeds 2.0. The pore pressure in the central Junggar Basin was jointly predicted by combining a number of methods, such as the Eaton, Bowers, and equilibrium depth methods based on logging data, with the D_C method and Fillippone formula approach based on drilling and seismic interval velocity data, respectively. The findings indicate that, among the logging-based prediction methods, the Bowers method prediction of the pore pressure may more closely match the pore pressure. Based on seismic layer velocity data, the Fillippone approach can more precisely predict the change in section pressure by simulating pressure in space. The full forecast results show that two overpressure systems formed in the Jurassic system at Mbr. 1 (Badaowan) and Mbr. 3 (Xishanyao). The transfer of overpressured fluid also resulted in the development of localized overpressure in the Mbr. 2 (Sangonghe) and Mbr. 4 (Toutunhe) formations, which serve as transition zones of overpressure. The top interface of the overpressure section shows an increasing trend in burial depth from the deep concave to the slope region. The overpressure section also demonstrates outstanding low acoustic velocity characteristics. The Jurassic’s anomalous overpressure intensity decreased from the southwest to the northeast, and the overpressure gradient served as a dynamic mechanism for petroleum migration and accumulation.