Stress field modelling of the Late Oligocene tectonic inversion in the Liaodong Bay Subbasin, Bohai Bay Basin (northern China): Implications for geodynamics and petroleum accumulation

Abstract

The Liaodong Bay Subbasin (LDBS), Bohai Bay Basin, is one of the most petroliferous basins in China. The basin experienced a strong tectonic inversion in the Late Oligocene, which has been proven to have had a major influence on petroleum accumulation. However, the dynamic origin of this tectonic event is poorly understood. In this paper, we present a finite element-based dynamic modelling study of the Late Oligocene tectonic inversion in the basin based on geological, geophysical and geomorphological data with different boundary conditions. We compared the modelling results with actual geological data and concluded that the NE-SW-directed compression model (labelled with BC-1) is the preferred model, suggesting that the effects of the India-Eurasia collision were the main cause of the Late Oligocene tectonic inversion. The results suggested that the maximum horizontal principal compressive stress direction (σHmax) generally trends EN E-W SW in the whole basin. The majority of the basin features a strike-slip faulting stress regime; the normal fault regimes are limited to the major faults, and the thrust faulting regimes are present only in the northern area of the Liaodong Uplift and Liaozhong Depression. The predicted fault slip rates occurring along the LZ1 fault in the Liaozhong area are significantly higher than those in the Liaoxi and Liaodong areas. Two high shear strain rates belts are present along the major faults in the Liaoxi and Liaozhong areas, indicating that the major faults accommodated the majority of the strain rates. This tectonic inversion play a significant positive role in the accumulation of petroleum in the basin due to the favourable relationship among the high strain rates, the formation of inversion-related traps and the timing of hydrocarbon charging. The high strain rate belts are suggested as the preferred targets for oil and gas exploration.