Controls of the Himalayan deformation on hydrocarbon accumulation in the western Qaidam Basin, Northwest China

摘要

Himalayan deformation substantially impacts the hydrocarbon migration and accumulation in the western Qaidam Basin. In order to investigate how the Himalayan deformation influences the hydrocarbon migration and accumulation in fracture type reservoir, we took Shizigou oil field in the western Qaidam Basin as an example and studied the Himalayan deformation history based on the results from the balanced cross-section restoration of 2 sections across the Shizigou oil filed at first. Then we simulated the fluid potential of one particular section at different tectonic episodes by the numerical method to investigate how the Himalayan deformation effects on it. We conclude that the Himalayan deformation influences the hydrocarbon migration and accumulation in three aspects. Firstly, the faults which form during the structural evolution and communicate with the source rock can act as the primary pathways for the hydrocarbon migration. Secondly, the fracturing of rocks occurs during structural evolution owing to significant compression, which prefer occurring near the faults especially in hanging wall and the hinge zone of folds. These fractures significantly improve the permeability of the rock and result in good pathways for hydrocarbon migration and high-quality reservoirs for hydrocarbon accumulation. Thirdly, influenced by tectonic deformation, compaction of rock bulk volume generates the rising of fluid potential in the soft formation where fracturing is restricted, in contrast, expansion of rock bulk volume generates the chopping of fluid potential in the position where fracturing is enhanced. The change of fluid potential allows the hydrocarbon to migrate and accumulate rapidly along the faults where low fluid potential occurs attributed to fracturing. The impact of tectonic deformation on the hydrocarbon migration and accumulation results in that the hydrocarbon accumulates in fracture type reservoirs near the faults.