The depositional evolution and associated controls on reservoir property in the Permian Upper Urho Formation, Southern Zhongguai Rise, Junggar Basin, NW China

The Permian strata in southern Zhongguai Rise are famous for their abundant petroleum reservoirs. The depositional evolution of the Upper Urho Formation has been studied analyzing the interactions between the sedimentary environments and the diagenetic evolution based on the comprehensive analysis of geological and geophysical datasets. The obtained results have shown that fan delta deposits, overlain by lacustrine deposits, were deposited. Proceeding upwards, the fan delta succession is characterized by retrogradational patterns, including both sandstone facies and conglomeratic facies. These facies have shown different clay mineralogic composition, porosity and physical properties. The sandstone facies shows well-sorted and well-rounded sedimentological textures, with good physical properties. In contrast, the conglomeratic facies shows poorly-sorted and poorly-rounded sedimentological textures, with poor physical properties. All these characteristics leading to reservoir heterogeneity result from sedimentary facies and diagenesis.