Characteristics and controlling factors of petroliferous reservoirs in the Permian Lower Urho Formation, western Mahu Slope, Junggar Basin, NW China

Numerous hydrocarbon discoveries in the Lower Urho Formation of the western Mahu Slope, China indicate that potential petroliferous reservoirs may exist in that region. However, issues concerning the reservoir characteristics and associated controlling factors remain unclear. To determine the characteristics and associated controlling factors of those reservoirs, an integrated analysis of three-dimensional seismic volume, wireline logs, mud logs, cores, thin sections, porosity, and permeability data was conducted. Several lithological types were identified from the core, casting thin section, and mud log data (including mudstone, sandstone, gravity flow-derived glutenite, transitional glutenite, and traction flow-derived glutenite). The contact relationship was determined from the casting thin section data, and it included point contact and lineal contact, followed by concavo-convex contact and suture contact. The dominant pore types were found to be intergranular pores, followed by intragranular pores, intramatrix pores, and cracks. The porosity and permeability data reveal that sandstone and traction flow-derived glutenite commonly form low-porosity and low-permeability reservoir, whereas transitional glutenite commonly forms low-porosity and ultralow-permeability reservoirs and gravity flow-derived glutenite generally forms low-porosity and ultralow-permeability reservoirs. This integrated analysis shows that tectonic movements and sedimentary environment control the physical properties of the reservoirs. The tectonic movements control reservoir characteristics through thrust fault systems and the large-scale provenance, and the sedimentary environment controls reservoir characteristics via facies distribution and lacustrine fluctuation. The insights gained from this study can provide knowledge about the characteristics and associated controlling factors of the reservoirs in the Permian Lower Urho Formation within the western Junggar Basin. These insights can also benefit petroleum reserve and hydrocarbon production exploration in the study area and further petroleum exploration in other areas with similar sedimentary/tectonic settings.