Multi-layer Hydrocarbon Accumulation Model in Yuqi area, Tarim Basin, China

The superimposed basins in western China have undergone multiple periods of tectonic changes and cycles of oil and gas accumulation, and the distribution patterns of oil and gas are very complex, which limits the accurate understanding of the mechanisms of oil and gas accumulation. In this paper, Yuqi area in Tarim Basin is taken as the research area, and based on the geological background, fluid inclusion-homogenization temperature, hydrocarbon inclusion abundance analysis, reservoir quantitative fluorescence technology, infrared spectrum, crude oil geochemical analysis, reservoir asphalt identification and other technologies, the Ordovician-Triassic oil and gas accumulation, migration and adjustment process in Yuqi area is studied. The results indicate that the Ordovician system in the study area developed oil injection during the Late Caledonian, Yanshanian, and Himalayan periods. The Triassic system only had oil injection during the Himalayan period, slightly later than the Ordovician system during the same period. The crude oil injected by the Ordovician in the late Caledonian period was biodegraded into heavy oil and carbonaceous bitumen due to tectonic uplift. Light oil from the Yuertus Formation source rock during the Yanshan-Himalayan period was vertically injected into the Ordovician reservoir along activated faults, and then mixed and transformed early heavy oil reservoirs through lateral adjustment along karst. A certain range of light oil reservoirs were formed in the heavy oil reservoir area. In the late Himalayan period, the light/heavy oil reservoirs mixed and filled by the Ordovician system were locally adjusted upwards along faults to the Triassic system, making the crude oil of the Triassic system, which had stable structures and no degradation conditions, similar to the crude oil of the Ordovician system in terms of crude oil density, maturity, inclusion abundance, biodegradation characteristics, and partially mix with late mature oil and gas that migrated along the Luntai fault-sand body, forming the sporadic distribution characteristics of light and heavy oil reservoirs in the Triassic system today. Therefore, a reservoir formation model of "vertical transport along faults, lateral adjustment along karst, strong degradation, and differential superposition" was established for the Ordovician, and " T-shaped transport along fault-sand and late stage reservoir formation " was established for the Triassic in the Yuqi area.The research have important guiding and reference significance for shallow-deep oil and gas exploration in the Yuqi area.