Hydrothermal alteration and hydrocarbon accumulations in ultra-deep carbonate reservoirs along a strike-slip fault system, Tarim Basin, NW China

Abstract

Abstract In recent years, petroleum exploration has extended from shallow to deep reservoirs in the globle petroliferous basins. In contrast to conventional carbonate reservoirs, the fractures and hydrotherm related karst reservoirs could mainly be developed in deep strata along the tectonic deformation and fault zone. The seismic imaging and tectonic analysis have been combined to identify the scale and features of the deep fault system in the Tarim Basin, NW China. It was found that the tectonic collision and movement generated a prevalent strike-slip fault system, which was conjugated and extended from paleo-uplift to the inside of the Manjar Sag (source kitchen) in the Tarim Basin. The micrograph of cores and images of well logging demonstrated that deep reservoirs are dominated by porosities, fractures, and hydrothermal minerals (e.g., fluorite, pyroxenite). Burial dissolution and thermohydrology along strike-slip fault have greatly contributed to the formation of deep carbonate reservoirs, meanwhile controled the accumulation and hydrocarbon properties in the deep carbonates reservoirs of Tarim Basin. The analysis of adamantane, dibenzothiophene, and carbon isotopes indicated that oil-cracking, thermochemical sulfate reduction (TSR), and gas-washing fractionation could be the main factors to control the sequential accumulation of various hydrocarbons around Manjar Sag. The formation and hydrocarbon accumulation of the deep carbonate reservoirs along this strike-slip fault system could provide important details regarding deep petroleum geological processes from both scientific and practical aspects. These findings could be applied to future studies and the exploration of deep potential marine reserves worldwide.