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Constraining the Timing of Tectonic Compression of the Tianshan Mountain From Reservoir Pressure Evolution in the Kuqa Foreland Basin, NW China

Abstract

The Kuqa Depression is a foreland basin adjacent to the South Tianshan Mountains, NW China and is one of major hydrocarbon producing basins in China. Tectonic compression played an important role in the development of the petroleum system including petroleum generation, migration, accumulation and preservation. Widespread overpressures have been found in both the Eocene and Cretaceous reservoirs with pressure coefficients (the ratio of measured reservoir pressure over the hydrostatic pressure) up to 2.2. Horizontal tectonic compression relating to the Tianshan Mountains uplift is identified as the dominant overpressure mechanism. To constrain the timing of the tectonic compression, the overpressure evolution in the sandstone reservoirs was determined through basin modeling combined with fluid inclusion analysis and PVT modeling. The results show that the overpressure evolution for the reservoir sandstone units in the Kuqa Depression can be summarized into four stages: an initial period of normal hydrostatic pressure before 12–5 Ma, a period of rapid pressure increasing (overpressure) between approximately 5 Ma and 3 Ma, a subsequent period of overpressure release around 3–2 Ma and a final period of subdued increasing overpressure between approximately 2–0 Ma. Combined with the burial history, the reservoir pressure evolution history indicates that the tectonic compression of the Tianshan Mountain occurred from approximately 5 Ma to present with the intensity of the tectonic compression initially increasing rapidly from 5 Ma to 2 Ma, then at a slightly reduced rate from 2 Ma to present after a pressure release around 3–2 Ma.