Fluid Phase Modeling and Evolution of Complex Reservoirs in the Halahatang Depression of the Tabei Uplift, Tarim Basin.

The diversity of fluid phases in the oil-gas system and complexity of petroleum genesis bring difficulties to the exploration and development of oil and gas. The phase state and evolution of the complex reservoirs in the Halahatang Depression, Tabei Uplift of the Tarim Basin remains unresolved. In this paper, we simulated the phase characteristic of reservoirs in different blocks and layers including Xinken (O), Ha6 (C), Repu (K), and Yueman (O) distributed from north to south of this area using PVTsim software; rebuilt the burial, temperature, and pressure histories of different blocks and layers by using the PetroMod (1D) software; and recovered the fluid phase evolution process by combined basin modeling, PVT simulation, and fluid inclusion thermal metrics results. The phase modeling results show that the Xinken (O), Ha6 (C), and Yueman (O) reservoirs are confirmed to be oil reservoirs, and the Repu (K) reservoir is in the condensate gas phase currently. The vital time points and temperature and pressure conditions for the three oil reservoirs of Xinken (O), Ha6 (C), and Yueman (O) that transited from the gas-liquid phase to the liquid phase are 356 Ma (57.45 °C, 12.93 MPa), 331 Ma (35.67 °C, 4.03 MPa), and 454 Ma (63.63 °C, 13.27 MPa), respectively. The Ordovician reservoir in the Xinken block underwent three stages of accumulation, which occurred at 400-379 Ma (Devonian), 282-256 Ma (Permian), and 18-16 Ma (Neogene), respectively, and after final accumulation, it remained in a single oil phase state. The Ordovician reservoir in the Yueman block underwent two stages of accumulation in the 294-290 Ma (Permian) and 25-12 Ma (Paleogene-Neogene) and remained in a single oil phase state until now. The Carboniferous reservoir in the Ha6 block was deduced to be charged in the 94-86 Ma (Cretaceous) according to the published authigenic illite K-Ar isotope dating results and then stayed in a single oil phase state unalterably. As for the Cretaceous reservoir in the Repu block, the time point of 11 Ma (98.86 °C, 35.56 MPa) is vital for changing from the gas-liquid coexistence phase state to the condensate gas phase one. In contrast with the Ordovician (ZG7-5) and Cambrian reservoirs (ZS1, ZS5) in the Tazhong Uplift, the oil and condensate gas reservoirs in the Tabei Uplift enjoy a lower pressure range, lower GOR, and a heavier oil density and viscosity. This study provides a quantitative way to rebuild the geologic evolutionary process, phase characteristics, and phase evolution process in complex reservoirs.