ABSTRACT Fluid diapirs are formed through the upward intrusion of fluids along fracture zones, with hydraulic fracturing and fluid charge occurring at the uplift point of the overpressure interface. The DF1-1 diapir is the most typical fluid diapir in the Yinggehai Basin, characterized by multilayer gas accumulation. In this study, petrographic observation, laser Raman spectroscopy analysis, microthermometry, approximate calculation of fluid inclusion capture pressure and natural gas characteristics have been integrated to delineate the natural gas dynamic accumulation process and summarize the accumulation model of DF1-1 diapir. Results suggest that four episodes of natural gas charging with distinct compositions have been documented. The first two episodes, dominated by hydrocarbon gases, occurred at 3.4 to 2.9 Ma and 1.8 to 0.4 Ma, respectively. The latter two episodes were characterized by dry gas and inorganic CO2, which occurred at 0.4 to 0 Ma. The paleopressure evolution of Huangliu Formation was reconstructed following a model of “pressurization-release-pressurization.” Furthermore, the coupling relationship between the formation paleopressure evolution and the natural gas charge history was elucidated. Based on these analyses, this conformed to an overpressure-controlled episodic gas accumulation model, and the accumulation process can be summarized as follows: initially, gas accumulated in deep reservoirs, with formation pressure increasing to fracture pressure, leading to diapir opening and subsequent gas loss or adjustment to shallower reservoirs along diapiric faults for further accumulation. Simultaneously, gas filled the reservoir and episodic diapir activity in the later stages resulted in rapid gas charging. This process is the primary factor contributing to the heterogeneity of gas distribution.
He et al. (Mon,) studied this question.