Abstract
According to conventional views, cracking of oil to gas is expected to occur in sedimentary petroliferous basins. The recognition of exceptionally high pressure generated as a result of this process is crucial for evaluating the accumulation and preservation conditions of natural gas in these basins, and fluid inclusions in associated minerals can provide direct evidence. The presence of methane–bitumen two-phase inclusions in the Sinian Dengying Formation of the Gaoshiti–Moxi area in the central Sichuan Basin is a significant finding. These inclusions formed during the cracking period can provide effective assistance for our study of cracking overpressure. The densities of methane in gas–solid two-phase inclusions were determined by using a well-established method based on methane Raman shift measurements. Combined with the trapping temperature of coexisting aqueous inclusions, the trapping pressures of the methane–bitumen inclusions with different volumetric proportions of methane and bitumen were obtained, ranging from 161.9 to 190.2 MPa, with an average of 174.5 MPa. These trapping pressures consistently exceed the lithostatic pressures at corresponding depths, indicating a typical abnormal overpressure condition, and serve as the most direct evidence for the generation of abnormal overpressure in the reservoir derived from crude oil cracking. This information can give a valuable reference for our understanding of the preservation conditions of cracked gas reservoirs in sedimentary basins and is particularly useful in guiding our future oil exploration and development efforts.
Paper Information：
Song, Y.F., Chen, Y., Lin, T., Wang, M., Tian, H., 2025. Direct evidence for abnormal overpressure generated by crude oil cracking in the Sinian Dengying Formation, Central Sichuan Basin, southwestern China. AAPG Bulletin, 109 (6): 845–861. doi: https://doi.org/10.1306/05192524021
