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<p>Hydrocarbon evolution is a crucial part of the global organic carbon cycle, and controls the distribution of hydrocarbon phases within the Earth’s crust. However, the pathway and boundary conditions of hydrocarbon phase evolution remain poorly constrained due to the lack of reliable geological records. Here we present a unique assemblage of sequentially trapped oil, wet gas (C<sub>1</sub>/ΣC<sub>1−5</sub>=0.74±0.03–0.91±0.01) and dry gas (C<sub>1</sub>/ΣC<sub>1−5</sub>=0.96±0.01–1) fluid inclusions from the Ediacaran dolomite reservoirs in the central Sichuan Basin, South China, which constrains the pathway and conditions of <i>in situ</i> hydrocarbon phase evolution. Notably, the early trapped oil inclusions (∼247 Ma) exhibit abnormally low maturity (0.75%–0.97% vs. 2.67%–2.79% VRE for reservoir pyrobitumen). The formation of these oil inclusions is attributed to three key processes: (1) pressure buildup during inclusion oil cracking; (2) leakage of volatile components through decrepitation; and (3) retention of heavy hydrocarbons in the re-equilibrated oil inclusions. In contrast, the reservoir oil underwent <i>in situ</i> cracking and was successively transformed to wet gas (∼197 Ma) and dry gas (∼116 Ma) with increasing temperature. During this process, a self-regulating mechanism of fluid overpressurization (e.g., 59–86 MPa in 197–182 Ma and 114–151 MPa in 116–109 Ma) and pressure release was identified to facilitate the hydrocarbon-bearing fluid migration. Integration of coexisting aqueous inclusion analyses with burial history reconstruction refines the oil (⩽156°C) and wet gas (⩽213°C) preservation windows, respectively, in prolonged heating reservoirs. These findings shed new light on hydrocarbon evolution and petroleum exploration in deep strata.</p>

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Fluid inclusion records abnormally low-maturity oil and hydrocarbon evolution in high-temperature reservoirs

  • 期刊论文

  • 发表日期：

    2025年10月14日

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  • Dongquan Sun,
  • Xiaolin Wang,
  • Wenxuan Hu,
  • Xuesong Lu,
  • Junjia Fan,
  • Shaobo Tang

摘要

Hydrocarbon evolution is a crucial part of the global organic carbon cycle, and controls the distribution of hydrocarbon phases within the Earth’s crust. However, the pathway and boundary conditions of hydrocarbon phase evolution remain poorly constrained due to the lack of reliable geological records. Here we present a unique assemblage of sequentially trapped oil, wet gas (C1/ΣC1−5=0.74±0.03–0.91±0.01) and dry gas (C1/ΣC1−5=0.96±0.01–1) fluid inclusions from the Ediacaran dolomite reservoirs in the central Sichuan Basin, South China, which constrains the pathway and conditions of in situ hydrocarbon phase evolution. Notably, the early trapped oil inclusions (∼247 Ma) exhibit abnormally low maturity (0.75%–0.97% vs. 2.67%–2.79% VRE for reservoir pyrobitumen). The formation of these oil inclusions is attributed to three key processes: (1) pressure buildup during inclusion oil cracking; (2) leakage of volatile components through decrepitation; and (3) retention of heavy hydrocarbons in the re-equilibrated oil inclusions. In contrast, the reservoir oil underwent in situ cracking and was successively transformed to wet gas (∼197 Ma) and dry gas (∼116 Ma) with increasing temperature. During this process, a self-regulating mechanism of fluid overpressurization (e.g., 59–86 MPa in 197–182 Ma and 114–151 MPa in 116–109 Ma) and pressure release was identified to facilitate the hydrocarbon-bearing fluid migration. Integration of coexisting aqueous inclusion analyses with burial history reconstruction refines the oil (⩽156°C) and wet gas (⩽213°C) preservation windows, respectively, in prolonged heating reservoirs. These findings shed new light on hydrocarbon evolution and petroleum exploration in deep strata.