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Geochemical Characteristics and Geological Significance of the Anaerobic Biodegradation Products of Crude Oil

Anaerobic biodegradation of crude oil is one of the main mechanisms for the formation of heavy oil and gas (referred to as crude oil degradation gas). With the Linfanjia area in the Jiyang Depression of the Bohai Bay Basin in eastern China taken as an example, we conducted a biodegradation simulation experiment on the conventional crude oil of well Y141-1 using cultured anaerobic microbial flora. The causes and characteristics of crude oil alteration and natural gas formation were studied by combining oil and gas geochemistry and carbon isotope data. The theoretical analysis and experimental results show that the saturated hydrocarbon content of crude oil is significantly reduced with the progress of anaerobic biodegradation, while the contents of aromatic compounds, resins, and asphaltenes remain relatively high. Crude oil components, such as n-alkanes and isoparaffins, undergo different degrees of biodegradation. The values of pristane (Pr)/phytane (Ph) and ∑C21–/∑C22+ are significantly reduced, while t...