Abstract:

Based on the information about reservoir bitumen, such as occurrences, elemental composition, carbon isotope, gas chromatogram for saturated hydrocarbons, the characteristics of biomarkers and aromatic hydrocarbon, this paper analyzes the geochemical characteristics, genesis and source of reservoir bitumen from Longwangmiao Formation in Moxi area. The bitumen is primarily characterized by high reflectance (equivalent Ro＞2.0%) and low H/C atomic ratios, suggesting that they are residuals generated from oil cracking, belonging to a pyrobitumen. N-alkane in reservoir bitumen distributes integrally with the carbon number ranging from C₁₆ to C₃₁, without obvious trace of biodegradation. Its possible source rock developed in reducing environment and the bitumen mainly derived from aquatic algae and the source rock might be shale. Its carbon isotope value(-33.1‰~-35.4‰) and the biomarker are very comparable to the kerogen’s in the Lower Cambrian source rock, demonstrating that the bitumen came from Qiongzhusi Formation.

Key words: reservoir bitumen, geochemical characteristics, genesis of bitumen, Longwangmiao Formation, Moxi area