Geochemical characteristics of reservoir bitumen and its relationship with hydrocarbon evolution in well SHB1-X-3, Shunbei No.1 fault zone, Tarim Basin

Abstract

Three sections of fracture-cave filling bitumen with a total thickness of approximately 3.25 m were discovered between 7 265 m and 7 275 m in Ordovician Yijianfang Formation micrites in the well SHB1-X-3, Shunbei No.1 fault zone, central Tarim Basin. In this paper, detailed organic petrological and geochemical analyses were carried out on solid bitumen and related extracts. The matrix minerals and argillaceous belts within micrites showed obvious fluorescence characteristics. The fractures of micrites are filled with gas-liquid hydrocarbon inclusions in calcite and quartz veins. The above occurrence relationship shows that there are at least two stages of hydrocarbon charging, and bitumen and gas-liquid hydrocarbon inclusions are the products of hydrocarbon charging in the early and late stages, respectively. Geochemical characteristics of the extracts of bituminous limestones and the crude oil in Shunbei No.1 fault zone indicate that the biogenic conditions of bitumen and crude oil are similar, both of which come from marine decay under reducing environment. The Cambrian Yu'ertusi mudstones with algae as the main hydrocarbon source may be the major source rocks of bitumen and crude oil discovered. The proportion of crude oil cracked gas in the current oil and gas reservoirs is very low. It is speculated that the contribution of cracked gas to the current oil and gas reservoirs is limited.

Keywords

• hydrocarbon filling period
• oil and source correlation
• bitumen in reservoir
• yijianfang formation
• ordovician
• shunbei no.1 fault zone
• tarim basin