塔里木盆地顺北1号断裂带SHB1-X-3井储层沥青地球化学特征及其与油气演化的关系

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

塔里木盆地塔中北坡顺北1号断裂带SHB1-X-3井在奥陶系一间房组7265~7275 m泥晶灰岩钻遇三段缝洞充填沥青,累计厚度约3.25 m。为厘清该区的油气演化特征,对该储层固体沥青及其抽提物开展了有机岩石学以及有机地球化学方面的研究。显微镜下观察到泥晶灰岩的基质矿物以及泥质条带呈现出明显的荧光特征,并且在切割泥晶灰岩的方解石脉和石英脉中发育气液烃包裹体,上述产状关系说明至少存在早晚两期油气充注,其中沥青和气液烃包裹体分别为早、晚两期油气充注的产物。对含沥青灰岩的抽提物和顺北1号断裂带上原油进行有机地球化学对比分析认为,沥青和原油的生源条件相似,均来自还原环境下、以藻类等低等生物为主要成烃母质的海相泥质烃源岩,与寒武系玉尔吐斯组烃源岩有较强亲缘关系。原油裂解气在现今油气藏中占比低,推测早期充注的原油规模小,裂解生成气对现今油藏贡献不大。

Three sections of fracture-cave filling bitumen with a total thickness of approximately 3.25 m were discovered between 7265 m and 7275 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.