鄂尔多斯盆地平凉北地区M53井烃源岩地球化学特征与长8段油层油源

Geochemical Characteristics of Source Rocks of M53 Well and Chang-8 Member Oil-source in Pingliangbei Exploration Area,Ordos Basin

综合应用有机地球化学和有机岩石学的测试手段和研究方法,对鄂尔多斯盆地西南缘平凉北地区M53井三叠系延长组长7段暗色泥岩进行了定量评价,开展了M53井延长组长8段含油砂岩和邻井长8段原油分子地球化学特征分析和精细对比研究。首次揭示了平凉北地区长7段暗色泥岩地质地球化学特征和油源贡献。结果表明,M53井及邻近区域长7段泥岩有机质丰度参数中等-高、类型以Ⅰ型和Ⅱ1型为主,且接近热平衡成熟阶段,沉积水体呈淡水-微咸水,与盆地本部长7段富有机质泥页岩地质和地球化学特征相近,具备较好生烃能力。M53井延长组长8段含油砂岩抽提物和邻井长8段原油生物标志化合物中正构烷烃碳数呈单峰态,规则甾类化合物C29含量相对较高,烃类生源母质中含陆源高等植物且形成于弱还原-弱氧化环境,原油成熟度相对较高。长8段原油和含油砂岩抽提物生物标志化合物参数、碳同位素参数与M53井及邻近地区长7段烃源岩特征相近,即长8段烃类来源于本区长7段烃源岩。平凉北地区发育较好的烃源岩,该区具备良好的资源潜力和勘探前景。

Based on organic petrology and geochemistry,the dark mudstones of the Chang-7 Member(M53 well,Triassic Yanchang Formation)at Pingliangbei on the southwestern Ordos Basin margin was analyzed.Molecular geochemical characteristics and fine oil source comparison of Chang-8 Member oil(M53 well)and its surrounding was studied.We newly reveal the geological and geochemical characteristics,hydrocarbon generation potential and oil source of the dark Chang-7 Member mudstone in the Pingliangbei area.The results show that the Chang-7 Member mudstone in Pingliangbei area has medium-high organic contents,of I-and II1-type and mature,and was formed in freshwater-brackish water environment.The source rocks have relatively good hydrocarbon generation capacity,and share much geological/geochemical similarities with the high-quality source rocks inside the basin.The Chang-8 Member crude oil has similar characteristics to the Chang-7 Member source rocks,in terms of maternal properties,sedimentary environment and maturity,and both have good genetic relationship.The Chang-8 Member crude oil in the Pingliangbei area may have come from the Chang-7 Member source rocks at/around M53 well.Our results expand the range of source rocks and broaden the field and scope of Mesozoic oil and gas exploration at Pingliangbei in the southwestern margin of the Ordos Basin.