河套盆地吉兰泰凹陷烃源岩展布与勘探潜力

河套盆地吉兰泰凹陷西北坡的金属探矿井在数百米深的元古界变质岩裂缝中发现轻质原油，揭示了该凹陷存在一定生烃潜力。利用地震相分析来解决固阳组沉积相带和烃源岩展布已成为评价该凹陷勘探潜力的重要问题。根据露头、钻井和地震等资料重点开展了地层对比、地震相和烃源岩展布等综合研究。结果表明:河套盆地吉兰泰凹陷下白垩统固阳组为断陷盆地近源旱地扇沉积，在固一段发育两期扇三角洲—半深湖沉积，松探1井、松探2井和吉参1井在固一段钻遇薄层暗色泥岩；暗色泥岩波阻抗高于砂岩，在地震剖面上形成强振幅反射；地震模型和属性分析表明湖相暗色泥岩沿NE向凹陷中心分布，最大累计厚度为45 m，一般为20~30 m；暗色泥岩总有机碳介于0.31%~2.63%，为Ⅱ_a-Ⅲ型，露头区烃源岩过成熟，松探1井为未熟—低熟状态；金属探矿井（ZK500井）540 m深度处变质岩裂缝原油和松探1井2 270 m深度处的4 m油砂含油属于同一油源，生烃期为上新世末期；地震剖面和航磁异常指示了ZK500井附近存在上拱的侵入体，导致了凹陷烃源岩成熟度的横向快速变化；有利生烃和勘探区应位于埋深较大的吉兰泰凹陷北部深凹带。

Source Rock Distribution and Exploration Prospect of Jilantai Sag in Hetao Basin,China

In the northwest slope of Jilantai sag, Hetao Basin, the light crude oil display is found in the fractures of Proterozoic metamorphic rocks buried in hundreds of meters. This reveals that there is a certain hydrocarbon generating potential in the area. Using seismic facies analysis to solve sedimentary facies belts and distribution of source rocks of Guyang Formation is an important issue for evaluating the exploration potential of Jilantai sag. According to the outcrops, drilling and seismic data, the stratigraphic correlation, seismic facies and distribution of source rocks were comprehensively studied. The results show that the Lower Cretaceous Guyang Formation in Jilantai sag of Hetao Basin is a rift basin with dry climate proximal fan deposits intercalated by two periods of fan dalta-semi deep acustrine facies; wells TS1, TS2 and JC1 drilled in the sag have a number of thin layers of dark mudstone in Gu1 Member; the acoustic impedance of lacustrine shale and limestone is higher than that of sandstone, and the lacustrine deposition forms strong amplitude reflection on seismic sections; the thickness of dark shale is 20-30 m with the maximum of 45 m, and it distributes along the center of NE sag; the total organic carbon(TOC) of dark shale is 0.31%-2.63% with the type of Ⅱ_a-Ⅲ; the source rocks in outcrop are overmature, but well ST1 is immature-low mature; the oil from fractures of metamorphic rock at the depth of 540 m in metal exploration well ZK500 belongs to the same source of oil from 4 m oil sand at the depth of 2 270 m in well ST1, and the hydrocarbon generation periods should be the end of Pliocene; the aeromagnetic anomaly and seismic reflection suggest that there is upwarp intrusion near well ZK500, resulting in the fast lateral change of source rock maturity in Jilantai sag; the favorable hydrocarbon generating and exploration areas should be located in a fault convex zone with greater depth, the northern part of Jilantai sag.