摘要:
柴达木盆地北缘(柴北缘)侏罗系层序发育完整,为一套富含化石的碎屑岩,自下而上为小煤沟组、大煤沟组、采石岭组和红水沟组。下侏罗统包括小煤沟组、大煤沟组下部;中侏罗统为大煤沟组中、上部。柴北缘一带早、中侏罗世所受应力复杂,构造运动强烈,形成多沉积中心的小型断陷型盆地。早侏罗世时期,柴北缘的沉积相类型有滨浅湖、河流—泛滥平原、扇三角洲、辫状三角洲;中侏罗世时期,该区广泛发育湖底冲积平原,以滨浅湖—半深湖—深湖相为主,趋向于深水的较还原环境。下侏罗统岩性以细砾岩,细—粉砂岩与炭质泥岩和页岩的不等厚互层为特征;中侏罗统则以较细结构的碎屑岩为主,局部发育较厚的黑色页岩。柴达木盆地北缘发育有巨厚的下侏罗统湖相泥岩和中侏罗统煤系地层,烃源岩有机质丰度高,有机质类型主要为Ⅱ—Ⅲ型,生烃潜力大;柴北缘碎屑岩孔隙发育,可称为较好的储集岩;柴北缘泥岩、页岩可称为优质的盖层,生储盖配置较好。但油气藏以小型为主,且以气藏为主。
Abstract:
On the northern margin of the Qaidam Basin (NQB), a Jurassic fossil-rich clastic sequence is well developed. From bottom to top it composed of the Formations of Xiaomeigou, Dameigou, Caishiling and Hongshuigou. The Lower Jurassic includes the Xiaomeigou FM and the Lower Dameigou FM and the Middle Jurassic consists of the Upper and middle of Dameigou FM. During the Early-middle Jurassic, NQB was suffered from intensive and complicated tectonic movement. As the result, there formed many small fault basins, filled by the deposits of shallow lakes, river-flood plains, lake-fan deltas and braid deltas in Early Jurassic, and the deposits of lake alluvial plain, shallow-deep lake in the Middle Jurassic,as the environment changed into a reducing deep water. The Lower Jurassic consists of conglomerate, fine sandstone, siltstone, carbonaceous mudstone and shale, characterized by changing thickness; The Middle Jurassic mainly consists of fine-grained clastic deposits and thick black shale. Thick lacustrine mudstone occurs in the Lower Jurassic and a coal-bearing sequence in the Middle Jurassic in the NQB. Source rocks are rich in organic matters of typeⅡand III. The clastic deposits with high porosity could be a high quality reservoir, with mudstone and shale acting as seal rocks. The combination of source rocks, reservoirs and seals has provided excellent geological conditions for the accumulation of small scale hydrocarbon deposits, in particular gas deposits, in the Jurassic of the region.
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