喀什坳陷侏罗纪沉积环境及其对油气成藏的意义

Jurassic Sedimentary Environment and Its Significance for Oil-Gas Accumulation in Kashi Depression,Tarim Basin

喀什坳陷的下-中侏罗统分别形成于两个沉积体系,即库孜贡苏-克孜勒陶走滑拉分断陷体系和山前断陷沉积体系,二者在岩性、岩相、沉积厚度和空间分布等方面均具有不同的特征。走滑拉分断陷体系的侏罗系厚度巨大,其中的含煤岩系和深湖-半深湖相泥岩构成良好的烃源岩,其分布受到塔拉斯-费尔干纳断裂的控制。山前断陷体系的侏罗系厚度相对较小,其中的含煤岩系在南天山山前和西昆仑山前局部构成比较好的烃源岩,源自下-中侏罗统烃源岩的油气分别在古近纪末和上新世初达到油气成藏的关键时刻。针对侏罗系含油气系统的油气勘探应致力于后期改造相对较弱的构造部位,或者致力于寻找次生油气藏。

The analysis of Early-Middle Jurassic structural and lithofacies in Kashi sag shows that the Lower-Middle Jurassic strata developed respectively in two sedimentary systems, namely Kuzigongsu-Keziletao strike-slipping pull-apart faulted-depression and piedmont faulted- depression. Both of the sedimentary systems resulted in the different features of lithology, lithofacies, sedimentary thickness and distribution. The system of strike-slipping pull-apart faulted-depression of great thickness of Jurassic is controlled by the Talaso-Ferghana fault, with high-quality source rocks made up of coal-bearing strata and deep-semideep lake mudstone. The system of piedmont faulted-depression with relative thinner thickness of Jurassic possesses good source rocks formed by locally distributed coalmeasure strata in south Tianshan mountain and west Kunlun mountain. The oil and gas derived from the Lower-Middle Jurassic source rocks reach the key moments for hydrocarbon accumulation at end of Paleogene and Pliocene, respectively. It is concluded that the petroleum exploration in view of the Jurassic petroleum system should focus on the structural positions where the later structural transformation is relatively weak, or on the secondary oil-gas accumulation.