额济纳旗地区侏罗—白垩纪盆地演化与油气特征

EVOLUTION AND HYDROCARBON FEATURES OF THE JURASSIC AND CRETACEOUS BASINS, EJINAQI

额济纳旗地区侏罗纪以来经历了两期断陷盆地的发育。早—中侏罗世研究区处于一种张扭构造环境之中，晚侏罗世盆地发生明显抬升和反转。日垩纪—早第三纪盆地演化为一个完整的裂谷发育过程，下白垩统是裂谷早期断陷作用的产物，而上白垩统和下第三系则代表裂谷后期热沉降（或区域坳陷）沉积。侏罗纪盆地和白垩纪盆地应属两类不同性质盆地。两期盆地的不同叠置关系控制了本区烃源岩的发育，影响到这一地区坳陷的油气潜力。下白垩统烃原岩为较差—较好烃源岩，中—下侏罗统为好烃源岩。各凹陷的生烃潜力取决于两期生烃洼陷的规模和叠置关系，天草凹陷继承性发育，中—下侏罗统和下白垩统两套烃源岩叠置关系较好，是额济纳旗地区最有远景的凹陷。

Two periods of rifting basins had developed in the Ejinaqi region since the Jurassic. The study area was in a tectonic settingof transtension during Early and Middle Jurassic, and the basins were reversed and uplifted in Late Jurassic. The basin evolutionfrom the Cretaceous to the Palaeogene shows a complete process of rifting development, in which the Lower Cretaceous is theproduct of early rifting and the Upper Cretaceous and the Eogene represent the sediments of thermal subsidence in late riftingstage. The Jurassic and Cretaceous basins belong to two different types of basin. The superimposition styles of the two types ofbasins controlled the source rock development and have an impact on the hydrocarbon potential in this region- The source rocksin the Lower and Middle Jurassic are good and better than those in the Lower Cretaceous. The hydroc arbon-generation potentialof depressions was determined by the scale and superimposition of two hydrocarbon-generation sags. Tiancao depression is themost perspective area where the sag developed successively and the Lower-Middle Jurassic and the Lower Cretaceous sourcerocks have a good superimposition.