鄂尔多斯盆地基底断裂在上三叠统延长组石油聚集中的控制作用

鄂尔多斯盆地基底非均质性导致一组北东向基底断裂在中生代“隐性”活动，不仅控制了晚三叠世一系列古水系的流向，而且后期小规模活动在上覆砂体中还产生微裂隙和小断层，既为油气运移提供通道．也改善了储集层物性条件，在上三叠统延长组岩性油气藏形成中发挥了重要作用；同时．基底断裂分布区的异常高古地热加速了有机质生烃演化。靖安陇东地区位于北东向基底断裂分布带内，成藏条件最好，是已经发现和将要发现三叠系油田的主要地区。图8参16

Key role of basement fault control on oil accumulation of Yanchang Formation, Upper Triassic, Ordos Basin

The heterogeneity of basement in Ordos Basin has led to the activity with minor scale of basement faults in the dominant NE orientation in particular since Mesozoic, which had given strong influence not only on the Late Triassic depositional system, but also the occurrence of fractures and minor normal faults in Upper Triassic reservoirs. Fractures and minor faults are believed to have improved the reservoir quality and provided path for oil migration from source kitchen to the lithological traps at Yanchang different intervals. It is considered that the basement faults existing in southern Ordos Basin played an important role in oil migration, accumulation and distribution of Upper Triassic Yanchang Formation and Lower Jurassic Yan'an Formation, etc. Meanwhile, NE basement faults caused the abnormal high geothermal field during Late Jurassic-Cretaceous, which accelerated the thermal evolution of source rock in Yanchang Formation. And, the Longdong Jing'an NE zone, where has so far accumulated the majority of discovered oil fields and proven reserves of the basin, coincides in position with the development area of NE basement faults, and has the most favorable conditions for the formation of oil accumulation. Hence, the new and main oil discoveries are believed to be obtained in the future exploration and mainly concentrated in this zone.