Abstract:

According to large geological profiles of field survey and synthetic studies indoor, It was thought that Devonian Pingyipu Formation and Jurassic Shaximiao Formation in the Northern Longmen Mountain are two most important oil sandstone strata, which spread zonally towards north east and make of two regional oil sandstone zones. This two regional oil sandstone zones overlay Kuangshanliang, Tianjingshan and Erlangmiao thrust anticline subzone and Xiasi, Jinzishan and Qinglinkou foreland zone in the regional structural location respectively. Different structural styles restrict reservoir forming mode and process of different oil sandstone zones，which shows that there is a close genetic relationship between oil sandstone zones and regional structural-stratigraphic zones. Because oil sandstone characteristics and regional structural-stratigraphic zones control oil sandstones formation and distribution in the northern Longmen Mountain，it was first thought that the northern Longmen Mountain can be divided into two regional oil sandstone metallogenic zones, namely Kuangshanliang, Tianjingshan and Erlangmiao oil sandstone metallogenic zone and Jinzishan, Qinglinkou and Houba oil sandstone metallogenic zone. The multizone is characteristic of source rocks of oil sandstone in study area，where is abundant in oil source. Devonian Pingyipu Formation and Jurassic Shaximiao Formation contain better reservoir physicality, which provides a favorable reservoir space for oil gas accumulation. Different structural types play important controlling role in accumulation mode of the oil sandstone and asphalt vein. Some following better configurations are main controlling factors of oil sandstone reservoir, one is that of Indosinianfolds and high-porosity, medium-coarse sandstone in Kuangshanliang, Tianjingshan and Erlangmiao oil sandstone metallogenic zone, and another one is that of Indosinian thrust faults reactivated in Himalayan and developed joint zone formed in Himalayan and high-porosity medium-coarse sandstone in Jinzishan, Qinglinkou and Houba oil sandstone metallogenic zone. The strata tectonic tilting, foreland erosion, fault transport and overlying enclosing cover of mudstone of Jurassic Shaximiao Formation and uplift denudation of Devonian Pingyipu Formation in Himalayan Period are essential conditions for oil sandstone’s formation and reservoir. On the basis of comprehensive study, the authors establish an reservoir forming mode of oil sandstone in the northern Longmen Mountains.

Key words: Longmen Mountains, thurst zone, structural-stratigraphic zone, Pingyipu Formation, Shaximiao Formation, oil sandstone, reservoir forming characteristics