Relation Between Pre-Jurassic Paleogeomorphology And Hydrocarbon Accumulation In Zhenyuan Area

Zhenyuan area is located in the south-western Ordos basin. Yan 10- Yan 8 oil-bearing Formation are main productive layers of Jurassic reservoir. During the late Triassic the Indosinian movement made Ordos Basin uplifted fast and the upper of Yanchang Formation eroded. After the Indosinian movement Yan'an Formation started to deposit on the Yanchang formation. So the distribution of Yan'an Formation reservoir is controlled by paleogeomorphology background and depositional environment. Using the method of impression recover paleogeomorphology background of Yan'an Formation in Zhenyuan area, basing on stratigraphic division for Yan 10- Yan 8 oil-bearing formation and combining with the top of structure and sedimentary facies discovered the factors that paleogeomorphology background controlling reservoir distribution of Yanan formation. The research shows:1. Using the method of impression recover paleogeomorphology background, and it is divided into five paleogeomorphology units including the valley, incised valley, highland, slopes and mound.2. Study on sedimentary facies of Zhenyuan area show : Yan 10 oil-bearing formation is braided river facies and Yan 9- Yan 8 oil-bearing formation are delta plain facies.3. The distribution of Jurassic reservoir is controlled by paleogeomorphology background, dividing three models:(1)the area of the slope-mouth combining with lithologic trap is favorable reservoir places;(2)the area of the paleo-highland combining with litholigic trap and structure trap is the most main oil storage places;(3)the low relief structure area is main places of Jurassic reservoir.4. The control factors of reservoir are proposed of Yan 10- Yan 8 oil-bearing formation in Zhenyuan area: paleogeomorphologic background, structure leading, lithological control, source of subprime river and secondary slope-mouth. The nature of reservoir is the structure reservoir controlled by the low relief anticline, and the three accumulation models are: slope-mouth, mound and source of subprime river of paleo-highland.