The Study Of Low-amplitude Structure Of Triassic Yan’chang Formation In Ansai Oilfield, Ordos Basin

The simple structure and formation smoothly in Ordos, generally believed that reservoir is mainly controlled by sedimentary facies and lithology, but with the deepening of the reservoir development, people found inside the basin are widely development of low-amplitude structure also has obvious control effect on the reservoir distribution. In this paper, take Yan’chang Formation of Triassic in Ansai oilfield for example, combined with regional tectonic evolution background and formation lithology characteristics in the study area, on the basis of well logging, seismic and core data, used the methods of scan electron microscopy, geological model, inside and outside of production areas dynamic analysis, further study of low-amplitude structure, provide the basis for oil and gas exploration in the area. Studies have shown that:(1) low-amplitude structure has the characteristics of universality, extended directionally, evolved inheritedly and nearly east-west along, that basic unit can be divided into nose-shaped, anticline, fornix, deflection and so on.(2) As for the cause, the low-amplitude structure mainly divided into the paleo-protuberance, regional stress, differential compaction and composite geneses, and some of larger and rows distribution is mainly controlled by paleo-protuberance and regional stress, other of smaller are mainly controlled by the differential compaction and composite geneses in Yan’chang Formation.(3)Low-amplitude structure has significant effect on the migration, enrichment and accumulation of oil, under the action of buoyancy, oil upward migration along two wings accumulation at the top of the nose-shaped, and the change of formational occurrence also has effect on power, speed and direction of oil migration.(4) Within the scope of the low-amplitude structure control the oil well-productivity efficiency is significantly higher than the outer oil Wells, the larger low-amplitude structure and the large favorable facies belts control oil distribution of Yan’chang Formation reservoir in Ansai oilfield, that is an important direction of oil and gas exploration in the future.