Research On The Rule Of Hydrocarbon Accumulation In Yan-8Oil Reservoir In The Western Zhidan Oil Field, Ordos Basin

Jinding-Zhifang area of the Zhidan oil field is located in Shanbei slope of the Ordos Basin. The Yan-8is the main oil producing zone. Based on the synthetic research of lithology, electricity, the Yan-8oil-bearing zone is subdivided into the Yan-81and the Yan-82.According to the rock types, characteristics, structural features, sedimentary characteristics, and log interpretation, it is found that Yan-8oil-bearing zone is the trangressive lacustrine-deltaic depositional system. On the basis of study the structure and sedimentary background, combined with geologic feature and available well log, the results show that the main sub-facies are delta subaqueous plain and delta front.The research and analysis of data indicate that Yan-8reservoir sandstones the colors are from grayish to grey, the grain size includes fine to medium-fine grained feldspathic sandstone, and fine-grained feldspar sandstone.Yan-8oil-bearing zone has a positive correlation of porosity and permeability. From the half logarithm map, we can learn that the relationship between porosity and permeability indicates positive linear correction; and that the permeability increases with the porosity.Pore types are mainly the inter-granular pores and dissolved pore, the residual inter-granular pores. The mainly combination porosity are between the grains, dissolve hole-between grains, composite solution pores-micro holed etc. The main types of study area are pore combination with a large hole in the thin throat (type Ⅱ) and the small hole in the thin throat (type Ⅲ), and less little hole in the middle throat (type Ⅳ).Through the evaluation of the reservoir, we mainly obtained:the main reservoir for the Yan-8are type Ⅰ-high permeability reservoir and type Ⅲ-permeability reservoir.We summarized the oil and gas accumulation rule of Yan-8:the flank of subaqueous distributary channel and the confluence of the river are the important oil and gas accumulation areas.Effective combination of source rock, reservoir and cap rock is the favorable conditions of oil and gas accumulation; low amplitude nose-like uplifts play an important role in the control of oil and gas abundance zone. The main channel has thick sand bodies; however, it does not have good cap rock, and has a bad connection, either, which can not format favorable reservoirs. Permeability sand body and unconformities are the main channels of hydrocarbon migration. We have comprehensively analyzed the Yan-8oil and gas reservoir; and pointed out that the main types of Yan-8oil and gas reservoirs is lithology-structural composite reservoir.We conclude the hydrocarbon accumulation model of Yan-8oil-bearing beds in Zhidan oilfield Jinding-Zhifang areas Triassic Yanchang formation:Chang-7is the main effective hydrocarbon source rocks. Through the advantages channels of permeable sandstone, micro-cracks and fracture, and the combined drive of buoyancy and capillary pressure, oil and gas can slope upward the reservoir. Under the unidirectional anticline background, nose-like structure and sand lens sand body caused by physical properties difference conditions can form a good oil and gas accumulation and reservoir.