A Study On The Microfacies And Characteristics Of Chang 4+5 Reservoir Of Yanchang Formation In Fanxue Oil Field, Ordos Basin

Fanxue area is located in the middle of Shanbei slope of Ordos Basin, and Chang 4+5 of Yanchang formation of Triassic is one of the important oil-bearing series. It is necessary to study the sedimentary microfacies and reservoir characteristic of Chang 4+5 reservoir of Yanchang formation in the Fanxue areas to study the method of oil and gas accumulation further.Combined with outcrop, core observations, sheet rock of purpose layers, log data and other comprehensive information in Shanbei slope of Ordos Basin, Chang 4+5 oil layer group was divided into Chang 4+51 sands group and Chang 4+52 sands group, Chang 4+51 sands group were subdivided into two sublayers of Chang 4+511and Chang 4+512; Chang 4+52 sands group were subdivided into two sublayers of Chang 4+521and Chang 4+522. Small layer division of the study area laid a good foundation for the study of sedimentary microfacies, reservoir characteristics and oil and gas enrichment.On the base of outcrop, core observations, thin section analysis, scanning electron microscopy, conventional mercury and electrical characteristics of rocks, space distribution characteristics of the sand bodys, plane spread and space evolution of sedimentary microfacies and microfacies were researched, and delta-front deposits about Chang 4+5 reservoir group of Fanxue region were determined. Spread of sand bodys were controlled by the depositional system, sand bodys of delta underwater distributary channel were skeleton sand,which were oil and gas reservoir group of Chang 4+5 in Fanxue region.Sandstone rock types of Chang 4+5 oil layers group of Fanxue area are mainly lithic sandstone and Feldspathic sandstone; cements are mainly kaolinite, iron calcite, chlorite, and cement types are mainly substrate pore-type and pore-type; pore-types are mainly the remaining intergranular pores, corrosion intergranular pore, dissolution of feldspar grains within the pore, mixed pore size and poor sorting of pore, the average pore radiu of 8～10μm; capillary pressure of reservoir showed the middle-discharge pressure (average discharge pressure 1.27MPa), poor sorting of throat, slight skewness, the average throat radius of 0.18～1.2μm; porosity was between 8～13% and the penetration rate was relatively small and between 0.1×10-3～50×10-3μm2, which showed thin throat, small pore and reservoirs of low porosity, low permeability.On the base of sedimentary characteristics, reservoir performance, reservoir type, and other Comprehensive factors, regularity of oil and gas enrichment of the study area were analyzed. Reservoir types of Chang 4+5 oil layers group of Fanxue area were lithologic reservoir, underwater distributary channel sand body of delta front system is the main oil and gas reservoirs.