Study on reservoir characteristic and sedimentary facies of Chang 8 Oil-bearing Formation in Wuqi-Dingbian area, Ordos Basin

Recent few years great breakthroughs have been made in oil exporation activities at Chang 8 Oil-bearing of Yanchang Formation in southwest and south-mid of Ordos basin, several hundred million geological oil reserves have been confirmed. Therefore, it is of great value to study reservoir characteristic and sedimentary facies at the Chang 8 Oil-bearing of Yanchang formation in Ordos basin. Taking Wuqi-Dingbian area in the middle of the west Ordos basin as an example, reservoir petrological characteristics, pore structure characteristics and physical property distribution characteristics are studied, based on routine thin section, casting thin section, particle size analysis, scanning electron microscope, mercury injection and other laboratory analysis data. On basis of petrofacies characteristics of drill cores and analysis of well logging electrofacies, it is studied by means of comparison profile of joint well sedimentary facies and distribution regulations of sandy land ratio. The results of the study show that reservoir characteristics studies have shown that the rock of Chang 8 reservoir of the study area is mainly composed of lithic feldspathic sandstone. Cementing materials is mainly composed of the authigenic clay mineral mainly consisting of kaolinite, chlorite and illite and carbonate cements consisting of ferrocalcite, calcite and dolomite. Pore types of the reservoir develops mainly intergranular dissolved pore. The result of the mercury penetration experiment suggest that the reservoir has a characteristic of low initial expulsion pressure and high median expulsion pressure. Chang 8 oil-bearing formation in Wuqi-Dingbian area develops frontal deposition of shallow water terrace type deltas, which were sourced from northwest, northeast and southwest, of which deltas frontal depositions of northwest and northeast sources are dominated. Distributions of subaqueous distributary channels of deltas front in different directions have the characteristics of becoming width and sheet like overiding along river mouth.