Study On Remaining Oil Distribution Within Low Permeability Reservoir Of The8th Member Of Yanchang Formation In Zhenbei Area,Ordos Basin

Low permeability reservoirs account for a certain proportion of the developedreservoirs in China, along with the development of oil&gas production, these reservoirsare becoming more of a concern. This paper focuses on reservoir of the8th member ofYanchang formation in Zhenbei area, Ordos basin, which is characterized with lowpermeability. Due to water cut rising rapidly, low recovery level and uncertainty ofpotential target, the further development of is constrained. To solve these problems, thispaper studies sedimentary microfacies, reservoir heterogeneity characteristics andquantitative evaluation of remaining oil. In summary, the following conclusions arereached:(1) The8th member of Yanchang formation in Zhenbei area are braided delta frontfacies, subaqueous distributary channel, lateral border of subaqueous distributary channel,fluvial channel sandstones, and channel sandbar are the main microfacies. Among thesemicrofaices, subaqueous distributary channel are most developed, which is also enriched ofremaining oil.(2) By introducing heterogeneous synthetic index, reservoir heterogeneity of Zhenbeiarea are calculated and characterized quantitatively. It shows the8th member of Yanchangformation has moderate to strong heterogeneity, with diverse diagenesis and pore throatstructure. Microscopic heterogeneity is moderate. Areas with relative weak heterogeneityare enriched of remaining oil.(3) According to the characteristics of low permeability reservoir, a relationshipbetween remaining oil saturation and water content is established. Remaining oil saturationin research area is accurately calculated. Remaining oil is quantitatively evaluated by thegrey-clustering analyses method. According to the size of remaining oil potential,remaining oil enrichment region can be divided into three types: type Ⅰ, type Ⅱ, and typeⅢ. (4) Chang81sub member are enriched of remaining oil, well Z277in the middle ofresearch area are type Ⅰ enrichment region, Type Ⅱ are mainly spread over south and eastof research area. The main influencing factors of remaining oil enrichment are sedimentarymicrofacies, reservoir heterogeneity and development technique.(5) Four distribution patterns of remaining oil are proposed, namely incompletion ofinjection-production pattern, thick channel sand body pattern, oil reservoir heterogeneitycontrol pattern, discontinuous oil layers pattern. As to enrichment regulation anddevelopment characteristics in Zhenbei area, three suggestions are proposed to tapping thelatent of remaining oil: improve development performance, comprehensive control indifferent well blocks and well pattern optimization. The applied effectiveness showed typeⅠ and Type Ⅱremaining oil enrichment region have abundant resource, by enhancingtapping the latent of remaining oil, recovery percent can be improved.