Chang 8 Reservoir Characteristics Of Fanxue Oilfield Ordos Basin

Erdos Fanxue oilfield is located in the north of Shaanxi Dingbian county Fan Xue Xiang,Which is the largest capacity and the most abundant oil reserves in Dingbian area.In recent years,with the deepening of exploration and development,Yanan formation and the upper reservoir productivity of Yanchang formation is decreasing year by year.Therefore,the exploration and development of the deep formation of Yanchang formation,especially Chang 8 reservoir,is very difficult.In this paper,we analyze the sedimentary microfacies and sedimentary stages of Chang 8 reservoir in Fanxue oil area by means of core analysis,logging,logging and other static data,combined with scanning electron microscopy,also an,alyzed and summarized the petrological characteristics,pore structure characteristics and physical characteristics of Chang 8 reservoir.The characteristics of the sand body at the top of Chang 8 oil-bearing formation are obvious,with the characteristics of low acoustic wave time difference,low natural gamma,low natural potential and high resistivity.Sand body thickness is relatively stable,between 80m-90m.According to the sedimentary cycle,the Chang 8 oil-bearing formation can be divided into two oil-bearing formations:Chang 81 and Chang 82.Each reservoir formation is composed of two sets of positive cycle sequences.The length 81 and the length 82 are approximately the same in the stratigraphic thickness,and are basically equal.Chang 8 reservoir is dominated by the delta front sedimentary facies,and the whole is northeast to southwest.The microfacies of underwater distributary channel are the most developed.The sandstone type of Chang 8 reservoir sandstone is mainly feldspar sandstone,the average content is 49.1%,the sorting is medium-good,and the whole has poor grinding roundness and maturity.The reservoir interstitial material is mainly cement,and the interstitial content is between 20%-30%.The cementation types are mainly pore type and basement pore cementation.The reservoir sandstone is mainly composed of remaining intergranular pores,which accounts for about 65%of the face rate.It is the main oil and gas storage space for Chang 8 Formation.The diagenesis types in the study area are compaction,pressure dissolution,cementation,dissolution and metasomatism.According to the quantitative analysis of pore evolution of Chang 8 reservoir,the core factors causing the reservoir physical condition variation are compaction and cementation of carbonate rocks.The diagenesis of Chang 8 reservoir of Yanchang Formation in fan oil field belongs to middle diagenetic stage A,and part of it belongs to middle diagenetic stage B.According to the above research combined with the analysis of coring data,the permeability of Chang 8 oil reservoir generally ranged from 0.001×10-3?m2 to 0.5×10-3?m2,the total porosity is from 10%to 12%,the average permeability is 0.95×10-3?m2,the average porosity is 10.11%.Through the capillary pressure analysis and practical exploration and development situation,combined with the North Shaanxi area reservoir classification standard Ordos basin of Fanxue oil 8 reservoirs are classified,Chang 81 reservoir in III reservoir,accounted for 35.1%of the total,II class reservoir level,accounting for 26.8%of the total I the reservoir accounted for 12.2%of the total.Chang 82 reservoir is also dominated by III reservoirs,accounting for 39.7%of the total,and the II reservoir accounts for 29.3%of the total,and the I reservoir accounts for 9.4%of the total.