Reservoir Characteristic Study Of The Chang-8 Member Of Yanchang Formation In Jiyuan Area, Ordos Basin

Jiyuan area is at the conjunction of Tianhuan sag on west and the slope on the northern Shanxi, in which the Chang-8 member of Yanchang Formation, as the reservoir, is of significance in controlling and predicting the reserve. While much research on this region is about the sedimentary, study in diagenesis and reservoir characteristics is scarce. Therefore, according to the theory of geology of petroleum, core data, thin section analysis, SEM and vitrinite reflectance, the author has deeply studied about the microfacies, the Sedimentation and the reservoir characteristics of the Chang-8 member of Yanchang Formation :Research on the sedimentary facies illustrates that the target sand reservoir developed on braided delta and is represented by the sand bodies of subaqueous distributary channels, mouth bar and distributary channels of delta plain.Research on rock characteristics indicates a prevail presence of lithic arkose and feldspathic litharenite that is homogeneous and is basically made up of packsand, calcite cement, and quartz cement. EMP shows calcite cement consists of ferrocalcite and nonferrous calcite. Quartz content ranges from 29.4% to 71.4% with an average of 50.6%; feldspar content ranges from 19% to 58.8% with an average of 25.5%; cuttings account for 10.9%-49.4% of total with average of 23.8%. Meanwhile, Ch8 is occupied by mainly primary intergranular pores and secondarily arkose dissolved pore.Research on diagenesis demonstrates over this area, compaction, cementation, denudation and metasomatism have had operated the geological development. Quantitative analysis on porosity evolution, moreover, illustrates that compaction and cementation should be substantially responsible for the deterioration of reservoir properties. Consequentially, the diagenetic process in the area can be described as seven steps: compaction→early disposition of clay film→feldspar dissolution→quartz secondary growth→late ferrocalcite cementation→late part corrosion→hydrocarbons emplacement. The area arrivaed in A period of the secondary diagenetic stage. Finally we classify the sandstone in the area into 5 categories, of which the ? and II categories represent qualified and less qualified reservoirs respectively.Combined with analyses above, research on reservoir characteristics summarise that the Chang-8 member of Yanchang Formation in Jiyuan area is a typical reservoir of poor poroperm characteristics. Specifically, the porosity of Ch81 fluctuates between 3.62% and 16.41% with an average of 10.9% and, its permeability ranges from 0.001×10-3μm2 to 13.69×10-3μm2 with an average of 1.1×10-3μm2; Ch82 has a porosity fluctuating between 3.06% and 13.61% with an average of 9.44% and a permeability that is from 0.001×10-3μm2 to 0.49×10-3μm2 with average of 0.75×10-3μm2.In general the pore configuration here is complex and unpredictable and, original disposition and late diagenesis affect the Chang8 fundamentally.Base on the area actual exploration situation,through reservior classification and the reservior appraisal research, reserviors of Chang81 principally belong to II and III categories of the sand body classification with four relatively advantaged regions that can be aimed to in the following exploration.