Comprehensive Evaluation And Reservoir Characteristics Of Chang 6 Oil-bearing Sets Of Yanchang Formation In Zhengzhuang Area, The Ordos Basin

Zhengzhuang area is located in the north of Shanbei slope, Ordos Basin. The Chang-6 oil-bearing beds of Triassic Yanchang Formation is the research horizon of this paper.Applied with core descrip tion, outcrop observation, electro facies analysis, cast thin section examination, mercury penetration, and other analysis methods, comprehensive study is pursued for the sedimentary environment of Chang 6 reservoir in research area, the Chang-6 oil-bearing bed is subdivided into Chang-61,Chang-62,Chang-63,Chang-64, we find the main sedimentary system is shallow lake subfacies, platform-type meandering river delta front and deltaic-plain meandering river deposition. deltaic plain distributary channel sand body and deltaic front subaqueous distributary channel sand body are main reservoir sands.The research on flakes,properties and so on show that reservoir is main consist of fine feldspathic sandstone, It shows that tie diageneses mainly include compaction, pressure solution, cementation, packing action, dissolution and fracturing. It is concluded that the diagenetic evolution of Chang-6 sandstone has mainly been in the middle diagenetic stage A-B. The main reser space of the research area is feldspar and laumontite solution pore, residual pore; the average porosity is 8.2%, and the average permeability is 0.28×10-3μm2; The porosity is mainly the kind of dissolution porosity, and the composition of pore throat is the fine pore with Micro-throat type. It is also typical low porosity and low permeability reservoir. The reservoir physical property of Chang-62 is the best, Chang-61 is the secondary, Chang-64 is the worst.By the analysis of the sedimentary facies and reservoir characteristics, we find that deposition is the basic reason controlling of hydrocarbon source rocks and reservoir spreading, diagebesis mainly determines the reservoir quality:The mechanical compaction and cementation which result in primary porosity loss almost are the main factor causing the lowest perm eability in the early diagenetic phase; the dissolution of laumontite and feldspar that is dissolved improves the porosity and perm eability. The reservoir heterogeneity controies the scale and distribution of oil reservoir.Based on the features of sedimentation,diagenesis,pore structure and property distribution in this area to conduct comprehensive evaluations of the reservoir, the sandstone reservoirs are divided into four types:good reservoirs(Ⅰ), appreciably Good reservoirs(Ⅱ), poor reservoirs(Ⅲ) and non-reservoirs(Ⅳ). In Zhengzhuang area, II-appreciably Good reservoirs andⅢ-poor reservoirs are occur in the deltaic plain distributary channel sands and deltaic front subaqueous distributary channel sands.All these works that provide the credibility geology gist for further exploration and exploitation in this area.