| Ordos Basin is an important energy basin of china,and oil, gas, coal, uranium, water and other energy symbiose in the basin.Yanchang formation is a typical reservoir of low permeability. The eastern region in which delta sand body is well-developed has been an important area for oil and gas exploration. Less studied,ShiJiapan region in eastern region was choosed,as our study area,Under the guidance of advanced theories and methods such as sedimentology,sequence stratigraphy,reservoir geology,petroleum geology and so on, on the basis of a large number of logging and drilling, outcrop and testing,stratum,sedimentary facies,sedimental model, reservoir characteristic, reservoir inhomogeneity, play accumulation model and so on,are studied comprehensive, which can enrich the study of continental low-permeability reservoir theory and guidance the oil exploration.1.According to physical manifestations of sequence boundaries in Yanchang formation in study area,such as unconformity surface,scour erosion surface,maximum flooding surface,regional flood event marker,lithology-lithofacies conversion surface, symbol layor of strata comparison, Yanchang formation can be divided into a second-order sequence,in which the maximum flooding surface (condensed layer) is the ZhangJiatan shale on the bottom of Chang 7,and can be further divided into five third-order sequences.The average life span of each sequence is 5.2 Ma,and each third-order sequence is composed of LST,TST,HST and are compared with lithology stratigraphic division.2.Sedimentary facies analysis indicates that the major developed delta, lacustrine, and carry out sub-facies and micro-facies, the main source of the North East with the impact of the North East or the delta of the main north-south distribution, during the palaeogeographic evolution, Chang 10 is delta plain; Chang 9-Chang 7 is delta front; Chang 64, Chang 63, Chang 62, Chang 61, Chang 4+52, Chang 4+51, Chang 3, Chang 2 are delta plain; because of differential subsidence during Chang 1, basin migrated to Zichang area, the vicinity of the study area is delta front sub-facies, and the shallow water delta depositional model was established in study are.3 Reservoirs are mainly gray, light gray green feldspathic sandstone, lithic feldspathic sandstone partly, mainly fine sand and secondly silt and medium sand with respect to grain size. Mica and mud mixed is the main matrix, the quality of cement are mainly quartz, feldspar, calcite, a small amount of dolomite, pyrite.Better selected.sub-angular to sub- rounded with respect to psephicity. Granular supported type and line contact between Granular, pore type and overgrowth are main cement type.4.In the process of diagenesis, reservoir experienced various degrees of compaction, cementation, replacement and dissolution.In which compaction and cementation is harmful to the preservation of pore, while replacement and dissolution improved to some extent the reservoir. According to clay minerals, quartz overgrowth, pore type and other parameters, the reservoir has entered to the stage A,and Chang 6 to stage A-B of late diagenesis. Weak compaction-chlorite cementation, weak compaction-carbonate cementation, weak compaction-quartz and feldspar cementation, compaction-pressure solution facies, weak compaction-dissolution facies, laumontite-feldspar dissolution facies. In which weak compaction-chlorite cementation, dissolution of feldsparfacies arefavorable diagenetic facies. As a whole,Reservoir is belong to low porosity, Medium-low permeability with strong heterogeneity. In plane, there is a good relationship for high porosity and high permeability zones with distributary channel (subaqueous distributary channel) area. Properties and heterogeneity of reservoir are controlled both by sedimentation and diagenesis. Distributary channel and subaqueous distributary channel are favorable micro-facies; There is negatively correlated for calcite and mica with porosity and permeability;while the presence of chlorite film is beneficial to the preservation of porosity and can increase the reservoir properties. According to parameters influencing reservoir properties, the reservoir is classified, and reservoir changes in vertical and horizontal are analyzed.â…¡,â…¢andâ…£type reservoirs are all developed,in which type III (can be divided intoâ…¢a,â…¢b) is the main reservoir of the study area.5. According to the quantitative formula of porosity and diagenetic evolution, the original sandstone porosity, intergranular volume after compaction, intergranular volume after cementation, volume after dissolution, and such rates as compaction, cementation, micro-pore, dissolution pore are resumed of Chang 4+5 and Chang 6..In the end, quantitative evolutionary relationships between different diagenesis and porosity are established in the study area.6.The analysis result of reservoir control factors and accumulation of oil and gas, shows that Yanchang formation in study area has favorable combination of source bed,reservoir and seal,and good conditions for oil and gas traps. According to favorable reservoir development, combined with deliverability features and the top surface elevation of the study area, favorable blocks are predicted,and main exploration.targets in the near future in different layers...
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