| The Xiqu oilfield of Zhidan area is located in the middle of Yishan slope, which contains Zhaike area, Danba area and Yiwu area. Yanchang formation and Yanan formation, which belong to lithologic reservoir, are the two important oil-bearing series, and they are typical extra-low permeable oilfield. In this research, the Chang 4+5 reservoir of southern Danba area is regarded as main research object, through the depth and detailed study on the method of sedimentary facies and sand body distribution, reservoir characteristics and its effect factors, we finally obtained the following results and understanding of several aspects:1. Combined with core observation, sheet rock of pupose layers, log data and other comprehensive information in Yishan slope, Chang 4+5 oil layer can be divided into upper Chang 4+5 oil member and lower Chang 4+5 oil member.2. The regional tectonic of Danba oilfield performances as west dipping monocline form. Each small layer of Chang 4+5 reservoir group develops nose shape uplift structure of nearly east-west trend, which caused by the differential compaction and the influence of tectonic compression; The oblique-crossing between structure trend and sand trend provides favorable conditions for the formation of lithologic reservoir.3. The oil sections of Danba area distribute stability, and lithologic and electrical property during different wells shows similarity. The sandstone of lower Chang 4+5 is better than upper Chang 4+5 in aspects of thickness and contiguous.4. Distribution of sedimentary facies mainly appears south-north or northeast-southwest trend, the sand body of underwater distributary channel were oil reservoir group of lower Chang 4+5, which show good contiguous of the entire sands and high sandstone content. The distribution of sedimentary facies of upper Chang 4+5 shows that the sandstone content decreased sharply.5. On the base of lithologic characteristics, the detrital composition of reservoir are mainly composed of quartz and feldspar, secondly are cuttings; Interstitial material are mainly composed of cement and miscellaneous base, and cements are mainly chlorite, illite and other antigenic clay mineral and quartz overgrowth. Types of diagenesis include mechanical compaction, cementation, metasomatism and dissolution.6. Pore types can be divided into primary pores and secondary pores. The degree of reservoir's development is closely related with the distribution of pore types. According to the lithology, physical properties, characteristics of sand distribution and other factors of southern Danba region, sandstone reservoirs in this area can be divided intoâ… ,â…¡,â…¢class.
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