| This paper take Tanan area of Tamuchage Basin for example, studying on the diagenesis, the reservoir characters,Pore structure and evaluate the reservoir by use of"grey theory".Routine thin sections identification, observation of casting thin sections, observation of SEM and image analysis were adopted on the study.Through date collection and thin sections identification the mainly rock types of tongbomiao formation were tuffaceous sandstone, secondary of sandstone, a mount of sedimentary tuff.The frist member of nantun formation was made up by sandstone and tuffaceous sandstone, little tuff while the second member was composed of sandstone and tuffaceous sandstone.The diagenesis characteristics of Tongbomiao Formation and Nantun Formation was investigated by ordinary thin-section,casting thin-section identification and SEM analysis,combining with the data collected. The main types of diagenesis included compaction, devitrification, alteration, cementation,clay minerals,erosion and dissolution, among this cementation and erosion and dissolution were most;According to the symbiosis of authigenic minerals, the paragenesis of diagenetic was mechanical filtration,authigenic clay mineral coating - devitrification, compaction- erosion and dissolution, chlorite, quartz secondary overgrowth, illite, authigenic quartz microlite - siderite, micritic carbonate, kaolinite, albite, sericite - calcite, dolomite. According to vitrinite reflectance and authigenic clay mineral association,the diagenetic phase of sandstones from Tongbomiao Formation and Nantun Formation was mostly in middle diagenetic A phase, little early diagenetic B phase.Through the study of casting thin-section identification and image analysis we conclude the mainly type of reservoir space was solution intergranular pore and solution intragranular pore and the solution intergranular pore was made up by feldspar dissolution and debris dissolution in sandstone while volcanic material dissolution in tuff. Based on the analysis of the mercury penetration data, the grade of the reservoir pore structure was mainly better, the other is poor and a little of good grade, the rock style has influenced reservoir pore structure for the grade in sandstone is better than tuffaceous sandstone, tuff worst.The porosity and permeability of reservoir indicate that the Objective Formation was extra middle-low porosity, extra middle-low permeability and high carbonate cementation. The reservoir physical properties has tendency to increase from tongbomiao Formation to secondary member of nantun Formation, The reservoir physical properties distribution circle in the plane. In the middle part of depression was poor, lower-level, while the edge of the depression is relatively good physical properties. There were there abnormally high porosity zone in vertical, corresponding to 1900m ~ 2100m, 2500m ~ 2900m and 3400m, guess the cause of abnormally high porosity maybe connect with chlorite content, erosion and dissolution and mechanical filtration .Select the porosity, permeability, carbonate content, mean size and displacement pressure as parameters, using the "Grey theory" principle to evaluation reservoir of the Objective Formation in Tanan depression and divided the reservoir into four levels, from one to four levels corresponding to good, better, middle and poor grades, mainly composed of two and there levels. Meanwhile determine the relationship between distribution of favorable reservoir and the sedimentary facies, the good levels of favorable reservoir mainly distribution in the fan delta front areas. In addition, Nantun Formation reservoir grade is better than Tongbomiao Formation. For Tongbomiao Formation, high tuffaceous material erosion and tectonic activity were the influence factors for good reservoir, while provenance areas and Sedimentary facies as influence factors for frist member of Nantun Formation, there is no understanding of secondary member of Nantun Formation for data limitation.
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