Study On Coal Reservoir Physical Properties In Eastern Margin Of Ordos Basin

Base on the existing coalfield geological data in eastern margin of Ordos Basin, have an in-depth study of CBM reservoir characteristics such as coal macerals, coal rank, coal quality and coal type, porosity, pore structure, specific surface area, permeability by applying theories and methods such as coal and CBM geology, surface chemistry, fractal science etc. Some geological models of CBM reservoir pore system were built, and the main factors controlling the development of CBM reservoir in different ways was analyzed with statistical method. The development law of 12 ore spots reservoir physical properties was studied in mining area such as Hequ, Baode, Liulin, Hancheng, Pucheng, Chenghe, etc.The mercury injection test shows that the coal reservoir pore systems in eastern margin of Ordos Basin have the features as followed: the pore system is dominated by micropores and transition pores, especially the micropores, and macropores take the second place, and mesopores are nearly absent. The cryogenic nitrogen isothermal adsorption test results indicate that the area, which is relatively large in north area, and decrease to central ,southern area with coal rank rising, change from 0.092 to 20.480 m2/g, with an average 2.046 m2/g. Furthermore, the clay minerals have an obvious impact on the BET specific surface. The isothermal adsorption curve is divided into one series with 4 types. Every one represents a certain storage and transportation type of CBM.Base on analysis and comparisons of plenty of experiment data, four types of geological model and the corresponding fractal mathematical models of pore system of middle coal rank reservoirs in eastern margin of Ordos Basin are established. Then the contributions of every pore system model to petrophysics of the reservoirs are analyzed. Comparatively, the pore system model 1 and 2 are more reasonable in pore system structure, which indicate superior coal reservoirs of good petrophysics, and pore system model 3 and 4 are a little unreasonable in pore system structure. As the differences in physical properties for the diverse pore structure system, the superior or inferior coal reservoirs alternate in one coal seam. Application of variation coefficient, graded coefficient and mutation coefficient, the reservoir heterogeneity models of No.9 Coal Seam in Longmenta Mine (Liulin), No.13 Coal Seam in Xiaosuanta Mine (Hequ), No.11 Coal Seam in Sangshuping Mine (Hancheng) are described.The different developments of the Low-medium rank coal reservoir are both controlled by metamorphic grade and coal-forming environment. The R-type cluster analysis indicates that the plant development condition reflected by wood index (WI), sediment source condition reflected by ash composition and content are closely relative with BET specific surface area, content of inertinite , and effect the development of transition pores with coal rank rising. Coal facies controlling the reservoir heterogeneity, bright coal and semibright coal, which developed in forest peat swamp facies and transition peat swamp facies consists of superior coal reservoirs, and semidull coal and dull coal which developed in drained peat swamp facies and fresh-water peat swamp facies consists of the inferior coal reservoirs. Relatively, the coal reservoir with better physical properties in Hequ, Baode which formed in delta plain made the good reservoir, the reservoir in Hancheng which developed in epiric sea take the second place, and the reservoir formed in delta fronts in liulin is worst...