Sedimentary Facies Of Shanxi Formation Of The Qinshui Basin And The Control Factors To Coal Reservoir

Base on the existing coalfield geological data in Qinshui Basin, through observing outcrops , identifying the thin sections , drawing single well phases and connected well phases, coal seam and the ancient environment of Shanxi Formation were analyzed in detail in Qinshui Basin. The northern basin consists mainly of fluvial facies and delta plain facies ,the central that of lake facies and Delta front facies and the southern that of lakes facies respectively.The characteristics of coal seam had been an in-depth study such as coal macerals, coal ranks, coal quality and coal types, pores and the number and the form of fracture by applying theories and methods such as coal and CBM geology and coal petrology. The pore systems of coal reservoir in Qinshui Basin have the features as followed: the pore system is dominated by micropores and transition pores, macropores and mesopores take the second place. The development characteristics and shape of fracture of coal reservoir of 7 mine sites were focusedly analyzed in Yangquan、Shouyang、Qinyuan、Changzhi、Jingfang、Jincheng and Gaoping. The results show that most of the fractures are shaped of branches and feather, mostly extend in a direction, have a little fillings, dominated by the frequency of 10-50 number s/9cm~2.Xinjing in Yangquan in the northern basin and the Changzhi、Gaoping in the southern basin are richest of fracture, fracture in Shouyang,Jincheng take the second place, and the fracture formed in Yangquan and Zuoquan is worst.The different developments of the high rank coal reservoir are controlled mainly by coal-forming environment. Which not only control the thick and distribution of coal reservoir ,but also the Properties by controlling coal macerals and types ,Coal structures and facies, development of transition pores with coal rank rising. Coal reservoir which formed in delta plain are generally thick and successive. Fracture are selectively developed in the submacerals of telocollinites , the lithotype of banded bright coals and vitrite, which made good reservoir. Mineral will reduce permeability of the coal reservoir, so far , the coal seam which is far from the source area is likely to form the high-quality coal. Coal facies controll the reservoir heterogeneity, which developed in forest peat swamp facies and fresh-water peat swamp facies consists of superior coal reservoirs, and semidull coal and dull coal which developed in drained peat swamp facies consists of the inferior coal reservoirs.The properties of coal reservoir was evaluated by“the ratio of vitrinite strips”. The research show that the ratio increase gradually from the southern to northern basin, the other meaning is that the coal reservoir containing high ratio of vitrinite strips is more than that of the medium and low vitrinite strips.The properties of the southeastern basin is better than that of the north .the best reservoir is located on the southeastern basin.