The Study Of Reservoir Characteristics Of Shanxi Formtion No.3 And Taiyuan Formtion No.15 Coalseams In Southern Qinshui Basin

On the basis of the existing coalfield geological data in Qinshui Basin, the author collected some samples of No.3 and No.15 coalseams in Southern Qinshui Basin. This paper applied several methods including geology, coal petrology and coal quality to study the thickness distribution of the main coalseam and the function of sedimentary environment on the coalseam in Southern Qinshui Basin. Compare the difference of coalseam reservoir properties from pores and fractures of No.3 and No.15 coalseams. Meanwhile, the author observed the minerals of coalseams in Southern Qinshui Basin, studied the impact of minerals on reservoir properties, and revealed the reasons why No.15 coalseam of Taiyuan Formtion has poor gas production.This paper analyzed the effect of sedimentary environment on coalseam thickness in Southern Qinshui Basin. Basised on the collected information, the author re-drawn the contour maps of No.3 and No.15 coalseams depth and thickness. In addition, this paper studied the coalseams in Southern Qinshui Basin. No.15 coalseam of Taiyuan Formtion has more bright coal, and of more wide vitrain and clarain strips. The content of vitrinite (above 7.96%) and mineral (above 2.36%) in No.15 coalseam is higher, and the inertinite is lower (about low 10.33%). No.15 coalseam also contains more pyrite which shows the characteristics of the sea causes.The pores of No.3 coalseam have little changes. Pore connectivity is better and coal reservoir has higher permeability. Pore types are conducive to CBM enrichment and outputs. While the pores of No.15 coalseam are different, No.15 coalseam of Longdingshan mine has poor pore connectivity, lower permeability. So the migration of CBM in coal reservoir is weak. Better pore connectivity of No.15 coalseam and higher permeability in the areas of Bocun and Chuandi mines result in good migration of CBM.The two coalseams in Southern Qinshui Basin develop two group macroscopical fractures,20?50° and 272?357° respectively. The dip angle of cracks in No.3 coalseam is larger; the density of exogenous fractures in No.15 coalseam is higher, and lower in No.3 coalseam. The fillings are mainly calcite and pyrite in the hand specimen, which indicates these fractures are the main channels of fluid exchange. The micro-fractures of two coalseams are mainly type D and C, and have different combination types. No.15 coalseam has more micro-fractures.The fractures of No.15 coalseam are filled seriously with mineral, which affects the exploitation of CBM. No.15 coalseam formed in marine environment, and pyrite can be formed in alkaline environment. The roof of No.15 coalseam is mostly limestone. Limestone can be dissolved in the groundwater, and the calcium-rich karst water seepaged into No.15 coalseam then precipitated, which has a more serious impact of the coal reservoir properties. So the largely filled thicker calcite and pyrite has a serious effect on the exploitation of CBM in No.15 coalseam.