Coalbed Methane System And Drainage Optimization Of Taiyuan Formation In Southern Qinshui Basin

For a long time, the scale development of coalbed methane(CBM) in southern Qinshui basin is confined to Shanxi Formation, and the CBM Productivity of Taiyuan Formation is difficult to be released. Aiming at this technical bottleneck, the method combining fluid pressure system analysis with numerical simulation was adopted in this paper. The basic characteristics of CBM systems of Shanxi Formation and Taiyuan Formation were discussed; the objective existence and appearance characteristics of superposed fluid pressure system in the coal-bearing strata were discovered, and the geologic origin of such system was elucidated preliminarily. The law and geological controls of CBM productivity of independent drainage of No.15 coal reservoir were analyzed, and reservoir permeability and hydrogeological condition were considered to be the key geological factors restricting high-efficient development of the CBM in Taiyuan Formation. Accordingly, a fuzzy analytic hierarchy process evaluation system for evaluating the potentially favorable regions of CBM drainage from No.15 coal seam in Taiyuan Formation was established, and the plane distribution pattern of different potential subareas was identified. The permeability of No.15 coal reservoir and the water supply from underground water to coal seam gravitational water is analyzed, combining with drainage history analysis of CBM wells, the CBM productivity wells of independent drainage of No.15 coal reservoir were refined and summed up to 5 types, and the dynamic variation rule of fluid pressure system of each type of CBM well was described. The well pattern of independent drainage of No.15 coal reservoir was optimized and designed. Standard templates based on characteristic trace elements of produced-water, and fuzzy matter-element model based on analysis of geological factors were established, and the evaluation methodology of joint drainage feasibility discrimination was formed. Based on the above understanding, the geologic and mathematic models of joint CBM drainage of two formations were established, the influences of K2 limestone aquifer on the joint drainage under the condition of combination of different producing layers were simulated and analyzed. Finally, the optimum design method of joint drainage and progressive drainage schemes were put forward.