Analysis of coal reservoir characteristics in the Qinnan-East block and its spacing optimization of CBM development well networks

Well pattern optimization and deployment of coalbed methane (CBM) are the important part to the develop- ment scheme of CBM. A reasonable well pattern can dramatically increase the CBM production as well as reduce the development costs. For this problem,based on the Qinnan-East block in the Qinshui basin,this paper systematically analyzed coal seam conditions and distribution characteristics of gas contents and permeability in study area. By calcu- lating the production dynamics of different well pattern schemes on the basis of numerical simulation,an optimization method for determining reasonable well spacing is put forward by synthetically considering the economic evaluation pa- rameters including cumulative cash flow and recovery rate. It is shown that the thickness of No. 3 coal seam in Shanxi formation varies from 4 to 6 m with average of 5. 61 m,and burial depth varies between 417. 93 and 1 527. 49 m. Gascontents of No. 3 coal seam vary from 2. 87 to 24. 63 m3 / t with average of 13. 78 m3 / t and increase with burial depth by the law of logarithmic function. Well test permeability of target coal seam is lower,which vary from 0. 01×10-15 to 0. 2×10-15 m2 with average of 0. 06×10-15 m2 and decrease with burial depth by exponential function law. According to the coal reservoir conditions in study area,CBM production with well spacing of different burial depths well pattern was calculated on the basis of numerical simulation as well as determined the reasonable well spacing of different burial depths by synthetically considering cumulative cash flow and recovery rate. It is analyzed that well spacing in study ar- ea is 350 m×300 m for the burial depth shallower than 500 m,350 m×250 m for the burial depth between 500 m and 100 0 m and 250 m×200 m for the burial depth deeper than 1 000 m. But the actual well pattern deployment should be adjusted according to the actual geological conditions. These understandings provide a theoretical basis for the reasona- ble formulation of well pattern in the CBM development in this area.