Evaluating the influence of geological structure to CBM productivity based on AHP and fuzzy mathematics

In order to understand the influence laws of geologic structure on the gas production of coalbed methane (CBM) well,the paper made the Changzhi Block,Qinshui basin,as an example,and introduced the variation coeffi- cient of coal thickness to express the complexity degree of geologic structure. Then the complexity degree of geologic structure was evaluated and structure network units were divided by means of analytic hierarchy process (AHP). Fur- thermore,based on the results of fuzzy mathematics analysis on the factors affecting CBM productivity,including the geological condition,reservoir physical property and gas content,the relative evaluation method of AHP-fuzzy mathe- matics about the influence degrees of geologic structure on the production effect of CBM wells were established. The re- search showed that Changzhi block could be classified as simple structure area,relative simple structure area and secondary development structure area by the complexity degree of geologic structure. The evaluation scores of productivity of CBM wells from high to low are relative simple area,simple area,secondary development area in order. In other words,there is the greatest productivity of CBM wells in the relative simple area,the second in the simple,and the least in secondary development area. Meanwhile the effect of gas and water production and production curves features show that this evaluation results are in agreement with actual situation. It reflects that the evaluation method of AHP- fuzzy mathematics which is established about the influence of geological structure to CBM productivity is reasonable. Finally the evaluation results could provide references for choosing wells and improving productivity.