Evaluation of Favorable Area for Coalbed Methane Development Based on Local Variable Weight Theory

Abstract

The evaluation of a favorable area is crucial for the exploration and exploitation of coalbed methane (CBM) resources. In traditional evaluation methods, the weight of controlling factors for the evaluation of favorable area is often obtained from different models and calculation methods, and the constant weight is commonly used in the entire target area. The influence of the index value of controlling factors and the combination state of these values on the weight is consistently overlooked during the evaluation process. In view of this phenomenon, a new evaluation method based on variable weight theory was introduced to enhance the accuracy of the result from evaluation (i.e., favorable area for CBM development) in this paper. Based on the raw data of controlling factors, the evaluation area was divided into a finite number of regular grids; each grid could be seen as an evaluation unit, and different attribute values were assigned to them. The constant weights are determined by the analytic hierarchy process (AHP), while the variable weight of controlling factors in each unit was calculated by a partitioned variable weight model (VWM) which constructed based on variable weight theory. Finally, the VWM for the evaluation of favorable area was constructed and applied in the Weibei CBM field. The influence of variability in index values on the weight was taken into consideration in this model, which can complement the disadvantage of the constant weight model (CWM). The accuracy of the result from the evaluation of favorable areas for CBM development could be improved by using this VWM, which provides a reasonable idea and method for the selection of target areas in CBM fields.