Study On Permeability Influencing Factors In Cbm Well Drainage And Production

During CBM well drainage and production process,permeability change is obvious and some sometimes spanning 2 orders of magnitude.Permeability change in CBM well drainage and production process is mainly affected by the stress sensitivity effect and matrix shrinkage caused by air phase and water phase.To establish a related comprehensive analytical model for predicting the dynamic permeability change of CBM wells and to evaluate the actual permeability performance of CBM wells is of great significance for design of CBM development scheme and reservoir dynamic evaluation.Firstly,this paper establishes a reservoir geometric model that takes the characteristics of face cut and end cut into account.On this basis,the stress sensitivity effect caused by the bidirectional strain of X-axis and Y-axis and the matrix shrinkage effect caused by gas-water desorption are considered.The rationality of the model is verified by analysis,comparison and numerical simulation.It is concluded that the matrix shrinkage effect caused by water desorption is generally weak.Then based on the dynamic permeability model,the sensitivity analysis of each factor is carried out.The main control factors affecting the permeability and productivity of coalbed methane Wells are obtained.Finally,the method of calculating the permeability and permeability saturation curve during the whole stage is derived.This study provides a theoretical basis for the prediction and evaluation of the dynamic permeability change of CBM wells and has a guiding significance for the formulation of the drainage and production plan of CBM wells.