Production decline types and their control factors in coalbed methane wells： a case from Jincheng and Hancheng mining areas

Based on the analysis and study on production dynamic data of CBM wells in Jincheng and Hancheng mining areas, index decline, harmonic decline, composite decline, abrupt decline and periodic decline are suggested as five types in CBM production decline period. Boundary condition, adsorption feature of CBM, coal-seam permeability, permeability rebound in desorption, interference between wells, interlayer interference and production system are major factors for CBM yield and its decline features. This research also shows that twice fracturing, reasonable well grid, adjusting production system reasonably, sealing some layer of low-yield wells, choosing right time to commingle and applying sidetracking well technology are effective strategies to recover and raise CBM yield of single well, delay decline period and decrease decline rate. These measures can make production decline trend to hyperbolic decline and harmonic decline, and improve final recovery of CBM.