Production characteristics and affecting factors of high-mid rank coalbed methane wells: Taking Fanzhuang and Hancheng mining areas as examples

Production characteristics of coalbed methane wells in Fanzhuang and Hancheng mining areas, which are typical high and mid rank coal fields, are analyzed, compared, and summarized. And the effects of perforating thickness, number of perforated layers, unloading technology and stimulation treatment on gas production are analyzed. Coalbed methane wells in Fanzhuang and Hancheng mining areas are divided into four categories: high gas-production wells, middle gas-production wells, low gas-production wells and little gas-production wells. High gas-production wells have gas production of more than 3 000 m(3)/d, long stable production period, slow and smooth declining rate, high peak production and short unloading period. Middle gas-production wells have gas production between 1 000 m(3)/d and 3 000 m(3)/d, shorter stable production period, longer unloading period and quick declining rate at the early stage. Low gas-production wells have gas production of less than 1 000 m(3)/d, short stable production period, high water output, long unloading period and discontinuous production. Little gas-production wells have large water output, slow reducing rate of liquid level and a low or zero surface casing pressure. Based on the production characteristics, three types of production modes of coalbed methane wells are summed up. In view of specific examples, it is discussed quantitatively and qualitatively how different factors affect the gas production of coalbed methane wells. It turns out that, generally, the perforating thickness of coalbed methane wells should be larger than 5 m and the layers of perforation should not exceed 3 layers. A proper unloading system is needed to maintain stable and persistent high gas production, and secondary stimulation treatments can bring about significant production increase.