Desorption characteristics of coalbed methane reservoirs and affecting factors

The desorption characteristics of coalbed in China are affected by many factors. The desorption ratio of coalbed gas is approximately 40%, and mostly less than 70%, and it is affected by gas content and coalbed pressure. Most of the desorption time values are between 0.1883 and 19.17d, and the time span of high-rank coal is the highest, which can reach 30 d. The value has a positive correlation with coal rank. A great number of experimental data show that temperature, coal dimension and shape, coal rank, ash content, gas content, cleat, sediment environment, and coal style are the main factors affecting desorption time. According to the numerical simulation result, coal desorption volume affects the single well production. And the single well output has a positive correlation with the desorption. The variation of coal desorption time value can induce the change of output peak value of a single well and its occurrence time.