Study on gas production laws of supersaturated CBM reservoir in Guizhou Province

The discharge process based on supersaturated CBM reservoirs has the characteristics of production of free gas and adsorbed gas. In order to understand the inherent causes and mechanisms of gas production characteristics of such supersaturated gas reservoirs, and explore the main controlling factors affecting high yield and stable production, and provide guidance for the exploration and selection of wells, well location, fracturing and drainage design of such gas reservoirs, the production mechanism of free gas and adsorbed gas are deeply analyzed and the isothermal adsorption curves are therefore divided into two classic types. Combining with the on-site production examples, their output characteristics and capacity control factors are wholly described respectively. The results of the study show that the isothermal adsorption characteristics of coal reservoirs determine the time of rapid desorption of adsorbed gas and the trend of reservoir diversion capacity, thus affecting the propagation of pressure drop and the effective output of free gas and adsorbed gas. The supersaturated CBM reservoir has the characteristics of rapid gas production and fast growth of gas production in the early stage of drainage. The stable gas production, stable production period and decay rate in the middle and later stage of drainage mainly depend on the isothermal adsorption characteristics of the production layer, the structure of coal and the rationality of the drainage system, among which the isothermal adsorption characteristics are the main controlling factor.