Abstract:

The transport of gas through a coal seam is generally considered a two-stage process. Gas desorption from the coal matrix followed by its flow along the fractures. If the release rate of gas from the matrix to the cleats is faster than the flow rate of gas and water in the cleats, the desorption kinetics are relatively less important in modelling coalbed methane production. Under this assumption, the gas held by the coal is similar to that dissolved in the black oil at a given pressure. The solution gas-oil ratio of this immobile oil is calculated from the Langmuir adsorption isotherm curve. A conventional black oil simulator can be used to simulate coalbed gas reservoir by treating gas adsorbed to the surface of coal block as gas dissolved in the immobile oil. Based on the ideas above, a coalbed methane reservoir has been studied by using black oil simulator, and the results are very close to those from a coalbed methane reservoir simulator(COMETPC).

Key words: black oil model, coalbed gas, desorption, simulation, cleat