Modeling of gas extraction from closed coal mines

Abstract : The closed coal mines carry on releasing firedamp. In some cases, the quantity of gas released is not negligible and it can induce an overpressure in old works. A means to avoid hazards related to these gas emissions at the surface is to put in drainage installations and to keep the pressure of the underground reservoir under the atmospheric one. This practice has been used in several mines in France like in the Lorraine basin. A mathematical model has been developed by INERIS in order to improve operation of such installations. This model needs to determine 4 main parameters of reservoir. After its calibration, it is possible to forecast daily variations of pressure and methane content in drained gas as a function of daily extracted gas flow rate. Validations were made for several years. This model is able to evaluate firedamp quantity which may be extracted for a givent period to characterize the extraction conditions allowing an optimal production and its durability.