Modeling and Simulation of Moisture Effect on Gas Storage and Transport in Coal Seams

It has been observed in a series of experiments that the presence of moisture in the coal matrix has profound influences on the gas storage and transport in coal seams by reducing the gas adsorption capacity of the coal, decreasing the gas effective diffusivity through the coal matrix, and varying the coal swelling strain. A striking piece of evidence of the loss of moisture content in field is the increasing dustiness during the ventilation in coal mining, and this may definitely affect the gas production. However, the combined effect of these processes on coalbed methane production has not been studied in previous works. Therefore, an initial reservoir simulation model has been constructed to investigate the magnitude and interplay of the moisture effect on coalbed methane production. To develop the aforementioned model, approximate relationships have been built to quantify the moisture effect on the gas adsorption capacity, the gas effective diffusivity and the coal swelling strain. These relationships have been validated by comparison with a selection of literature data. The results of the reservoir model show that the combined moisture effect can significantly affect the overall gas storage and transport behavior. For the reservoir simulation conducted in this work, the gas production is enhanced as a result of the moisture loss by the ventilation air in the underground coal mining. The magnitude of this effect is sufficient to warrant additional research and modeling studies on the effect of moisture on coalbed methane drainage and production.