Application of temperature-dependent adsorption models in material balance calculations for unconventional gas reservoirs

Langmuir isotherm is the most common adsorption model used in the prediction of gas adsorption in most shale and coal bed methane reservoirs. However, due to the underlying assumption of single temperature, it fails to model gas adsorption where temperature differential exists in the reservoir. To address this shortcoming, temperature-dependent gas adsorption models have been incorporated into material balance calculations for accurate prediction of original gas in place as well as determining both average reservoir pressure and future performance in coal/shale gas reservoirs. The material balance equation has been expressed as a straight line with both Bi-Langmuir and Exponential models used in prediction of gas adsorption rather than the Langmuir isotherm. With this methodology, several adsorption capacities can be obtained at multiple temperatures which will allow for better estimation of original gas in place and future gas production. The results from this works show that temperature-dependent gas adsorption models can be used in place of Langmuir isotherm to account for the effect of temperature variations and more accurate representation of the adsorption of gas in coal/shale gas reservoirs.