A simple method for correcting for the presence of minor gases when determining the adsorbed methane content in shale

• Develop an approach to use the HS-GC determined parameters in gas calculation.
• Convert the adsorption equilibration partition coefficient to Langmuir constants.
• The Langmuir constants of minor gases used in gas calculation are from HS-GC test.

This paper demonstrates a novel approach for correcting for the presence of minor gases when determining the adsorbed methane content in shale. Based on the widely used Langmuir isotherm in calculating the adsorbed gas, an equation is derived that converts the adsorption equilibrium partition coefficient (Kd) and maximal amount of adsorbed gas (N) at low pressure to Langmuir pressure (pL). Headspace gas chromatography (HS-GC) is used to determine the Kd and N of the minor gas species present in the shale. The results indicate that the method satisfactorily accounts for the presence of minor gases when estimating the amount of adsorbed methane. This HS-GC method is much more efficient than the isothermal adsorption test currently used for the measurement of adsorption parameters of minor gas species in shale. Therefore, this new approach will improve the speed and accuracy of estimating the amount of adsorbed methane in shale deposits.