(589d) Measurement and Modeling of Competitive Sorption of Methane/Ethane Mixtures on Marcellus Shale – Isotherms and Kinetics

Authors: 
Dasani, D., University of Southern California
Wang, Y., University of Southern California
Tsotsis, T., University of Southern California
Jessen, K., University of Southern California
As the primary mechanism of gas storage in shale, sorption phenomena of CH4 and other hydrocarbons in the micropores and mesopores are critical to estimates of gas-in-place and of the long-term productivity from a given shale play. Since C2H6 is another important component of shale gas, besides CH4, knowledge of CH4-C2H6 binary mixture sorption on shale is of fundamental significance and plays a central role in understanding the physical mechanisms that control fluid storage, transport, and subsequent shale-gas production.

In this work, measurements of pure component sorption isotherms for CH4 and C2H6 for pressures up to 114 bar and 35 bar, respectively, have been performed using a thermogravimetric method in the temperature range (40-60 oC). Sorption experiments of binary (CH4-C2H6) gas mixtures containing up to 10% (mole fraction) of C2H6, typical of shale-gas compositions, for pressures up to 125 bar under the aforementioned temperature conditions have also been conducted.

To facilitate investigation of depletion dynamics (e.g. via application of the Extended Langmuir Model), excess sorption measurements must be converted to absolute sorption. This conversion requires accurate estimates of the adsorbate density. Here we investigate the performance of several of such methods proposed for evaluating the adsorbate density. We demonstrate that the equilibrium constant and hence the adsorption and desorption kinetic constants are sensitive to the choice of the adsorbate density model and conclude by providing recommendations for selection of adsorbate density modeling. Lastly, we apply the best-fit adsorbate density method to model the sorption dynamics of pure and binary gas mixtures on to the shale.

To the best of our knowledge, this is the first time that systematic measurements of CH4, C2H6 pure and binary mixture sorption on the Marcellus shale have been conducted, thus providing a comprehensive set of CH4-C2H6 competitive sorption data, which can help to improve the fundamental understanding of shale-gas storage mechanisms and its subsequent production.

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