Determination of the Absolute Adsorption Isotherms of CH4 on Shale with Low-Field Nuclear Magnetic Resonance

Understanding of the absolute adsorption behavior of CH4 on shale is critically important in estimating shale gas storage in shale gas reservoirs. In this work, two approaches are applied to obtain the absolute adsorption isotherms of CH4 on shale samples. In the first approach, we first measure the excess adsorption isotherms of CH4 on two shale samples at the temperature of 298.15 K and pressures up to 12.0 MPa. Then, grand canonical Monte Carlo (GCMC) simulations are used to calculate the adsorption-phase density; such density values are consequently applied to calibrate the measured excess adsorption and obtain the accurate absolute adsorption isotherms. As for the second approach, we apply the low-field nuclear magnetic resonance (NMR) method to describe the absolute adsorption of CH4 on shale. A NMR-based setup is designed to measure the T2 spectrum distributions in shale samples by injecting CH4 into dry shale samples. The injecting pressure is set up to 12.0 MPa, which is similar to the conditions...