A novel experimental system for accurate gas sorption and its application to various shale rocks

Accurate measurement of shale gas adsorption capacity is crucial for reservoir appraisal and production stimulation. Because of the limited adsorption capacity and finer pore size distribution in shale matrix, it is difficult to precisely quantify the adsorption capacity using traditional volumetric methods for coal adsorption measurement. An improved lab method for shale adsorption measurement and diffusivity evaluation was introduced by using a control group connected through a high accuracy differential pressure transducer. Isotherm curves of five shale samples from different basins were acquired using this system. For all shale samples, adsorption capacity for CO₂ is 2–3 times of that for CH₄. Adsorption isotherms for shale exhibited a better fitting trend with the BET model at the pressure range of lab scale, indicative of the quick decline at the diffusion-dominant region of reservoir production curve. It is found that the improved adsorption measurement method can effectively reduce the average accumulated error from 24.3%–11.3%, and it is qualified for measurement of materials with limited adsorption capacity.