Adsorption of CH4, CO2 and 10%CO2/CH4 on mature Qusaiba shale (1.81% TOC) is studied at 50, 100 and 150°C and 45 bars maximum pressure. Adsorption of CH4 was the lowest at all temperatures. As CO2 percentage increased, adsorption uptake increases concluding that CO2 is highly competitive and can be used to desorb CH4 and enhance gas recovery. Maximum adsorption uptakes were observed at 100°C because of the thermal decomposition of organic matter which opens more adsorption sites. Adsorption isotherms including Langmuir, Freundlich and BET are fitted to adsorption data. Langmuir isotherm showed the poorest fit with high errors and lowest coefficient of determination (R2). Nevertheless, Freundlich isotherm fitted the adsorption data perfectly with lowest errors and highest R2 reaching 0.999. Furthermore, adsorption thermodynamics parameters have also been determined. Heat of adsorption (ΔHads) negative values showed that adsorption is exothermic physical adsorption. Negative ΔGads showed that adsorption of CO2 is more spontaneous than CH4 with strong affinity at high temperatures. This work confirm that CO2 is viable candidate to shale gas enhanced gas recovery and Qusaiba shale can store huge amounts of CO2 especially at high temperatures.

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