Surfactants Impact on CO2 Sequestration for Enhanced Gas Recovery and in Depleted Carbonate Reservoirs

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Abstract
Indiana limestone cores were crushed and sieved to particle size of 125-250 microns, half of the sample was kept pure and the remaining has been treated with NaCl brine containing 0.1% (VES) viscoelastic surfactant to study the effect of surfactant on CO2 and CH4 adsorption. The carbonate rock was characterized using X-ray diffraction to determine the crystallinity. The adsorption measurement has been conducted at 50, 100 and 150°C and to 45 bars maximum pressure. At 50°C, adsorption uptake of CH4 and CO2 for untreated samples was higher than VES treated samples. However, at 100 and 150°C Both CH4 and CO2 adsorption capacities of untreated limestone was considerably lower than VES treated limestone. Thermodynamic studies indicate that adsorption on untreated samples was exothermic with ΔHads of -16.7 and -13.5 KJ/mol for CH4 and CO2 respectively and spontaneous adsorption at 50°C. In contrast, adsorption of CH4 and CO2 is endothermic with corresponding ΔHads of 60.1 and 36.2 KJ/mol and spontaneous at high temperatures. through all measurements CO2 adsorption was three times CH4 adsorption uptake due to high affinity between CO2 and calcite. Adsorption isotherms fitting shows that Freundlich isotherm is the best model to represent the adsorption behavior for all conducted experiments at all temperatures with lowest sum of squared errors (SSE) and highest R2. These results suggest that previously treated carbonate reservoirs that has mid-high temperatures has great adsorption potential for CO2 and CH4 making them an excellent candidate for CO2 sequestration.

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