Experimental investigation on effect of reservoir conditions on stability and rheology of carbon dioxide foams of nonionic surfactant and polymer: Implications of carbon geo-storage

Abstract

Carbon dioxide (CO2) injection, in form of a viscous foam, is one of the effective techniques to control premature CO2 breakthrough in subsurface carbon storage and utilization (CSU). Polysaccharides are often used in oilfield and its use for developing viscous CO2 foam will make the process reservoir compatible and economic. However, their efficacy should be tested at real conditions to promote better CO2 utilization in oilfield projects. This study aims to quantify the role of subsurface conditions viz., pressure, temperature, and salinity on CO2-foams prepared by non-ionic polymer (guar gum, 4000 ppm) and surfactant (TX-100, 0.25 mM). Salts i.e. potassium chloride (KCl) and magnesium sulfate (MgSO4) of varying concentration (0–8 wt%) were used. Increasing salt concentration were found to significantly affect foam stability (maximum fall of 88.88%) and CO2 molality in surfactant-polymer (SP) solution (by 73.1% at 70 bar pressure). KCl showed a greater reduction (≈8–15%) than MgSO4 (6–12%) however, increasing surfactant amount had negligible impact on CO2 molality. Additionally, microscopic analysis was performed in which initial bubble size (i.e. 40-60 μm) due to coalescence phenomenon was observed to increase to (400–460 μm) after 1 h. CO2 foams exhibited non-Newtonian shear thinning behavior where foam viscosity and elasticity were positively influenced by increase in pressure, which suggested foam potential for enhanced oil recovery (EOR) and carbon storage in subsurface environment. Foam viscosity decreased with increasing salt concentration (fall of maximum 55% when compared to zero salt content) and temperature resulting at 90 °C, foam viscosity reduces to a value of 0.05 Pa s at pressure≈ 70 bar. Finally, dynamic rheological measurements were reported to visualize viscoelastic response of foams. The viscoelastic response of CO2 foams by strain sweep measurements reported a maximum fall of 60% while 40% reduction in case of frequency sweep measurements was observed. Also, foams exhibited both elastic and viscous effects with clear cross-over between G′ and G″ at each test pressure and temperature.