Implications of sand mobilization on stability and rheological properties of carbon dioxide foam and its transport mechanism in unconsolidated sandstone

This study reports the role of sand grain (of varying size: 60-380 mu m and concentration: 0-3 wt%) on stability and properties of Pickering carbon dioxide (CO2) foam, which relates to foam transport problem during oil re- covery practice in unconsolidated formation. For foams, anionic surfactant (sodium dodecyl sulfate: 0.2 wt%) and single-step silica nanofluid (0.1 wt%, size: 33-38 nm) were used and Pickering foams were prepared by mechanical agitation in the presence of different sand (comprised mainly of quartz with traces of clay), to mimic the effect of grain on foam stability. Interestingly, a varying stability exists in presence of sand. Thus, foam volume increased from 48 ml (without sand) to 58 ml when 1 wt% sand (of size approximate to 60-120 mu m) was added while it further reduced to 46 and 40 ml with 2 and 3 wt% sand, respectively. On the contrary, foam stability continuously reduced with increment in sand size (from 60 to 120 to 200-380 mu m), indicating unfavorable role of sand size on foam stability. Thus, sand production during oil recovery process is unfavorable for the stability of foam systems. The effect of sand concentration and size on foam properties was validated by interfacial tension and rheological measurements. Interfacial tension between CO2-nanofluid decreased till 1 wt% sand, suggesting favorable role of sand on CO2-nanofluid interaction. Similarly, CO2 foam showed maximum viscosity (72.8 mPa s) at 1 wt% sand (of size approximate to 60-120 mu m) while further increase in concentration (>1 wt%) and size (>120 mu m) reduced foam viscosity. These foams also exhibited viscoelastic characteristics with presence of both storage and viscous moduli. The solid-like nature of foam was least affected by the increase in deformational strain and foams exhibited dominating storage modulus over the range strain explored. Thus, the observation of this study can be used to optimize foam flooding in sandstone reservoirs which exhibit sand/fines production.

Automated summary

This study investigates the influence of sand grain (size and concentration) on the stability and properties of Pickering CO2 foam. The results show that the presence of sand grain has an unfavorable effect on foam stability under certain conditions. Additionally, sand grain size and concentration also affect the interfacial tension and rheological properties of the foam.