The foaming behavior of a CO₂-soluble, viscoelastic diamine surfactant in porous media

Date

2018-05

Authors

Ramadhan, Galang Bintang

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Abstract

Aqueous foam has been demonstrated through laboratory and field experiments as an effective conformance control mechanism for gas enhanced oil recovery and carbon sequestration operations. The use of a polymer as an additive to an aqueous foam has been suggested to increase the viscosity of the foam liquid phase. This viscosification of the liquid phase improves the foam conformance performance by increasing the foam apparent viscosity and reducing the rate of foam bubble coalescence. This study explores the use of worm-like micelle (WLM) as an alternative viscosifying agent to polymer. We utilized a cationic, amine-based surfactant; whose micelle transforms from spherical conformation to WLM at an elevated salinity. Another distinguishing feature of this surfactant is its ability to dissolve in supercritical carbon dioxide (CO₂). The delivery of surfactant in the gaseous phase may alleviate injectivity issue around the injection well, typically associated with high viscosity polymer-surfactant solution. Additional potential advantages of WLM over polymer include reversible shear degradation, reduced filtration in low permeability formations and resistance to extreme temperature and salinity. This study investigates how the presence of WLM structures affect the transient foam behavior in microfluidic porous media model, sand pack, and limestone core. In these porous media, we performed various foam floods with two liquid phase salinities: low salinity (15 wt. % NaCl or below) associated with spherical-shaped micelle and high salinity (20 wt. % NaCl or above) associated with WLM. The microfluidic experiments were conducted at 55 psi back pressure and 22°C. In these experiments, the DTM surfactant was solubilized in the liquid phase. Foaming experiments of two DTM salinities (5 wt. % NaCl vs. 20 wt. % NaCl) revealed that the DTM foam with the lower salinity liquid phase produced a finer foam texture. The DTM foam with the higher salinity liquid phase possesses a higher foam apparent viscosity, despite its coarser texture. The high salinity DTM foam also exhibited better stability. The sand pack (~3.5 Darcies permeability) experiments were conducted at 1700 psi back pressure and 40°C. In these experiments, the DTM surfactant was solubilized in the gaseous phase (CO₂). We compared the foaming behavior of two DTM salinities (15 wt. % vs. 20 wt. % NaCl) in co-injection and water-alternating injection (WAG) strategies. In co-injection, we observed an earlier onset of strong foam generation and a more rapid rate of apparent viscosity buildup in the higher salinity DTM case. In WAG, we observed a strong foam generation delay in the higher salinity DTM case due to severe gas fingering. The rate of apparent viscosity buildup of the DTM high salinity case was higher in WAG experiments. The limestone core (~80 mDarcies permeability) experiments were conducted at 1700 psi back pressure and 40°C. We compared the foaming behavior of two DTM salinities (15 wt. % vs. 20 wt. % NaCl) in co-injection and water-alternating injection (WAG) strategies. In the WAG experiments, we performed a comparison between DTM delivery in the gaseous phase vs. DTM delivery in the liquid phase. We were not able to generate strong foam in the co-injection and WAG foam floods when the DTM was delivered in the gaseous phase. A strong foam was generated in the WAG flood where the DTM was delivered in the liquid phase. We propose that the lack of strong foam development, when DTM was delivered in the gaseous phase, is due to insufficient DTM protonation

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