CO2-Soluble, Nonionic, Water-Soluble Surfactants That Stabilize CO2-in-Brine Foams

Abstract

Several commercially available and a few experimental, nonionic surfactants were identified that are capable of dissolving in carbon dioxide (CO 2 ) in dilute concentration at typical minimum-miscibility-pressure (MMP) conditions and, upon mixing with brine in a high-pressure windowed cell, stabilizing CO 2 -in-brine foams. These slightly CO 2 -soluble, water-soluble surfactants include branched alkylphenol ethoxylates, branched alkyl ethoxylates, a fatty-acid-based surfactant, and a predominantly linear ethoxylated alcohol. Many of the surfactants were between 0.02 to 0.06 wt% soluble in CO 2 at 1,500 psia and 25 C, and most demonstrated some capacity to stabilize foam. The most-stable foams observed in a high-pressure windowed cell were attained with branched alkylphenol ethoxylates, several of which were studied in highpressure small-angle-neutron-scattering (HP SANS) tests, transient mobility tests using Berea sandstone cores, and high-pressure computed-tomography (CT)-imaging tests using polystyrene cores. HP SANS analysis of foams residing in a small windowed cell demonstrated that the nonylphenol ethoxylate SURFONIC V R N-150 [15 ethylene oxide (EO) groups] generated emulsions with a greater concentration of droplets and a broader distribution of droplet sizes than the shorter-chain analogs with 9-12 ethoxylates. The in-situ formation of weak foams was verified during transient mobility tests by measuring the pressure drop across a Berea sandstone core as a CO 2 /surfactant solution was injected into a Berea sandstone core initially saturated with brine; the pressure-drop values when surfactant was dissolved in the CO 2 were at least twice those attained when pure CO 2 was injected into the same brine-saturated core. The greatest mobility reduction was achieved when surfactant was added both to the brine initially in the core and to the injected CO 2 . CT imaging of CO 2 invading a polystyrene core initially saturated with 5 wt% KI brine indicated that despite the oilwet nature of this medium, a sharp foam front propagated through the core, and CO 2 fingers that formed in the absence of a surfactant were completely suppressed by foams formed because of the addition of nonylphenol ethoxylate surfactant to the CO 2 or the brine.

Understanding aqueous foam with novel CO2-soluble surfactants for controlling CO2 vertical sweep in sandstone reservoirs

“…Sagir et al (2014c, d) conducted pure CO 2 injection after surfactant solution flooding to mimic FAWAG with a new CO 2 -soluble surfactant using Berea cores, during which a mobility reduction factor of 3.1 was achieved. Similar results were demonstrated by Xing et al (2012) and McLendon et al (2014) relative to pure CO 2 injection on carbonate and sandstone cores. Recently, 80 cP of foam apparent viscosity was achieved by Chen et al (2015) in a 49-mD dolomite core with a switchable ethoxylated cationic CO 2 -philic surfactant.…”

“…Similar to WAGS, this method improves in situ foam generation, drastically lowers the injection costs, and reduces the loss of surfactant onto the rock surface due to adsorption. Xing et al (2012) and McLendon et al (2014) showed that the mobility reduction factor was around two, which was slightly higher than pure CO 2 injection on pre-saturated cores. In Le et al (2008), experimental and field scale simulation results show this is the most promising injection scenario which gave highest oil recovery and injectivity.…”

“…Later, further tests on a 1.2 Darcy glass bead pack and a 49-mD dolomite core gave apparent viscosities of foams as high as 390 and 100 cP, respectively (Chen et al 2015). Xing et al (2012) and McLendon et al (2014) measured the pressure drop across a Berea sandstone core as the CO 2 /surfactant solution was injected with selected branched ethoxylated CO 2 -soluble surfactants, which gave a weak foam with a mobility reduction factor around five. Through simulation with an analytical model, Rossen et al (2006) drew a series of conclusions concerning the optimal injection strategy for co-injection with conventional water-soluble surfactants, regarding longer gravity segregation length.…”

“…A review article from Eastoe et al (2006) told the story of small-molecule CO 2 -active surfactants, from fluorinated compounds to oxygenated amphiphiles. Xing et al (2012) screened solubility of several commercially available nonionic surfactants in CO 2 , and the most stable foams were obtained with branched alkylphenol ethoxylates which exhibited 0.01wt%-0.1wt% solubility in CO 2 . A lot of effort has put into obtaining low toxicity and low price CO 2 -soluble surfactants, of which non-fluorinated AOT (sodium bis(2-ethylhexyl)-sulfosuccinate) (Eastoe et al 2001;Liu and Erkey 2001) and nonionic surfactants Xing et al 2012) were of most interest.…”

“…Xing et al (2012) screened solubility of several commercially available nonionic surfactants in CO 2 , and the most stable foams were obtained with branched alkylphenol ethoxylates which exhibited 0.01wt%-0.1wt% solubility in CO 2 . A lot of effort has put into obtaining low toxicity and low price CO 2 -soluble surfactants, of which non-fluorinated AOT (sodium bis(2-ethylhexyl)-sulfosuccinate) (Eastoe et al 2001;Liu and Erkey 2001) and nonionic surfactants Xing et al 2012) were of most interest. Dhanuka et al (2006) noted that DOW Tergitol TMN 6 was an effective foaming agent characterized by stable, white, and opaque foams formed at 25°C and 345 bar.…”