Evaluation of an Amphoteric Surfactant for CO2 Foam Applications: A Comparative Study

Abstract

In a surfactant-alternating-gas (SAG) injection, stable foams form viscous barriers and divert fluids, thereby providing conformance for enhanced oil recovery (EOR). Once foam decays, injected gas resumes preferential flow through thief zones, demonstrating the need for higher foam stability. Thus, longer foam half-lives or stability is one of the key factors determining the success of any foam-field application. The ability of surfactants to stabilize foam depends on the gas type. Many surfactants that form stable foam with nitrogen (N2) and hydrocarbon gas are not able to form a stable foam with carbon dioxide (CO2), which could be due to the presence of low pH environment in CO2 floods, relatively high solubility of CO2 in water, and CO2 permeability through liquid films. To improve the performance of CO2 floods, it is imperative to identify surfactants that can enhance the stability of CO2-foam. This work investigates an amphoteric surfactant, which is commercially available and priced similarly to other commonly used EOR foamers, for its ability to stabilize CO2-foam. Static stability and dynamic coreflood tests were conducted at high pressure and high temperature conditions, where CO2 remained in the supercritical state. The performance of the amphoteric surfactant was compared with another good foamer on the basis of foam stability and strength, both in bulk and in porous media. Dynamic adsorption tests were conducted to compare the adsorption of amphoteric and anionic surfactants on both sandstone and carbonate rock surfaces. Ways to mitigate surfactant adsorption on rock surfaces were studied. In terms of CO2-foam stability, the amphoteric surfactant performed much better than the anionic and nonionic surfactants evaluated in this study. In the presence of oil, foam stabilized by the amphoteric surfactant exhibited the longest half-life in static tests. However, the amphoteric surfactant performed similarly to other surfactants with nitrogen or hydrocarbon gas. Compared to other surfactants, foam stabilized by the amphoteric surfactant remained stable and exhibited higher apparent viscosity at high foam qualities. Foam stability at higher qualities improves the performance of SAG process as it can lengthen the gas cycle and reduce the amount of surfactant needed, a beneficial outcome when water supply is limited. We found the adsorption of amphoteric on carbonate rock to be much lower than on sandstone rock. Compared to ionic and nonionic surfactants, amphoteric surfactants are usually avoided for oilfield applications due to potential for high retention. Based on systematic evaluation, our work demonstrates the unique ability of amphoteric surfactants to enhance the stability of CO2-foams at reservoir conditions.

CO2 Foam Behavior in Carbonate Rock: Effect of Surfactant Type and Concentration

“…It is possible that the lower apparent viscosity in the low-foam-quality regime, which causes this curve shape, is due to the dissolution of some of the CO 2 into the injected water (thus reducing the foam quality and the total flow velocity at the same time), but corrections were already made for the solubility of the CO 2 during the calculation of the gas injection rate. Others have also seen this type of concave curve shape, both with CO 2 in sandstone ,,, and in limestone , and also in tests in capillary tubes. ,, It is known that gas diffusion through the bubble films is significantly higher for CO 2 than for N 2 , which would lead to more rapid foam coarsening. This coarsening, along with the lower pH produced by the CO 2 dissolution, explains the generally weaker foams observed with CO 2 .…”

“…Others have also seen this type of concave curve shape, both with CO 2 in sandstone ,,, and in limestone , and also in tests in capillary tubes. ,, It is known that gas diffusion through the bubble films is significantly higher for CO 2 than for N 2 , which would lead to more rapid foam coarsening. This coarsening, along with the lower pH produced by the CO 2 dissolution, explains the generally weaker foams observed with CO 2 . If this weakening effect becomes more significant at lower foam qualities, this would result in the concave curve shape.…”

“…This coarsening, along with the lower pH produced by the CO 2 dissolution, explains the generally weaker foams observed with CO 2 . 49 If this weakening effect becomes more significant at lower foam qualities, this would result in the concave curve shape.…”

Research on foaming agents for gas flooding in medium-temperature and high-salinity clastic reservoirs

“…Surfactants with strong adsorption have higher losses in the formation process. Zhou Jimin suggested that the static adsorption of the foaming agent should be at least 1mg/g or less [6]. In this paper, the adsorption of FM51 on the surface of quartz sand was measured.…”

CO2-Soluble Nonionic Surfactants for Enhanced CO2 Storage via In Situ Foam Generation

“…26,27 Zhou et al evaluated amphoteric surfactants to enhance the stability of CO 2 -foams at reservoir conditions. 29 Rossen et al addressed challenges associated with foam-assisted CO 2 storage where the surfactant is added to the aqueous phase. 28 To the best of our knowledge, this work represents the first laboratory assessment of CO 2 -soluble surfactants to improve CO 2 storage.…”