Evaluation of an Amphoteric Surfactant for CO2 Foam Applications:AComparative Study

摘要

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 resumespreferential flow through thief zones,demonstrating the need for higher foam stability.Thus,longer foamhalf-lives or stability is one of the key factors determining the success of any foam-field application.Theability of surfactants to stabilize foam depends on the gas type.Many surfactants that form stable foam withnitrogen(N2)and hydrocarbon gas are not able to form a stable foam with carbon dioxide(CO2),whichcould 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 toidentify surfactants that can enhance the stability of CO2-foam.This work investigates an amphoteric surfactant,which is commercially available and priced similarlyto other commonly used EOR foamers,for its ability to stabilize CO2-foam.Static stability and dynamiccoreflood tests were conducted at high pressure and high temperature conditions,where CO2 remained in thesupercritical state.The performance of the amphoteric surfactant was compared with another good foameron the basis of foam stability and strength,both in bulk and in porous media.Dynamic adsorption testswere conducted to compare the adsorption of amphoteric and anionic surfactants on both sandstone andcarbonate 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 andnonionic surfactants evaluated in this study.In the presence of oil,foam stabilized by the amphotericsurfactant exhibited the longest half-life in static tests.However,the amphoteric surfactant performedsimilarly to other surfactants with nitrogen or hydrocarbon gas.Compared to other surfactants,foamstabilized by the amphoteric surfactant remained stable and exhibited higher apparent viscosity at high foamqualities.Foam stability at higher qualities improves the performance of SAG process as it can lengthen thegas 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 oilfieldapplications due to potential for high retention.Based on systematic evaluation,our work demonstrates theunique ability of amphoteric surfactants to enhance the stability of CO2-foams at reservoir conditions.