Investigation on a novel polymer with surface activity for polymer enhanced CO2 foam flooding

Abstract

CO2 foam flooding has been widely researched due to its outstanding capacity to mitigate viscous fingering, gravity override and unfavourable injectivity profile, which enables CO2 flooding to be more applicable and economical. Yet the primary concern of CO2 foam flooding is the instability or rupture of bubbles under harsh reservoir condition, thus a great number of investigations have been conducted to address this issue. Through adding polymer into surfactant solution, Polymer Enhanced Foam (PEF) technique could stabilize foams due to dramatical increase in apparent viscosity. However, hydrolysed polyacrylamide (HPAM), the most used polymer, will greatly reduce the foamability of surfactant solution, which means sufficient foam may not be generated and sweep efficiency remains poor. What's more, HPAM is sensitive to salinity and temperature, affecting its behaviour in reservoirs. This research aims to study the performance of PEF using AOS as the foaming agent which is enhanced by polymer (HPAM/a novel polymer with surface activity, named AVS). One on hand, because of the surface active group on the molecular chain, this polymer can thicken surfactant solution without greatly affecting its foamability; on the other hand, phenyl group, sulfo group and other functional groups are introduced into polymer molecule, making AVS more salt and temperature tolerance.The results demonstrated: 1) Under harsh condition (high salinity and temperature), viscosities of AVS solution were higher than that of HPAM; 2) The surface tensions between AVS solution and CO2 were lower, which was attributed to the introduction of surface activity group;3) The foaming factors of AOS/AVS were remarkable in a wide range of brine salinity (1000-50000 ppm) and temperature (25 °C-60 °C); 4) At high pressure (2000psi), the blockage of CO2 foam enhanced by AVS was encouraging and satisfactory; 5) During core flooding, if under same test conditions, tertiary oil recoveries obtained by AVS/AOS were 5% -7% higher than that of HPAM/AOS. It is believed that this novel polymer has great potential in application of polymer enhanced CO2 foam flooding under various reservoir conditions.