Abstract
Aiming at improving the stability of Supercritical CO2 (SC-CO2) foam in high temperature and salinity reservoirs, a kind of betaine surfactant, Hexadecyl Hydroxypropyl Sulfo Betaine (HHSB), was screened to stabilize SC-CO2 foam. The properties of SC-CO2 foam were improved at elevated temperature and pressure. The effects of surfactant concentration, temperature, pressure and salinity on film drainage rate were measured to explore the stability of SC-CO2 foam. The results showed that an increase of surfactant concentration, pressure and salinity can decrease film drainage rate and enhance the foam stability, which was attributed to the increase of surfactant adsorption at the gas–liquid interface. The performance of SC-CO2 foam formed by HHSB was improved and the tolerant temperature was up to 100 °C. 1-D core flooding experiments indicated that compared with Coinjection of Surfactant and Gas (CSG) method the SC-CO2 foam generated through Surfactant-Alternative-Gas (SAG) method had lower foam strength but better in-depth migration capacity. The high temperature and pressure 3-D sand showed that in Water-Alternative-Gas (WAG) case CO2 broke early through the high permeability layers. In SAG case, SC-CO2 foam can improve the macroscopic sweep efficiency by reducing the CO2 mobility.
Highlights
CO2 flooding has been becoming a popular EOR method in the low-permeability reservoirs (Ghasemi et al, 2018; Patil et al, 2018)
When the foaming agents were injected into the reservoir, the surfactant solutions would suffer from adsorption and dilution, leading to reduction of effective concentration of foam agents (Chen and Zhao, 2015)
It can be seen that the surfactant concentration has little effect on foaming volume, which ranged from 500 mL to 600 mL as surfactant concentration was increased from 0.03% to 1%
Summary
CO2 flooding has been becoming a popular EOR (enhanced oil recovery) method in the low-permeability reservoirs (Ghasemi et al, 2018; Patil et al, 2018). The adsorption of surfactant at the interface will lead to some surface properties, such as surface viscosity, surface elasticity and surface tension These surface properties will affect the lamellae stability. Higher surfactant adsorption and lower interfacial tension will reduce the formation of open holes at the interface, which will increase the coalescence rate of SC-CO2 foam (Golemanov et al, 2008). Under high temperature and pressure, the change of chemical properties of CO2 will inevitably affect the application of CO2 foam in oil reservoirs (Holt et al, 1996). Based on the above problems, the drainage rate and interfacial tension of SC-CO2 foams were explored as a function of different parameters, including temperature, pressure, salinity and surfactant concentration. Because oil can be very detrimental to foam, all the work has been carried out in the absence of oil
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