Performing Surfactant-Polymer (SP) flooding in High Salinity and High Temperature (HS-HT) conditions - up to 297 g/L TDS formation brine and 105°C-120°C - is challenging, both as regards the products selection and the implementation of the experimental workflow, from the selection tests of the surfactants and polymers to the corefloods, which need to be performed in an oxygen-free environment to reproduce field test conditions. In this work, we show our recent lab developments of SP formulations for different HS-HT conditions for limestone and sandstone reservoirs, both in terms of efficiency of chemicals in such conditions, and technical aspects. Specific polymers and surfactants have been selected based on chemical stability and efficiency. The main surfactants have been chosen in the ethoxylated carboxylates and ethoxylated sulfonates series, and they have been formulated in order to reach optimal salinities in the 80-130 g/L TDS range. Special attention has been paid to the impact of the divalent cations on the physicochemical behavior. These surfactant formulations were tested in corefloods using SAV10 as thermally stable polymer and taking into account the change in physicochemical phase behavior with oil saturation. Corefloods were carried out in oxygen-free conditions as well as pipettes study and surfactant thermal stability tests, since polymer and surfactants degrade in presence of oxygen at such high temperature. Our results show a good efficiency of the formulations based on ethoxylated sulfonates on limestones (Residual oil saturation (Sorc) ~9%) with a retention of 0.26 mg/g of rock, whereas formulations based on ethoxylated carboxylates performed well on quartz sandpack (Sorc ~ 1-5%). The latter however gave lower recovery and high retention on limestones. This work describes the development workflow and testing procedures to operate chemical EOR in very harsh conditions. As a result, we demonstrate that efficient HS-HT SP formulations are now available.

Novel CO2-soluble surfactants are designed for generating stable CO2 emulsion/foam at high temperature (110 °C) and high salinity (220 g/L NaCl). The novel surfactants only consist of alkyl chains and amine heads without any fluorine, silicon, or poly alkyl-oxide groups and outperform the surfactants in literature regarding the solubility, thermal stability, and emulsifying ability in harsh conditions. 0.2 wt % of the novel surfactants are soluble in 220 g/L NaCl brine at pH ≤ 8 from 20 to 120 °C and are soluble in CO2 at high temperature (110 °C) and relatively low pressure (91 bar). The surfactants are thermally stable at 110 °C and pH = 4 under anaerobic conditions. Strong CO2 emulsion can be readily generated in bulk and in porous media at 25–110 °C and 150 bar. Unlike the common surfactants in literature, the performance of the novel surfactants can be profoundly enhanced by salinity and temperature. The strategy for designing these novel molecules and tuning the surfactant formulation for emulsion-assisted CO2 enhanced oil recovery (EOR) is discussed as well.

CO2 emulsion/foam is a promising method for controlling the mobility and improving the volumetric sweep efficiency in CO2 enhanced oil recovery (CO2-EOR) process. Recently, amine surfactants attract the attention of the researchers as CO2 emulsifiers/foamers, because of their switchable property: the surfactants are nonionic and CO2 soluble at high pH, and are cationic and water soluble at low pH. However, the efficiency of the commercial switchable amine surfactants is usually suppressed at high salinity (> 200 g/L TDS) and temperature (> 100 °C). Thus, novel switchable alkyl-amine surfactants are designed in house based on the hydrophilic and CO2-philic balance for rapidly generating strong and stable CO2 emulsions at high salinity and high temperature. These novel surfactants are evaluated and compared to a commercial one with respect to the solubility in brine and CO2, and emulsifying ability in bulk and in porous media at high temperature, high pressure and high salinity. The novel surfactants show outstanding performance: soluble in 220 g/L NaCl brine at pH≤8 from room temperature to 120 °C, soluble in CO2 at relatively low pressure (91 bar) and high temperature (110 °C). The surfactants are thermally stable at 110 °C and pH=4 in the absence of O2. Strong CO2 emulsion/foam is observed in both bulk test and in silica sandpack with 0.2 (wt)% of the surfactant in brine. Additionally, the apparent viscosity of the CO2 emulsion/foam at 110 °C is significantly higher than that at lower temperatures. Comparing to the commercial surfactants, the CO2 emulsion/foam is stronger and generated faster by the novel surfactants. These novel surfactants can be synthesized using commercially available feeds and simple industrial processes. Thus, the novel surfactants are promising for generating the CO2 emulsion/foam, especially in the hot and salty carbonate reservoirs.