Utilization of Surfactants for Enhancing the Recovery of Medium-Viscosity Crude Oil From Low-Permeability Carbonate Reservoirs

The use of enhanced oil recovery (EOR) techniques can pose a significant challenge in scenarios where the reservoir rock displays low permeability and the oil exhibits high viscosity, leading to inadequate oil recovery. To address this challenge, one potential solution is the application of surfactant-based EOR. This approach entails formulating surfactant solutions to align with specific reservoir conditions, with the objective of improving oil extraction efficiency.

In this dissertation, a novel class of Alfoterra surfactants, which are based on alcohol propoxy sulfates, were experimentally evaluated for their potential application in EOR. The performance of the anionic Alfoterra surfactants was compared to that of other surfactant types, including anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB), and nonionic t-Octylphenoxypolyethoxyethanol (Triton X-100). The critical micelle concentration of the surfactants was initially determined, followed by an evaluation of the aqueous stability of surfactants at reservoir temperature and under a wide range of salinities. Subsequently, the impact of stable surfactant formulations on interfacial tension (IFT) and rock wettability was examined. Results indicated that the presence of surfactants and increasing salinity both resulted in significant reductions in oil-water IFT. Additionally, all surfactant formulations effectively altered the wettability of carbonate rock from intermediate to more water-wet conditions. Further, surfactant adsorption onto a carbonate-rock adsorbent was evaluated, revealing a tendency for anionic surfactants to adsorb more onto the adsorbent compared to other surfactant types. Finally, core flooding tests involving medium-viscosity oil recovery from tight carbonate samples demonstrated EOR values of 25.7% to 39.4% of original-oil-in-place (OOIP) above that achieved through regular waterflooding. Further, adjusting the salinity of the injected seawater raised the EOR value to 43.3% of OOIP.