Abstract
Wettability alteration in Unconventional Liquid Reservoirs (ULR) can improve fracture treatment performance and consequently oil recovery by changing capillary forces when shifting intermediate and oil-wet reservoirs to water-wet. Altering wettability can be reached while fracking the formation by adding surfactants, in proper concentrations, to frac water favoring the process of imbibition. This study combines the effect of wettability and IFT alteration by surfactants and the corresponding impact on spontaneous imbibition in ULR from the Permian Basin by conducting contact angle experiments, IFT measurements, and spontaneous imbibition experiments to evaluate and compare the efficiency of anionic and nonionic surfactants in altering wettability and recovering hydrocarbons from siliceous side-wall core at reservoir temperatures.
Contact angle (CA) experiments were performed, using the captive bubble method, for original wettability characterization and to measure wettability alteration on ULR core at reservoir temperature. Anionic and nonionic surfactants, at field concentrations, were tested. The results showed that all surfactants change the CA at the concentration used. However, anionic surfactant showed better results in lowering contact angles. In addition, IFT measurements were performed, using the pendant drop method, with anionic and nonionic surfactants and reservoir crude oil at reservoir temperature. Anionic surfactant reduced better IFT than nonionic surfactants, and both surfactants performed better than regular frac fluid without any surfactant.
Spontaneous imbibition experiments were performed using modified Amott cells, at reservoir temperatures, to investigate the capability of anionic and nonionic surfactants of imbibing ultralow permeability siliceous shale cores. Oil recovery was measured with time and computed tomography (CT) scan methods were used to gauge the performance of these surfactants in improving oil recovery. To measure penetration numerically and trace movement in real time, frac fluids containing surfactants were mixed with a dopant salt. The results showed that anionic surfactant was better on recovering oil from shale core, which agrees qualitatively with the previous results where anionic surfactant showed the lowest contact angles and IFT. However, both, anionic and nonionic, surfactants were better in displacing liquid hydrocarbons and had higher penetration magnitudes compared to frac water without surfactant. From the results obtained, it can be concluded that the addition of surfactants in frac fluids can improve oil recovery by wettability alteration and IFT reduction, being anionic surfactant the one that showed lower CA and IFT, better imbibition and higher oil recovery compared to nonionic surfactants in these ULR from the Permian Basin.
