Wettability Alteration of the Oil-Wet Carbonate by Viscosity-Augmented Guar Galactomannan for Enhanced Oil Recovery

The exhaustion of oil reserves encourages enhanced oil recovery (EOR) from mature oil fields. Hence, several polymers, surfactants, and nanofluids are developed, improving the recovery of additional oil from such mature wells. However, increased cost, harsh reservoir environment, and lower stability presents a significant challenge in developing a multicharacteristic injecting fluid, addressing all the past issues during oil recovery. Besides, almost all the earlier studies have demonstrated only higher viscosifying properties of polymers and rarely inspected the polymers' capabilities in altering surface wettability. In the present study, a guar galactomannan solution called viscosity-augmented guar (VAG) was prepared by the heat treatment of crude guar and removal of insoluble impurities. The resulting VAG solution demonstrated stable viscosity at higher temperatures (65 °C) under changing reservoir conditions. Additionally, the wettability alteration potential of VAG was evaluated by investigating the changes in the contact angle of oil-wet carbonate surfaces when treated with the VAG solution. Experimental results showed a reduction in the contact angle of the oil-wet surface to 81° after treatment with VAG from original surface values of 102° with the brine solution, indicating wetting transition from oil-wet to intermediate water-wet conditions. Moreover, the Fourier transform infrared spectroscopy and thermogravimetric analysis revealed the VAG's ability to displace oil components from the oil-wet surface. Additionally, emulsification studies showed a birefringence phenomenon of oil-water emulsions with VAG, reinforcing a proposed mechanism for wettability alteration by forming structured films oriented around the oil droplets in emulsions. The EOR potential of VAG showed an additional oil recovery of 7.31% of original oil in place compared to 3.59 and 2.98% by commercial polymers like xanthan gum (XGU) and partially hydrolyzed polyacrylamide, respectively. Overall, the favorable results of the VAG polymer are promising for promoting EOR, and for the first time, this study shows a polymer behavior in altering surface wettability of reservoir rocks and adds up different dimensions for future studies.