Modifying the Wettability of Sandstones Using Nonfluorinated Silylation: To Minimize the Water Blockage Effect

Multiphase fluid flow characteristics of a reservoir rock, such as capillary pressure, displacement efficiency, relative permeability, and saturation distribution are substantially influenced by the wettability state of the rock. Being able to change the affinity of the rock toward different fluid phases present in the formation has implications in various petroleum applications (e.g., CO2 geo-sequestration, EOR, gas production). In this study, silylation of sandstone core samples using nonfluorinated compounds is accomplished using supercritical CO2 as a solvent and carrier. This approach is cost-effective and less environmentally sensitive compared to other approaches which use fluorinated silylation reagents. By using small molecules to only change the wettability characteristics of core samples without altering other parameters (e.g., rock pore structure) noticeably, the effects of wettability alteration alone on multiphase flow (i.e., relative permeability) can be identified. Spontaneous imbibition tests were conducted on Gray Berea sandstone before and after silylation treatment, which showed a diminished rate of water uptake in the post-treatment sample. The wettability alteration caused by this functionalization and its impact on multiphase flow characteristics were analyzed using core flooding tests. The experimental results show that supercritical CO2-based (scCO2-based) silylation changes the wettability of the formation from strongly water-wet to intermediate gas-wet. Core flooding tests showed that the effective permeability for the water phase was significantly increased, resulting in higher water removal from the rock matrix. Furthermore, the relative permeability for the gas phase (in this study, CO2) at residual water saturation is higher after treatment. Such an outcome confirms that the change in wettability could be beneficial in geological CO2 storage as well as gas production.