Mojtaba Norouzisadeh PhD Thesis Defense

Abstract

Trapping fluid in porous media by capillary forces is critical in many subsurface processes, such as carbon capture and storage in deep saline aquifers, groundwater remediation, and enhanced oil recovery in petroleum reservoirs. In such processes, wettability properties near the three-phase contact region are crucial in deciphering trapping mechanisms and the long-term stability of trapped droplets. However, the rock wettability and, consequently, the multiphase flow can be altered by a change in pore water physico-chemical properties (pH, salinity) and interfacial physical and physico-chemical properties. For instance, in low-salinity water injection for enhanced oil recovery, a trapped oil phase in a pore may be more easily remobilized due to wettability alteration. The dissolution of carbon dioxide in the aquifer can change the wettability and trapping capacity and storage security. Mineral surface wettability is traditionally described via contact angles, measured visually in the lab experiments. This approach does not reflect well the effective wettability alteration due to the changes in the system properties such as pH and salinity. Alternatively, the wettability of the system can be estimated via the intermolecular interactions.

The inter-molecular interaction for the three-phase contact region is studied through the different components of the disjoining pressure. The disjoining pressure comprises Van der Waals (VDW), electric double layer (EDL), and structural interaction. The role of the geometry of the domain close to the contact is often ignored in the literature. In this study, we investigated the role of wedge-shaped geometry of the contact region for the VDW in the literature. In the case of EDL, we solved the Poisson-Boltzmann (P-B) equation in two dimensions to evaluate the role of the three-phase contact region on the inter-molecular interactions. In addition, the charge interactions on the domain surfaces is often neglected in the literature in the EDL evaluation. Here, we considered the interaction of the charges on the domain boundaries by coupling the P-B with a surface complexation model (SCM). We validated the scheme’s implementation and studied the electrostatic interaction for a quartz/water/air system. The results show the dependency of the electrostatic interaction on the contact angle and charge regulation that becomes important close to the contact. In addition, the results show a change in surface energy due to electrostatic forces.

Finally, we developed a physically-rooted lubrication model for thin films to model wettability alteration. The model replaces the concept of the contact angle by accounting for inter-molecular forces, including van der Waals, electric double layer, and hydration potential through a disjoining pressure. Unlike other approaches, we introduce a slope-dependent disjoining pressure that originates from the assumption of wedge-shaped geometry. The model has been thoroughly verified and used to investigate the role of salinity and pH on wettability. We find out that the slope-dependent disjoining pressure and the precursor film thickness alter the stability of the spreading. Future work will focus on integrating the lubrication model in a two-phase flow simulator and studying the effect of wettability in a geological porous medium.