Pore-Scale dynamics of wettability alteration for modified salinity waterflooding

Modified salinity waterflooding is a promising technique in the field of Enhanced Oil Recovery (EOR) that has demonstrated improved oil recovery at both core and field scales. The most significant mechanism behind this enhanced recovery method is the alteration of wettability, wherein the rock surface changes from an oil-wet state to a more water-wet state. However, the understanding of how wettability alteration, a fluid-rock interaction process, affects continuum scale processes is currently limited. This PhD thesis investigates the complex dynamics of modified salinity water injection in carbonate rock and its implications for oil mobilization, focusing on various aspects of the process in three main chapters.
Chapter 2 develops a pore-scale reactive multi-component two-phase flow and transport model to study water injection in carbonate rock. The model uses a surface complexation model for brine/calcite interactions and employs Direct Numerical Simulation of Navier-Stokes equations to describe the two-phase flow in porous media. The study explores the impact of brine composition, injection sequence, matrix connectivity, and injection rate on pore-filling sequence and sweep efficiency. It reveals that contact angle modification controls displacement processes, and the distribution of residual oil is significantly affected by wetting conditions, pore connectivity, and injection rate. Changing brine composition has a significant impact on oil displacement.
Chapter 3 analyzes imbibition dynamics in a fractured medium using the Direct Numerical Simulation of Navier-Stokes equations. The study considers factors like wettability, viscosity ratio, injection rate, and interfacial tension on mass exchange between matrix and fracture. It identifies two regimes of imbibition: co-operative (co-current) before wetting phase breakthrough and counter-current afterward. Cooperative imbibition exhibits higher displacement efficiency, while counter-current imbibition is slower. Lower fracture injection rates improve displacement efficiency, and higher wettability and interfacial tension enhance wetting fluid penetration into the matrix.
Chapter 4 focuses on changing the wetting state of the porous matrix to enhance oil mobilization in fractured media. By injecting water with wettability-determining elements (WDE), this shift in wettability improves imbibition, consequently enhancing displacement efficiency in oil-wet or weak water-wet matrices. Computational fluid dynamics simulations are used to study the transport of WDE in a fractured porous medium at the pore scale. The results indicate anomalous transport of WDE, with complex behavior influenced by diffusive transport and capillary-induced advection. WDE flooding is shown to be more efficient in oil mobilization under secondary flooding.
The thesis provides a comprehensive understanding of the pore-level dynamics of water injection in carbonate rock, the factors influencing imbibition in fractured media, and the role of wettability alteration in improving oil recovery. These findings have implications for both environmental remediation and enhanced oil recovery processes.