Title: Assessment of Carbonated Brine Injection as Low-risk Strategy for Geologic Carbon Storage

The main objective of this early-phase research was to evaluate the techno-economic feasibility and risk associated with combined brine and CO₂ storage in SWD wells using brine dissolution in the North Dakota portion of the Williston Basin. Three simulation studies were conducted to investigate: (1) CO₂ phases at different conditions, (2) wellbore compatibility, and (3) long-term storage fate in reservoir. (1) A simple reservoir model and injection simulations were created using data to represent the BEST (brine extraction and storage test) site, an operational SWD facility located near Watford City, North Dakota. The pressure evolution caused by CO₂ comingled in produced water injectate in a layer cake reservoir was then modeled while tracking aqueous CO₂ throughout the project. The salinity of the injection water, the salinity of the reservoir brine, and the amount of dissolved CO₂ comingled in the injection water were varied. (2) A wellbore corrosion model was performed using the CO₂ concentrations selected based on the reservoir modeling to examine the carbonated produced water impact on wellbore. (3) Reactive transport modeling was conducted with the optimal CO₂ concentration for this injection site to study the rock-fluid interactions and CO₂ fate in the reservoir. Results suggest that CO₂ dissolved in produced water can be injected without appreciably increasing subsurface pressure or leakage risks. Pressure buildup was found to vary with salinity but not with CO₂ mass fraction. Simulation results show that lower CO₂ percent mass fraction leads to a higher amount of CO₂ that can be dissolved at a higher injection salinity. Furthermore, the long-term goal of dissolution trapping in a traditional carbon storage project is accomplished from the start, mitigating risks associated with potential migration of buoyant CO₂, so long as the reservoir pressure and temperature are used to determine the maximum mass fraction of the dissolved CO₂.