Simulation case studies of aqueous formate solution for geological carbon storage

Abstract

Carbon storage in geologic formations has been considered an important technology that reduces the carbon intensity of industrial processes based on fossil fuels. Carbon capture and storage (CCS) conventionally uses carbon dioxide (CO2) as a carbon carrier. However, various shortcomings of the conventional CCS are related to the physical properties of CO2, such as low carbon density at low to moderate pressure, low mass density, low viscosity, immiscibility with water, and corrosivity. In particular, CO2 injection often results in inefficient use of pore space in the formation under geophysical heterogeneities.This paper presents case studies of using aqueous formate solution as carbon-bearing water for geological carbon storage. Properties of aqueous formate solutions were measured. Experimental results showed that the formate solubility in 102,600-ppm NaCl + CaCl2 brine ranged from 30 wt% to 35 wt% between 25 and 75 °C. Viscosities of 30 wt% formate solutions in the brine were approximately 12 cp at 25 °C, 5 cp at 50 °C, and 3 cp at 75 °C with Newtonian behavior.Numerical reservoir simulations were performed for an aquifer and an oil reservoir. Simulation results consistently showed that the formate injection case resulted in more stable fronts of oil and water displacement. The more stable fronts yielded the oil recovery and carbon storage that were insensitive to the injectant breakthrough. This is a substantial advantage of using formate as a carbon carrier for controlling the risk of CCS associated with the permeability heterogeneities and their impact on the subsurface flow regime.The case study of enhanced oil recovery and carbon storage in an oil reservoir showed that the net present value (NPV) of the formate injection case would be equivalent to that of the CO2 injection case when the cost of CO2 electrochemical reduction (ECR) into formate was $269/t-CO2 for year 20. The breakeven cost of CO2 ECR for the formate injection case was $575/t-CO2 for year 20. Although the estimated CO2 ECR costs are sensitive to many factors, they are not unrealistically higher than the current costs of CO2 ECR reported in the literature.