Investigation of geochemical interactions of carbon dioxide and carbonate formation in the Northwest McGregor oil field after enhanced oil recovery and CO2 storage

The Plains CO2 Reduction Partnership, one of the seven U.S. Department of Energy National Energy Technology Laboratory Regional Carbon Sequestration Partnerships, is conducting a carbon dioxide (CO2) huff ‘n’ puff (HnP) project in the Northwest McGregor oil field in North Dakota to determine the effects CO2 has on the productivity of the reservoir, wellbore integrity, and the carbonate formation into which the CO2 was injected. This paper outlines the approach and current observations derived from numerical modeling and laboratory simulations of potential geochemical reactions to evaluate the short-term risks for operations (e.g., porosity and permeability decrease) and long-term implications for CO2 storage via mineralization. The integration of data obtained during mineralogical analyses, fluid sampling, and laboratory experiments proved to be a key for the better understanding of the dynamic geochemical processes that happen in the reservoir after CO2 injection and was necessary for successful completion of the numerical modeling. Results of the numerical modeling suggest that the already acidic and highly saline environment (pH <4.5 and total dissolved solids ∼300,000 mg/kg) of the Northwest McGregor oil field should not experience any significant changes in mineralogy as a result of CO2 injection, especially in the near term, which correlates with the postinjection field geochemical analyses