Sorensen, James A. (Energy & Environmental Research Center) | Braunberger, Jason R. (Energy & Environmental Research Center) | Liu, Guoxiang (Energy & Environmental Research Center) | Smith, Steven A. (Energy & Environmental Research Center) | Hawthorne, Steven A. (Energy & Environmental Research Center) | Steadman, Edward N. (Energy & Environmental Research Center) | Harju, John A. (Energy & Environmental Research Center)
The Bakken petroleum system is an unconventional oil resource with over 300 billion barrels (Bbbl) of oil in place. However, primary recovery is typically below 10%. To improve Bakken recovery factors, many companies are considering the use of carbon dioxide (CO2) for enhanced oil recovery (EOR). Since 2012, a research program to evaluate the potential for CO2-based EOR in the Bakken and attendant storage of CO2 for greenhouse gas emission mitigation has been conducted by the Energy & Environmental Research Center (EERC) with broad-based financial support from producers, service companies, government organizations, and CO2 suppliers. The ultimate goal of the program is to provide stakeholders with new knowledge that can be applied toward the design and execution of a pilot injection and production test in a Bakken reservoir. From 2012 to 2014, program activities were conducted on samples of key Bakken lithofacies, including the shales, from several wells. These resulted in the generation of reservoir characterization data (e.g., core analyses, well logs, oil analyses, etc.) and laboratory experimental data on CO2 permeation and hydrocarbon mobility. Detailed evaluations of porosity and permeability, including naturally occurring microfractures that will serve as key pathways for CO2 migration, were conducted using several techniques, including focused ion beam scanning electron microscopy, dual-energy x-ray computerized tomography (CT) and micro-CT scanning, ultraviolet fluorescence, and standard optical microscopy. Data generated from laboratory-scale CO2 penetration and hydrocarbon extraction experiments indicate that diffusion is a primary mechanism driving fluid mobility. Fluid mobility rates within the matrix were also quantified for each key lithofacies. The characterization and experimental data were incorporated into modeling efforts, including simulations of a variety of injection and production schemes. The best-case simulation results showed over 50% improvement in oil production. While the production response was predicted to be delayed compared to EOR in a conventional reservoir, patience may be rewarded by substantial increases in the estimated ultimate recoveries of Bakken wells. Application of the findings to the U.S. Department of Energy methodology for estimating CO2 EOR and storage capacity suggests that 4 Bbbl to 7 Bbbl of incremental oil could be produced from the Bakken, resulting in a net storage of 1.9 to 3.2 billion tons of CO2.