Total oil-in-place estimates for the Bakken petroleum system range from 160 billion barrels (Bbbl) to over 900 Bbbl. Most estimates for primary recovery range from 3% to 12%, depending on reservoir characteristics. With such low primary recovery factors and such a large resource, small improvements in productivity could increase technically recoverable oil in the Bakken by billions of barrels. While the use of carbon dioxide (CO2) in conventional reservoirs is a widely applied and well understood practice, its use for EOR in tight oil reservoirs is a relatively new concept. The EERC is conducting a multidisciplinary research program with the ultimate goal of providing industry with insight regarding the potential to use CO2 for EOR in the Bakken and Three Forks Formations. This research program is being conducted in two phases.

Results of Phase I Efforts

Program Partners

Continental Resources
North Dakota Oil and Gas Research Program
Marathon Oil

Phase I of the Bakken CO2 Enhanced Oil Recovery and Storage Program began in 2012 and will be completed in 2013. The objective of this first phase is to use reservoir characterization and laboratory analytical data (e.g., core analyses, well logs, oil analyses, etc.) coupled with state-of-the-art modeling to examine the viability of using CO2 for EOR in the Bakken. Key results include the following:

  • CO2 extraction studies indicate that CO2 can remove over 90% of hydrocarbons from Bakken reservoir rocks and over 60% from Bakken shales in small-scale experiments.
  • In the Bakken, CO2 flow will be dominated by fracture flow—not significantly through the rock matrix. Fracture-dominated CO2 flow could essentially eliminate the displacement mechanisms responsible for increased recovery in conventional reservoirs.
  • Understanding the natural fracture network is essential because fractures will play a dominant role in CO2 flow through the Bakken. A variety of techniques, including scanning electron microscopy (SEM), ultraviolet fluorescence (UVF), and standard optical microscopy, have shown promise with respect to identifying and describing microfractures.
  • Results of initial dynamic simulation modeling of an area in Dunn County suggest that CO2-based EOR is technically possible.
  • The results of the modeling efforts underscore the importance of having detailed knowledge of both the natural fracture network and induced hydraulic fractures when the effectiveness of CO2 injection for EOR in the Bakken is predicted.

Remaining Questions

While results of the Phase I activities are encouraging, there is no clear-cut answer regarding the most effective approach for using CO2 to improve Bakken productivity. Some of the key questions that remain after the Phase I work include the following:

  • How far into the matrix can CO2 penetrate Bakken (Lower and Middle) rocks at larger scales? What is the time frame of that penetration? Does CO2 affect matrix porosity and permeability?
  • Is it possible to identify natural microfractures in the Lower Bakken shale?
  • How would CO2-based EOR and related pressure changes affect reservoir permeability?
  • How much injected CO2 can be recycled, and how much is permanently stored in the formation?
  • How well do the lessons learned on Bakken rocks translate to the Three Forks Formation?

With these questions in mind, the EERC is planning a second phase of the Bakken CO2 Enhanced Oil Recovery and Storage Program. The objective of Phase II is to refine the techniques and approaches developed under Phase I and apply them to the design and implementation of an injection test in the field.