(84e) Revitalize Conventional Legacy OIL Fields in North Dakota with Waterflooding and CO2 EOR

There are 280–630 MMbbl of incremental oil recovery potential through the use of tertiary CO₂ enhanced oil recovery (EOR) in 86 North Dakota unitized conventional oil fields (KLJ, 2014). A joint industry research program led by the Energy & Environmental Research Center (EERC) was established to investigate the effectiveness of implementing waterflooding and optimizing it as a precursor for CO₂ EOR and to develop cost-effective pathways for a legacy oil field, Foreman Butte Field, as a prototype for revitalizing the analogous conventional oil fields in North Dakota to prolong the operational lifetime of the fields with low carbon intensity.

A horizontal well was first drilled into the Flat Lake subinterval of the Foreman Butte Field in 2003, and wireline logs suggested a 12-foot section of limestone within the Flat Lake subinterval contained an average of 5% porosity with 70% hydrocarbon saturation (Nordeng, 2007). Production data from 40 subsequently drilled horizontal wells on 640-acre spacing exhibited rapid production declines and production of more water than oil without waterflooding. A legacy field like this typically lacks characterization data for detailed geologic modeling, so additional strategic characterization data were acquired to improve understanding of the reservoir and optimize production. The presence of the natural fracture networks from the newly collected cores confirmed in assessing this type of reservoir. Thus a high-efficiency fracture modeling approach, embedded discrete fracture modeling (EDFM), was used in numerical simulation to capture the complex fracture networks and heterogeneity of the reservoir. This approach helped to improve the accuracy of history matching and predict the performance of waterflooding and CO₂ EOR with higher confidence.

Implementing a waterflood after primary production usually presents the most cost-effective approach to increasing oil recovery in terms of additional oil produced per dollar of capital investment. The development of a CO₂ EOR project after waterflooding could further recover a significant volume of oil. Both water and CO₂ flooding experiments were conducted in this study, with results suggesting that a considerably higher oil recovery could be achieved by CO₂ EOR rather than waterflooding in this field. However, it would require much higher capital investment for surface facilities and CO₂ sourcing and transportation in the field application process.

North Dakota has permitted a few carbon capture and storage (CCS) projects where the captured CO₂ could be readily available for EOR purposes, but building pipeline systems accessible to those sources may also require obtaining new separate right-of-way agreements to the legacy field. Though the CO₂ sourcing, transportation of the sourced CO₂, and the expanded separation facilities for recycling the produced CO₂ pose a higher cost and could be offset by certain regulatory incentives, such as federal- and state-level tax credits and tax exemptions, a necessary economic evaluation with detailed geologic modeling and reservoir simulation studies can provide a basis for such project implementation.

This research program will generate new information to enable operators, investors, regulators, and other stakeholders to make informed decisions regarding the revitalization of North Dakota’s vast conventional oil resources using CO₂ capture and utilization techniques.