Demonstration of Secure CO2 Geologic Storage Associated with Enhanced Oil Recovery in the PCOR Partnership Region

The Regional Carbon Sequestration Partnerships (RCSP) Initiative developed by the U.S. Department of Energy National Energy Technology Laboratory has, since its inception in 2003, been one of the leading international applied research initiatives focused on proving the security and effectiveness of CO₂ geologic storage to support the widespread deployment of carbon capture and storage (CCS). The Plains CO₂ Reduction (PCOR) Partnership, one of seven regional partnerships within the RCSP program, is led by the Energy & Environmental Research Center (EERC) at the University of North Dakota. The aim of the PCOR Partnership is to foster the deployment of CCS in a large region of central North America covering nine U.S. states and four Canadian provinces.

The PCOR Partnership has applied an adaptive management (AM) approach to the main components of storage assessment: site characterization; technical risk assessment; modeling and simulation; and monitoring, verification, and accounting (MVA). The application of AM enables an iterative approach to storage assessment, with each assessment component informing parallel activities over the course of a project—for example, use of MVA data to refine predictive modeling efforts. Ultimately, the AM approach fosters the development of an integrated storage assessment, and this has formed the basis for applied research by the PCOR Partnership on storage associated with CO₂ EOR at the Bell Creek oil field in Montana, operated by Denbury Onshore, LLC.

The MVA program employed by the PCOR Partnership, in common with other storage projects, can be broadly divided between deeply focused and near-surface techniques. Deep focused techniques track the distribution and movement of injected CO₂ and check for any “out-of-zone” CO₂ migration beyond the intended storage reservoir or complex. Near-surface techniques include monitoring of shallow groundwater and soil gas to demonstrate the absence of impacts to sensitive environmental receptors resulting from CO₂ injection.

The deep focused MVA program at Bell Creek employed by the PCOR Partnership has built on routine injection and production data collected as part of CO₂ EOR operations. Casing-conveyed downhole pressure and temperature sensors, pulsed-neutron logs (PNLs) and 4-D seismic surveys are among the techniques focused on the reservoir, comprising a Lower Cretaceous age sandstone at a depth of 1370 m. Time-lapse seismic data have provided a means of successfully tracking CO₂ distribution in the relatively thin (9 m to 14 m thickness) reservoir and have enabled improved understanding of reservoir characteristics, for example, the nature of compartmentalization. PNLs have provided insights into the vertical distributions of CO₂ in the reservoir and assurance monitoring to show that out-of-zone migration has not occurred from over 3 million tonnes of associated CO₂ storage.

Near-surface monitoring techniques have demonstrated the inherent variability of shallow environmental systems and the associated challenges of defining baseline characteristics. However, anomalous data due to natural processes can be readily identified as resulting from natural processes (for example, through isotopic analyses), and the data sets acquired from Bell Creek show no evidence of impacts resulting from CO₂ injection.