A Nonconventional CO2-EOR Target in the Illinois Basin: Oil Reservoirs of the Thick Cypress Sandstone
- Univ. of Illinois at Urbana-Champaign, IL (United States)
The Illinois State Geological Survey (ISGS) identified and quantified nonconventional carbon dioxide (CO2) enhanced oil recovery (EOR) target opportunities within the thick Cypress Sandstone in the Illinois Basin. Up to 60 m thick Cypress Sandstone bodies define a northeast-southwest fairway that is approximately 230 km long and 100 km wide across the central portion of the Illinois Basin. These sandstones commonly contain relatively thin oil reservoirs and were found to have associated underlying residual oil zones (ROZs). The presence of a thick brine aquifer underlying the ROZ and high vertical permeability results in characteristic low primary oil recovery caused by excessive brine production from the aquifer. Nonconventional CO2-EOR in these oil reservoirs are expected to require more CO2 to produce a unit of oil compared to conventional CO2-EOR. Consequently, nonconventional CO2-EOR will have a higher storage component and offer a unique storage opportunity. An integrated approach of detailed site-specific geologic reservoir characterization, three-dimensional geocellular modeling, and reservoir simulation of multiple development cases at Noble Field was employed to determine development strategies for CO2-EOR and storage. The findings of Noble Field research were leveraged to assess the regional CO2-EOR and associated storage resource within the nonconventional reservoirs of the thick Cypress Sandstone in the Illinois Basin. Regional characterization shows that thick, multistory fluvial facies of the Cypress Sandstone exhibits porosity from 15% to 21% and horizontal and vertical permeability up to approximately 0.98 µm2 (1,000 mD). Oil saturation indicators screened from well records and well log analyses were used to map 27 brownfield and greenfield ROZ prospects with residual oil saturation (SOR) values ranging from 14 to 35%. ROZ thickness varies from 2.7 to 21.6 m (9 to 71 ft). The 27 Cypress Sandstone ROZ prospects have approximately 290.8 million m3 (1.8 billion barrels) of oil in place. Specific CO2-EOR development strategies depend on the goals of the project (prioritizing EOR performance vs. storage performance and NCNO) and geologic setting (brownfield vs greenfield), and company’s business strategies (economic metrics). Nevertheless, applying two unique development strategies derived from reservoir simulation of the depleted main pay zone and ROZ in the Cypress Sandstone at Noble Field, 31.1 million m3 (196 million barrels) of oil is estimated to be recoverable using the 80-acre blanket WAG development strategy (which favors EOR and economic metrics, but is carbon positive) whereas 21.3 million m3 (144 million barrels) of oil is estimated to be recoverable using the 40-acre high CO2 injection rate development strategy (which favors storage and economic metrics and results in net carbon negative oil production). Storage of CO2 associated with EOR in these ROZ prospects alone, not accounting for associated main pay zones, underlying brine formation, or intervals adjacent to or between prospects, is estimated to be up to 10.4 billion tonnes using the latter development strategy.
- Research Organization:
- Univ. of Illinois at Urbana-Champaign, IL (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy and Carbon Management (FECM)
- DOE Contract Number:
- FE0024431
- OSTI ID:
- 1545654
- Report Number(s):
- DOE-UofI-24431
- Country of Publication:
- United States
- Language:
- English
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