Circulars 601 and 602: Assessing the Cypress Sandstone for Carbon Dioxide-Enhanced Oil Recovery and Carbon Storage

The Illinois State Geological Survey has published an assessment of the Cypress Sandstone for carbon dioxide-enhanced oil recovery and carbon storage. 

Part I, published as Circular 601, focuses on characterizing the Cypress Sandstone reservoir at Noble Field in Richland County, Illinois, which is the most productive oil field in the fluvial valley-fill facies of the Cypress in the Basin. Approximately half of the cumulative oil production from the field is attributed to the Cypress Sandstone (with the remainder attributed to commingled production from older formations). As part of the reservoir characterization, the geology of the Cypress Sandstone, its historical oil production, and the properties of the oil reservoir were examined. This contribution is part of a research project to assess the valley-fill Cypress for the presence of residual oil zones (ROZs) and the potential for nonconventional carbon dioxide (CO₂)-enhanced oil recovery (EOR), meaning CO₂-EOR that includes geologic storage of CO₂ as a significant component of the process. This study also provides the foundation for geocellular modeling (see Circular 602) and future reservoir simulations of nonconventional CO₂-EOR within the Cypress Sandstone at Noble Field. Additionally, we have documented the process of using indirect indicators to identify a possible ROZ. These results will serve as an analog for characterizing the geological parameters relevant to improving oil production from and identifying ROZs in similar thick sandstone deposits elsewhere in the Basin.

Part II, published as circular 602, leveraged the geologic characterization of Circular 601 to develop a geocellular model that represents the static reservoir properties (porosity and permeability) of the Cypress Sandstone at Noble Field in Richland County. This model will be used to create hypothetical CO₂-EOR injection simulations to determine whether, and under what conditions, the reservoir and its underlying ROZ could add to incremental oil production at the field. Geologic characterization played a key role in model development. It was necessary to clearly delineate the contact between the thick fluvial sandstone interval and the overlying shaley estuarine interval so that a geostatistical analysis could isolate and detect the anisotropy and transitional behavior within each element. In addition, this new understanding of the sedimentology and depositional environment provided context for inferring interwell characteristics and small-scale features that were believed to have a substantial impact on fluid flow without producing a strong signal on geophysical logs. Combining a model based on spontaneous potential logs with a model based on neutron-density porosity logs resulted in a model that properly represented the distribution of depositional (sandstone and shale) and digenetic (calcite cement) geologic features that control fluid flow.

Both circulars, authored by by Nathan D. Webb and Nathan P. Grigsby, are available as digital downloads from the University of Illinois' IDEALS repository: Circular 601, Assessing the Cypress Sandstone for Carbon Dioxide-Enhanced Oil Recovery and Carbon Storage: Part I—Reservoir Characterization of Noble Oil Field, Western Richland County, Illinois, and Circular 602, Assessing the Cypress Sandstone for Carbon Dioxide-Enhanced Oil Recovery and Carbon Storage: Part II—Leveraging Geologic Characterization to Develop a Representative Geocellular Model for Noble Oil Field, Western Richland County, Illinois