(289e) Unveiling the CO2 Storage Resources of the St. Peter Sandstone and Everton Formation in the Illinois Basin

This study explores the Middle Ordovician St. Peter Sandstone and the Everton Formation within the Illinois Basin, highlighting their potential as significant geological storage reservoirs. In particular, the St. Peter Sandstone and Everton Formation emerge as promising targets for CO2 storage in southwestern Illinois, especially in areas where the Mt. Simon Sandstone is absent or has a low thickness. Through a detailed examination of their porosity, permeability, and spatial variation in thickness and modeling to support volumetric estimations, this research underscores the formations' resources for CO₂ storage and their role in climate change mitigation.

The St. Peter Sandstone Formation, characterized as a mature pure quartz arenite, spans the entirety of the Illinois Basin. Within the basin, the thickness of the St. Peter Sandstone varies significantly, ranging from approximately 33 to 656 feet (10 to 200 meters). This formation has undergone extensive diagenetic changes, including mechanical compaction and cementation. The Everton Formation, deposited in the early Middle Ordovician period, primarily consists of dolomite and sandstone intervals. The thickness of the Everton Formation varies, extending from less than 100 to about 125 feet (30 to 38 meters), and its presence is primarily confined to the southern regions of Illinois.

Porosity estimations and trends were derived from an analysis of approximately fifty wells in southern Illinois and over twenty wells in Indiana. To estimate permeability, a complex approach was adopted, involving the creation of a supervised machine learning algorithm. This algorithm was trained utilizing a dataset comprising core sample data alongside permeability estimations inferred from Nuclear Magnetic Resonance (NMR) log data and additional petrophysical logs, enabling the prediction of permeability across more than thirty wells. Subsequently, a rigorous geocellular model was developed and populated with porosity and permeability values that were geostatistically distributed. This modeling approach enabled the calculation of both bulk and pore volumes, facilitating a thorough evaluation of the potential storage resources within the St. Peter Sandstone and Everton Formation.

The porosity and permeability analyses conducted across these formations revealed a broad spectrum of values, with porosity figures ranging from less than 1% to upwards of 20%, and permeability rates spanning from less than 0.01 millidarcies to over 500 millidarcies. Significantly, this research uncovered a pronounced correlation between increasing depth and reduction in both porosity and permeability that can be attributed to compaction. Adapting methodologies from the DOE/NETL Carbon Storage Atlas (2015), the potential CO₂ storage resources within the St. Peter Sandstone and Everton Formation were calculated, factoring in geographical extent, stratigraphic thickness, and formation porosity, alongside adjustments for temperature and pressure variations. This analysis suggests a substantial sequestration potential, projecting prospective storage resources to range from 680 million tonnes to 7,300 million tonnes of CO₂ in southern Illinois for worst-case and best-case scenarios, respectively.

This research emphasizes the role of geological storage as a technology to lower atmospheric CO₂ concentrations, marking a critical step forward in combating climate change. Moreover, it highlights the St. Peter Sandstone and Everton Formation as indispensable components within a portfolio of carbon storage targets in the Illinois Basin. Significantly, the modeling indicates the southwest-central part of Illinois, particularly in Washington, Madison, Clinton, and Bond Counties, possesses reservoir properties within these formations that are suitable for CO₂ storage. This insight is critical for providing optionality in the development of CO₂ storage projects in the Illinois Basin that are not only geologically suitable, but also commercially attractive and publicly acceptable.