173-7 Developing a Novel Classification System for Confining Units in CCUS: A Case Study from the Michigan Basin

Session: Geologic Energy Resources and Storage for Now and the Future

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Abstract:

Carbon capture, utilization, and storage (CCUS) projects require rigorous evaluation of both storage and confining units. However, confining units are often under-characterized due to limited well penetrations and minimal industry interest, leading to a reliance on regional correlations and sparse petrophysical data.

Traditionally, a formation is designated as a confining unit if it contains lithologies with low porosity and permeability—such as shale, tight carbonates, or mudstones—and exceeds an arbitrary thickness threshold (e.g., >100 ft). Many assessments generalize these properties, grouping results across formations and assigning confining status based on a narrow set of parameters. This approach often ignores critical factors such as data availability and quality, regional continuity, facies variability, and internal heterogeneity. As a result, the assumption that all confining units provide equivalent seal potential is flawed, particularly for CCUS applications that require site-specific risk assessment.

This study presents a multi-scale framework for assessing and classifying confining units in the Michigan Basin, using the Eau Claire and Trempealeau formations as case studies. A comprehensive dataset was developed that includes lithologic and mineralogic descriptions, traditional petrophysical evaluations, core characterization, laboratory analyses, and legacy data. Each method was critically evaluated for its contribution to confining unit assessment, including data quality, applicability to site characterization, and scalability.

The Eau Claire and Trempealeau formations exhibit considerable variability in mineralogy, lithology, and petrophysical properties across the basin. These differences significantly affect their effectiveness as confining units. By quantifying these properties and assigning weighted values to their impact on seal quality, a classification system was developed to rank confining unit potential from high to low.

This approach moves beyond generalized or outdated criteria and provides a more realistic, data-driven method for assessing seal capacity. The resulting classification system supports improved site screening and risk evaluation for CCUS, waste isolation, and pressure containment applications, particularly in geologically complex basins.

This project is funded by the U.S. Department of Energy (DOE) under DE-FE0032368.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9755

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