Stratigraphic and Structural Controls on a Carbon Sequestration Reservoir in Shelby County, Alabama

Abstract

This study evaluates the suitability of the fold-and-thrust belt in Shelby County, Alabama, for carbon storage, focusing on its structural and lithological integrity. Orogenic events in the region have thickened the strata, forming unique structural features known as mushwads (Malleable, Unctuous SHale, Weak-layer Accretion in a Ductile duplex), which can reach several thousand feet in thickness. The Lower Paleozoic strata, primarily the Knox Group, are identified as potential reservoir rocks due to their fractured carbonate composition. As determined of this study, the porosity and permeability of these crystalline carbonates are highly dependent on fractures resulting from orogenic processes.

Characterization was conducted using data from three regional wells: ARCO/Anschutz #1, Westover #1, and Westover #2. These wells provided 49 thin sections for analysis, along with associated cuttings. To assess the regional structure, three seismic lines were acquired, capturing both strike and dip profiles. Additionally, X-ray diffraction analysis of the Copper Ridge Dolomite, a Knox Group member selected as the target formation, provided geochemical insights.

A potential sampling bias is acknowledged due to the inability to create thin sections from fractured samples. However, given the samples of this study, tight carbonates, both observed and calculate, prove as a hurtle for long term carbon dioxide storage. Further research and methods of the OASIS (Optimizing Alabama’s CO₂ Storage in Shelby County) project group needs to be conducted to prove the viability of carbon capture and storage in Shelby County, Alabama.