56-5 Mineralogical and Microstructural Controls on CO2 Trapping Potential in the Silurian Lockport Dolomite, Appalachian Basin

Abstract:

Carbonate formations are attractive targets for subsurface carbon storage, yet mineralogical heterogeneity and diagenetic overprinting complicate prediction of pore evolution and fluid-rock interaction. The Silurian Lockport Dolomite in Wayne County, West Virginia, Appalachian Basin, is being evaluated as a potential reservoir within the Tri-State CCS Hub CarbonSAFE project (DOE Award DE-FE0032441). This study integrates bulk X-ray diffraction (XRD; n = 10) and field emission gun scanning electron microscopy with energy-dispersive spectroscopy (FEGSEM-EDS; n = 15) on continuous core from well API #4709901549 to characterize mineral composition, diagenetic fabrics, and pore-network architecture.

The interval is dominated by non-stoichiometric dolomite with subordinate calcite, quartz, anhydrite, and trace pyrite, and is subdivided into three zones: (1) a dolomite-dominated upper zone (dolomitization index 97-100%), (2) a transitional zone containing the most calcite-rich and Fe-dolomite-rich samples, and (3) a mixed calcite-dolomite lower zone. These zones reflect six diagenetic stages, from early marine conditions through reflux dolomitization and meteoric dissolution to burial and late-stage modification.

FEGSEM-EDS imaging reveals a complex pore system comprising intercrystalline, fracture-controlled, dissolution-enhanced, and inter-plate microporosity. Stylolites are pervasive and exert dual control on reservoir quality, locally occluding porosity through clay- and pyrite-rich residues while enhancing permeability along dissolution seams that act as fluid pathways.

These diagenetic features control mineral reactivity and pore accessibility, with implications for CO₂-brine-rock interaction. Calcite dissolution may buffer fluid acidity and release Ca²⁺, whereas reactions involving dolomite and Fe-dolomite may promote mineral trapping through secondary carbonate precipitation. These results demonstrate that diagenetic heterogeneity drives spatial variability in reservoir quality and reactive potential within the Lockport Dolomite and highlight the importance of sedimentological and microstructural characterization in evaluating carbonate reservoirs for subsurface fluid storage.

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