Dissolution-Driven Permeability Reduction of a Fractured Carbonate Caprock

Area of Science:

• Geochemistry
• Geology
• Carbon Sequestration

Background:

• Caprocks are crucial for confining CO2 during geologic carbon sequestration.
• Geochemical reactions within caprocks can alter the permeability of potential CO2 leakage pathways.

Purpose of the Study:

• To investigate the impact of geochemical reactions on fractured carbonate caprock permeability.
• To understand the mechanisms controlling permeability evolution in CO2-exposed caprocks.

Main Methods:

• High-pressure core flow experiment using a fractured carbonate caprock specimen.
• Analysis using electron microscopy, synchrotron-based X-ray diffraction imaging, and microbeam Ca K-edge X-ray absorption near edge structure.
• X-ray computed tomography to visualize rock mass changes and fracture closure.

Main Results:

• Fracture permeability decreased significantly during the experiment.
• Calcite dissolution, not precipitation, was observed.
• Mobilization of host rock particles clogged the fracture, and dissolution caused mechanical closure.
• Significant rock mass loss occurred in preferential flow paths.

Conclusions:

• Permeability reduction in fractured carbonate caprock is driven by dissolution-induced particle mobilization and mechanical closure, not secondary mineral precipitation.
• This demonstrates a nonintuitive inverse relationship between dissolution and permeability evolution in such systems.
• Findings are critical for assessing the long-term integrity of caprocks in carbon sequestration.