Hydrothermal flow experiments of single-pass injection of CO2-charged brine were conducted on nine dolomite cores to examine fluid-rock reactions in dolomite reservoirs under geologic carbon sequestration conditions. Post-experimental X-ray computed tomography (XRCT) analysis illustrates a range of dissolution patterns, and significant increases in core bulk permeability were measured as the dolomite dissolved. Outflow fluids were below dolomite saturation, and cation concentrations decreased with time due to reductions in reactive surface area with reaction progress. To determine changes in reactive surface area, we employ a power-law relationship between reactive surface area and porosity (Luquot and Gouze, 2009). The exponent in this relationship is interpreted to be a geometrical parameter that controls the degree of surface area change per change in core porosity. Combined with XRCT reconstructions of dissolution patterns, we demonstrate that this exponent is inversely related to both the flow path diameter and tortuosity of the dissolution channel. Even though XRCT reconstructions illustrate dissolution at selected regions within each core, relatively high Ba and Mn recoveries in fluid samples suggest that dissolution occurred along the core's entire length and width. Analysis of porosity-permeability data indicates an increase in the rate of permeability enhancement per increase in porosity with reaction progress as dissolution channels lengthen along the core. Finally, we incorporate the surface area-porosity model of Luquot and Gouze (2009) with our experimentally fit parameters into TOUGHREACT to simulate experimental observations.
Bibliographical noteFunding Information:
We thank Rick Knurr for the fluid and rock analyses, Shijun Wu and Chunyang Tan for creating Fig. 1 b–c, Scott Alexander for assistance during field sample collection, Anette von der Handt for the electron microprobe analyses, and the Micromeritics Analytical Services Lab in Norcross, GA, USA for the BET analyses. We also thank two anonymous reviewers for their helpful reviews. The XRCT data and images were produced at the X-ray Computed Tomography Laboratory in the Department of Earth Sciences, University of Minnesota (UMN), which is funded by a UMN Infrastructure Investment Initiative Grant. Research support was provided by the Initiative for Renewable Energy and the Environment ( IREE ), a signature program of the Institute on the Environment at UMN and by the US Department of Energy (DOE) Geothermal Technologies Program under Grant Number DE-EE0002764 . M.O.S. thanks the George and Orpha Gibson endowment for its support of the Hydrogeology and Geofluids Research Group. Any opinions, findings, conclusions, or recommendations in this material are those of the authors and do not necessarily reflect the views of the DOE or IREE.
- Damköhler number
- Dolomite dissolution
- Fluid-rock reaction
- Porosity-permeability relationship
- Reactive surface area
- X-ray computed tomography