Permeability, porosity, and mineral surface area changes in basalt cores induced by reactive transport of CO₂‐rich brine

Abstract

Four reactive flow‐through laboratory experiments (two each at 0.1 mL/min and 0.01 mL/min flow rates) at 150°C and 150 bar (15 MPa) are conducted on intact basalt cores to assess changes in porosity, permeability, and surface area caused by CO2‐rich fluid‐rock interaction. Permeability decreases slightly during the lower flow rate experiments and increases during the higher flow rate experiments. At the higher flow rate, core permeability increases by more than one order of magnitude in one experiment and less than a factor of two in the other due to differences in preexisting flow path structure. X‐ray computed tomography (XRCT) scans of pre‐ and post‐experiment cores identify both mineral dissolution and secondary mineralization, with a net decrease in XRCT porosity of ∼0.7%–0.8% for the larger pores in all four cores. (Ultra) small‐angle neutron scattering ((U)SANS) data sets indicate an increase in both (U)SANS porosity and specific surface area (SSA) over the ∼1 nm to 10 µm scale range in post‐experiment basalt samples, with differences due to flow rate and reaction time. Net porosity increases from summing porosity changes from XRCT and (U)SANS analyses are consistent with core mass decreases. (U)SANS data suggest an overall preservation of the pore structure with no change in mineral surface roughness from reaction, and the pore structure is unique in comparison to previously published basalt analyses. Together, these data sets illustrate changes in physical parameters that arise due to fluid‐basalt interaction in relatively low pH environments with elevated CO2 concentration, with significant implications for flow, transport, and reaction through geologic formations.

A review of geochemical–mechanical impacts in geological carbon storage reservoirs

“…123 A value of R = 1.2 × 10 −8 m s −1 118,124 was employed for this purpose. Notably, similar trends in dissolution behavior are reported for both fractured media (red arrow) 25,110,118,125 and in porous media (green arrow), 110,117,119,126 and thus offer a potentially robust relationship to predict transport parameter alteration and related changes in mechanical properties across highly diverse physical flow field structures.…”

“…[133][134][135][136][137] In carbonate-rich cores, CO 2 injection often results in carbonate dissolution, pore widening, and increased permeability. 117,126 In contrast, for a fractured oolitic limestone, the increase in permeability was shown in two stages; initially, there was a period of slow permeability increase resulting from an increase in pore connectivity, and next, wormhole breakthrough was observed across the sample, as evidenced by a large and sudden increase. 118 Such a range of behavior is widely observed in the literature, indicating the high degree of complexity between pore alteration and transmission of fluids.…”

“…Dissolution patterns as a function of Péclet and Damhöler numbers from different experiments reported in fractured media (dark symbol) and porous media (open symbol), modified by Szymczak and Ladd and Garcia‐Rios et al . The Smith et al .…”

“…Changes in pore structure, together with the feedback between dissolution and flow that creates preferential flow paths in carbonate systems, directly affect permeability and other continuum‐scale transport properties . In carbonate‐rich cores, CO 2 injection often results in carbonate dissolution, pore widening, and increased permeability . In contrast, for a fractured oolitic limestone, the increase in permeability was shown in two stages; initially, there was a period of slow permeability increase resulting from an increase in pore connectivity, and next, wormhole breakthrough was observed across the sample, as evidenced by a large and sudden increase .…”

Permeability Prediction in Rocks Experiencing Mineral Precipitation and Dissolution: A Numerical Study

“…To date, there have been many studies on the microstructural and permeability variations of rocks during mineral precipitation and/or dissolution (e.g., see a recent study in Luhmann et al, , and the references therein). These studies can be grouped into two categories: laboratory experiments and pore‐scale numerical simulations.…”