The influence of CO 2 -transformed iron oxide grain coatings on the frictional stability and transport properties of sim
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ORIGINAL ARTICLE
The influence of CO2-transformed iron oxide grain coatings on the frictional stability and transport properties of simulated faults in sandstones Chaoyi Wang
. Derek Elsworth
Received: 6 December 2019 / Accepted: 22 October 2020 Springer Nature Switzerland AG 2020
Abstract Carbon sequestration involves long-term containment of CO2 in ideally sealed reservoirs. However, CO2 migration can weaken rocks and faults by geochemical alteration, elevate risks of seismic hazards, and loss of inventory. Recent studies show that CO2 bleaching can alter the iron oxide grain coating of sand-sized quartz in sandstones, which may impose a significant influence on frictional stability and permeability evolution of faults in sandstones. This study investigates the influence of iron oxide grain coatings via coupled shear-flow experiments on uncoated, hematite-coated, and CO2-transformed goethite-coated synthetic sand gouge. Shear strength, frictional stability, healing/relaxation, and shear-parallel permeability are measured in velocity-stepping and slide-hold-slide loading modes. Hematite-coated sand exhibits the highest shear strength, followed by goethite-coated and uncoated sand. All samples, both C. Wang (&) D. Elsworth Department of Energy and Mineral Engineering, EMS Energy Institute, and G3 Center, The Pennsylvania State University, University Park, PA, USA e-mail: [email protected] Present Address: C. Wang Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA D. Elsworth Department of Geosciences, Pennsylvania State University, University Park, PA, USA
coated and uncoated, show similar residual shear strength. Frictional stability measurements suggest hematite-coated sand may undergo potential seismic slip (negative (a - b) values); goethite-coated sand is aseismic (positive (a - b) values) but features higher frictional healing and relaxation. Shear-parallel permeability enhances during initial shear in all samples, followed by a sharp decline after the peak strength, except for goethite-coated sand, for which permeability reduction is moderate. SEM characterizations preand post-shear suggest that the competitive liberation, transport, and clogging of coating particles and shearproduced wear products can be an important mechanism in permeability evolution. Keywords CO2 alteration Grain coating Fault breaching Fault permeability Frictional stability
1 Article Highlights • Novel miniaturized double direct shear (DDS) apparatus enables coupled shear-flow experiments. • Goethite-coated sand features lower friction but higher permeability and rates of relaxation and healing than hematite-coated sand. • Clogging caused by clustering of coating material and transport of wear products may significantly reduce permeability.
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Geomech. Geophys. Geo-energ. Geo-resour. (2020)6:65
2 Introduction Geological carbon sequestration injects carbon dioxide (CO2) into aquifers or reservoirs. It is a promising technology for removing atmospheric CO2 while repl
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