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Conference Proceeding

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In large scale subsurface injection of carbondioxide (CO ) as obtainable in carbon sequestration programs and in environmentally friendly hydraulic fracturing processes (using supercritical CO ), long term rock-fluid interaction can affect reservoir and seal rocks properties which are essential in monitoring the progress of these operations. The mineralogical components of sedimentary rocks are geochemically active particularly under enormous earth stresses, which generate high pressure and temperature conditions in the subsurface. While geomechanical properties such as rock stiffness, Poisson's ratio and fracture geometry largely govern fluid flow characteristics in deep micro-fractured formations. Simulation results suggested that influx-induced mineral dissolution/precipitation reactions within clay-based sedimentary rocks can continuously close micro-fracture networks, though injection pressure and effective-stress transformation first rapidly expand the fractures. This experimental modelling research investigated the impact of in-situ geochemical precipitation on conductivity of fractures under geomechanical stress conditions. Bulk rock geomechanical hardness was determined using Vickers' micro-indentation. Differential pressure drop data across fractured composite core were also measured with respect to time over a five day period. This was used in estimating the conductivity of the artificially fractured cores with 25 μm-bore microtubings embedded. Three experimental runs per sample types were carried out in order to check the repeatability of observed changes. The results showed that most significant diagenetic changes in shale rocks after flooding with CO -brine, reflect in the effluent fluid with predominantly calcium based minerals dissolving and precipitating under experimental conditions. Micro-indentation results suggested slight reduction in the hardness of the shale rocks and this reduction appears dependent on diagenetic quartz content. Estimated fracture conductivity indicated that reactive transport of dissolved minerals can occlude micro-fracture flow paths, thereby improving caprock seal integrity with respect to leakage risk under CO sequestration conditions. 2 2 2 2

Publication Source (Journal or Book title)

Energy Procedia

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