Fluid segregation and chemical compaction in deep-seated rocks: A combined experimental and digital rock physics approach

概要

To understand the elementary processes of fluid segregation in texturally equilibrated rocks, we synthesized C–H–O fluid bering quartzite having 1.9–18.0% fluid in volume fraction and XCO2 = 0–0.44 at 1 GPa and 900 °C. The microstructure of the obtained run products was captured by the scanning electron microscope and synchrotron radiation X-ray computed microtomography (SRμCT). In chapter 1, we focus on the observation of the capsule-scale fluid segregation (CFS) which was identified by the heterogeneity in porosity distribution in the obtained quartzite and quartzite retaining much lower porosity (~0.3%) than added fluid fraction. Because CFS occurred irrelevantly to the expected thermal gradient in the capsule, we assumed the driving force of CFS as the pressure difference between fluid rich and poor domains invoked by the different poroelastic response under a stress change. We estimated the flux of the dissolved SiO2 transport through thin fluid tubules along the grain edges. A porosity-evolution model was applied to the formation of the syn-metamorphic veins in schists and fluid segregation in subducting eclogite to deduce the time-scale of the poroelastic cementation. In chapter 2, we focus on the grain-scale fluid pools retained in the quartzite which was formed by grain-scale fluid segregation (GFS) during grain growth. Through the digital rock physics approach, I investigated the three-dimensional pore structure using the Pore Network Model (PNM) to show the distinct difference between CO2-free and CO2-bering samples. Permeability was computed by using image subvolumes obtained by SRμCT, which showed an agreement with the laboratory measurements. By analyzing the computed fluid velocity, I found a subvolume which has high permeability even at low connected porosity. By combining the experimental observation and the computed results, I discussed the effect of GFS and the specific surface area on permeability

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