Rapid In Situ Neutron Tomography and X-ray Imaging of Vapor Condensation in Fractured Sandstone.

Despite their diverse applications, experimental studies on multi-phase flow with phase change in fractured porous media are rare in the literature. In this study, water condensation of vapor in a fractured sandstone is investigated by means of 3D rapid in situ neutron tomography (30 s per tomogram). A water vapor and air mixture is injected at a constant rate, and the accumulation of condensed water is characterized through neutron tomography. Both phase-contrast and absorption-contrast X-ray tomography are jointly used to study the microstructure of the sandstone and measure the morphology of the splitting crack. The interplay between the pore matrix and fissure on the spatiotemporal distribution of water is studied through a combination of these techniques. The condensed water accumulates at the inlet boundary and gradually diffuses into the sample. Once the extracted crack is correctly aligned with with the neutron tomographies (registered), a propensity is seen for water to accumulate in small crack openings close to the cracks and migrate into the porous matrix predominantly due to the capillary effect. When enough liquid water condenses beyond a critical content, the air pressure in the crack transfers it into the porous matrix. This results in higher water content away from the crack. The water front propagates both along and transversely to the crack at a linear rate, albeit at different velocities. The final water distribution is found to be the result of two competing processes: condensation, occurring predominantly in the crack, and diffusion toward the matrix due to the capillary effect, as well as the pressure acting on the bottom of the sample and the crack walls. [ABSTRACT FROM AUTHOR]