Tracking Microstructure Variations of CO₂–hydrate Formation in Porous Sandstone from µCT Images During Cold CO₂ Injection

Depleted reservoirs are possible candidates for long-term CO₂ storage, but the risk of the Joule Thomson effect causing near-well cooling and hydrate formation under CO₂ injection is calling for an in-depth understanding of the process in porous media to avoid injection issues.Query Whereas much has been learned from detailed experimental studies on the micro-scale, challenges remain in how these observations upscale to the reservoir scale. In this study, we aim to provide a link between micro- and meso-scale—performing an in-situ core-flooding experiment in a micro-computed tomography (μCT) system, enabling repeated imaging of pore-scale structural evolution throughout a 24.5-cm-long, 3.7-cm-diameter sandstone core. Under controlled pressure and temperature conditions, full μCT scans were acquired at successive cooling steps during CO₂ injection. Hydrate formation initiated at 2 °C and revealed spatially variating microstructural—from patchy/finger-like structures to a fully reacted main hydrate “plug”, larger residual brine “channels”, a diffuse decrease in the amount of hydrate in the upper regions of the vertically oriented core and a spherical shaped zone devoid of hydrate directly under the injection point. Showcasing the higher degree of complexity that should be expected in larger-scale systems. With a relatively simple image processing workflow, our approach shows the feasibility of studying hydrate growth at micro-scale resolution over meso-scale volume with in-house μCT facilities.