Two-phase flow visualization under reservoir conditions for highly heterogeneous conglomerate rock: A core-scale study for geologic carbon storage.

Geologic storage of carbon dioxide (CO2) is considered a viable strategy for significantly reducing anthropogenic CO2 emissions into the atmosphere; however, understanding the flow mechanisms in various geological formations is essential for safe storage using this technique. This study presents, for the first time, a two-phase (CO2 and brine) flow visualization under reservoir conditions (10 MPa, 50 °C) for a highly heterogeneous conglomerate core obtained from a real CO2 storage site. Rock heterogeneity and the porosity variation characteristics were evaluated using X-ray computed tomography (CT). Multiphase flow tests with an in-situ imaging technology revealed three distinct CO2 saturation distributions (from homogeneous to non-uniform) dependent on compositional complexity. Dense discontinuity networks within clasts provided well-connected pathways for CO2 flow, potentially helping to reduce overpressure. Two flow tests, one under capillary-dominated conditions and the other in a transition regime between the capillary and viscous limits, indicated that greater injection rates (potential causes of reservoir overpressure) could be significantly reduced without substantially altering the total stored CO2 mass. Finally, the capillary storage capacity of the reservoir was calculated. Capacity ranged between 0.5 and 4.5%, depending on the initial CO2 saturation.

Exploring pore water biogeochemical characteristics as environmental monitoring proxies for a CO2 storage project in Pohang Basin, South Korea.

Biogeochemical parameters of pore waters, including dissolved organic matter, nutrients, sulfate, alkalinity, and chloride are explored as convenient and sensitive proxies to monitor the CO2 geological storage sites. Five sites for a CO2 storage project in the Pohang Basin of the East Sea in South Korea were investigated for the pre-injection biogeochemical conditions of these sites. Higher dissolved organic carbon (~36 mg L-1), chromophoric and fluorescent dissolved organic matter, nutrients, and alkalinity were observed in a fluvially affected acoustic blanking site with geological faults. A general increasing downcore trend of measured DOM parameters, nutrients, and alkalinity with depth was found at the acoustic blanking site affected by riverine runoff with significant correlations among the parameters (R2: ~0.4-0.8), highlighting the impact of geological features and external inputs on the downcore biogeochemical properties. The results presented in this study suggest that DOM could be utilized as a robust and complementary biogeochemical parameter.