Impact of CO2 Storage Time on CO2-Brine Relative Permeability in Berea Sandstone

Abstract

Prolonged exposure of reservoir sandstone to injected CO2 may alter rock–fluid interactions and potentially affect multiphase flow behavior. While geochemical effects of CO2 storage have been widely studied, the time-dependent impact on CO2–brine relative permeability remains insufficiently quantified. This study evaluates whether extended CO2–brine–rock interaction modifies relative-permeability behavior in quartz-rich Berea sandstone under representative reservoir conditions. Core samples were aged in CO2-saturated brine for one and three months at 1500 psi and 150 °F, alongside a brine-only control to isolate CO2-specific effects. Pre- and post-aging characterization included mineralogical analysis using X-ray diffraction (XRD), pore-structure evaluation via mercury intrusion capillary pressure (MICP) and NMR, and routine core analysis for porosity and permeability. Wettability behavior was evaluated by estimating contact angle from CO2–brine interfacial tension (IFT) measurements using Neumann's equation of state, while brine chemistry was quantified using inductively coupled plasma–optical emission spectroscopy (ICP-OES) and titration techniques. Relative-permeability behavior was estimated by deriving Brooks–Corey parameters from capillary-pressure data in combination with machine-learning predictions trained on published CO2–brine datasets. Together, the two approaches provide complementary indirect estimates for assessing aging sensitivity. Results indicate minimal geochemical and petrophysical alteration following CO2 exposure within the time frame considered. Minor mineralogical changes were detected, including the disappearance of trace siderite cement and slight reduction in chlorite clay content; however, overall mineral composition remained within experimental uncertainty, suggesting geochemical stability of the quartz-rich matrix. For the CO2-exposed samples, porosity increased by only 0.17–0.59 percentage points, while permeability declined modestly (~6–12%), with no evidence of severe pore clogging or structural compaction. Brine chemistry analysis confirmed limited dissolution consistent with the low abundance of reactive mineral phases. Critically, the pre- and post-aging CO2–brine relative-permeability estimates remained closely overlapped. Brooks–Corey/Burdine parameterization and machine-learning predictions showed no resolved systematic shift beyond the resolution and uncertainty of the two indirect methods. These findings support use of a time-invariant relative-permeability description as a practical first-order assumption during early-stage CO2 injection in comparable quartz-rich sandstone systems, when advective multiphase flow is active, while longer-term reactive-transport effects should be evaluated separately. This work provides an integrated experimental assessment of time-dependent CO2 exposure on relative permeability, combining mineralogical, petrophysical, capillary-pressure, wettability, and fluid-chemistry analyses within a unified framework. The study provides an experimentally constrained assessment of a modeling assumption frequently used in CO2-storage simulation and quantitative evidence that no systematic aging-related relative-permeability change was resolved in quartz-dominated Berea sandstone over the tested 1–3 month period.