Impact of CO₂ Storage Time on the Physicochemical and Mechanical Properties of Sandstone Formations: Insights for Long-Term CCS Applications

Carbon Capture and Storage (CCS) is a critical technology for mitigating CO₂ emissions and combating climate change. However, ensuring the long-term stability and integrity of subsurface formations used for CO₂ storage remains a major global challenge, as the formations of interest may be exposed to CO₂ for hundreds or even thousands of years. This study addresses this challenge by evaluating the impact of CO₂ storage time on the petrophysical, chemical, and geomechanical properties of Berea sandstone, a commonly used analog for saline aquifers. The objective of the research is to assess early-stage alterations in sandstone properties during CO₂ exposure, providing insights for predictive modeling and long-term CCS performance assessments. By understanding these early transformations, we aim to offer a clearer picture of the implications for long-term storage, enhancing CCS monitoring and strategy optimization. In this experimental investigation, Berea sandstone samples were exposed to CO₂-saturated brine under reservoir conditions (1500 psi and 150°F) for 30 and 90 days. These controlled laboratory experiments, while short relative to geological timescales, are designed to simulate key early-stage interactions between CO2, rock, and fluid. A comprehensive suite of characterization techniques was employed to capture changes in the rock's physicochemical and mechanical properties. These techniques included Routine Core Analysis (RCA) to measure porosity and permeability, Nuclear Magnetic Resonance (NMR) for pore structure analysis, Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) to assess fluid chemistry changes, X-ray Diffraction (XRD) for mineralogical changes and ultrasonic acoustic velocity testing to evaluate elastic properties. This approach allows us to analyze both the near-term effects of CO₂ exposure and the potential for scaling up observations to long-term predictions. The study revealed limited early-stage alterations in the physicochemical and and mechanical properties of Berea sandstone during CO₂ exposure. Minor changes were observed in mineral composition, fluid chemistry, and pore structure after 30 and 90 days of storage under representative-reservoir- conditions. These changes, including trace mineral dissolution, modest shifts in pore size distribution, and slight reductions in permeability, and stable dynamic moduli across all samples—remained within the range of experimental variability and did not indicate significant degradation. While the extent of transformation was minimal, the findings provide important early evidence of CO₂–rock–brine interactions that may evolve over extended timeframes. This highlights the value of controlled short-term laboratory experiments in informing long-term CCS behavior, particularly when coupled with reactive transport modeling. Ultimately, the results contribute to improved predictive frameworks, better risk assessment, and more effective design of monitoring and storage strategies for secure geological CO₂ sequestration.