The quantity of CO2 being released into the atmosphere from energy production associated with fossil fuels, fertilizer production, and cement manufacturing is an environmental concern and efforts are underway to decrease emissions. One such method is carbon capture and storage. Carbon capture and storage is the process of capturing waste CO2 from large point sources and injecting it into subsurface reservoirs systems for long term storage, thereby preventing atmospheric release. These target reservoir systems consist of a porous and permeable storage formation capable of maintaining high injection rates overlain by a tight and impermeable caprock formation that will prevent injected CO2 from escaping back to the surface. The integrity of the caprock will largely determine the success of capture and storage projects over long time periods. Developing methods to assess the caprock integrity will be crucial in assessing the viability of a storage location.
Sandia National Laboratories has conducted studies focusing on coupled chemical-mechanical processes in caprocks triggered by the injection of CO2. Sandia used its combined experimental, analytical, and modelling capabilities to analyze caprock stability under geological carbon storage conditions. The team examined mineralogical changes in shale and the corresponding changes in micro-mechanical properties following the reaction with carbon dioxide and brine. Using experimental data, the team was able to model changes in the mineral assemblages in Mancos Shale over a 5,000 year time period. Modeling results demonstrated limited mineralization and alteration that would correspond to minor shifts in the bulk density and hardness over long time periods. Additionally, the team simulated the injection of supercritical CO2 at the In Salah field using the Sierra Mechanics FEA suite. This model simulated multiphase flow of injected CO2 into a water bearing formation, combining anisotropic geomechanicaland hydrologic properties of the reservoir formation and caprock. The simulation demonstrated the importance of defining poroelastic properties to match the observed surface uplift.
Combining Sandia’s historical expertise in experimentation and high performance computing, caprock stability of potential carbon storage sites can be assessed with a high degree of certainty.
Sandia’s combined expertise provides an integrated analysis of caprock stability under geologic carbon storage. Alterations of Mancos, Marcellus, Eaglefordshales were identified, mineralogical heterogeneities in different lithofacies were noted, chemical reactions were observed as they occurred over time, and it was observed that chemical alteration depends on reactive minerals present and CO2 pressure. All of these factors provide the data necessary to determine the ultimate usability of a potential storage site.