Experimental Investigation of CO2 Trapping and Leakage Mechanisms in Deep Geologic Formations for Model Improvement

Abstract:

A fundamental and a comprehensive understanding of trapping and leakage processes will be of value to develop strategies for efficient and secure storage of CO₂ in deep geologic formations and assess environmental and ecological risks associated with potential leakage. It is our contention that to make observations and collect data to obtain a fundamental understanding of how the natural formation heterogeneity manifested at all scales affects trapping is highly challenging or impossible to obtain in real field settings in deep geologic formations. A test scale intermediary between small laboratory columns and field scales that is referred to as “intermediate scale” provides an attractive alternative to investigate these processes under controlled conditions in the laboratory. Heterogeneities at all needed test scales can be designed using soils with known properties and experiments can be conducted under controlled conditions to obtain accurate data. Conducting intermediate scale laboratory experiments under ambient pressure and temperature conditions to understand the processes that occur in deep formations with very higher pressures and drastically different temperatures pose many challenges. This paper presents the approaches that were used to conduct multi-scale experiments from column to intermediate scale to understand the factors that contribute to capillary and dissolution trapping using surrogate fluids for supercritical CO₂ and saline water combination. In addition, experiments were conducted in soil columns and two-dimensional tanks to study the effects of formation heterogeneity on CO₂ gas evolution during leakage of water with dissolved CO₂. The results from these experiments are presented to show how the new insights have helped to improve the conceptual understanding of effects of heterogeneity on CO₂ trapping and leakage. This understanding has helped to improve numerical models that can be used to better engineer CO₂ storage systems for permanence and evaluate possible failure risks.