Evaluating the impact of caproek and reservoir properties on potential risk of CO_2 leakage after injection

摘要

Numerical models are essential tools in fully understanding the fate of injected CO_2 for commercial-scale sequestration projects and should be included in the life cycle of a project. Common practice involves modeling the behavior of CO_2 during and after injection using site-specific reservoir and caproek properties. Little has been done to systematically evaluate and compare the effects of a broad but realistic range of reservoir and caproek properties on potential CO_2 leakage through caprocks. This effort requires sampling the physically measurable range of caproek and reservoir properties, and performing numerical simulations of CO_2 migration and leakage. In this study, factors affecting CO_2 leakage through intact caprocks are identified. Their physical ranges are determined from the literature from various field sites. A quasi-Monte Carlo sampling approach is used such that the full range of caproek and reservoir properties can be evaluated without bias and redundant simulations. For each set of sampled properties, the migration of injected CO_2 is simulated for up to 200 years using the water-salt-CO_2 operational mode of the STOMP simulator. Preliminary results show that critical factors determining CO_2 leakage rate through caprocks are, in decreasing order of significance, the cap-rock thickness, caproek permeability, reservoir permeability, caproek porosity, and reservoir porosity. This study provides a function for prediction of potential CO_2 leakage risk due to permeation of intact caproek and identifies a range of acceptable seal thicknesses and permeability for sequestration projects. The study includes an evaluation of the dependence of CO_2 injectivity on reservoir properties.