Identifying diagnostics for reservoir structure and CO₂plume migration from multilevel pressure measurements

[1] Important to large-scale implementation of Carbon Capture and Sequestration is the ability to monitor the carbon dioxide (CO2) that has been injected underground. The focus of this study is to understand how flow processes during CO2 injection impact the pressure observed at a nearby monitoring well. In particular, we are interested in how the reservoir structure (layering and anisotropy) and CO2 plume migration influence the pressure transients at different depths. For a multilayered geologic model, four basic combinations of homogeneity/heterogeneity and isotropy/anisotropy conditions are examined. Numerical simulations using TOUGH2 show different CO2 plume migration and large pressure buildups in the storage reservoir and the seal for each scenario. Pressure buildups normalized to the pressure buildup at the depth of injection are diagnostic of the approximate height of the CO2 plume and provide information on the reservoir structure. Vertical pressure gradients normalized to the initial hydrostatic pressure gradient are diagnostic of reservoir structure soon after the start of injection. Over time, they provide information on the height of the CO2 plume. The diagnostic features in the pressure response are evident long before the CO2 arrives at the monitoring well and can be attributed to buoyancy induced and gravity segregated aqueous flows caused by the advancing CO2 plume. The identified diagnostics will aid in the ultimate goal, which is to develop a monitoring technique based on multilevel pressure measurements.