Evaluation of the spread of acid-gas plumes injected in deep saline aquifers in western Canada as an analogue for CO₂ injection into continental sedimentary basins

Injection of CO₂ into deep saline aquifers in sedimentary basins appears to be an important means for reducing anthropogenic emissions of CO₂ into the atmosphere. In the design, approval and monitoring of such operations it is important to predict the evolution of the plume of injected CO₂ and identify potential leakage pathways. In mature sedimentary basins such as those in North America that underwent intense exploration for and production of hydrocarbons, the number and density of wells is extremely high, and a plume of injected CO₂ is likely to encounter many wells that have to be identified and monitored. Under these circumstances, running full-blown numerical models becomes impractical and resource intensive, and simpler and faster tools are needed. An analytical model has been developed that, under a set of simplifying assumptions, can provide a rapid estimate of the shape and extent of a plume of CO₂ injected into an aquifer. The method assumes constant gas properties, which is a valid assumption for a wide range of conditions found in sedimentary basins, and homogeneous and uniform aquifer properties, which, depending on scale, can be assumed for many aquifers at least in a statistical sense. The aquifer is assumed to be horizontal, and there is no mixing, diffusion or dissolution between the injected gas and formation water.