CO2 Sequestration through Deep Saline Injection and ...

[56], and is accessible from most locations in the basin, it also has potential for CO2 leakage
along the many wells that have been drilled into or through the formation. The wells are
distributed over most of the 468,000 km 2 area, giving an overall average well density of 1 well
every 2 km 2 . Over half of all wells that penetrate the Viking aquifer are classified as abandoned
wells [54]. This concern will be addressed in detail below.
5.2. TRAPPING MECHANISMS AND SEQUESTRATION CAPACITY
Upon injection into saline aquifers, CO2 may be stored by one or more of three processes,
hydrodynamic trapping, solubility trapping, or mineral trapping [7]. The most critical concern of
hydrodynamic trapping is the potential for CO2 leakage through imperfect confinement.
Solubility trapping is not subject to buoyancy and is therefore less likely to leak. In mineral
trapping, CO2 is stored for very long periods by conversion into carbonate. Solubility and
mineral trapping are the most important long term solutions to CO2 sequestration in geologic
media [29], while hydrodynamic trapping represents the crucial short term step in the trapping
process, as CO2 must remain hydrodynamically trapped for sufficient time to allow the other
processes to take hold.
Figure 35
Alberta Basin Stratigraphy [57]
5.2.1. Hydrodynamic Trapping
Crucial to all mechanisms of CO2 capture in a reservoir system is the ability of the reservoir to
maintain the injected volume of CO2 for a sufficient residence time for other mechanisms to
succeed (hydrodynamic trapping). Hydrodynamic trapping may occur via the existence of a
slow transport gradient over a long distance or via structural traps which may serve to coral the
CO2 and prevent migration. In either case, caprock integrity is of primary interest to prevent
leakage over an extended period of time. Accurate prediction of the hydrodynamic behavior of
CO2 is a complex venture into many critical parameters, and numerical modeling is often
required. A detailed numerical modeling analysis has been conducted for this purpose, and is
presented later in this report.
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