Differing physical processes in off-shore and on-shore CO2 storage|
K.U. Weyer Ph.D., P.Geol., P.HG.
WDA Consultants Inc., 4827 Vienna Drive NW, Calgary, Alberta, Canada
© 2012 K. U. Weyer
The geological storage of CO2 demands a new type of subsurface fluid mechanics
extending beyond that required for hydrocarbon production and application of EOR. Traditional
subsurface fluid mechanics deals with hydrocarbon reservoirs primarily as sinks for flow of
water, hydrocarbons and CO2 or other EOR enhancers. CO2 sequestration,
however, leads us to deal with reservoirs and saline aquifers as sources for flow of CO2
into the geological environment. In the past the question of physical causality of fluid
mechanics was not one of importance as the fluids would enter the production wells in any
case and the actual flow paths usually were not of great significance. What was important
was the success in resource extraction and the ensuing and proven economic profitability.
Thus traditional fluid mechanics was and is sufficient for successful resource extraction.
Geological CO2 storage, however, causes a paradigm shift in the sense that the
application of fluid dynamics now must ensure as much storage volume as possible and needs
to predict how much CO2, after large scale injection, may return to the surface
as well as the time scales and migration paths involved. These new goals, for the first
time in its history, will require subsurface fluid mechanics to apply systems which are
physically consistent and are based on the application of physical causality throughout.
For example, it will not suffice to relate the energy to unit volume and to assume
incompressibility of water or to assume hydrostatic conditions for the application of
so-called buoyancy forces. All of this is done in continuum mechanics and the brand of
thermodynamics derived from these assumptions. Instead a subsurface fluid mechanics, adopted
to CO2 sequestration, will need to apply Hubbert’s Force Potential [1,2] which
relates energy to mass and does not need to assume incompressibility or vertical buoyancy
forces, as well as Groundwater Flow Systems Theory.
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