InterPore2021

Porosity Dynamics through Carbonate-Reaction Kinetics in High-Temperature Aquifer Storage Applications

2 Jun 2021, 14:30

15m

Oral Presentation (MS7) Mathematical and numerical methods for multi-scale multi-physics, nonlinear coupled processes MS7

Speaker

Burt Tilley (Worcester Polytechnic Institute)

Description

While near-surface geothermal energy applications for the heating and
cooling of buildings have been in use for decades, their practical adoption is
limited by the energy transport rates through soils. Aquifers provide a means
to use convective heat transport to improve heat transfer between the building
and the aquifer. However, the solid matrix in the aquifer is carbonaceous in
nature, and calcification prevention techniques in the heat exchangers for
the building also lead to dissolution of the aquifer matrix. Due to the
Arrhenius nature of the reaction, dissolution rates may decrease with increasing
temperature. An effective medium model is derived for the energy, calcium
species, and fluid transport through a dynamic calcite porous medium which
undergoes a reaction between the matrix and fluid. To better discern how these
competing phenomena affect thermal transport in the aquifer, a two-dimensional
Cartesian system is considered, where the vertical axis is parallel to the
borehole axis, and flow is in the horizontal direction. An effective medium
model is derived for the energy, calcium species, and fluid transport through a
dynamic calcite porous medium which undergoes a reaction between the matrix and
fluid. Since the fluid velocity decays algebracially with radial distance from
the borehole axis, two flow regimes are considered. One regime, far from the
borehole where flow rates are small, conductive thermal transport acts faster
than the species transport, leading to a case where precipitation dominates and
regions of the smallest porosity contract to limit energy recovery. In regions
with larger porosity, moderate advection of the species is sufficient to prevent
significant pore closures over the time scale of exploration. The second regime,
closer to the borehole, larger flow rates reduce species concentrations
sufficiently to dissolve the solid phase between pores. In this second regime,
Taylor dispersion effects in both energy and species transport compete, but
thermal conduction acts more slowly than advection, promoting dissolution. The
critical limitation in modeling the long-term evolution of the aquifer structure
is the in situ dissolution rate.