(562j) Dissolution Patterns: Imprinted or Emergent?

When water percolates
through a carbonate bed containing faults or fractures, the
solutional attack of dissolved CO₂ starts to widen them.
Dissolution of fractured carbonate rocks is often accompanied by the
formation of highly localized flow paths. An example can be seen in
the top panel of the figure, which shows the outlet face of a
limestone fracture (marked by arrows). The two holes (about 10cm
across) are dissolution channels or wormholes, which develop by
steadily accumulating more of the flow and reactant; the spacing
between the wormholes is much larger than their diameter. The lower
left panel shows the inlet face of a fracture; here the
wormhole spacing is much smaller, comparable to their diameter.
Numerical simulations of fracture dissolution (lower right) show a
similar weeding out of the flow paths as dissolution progresses.

Our research applies
chemical engineering principles to the study of the evolution of
geological formations. The aim of the present work is to study the
development of competing flow paths in fractures and the coupling
between fluid flow, reactant transport and chemical reactions at the
surfaces.

We have simulated the
dissolution of a single fracture, starting from random but spatially
correlated distributions of fracture aperture. Our results show a
surprising insensitivity of the evolving dissolution patterns and
fluid flow rates to the amplitude and correlation length
characterizing the initial aperture field. We connect the similarity
in outcomes to a self-organization of the flow into a small number of
channels, with the spacing between each channel determined by the
length of the longest channel.

Figure 1. Outlet face
from a limestone quarry in Smerdyna, Poland (top) and the inlet face
of a vertical fracture from a limestone quarry in Katowice, Poland
(lower left: photo courtesy of Daniel Koehn, University of Glasgow).
Numerical simulations of the evolving fracture aperture (bottom
right) show a reduction in the number of flow paths as dissolution
proceeds (left to right). The images show results for different
correlation lengths in the roughness of the initial aperture; from
small (left) to large (right).