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Reaction‐driven fracturing of porous rock
Author(s) -
Ulven O. I.,
Jamtveit B.,
MaltheSørenssen A.
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2014jb011102
Subject(s) - porosity , carbonation , reaction rate , volume (thermodynamics) , mineralogy , volume fraction , chemical kinetics , porous medium , weathering , materials science , geology , chemical engineering , thermodynamics , kinetics , chemistry , composite material , catalysis , geochemistry , biochemistry , physics , quantum mechanics , engineering
Abstract A 2‐D computer model has been developed to investigate fluid‐mediated transformation processes such as chemical weathering, mineral carbonation, and serpentinization that require transport of H 2 O and/or CO 2 into reacting rock volumes. Hydration and carbonation cause local volume expansion, and the resulting nonuniform stresses may drive fracturing, which increases both the rate of transport and the accessible reactive surface area in the system and thus accelerates the rate of the transformation process. The model couples reactions, fracturing, and fluid transport for systems with a range of initial porosities, assumed constant throughout the process. With low initial porosity, a sharp reaction front between completely reacted material and unreacted material propagates into unaltered rock, while for high porosities, diffuse reaction fronts are formed in which a large fraction of the initial volume is partly reacted. When diffusive transport is rate limiting, the total reaction rate depends on porosity to a power N , where N is in the range 0.45–2. The exponent N increases as the reaction‐generated expansion decreases. In high‐porosity rocks, the total reaction rate is limited by reaction kinetics, and it is thus insensitive to porosity variations. As the volume increasing reaction proceeds, fracturing divides the unreacted porous material into subdomains, which may undergo further subdivision as they are consumed by the reaction. The total reaction rate and progress depend on the initial geometry of a reacting domain, and this significantly affects the weathering profiles for systems that evolve from an initial assembly of blocks with different sizes and shapes.