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Mixing-induced dissolution in fingering reactive flow

AuthorsHidalgo, Juan J. ; Cabeza, Yoar ; Dentz, Marco ; Carrera Ramírez, Jesús
Issue Date2014
PublisherEuropean Geosciences Union
CitationEGU General Assembly (2013)
AbstractThe evolution of porosity in carbonate reservoirs during CO2 injection, and the wormhole formation in karst aquifers can be attributed to fast equilibrium reactions, which are characterized by large Damköhler numbers. Under these conditions the reaction rate is mixing-controlled, and can be quantified in terms of the mixing rate of the conservative components of the chemical system [De Simoni et al. (2005), Water. Resour. Res.]. Here, we study the calcite dissolution during the convective-driven mixing of CO2 in a carbonate saline aquifer. The CO2-brine mixture is denser than the two initial fluids, leading to a Rayleigh-Bénard-type instability known as convective mixing, which greatly accelerates CO2 dissolution. The dissolution front can display a stable or fingering shape depending on the relation of the governing forces. We explore the feedback between fluid instabilites, porosity evolution, and permeability changes by means of numerical simulations of a CO2 stationary layer dissolving into brine using an analogue-fluid system with a nonmonotonic density-concentration curve [Neufeld et al. (2010), Geophys. Res. Lett.; Backhaus, et al. (2011), Phys. Rev. Lett.; Hidalgo et al. (2013), Adv. Water Resour.]. We derive an analytical expresion for the speciation contribution to the reaction rate which is valid under a wide range of reservoir conditions (pH< 8:3). This allows us to analyze systematically the impact of conservative mixing mechanisms on the dynamics of the complex reactive flow system. Our findings show how the developed porosity patterns depend on the fingering instabilities caused by the convective-driven dissolution of the CO2, the movement of the receding CO2-brine interface, and the properties of the chemical system.
DescriptionPonencia presentada en la European Geosciences Union General Assembly, celebrada en Viena del 27 de abril al 2 de mayo de 2014.
Appears in Collections:(IDAEA) Comunicaciones congresos
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