Geometry‐coupled reactive fluid transport at the fracture scale: application toCO2geologic storage

Abstract

AbstractWater acidification followsCO2injection and leads to reactive fluid transport through pores and rock fractures, with potential implications to reservoirs and wells inCO2geologic storage and enhanced oil recovery. Kinetic rate laws for dissolution reactions in calcite and anorthite are combined with the Navier‐Stokes law and advection–diffusion transport to perform geometry‐coupled numerical simulations in order to study the evolution of chemical reactions, species concentration, and fracture morphology. Results are summarized as a function of two dimensionless parameters: the Damköhler numberDawhich is the ratio between advection and reaction times, and the transverse Peclet numberPedefined as the ratio between the time for diffusion across the fracture and the time for advection along the fracture. Reactant species are readily consumed near the inlet in a carbonate reservoir when the flow velocity is low (low transverse Peclet number andDa > 10−1). At high flow velocities, diffusion fails to homogenize the concentration field across the fracture (high transverse Peclet numberPe > 10−1). When the reaction rate is low as in anorthite reservoirs (Da < 10−1), reactant species are more readily transported toward the outlet. At a given Peclet number, a lower Damköhler number causes the flow channel to experience a more uniform aperture enlargement along the length of the fracture. When the length‐to‐aperture ratio is sufficiently large, sayl/d > 30, the system response resembles the solution for 1D reactive fluid transport. A decreased length‐to‐aperture ratio slows the diffusive transport of reactant species to the mineral fracture surface, and analyses of fracture networks must take into consideration both the length and slenderness of individual fractures in addition toPeandDanumbers.