Pore‐space structure and average dissolution rates: A simulation study. Issue 9 (22nd September 2016)

• Record Type: Journal Article
• Authors: Pereira Nunes, J. P.; Bijeljic, B.; Blunt, M. J.
• Is Part Of: Water resources research. Volume 52:Issue 9(2016:Sep.)
• Page Start: 7198
• Page End: 7212
• Publication Date: 2016-09-22
• Subjects: reactive transport -- pore‐scale modeling -- average dissolution rates; Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2016WR019313
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: We study the influence of the pore‐space geometry on sample‐averaged dissolution rates in millimeter‐scale carbonate samples undergoing reaction‐controlled mineral dissolution upon the injection of a CO 2 ‐saturated brine. The representation of the pore space is obtained directly from micro‐CT images with a resolution of a few microns. Simulations are performed with a particle tracking approach on images of three porous rocks of increasing pore‐space complexity: a bead pack, a Ketton oolite, and an Estaillades limestone. Reactive transport is simulated with a hybrid approach that combines a Lagrangian method for transport and reaction with the Eulerian flow field obtained by solving the incompressible Navier‐Stokes equations directly on the voxels of three‐dimensional images. Particle advection is performed with a semianalytical streamline method and diffusion is simulated via a random walk. Mineral dissolution is defined in terms of the particle flux through the pore‐solid interface, which can be related analytically to the batch (intrinsic) reaction rate. The impact of the flow heterogeneity on reactive transport is illustrated in a series of simulations performed at different flow rates. The average dissolution rates depend on both the heterogeneity of the sample and on the flow rate. The most heterogeneous rock may exhibit a decrease of up to two orders of magnitude in the sample‐averaged reaction rates in comparison with the batch rate. Furthermore, we provide new insights for the dissolution regime that would be traditionally characterized as uniform. In most cases, at the pore‐scale, dissolution preferentially enlarges fast‐flow channels which greatly restricts the effective surface available for reaction. Key Points: Pore‐scale modeling of carbonate dissolution in three‐dimensional micro‐CT images Predict average dissolution rates in heterogeneous rocks at reservoir conditions without fitting parameters Study the impact of the pore‐space morphology on the dissolution regimes in heterogeneous porous media