Interaction between a fractured marl caprock and CO2-rich sulfate solution under supercritical CO2 conditions

Abstract

Please cite this article in press as: Dávila, G., et al., Interaction between a fractured marl caprock and CO 2 -rich sulfate solution under supercritical CO 2 conditions. Int. J. Greenhouse Gas Control (2015), http://dx.doi.org/10.1016/j.ijggc.2015.11.005 Geological CO 2 sequestration at pilot-plant scale will be developed at Hontomín (Spain). CO 2 will be injected into a limestone reservoir that contains a NaCl-and sulfate-rich groundwater in equilibrium with calcite and gypsum. The caprock site is composed of marl. The present study seeks to evaluate the interaction between the Hontomín marl and CO 2 -rich sulfate solutions under supercritical CO 2 conditions (P Total = 150 bar, pCO 2 = 61 bar and T = 60 • C). Flow-through percolation experiments were performed using artificially fractured cores to elucidate (i) the role of the composition of the injected solutions (S-free and S-rich solutions) and (ii) the effect of the flow rate (0.2, 1 and 60 mL h −1 ) on fracture permeability. Major dissolution of calcite (S-free and S-rich solutions) and precipitation of gypsum (S-rich solution) together with minor dissolution of the silicate minerals contributed to the formation of an altered skeleton-like zone (mainly made up of unreacted clays) along the fracture walls. Dissolution patterns changed from face dissolution to wormhole formation and uniform dissolution with increasing Peclet numbers. ARTICLE IN PRESSIn S-free experiments, fracture permeability did not significantly change regardless of the flow rate despite the fact that a large amount of calcite dissolved. In S-rich solution experiments, fracture permeability decreased under slow flow rates (0.2 and 1 mL h −1 ) because of gypsum precipitation that sealed the fracture. At the highest flow rate (60 mL h −1 ), fracture permeability increased because calcite dissolution predominated over gypsum precipitation.

A review of geochemical–mechanical impacts in geological carbon storage reservoirs

“…On these materials, it adsorbs within the interlayer spaces and can displace water . This process can result in shrinkage, altering the intergranular pore space and possibly the transport flow paths and mechanical properties . CO 2 as carbonic acid in water can also promote the dissolution of minerals and, in some cases, secondary mineral precipitation; this results in changes to the pore space, which affects transport flow paths and, in some cases, mechanical properties .…”

“…Local heterogeneity exerts a strong control on the location of preferential fluid transport pathways at the microscale . This transport in turn governs the rates and extent of the solute generation and movement through a sequence of (1) hydrodynamic transport of the reactants toward the surface of reaction, (2) reaction at the mineral surface, and (3) transport of reaction products away from the surface of reaction .…”

“…Expanding from this pore‐scale perspective to continuum behavior, local Péclet numbers have been defined in fractured core samples as Pe = h · q / Do , where h is the fracture aperture. In general, it is commonly observed that solute transport in fractures is transport limited and controlled by advection in the principal direction of flow and by diffusion across the rock matrix interface …”

“…Dissolution patterns as a function of Péclet and Damhöler numbers from different experiments reported in fractured media (dark symbol) and porous media (open symbol), modified by Szymczak and Ladd and Garcia‐Rios et al . The Smith et al .…”

“…Local heterogeneity exerts a strong control on the location of preferential fluid transport pathways at the microscale. 25,116,117 This transport in turn governs the rates and extent of the solute generation and movement through a sequence of (1) hydrodynamic transport of the reactants toward the surface of reaction, (2) reaction at the mineral surface, and (3) transport of reaction products away from the surface of reaction. 59,107,119 Thus, the overall or effective rate of reactivity is controlled by the slowest of these three steps, leading to the use of characteristic time scales to provide metrics for the behavior of these systems relative to one another.…”