Numerical experiments of density driven CO2 saturated brine migration in heterogeneous two-dimensional geologic fabric materials

Abstract

CO 2 geological sequestration has been recognized as one of the potential solutions for reducing anthropogenic atmospheric emissions. To better estimate the storage efficiency (capacity) of subsurface geologic formations and to understand the plume migration mechanism through porous geologic formations, this study performs numerical simulations of density driven CO 2-saturated brine flow in highly resolved heterogeneous 2D fabrics. While large-scale convective currents driven by gravity have been cited as important for dissolution of CO 2 into brine, the impact of small-scale heterogeneity on the time scale of dissolution and final dissolved concentration is not well understood. Two aspects of smallscale geologic heterogeneity are examined here: 1) the correlation length of the sedimentary structures, or depositional fabric, of the material; and 2) grain size distribution (range of porosity and permeability). Twenty seven clastic facies with three different fabrics were evaluated. These materials have variable horizontal correlation lengths (1:1 to 50:1) and range from extremely well sorted upper-coarse sand to very poorly sorted upper-coarse silt. We consider density contrast between CO 2-saturated brine and initial brine as the main driving force of plume migration due to natural convection. Migration behavior from both vertical and horizontal line sources are explored. The analysis is done using conservation of mass and momentum, governed by Darcy's law. Results show that effective convective migration is possible only in a limited range of facies at the scales investigated (100's sq. cm.).Only the extremely well and well sorted coarse sands have mean permeability and porosity that exceed the critical Rayleigh number (≈4π 2). Results indicate that convective and dissolution processes are influenced primarily by the range in grain size (permeability), while the correlation length of the sedimentary fabric has minor effect.

Experimental Study on the Density-Driven Carbon Dioxide Convective Diffusion in Formation Water at Reservoir Conditions

“…In the Fickian diffusion process, CO 2 diffuses into brine and forms a diffusive boundary layer 11 that grows in proportion to the square root of time (), where perturbations to the stable layer are damped. 5 The relationship curve between the mole number of CO 2 dissolved in resident brines ( n t ) and the root of time () is drawn in Figure 4.…”

“…3,4 The molecular diffusion of CO 2 in brine is woefully slow. 5 The key issue for accurate assessment of the dissolution trapping is the dissolution rate. As illustrated in Figure 1, many mechanisms accelerate the diffusion of CO 2 in brine and involve dispersion, 6 advection, and gravitational convection.…”

Mathematical modelling of concrete carbonation with moving boundary

“…The air density can be approximately taken as 1.225 kg/m 3 . This gives the content of CO2 in air is about 0.479 g/m3 . The maximum amount of CO2 that can be consumed in concrete carbonation can be estimated as follows[33], CaO (≈0.64) is the amount of calcium oxide per weight of cement, Cem is the content of cement used in concrete, MCO2=44 g/mol and MCaO=56 g/mol are the molar weight of CO2…”

“…Two major causes that are connected to corrosion of reinforcing steel in concrete structures are the carbonation and chloride attack. Carbonation is a set of reactions between atmospheric carbon-dioxide and alkaline components of concrete, producing a carbonated surface layer in which the pore solution pH value is depressed to nearneutral levels [1,2,3]. A secondary effect of carbonation, also significant in terms of its influence on reinforcing steel corrosion, is that it can cause the release of bound chloride ions into the pore solution phase of concrete that contains a modest level of chloride salts as a contaminant, thus exacerbating the corrosive nature of the electrolyte [4,5].…”

Convective-reactive transport of dissolved CO2 in fractured-geological formations

“…For instance, Kong and Saar (Kong and Saar, 2013) investigated the effect of stochastic heterogeneity on DDC processes during the dissolution of CO2 in brine. Based on numerical experiments, Islam et al (2016b) showed that DDC and dissolution processes are influenced primarily by the heterogeneity in grain size. Dai et al (2018) investigated the effectiveness of the heterogeneity-induced trapping mechanism.…”