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Reactive Transport Modeling of the Enhancement of Density-Driven CO2 Convective Mixing in Carbonate Aquifers and its Potential Implication on Geological Carbon Sequestration.

Islam A, Sun AY, Yang C - Sci Rep (2016)

Bottom Line: We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing.The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system.Early saturation of the reservoir can have negative impact on CO2 sequestration.

View Article: PubMed Central - PubMed

Affiliation: Bureau of Economic Geology, The University of Texas at Austin, TX, USA.

ABSTRACT
We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO2 sequestration.

No MeSH data available.


Related in: MedlinePlus

Concentration maps of Ra = 1000, homogeneous case; (a,c,e and b,d,f) show results of with and without reactions, respectively.
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f2: Concentration maps of Ra = 1000, homogeneous case; (a,c,e and b,d,f) show results of with and without reactions, respectively.

Mentions: Figure 2 show time lapse of dissolved CO2 fronts from 20 years period to the time the reservoir domain becomes completely saturated. In the case of no reactions, because Ra is low, convection is diffusion dominated, resulting in very slow plume advancement. Even after 900 years CO2 propagation is still limited to upper 10% of the reservoir. However, reaction activities with calcite and dolomite make results completely different. By that time the entire porous formation becomes saturated with CO2. Whenever CO2 arrives at any particular domain after equilibrium reactions, CO2 stream in the form of is dissolved from resident rocks, increasing local density of the brine. The increased density drives more instability which, in turn, causes plume boundaries to advance further downward. For this specific reservoir and thermophysical conditions in 900 years the pore volume is chock-full with dissolved CO2. The process adds significant feedback, however, in a negative sense because of early shutdown of both solubility and mineral trapping processes. Reactions constantly accelerate motion of the fronts. Because convective mixing shows diffusion dominance and the medium is homogeneous the cells do not form wormholes. Therefore, reaction fronts are planar throughout the process. No bifurcation occurs. Figure 3 exhibit results of same Ra, however for heterogeneous permeability formation. Dykstra-Parson coefficient of 0.55 was applied in generating the distributions shown in Fig. 4. Initially, results do not vary much from its homogeneous counterpart other than the pattern of plume evolution. As convection proceeds in addition to heterogeneity effects concurrent geochemical reactions make noticeable difference in dissolution process. Because of local permeability variations and nonlinear flow dynamics from the beginning of plume development hopf-bifuraction of the cells occur and CO2 stream added from carbonates help spread initially laterally and then finally dense phase sinks down. Thus, compared to no permeability contrasts, average concentration of CO2 in the aquifer differs significantly with time. ~100% saturation is reached 50 years earlier. On the other hand, <20% saturation only by reverse buoyant flow conveys clear message of reaction effects on CO2 convection (see Fig. 5). We have also tested results of layered anisotropic heterogeneity . Mean permeability is too small to add any effect resulting in almost same results as homogeneous reservoir.


Reactive Transport Modeling of the Enhancement of Density-Driven CO2 Convective Mixing in Carbonate Aquifers and its Potential Implication on Geological Carbon Sequestration.

Islam A, Sun AY, Yang C - Sci Rep (2016)

Concentration maps of Ra = 1000, homogeneous case; (a,c,e and b,d,f) show results of with and without reactions, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837360&req=5

f2: Concentration maps of Ra = 1000, homogeneous case; (a,c,e and b,d,f) show results of with and without reactions, respectively.
Mentions: Figure 2 show time lapse of dissolved CO2 fronts from 20 years period to the time the reservoir domain becomes completely saturated. In the case of no reactions, because Ra is low, convection is diffusion dominated, resulting in very slow plume advancement. Even after 900 years CO2 propagation is still limited to upper 10% of the reservoir. However, reaction activities with calcite and dolomite make results completely different. By that time the entire porous formation becomes saturated with CO2. Whenever CO2 arrives at any particular domain after equilibrium reactions, CO2 stream in the form of is dissolved from resident rocks, increasing local density of the brine. The increased density drives more instability which, in turn, causes plume boundaries to advance further downward. For this specific reservoir and thermophysical conditions in 900 years the pore volume is chock-full with dissolved CO2. The process adds significant feedback, however, in a negative sense because of early shutdown of both solubility and mineral trapping processes. Reactions constantly accelerate motion of the fronts. Because convective mixing shows diffusion dominance and the medium is homogeneous the cells do not form wormholes. Therefore, reaction fronts are planar throughout the process. No bifurcation occurs. Figure 3 exhibit results of same Ra, however for heterogeneous permeability formation. Dykstra-Parson coefficient of 0.55 was applied in generating the distributions shown in Fig. 4. Initially, results do not vary much from its homogeneous counterpart other than the pattern of plume evolution. As convection proceeds in addition to heterogeneity effects concurrent geochemical reactions make noticeable difference in dissolution process. Because of local permeability variations and nonlinear flow dynamics from the beginning of plume development hopf-bifuraction of the cells occur and CO2 stream added from carbonates help spread initially laterally and then finally dense phase sinks down. Thus, compared to no permeability contrasts, average concentration of CO2 in the aquifer differs significantly with time. ~100% saturation is reached 50 years earlier. On the other hand, <20% saturation only by reverse buoyant flow conveys clear message of reaction effects on CO2 convection (see Fig. 5). We have also tested results of layered anisotropic heterogeneity . Mean permeability is too small to add any effect resulting in almost same results as homogeneous reservoir.

Bottom Line: We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing.The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system.Early saturation of the reservoir can have negative impact on CO2 sequestration.

View Article: PubMed Central - PubMed

Affiliation: Bureau of Economic Geology, The University of Texas at Austin, TX, USA.

ABSTRACT
We study the convection and mixing of CO2 in a brine aquifer, where the spread of dissolved CO2 is enhanced because of geochemical reactions with the host formations (calcite and dolomite), in addition to the extensively studied, buoyancy-driven mixing. The nonlinear convection is investigated under the assumptions of instantaneous chemical equilibrium, and that the dissipation of carbonate rocks solely depends on flow and transport and chemical speciation depends only on the equilibrium thermodynamics of the chemical system. The extent of convection is quantified in term of the CO2 saturation volume of the storage formation. Our results suggest that the density increase of resident species causes significant enhancement in CO2 dissolution, although no significant porosity and permeability alterations are observed. Early saturation of the reservoir can have negative impact on CO2 sequestration.

No MeSH data available.


Related in: MedlinePlus