### Abstract

Previous research suggests that for many geological CO_{2} sequestration reservoirs, up to 60% of the injected CO_{2} will be trapped by capillary forces (irreducible saturation), a mechanism termed residual CO_{2} trapping. More specifically, our recent models of ongoing field tests of geological sequestration suggest that residual CO_{2} trapping can be maximized if the CO_{2} plume rises a greater distance due to buoyancy (i.e., injection at the deepest part of a thick reservoir) and sweeps a larger area before coming in contact with low permeability caprock. Although this strategy maximizes the residual CO_{2} trapping in theory because CO_{2} plume contacts more pore spaces, it also increases the probability that upwelling- CO_{2} may come into contact with faults or other leakage pathways. Geological heterogeneity seems to play greater role with respect to residual CO_{2} trapping potential. To help clarify what processes and properties will maximize residual CO_{2} trapping and minimize CO_{2}-buoyant flow, we conducted a systematic analysis of permeability (k) fields and its correlation structures. The k fields served as primary parameterization of a numerical model describing CO_{2} migration during a 100-year simulation period. We compared various permutations of two-dimensional conceptual models, including homogeneous, random, homogenous with low-k lens, and anisotropically-correlated k fields. Using a Sequential Gaussian Simulation method, for most of models, we generated 10 realizations in each model permutation. In each simulation, the amount of mobile-, residual-, and aqueous-trapped CO_{2} was calculated and the spatial distribution of the CO_{2} plume was quantified using the first and second spatial moments. Both homogeneous and random simulation results suggest that the amount of residual trapped CO_{2} increases as the effective k increases. These results imply that the overall velocity distribution, which governs the sweeping area of the CO_{2} plume, is a critical factor for residual CO_{2} trapping. However, as overall velocity (or k field) increases, we observed that the CO_{2} plume reaches the caprock more quickly. In simulations of anisotropically correlated k fields with specific correlation length ratios of 25 m×10 m,50 m×10 m, and 100 m×10 m in x (horizontal) and z (vertical) directions, respectively, the CO_{2} migration distance due to buoyancy force is shorter as the horizontal correlation length becomes greater. In addition, as the horizontal correlation length becomes greater, residual trapping increases because the CO_{2} plume spreads farther laterally, sweeping a larger area. In sum, results of this analysis suggest that heterogeneous k fields with greater anisotropic correlation ratios tend to maximize residual trapping and minimize buoyancy-driven CO_{2} migration. Our findings also suggest that k correlation structures, especially anisotropic media with specific ratios of correlation lengths, can strongly impact CO_{2} trapping mechanisms by controlling velocity and tortuosity, which in turn determines the sweeping area of CO_{2} plumes.

Original language | English |
---|---|

Pages (from-to) | 3493-3498 |

Number of pages | 6 |

Journal | Energy Procedia |

Volume | 1 |

Issue number | 1 |

DOIs | |

Publication status | Published - 2009 Feb 1 |

Event | 9th International Conference on Greenhouse Gas Control Technologies, GHGT-9 - Washington DC, United States Duration: 2008 Nov 16 → 2008 Nov 20 |

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### All Science Journal Classification (ASJC) codes

- Energy(all)

### Cite this

_{2}migration.

*Energy Procedia*,

*1*(1), 3493-3498. https://doi.org/10.1016/j.egypro.2009.02.141

}

_{2}migration',

*Energy Procedia*, vol. 1, no. 1, pp. 3493-3498. https://doi.org/10.1016/j.egypro.2009.02.141

**Role of correlation structures of permeability field on residual trapping mechanisms and buoyancy-driven CO _{2} migration.** / Han, Weon Shik; Lee, Si Yong; Lu, Chuan; McPherson, Brian J.; Esser, Richard.

Research output: Contribution to journal › Conference article

TY - JOUR

T1 - Role of correlation structures of permeability field on residual trapping mechanisms and buoyancy-driven CO2 migration

AU - Han, Weon Shik

AU - Lee, Si Yong

AU - Lu, Chuan

AU - McPherson, Brian J.

AU - Esser, Richard

PY - 2009/2/1

Y1 - 2009/2/1

N2 - Previous research suggests that for many geological CO2 sequestration reservoirs, up to 60% of the injected CO2 will be trapped by capillary forces (irreducible saturation), a mechanism termed residual CO2 trapping. More specifically, our recent models of ongoing field tests of geological sequestration suggest that residual CO2 trapping can be maximized if the CO2 plume rises a greater distance due to buoyancy (i.e., injection at the deepest part of a thick reservoir) and sweeps a larger area before coming in contact with low permeability caprock. Although this strategy maximizes the residual CO2 trapping in theory because CO2 plume contacts more pore spaces, it also increases the probability that upwelling- CO2 may come into contact with faults or other leakage pathways. Geological heterogeneity seems to play greater role with respect to residual CO2 trapping potential. To help clarify what processes and properties will maximize residual CO2 trapping and minimize CO2-buoyant flow, we conducted a systematic analysis of permeability (k) fields and its correlation structures. The k fields served as primary parameterization of a numerical model describing CO2 migration during a 100-year simulation period. We compared various permutations of two-dimensional conceptual models, including homogeneous, random, homogenous with low-k lens, and anisotropically-correlated k fields. Using a Sequential Gaussian Simulation method, for most of models, we generated 10 realizations in each model permutation. In each simulation, the amount of mobile-, residual-, and aqueous-trapped CO2 was calculated and the spatial distribution of the CO2 plume was quantified using the first and second spatial moments. Both homogeneous and random simulation results suggest that the amount of residual trapped CO2 increases as the effective k increases. These results imply that the overall velocity distribution, which governs the sweeping area of the CO2 plume, is a critical factor for residual CO2 trapping. However, as overall velocity (or k field) increases, we observed that the CO2 plume reaches the caprock more quickly. In simulations of anisotropically correlated k fields with specific correlation length ratios of 25 m×10 m,50 m×10 m, and 100 m×10 m in x (horizontal) and z (vertical) directions, respectively, the CO2 migration distance due to buoyancy force is shorter as the horizontal correlation length becomes greater. In addition, as the horizontal correlation length becomes greater, residual trapping increases because the CO2 plume spreads farther laterally, sweeping a larger area. In sum, results of this analysis suggest that heterogeneous k fields with greater anisotropic correlation ratios tend to maximize residual trapping and minimize buoyancy-driven CO2 migration. Our findings also suggest that k correlation structures, especially anisotropic media with specific ratios of correlation lengths, can strongly impact CO2 trapping mechanisms by controlling velocity and tortuosity, which in turn determines the sweeping area of CO2 plumes.

AB - Previous research suggests that for many geological CO2 sequestration reservoirs, up to 60% of the injected CO2 will be trapped by capillary forces (irreducible saturation), a mechanism termed residual CO2 trapping. More specifically, our recent models of ongoing field tests of geological sequestration suggest that residual CO2 trapping can be maximized if the CO2 plume rises a greater distance due to buoyancy (i.e., injection at the deepest part of a thick reservoir) and sweeps a larger area before coming in contact with low permeability caprock. Although this strategy maximizes the residual CO2 trapping in theory because CO2 plume contacts more pore spaces, it also increases the probability that upwelling- CO2 may come into contact with faults or other leakage pathways. Geological heterogeneity seems to play greater role with respect to residual CO2 trapping potential. To help clarify what processes and properties will maximize residual CO2 trapping and minimize CO2-buoyant flow, we conducted a systematic analysis of permeability (k) fields and its correlation structures. The k fields served as primary parameterization of a numerical model describing CO2 migration during a 100-year simulation period. We compared various permutations of two-dimensional conceptual models, including homogeneous, random, homogenous with low-k lens, and anisotropically-correlated k fields. Using a Sequential Gaussian Simulation method, for most of models, we generated 10 realizations in each model permutation. In each simulation, the amount of mobile-, residual-, and aqueous-trapped CO2 was calculated and the spatial distribution of the CO2 plume was quantified using the first and second spatial moments. Both homogeneous and random simulation results suggest that the amount of residual trapped CO2 increases as the effective k increases. These results imply that the overall velocity distribution, which governs the sweeping area of the CO2 plume, is a critical factor for residual CO2 trapping. However, as overall velocity (or k field) increases, we observed that the CO2 plume reaches the caprock more quickly. In simulations of anisotropically correlated k fields with specific correlation length ratios of 25 m×10 m,50 m×10 m, and 100 m×10 m in x (horizontal) and z (vertical) directions, respectively, the CO2 migration distance due to buoyancy force is shorter as the horizontal correlation length becomes greater. In addition, as the horizontal correlation length becomes greater, residual trapping increases because the CO2 plume spreads farther laterally, sweeping a larger area. In sum, results of this analysis suggest that heterogeneous k fields with greater anisotropic correlation ratios tend to maximize residual trapping and minimize buoyancy-driven CO2 migration. Our findings also suggest that k correlation structures, especially anisotropic media with specific ratios of correlation lengths, can strongly impact CO2 trapping mechanisms by controlling velocity and tortuosity, which in turn determines the sweeping area of CO2 plumes.

UR - http://www.scopus.com/inward/record.url?scp=79955442043&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79955442043&partnerID=8YFLogxK

U2 - 10.1016/j.egypro.2009.02.141

DO - 10.1016/j.egypro.2009.02.141

M3 - Conference article

AN - SCOPUS:79955442043

VL - 1

SP - 3493

EP - 3498

JO - Energy Procedia

JF - Energy Procedia

SN - 1876-6102

IS - 1

ER -

_{2}migration. Energy Procedia. 2009 Feb 1;1(1):3493-3498. https://doi.org/10.1016/j.egypro.2009.02.141