## 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 |
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Pages (from-to) | 3493-3498 |

Number of pages | 6 |

Journal | Energy Procedia |

Volume | 1 |

Issue number | 1 |

DOIs | |

Publication status | Published - 2009 Feb |

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

## All Science Journal Classification (ASJC) codes

- Energy(all)

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