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Reactive transport modelling insights into CO 2 migration through sub-vertical fluid flow structures

Reactive transport modelling insights into CO 2 migration through sub-vertical fluid flow structures
Reactive transport modelling insights into CO 2 migration through sub-vertical fluid flow structures

Sub-vertical geological structures that cut through the overburden, usually called chimneys or pipes, are common in sedimentary basins. Chimneys behave as conduits that hydraulically connect deep strata with the overburden and seabed. Hence, if stored CO 2 migrates to a sufficiently high permeability chimney the risk of CO 2 leakage at the seabed increases. Despite the possible negative effects these structures may have on the integrity of CO 2 storage sites, little is known about (i) their effective permeability distribution, controlled by the combined role of fractures and matrix, and (ii) feedback mechanisms between porosity-permeability, CO 2 reactivity and mineralogy within them. Reactive transport modelling is used to perform 2D axisymmetric radial simulations of geological systems containing chimneys. CO 2 saturations of 10%, 30% and 50% are imposed on a cell located next to the symmetry axis at the base of the model. Under hydrostatic conditions, CO 2 reaches the seabed, at 500 m above the injection point, in less than 100 yr using injected CO 2 saturations at or above 30% and with overburden isotropic permeabilities and chimney vertical permeabilities above 10 −14 m 2 . Vertical fractures with apertures larger than 0.05 mm for volume fractions below 1% are sufficient to sustain such high vertical permeabilities in the chimney with a relatively high cap rock matrix permeability of 10 −16 m 2 . Over 100 yr of CO 2 injection, changes in porosity and permeability due to mineral precipitation/dissolution are negligible. For this time scale, in systems containing chimneys sufficiently far away from the injection well, the risk of CO 2 leakage at the seabed is primarily controlled by the pre-existing hydrogeological state of the system.

Chimney, CO leakage, Fractures, Marine environment, Numerical modelling, Reactive transport
1750-5836
82-92
Marín-Moreno, H.
3fe1141c-c2f4-475a-89ea-bec8a87388bd
Bull, Jonathan M.
974037fd-544b-458f-98cc-ce8eca89e3c8
Matter, Juerg M.
abb60c24-b6cb-4d1a-a108-6fc51ee20395
Sanderson, David J.
5653bc11-b905-4985-8c16-c655b2170ba9
Roche, Ben J.
2746ee9e-1b87-4d2f-b4e1-dcdc0ca7a719
Marín-Moreno, H.
3fe1141c-c2f4-475a-89ea-bec8a87388bd
Bull, Jonathan M.
974037fd-544b-458f-98cc-ce8eca89e3c8
Matter, Juerg M.
abb60c24-b6cb-4d1a-a108-6fc51ee20395
Sanderson, David J.
5653bc11-b905-4985-8c16-c655b2170ba9
Roche, Ben J.
2746ee9e-1b87-4d2f-b4e1-dcdc0ca7a719

Marín-Moreno, H., Bull, Jonathan M., Matter, Juerg M., Sanderson, David J. and Roche, Ben J. (2019) Reactive transport modelling insights into CO 2 migration through sub-vertical fluid flow structures. International Journal of Greenhouse Gas Control, 86, 82-92. (doi:10.1016/j.ijggc.2019.04.018).

Record type: Article

Abstract

Sub-vertical geological structures that cut through the overburden, usually called chimneys or pipes, are common in sedimentary basins. Chimneys behave as conduits that hydraulically connect deep strata with the overburden and seabed. Hence, if stored CO 2 migrates to a sufficiently high permeability chimney the risk of CO 2 leakage at the seabed increases. Despite the possible negative effects these structures may have on the integrity of CO 2 storage sites, little is known about (i) their effective permeability distribution, controlled by the combined role of fractures and matrix, and (ii) feedback mechanisms between porosity-permeability, CO 2 reactivity and mineralogy within them. Reactive transport modelling is used to perform 2D axisymmetric radial simulations of geological systems containing chimneys. CO 2 saturations of 10%, 30% and 50% are imposed on a cell located next to the symmetry axis at the base of the model. Under hydrostatic conditions, CO 2 reaches the seabed, at 500 m above the injection point, in less than 100 yr using injected CO 2 saturations at or above 30% and with overburden isotropic permeabilities and chimney vertical permeabilities above 10 −14 m 2 . Vertical fractures with apertures larger than 0.05 mm for volume fractions below 1% are sufficient to sustain such high vertical permeabilities in the chimney with a relatively high cap rock matrix permeability of 10 −16 m 2 . Over 100 yr of CO 2 injection, changes in porosity and permeability due to mineral precipitation/dissolution are negligible. For this time scale, in systems containing chimneys sufficiently far away from the injection well, the risk of CO 2 leakage at the seabed is primarily controlled by the pre-existing hydrogeological state of the system.

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Accepted/In Press date: 25 April 2019
e-pub ahead of print date: 2 May 2019
Published date: 1 July 2019
Keywords: Chimney, CO leakage, Fractures, Marine environment, Numerical modelling, Reactive transport

Identifiers

Local EPrints ID: 434194
URI: https://eprints.soton.ac.uk/id/eprint/434194
ISSN: 1750-5836
PURE UUID: 4f372d5d-681f-4a77-92dd-265ff0398e4c
ORCID for David J. Sanderson: ORCID iD orcid.org/0000-0002-2144-3527

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Date deposited: 13 Sep 2019 16:30
Last modified: 14 Sep 2019 00:34

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