CO2 Dissolution Trapping Rates in Heterogeneous Porous Media

K A Gilmore,J A Neufeld,M J Bickle

doi:10.1029/2020gl087001

K A Gilmore, J A Neufeld + Show 1 more

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https://doi.org/10.1029/2020gl087001

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Abstract

AbstractThe rate of carbon dioxide (CO2) dissolution in saline aquifers is the least well‐constrained of the secondary trapping mechanisms enhancing the long‐term security of geological carbon storage. CO2 injected into a heterogeneous saline reservoir will preferentially travel along high permeability layers increasing the CO2‐water interfacial area which increases dissolution rates. We provide a conservative, first‐principles analysis of the quantity of CO2 dissolved and the rate at which free‐phase CO2 propagates in layered reservoirs. At early times, advection dominates the propagation of CO2. This transitions to diffusion dominated propagation as the interfacial area increases and diffusive loss slows propagation. As surrounding water‐filled layers become CO2 saturated, propagation becomes advection dominated. For reservoirs with finely bedded strata, ∼10% of the injected CO2 can dissolve in a year. The maximum fraction of CO2 that dissolves is determined by the volumetric ratio of water in low permeability layers and CO2 in high permeability layers.

Highlights

Worldwide carbon dioxide (CO2 ) emission targets are unlikely to be met without large scale geological CO2 storage (Intergovernmental Panel on Climate Change, 2018).Assessments of global CO2 storage capacity (e.g. Michael et al (2010)) suggest that saline aquifers could account for around 90% of the total potential storage volume
Quantifying total dissolution rates post injection is important for assessing the contribution of CO2 dissolution to the long-term security of stored CO2
The total dissolution into the low permeability layers is the sum of the total flux over time and so scales as t3/2

Summary

Introduction

Assessments of global CO2 storage capacity (e.g. Michael et al (2010)) suggest that saline aquifers could account for around 90% of the total potential storage volume. The dissolution of injected CO2 into the ambient brine within a saline aquifer is a key mechanism for increasing the security of long-term storage. At typical storage reservoir conditions, CO2 is in the supercritical phase and is buoyant with respect to the surrounding reservoir fluid, presenting the risk of migration to the surface. As CO2 dissolves into water the density of the water increases (Teng & Yamasaki, 1998), eliminating the buoyancy of free-phase CO2 and reducing the risk of leakage. Quantifying total dissolution rates post injection is important for assessing the contribution of CO2 dissolution to the long-term security of stored CO2

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Discussion

Conclusion