Project Summary

Numerical simulations are an essential tool for assessing the long-term storage of CO2 in saline aquifers, such as the proposed pilot project at the Wandoan site in Queensland’s Surat Basin.

However, the robustness of the numerical predictions depends on accurately modelling the important physical processes involved. Numerical predictions of the amount of dissolved COduring the early stages of a COstorage project, particularly during the injection period where the COplume grows rapidly, overestimate the actual amount of dissolved COdue to the use of finite-sized grid blocks. A simple theoretical scaling has been used to demonstrate that this discretisation error can be accurately accounted for and effectively removed in numerical simulations.

In the long-term, the necessary use of coarse grid blocks in a computational model prohibits the accurate simulation of enhanced dissolution due to density-driven convective mixing. This type of mixing typically occurs at a spatial length scale that is smaller than the size of the grid blocks necessary in a field-scale simulation. In order to improve the long-term numerical predictions of COdissolution in models that feature large grid blocks, a better understanding of the convective mixing process in heterogeneous reservoirs and the role of geochemical reactions is required.

A simple heterogeneity model consisting of a random distribution of impermeable horizontal barriers in an otherwise homogeneous porous media was used to demonstrate that an equivalent anisotropic model provided an adequate approximation of the long-term flux. The long-term flux for an anisotropic reservoir was shown to scale as (kv/kh) 1/2 times the isotropic estimate, a result that was confirmed by numerical simulations

A sub-grid-scale scheme, for reducing the error in the numerical predictions of long-term COdissolution due to convective mixing, was developed. Several possibilities for implementing the scheme using grid-corrected properties were proposed and assessed using numerical simulations. This correction significantly reduced the difference between the fine-scale results and the results using much coarser models.

Key outcome:

The results obtained in this project can be implemented in commercial simulation software to improve the modelling of the short-term and long-term behaviour of injected carbon dioxide.

Available Reports

Improved discretisation and dynamic modelling of CO2 solubility during injection and subsequent convective dispersion

This study addresses some of the shortcomings in the scienti c literature regarding the e ffect of coarse grids on the convective mixing process. An important estimate of the long-term stable mass flux during steady convective mixing is extended to the case of an anisotropic homogeneous reservoir, which is shown to provide an adequate representation of a heterogenous model using flow barriers to introduce vertical heterogeneity.

Project Name:
Improved discretization and dynamic modelling of CO2 solubility during injection and subsequent convective dispersion

Research Organisation:
CSIRO

Status:
Completed, 2014

Authors:
C Green, J Ennis-King

Reference:
7-1011-0190

Research Program: Carbon Transport + Storage
Demonstration: Surat Basin, CTSCo-Wandoan
Research Focus: Injectivity, Model calibration and injection forecast, Modelling Errors & Uncertainties

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