Injection Strategies for CO₂ Storage Sites

Publication Overview

The project has two main deliverables: 1) A comprehensive review of international research and current understanding with respect to the strategies, technologies and economics of CO₂ injection into subsurface formations and 2) spreadsheet applications based on analytical methods and look-up tables for the planning of CO₂ injection schemes. The review part of the report addresses the following main topics: a) injection well hydraulics and numerical modelling of CO₂ injection; b) proposed strategies for storage optimisation and experience from existing injection operations; c) economics and trade-offs of CO₂ injection schemes; and d) injection well design and remediation methods. More specifically, the following are covered:

Publication Summary

It can be concluded that pressure build-up due to injection in DSF and depleted hydrocarbon reservoirs is potentially the most significant limiting factor for large-scale geological storage. Due to this, strategies for pressure management as an element of injection strategies will need substantial consideration for future CCS projects.

As more large-scale demonstration projects are commenced, knowledge will increase, and uncertainties and variables should decrease accordingly, but at the present time, there are significant variations in opinions throughout the scientific community. It should also be noted that although the requirements for pressure control wells will increase the costs of a project, the knock-on effect should compensate for the increased initial outlay. These pressure control wells will also allow operators to manage to some degree the migration of the injected CO₂ plume, and this has proven a significant safety benefit in CO₂EOR operations, and can increase the CO₂ dissolution in formation waters.

Direct comparisons of different studies are not yet possible because the inherent properties of the models and variation in parameters and boundary conditions. This leaves much further work to be completed to allow narrower predictions on injection strategies. However, available data tends to suggest that the more optimistic estimates are potentially more realistic than some of the less optimistic. Low permeability reservoirs such as In Salah are demonstrating the ability to inject in the order of 1 Mt/yr, despite the low reservoir permeability. It is noted that optimisation of injection schemes using horizontal wells or pressure management may be necessary for such operations, but there are associated benefits of such requirements.

The economics of injection and storage are also liable to play a significant role in the future, and the effect that formation characteristics can play on the economics is considerable. Site characterisation should identify these factors at an early stage, and subsequently these should not be difficult to anticipate.

The Injection Cost Calculation tool developed as part of this report should be beneficial in the future development of commercial scale CCS, despite the restrictions on its use; it could be used as part of the site characterisation process, and give a good indication of site suitability.

Strategies for injection will vary greatly in the future from site to site, as the uncertainties involved in predicting reservoir properties imply that there will be a range of views regarding the number and type of injection wells needed for any given operation, and it can be assumed that different companies will likely follow different strategies.