Reduction of Residential Carbon Dioxide Emissions through the Use of small Cogeneration Fuel Cell Systems

Publication Overview

The study, comprising a literature review and desk-based assessment, aimed to produce a ‘high level’ overview of potential impacts on groundwater resources from storage operations, concentrating on DSF storage across a range of typical regional settings. The study also highlighted the current state of knowledge and/or gaps, recommending further research priorities where appropriate.

Publication Summary

Areas of geographical overlap between potential DSF CO₂ storage and overlying fresh water aquifers have been identified by combining available datasets to map the global and regional juxtaposition of groundwater resources and potential CO₂ storage sites. A classification scheme has been developed for the various geological settings in which overlap may occur. This was then tested for Europe where groundwater resources and potential CO₂ storage sites are relatively well documented and understood. In central Europe, potential storage areas coincide with areas of large, uniform potable aquifers and this could lead to potential conflicts in instances where potable aquifers extend to considerable depth, or low permeability caprock layers are scarce. In southern Europe, more complex aquifer systems (e.g. limestone karst) tend to coincide with potential storage resources. In North America it is the reversed situation, with the majority of geographical overlap occurring between complex aquifer systems and DSF and in Australia, there is overlap with deep freshwater aquifers. The situation in Australia is interesting to note as deep freshwater may coincide with potential DSF.

Two approaches have been used to address potential impact mechanisms of CO₂ storage projects on the hydrodynamics and chemistry of shallow groundwater. The first approach classifies and synthesises observations of water quality changes obtained in natural or industrial analogues, and in laboratory experiments. The second approach reviews hydrodynamic and geochemical models, including coupled multiphase flow and reactive transport, with the aim of linking leakage scenarios to possible impacts on groundwater resources

The findings of the study emphasise the current state-of-the-art regarding potential groundwater resource impacts to be based largely on theoretical considerations. Selection of appropriately characterised and risked storage sites should negate concerns over potential impacts on groundwater resources. Nevertheless, further research is required to better characterise potential leakage mechanisms and impacts, to inform the risk assessments required by regulators.

Possible mitigation options to stop or control CO₂ leakage have been discussed. In particular, the effect of CO₂ pressure in the host DSF and potential effects on shallow fresh water aquifers have been examined. In the literature, such options are mainly addressed through modelling approaches. Techniques for proper and effective mitigation of the impact of stored CO₂ on fresh water resources have been identified. These include: interception and extraction of CO₂ from the plume or brine from the storage reservoir; increase in pressure in formations above the leak; isolation or shut-off of leaks in accessible locations; creation of hydraulic barriers within the reservoir; and treatment of contamination caused by leakage, either in-situ or by ‘pump and treat’ technologies. Increased monitoring and investigation can also be regarded as an effective mitigation option in some instances.

Formulation of a credible mitigation strategy may form an important element of regulatory requirements for commercial scale storage sites. Also to be noted is that there is currently limited practical experience of CO₂ storage on the industrial scale and knowledge of managing potential impacts is largely theoretical based on modelling studies.