Deep aquifer storage of CO2 captured from point sources, such as power plants, is a technologically mature and economically feasible CO2 storage option. A main challenge is however to find geological settings and storage designs that can keep the captured CO2 isolated from the atmosphere for sufficiently long time to mitigate climate change. At many sites, unwanted CO2 return flows could occur preferentially through rock fractures. Current numerical models are however based on constitutive relations that were developed and verified for mixed gas – water flows in soil. Their parameters cannot be independently measured in rock fractures. We here consider geophysical data from 20 different rock fractures, and show that although predictive modelling of gas-water flows through fractures should be based on a different parameterisation than modelling of gas-water flows through soil, the underlying characteristic shapes of soil drainage curves can be matched to fracture-based characteristic relations. This means that gas-water flows through soil and fractured rock in many cases share similar, basic gas-water flow behaviours. Through a proposed curve-matching procedure, site-specific fracture aperture-based parameters can be translated into a set of soil parameters that are accepted by current numerical models, which then can be directly used for predicting e.g. CO2 flows through fractured rock environments. However, parallel research has shown that gas bubble immobilisation through capillary trapping mechanisms, and flow channelling, can in some cases be considerable and may need to be accounted for in predictions of CO2 return-flows from geological storage sites.
2009. 1313-1322 p.