oa Predicting Spatial and Temporal Variations in Along-fault Fluid Flow

In June 2008 the UK Government launched the White Paper ‘Managing Radioactive Waste Safely’ proposing construction of a deep Geological Disposal Facility. The GDF will be supported by an accompanying safety case that will include providing risk based estimates of the travel times for radionuclides leaving the GDF and travelling through the geosphere. This will require characterisation of the structural geological features surrounding the GDF in terms of location and associated permeability. Faults are heterogeneous in time and space. Few data are available on which to base quantitative predictions of long-term temporal variations in along-fault flow. No published research to-date enables quantitative predictions of temporal variations in along-fault flow. Episodic fault flow has been proposed by a number of authors to explain indirect observations of fault behaviour as diverse as hydrothermal springs, temperature anomalies, cementing phases, gas-related amplitude anomalies and earthquake triggering. We present here a summary of research from an innovative range of sources to support the hypothesis that along fault flow commonly varies over both space and time. We also present the results of field investigations of faults in mudstones to explore how field data can be used to characterise along fault flow.