DEVELOPMENT OF PRACTICAL FRACTURE-HYDROGELOGY WORKFLOWS FROM EXPERIENCE IN RESEARCH FACILITIES

The past forty years have seen major advances in the assessment of fracture hydrogeology. The impetus for these developments has come from underground research laboratories for radioactive waste disposal, research sites for contaminant transport studies, and developments in the oil and gas industry. The key tools and techniques have passed from research and development into commercialization and support a practical workflow for working in fractured rock.

The key elements of a fractured bedrock workflow are:

1. Identifying the controlling flow features using flow logging or detailed well testing
2. Determining the geologic nature of the conducting features using core and borehole imaging tools
3. Isolating major flowing features in wells using multi-zone completions
4. Applying single hole and cross-hole transient well-test methods based on fracture networks to assess the flow geometry and connectivity of fracture networks
5. Assessing the significance of fracture-matrix interaction
6. Using numerical tools, such as but not exclusively discrete fracture network models, that represent the major conducting features with sufficiently realistic geometries.

Experience from underground research laboratories, such as the Äspö Hard Rock Laboratory in Sweden and the Kamaishi Laboratory in Japan, shows that an iterative approach to drilling is effective for building a conceptual model of the flow system. The iterative method applies the steps above through installation of the multi-zone completion on the first borehole. The drilling and testing of each subsequent borehole produces responses in the existing monitoring network that indicate connectivity and compartmentalization in the fracture network. Knowledge gained from each new borehole supports multiple working hypotheses that may be tested by the results of subsequent boreholes. Numerical modeling is an essential step for evaluating alternative hypotheses and assesing their consequences for site performance.