Skip to main content

Evaluation of a Self-Consistent Approach to Fractured Crystalline Rock Characterization

Objective

The aims of the project are:

(I) to assess the errors in predictions of a nuclide migration in fractured crystalline rocks resulting from the application of inappropriate interpretation techniques;
(ii) to assess the impact of the "partial flow dimension" approach on the results derived from hydrogeological testing; and
(iii) to develop a methodology for constructing fracture network models to incorporate field flow dimensional information directly.
The aims of the project are:
to assess the errors in predictions of nuclide migration in fractured crystalline rocks resulting from the application of inappropriate interpretation techniques;
to assess the impact of the fractional dimension approach on the results derived from hydrogeological testing;
to develop a methodology for constructing fracture network models to incorporte field dimensional information directly.

A well documented and monitored set of pumping tests was required in order to evaluate the applicability of the approaches under consideration. In addition, the fractures, fracture zones and faults throughout the experimental region needed to be well characterised.

The Large Scale Croshole (LSCH) tests which took place in the Swedish Stripa mine laboratory during the year 1989, fulfil the criteria outlined above. These were a series at constant rate tests with durations of days, for which drawdown and recovery information was recorded. One pumping test from the LSCH programme was chosen for a more detailed analysis. Preliminary examination of the data indicates that equilibrium conditions are never achieved. It is observed that the dimension of flow varies throughout the period of pumping, generally increasing with the duration of pumping. There are a number of ways in which this effect can be interpreted. Firstly, early time data may be distorted by earlier hydraulic events so that anomalously low estimates of flow dimension are obtained. Secondly, the flow geometry may be different on differing scales. A third possible interpretation is that at late times leakage into the solid matrix is significant. Finally, some combination of the above three explanations may be appropriate.

To account for significant leakage, and for fractional dimension flow, methods for analysing pumping test data based on the fractal reservoir model must be sought. This is currently being investigated.
Work programme:

The project has been subdivided into the following five tasks:

(1) to provide a literature review of the impact of the application of "partial flow dimension" interpretation on hydrogeological tests in fractured crystalline rocks;
(2) to evaluate, present and assess the impact of "dimensional" interpretation on some existing data sets;
(3) to simulate "dimensional" results within a fracture network model;
(4) to assess the available methods by which "dimensional" results would be incorporated explicitly into as fracture network model; and
(5) to demonstrate the impact of cylindrical flow versus variable dimension results on the output from a transport version of the fracture network model.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Golder Associates (UK) Ltd
Address
54 Moorbridge Road
SL6 8BN Maidenhead
United Kingdom