| Title | Modelling of Turbulent Flow Transients Within Hot Dry Rock Fracture Systems: Preliminary Results |
|---|---|
| Authors | T. Kohl, K.F. Evans, R.J. Hopkirk, R. Jung and L. Rybach |
| Year | 1995 |
| Conference | World Geothermal Congress |
| Keywords | forced fluid flow, fractured rock, hydraulic testing, non-laminar flow model |
| Abstract | During the HDR site investigation studies in Soultz (France) stepwise hydraulic injection and production tests have been conducted in the borehole GPKl. The datasets that were obtained from the lowermost depth domain between and demonstrate non-laminar hydraulic behaviour. At near steady state conditions changes in flow rate invoke parabolic pressure changes. This observation together with earlier datasets from the same site are corresponding to empirical flow laws established for turbulent hydraulic regimes. As a consequence from this non-linearity, conventional hydrological models cannot be used to interpret these hydraulic tests. In this paper we describe a model which permits non-laminar flow in fractures that is being developed for this purpose. As a first exercise, the model has been applied to the injection test at GPKl. The results show that certain features of the observed transient response which cannot be explained by a conventional laminar flow model are predicted by the non-linear flow law. A preliminary evaluation of the parameters resulting from both, steady state and transient analysis leads to assumptions on the geometry of the main fracture system. Depending on the assumption for the surrounding matrix, our calculations provide the basis for a large surface area of the fracture. |