Scale Dependence of Hydraulic and Structural Parameters in Fractured Rock
Abstract
Fundamental understanding of the origin, geometry, extension and scale dependence of fluid pathways in fractured rock is still incomplete. We analysed a broad spectrum of fracture networks on different scales based on data from fluorescent thin sections, FMS and BHTV data and seismic structures to obtain geometrical network parameters and to estimate fracture permeability at the KTB site (Continental Deep Drilling Programme) and in the vicinity of a mantle plume (Hawaii Scientific Drilling Project). The problem is highly underdetermined, therefore, additional assumptions like the percolation threshold and calibrations using measured permeability from hydraulic tests and core measurements were also included. The hydraulic situation at the KTB site requires a macroscopic fracture connectivity, which restricts the lower boundary of the mean macroscopic fracture lengths. Assuming a hydraulic situation at the edge of the percolation threshold, networks with fracture lengths of 20m-30m seem to be the most probable. This agrees with suggestions of other authors, who assume that fractured rocks are close to the percolation threshold. The density of the connected fracture networks as a function of the mean fracture length follows a power law distribution, which documents the fractal nature of fractures in crystalline rock. Similar results were obtained for the Hawaii drill hole from thinsection analysis and BHTV measurements indicating a potentially universal power law relation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMNG31B0367Z
- Keywords:
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- 5104 Fracture and flow;
- 5114 Permeability and porosity;
- 5139 Transport properties