Scale Dependence of Hydraulic and Structural Parameters In Fractured Rock From Borehole Data (ktb and Hsdp)
Abstract
Fundamental understanding of the origin, geometry, extension and scale dependence of fluid pathways in fractured rock is still incomplete. We analysed fracture networks on different scales based on data from fluorescent thinsections and BHTV images from the same depth range to obtain geometrical network parameters and to estimate frac- ture permeability in the vicinity of a mantle plume (Hawaii Scientific Drilling Project, HSDP). A first modelling of a microscopic network from the fluorescent thinsection of a highly olivine phyric basalt gives a clear indication, that the preferential hydraulic pathways on the microscopic scale are in this particular case the micro fractures in the olivine crystal. This is the only plausible explanation of high porosity (16.6 %) due to the observed vesicles and a corresponding low permeability of 10 µD measured on core samples. Modelling hydraulic flow and calculation of permeability leads to simi- lar values of permeability of 12.3 µD assuming a mean fracture aperture of 1 µm and an exponential distribution function of the fractures. Detected structures from BHTV measurements were used to construct a macroscopic stochastic network to simulate the hydraulic flow on a macroscopic scale. We found 337 fractures in the depth section from 783.5 m to 1147.5 m, which result in a linear frequency of 0.927 1/m. Assum- ing horizontal layers and constant fracture apertures of 100 µm for all structures lead to a first estimate of permeability of 77 mD in this depth section. In a recent work, we showed for data from the Continental Deep Drilling Project (KTB) that the frac- ture density versus fracture length follows a power law. The results from the Hawaiian data suggest a similar relationship, despite all differences in the lithological conditions between both sites.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.3258Z