Effects of fracture roughness on fluid flow through a single deformable fracture
The cubic law for fluid flow through a single fracture commonly employed in simulations of fluid flow through a fractured medium assumes the smooth parallel-plate idealization of each fracture. This paper summarizes results of theoretical investigations on the effects of fracture surface roughness on fluid flow through a single deformable fracture. We constructed a theory to relate the geometrical characteristics of the fracture to its mechanical properties so that an aperture density distribution for the fracture may be derived from fracture stress-strain measurements. A review of available fracture roughness profiles showed that the aperture density distributions of real fractures may take on various shapes: sharply peaked, broad and flat, skewed and peaked toward the large apertures or toward the small apertures. The different shapes give rise to qualitatively different variations of flow rate with normal stress applied to the fracture. Calculations were first carried out for flow with no tortuosity; then the effect of path tortuosity and connectivity on fluid flow rate were investigated. Our calculations show that for fractures with aperture distribution that is sharply peaked toward the large apertures, the effect of tortuosity is minimal and the fracture remains hydraulically open though its mechanical properties may approach that of an intact rock. On the other hand, when the aperture distribution is dominated by small apertures and when the contact area of the fracture surfaces is above 30%, the effect of tortuosity may depress the fluid flow rate by two or three more orders of magnitude from that predicted by the parallel-plate idealization of the fracture. Thus the applicability of a parallel-plate mean aperture to the description of flow behavior in a rough fracture is limited. 21 references, 10 figures.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6249683
- Report Number(s):
- LBL-17514; CONF-850101-4; ON: DE85004593
- Country of Publication:
- United States
- Language:
- English
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