Fluid Flow through Natural Single-Rock Fractures: Experimental and Numerical Investigations

Abstract

Fluid flow through three natural single rough-rock fractures were measured at different normal stresses. The surface height of both halves of each of these fractures was measured with and without solidified Wood's metal filling using a laser profilometer to calculate the aperture distribution of the three fractures under different normal stresses. The flow calculated for the three fractures according to the sample scale cubic law using the mean apertures overestimated the experimental flow by 2.5–342 times, within a normal stress range of 0–8 MPa. The elementally applied cubic law (EACL) through a finite-element model also overestimated the experimental flow by 2.0–117 times within the same normal stress range. As the normal stress applied on a natural rough-rock fracture increases, the overestimation increases due to increasing contact areas and increasing tortuous behavior of flow. At the sample scale, mean apertures to the powers between 4.03 and 6.47 were required for the three fractures to produce the experimental flows in the same normal stress range. At the FEM elemental scale, apertures to the powers between 3.65 and 5.74 were required for the three fractures to produce experimental flows in the same normal stress range. The required aperture to the power to produce experimental flow was found to increase with increasing normal stress. These findings clearly show the inapplicability of the cubic law to estimate flow through natural rough-rock fractures, especially under high normal stresses.