Hydraulic And Mechanical Properties of Natural Fractures In Low Permeability Rock

TLDR

A metal‑injection method was used to quantify the void geometry and contact area of quartz monzonite fractures under varying stresses. Below 20 MPa, fluid flow scales with the mean aperture to a power >3, while increasing stress enlarges contact area and creates tortuous channels that limit flow; above 20 MPa, aperture decreases but flow remains unchanged because the tortuous channels deform minimally.

Abstract

The results of a comprehensive laboratory study of the mechanical displacement, permeability, and void geometry of single rock fractures in a quartz monzonite are summarized and analyzed. A metal-injection technique was developed that provided quantitative data on the precise geometry of the void spaces between the fracture surfaces and the areas of contact at different stresses. At effective stresses of less than 20 MPa fluid flow was proportional to the mean fracture aperture raised to a power greater than 3. As stress was increased, contact area was increased and void spaces become interconnected by small tortuous channels that constitute the principal impediment to fluid flow. At effective stresses higher than 20 MPa, the mean fracture aperture continued to diminish with increasing stress, but this had little effect on flow because the small tortuous flow channels deformed little with increasing stress.