Single-Phase Flow Through Natural Fractures

Abstract

ABSTRACT It is well known that for a single-phase fluid flowing between smooth parallel plates, the pressure drop is proportional to the cube of the aperture separating the plates. Some investigators2,3 have looked at the effect of surface roughness on flow using fabricated surfaces, induced fractures, or sawed surfaces and have found deviation from that law at small apertures. This paper presents new laboratory data for single-phase flow through open rough natural fractures. Two types of petroleum reservoir rocks (sandstones and cherts) were used, each having a different surface roughness. Flow through both open and closed fractures is evaluated with apertures ranging between 0.002 to 0.0253 in. A technique for measuring apertures in-situ has been developed which avoids back-calculating apertures from flow data, as other investigators have had to do. Fluids with viscosities of about 1 and 18 cp were used. At large apertures (0.0253 in), compared to the surface roughness, the cubic law is followed; at smaller apertures for rough fractures, deviation is seen. Transition from laminar to turbulent flow is smooth but is dependent on surface roughness for smaller fracture apertures. Critical Reynolds Number, the Reynolds Number where laminar flow ends, is seen to decrease with decreasing fracture aperture for rough fractures. Data are correlated using plots of friction factor versus Reynolds Number.