FracRough—Computer program to calculate fracture roughness from reservoir rock core

Abstract

Measuring roughness of fractures in buried rock is challenging, but important in estimating fracture shear strength and permeability. Here, we present FracRough, a first-of-its-kind computer program that was developed to calculate the joint roughness coefficient (JRC) of reservoir rock fractures from core exterior. Core is often acquired from oil and gas wells using particular drilling bits that cut rocks in a cylindrical shape. The reservoir fractures that are intersected by core typically have planar shapes, and can be profiled and digitized from 360° photographs of the core exterior. The digital profiles appear on the unrolled 360° core photographs as sinusoids, reflecting the elliptical intersections of fracture planes with cylindrical core. Wavelength of the sinusoid is equal to the circumference of the core and amplitude is related to the angle between the core and the fracture. A planar fracture has a profile of perfect sinusoid. However, the actual fractures have a rugged, rough, irregular top and bottom traces (profiles). The purpose is to calculate the degree of roughness denoted as JRC. The way to accomplish this is to fit a sinusoid to the irregular fracture profile. JRC is calculated using the distance of the obtained fracture profiles from a fitting sinusoid at original measurement points. For each fracture, JRC is calculated for top and base profiles separately. FracRough also calculates correlation coefficient and standard deviation of aperture between top and base profiles as mismatch parameters. Mismatches in fracture walls indicate slippage along fracture and/or diagenetic cementation and dissolution.