AREAL SURFACE CHARACTERIZATION OF ACID-FRACTURES IN CARBONATE ROCKS

Abstract

Fracture surface characteristics have significant effect on fracture hydraulic conductivity. The available acid-fracture conductivity correlations do not
consider surface characteristics or make an incipient use of it. A proper description of the acid-fracture surfaces is the initial step towards the right consideration of surface roughness in hydraulic conductivity. This paper presents an areal (3D) surface evaluation of acid-etched fractures, simulated in samples taken from whole cores of an oil producer limestone. The topography of acid-fractured surfaces was assessed using a laser profilometer. The surfaces were evaluated with a set of 3D surface parameters. The results showed that the main features of acid-etched surfaces are large roughness, negative skewness, high kurtosis, and intermediate isotropy, mostly random, but with some spatial orientation. The acid-fractured surfaces can be represented by the rms height, which showed great linear correlation with most of the surface parameters. The parameters texture aspect ratio, bearing index, valley retention index, and density of summits showed low correlation with rms height. A method to calculate fracture width from surface topography was developed. An attempt to explain abnormal behavior in initial conductivity tests revealed the potential use of surface characterization for management of fine particles in oil and gas reservoirs. It is suggested to search improved fracture conductivity correlation through the relationship between lab measured conductivities and surface characterization parameters.

Keywords: acid-fracture, surface characterization, surface metrology, asperity tribology.