Three Dimensional Numerical Modeling of Fracture Flow for Rock Core Coupled with X-Ray Computed Tomography

Abstract

A three dimensional numerical modeling coupled with X-ray Computed Tomography (CT) for fracture flow was applied to fractured granite core samples. One of the samples had an artificial single fracture, and the others had natural multiple fractures. A relationship between CT value and fracture aperture (fracture aperture calibration curve) was first obtained by X-ray CT scanning for a fracture calibration standard with varying fracture apertures (0.1-0.5 mm). As a result, a linear relationship was obtained. With the fracture aperture calibration curve, three dimensional distributions of CT values of the samples were converted into fracture aperture distributions to obtain fracture models of the samples. Porosities of the fracture models could provide good agreement with experimentally determined porosities for all the samples. By using the fracture models, a fluid flow simulation was also performed with a local cubic law-based fracture flow model. Numerical permeabilities by the flow simulation were much higher than experimentally determined permeabilities of the samples. It was however possible to match the numerical permeabilities with the experimental permeabilities for all samples, by using a unique modification coefficient of 0.5 for the fracture aperture in the fracture flow model. Although the X-ray CT scanning was performed at room temperature and pressure, it was expected that the numerical modeling had the possibility to provide insights into the heterogeneous nature of fracture flow, such as channeling in reservoirs, as well as porosity and permeability.