Prediction of fluid occupancy in fractures using network modeling and x-ray microtomography. I: data conditioning and model description.

This paper presents a two-dimensional pore-scale network model of a rough-walled fracture whose inner structure had been mapped using x-ray microtomography. The model consists of a rectangular lattice of conceptual pores and throats representing local aperture variations. It is a two-phase model that takes into account capillary, viscous, and gravity forces. Mapping of fluids and fracture topology was done at a voxel resolution of 0.027 x 0.027 x 0.032 mm(3) , which allowed the construction of realistic fracture representations for modeling purposes. This paper describes the necessary data conditioning for network modeling, a different approach to determine advancing and receding contact angles from direct x-ray microtomography scans, and the network model formulation and methods used in the determination of saturation, absolute and relative permeabilities, capillary pressures, and fluid distributions. Direct comparison of modeled results and experimental observations, for both drainage and imbibition processes, is presented in the companion paper [M. Piri and Z. T. Karpyn, following paper, Phys. Rev. E 76, 016316 (2007)].