| Better understanding of matrix-fracture interaction and imbibition, in general, is needed to model effectively multiphase flow in fractured porous media.; This dissertation provides physically-based information on how to model or simulate matrix to fracture transfer, aids efforts to derive general matrix-fracture transfer functions, and provides recommendations on appropriate assumptions while numerically simulating fractured systems. Using an X-ray computerized tomography (CT) scanner, and a novel, CT-compatible core holder, a series of experiments to study air and oil expulsion from rock samples by capillary imbibition of water in a three-dimensional geometry were performed. Various injection rates and fracture apertures were utilized. Two different fracture flow regimes were identified. The “filling-fracture” regime shows a plane source that grows in length due to relatively slow water flow through fractures. In the second, “instantly-filled fracture” regime, the time to fill the fracture is much less than the imbibition time. Here, imbibition performance scales as the square root of time. In the former regime, the mass of water imbibed scales linearly with time.; A micromodel and a micromodel holder were also designed and built that allow detailed visualization of fluid movement, matrix-fracture interaction, water advance in the fracture and the pattern, extent, and mode of imbibition in the matrix at the pore scale. The existence of the two different modes of matrix and fracture fill-up were verified and analyzed at the pore-scale. The filling-fracture regime provides more efficient recovery because imbibition occurs in a cocurrent mode.; A new analytical model is proposed for filling fractures incorporating implicit matrix/fracture coupling. Good agreement was found between experiments and calculations. The solution provides the location of the wetting phase front in the fracture and the saturation distribution in the matrix.; New time-dependent matrix-fracture transfer shape factor formulations and transfer functions for both filling- and instantly-filled fracture transfer were derived based on dimensional analysis. The parameters involved in the new formulations are obtained by means of, either the new analytical model for imbibition, or the experimental data. Fine-grid simulation was performed to determine the fracture relative permeabilities that best matched the experimental results, the analytical model and the transfer function. |
