In the numerical modeling of naturally fractured reservoirs, the multi-phase flow in the fractures and the flow between the m atrix and fractures need to be formulated accurately to represent the physics of imbibition.

Recent developments in computational techniques have made it possible to model complex dual porosity systems. However, due to lack of experimental support for the fracture properties and the matrix-fracture transfer process, the accurate performance prediction of such systems requires a realistic reservoir characterization and the reliable estimation of fracture and matrix-fracture interaction parameters.

Dual porosity systems consist of two different media having completely different properties. As such, separate input data are introduced into dual porosity simulators and the transfer between m atrix and fracture is defined with a transfer term . Fracture properties such as relative permeabilities and capillary pressure are very hard to estimate experimentally in the laboratory. Practitioners often use idealized models for such representations. Also, the heterogeneous and irregular structure of the fracture system in a reservoir makes it difficult to assign a single set of values to the fracture properties.

In this thesis, static and dynamic experiments were performed on fractured rock samples to study the physics of capillary imbibition and its influence on effective system relative permeabilities. Studies were focused on the effect of different matrix, fracture, and flow properties on the measurement of the relative permeabilities of a composite (dual-porosity) system consisting of matrix rock and fractures. Special attention was given to tight m atrix samples that represent a typical naturally fractured reservoir matrix. Unsteady and steady state experiments were performed for different flow and composite system parameters. A dual-porosity simulator was calibrated to simulate and match the observed laboratory derived measurements and to extend the sensitivity studies.

Unlike homogeneous porous media, effective relative permeabilities of the composite system (fracture and m atrix) are strong functions of additional parameters such as flow rate, matrix permeability and wettability, fracture aperture and density, initial matrix saturation, and flow direction.

The effect of these parameters were studied experimentally. Depending on the flow rate, wettability conditions and the fracture density, the counter-current imbibition can significantly alter the saturation profiles in the fracture. The relative permeability values associated with the bulk fracture-m atrix system become transient, influenced by prevailing flow velocities and saturation histories. Composite system relative permeabilities, developed for laboratory data and field scale performance, are shown to be a convenient tool for the simulation of two-phase flow in a fracture network when considering the m atrix as a sub-system of the fracture network. This new approach will puts less emphasis on the m atrix calculations in dual-porosity models, characterization of two-phase flow (oil-water) in the fracture network becoming the primary object.