For modeling naturally fractured reservoirs (NFR) under active water drive, the multi-phase flow in the fractures and the interporosity flow effects need to be formulated accurately to represent the physics of the countercurrent imbibition.

This paper presents experimental results on two-phase (oil and water) flow through natural fractures under many different configurations. Flow experiments were enhanced with the saturation measurement technique using the CT scan. Important variables in our experiments were the nature of the matrix rock and its wettability characteristics and fracture configuration. A wide range of matrix wettabilities were investigated. Flow rate in the fractures, which plays a significant role in effectiveness of the countercurrent imbibition, was carefully monitored.

Relative permeability measurements for the bulk system were conducted under unsteady state flow conditions. Unlike homogeneous systems with a single set of relative permeability plots, for the fractured systems under study, a series of plots are generated. Composite system relative permeability response, which are referred to as Effective Fracture Relative Permeability (EFRP) curves, are formulated. This formulation is a potential tool for reducing the dual-porosity model to a fracture network model, where the matrix is a sub-system of the fracture network, and the matrix-fracture interaction is represented by the EFRP.

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