Imbibition Assisted Two-Phase Flow in Natural Fractures

Abstract

SPE Members Abstract 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-characteristic 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. Introduction The essence of commercially available simulators for NFR is the dual system (dual porosity or dual permeability). Matrix and fractures sub-systems constitute the main elements of NFR simulators. Variations have been introduced with the application of sub-domaining concept for further characterization of the matrix. A fundamental assumption in dual porosity systems is the predominant transport role of the fractures. Properties of both the matrix and the fracture are assigned values at each grid block. Solution of flow equations for the fractures coupled with transfer functions between matrix and fractures is carried out for history matching or prediction purposes. Fracture network representation in dual systems are often orderly and systematic with a parallel or orthogonal configuration. In recent years, alternative modeling aproaches for representation of network of natural fractures have been proposed. An example is the potential use of fractal geometry (Fig. 1).In this study, our main focus is the properties assigned to the fracture system and specifically the relative permeability aspect of such networks for two phase flow. The two phases considered are oil and water with situations encountered in water drive, water injection or water coning. We conducted experiments coupled with numerical modeling to scrutinize two-phase flow in natural fractures and to propose an alternative conceptual model for such representation.