An Experimental and Numerical Study of Compositional Displacements in Fractured Reservoirs

Abstract

This paper presents an experimental and numerical simulation study to investigate the effects of driving forces on non-equilibrium compositional displacements in naturally fractured reservoirs. A quasi 2-D glass bead pack is used to represent a cross section of small sector in a fractured reservoir. The matrix and fracture of the reservoir are represented by glass beads and a grooved glass strip, respectively. Conductive, isolated and inclined fractures are studied. A complex fracture network is also investigated by building two fractures crossing each other. An analogue ternary fluid system (isooctane, brine and isopropanol) is used to control the interfacial tension (IFT) between the phases at ambient conditions. Immiscible, near-miscible and miscible floods are conducted. Recovery of phases, compositional analysis and snapshots of saturation distributions are reported. Numerical simulations are used to interpret experimental observations. In all fractured models, capillary forces are found to be the main controlling factor in immiscible displacements. However, in miscible displacements, the balance between gravity and viscous forces leads to higher swept area and may be higher recovery in some of the cases. The position of a fracture affects the displacement performance significantly. Compositional analysis of the effluent indicates that the compositional path changes between tie-lines of initial and injection liquids based on saturation profile development. Force-balance scaling criteria (i.e. capillary, gravity and Bond numbers) were used to diagnose flow regimes during displacements. Then experimental results have been interpreted by black oil simulator. Experimental observations of immiscible displacements were sufficiently predicted. However, in order to accurately predict the results of miscible displacements, a fully compositional simulator is recommended.