Gravity Drainage Effects on Compositional Displacements in Fractured Reservoirs

Abstract

This paper investigates the effects of gravity drainage on non-equilibrium compositional displacements in naturally fractured reservoirs (NFRs) by presenting an experimental and numerical simulation study. A quasi 2-D glass bead pack is used to represent a NFR. The matrix and fracture are represented by glass beads and a grooved glass strip, respectively. Conductive fractures are studied. 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 studied. Recovery of phases, compositional analysis and snapshots of saturation distributions are reported. Numerical simulations are used to interpret experimental observations.In immiscible displacements, capillary forces are found to be the main controlling factors for the vertical cross-section reservoir model while a balance between capillary and gravity forces governs gravity drainage displacements. In miscible displacements, the balance between gravity and viscous forces controls sweep efficiency and recovery factor for both reservoir models. Near-mmiscible miscible floods give higher recovery than first-contact miscible floods under gavity drainage. This opposes to the observation made for the horizontal floods. This is in line with the finding reported in the literature using numerical simulations.Force-balance scaling criteria (i.e. capillary, gravity and Bond numbers) diagnose flow regimes during displacements satisfactorily. Black oil simulations sufficiently predict experimental observations of all displacements examined provided that history-matched capillary pressure and relative permeability are used. Compositional analysis of the effluent indicates that the compositional path changes between tie-lines of initial and injection liquids based on saturation profile development.