VIDEO MICROSCOPY OF MULTIPHASE FLOW IN A MODEL POROUS MEDIUM

Abstract

A novel flow cell has been developed to study the mechanisms of steady state, cocurrent, multiphase flow through porous media on a microscopic level. It consists of a rectangular capillary tube packed with a bilayer of monodisperse glass beads 109 microns in diameter. The pore sizes in the model are of the order of magnitude of those in actual petroleum reservoirs. An enhanced video microscopy and digital image processing system was used to record and analyze the flow data. Several pre-equilibrated fluid systems covering a wide range of interfacial tensions were studied using a syringe pump capable of producing superficial velocities of 0.1 to 2,000 ft/day. With this combination the capillary number Ca was studied from 10\sp{-7} to 1.0. Displacement experiments were performed to investigate the qualitative behavior of flow in the novel micromodel. Nonwetting oleic phase was trapped at low Ca (<10\sp{-3}), and improved recovery was observed as Ca was increased. Complete recovery of nonwetting phase was obtained with both liquid crystalline and middle phase microemulsion/excess oil systems at high Ca = 0.01. For the steady cocurrent flow experiments a volumetric injection ratio of 1:1 was primarily used, but experiments with various ratios up to 10:1 were performed, with no basic change in observed flow mechanism. At low capillary numbers, the expected stable continuous tortuous paths are observed. At a capillary number of about 0.001 these continuous paths break down and the nonwetting phase starts flowing freely in large regions 10-20 pore diameters in length in the direction of flow. A steady state equilibrium mobile ganglion size is observed at a given capillary number. As the capillary number is increased, these regions become smaller until finally single pore size ganglia are flowing freely at a Ca of about 0.01. If the capillary number is increased above this value, the size of the nonwetting phase ganglia continues to decrease, even falling below the pore throat diameter. Eventually the small drops stretch out into a filament type flow where viscous forces predominate and several filaments pass through a pore throat simultaneously