Visual micromodels are a powerful tool for examining the mechanisms of oil recovery from porous media at the pore level. To this end, an algorithm has been developed to create 2- dimensional flow network patterns simulating porous media with controlled properties. This has been used to manufacture flow micromodels that have different grain size distributions, permeabilities, and heterogeneities. CO2 floods were carried out to determine the effect of several factors, such as injection rate, oil viscosity, and the coinjection of water with CO2, on the displacement process and the oil recovery mechanism.
Viscous fingering was found to be the dominant displacement mechanism up to solvent breakthrough at all the flooding conditions. Subsequent growth of the fingers was by a much slower dispersion-type process. A mechanism for recovering water-shielded oil by a cyclic build-up, thinning-out, and then snap-off of the shield has been observed.
Visual micromodels as used in this study can be defined as flow apparatuses that enable visual observation of multiphase flow behaviour in porous media at the pore level. The glass micromodels used in this study of enhanced oil recovery are essentially a flow network etched onto the surface of a glass plate. The first step in building a micromodel is obtaining a high contrast diagram of a flow network pattern. The flow network pattern is then etched onto a glass plate to produce a micromodel. This plate is then sandwiched with another flat plate to seal the channels. This assembly then forms a twodimensional path through which various flow phenomena may be visually observed. A special micromodel holder enables carrying out floods at reservoir temperature and pressure. Other researchers (included in the survey below) use glass beads, sand grains, or even thin sections of rock sandwiched between glass plates.
Micromodels have proved to be very useful for studying a variety of oil recovery processes such as waterflooding(1); gels for conformance control(2); immiscible displacements(3–6); surfactant floods(7, 8); foam injection(9–12); foamy oil flow(13); microbial EOR(14), and solution gas drive(15–17).
Micromodels have also been used to study specific aspects relating to flow in porous media such as wettability(16, 18–20); capillary pressure(21); interfacial tension(22); asphaltene deposition(23); heterogeneity(24); mass transfer(25, 26), scaling(27); multiple contact miscibility(28, 29), and gravity drainage(30).
Works more closely related to the present study of miscible and immiscible gas injection include Sohrabi et al.(31, 32); Dong, et al.(33); Chatzis et al.(34); Danesh et al.(23, 35); Peden and Husain(36, 37) and van Dijke et al.(38)
This paper presents an innovative method for the design of the flow network pattern in the next section. This is followed with a description of the etching procedure and of the experimental apparatus for carrying out visual micromodel floods at reservoir conditions. Results of several micromodel floods designed to investigate parametrically the influence of several factors on the flooding process are then presented and discussed. Finally, conclusions are drawn.
A variety of approaches have been used in the literature to develop the pore network patterns.
