Series of tests were carried out to examine the effect of several factors on the mobility of carbon dioxide/foaming agent coinjected in cores. These factors include the permeability of the porous media, the f low rate, the temperature, and the pressure. The latter two were selected so that the state of the injected carbon dioxide was varied from a gas to a liquid, to a supercritical low density fluid, and to a supercritical dense fluid.
Alipal CD-128 was selected for the flow tests in oil-free cores. The mobility of the injected carbon dioxide was appreciably reduced at all the test conditions in the relatively less permeable Berea core (0.757 μm2). In the more permeable glass bead packs (3.5 and 20.2 μm2) the foaming agent was most effective at the supercritical test temperature and pressure (~45 ºC and 13.79 MPa). i.e. when carbon dioxide was a dense fluid. A flow rate dependency of the mobilities was observed at many test conditions: A minimum flow rate was sometimes required, presumably to generate a foam. In other cases the injection rate affected the rate at which the mobilities were reduced to their steady values but had little effect on the level of these steady values.
Horizontal gas injection enhanced oil recovery schemes have two inherent disadvantages: Viscous instability and gravity override. The first is caused by the fact that the injected gas is more mobile than the reservoir oil, hence it tends to finger through the oil instead of sweeping it in a piston-like manner. Gravity override is caused by the density of the injected gas being less than that of the oil, thus the gas tends to rise over the oil and does not sweep the reservoir uniformly. Both these factors decrease the sweep efficiency of horizontal gas floods and consequently lower oil recovery.
The work described in this paper is directed towards controlling injected gas mobility through the use of foams. The objectives of this research include gathering data on the mechanics of foam flow in porous media under a variety of conditions likely to be encountered during enhanced oil recovery operations. The topics discussed here include the effects of the physical state and flow rate of Injected fluids on foamed gas mobilities, and foam flow through stratified cores.
The flow of foams in porous media is a topic that has recently come to prominence In the petroleum engineering community. The reason for this is the potential of using foams as mobility control and sweep improvement agents to increase the yield of oil from gas flooding operations.
There are several recent reviews1,2,3 of the various aspects of the use of foams in enhanced oil recovery. For the purpose of the present work, a quick summary will be made of the results of research efforts dealing specifically with the rheology of foam. There does not appear to be up to now a model that can quantitatively describe the rheology of foams in porous media over a wide range of conditions, but progress in this field is being made4,5.
