Foamy oil ow in porous media

This model is motivated by the need to explain anomalous features associated with production from reservoirs of so-called foamy oils. These oils are described by some of their properties of response to pressure declines; it is noted that they nucleate dispersed gas bubbles and display obvious foaminess in well head samples produced by solution gas drive in which oil and gas is produced by the draw down of pressure. When compared with the response of conventional oils, the response of foamy oils to draw down of pressure is more favorable; primary recovery factor (percentage of the oil in the reservoir which can be recovered) the rate of production, the ratio of oil to gas which is recovered and the length of time that a given pressure gradient can be maintained are all increased substantially; the reasons for the favorable response of foamy oils in solution gas drive are not well understood and tentative explanations which have been put forward are controversial (see Maini (1996) and Pooladi-Darvish and Firoozabadi (1997) for recent reviews). One property of foamy oils which has not been emphasized in the literature on solution gas drive is that these oils carry copious amounts of dissolved gases in the condensed state. The relevant thermodynamic property for this is \gas solubility"; a function of temperature and pressure at equilibrium which gives the volume fraction of dispersed gas from the crude oil by outgassing. Tables of solubility of methane, carbon dioxide and other gases in various Canadian crude oils have been given by Svrcek and Mehorta (1982), Peng, Fu Bird and Hsi ( )1 and others. Naturally, if there is a lot of dissolved gas in, there is potential for a lot of gas to come out. The oils considered to be foamy evidently cavitate small dispersed bubbles which move with the crude oil in which they are dispersed. Experiments done by Pooladi-Darvish and Firoozabadi (1997) have shown that bubbles which arise from depressurization of silicone oil and heavy crude of equivalent vis-