Heavy-oil production from a steamdrive may be improved by adding gases to reduce the steam requirement, to swell the oil, and to reduce oil viscosity. To help compare carbon dioxide (CO2) and methane (CH4), two of the most reasonable choices of gaseous additives, we measured the viscosity and density of a Lloydminstertype heavy oil when saturated with each gas at a single pressure at25°, 80°, and 150°C. Our measurements were repeated in the presence of a waterphase to address the lingering questions about the effect of water on this equilibrium, especially at 150°C.
In addition to confirming trends identified by previous authors, the results showed that the benefit of dissolved CH4 diminishes much less rapidly withrising temperature than for CO2. By 150°C the differences in benefit are small, which indicates that CH4 could be a more economical choice than CO2 as a steam additive in many reservoirs. In addition, no effect of equilibrium water was detected.
The use of gaseous additives to improve the performance of steam-assisted oil recovery has received increasing interest. Field tests as early as 1972were reported by Sperry1 for the Vapor Thermy process, and in 1974, Weinstein2proposed the idea on the basis of computer modeling tests. Later Meldau et al.3reported favorable results of field trials in the Paris Valley field.