The steam and gas push (SAGP) - 2: Mechanism analysis and physical model testing

At the 48(th) Annual Technical. Meeting of the Petroleum Society, one of us presented a paper that showed that there was a possibility of making the S AGD process more efficient by adding a small concentration of a non-condens ible gas such as methane to steam((1)). For this to be effective the steam injection well should be located slightly above the production well. With t his configuration, and with a small continuous production of gas with the p roduced oil and condensate, the non-condensible gas becomes concentrated in the upper part of the chamber and the heat loss to the overburden, and for the heating of the cham; her, is greatly reduced; the steam oil ratio is m uch lower. Another configuration involves the continuous injection of a small stream o f non-condensible gas from a well or wells near the top of the chamber with steam injection from a lower well or even into the production well. The he at is confined to the near wellbore region and again there is a considerabl e economy. The present paper discusses further analysis of these configurations and al so results from physical model tests that are being carried our at the Univ ersity of Calgary. The results of these experiments have been very positive and it appears that the concept may be even more effective than was predic ted originally. The reason for this appears to be that the introduction of gas with steam invokes a new mechanism as the gas flows counter-currently t o the falling liquids; this mechanism involves the creation of a large surf ace area for mass transfer. As a result, the steam chamber is not only much lower in temperature, particularly at the top, but it also rises more slow ly and spreads laterally more quickly. A larger volume is draining at a muc h lower temperature. Measurements made in our model show large improvements in the steam/oil ratio. The observation of the new mechanism suggests that this approach may have e conomic applications in fields having top water such as Surmont as well as in more normal type reservoirs. In general, the improved performance should broaden the range of reservoirs that can be produced economically.