The Steam And Gas Push (SAGP)-2: Mechanism Analysis And Physical Model Testing

Abstract

Abstract At the 48th Annual Technical Meeting, one of us presented a paper that showed that there was a possibility of making the SAGD process more efficient by adding a small concentration of a non-condensible gas such as methane to steam. For this to be effective the steam injection well should be located slightly above the production well. With this configuration, and with a small continuous production of gas with the produced 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 chamber, is greatly reduced; the steam oil ratio is much lower. Another configuration involves the continuous injection of a small stream of 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 heat is confined to the near wellbore region and again there is a considerable economy. The present paper discusses further analysis of these configurations and also results from physical model tests that are being carried out at the University of Calgary. The results of these experiments have been very positive and it appears that the concept may be even more effective than was predicted 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 to the falling liquids; this mechanism involves the creation of a large surface area for mass transfer. As a result, the steam chamber is not on & much lower in temperature, particularly at the top, but it also rises mare slowly and spread laterally more quickly. A larger volume is draining at a much lower temperature. Measurements ma & in our model show large improvements in the steam/oil ratio. The observation of the new mechanism suggests that this approach may have economic 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. Recently a consortium of eight companies has been formed to support the project and we are grateful for their continuing support. Introduction It is estimated that there are 273 billion m3 heavy oil and bitumen in place in Canada. They are deposited mainly in the Athabasca, Cold Lake, Lloydminster and Peace River areas. Conventional heavy oil (10 to 20 °API), which is partially recoverable by conventional in-situ methods, is less than 2% of the total resources. Most of the bitumen has a viscosity ranging from 100,000 to over 1.0 million mPa-s at reservoir temperature. It is present in a solid or semi-solid state in the porous media and there is almost no mobility at the initial reservoir conditions. The effective recovery of bitumen by in-situ methods is difficult. The current production of bitumen is over 400,000 barrels a day, which constitutes about 70% of the total heavy oil and bitumen production (AEUB, 1996) in Canada.