| Heavy oil reservoirs are suitable for the thermal recovery by Steam-Assisted Gravity Drainage (SAGD) process as long as the reservoir thickness is relatively thick. For thin reservoirs, the heat losses to the over/under burden are excessive. To overcome this difficulty, another approach has been proposed called Vapour Extraction, (Vapex) which utilizes the injection of saturated hydrocarbon vapours at approximately reservoir temperature. The determination of the swept volume in a SAGD/Vapex process provides an early means to evaluate the project's progress.; The pressure falloff test has been the most common well test used for estimating swept volume. The pressure analysis of this falloff test data is based on the pseudosteady state method. Further, this method has been used successfully to estimate swept volume/chamber size, from pressure falloff testing of horizontal wells. This method is easy to use and is similar in form to the well-known productivity equation for a vertical well. Due to the big contrast in mobility of the swept zone contrasted to the un-swept zone, the flood front behaves like a closed boundary. When the pressure falloff data is graphed against time, it is shown as a semi-log straight line with much fluid mobility in the swept region. This semi-log straight line is followed by a Cartesian straight line which is related to the volume of the swept region. The Cartesian straight line represents a period when the front behaves as a closed boundary. (Abstract shortened by UMI.)... |
