Many of the Lloydminster-type heavy oil reservoirs are unsuitable for thermal recovery by steam injection because they are relativelythin and the heat losses to the under- and overburden are excessive. To overcome this difficulty, a new approach has been proposed which utilizes the injection of saturated hydrocarbon vapours at approximately reservoir temperature. There are several modifications of the basic principle under development in which the amount of extraneous heat injected varies from none to moderate, and the vapour chamber is maintained at reservoir temperature to 30C above it. This flexibility allows the approach to be followed for the recovery of both conventional heavy oils and for bitumen.
The method, termed "Vapex", utilizes two horizontal wells and is closely related to the SAGD process but with the steam chamber replaced by a chamber containing hydrocarbon vapour near its dewpoint.
The quality of bitumen or heavy oil can be improved substantially by in situ deasphalting with propane vapour. The removal of asphaltenes reduces the viscosity of the produced oil and createsan oil that is more easily refined.
In this paper we present new experimental results obtained in ascaled physical laboratory model and discuss the effect of factors such as injected G/O ratio, different saturation pressures and vapour chamber temperatures on the rate of oil production, the extent of in situ deasphalting and the quality of the recovered oil.
A third of the world's oil is in Canada as heavy oil and bitumen. The deposits are located in Alberta and Saskatchewan. Heavy oil shaving an in situ viscosity less than about 10,000 Mpa.s can be produced by conventional means but only with low recoveries. Both bitumens and conventional heavy oils are produced with higher yields by thermal methods or, in case of shallow tar sand deposits, by surface mining. Thermal methods usually involve the intermittent injection of steam into the reservoir followed by soaking and production (cyclic steam injection), or the continuous injection of steam (steam drive, SAGD). Many of the heavy oil reservoirs are relatively thin and the resulting heat losses into the over- and underburden make steam-based recovery processes uneconomic.
Recent advances in horizontal drilling techniques make the drilling cost of horizontal wells per unit of total length comparable to that of vertical wells, and horizontal wells are being drilled extensively in different parts of the world. Recovery from reservoirs that used to be unattractive with vertical wells has become quite practical with long horizontal wells.
The use of horizontal wells for the non-thermal recovery of heavy oils, but at low recoveries, has been economically successful, particularly in Saskatchewan. Horizontal wells have also made the SAGD process practical and economically attractive.