Heavy Oil recovery through steam flood and steam stimulation method requires the injection of high pressure steam into the formation. The high temperature reduces the viscosity of the heavy oil and allows it to flow into wells from which it is pumped to the surface. This process can be described as an addition of thermal energy to a reservoir by steam injection. Production is therefore dependent on the amount of thermal energy received by the reservoir.
Most steam generators used for thermal recovery are designed to produce wet steam of up to 80% quality, because this requires less stringent water quality standard. The amount of thermal energy being injected into a well can be determined if steam quality, besides other parameters, such as pressure and flow rate are known.
Normally, in a heavy oil project, the steam generator and other surface facilities are located in a central position surrounded by the wells. Steam produced by one or more steam generators is carried through a single pipe to the wellhead area, where it is divided for injection into individual wells. In general, steam division is achieved by using a branch type manifold. When wet steam is divided through this kind of manifold, however, the resulting streams usually have different steam qualities all of which are unknown. Individual well therefore receive uneven and unpredictable amounts of thermal energy.
Unknown heat distribution results in poor reservoir analysis, and also limits the control operating personnel have on production rates. This paper describes a wet steam manifold system which has been introduced at Gulf Canada's Cold Lake heavy oil-pilot project, in order to achieve distribution of nearly identical steam quality into each well.
Figure I shows the relative location of the steam generation facilities and the wells. A cluster of 6 wells are located about 2,200 feet from the steam plant. A 6" main stream line delivers wet steam of approximately 80% quality to a junction point at a satellite, located 18 meters from the wellheads. The satellite is essentially a piping arrangement, which allows switching of steam, gas or production fluid to and from the wells.
If the main stream line were simply connected to the different wells through a steam header system, i.e. a conventional branch type manifold, the bends, and the tees of the piping system would cause unequal distribution of steam quality. Normally, the tee configuration of the conventional manifold acts as a separator, supplying high quality steam in the vertical branch while a much lower quality steam continues in the main line. This is because the liquid portion has difficulty turning corners at higher velocities due to its higher momentum. The steam quality is also divided unevenly if the manifold is horizontal, because flow velocity determines which line will have higher quality. Therefore, it was decided to use a different type of manifold system, which would split the wet steam more evenly.
A flow divider was designed based on a model tested at the University of Waterloo by Fouda and Rhodes (1).