| 摘要 |
The degradation of steam quality due to heat losses prior to its injection into a heavy oil reservoir is reduced by a process utilizing the heat contained in a stream of reservoir fluids produced from the same reservoir, following a cycle of steam injection. These hot reservoir fluids are produced from one of several horizontal drainholes connected to the same vertical cased well, while at least one of the other drainholes is under cyclic steam injection. Steam from a boiler located in close proximity of the well head is conveyed downhole through an insulated tubing to a Downhole Valve Section used to direct the flow of steam from the steam tubing to each of the drainholes in succession and to direct the flow of reservoir fluids from the previously steam-injected drainholes to the production tubing. Both tubings are installed within the casing of the vertical well and each of them is dedicated to carrying only one type of fluid: steam or reservoir fluids. Only the drainhole liners see an alternance of steam and of reservoir fluids. The heat contained in fluids supplied from the surface for lifting the produced fluids to the surface is also used to reduce heat losses from the steam tubing to the cold rocks surrounding the well. The heat loss reduction is achieved by reducing the temperature gradient across the insulation layer of the steam tubing. Detrimental heat losses through the well casing can also be reduced by using an insulated production tubing, concentric with the central insulated steam tubing.
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