Wells – Valves – closures or changeable restrictors – Longitudinally movable operator
Reexamination Certificate
2000-03-03
2001-12-04
Neuder, William (Department: 3672)
Wells
Valves, closures or changeable restrictors
Longitudinally movable operator
C251S344000
Reexamination Certificate
active
06325150
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a device designed to control the downhole flow rate of a petroleum fluid via production tubing.
Such a device may, in particular, be used in an oil well in production to optimize the production of the well over time. It is particularly applicable to the case when the petroleum fluid penetrates into a vertical, horizontal, or deviated well at at least two locations.
STATE OF THE ART
Valves of the on-off type are usually used down oil wells before they are brought on stream. Such valves are installed on the production tubing, where, either initially or at the end of the life of the well (when too much water is produced), they can close off the passage between the inside of the tubing and the annular space that surrounds it. Such a valve usually comprises a slidably-mounted sleeve placed inside the production tubing, and holes formed in the tubing at the level of the sleeve.
When the valve is to be driven in the opening direction or in the closing direction, a suitable tool suspended from a cable or from a tube is lowered inside the production tubing.
More recently, proposals have been made to place adjustable flow rate valves down certain wells in production, in particular in order to optimize production when the petroleum fluid flows into the well at at least two spaced-apart locations.
Documents GB-A-2 314 866 and WO-A-97/37102 relate to such variable flow rate valves.
The variable flow rate valves used for this purpose are derived directly from on-off type valves (internal slidably-mounted sleeve and production tubing provided with holes). They differ from on-off type valves essentially by the fact that they incorporate actuators placed outside the production tubing and remotely controlled from the surface.
Variable flow rate valves play an essential part in optimized well management in oil wells of recent design. It is thus important for them to offer good reliability so that they can operate without maintenance for several years. Any maintenance on such valves is costly (removal and re-insertion of the production tubing), and it results being interrupted, which goes against the object that they are supposed to achieve (optimized well profitability).
One of the essential problems lies in the need to provide dynamic sealing gaskets on the production tubing, on either side of the holes formed therein, so that the valve is properly closed when the closure sleeve occupies the corresponding position.
Such dynamic sealing gaskets are inevitably made of a relatively soft material such as an elastomer. They are thus very fragile. In particular, they are very sensitive to wear, to abrasion, and to fatigue, and they are very poor at withstanding the flow of the petroleum fluid.
Proposals are often made also to form holes in the sleeve. The valve is then fully open when the holes in the sleeve and the holes in the production tubing are in register. The valve is closed when uninterrupted portions of the closure sleeve are in register with the holes in the production tubing.
In the most common case, in which the closure sleeve is suitable for sliding axially relative to the production tubing, that solution leads to causing the holes in the sleeve to go past one of the gaskets when the valve goes from its closed state to its open state, and vice versa. The sealing gasket in question is thus subjected to successive compression and decompression states and might be nipped and cut by the sharp edges of the holes. That accelerates fatigue in the gasket and causes it to wear prematurely.
In addition, the petroleum fluid contains a certain number of impurities such as mud and sand that lodge in the holes in the closure sleeve when the valve is open. The impurities then come into contact with the gasket in question when the sleeve slides subsequently. The gasket is thus subjected to abrasion which accelerates wear on it.
Another problem appears when the valve is opened after being closed for a certain amount of time. There is then a pressure difference which is sometimes large between the dynamic pressure inside the production tubing and the higher static pressure outside the tubing in the underground reservoir being tapped. On valve opening, the pressure equalization that tends to occur between the outside and the inside of the production tubing immediately imparts a high flow rate to the petroleum fluid. The high-rate flow sweeps the surface of the sealing gasket which is then always situated facing the holes formed in the closure sleeve. If no particular precaution is taken, the gasket is then torn away or else it wears very rapidly.
In an attempt to remedy that drawback, it is common to limit the rate of the flow reaching the sealing gasket in question by interposing rings (generally made of metal or of polytetrafluoroethylene) between the gasket and the holes provided in the production tubing. However, such rings are not very effective, and they do not prevent the gasket from suffering accelerated damage as a result of the valve being opened.
Another problem caused by the use of a closure sleeve that is provided with holes is constituted by the edges of the holes wearing rapidly under the effect of the flow of the petroleum fluid. One known remedy to that problem consists in beveling the edges of the holes in the sleeve in the fluid flow direction. However, that also has a detrimental effect on the gaskets which tend to be cut by the beveled edges of the holes in the closure sleeve when said edges arrive at the gaskets.
SUMMARY OF THE INVENTION
According to the invention, there is provided a flow rate control device for controlling the flow rate through production tubing placed in an oil well, the device comprising at least one hole formed in the production tubing, a closure sleeve suitable for sliding over said hole, and sealing means mounted on the tubing on either side of said hole so as to co-operate in fluid-tight manner with the closure sleeve, said device further comprising a protective sleeve mounted in alignment with the closure sleeve, and return means for bringing the protective sleeve automatically into a covering position in which it covers first ones of the sealing means when they are not covered by the closure sleeve.
By means of this configuration, the first sealing means are always covered either by the closure sleeve, when the device is in the closed state, or by the protective sleeve, when the device is open, or else by both sleeves in end-to-end abutment, when the device is almost closed. The sealing means are thus never directly subjected to the flow of the petroleum fluid. Any abrasion wear on the sealing means is thus limited. In addition, the sealing means are permanently compressed so that any fatigue wear is prevented.
In a preferred embodiment of the invention, the return means comprise resilient means interposed between the production tubing and the protective sleeve.
When in the covering position, the protective sleeve is in abutment against an abutment surface associated with the production tubing.
Advantageously, the closure sleeve is suitable for moving between a closure position in which it covers the sealing means and a controlled opening position in which a front edge of the closure sleeve co-operates with said hole to form a through hole of variable section.
In which case, the protective sleeve preferably occupies the covering position so long as the closure sleeve occupies the controlled opening position, the front edge of the closure sleeve being suitable for engaging a rear edge of the protective sleeve while the closure sleeve is moving towards its closure position. The first sealing means are thus always covered fully by at least one of the sleeves, namely the closure sleeve or the protective sleeve.
In this configuration, the front edge of the closure sleeve is advantageously formed on a separate annular portion made of a material having high resistance to erosion wear, such as a ceramic. This characteristic makes it possible to improve the life-span of the closure sleeve significantly.
In comparable
Castano Jaime A.
Griffin Jeffrey E.
Neuder William
Schlumberger Technology Corp.
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