Wells – Processes – Operating valve – closure – or changeable restrictor in a well
Reexamination Certificate
2000-03-02
2001-08-14
Tsay, Frank S. (Department: 3672)
Wells
Processes
Operating valve, closure, or changeable restrictor in a well
C166S332100
Reexamination Certificate
active
06273194
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and a device designed to control the downhole flow rate of a petroleum fluid flowing 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 different locations.
STATE OF THE ART
It is known that adjustable flow rate valves can be placed down a well 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 adjustable flow rate valves.
Adjustable flow rate valves are installed on the production tubing so as to define a passage of adjustable section between the inside of the tubing and the annular space surrounding it. Such a valve commonly comprises a slidably-mounted closure sleeve placed inside the production tubing, and holes formed in the tubing at the level of the sleeve. Such valves further comprise actuators controlled remotely from the surface so as to move the closure sleeve parallel to the axis of the production tubing.
Usually, the actuator of an adjustable flow rate valve comprises an electrical actuator or a hydraulic actuator placed outside the production tubing and parallel to the axis thereof. The drive rod of the actuator is then fixed to a lug secured to or integral with the closure sleeve.
In such a conventional configuration, since the actuator is placed outside the production tubing while the closure sleeve is coaxial therewith, the mechanism is asymmetrical. The thrust force or the traction force exerted on the closure sleeve therefore generates torque which tends to cause the sleeve to tilt. Such tilting torque gives rise to friction between the sleeve and the production tubing. As a result, two reaction forces acting in opposite radial directions are applied to each of the ends of the sleeve. The reaction forces compensate for the tilting torque (radial components) but they also tend to oppose the movement in translation of the sleeve (axial components). The axial forces are proportional to the coefficient of friction between the two materials constituting the sleeve and the production tubing.
That purely mechanical effect is accentuated by the particularly unfavorable conditions that prevail at the bottom of the well, and that generally cause a deposit to form on the production tubing. In the presence of such a deposit, the front end of the closure sleeve (for a given sleeve displacement direction) is subjected to wedging caused by the deposit, at a place diametrically opposite from the force exerted by the actuator. Conversely, the front end of the sleeve must remove the deposit formed on the tubing in its portion situated on the same side as actuator.
That effect due to the deposit combines with the tilting effect due the asymmetrical nature of the mechanism to make it particularly difficult to cause the closure sleeve to move. It is thus necessary to use a very powerful actuator whenever a deposit tends to form on the production tubing, which occurs very frequently in an oil well. Very rapidly, the actuator can become too weak to drive the sleeve, and the mechanism seizes. The reliability of flow rate control devices designed in that way is thus poor.
Another problem that arises with adjustable flow rate vales of that type concerns their fluid-tightness when they are in the closed state. Fluid-tightness is generally obtained by means of two dynamic sealing gaskets mounted on the production tubing on either side of the holes passing through said tubing. When the valve is in the closed state, the closure sleeve extends across the holes and co-operates normally in fluid-tight manner with the two sealing gaskets.
Because of the asymmetrical nature of the mechanism, the closure sleeve is not exactly concentric with the production tubing. In particular, each time the sleeve moves, it tilts slightly in one or other direction depending on the direction of movement, as observed above. Thus, when the valve is caused to open starting from its closed state, the gasket situated frontmost relative to the direction of movement of the sleeve is compressed excessively on the side on which the actuator is situated, whereas it is not compressed sufficiently on the opposite side. The reverse applies to the gasket situated rearmost, which gasket is subjected to excessive compression on the side opposite from the actuator , while being insufficiently compressed on the side on which the actuator is situated. The respective over-compressed and under-compressed portions of the gaskets are reversed when the closure sleeve returns to the state in which the device is closed. The gaskets are therefore subjected to cycles of excessive compression and of insufficient compression, thereby accelerating ageing of said gaskets. Risks of leakage thus appear rapidly in the regions in which the gaskets are insufficiently compressed while the closure sleeve is moving.
This analysis shows that the current design of adjustable flow rate valves placed down wells is not satisfactory from the point of view of reliability. That goes against the function that such valves are supposed to perform, which is to provide optimized oil well management. Any maintenance on such adjustable flow rate valves is costly (removal and re-insertion of the production tubing), and it results in production being interrupted, which causes the yield of the well to drop.
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 slidably-mounted facing said hole, and drive means mounted eccentrically on the production tubing and suitable for moving the sleeve over a given path, said drive means acting on the sleeve via at least one intermediate part which co-operates with the production tubing via guide means that define said path, and that co-operate with the sleeve via coupling means that are flexible except along said path, and that are disposed symmetrically about the axis of the production tubing.
In such a device, the intermediate part and the flexible coupling means interposed between said part and the sleeve decouple the coupling between the drive means and the sleeve. The sleeve thus centers itself on the axis of the production tubing and it is not subjected to any tilting torque. For the same force exerted by the drive means, much greater reliability is thus obtained. In addition, the sealing means carried by the production tubing are subjected to compression forces that are constant and uniform, and that increase the life-span of the sealing means very significantly.
In a preferred embodiment of the invention, the path over which the sleeve moves is parallel to the axis of the production tubing.
In addition, the drive means advantageously act on the intermediate part via a drive rod extending parallel to the axis of the production tubing.
In which case, the coupling means are preferably installed at two places disposed symmetrically about the axis of the production tubing, in a first plane containing said axis and lying perpendicular to a second plane containing both said axis and also the axis of the drive rod.
In the preferred embodiment of the invention, the drive means, the intermediate part and the closure sleeve are mounted outside the production tubing.
The intermediate part is then advantageously connected to the production tubing by guide means so that circumferential clearance is provided between the tubing and the intermediate part. This characteristic makes it possible to prevent any deposit present on the tubing from hindering the movement of the intermediate part. Thus, the system is made more efficient, which makes it possible to limit the forces exerted by the ac
Hiron Stephane
Rayssiguier Christophe
Tourillon Vincent
Castano Jaime
Griffin Jeffrey
Schlumberger Technology Corp.
Tsay Frank S.
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