Bypass valve closing means

Details Bypass valve closing means Bypass valve closing means

2000-01-27

2001-09-25

Dang, Hoang (Department: 3672)

Wells

Valves, closures or changeable restrictors

Destructible element

C166S319000, C166S323000

Reexamination Certificate

active

06293342

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to bypass valves for use in wellbores, particularly but not exclusively to the secondary means for closing a bypass valve in the event that the primary means for closing the bypass valve fails to operate.
2. The Prior Art
It is common practice in the oil and gas drilling industry to incorporate a bypass valve in a drill string between a MWD (Measurement While Drilling) tool and a hydraulic anchor packer so that wellbore fluid may be pumped down the drill string to operate the MWD tool without prematurely setting the anchor packer. A conventional bypass valve typically incorporates a piston which slides within a cylinder in response to dynamic fluid pressure. The wall of the cylinder is provided with a plurality of holes which allows fluid to pass from the drill string bore to the wellbore annulus. The piston is held in an open position by biassing means (such as a spring or a shear pin) and thereby allows wellbore fluid to operate a MWD tool located uphole of the bypass valve whilst preventing the generation of a pressure differential between the interior and exterior of the drill string sufficient to set an anchor packer. When the setting of the anchor packer is required, the flow of wellbore fluid down the drill string is increased so as to generate a dynamic pressure sufficient to overcome the biassing means. The piston then slides within the cylinder to a closed position in which the holes are sealed. A cross-sectional side view of this type of bypass valve is shown in FIG.
1
.
Conventional bypass valves can occasionally fail to move to the closed configuration when the appropriate fluid pressure is applied and this will often lead to costly and time consuming delays in a given downhole operation. In an attempt to overcome this problem, a “sliding piston” type of bypass valve (such as the one described above) has been developed with a secondary closing means in addition to the primary closing means (the sliding piston). A cross-sectional side view of this improved bypass valve is shown in FIG.
2
. In the event that the primary piston within the cylinder fails to move to the closed position in response to an increase in dynamic pressure, the static pressure of the wellbore fluid in the annulus may be increased by a pump located at the surface, with the internal bore of the drill string having been sealed off, so as to generate a sufficient pressure above the downhole hydrostatic pressure to rupture a burst disc provided in the bypass valve casing. A pressure differential is thereby applied across the length of a second piston and acts to press the second piston into a closed position. The location of the second piston in the closed position is such that the holes in the wall of the cylinder are sealed. Thus, although the primary closing means may fail to operate correctly, the bypass valve can nevertheless be moved into a closed configuration by the operation of the secondary closing means.
SUMMARY OF THE INVENTION
A first aspect of the present invention provides a bypass valve for selectively isolating the interior of a downhole assembly from the exterior thereof, the bypass valve comprising: a body having a bore adapted to allow the passage of wellbore fluid therethrough; a chamber defined in the body; at least one aperture provided in the body adapted to allow fluid communication between the bore and the chamber; at least one aperture provided in the body adapted to allow fluid communication between the chamber and the exterior of the bypass valve; a piston slidably mounted in the chamber and movable between a first position in which fluid communication between the bore and the exterior of the bypass valve by means of the apertures is permitted and a second position in which fluid communication between the bore and the exterior of the bypass valve by means of the apertures is prevented, the piston being movable from the first position to the second position in response to a first predetermined fluid pressure differential; means for selectively exposing the piston to the first predetermined fluid pressure differential; and a cavity defined between the piston and the body such that the cavity changes volume when the piston moves from the first to the second position, wherein the cavity is sealed by sealing means comprising a one-way seal adapted to allow the passage therepast of fluid from the cavity in a first direction but adapted to prevent the passage therepast of fluid in a direction opposite to the first direction.
The bypass valve of the present invention may be closed by exposing the piston to the first predetermined fluid pressure differential and thereby moving the piston from the first position to the second position. In so doing, there is a change in the volume of the cavity defined between the piston and the body. This variation in cavity volume results in fluid attempting to flow past the sealing means provided to seal the interfaces between the piston and the body of the bypass valve. The one-way seal of the sealing means permits this flow of fluid in circumstances where the cavity air pressure is greater than the wellbore fluid pressure. However, a flow of fluid in the opposite direction is not permitted by the one-way seal and a pressure differential across the length of the piston may be thereby maintained so as to lock the bypass valve in the closed configuration. Whilst the bypass valve is located downhole, the cavity air pressure is unlikely to be greater than the wellbore fluid pressure when the piston is in either the first (open) or second (closed) position, and consequently, the air within the cavity is unlikely to flow past the one-way seal during the downhole operation of the bypass valve. However, as the bypass valve is tripped out of hole, the wellbore fluid pressure will drop below the pressure of the cavity air in circumstances where the piston is located in the second (closed) position. Cavity air will then flow from the cavity past the one-way seal. This facility for allowing air to flow from the cavity provides the bypass valve of the present invention with a pressure relief safety mechanism and can assist in ensuring that the piston remains in the second (closed) position once activated.
Preferably, the means for selectively exposing the piston to the first predetermined pressure differential comprises a passage defined in the body and extending between an opening on the exterior of the body and an opening in the chamber, said opening in the chamber being located adjacent the end of the piston distal to the fluid path extending through the apertures and between the bore and the exterior of the bypass valve, and said-passage being sealed by means of a burst disc. It is preferable for the burst disc to rupture at a second predetermined fluid pressure differential having a magnitude greater than that of the first fluid pressure differential. Furthermore, the chamber and piston may have an annular shape. A spring may also be provided to bias the piston towards the second position. Also, the cavity defined between the piston and the body is preferably filled with air. It is also desirable for the portion of the passage extending between the chamber and the burst disc to be filled with air. The air in the cavity and said portion of the passage is preferably at approximately atmospheric pressure. It is also desirable for the bypass valve to incorporate a second piston slidably mounted in the bore and moveable between a first position in which fluid communication between the bore and the exterior of the bypass valve by means of the apertures is permitted and a second position in which fluid communication between the bore and the exterior of the bypass valve by means of the apertures is prevented.
A second aspect of the present invention provides a bypass valve for selectively isolating the interior of a downhole assembly from the exterior thereof, the bypass valve comprising: a body having a bore adapted to allow the passage of wellbore fluid therethrough; a chamber d

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