Wells – Valves – closures or changeable restrictors – Fluid operated
Patent
1998-06-04
2000-08-01
Dang, Hoang
Wells
Valves, closures or changeable restrictors
Fluid operated
166320, 166324, 166331, E21B 3410
Patent
active
060952490
DESCRIPTION:
BRIEF SUMMARY
The invention relates to bypass valves for use in wellbores, particularly but not exclusively to bypass valves used during the setting of hydraulic anchor packers.
The drilling industry often has the need to monitor the axial position and angular orientation of a tool (such as a whipstock) within a wellbore, and to rigidly secure the tool within the wellbore once a required position and orientation has been achieved. The position and orientation of a tool may be determined by using a MWD or Measurement-While-Drilling tool. An MWD tool requires a flow of wellbore fluid through a drill string in order to communicate a measured position and orientation to the surface. The flow rates required are often sufficiently high to generate a pressure drop between the inside and the outside of the drill string to prematurely set the hydraulic anchor packer.
To overcome this problem, drill strings are often provided with a bypass valve located between the MWD tool and the anchor packers. When the position and orientation of the drill string is being monitored, wellbore fluid is pumped through the MWD tool via the bore in the drill string. The bypass valve prevents the setting of the anchor packers by allowing the wellbore fluid flowing downhole of the MWD tool to pass into the wellbore annulus. The fluid pressure differential across the hydraulic anchor packer is thereby maintained below the setting pressure.
Once the required drill string position and orientation is obtained, the hydraulic anchor packer is set by increasing the flow rate of the wellbore fluid down the drill string. The increase in flow rate results in an associated increase in dynamic pressure. Once the dynamic pressure increases to a predetermined magnitude, the bypass valve is activated and the fluid path between the wellbore annulus and the drill string bore is closed. The wellbore fluid is thereby directed downhole to the anchor packers where the appropriate setting pressure (typically a 1500-3000 psi differential between the inside and outside of the anchor packer) is then applied.
A conventional bypass valve incorporates a piston which slides within a cylinder in response to dynamic wellbore fluid pressure. The wall of the cylinder is provided with a plurality of holes through which fluid may pass from the drill string bore to the wellbore annulus. The piston is held in an open position by biasing means, such as a spring or a shear pin, or a combination of both. When the appropriate dynamic pressure is achieved, the biasing means is overcome and the piston slides within the cylinder so as to sealingly close the plurality of holes.
This type of bypass valve can be problematic when the wellbore fluid within the drill string carries a large amount of debris. This debris may be either pumped from the surface by accident, produced by component failure in the MWD tool or generated during the drilling of the wellbore. The debris can accumulate on the piston and increase the force exerted on the piston by any given flow rate of wellbore fluid. In certain circumstances, the accumulation of debris can be sufficient to cause the bypass valve to close prematurely. This in turn causes a premature setting of the hydraulic anchor packers. Premature setting can also occur if the piston biasing means in the bypass valve fails.
It is an object of the present invention to provide a bypass valve for use in a wellbore which resists any tendency to close prematurely and which communicates any such tendency to the surface.
The present invention provides a bypass valve for selectively isolating the interior of a down-hole assembly from the exterior thereof, the bypass valve comprising: a body incorporating a wall provided with at least one opening extending therethrough; a piston slidably mounted in the body; a longitudinal bore extending through the piston; a first position of the piston relative to the body establishing a passage from the bore of the piston to the exterior of the body via the opening; a second position of the piston relative to the body establishing a
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Barr Lawrence Robert
McGarian Bruce
Tulloch Rory McCrae
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