Patent Application
20170321495
The field of the invention is a compensating device that maintains a constant axial force on a borehole tool responsive to internal pressure in the tool created by fluid pumped through the compensating device and bound for the borehole tool.
Some borehole procedures such as section milling are sensitive to load variations which could adversely affect the cutting inserts on the mill. Floating vessels are subject to wave action and frequently contain heave compensation devices to even out the up and down motion of the vessel in response to wave action. These systems are not sensitive enough to stop all the force variations at the borehole tool, which can adversely affect the longevity of the tool. Heave compensation systems are large and very complex as illustrated in U.S. Pat. No. 3,905,580; US 2016/0039643; and U.S. Pat. No. 9,267,340. Thrusters are used as compensation device during drilling as illustrated in US 2001/0045300 and U.S. Pat. No. 6,102,138. Still other tool variations for force control during drilling applications are U.S. Pat. No. 7,284,606 and U.S. Pat. No. 6,705,411.
What is provided by the invention is a system that can apply a constant loading force in either a downhole or uphole direction based on internal pressure. The tool has the needed telescoping capability such that between opposed travel limits a predetermined force is applied in tension or compression to the attached borehole tool depending on the orientation of the compensation tool in the tubular string. The fluid pressure that regulates the force applied to the borehole tool is the same fluid pressure that is applied to the borehole tool in the case of a milling tool. The pressure exits nozzles and takes away cuttings. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.
The compensating device has a through passage that goes to the borehole tool. There is a lateral passage to a piston housing. Through the use of a differential piston area on the outer housing, a net uphole force results from backpressure as a result of flow pumped through a section mill that mills in an uphole direction. If the vessel moves down the mill is just pushed away from the tubular being cut. If wave action takes the vessel up fluid is displaced back into the mandrel but the constant force up that is dependent on the existing backpressure in the tubing keeps a steady uphole force on the mill. The tool can be reversed for applications that require a net down force during milling. Rotational locking between the mandrel and the outer housing can be used. Ports are sized to prevent damping responses.
Referring to
Mill M can be of a type that mills under a tensile force. The objective is to maintain a constant tensile force on the mill M during milling. Mill M also uses nozzles to clear milling debris and the pressure drop through those nozzles accounts for the back pressure in passage 12 during milling. With the opposed piston areas 32 on one hand and 34 and 36 on the other hand, the consistent back pressure from flow through passage 12 going to the nozzles of mill M results in a consistent tensile force applied to the mill M during milling. There can be some variation in the annulus 20 pressure but it should not materially affect the net force in the direction of arrow 30 on mill M. In most cases passage 12 pressure acting on area 48 will create a net force in the direction of arrow 30 on housing 16 slightly offset by pressure in annulus 20 acting on area 50.
When the vessel V moves downward due to wave action the vessel's heave compensator can offset some of that motion but there can be a net downward force on the mill in a direction opposite arrow 30. Mandrel 10 has the ability to move down until it shoulders out against shoulder 52. As this happens the pressure in passage 12 continues to provide the net force to the mill M in the direction of arrow 30 so that milling can continue with a uniform uphole force independent of the movement of mandrel 10 until mandrel 10 engages shoulder 52. At that point there is tandem movement of the mandrel 10 and the outer housing 16 which simply results in backing away the mill M from the object or tubular that is being milled.
On the other hand, if the vessel V moves upward raising mandrel 10, there is no effect on the mill M unless shoulder 54 on mandrel 10 engages shoulder 56 on the outer housing 16. The outer housing 16 is designed long enough to prevent these two shoulders from contacting since doing so will increase the stress on the outer housing 16 and the mill M that in the displayed configuration in
Those skilled in the art will appreciate that the internal configuration of mandrel 10 and outer housing 16 can be changed so that pressure in passage 12 will result in a net downhole force on outer housing 16 if a mill M is used that operates with a compressive load against the piece being milled rather than a tensile force against the piece as shown in
Those skilled in the art will appreciate that the described device is able to maintain a constant force on a tool in a designated direction whose magnitude depends on the internal pressure pumped to the tool while compensating for vessel movements as the mill operates consistently with a required applied force. As long as the telescoping components have room to move relative, the movement of the vessel will be immaterial to the operation of the mill M. In some applications torque can be transmitted through the tool as its telescoping components can be rotationally locked. The device is simple in construction and needs just three seals for a force to be generated in an uphole direction. To generate a steady force in the downhole direction a single seal is needed. The tool length can be configured to take into account the contemplated movement of the mandrel 10 attached to the vessel V so that the engagement with the travel stops is avoided.
While the layout of
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
