Patent Application
20070000695
1. Field of the Invention
The invention relates generally to torque and shock absorption devices that are used within a drill string during drilling operations.
2. Description of the Related Art
Traditionally, drilling of wellbores has been accomplished using drill bits that are affixed to the lower end of a drill string. The drill string is rotated in the hole to cause the bit to drill. As an alternative to traditional drill strings, drill bits are sometimes run in on a string of coiled tubing, which is run off of a spool located at the surface of the well. The coiled tubing is not rotated and, therefore, a downhole mud motor is used to rotate drill bit at the lower end. Coiled tubing is less rigid than a traditional drilling string and, therefore, may be more vulnerable to damage associated with axial and torsional shocks.
During drilling, the drill string is subjected to severe axial and torsional forces that can severely wear or damage components of the drilling string. Additionally, these forces can prevent the drill bit from maintaining good contact with the bottom of the borehole, thereby reducing the effectiveness of the drilling operation. Axial and torsional shock forces can significantly reduce the rate of penetration for a drilling tool.
A number of shock absorbing tools have been designed to absorb torsional and/or axial forces associated with drilling. However, most of these tools are primarily designed for use with rotary drilling strings. U.S. Pat. No. 6,543,556 issued to Anderson, for example, describes an torque and shock absorber for a traditional drill string wherein a mandrel is retained within a drive cylinder with a threaded or helical engagement between the two. Similar arrangements are found in U.S. Pat. Nos. 2,754,086; 4,443,206; 2,754,086, and 1,817,067.
Problems with prior art torque absorbing arrangements is that the spiral interface used with the tool is often insufficiently robust to stand up to the rigors of a drilling environment. The use of rollers or mere interfitting threads can cause the helical interface to bind up during operation. As a result, the tool will become inoperative. In an extremely undesirable situation, the mandrel may become canted or angularly slanted with respect to the outer housing due to the inadequate spiral interface. In this instance, the ability of the bit to drill is effectively destroyed, and the bit itself or other components may become damaged.
The forces produced when running a mud motor at the bottom of a drilling string versus rotating the entire drilling string without a mud motor are similar, but different in some important ways. In mud motor applications, fluid is pumped through the drilling string to the motor. The drilling string is not rotated and, therefore, torque and speed are produced at the bottom of the well, rather than at the top of the well, and is resisted by the string above.
The present invention addresses the problems of the prior art.
The invention provides devices and methods for absorbing torsional and axial forces associated with drill strings that use drill motors, or mud motors, to operate the drill bit. An exemplary force absorption tool is described that has an inner mandrel portion that is secured to the mud motor or associated component and an outer housing portion that is secured to the lower end of the coiled tubing or other drilling string. The inner mandrel portion and the outer housing portion are operably interengaged by a spiral or helical interface so that the inner mandrel portion will move axially and rotationally with respect to the outer housing portion. The force absorbing tool provides improved operation due to use of guide pins that engage helical grooves in the inner mandrel portion. The number and arrangement of pins is particularly advantageous for maintaining proper alignment of the inner mandrel portion and the outer housing portion in true alignment and helps prevent binding or canting of the inner mandrel portion with respect to the outer housing portion. Additionally, guide pins provide improved distribution of loads, in comparison to the use of rollers or roller balls. Guide pins also produce greater torque carrying capacity than rollers or roller balls, resulting in reduced wear and tear on mating parts.
A compressible spring force urges the tool to an axially extended position with the inner mandrel portion being extended outwardly from within the outer housing portion. In a currently preferred embodiment, a number of Belleville washers provide the spring force. An enlarged piston actuated by motor differential pressure is used in conjunction with the Belleville washers to bias the tool to the extended position. These combined forces allow for a shorter, lighter-weight tool. When the drill bit encounters axial or torsional shocks, these are absorbed, or at least reduced, as the tool moves to an axially compressed condition. While moving to the compressed condition, the inner mandrel portion rotates with respect to the outer housing portion due to the helical interface provided by the seating of the guide pins within helical grooves in the mandrel portion.
The lower end of the coiled tubing 16 is secured to a mud motor force absorbing tool 24, constructed in accordance with the present invention. The mud motor force absorbing tool 24 is, in turn, secured to a mud motor 26 of a type known in the art for creating rotational motion under the impetus of fluid flowed axially through the motor 26. The mud motor 26 is secured to a drill bit 28. The mud motor 26 rotates the drill bit 28 with respect to the coiled tubing 16 in response to fluid that is pumped through the mud motor 26 by the pump 22. It is noted that the system 14 may be used with a milling tool or other cutting tool rather than merely a drill bit. Thus, the terms “drilling system,” “drill bit,” and the like, as used herein, are intended to include any downhole cutting tool, such as a mill or other cutter.
The spring and bearing chamber 36 contains a plurality of axially compressible Belleville washers 52 that surround an interior tubular guide member 54. In a currently preferred embodiment, there are ninety Belleville washers that are stacked in an end-to-end, opposed relation, so that they are axially compressible. A thrust bearing 56 is located within the chamber 36 immediately below the washers 52. The thrust bearing 56 rests atop inner mandrel 58.
The inner mandrel 58 includes an enlarged upper piston head portion 60 that is secured by threaded connection 62 to guide member 54. An annular elastomeric fluid seal 63 radially surrounds the piston head 60. A reduced diameter shaft 64 extends downwardly from the piston head 60 to a threaded end portion 66 that is affixed to the bottom sub 44. A sleeve 68 surrounds the shaft 64 and has multiple helical grooves (indicated at 70 in
Lying radially outside of the sleeve 68 is a pin retainer sleeve 72, which is visible in
Alternatively, the pins can comprise short, helically-shaped pins that would lie within the helical grooves 70.
It is noted that an axial flow passage 76 is defined within the body of the tool 24 to allow the flow of fluids from the surface down to the mud motor 26. The inner mandrel 58, bottom sub 44, guide member 54, pin housing 72, pin retainer 42, and pins 74 collectively form an inner mandrel portion 81. The top sub 30 and outer housing 34 collectively form an outer housing portion 82.
During operation, the tool 24 is normally in the axially extended position shown in
Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.
