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Unsymmetrical profile threads for use in a positive displacement motor housing

a positive displacement motor and profile technology, applied in the direction of threaded fasteners, screw threaded joints, borehole/well accessories, etc., can solve the problems of reducing the wall thickness of the housing, particularly the bending stress fatigue failure of the threaded connection, etc., to reduce the fatigue experienced by the threaded connection, increase the root radius, and reduce the angle

Inactive Publication Date: 2005-07-28
SCHLUMBERGER TECH CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides an unsymmetrical thread profile for connecting stator housings of a positive displacement motor. The thread profile has one or more load bearing flanks angled at a first angle and one or more non-load bearing flanks angled at a second angle. The second angle is less than the first angle, resulting in a larger root radius than a symmetrical thread profile with the same pitch and first angle. The invention also provides a method for reducing fatigue experienced by threaded connections by reducing the angle of the non-load bearing flank to increase the root radius.

Problems solved by technology

The threaded connections are particularly susceptible to bending stress fatigue failures.
In part, such failures result because the wall thickness of these housings is typically smaller than that commonly found on the connections of drill collars.

Method used

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  • Unsymmetrical profile threads for use in a positive displacement motor housing
  • Unsymmetrical profile threads for use in a positive displacement motor housing
  • Unsymmetrical profile threads for use in a positive displacement motor housing

Examples

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Embodiment Construction

[0020]FIGS. 4 and 5 show a prior art conventional thread profile 30 that is used to connect stator housings of a positive displacement motor (PDM). FIG. 4 shows the threaded connection 32 on the pin-side 34 of the stator housing 36, while FIG. 5 shows an enlarged view of the threaded connection 32. As used in this application, the term “pin-side” refers to the end 34 of the stator housing 36 that is threadably received by the “box-side”38 of the adjacent housing / drill string component 40.

[0021] The illustrated conventional thread profile 30 of the threaded connection 32 is a tapered thread with a symmetrical V-profile and a symmetrical root radius 42. The thread root radius 42 governs the stress concentration and the level of fatigue resulting from the bending and axial stresses experienced in the threaded connection 32 during the drilling process. For a given pitch diameter and profile angle, the root radius 42 is limited by the useful mating area and the thread pitch P.

[0022]FIG...

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Abstract

The present invention provides an unsymmetrical thread profile used to connect stator housings of a positive displacement motor. The unsymmetrical thread profile comprises one or more non-load bearing flanks angled with respect to the longitudinal axis of the thread profile such that the root radius is greater than the root radius of a symmetrical thread profile having substantially the same pitch and first angle.

Description

FIELD OF THE INVENTION [0001] The invention relates to mud driven motors used in the drilling of oil wells. More particularly, the invention relates to an unsymmetrical thread profile for connection of a positive displacement motor (PDM) housing. BACKGROUND OF THE INVENTION [0002] Positive Displacement Motors (PDMs) are known in the art and are commonly used to drill wells in earth formations. PDMs operate according to a reverse mechanical application of the Moineau principle wherein pressurized fluid is forced though a series of channels formed on a rotor and a stator. The channels are generally helical in shape and may extend the entire length of the rotor and stator. The passage of the pressurized fluid generally causes the rotor to rotate within the stator. For example, a substantially continuous seal may be formed between the rotor and the stator, and the pressurized fluid may act against the rotor proximate the sealing surfaces so as to impart rotational motion on the rotor as...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): E21B4/02E21B17/042F16B33/02F16L15/06
CPCE21B4/02F16B33/02E21B17/042
Inventor KAUL, ANMOL
Owner SCHLUMBERGER TECH CORP
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