Mud motor force absorption tools

Abstract

A force absorbing tool is attached to a mud motor in a drilling string. The tool includes an outer housing portion that is secured to a drilling string, and an inner mandrel portion that is secured to a mud motor and is moveable axially and rotationally with respect to the outer housing portion between an axially compressed position and an axially extended position. Helical grooves are inscribed on the inner mandrel portion, and a plurality of guide pins are associated with the outer housing and disposed within the helical groove. A compressive spring member to urge the inner mandrel portion toward the axially extended position.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates generally to torque and shock absorption devices that are used within a drill string during drilling operations. [0003] 2. Description of the Related Art [0004] 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. [0005] During drilling, the drill string is subjected to severe axial and torsional forces that can seve...

AI Technical Summary

Benefits of technology

[0010] 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.

Problems solved by technology

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.

However, most of these tools are primarily designed for use with rotary drilling strings.

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.

Images