Downhole safety joint

Abstract

A downhole safety joint for use in a wellbore, including an upper tubular member having an upper threaded end and a lower external threaded section; a lower tubular member having a lower threaded end and an upper interior threaded section for engaging with the lower external threaded section to form a break joint, the break joint having one or more of a maximum compressive stress limit and a tensile stress limit; and one or more circumferential stress reliefs disposed into the outer diameter of at least one of the upper tubular member and the lower tubular member for transmitting a side load applied to the break joint to one or more of the circumferential stress reliefs less than one or more of the compressive stress limit and the tensile stress limit.

Description

TECHNICAL FIELD OF THE INVENTION[0001]This invention relates, in general, to a safety joint used in a wellbore and, in particular, to a downhole safety joint used with a work string in a wellbore that traverses a subterranean hydrocarbon bearing formation.BACKGROUND OF THE INVENTION[0002]Without limiting the scope of the present invention, its background will be described in relation to a downhole safety joint, as an example.[0003]There are many different operations involved in drilling and completing an oil and / or gas well; some of these operation include drilling, surveying, and completing a well. Oftentimes, these wells are drilled at extreme depths and many times they are drilled directionally such that one or more bends exist in the wellbore that can cause a pipe string, drillstring, tool string, service string, and the like (“work string”) to become stuck deep in the wellbore. Many times expensive tools, instruments, and the like are located towards the lower end of these work...

AI Technical Summary

Benefits of technology

[0012]The present invention disclosed herein is directed to a downhole safety joint that provides reduced wear to break joints of safety joints while running into highly deviated wellbores, improved coupling efficiency, and reduced chances of hydraulic lock when reconnecting safety joint. It further provides for improved fluid flow within the downhole safety joint during make up so as to avoid hydraulic locking.

Problems solved by technology

One of the problems associated with this procedure is that many times the work string may include equipment, tools, instruments, and their related components disposed in the inner diameter thus blocking the downward passage of the string shot and wire line past that point that would prevent locating and firing the string shot below that point.

Any expensive equipment and instruments located below that point would not be able to be retrieved typically using this method.

One problem associated with these types of safety joints is that the threaded sections of the subs making up a break joint may include seals disposed about the ends of the threaded sections that may trap fluids or mud within the safety joint when the upper sub is being reconnected with the lower sub in the wellbore.

The trapped mud or fluid located within the upper and lower subs is under extreme pressure and may cause the subs to become hydraulically locked.

This characteristic can cause difficulty in making up a safety joint downhole because the mud tends to plug off and seal inside the threads as they are screwed back together.

This can further add to the problem of hydraulic locking in the safety joint because the fluid is trapped inside the threaded connection and cannot be exhausted through the safety joint.

When hydraulically locked, operators may apply more torque in response to the hydraulic lock in an attempt to reach a proper seat of the upper and lower sub, which may damage the safety joint, subs, and / or other equipment in the wellbore.

Another problem associated with hydraulically locked subs is that when torque is backed off due to the operator's belief that the threaded ends of the subs are properly engaged, it will in fact mean that the safety joint is not properly made up and may become disconnected when it is retrieved from the wellbore, thus causing tubular members, equipment, instruments, and the like to be dropped into the wellbore.

In addition, the safety joint will experience a bending or side load when it is in these situations or environments.

It is this cyclical variation in stress state caused by the cyclic bending loads that causes break joints to tighten, loosen, cause total failure of the break joint.

Also, the shoulders of the break joint may become damaged by the cyclical loading causing the break joint to become looser than required, thus causing unreliable break joint connections that are difficult to reliably make up or break under desired torque ratings.

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