1. Field of Invention
The present invention relates to oil and gas production. More specifically, the present invention relates to a tool that creates a shockwave in a wellbore to “back-off” threads engaged in a threaded couplings within a tubular string.
2. Description of Prior Art
Typically, tubulars are connected together by threaded couplings to form a string that is suspended and cemented in a wellbore to create a casing for the wellbore. From time to time, the casing string may need to be removed from the wellbore and the threaded couplings are decoupled at surface. In some instances while removing the casing it may become wedged within the wellbore; further complicating string removal, while still downhole, one of the threaded couplings may resist detachment under an applied torque to become immovable. The immovable coupling is sometimes unseated by directing a shockwave at the coupling site to break loose the threaded connection.
A typical prior art tool used to create this shockwave consists of multiple strands of detonator cord wrapped around a shot rod in a rope-like fashion and wrapped with friction tape. Generally this tool employs a detonation cord having HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), which can withstand operating temperatures of 400 degrees Fahrenheit for only about an hour. While a detonating cord having HNS (1,3,5-Trinitro-2-[2-(2,4,6-trinitrophenyl)ethenyl]benzene) can operate at temperatures above those limiting use of HMX detonator cord, HNS detonating cord cannot side detonate and thus is not utilized in the above described prior art tool. Also, operating pressure of typical prior art is limited to 20,000 psi due to the use of exposed (to wellbore fluids) interface between detonator and detonating cord.
The present disclosure involves a method of unseating a threaded connection that connects sections of wellbore tubing. In an example the method uses a tool that includes a housing, a shaped charged located inside the housing, an HNS detonating cord and an energetic material attached to the steel housing. The tool is placed near the threaded connection, where it is detonated, creating a shockwave that contacts the threaded connection with sufficient force to unseat the threaded connection.
Also disclosed is a method of an operation in a wellbore that includes inserting an amount of reactive material within a string of wellbore tubular segments, where a threaded connection joins upper and lower adjacent tubular segments. A shockwave is generated by initiating the reactive material that unseats the threaded connection by directing the shockwave towards the threaded connection. The upper tubular segment is rotated thereby eliminating the threaded connection and the upper tubular segment is removed from the wellbore. In an example, the reactive material is initiated by a jet from a shaped charge that terminates proximate an outer surface of the reactive material. In one alternative embodiment, the reactive material includes a high explosive, wherein initiating the high explosive causes the high explosive to detonate. Optionally, the reactive material is a low explosive, wherein initiating the low explosive causes the low explosive to deflagrate. In another alternative, the reactive material includes a combustible material, wherein initiating the combustible material causes the combustible material to combust. Alternatively, initiating the reactive material includes using a detonation cord having HNS to detonate a shaped charge thereby forming a jet, and directing the jet at the reactive material. The pressure can be at least about 30,000 pounds per square inch within the string of tubular segments. At least a portion of the HNS detonating cord can be maintained at a temperature of at least about 480° F. and for a time up to about 1 hour.
Also disclosed herein is an embodiment of a back off tool for use in a downhole tubular. In one example the back off tool includes a body selectively suspended in the downhole tubular by attachment to a deployment member. A reactive material is included adjacent the body for generating a shockwave to unseat an immovable threaded connection between adjacent tubular segments. An initiator is provided in selective communication with the deployment member and in selective initiating communication with the reactive material. In one example, the initiator is a shaped charge that forms a jet to initiate a reaction in the reactive material. Alternatively, a detonating cord having HNS can be included with the back off tool. In an example embodiment, the body and the reactive material each include an axis, and the reactive material is disposed adjacent an end of the body and positioned so that the axis of the reactive material is substantially parallel with the axis of the body. Alternatively, the reactive material can be a high explosive.
Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.
It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims.
The material for the sleeve 30 can detonate, deflagrate, combust, or a combination thereof. In an example, the definition of detonation describes a reaction that can propagate through the material being detonated at the sound speed of the material. In a further example, detonation describes a reaction or decomposition of an explosive that, typically in response to a shock wave or heat, forms a high pressure/temperature wave. Example velocities of the high pressure/temperature wave can range from 1000 m/s to in excess of 9000 m/s. In an example, the definition of deflagration describes a rapid autocombustion of a material, such as an explosive. Generally, explosives that detonate are referred to as high explosives and explosives that deflagrate are referred to as low explosives. In an example, combustion describes an exothermic reaction of a material that can produce an oxide.
In one example of operation, and as provided in
Referring now to
In the example embodiment of
An alternate embodiment of a portion of a back off tool 20A is shown in a side sectional view in
The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, the back off tool 20 and its alternate embodiments can be disposed in other downhole tubulars, such as production tubing strings, caissons, risers, and the like. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.