String shot back-off tool with pressure-balanced explosives
OwnerWilliam T. Bell, James G. Rairighinventors
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Abstract
A “back-off” tool comprises a magazine cylinder having one distal end of a long mast rod secured to the lower end-face of a magazine cylinder. The magazine cylinder is attached to an electrically detonated firing head. A first plurality of blind hole cavities penetrate the magazine cylinder end-face around the mast rod junction. A second plurality of elongated detonation cord ends are inserted into high temperature grease filled magazine cylinder cavities. From the cavities, the detonation cord lengths are bound to the rod surface along the rod length by non-metallic cord. The tool assembly is secured to the end of a wireline or tubing string for downhole placement and detonation.
Claims28
A downhole back-off tool comprising:
- a firing head comprising an explosive detonator;
- a magazine cylinder housing a booster explosive and a plurality of detonation cord cavities, wherein the magazine cylinder is secured to the firing head;
- an elongated mast rod secured at one end thereof to the magazine cylinder;
- and
- a plurality of elongated detonation cords, wherein at least one of the plurality of elongated detonation cords has an end thereof inserted into a respective one of the plurality of detonation cord cavities, and a remaining length thereof secured along the elongated mast rod.
A method of assembling a downhole back-off tool, comprising the steps of:
- providing a firing head comprising a detonator sub and a magazine cylinder;
- providing a booster explosive in said detonator sub;
- providing a plurality of cavities in a distal end-face of said magazine cylinder;
- securing one end of an elongated mast rod to said distal end-face of said magazine cylinder;
- providing a plurality of elongated detonation cords;
- inserting a distal end of each elongated detonation cord into a respective magazine cavity within detonation proximity of said booster explosive;
- and
- securing a remaining length of said plurality of elongated detonation cords to said mast rod along a length of said mast rod.
A method of releasing a threaded pipe joint within a pipe string comprising the steps of:
- assembling a back-off tool having a firing head, a detonator magazine comprising an explosive booster initiated by said firing head and a plurality of cavities, a mast rod having one end secured to said detonator magazine and a plurality of elongated detonation cords;
- inserting one distal end of each detonator cord into a respective cavity of said detonator magazine for location within detonation proximity of said explosive booster;
- securing a remaining length of said detonator cords along a length of said mast rod;
- positioning said back-off tool within a flow bore of said pipe string and adjacent to said threaded pipe joint within said pipe string;
- applying torque in a thread separation direction at one end of said pipe string;
- and
- detonating said explosive booster.
A method of releasing an intended threaded pipe joint within a pipe string comprising the steps of;
- securing one end of an elongated mast rod to a magazine cylinder comprising a booster explosive and a plurality of cavities;
- tabulating a value representing a weight of an explosive distributed over a unit length of detonation cord corresponding to a type of pipe, a size of pipe, a well depth location of an intended threaded pipe joint, and a density of fluid within a well, such that when the explosive is detonated adjacent to the intended threaded pipe joint, while under moderate torque, the release of said threaded pipe is initiated;
- selecting a plurality of elongated detonation cords corresponding to the tabulated value for said intended threaded pipe joint and said well depth location within a flow bore of said intended pipe string adjacent to said intended threaded pipe joint;
- inserting distal ends respective to one or more of the selected plurality of elongated detonation cords into respective magazine cylinder cavities;
- and
- applying a torque in a thread separation direction to the said pipe string simultaneously with detonating the selected plurality of elongated detonation cords for release of said intended threaded pipe joint.
A downhole back-off tool comprising:
- a firing head comprising an explosive detonator in ignition proximity to an initiation explosive;
- a plurality of detonation cord cavities in a distal end of said firing head, distributed about an elongated mast rod secured to said firing head distal end;
- and
- a plurality of elongated detonation cords, wherein at least one of the plurality of elongated detonation cords has an end thereof inserted into a respective one of the plurality of detonation cord cavities in initiation proximity with said initiation explosive and a remaining length thereof secured along the elongated mast rod.
Dependencies are inferred from the claim text.