Ordnance – Well perforators
Reexamination Certificate
2000-10-17
2002-07-02
Poon, Peter M. (Department: 3641)
Ordnance
Well perforators
C102S312000, C102S313000
Reexamination Certificate
active
06412388
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to a safety arming device for use as part of an apparatus for perforating oil wells, etc. and to methods of providing an armed device. More particularly, the invention is related to a detonator assembly for initiating perforating charges in an underground perforating gun.
BACKGROUND OF THE INVENTION
Underground perforating guns are used in the production of oil and gas for provision of perforations through an oil well casing and into a hydrocarbon producing formation to provide access from the formation into the wellbore such that oil and gas may be produced.
After the oil well has been drilled, a steel casing is lowered into the wellbore and cemented into place to protect the wellbore and to prevent migration of formation fluid from one formation to another.
A perforating gun is then lowered into the steel casing and perforations are made at a desired spacing through the steel liner and into the formation such that hydrocarbons in the desired formation may flow into the oil wellbore and from there be produced to the surface.
An electrically-actuated or so-called “electric” detonator (initiator) is typically employed for operating the explosive charges on a perforating gun. In a typical arrangement, a gun is dependently supported in a wellbore by a so-called wireline (suspension) cable which has electrical conductors connected to a surface power source. The electric detonators that are most commonly used on oilfield well tools have a fluid-tight hollow shell in which is encapsulated an ignitor charge (such as a black powder or an ignition bead) that is disposed around an electrical bridge wire and positioned next to a primer explosive charge (such as lead azide or some other sensitive primary explosive). In some detonators, a booster charge of a secondary explosive (such as RDX, PETN, HMX, HNS or PYX, etc.) is arranged in a serial relationship with the primer charge to be detonated.
The electric detonator detonates an explosive detonating cord (detcord) which, in turn, sets off the charge(s) carried by the gun, once the tool is positioned at a desired depth location in a wellbore.
One practice in the industry is for an end user to purchase perforating guns in an unassembled or partially assembled condition and transport these to the oil well site. One reason for this is that the configuration of a perforating gun (spacing and number of charges, gun length and diameter, number of gun housings to be strung together, etc.) varies from wellbore to wellbore. Oil well sites are often in locations remote from assembly shops. For safety reasons, the shaped charges are transported separate from the detonating devices so that if the detonating devices were accidentally discharged, the shaped charge perforating units would not be detonated in turn.
A practice in the industry is thus to complete assembly and arm a gun on-site. A detonator is connected to an electrical conductor and then grounded to the gun housing. The detonating cord (previously strung between charges mounted on a charge holder and installed in the gun housing), an end of which sticks out of an end of the gun housing is clamped to the detonator or the detonator is slid axially onto the detonating cord. The detonator is inserted into the end of the gun housing, which can be either the top or bottom end of the gun. An end cap is then sealingly fastened to the end of the gun with the electrical conductor connecting the detonator and surface power source being strung through the cap, and/or through the gun, provision being made to seal the passage by which the conductor emerges from the gun to preclude entry of well fluids into the gun housing. As mentioned above, an alternative arrangement includes a booster.
In the context of this industry practice, the possibility exists of premature detonation of gun components during arming of the gun. In arrangements in which the detonator is directly connected to the detonating cord, it is possible to kink the detonating cord as the detonator is pushed into the gun housing and the sealing cap screwed onto the gun housing. In arrangements in which there is a booster attached to the detonating cord, it is possible to crush the booster. It is thus possible to short the wires when replacing the sealing cap in this manner.
This situation, which can lead to premature actuation, or unintended detonation, is clearly a hazard to the persons charged with gun assembly. While safe arm devices exist, many are designed to operate outside the practice of arming a gun on-site to meet the needs of a particular wellbore. It is in the context of this practice that the present invention presents a solution.
SUMMARY OF THE INVENTION
The invention includes a safety arming device for an underground well tool having an explosive charge mounted in a longitudinal housing. In one embodiment, the device includes:
a hollow member for connection at an end of the housing, the member having an outer wall which defines a window to permit lateral insertion therethrough of a detonator into an operable position in the member when the member is connected to the housing; and
a sealing member for mounting on the hollow member in sealing engagement therewith, so as to preclude ingress of liquids into the member through the window.
The sealing member of the device can be a hollow sleeve longitudinally movable with respect to the hollow member between an open position and a closed position, wherein:
in the open position, the sleeve is located to permit access to the window for said insertion of the detonator therethrough, and in the closed position, the sleeve is in said sealing engagement with the hollow member.
The hollow member can be provided with threads at a first longitudinal end thereof and the sleeve is provided with threads for engagement of the threads of the hollow member to secure the sleeve in the closed position.
The sealing engagement can be provided by first and second circumferential seals located between the sleeve and hollow member, the seals being positioned longitudinally on either side of the window.
The hollow member can be adapted to be connected directly to the gun housing.
The hollow member can include threads for threaded connection at said end of the housing.
In another aspect, the invention provides a safety arming device for an underground well tool having an explosive charge mounted in a tubular longitudinal housing, the charge being actuatable by a detonator connected thereto by a detonation cord. The device can include:
a first sleeve having a wall defining a sleeve interior, the sleeve being adapted to be sealingly affixed to the tubular housing, wherein the wall has an aperture therein sized to permit lateral insertion therethrough of the detonator into the sleeve interior and, when the sleeve and housing are connected, the sleeve interior is in communication with an interior of the housing containing the charge; and
a second sleeve, axially moveable with respect to the first sleeve, between an open position and a closed position; wherein,
in the open position, the second sleeve is located to provide clearance for the detonator to be inserted through the aperture into the interior of the first sleeve, and in the closed position, the second sleeve is in sealing engagement with the first sleeve to preclude ingress of liquids into the sleeve interior through said aperture.
In another embodiment, the invention is a safety arming device for an underground well tool having an explosive charge mounted in a tubular longitudinal housing, the charge being actuatable by a detonator in operable connection with a booster connected to the charge by a detonation cord. In this embodiment, the device includes:
a first sleeve having a wall defining a sleeve interior, the sleeve being adapted to be sealingly affixed to the tubular housing, wherein:
the wall has an aperture therein sized to permit lateral insertion therethrough of the detonator into the sleeve interior;
the wall defines an interior sleeve portion for receipt of the booster therein to locate the
Blake Cassels & Graydon LLP
Hunt John C.
Poon Peter M.
Sukman Gabriel S
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