Wells – Processes – Perforating – weakening – bending or separating pipe at an...
Reexamination Certificate
2002-05-16
2004-08-24
Bagnell, David (Department: 3672)
Wells
Processes
Perforating, weakening, bending or separating pipe at an...
C166S381000, C166S055100, C166S065100, C166S073000, C175S004560, C102S206000, C102S275110, C089S001150
Reexamination Certificate
active
06779605
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
NONE.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to devices and methods for preventing an unintended or premature activation of one or more downhole tools.
2. Description of the Related Art
One of the activities associated with the completion of an oil or gas well is the perforation of a well casing. During this procedure, perforations, such as passages or holes, are formed in the casing of the well to enable fluid communication between the well bore and the hydrocarbon producing formation that is intersected by the well. These perforations are usually made with a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on electric wireline, slickline or coiled tubing, or other means until it is adjacent the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow from the formation through the perforations and into the production string for flowing to the surface.
A number of arrangements can be used to actuate the firing head. For example, the firing head may be actuated by dropping a weight onto the firing head through tubing extending from the firing head to a wellhead or a platform at the earth's surface. The falling weight eventually strikes a firing pin in the firing head, thereby actuating a detonator explosively coupled to the perforating gun. Other tubing conveyed perforating systems employ a differential firing head that is actuated by creating a pressure differential across an actuating piston in the firing head. The pressure differential is created by applying increased pressure either through the tubing string or through the annulus surrounding the tubing string to move the actuating piston in the firing head. Typically, the firing head actuating piston will have hydrostatic pressure applied across the actuating piston as the tool is run into the well. When it is desired to operate the tool, the increase in pressure is sufficiently large to initiate detonation of the firing head and perforating gun. Often, perforating guns have been actuated electrically. The firing head and perforating gun are lowered into the well on a wireline. Electrical current is sent through the wireline to set off the firing head. The firing head in turn detonates the shaped changes in the perforating gun.
Regardless of the system used, it is desirable to ensure that the charges do not detonate prematurely. Premature detonation can be of particular concern when the perforating gun is on the surface; i.e., not within the confines of a well bore. For example, electrically actuated explosive device can be susceptible to detonation by stray electrical signals, radio signals picked up by the conductive wireline, static electricity or lightning strikes. Any electrical noise or discharges from any of these sources can cause the device to explode prematurely with the risk of damage to the production system and danger to operators on the oil production installation. Mishandling during transportation or during manual deployment may also inadvertently actuate mechanically actuated systems. Accordingly, a number of devices have been developed to prevent the premature detonation of charges carried by a perforating gun.
In an exemplary conventional safety system, a safety module associated with the perforating gun has a housing, a pressure sensitive switch and a temperature sensitive switch. The switches only allow an electrical command signal to be conveyed to the tool when the pressure and temperature both reach predetermined pressure and temperature values. In another exemplary safety system, applying fluid pressure to the exterior of a housing arms an electrical firing system. The firing system arms when the fluid pressure exceeds the well hydrostatic pressure. The firing system is controlled by a microprocessor that is preset to be responsive only to a selected value of fluid pressure surrounding the control housing. These systems depend, in part, on a reliable prediction of well bore conditions. If the temperature or pressure of the well bore at the desired depth does not match the pre-set values, then the gun will not arm. In these instances, the gun will have to tripped up and the safety module reset. It will be appreciated that this additional procedure lead to lost time and additional expenditures of effort and money.
Perforating guns are, however, only one example of downhole tools that require the use of safety mechanisms that control activation. Other tools, such as pipe cutters, use caustic acid to burn and sever a section of pipe. While the closed wellbore environment enables these downhole tools to operate safely, a common characteristic of these downhole tools is that unintended surface activation can cause injury to personnel and damage to nearby equipment.
The present invention addresses these and other drawbacks of the prior art.
SUMMARY OF THE INVENTION
The present invention provides devices and systems for controlling the activation of one or more downhole tools. In one aspect, the system prevents an unintended or premature activation of one or more downhole tools activated by an initiation device. A preferred system is configured to allow an initiation signal generated by a signal generator or source to reach the initiation device only after the downhole tool has reached a known pre-determined depth at a location that is substantially stationary relative to the earth's surface. The preferred safety system includes a first device associated with the downhole tool and a second device fixed at the stationary location. The first device is configured to permit an initiation signal transmitted by the generator to reach the initiation device upon reaching the stationary location (“signal pass-through”). The second device positively engages the first device to provide a positive indication that the specified depth has been reached. In another preferred embodiment, the system includes a bypass, a switch, and a trigger. The bypass is operably coupled to a signal conveyance medium connecting the generator to the initiation device. The bypass has a safe mode in during which it prevents signal pass-through and a fire ready mode during which it allows signal pass through. The switch is mechanically connected to the bypass and can move the bypass between the two modes. The trigger, however, is positioned at the relatively stationary location (e.g., in the wellhead or wellbore) and is configured to positively engage the switch. The trigger may be a rigid member, a biased member, or utilize hydraulic power. While at the surface, the bypass is by default set in the safe mode. During tool deployment, the switch engages the trigger during transit through a wellhead or well bore. This engagement may, for example, be facilitated by the cooperative action of alignment pins and channels. Engagement between the trigger and the switch causes the bypass to move from the safe mode to a fire ready mode. In a preferred embodiment, engagement between the trigger and the switch during tool extraction causes the bypass to move from a fire ready mode to a safe mode.
In a different aspect, a preferred safety system prevents an energy train generated by an initiation device from reaching the downhole tool until the downhole tool has reached a known depth in a well. The preferred safety mechanism includes a first device associated with the downhole tool and a second device fixed at a stationary location. The first device is configured to permit the energy stream to reach the downhole tool if the tool is below a specified depth below the earth's surface (“energy pass-through”). The second device positively engages the first device to provide an indication that the pre-defined or specified depth has been reached. In one preferred embodiment, the safety system includes
Bagnell David
Gray Jennifer H
Madan Mossman & Sriram P.C.
Owen Oil Tools LP
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