Wells – Means for perforating – weakening – bending or separating pipe... – Perforating or splitting cutter
Patent
1997-09-12
2000-02-15
Bagnell, David
Wells
Means for perforating, weakening, bending or separating pipe...
Perforating or splitting cutter
175 90, E21B 2900
Patent
active
060241667
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for forming a slot in a wellbore.
The wellbore may be cased in which case the apparatus of the present invention forms a slot in the casing. For many applications, in addition to forming a slot in the casing the apparatus of the present invention will be used to form the slot in any cement surrounding the casing and in the formation beyond the cement.
In the petroleum and gas extraction industries it is recognized that under certain circumstances it is desirable to form one or more openings in the casing of a wellbore. It is also recognized as desirable under certain circumstances to form openings in the formation surrounding a wellbore. Such techniques are often used for increasing the flow of oil or gas into a wellbore from surrounding formations.
The most common technique for forming the required openings is to lower one or more explosive charges into the well and to detonate those charges so as simultaneously to form openings within any casing located in the well and perforate the surrounding formation. Although such techniques are well established and, under many circumstances, result in an improved yield from a well they suffer from a number of disadvantages and, in particular, are in general unable to penetrate to any significant depth in the surrounding formations. Also, the detonation of the explosives inflicts physical damage on the formations which, at least to some extent, reduces the efficacy of the fractures produced, in terms of improved well yield.
With a view to overcoming the shortcomings of explosive perforation techniques it is proposed in U.S. Pat. No. 3,225,828 to make a slot in the casing of a well and into the formation surrounding the casing by means of a cutting device comprising a housing and a cutting wheel, the cutting wheel being displaceable in use from a position in which it is wholly contained within the casing to a position where the wheel has cut through the casing and into the surrounding formation. Such a system suffers from the disadvantage that the maximum penetration into the surrounding formation which can be obtained is limited by the diameter of the cutting wheel and, as a practical matter, because of the need to support and drive the cutting wheel at its centre the cutting wheel is unable to cut outwardly more than about 1/3 of the inside diameter of the casing.
According to one aspect of the present invention there is provided apparatus for forming an elongate slot in a borehole, the apparatus comprising an endless cutting chain mounted on a cutting arm; a motor for driving the chain, the motor having an output shaft located substantially coaxially with the borehole; drive means connecting the motor to a drive sprocket which itself is drivingly engaged with the chain; and means for rotating the cutting arm from an initial position in which the axis of the cutting arm is substantially parallel to the axis of the borehole and a final position in which the axis of the cutting arm extend obliquely or perpendicularly to the axis of the borehole for cutting a slot; the rotating means comprising a sleeve piston which surrounds the drive means and is located below the motor, a rack driven by the sleeve piston, and a pinion driven by the rack and connected to the chain arm.
Preferably, a gearbox is located between the output shaft and the drive sprocket, the gearbox comprising an epicyclic gear set formed by a sun gear, a ring gear and a set of planetary gears, one of the sun gear, the ring gear and the planetary gears being secured to the output shaft of the motor and another of the sun gear, the ring gear and the planetary gears being secured to the body of the motor.
The planetary gear set may be arranged to drive an output shaft at a speed faster than the rotational speed of the output shaft of the motor, or to drive an output shaft at a speed slower than the rotational output speed of the motor. The drive assembly of the present invention has general applicability to downhole tools, but is particularly advantageous for use in an e
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McGarian Bruce
Tulloch Rory M.
Bagnell David
The Red Baron (Oil Tools Rental) Limited
Walker Zakiya
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