Pipes and tubular conduits – Flexible
Patent
1999-06-08
2000-05-23
Brinson, Patrick
Pipes and tubular conduits
Flexible
138177, 138178, F16L 1100, F16L 900
Patent
active
060655003
DESCRIPTION:
BRIEF SUMMARY
This invention relates to expandable tubing comprising tubing have a multiplicity of overlapping longitudinally extending slots therein. In particular, but not exclusively, the invention relates to expandable tubing as utilised in downhole applications in the oil and gas exploration and extraction industries, such as the tubing sold under the EST trademark by the applicants.
WO93/25800 (Shell Internationale Research) discloses a tubing comprising lengths of tube which have been machined to create a large number of overlapping longitudinal slots. The tube may be expanded radially outwardly by running a mandrel through the tubing. The magnitude of the force necessary to expand the tubing is related to the number of slots in the tubing, that is the fewer the number of slots the greater the expanding force. Further, expandable tubing provided with relatively few slots is more prone to fracture and catastrophic failure of the tubing during expansion. However, forming a large number of slots in a section of tubing weakens the tubing and renders the tubing more susceptible to damage during handling and running into the borehole.
It is among the objectives of embodiments of the present invention to obviate or mitigate these difficulties.
According to the present invention there is provided expandable tubing comprising tubing having a multiplicity of overlapping longitudinally extending slots therein, at least some of the slots being wider at one or both slot end portions.
Surprisingly, it has been found that increasing the width of the slot ends, without increasing the width of the remainder of the slot, reduces the force required to expand the tubing without reducing the strength of the tubing to any significant degree. Without wishing to be bound by theory, it is believed that the force necessary to expand a section of tubing is a function of the width of the "finger" between adjacent overlapping slots; by enlarging the slot ends, the effective width of the finger is reduced to the circumferential spacing between the adjacent enlarged slot ends.
Preferably, each slot is wider at both ends.
Preferably also, a majority of the slots in the tubing are wider at one or both end portions.
Preferably also, the wider slot end portions are symmetrical about the respective longitudinal slot axis. Conveniently, the slot end portions are widened by provision of transverse slots at the slot ends, although other slot or recess forms, such as round holes, at or adjacent the slot ends, may be utilised. Such widening of the slot ends provides slots with a "dog bone" appearance.
As used herein, the term slot is intended to encompass any cutting, machining or weakening of the tubing intended to facilitate radial expansion, including slots which extend only partially through the tubing and which permit the remaining thinned sections to fracture or extend.
This and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a sectional view of a length of prior art expandable tubing, shown in an expanded configuration;
FIG. 2 is a sectional view on line 2--2 of FIG. 1 and also shows the prior art tubing in unexpanded configuration; and
FIG. 3 is a view of a portion of the wall of expandable tubing in accordance with a preferred embodiment of the present invention.
Reference is first made to FIGS. 1 and 2 of the drawings, which illustrate a length of conventional expandable slotted tubing 10. In its initially unexpanded configuration, the tubing 10 is simply a length of pipe in which a series of longitudinal slots 12 have been machined (shown as tube 10a with slots 12a in FIG. 2). Applying radially outward force to the tubing wall, for example by passing a mandrel through the tubing, causes the tube to expand such that the slots 12a become diamond-shaped openings 12b, as described in WO93/25800.
Reference is now made to FIG. 3 of the drawings, which illustrates a section of tubing wall in accordance with a preferred embodiment of the present inventio
REFERENCES:
patent: 1026598 (1912-05-01), Neff
patent: 1087443 (1914-02-01), Hallgreen
patent: 2633374 (1953-03-01), Boice
patent: 4349050 (1982-09-01), Bergstrom et al.
Brinson Patrick
Hwu Davis
Petroline Wellsystems Limited
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