FIELD OF THE INVENTION
This invention relates to deformable tubing, and in particular to deformable tubing for use in downhole applications.
BACKGROUND OF THE INVENTION
There have been numerous proposals for forms of deformable tubing for use in downhole applications. One such form is relatively thin-walled “C-shaped” or “folded” tubing which comprises tubing which is or has been collapsed, flattened, corrugated, folded or otherwise deformed to assume a smaller diameter configuration. One example of such tubing is described in U.S. Pat. No. 5,794,702 (Nobileau). For brevity, such tubing will hereinafter be referred to as “folded” tubing. The tubing, which is typically continuous and reelable, is run into a bore in the folded configuration and then unfolded, by use of an appropriately shaped cone or application of internal pressure, to assume a larger diameter cylindrical form.
Use of such folded tubing is also disclosed in EP 0 952 306 A1 (Shell Internationale Research Maatschappij B.V.), the various forms of folded tube being spooled around a reeling drum in their folded shape and reeled from the drum into an underground borehole.
WO 99/35368 (Shell Internationale Research Maatschappij B.V.) discloses methods for drilling and completing a hydrocarbon production well. The well is lined with tubing which is expanded downhole to provide a slim borehole of almost uniform diameter. In one embodiment, the tubing is made up of a series of pipe sections that are interconnected at the wellhead by screw joints, welding or bonding to form an elongate pipe of a substantially cylindrical shape that can be expanded and installed downhole.
It is among the objectives of embodiments of the present invention to facilitate use of folded tubing in downhole applications, and in particular to permit use of tubing made up from a plurality of folded pipe sections which may be coupled to one another at surface before being run into the bore.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided downhole apparatus comprising a plurality of tubing sections, each tubing section having substantially cylindrical end portions initially of a first diameter for coupling to end portions of adjacent tubing sections and being expandable at least to a larger second diameter, and intermediate folded wall portions initially in a folded configuration and being unfoldable to define a substantially cylindrical form at least of a larger third diameter.
The invention also relates to a method of lining a bore using such apparatus.
Thus, the individual tubing sections may be coupled together via the end portions to form a string to be run into a bore. The tubing string is then reconfigured to assume a larger diameter configuration by a combination of mechanisms, that is at least by unfolding the intermediate portions and expanding the end portions. The invention thus combines many of the advantages available from folded tubing while also taking advantage of the relative ease of coupling cylindrical tubing sections; previously, folded tubing has only been proposed as continuous reelable lengths, due to the difficulties that would be involved in coupling folded tubing sections.
Preferably, transition portions are be provided between the end portions and the intermediate portions, and these portions will be deformable by a combination of both unfolding and expansion. The intermediate wall portion, transition portions and end portions may be formed from a single piece of material, for example from a single extrusion or a single formed and welded sheet, or may be provided as two or more parts which are assembled. The different parts may be of different materials or have different properties. The end portions may be foldable, and may have been previously folded. Alternatively, or in addition, the end portions may be folded following coupling or making up with other end portions. This would allow cylindrical tubing sections to be made up on site, and then lowered into a well through a set of rollers which folded the tubulars including the end portions, into an appropriate, smaller diameter folded configuration. Indeed, in certain aspects of the invention the end portion may only be subject to unfolding, and may not experience any expansion.
The end portions may be provided with means for coupling adjacent tubing sections. The coupling means may be in the form of male or female threads which allow the tubing sections to be threaded together. Alternatively, or in addition, the coupling means may comprise adhesive or fasteners, such as pins, bolts or dogs, or may provide for a push or interference type coupling. Other coupling means may be adapted to permit tubing section to be joined by welding or by amorphous bonding. Alternatively, or in addition, the apparatus may further comprise expandable tubular connectors. In one embodiment, an expandable connector may define female threads for engaging male threaded end portions of the tubing sections.
Preferably, the first diameter is smaller than the third diameter. The second and third diameters may be similar. Alternatively, the unfolded intermediate wall portions may be expandable from the third diameter to a larger fourth diameter, which fourth diameter may be similar to the second diameter.
According to another aspect of the present invention there is provided a method of creating a bore liner, the method comprising:
providing a tubing section having a folded wall and describing a folded diameter;
running the tubing section into a bore;
unfolding the wall of the tubing section to define a larger unfolded diameter; and
expanding the unfolded wall of the tubing section to a still larger diameter.
This unfolding and expansion of the tubing section is useful in achieving relatively large expansion ratios which are difficult to achieve using conventional mechanisms, and also minimising the expansion forces necessary to achieve desired expansion ratios.
The unfolding and expansion steps may be executed separately, or may be carried out in concert. One or both of the unfolding and expansion steps may be achieved by passing an appropriately shaped mandrel or cone through the tubing, by applying internal pressure to the tubing, or preferably by rolling expansion utilising a rotating body carrying one or more rolling members, most preferably a first set of rolling members being arranged in a conical form or having a tapered form to achieve the initial unfolding, and a further set of rolling members arranged to be urged radially outwardly into contact with the unfolded tubing section wall. Of course, the number and configuration of the rolling member sets may be selected to suit particular applications or configurations. The initial deformation or unfolding may be achieved by simple bending of the tubing wall, and subsequent expansion by radial deformation of the wall, reducing the wall thickness and thus increasing the wall diameter.
The tubing section may be reelable, but is preferably formed of jointed pipe, that is from a plurality of shorter individual pipe sections which are connected at surface to make up a tubing string. Alternatively, the tubing section may be in the form of a single pipe section to be used as, for example, a straddle.
Preferably, an upper portion of the tubing section is deformed initially, into contact with a surrounding wall, to create a hanger and to fix the tubing section in the bore. Most preferably, said upper portion is initially substantially cylindrical and is expanded to create the hanger. The remainder of the tubing section may then be unfolded and expanded.
The tubing section may be expanded into contact with the bore wall over some or all of the length of the tubing section. Where an annulus remains between the tubing section and the bore wall this may be filled or partially filled by a settable material, typically a cement slurry. Cementation may be carried out before or after expansion. In other embodiments, a deformable material, such as an elastomer, may be provided on all or part of the exterior of the tubing section, to facilitate formation of a sealed connection with a surrounding bore wall or surrounding tubing.