Patent Application
20090178809
This invention relates to methods and apparatus for zonal isolation and borehole stabilisation that are particularly applicable to boreholes such as oil and gas wells, or the like. They provide techniques that can be used in addition to or as an alternative to conventional well completion techniques such as cementing.
Completion of boreholes by casing and cementing is well known. Following drilling of the borehole, a tubular casing, typically formed from steel tubes in an end to end string is placed in the borehole and cement is pumped through the casing and into the annulus formed between the casing and the borehole wall. Once set, the cemented casing provides physical support for the borehole and prevents fluid communication between the various formations or from the formations to the surface (zonal isolation). However, problems can occur if drilling mud remains in the borehole when the cement is placed, or microannuli form around the casing and/or borehole wall. The effect of these can be to provide fluid communication paths between the various formations or back to the surface and consequent loss of zonal isolation.
There are various well-known problems associated with conventional cementing operations. For example, drilling must be interrupted and the drill string withdrawn from the borehole each time a casing is to be set; and each casing reduces the diameter of the well.
WO 9706346 A (DRILLFLEX) 20 Feb. 1997 describes a technique in which a tubular preform is introduced into a well on an electric cable and expanded into contact with the wall of the well by inflation of a sleeve located inside the preform. Once inflated, the preform is solidified by polymerisation, typically by heating by means of an embedded heating wire, or by introduction of a heated liquid into the sleeve. Such a technique is typically used for repair of a casing or tubing that is already installed in the well, or to shut off perforations that are producing unwanted fluid such as water (see, for example, the PatchFlex service of Schlumberger/Drillflex).
This invention aims to address some of the known problems with borehole lining by providing a technique that can reduce the interruption to drilling and decrease in borehole diameter.
This invention is based on the extrustion or continuous placement of a concentric sleeve around a drill string that can be made to expand to line the borehole.
A first aspect of this invention provides method of constructing a borehole drilled with a drilling apparatus, the method comprising:
A method preferably comprises positioning the sleeve on a spool located at the borehole opening and spooling the sleeve into the well as drilling progresses, or positioning the sleeve on a spool located around the drilling apparatus and spooling the sleeve into the well as drilling progresses. The spool can hold the sleeve in a rolled or folded/pleated form prior to extension into the borehole.
Expanding the sleeve can be achieved by pumping a fluid under pressure into the sleeve.
It is also preferred to heat the sleeve prior to expansion to improve flexibility. After heating and expansion, the sleeve can be cooled so as to set the sleeve in its expanded state.
Where the sleeve comprises a polymer, the method preferably comprises heating to a temperature above the glass transition temperature, Tg, of the polymer prior to expansion, and cooling to a temperature below Tg after expansion.
Heating the sleeve can be achieved, for example, by means of a fluid used to expand the sleeve, by means of an electrical heating element, or by means of an exothermic reaction.
A second aspect of the invention comprises apparatus for use in a method according to the first aspect, comprising:
The apparatus preferably comprises a spool on which the sleeve is held and from which the sleeve is withdrawn as drilling progresses. The sleeve can be rolled on the spool or held in a pleated or folded form. The spool can be located at the first connector or the second connector.
Preferably, the apparatus also comprises a supply of pressurised fluid that allows the fluid to be pumped inside the sleeve so as to expand it into contact with the borehole wall. The drilling assembly can include ports for the delivery of fluid from the supply to the inside of the sleeve. The fluid can be drilling mud, for example.
The flexible sleeve can be formed from a polymer that is expandable when heated above Tg but sets in position when cooled below Tg. The sleeve can include heating elements and/or reinforcing elements. Other materials that can be used include thin metal sheets or foils, woven fibres and composite materials including reinforcing elements such as cross-weave fibres.
Downhole temperatures may be sufficiently high that the sleeve already has sufficient deformability for expansion and it is merely necessary to pump in fluid to cause expansion. Further softening of the sleeve may be used to improve flexibility for expansion.
In the accompanying drawings:
Referring now to the drawings,
As the drilling progresses, the drill string is lengthened (for example by adding drill pipe or by unreeling from a coil) and the sleeve 22 is correspondingly extended by unrolling from the spool 24. The sleeve 22 is later expanded to line the borehole 10 as will be explained below.
It will be appreciated that the two forms of spool shown in
When drilling has progressed to a depth at which it becomes necessary to line the borehole 10, drilling ceases and the sleeve 22 is expanded to contact the borehole wall 28 and set in place. Expansion is achieved by inflating the sleeve 22 with fluid pumped from the surface, down the drill string 20, through ports 32 in the drilling assembly 16 and into the interior 30 of the sleeve 22. The ports 32 in the drilling assembly 16 can be operated by means of a ball or dart pumped along the drill string 20 or by raising the fluid pressure in the drill string 20 to a suitable level. Alternatively, fluid can be pumped from the surface between the sleeve 22 and drill string 20 (reverse circulation). For the application of a heated fluid (see below), fluid can also be pumped from the surface between the sleeve and borehole wall 28, or through the drilling assembly so as to pass up the borehole between the sleeve 22 and borehole wall 28.
Once the sleeve is set, drilling can proceed. In the embodiment of
The sleeve 22 is preferably formed from a thermoplastic polymer that transforms rapidly from a hard, relatively inflexible solid to a flexible, deformable rubber when it is heated above its so-called glass transition temperature Tg. This thermal trigger is used to provide continuous zonal isolation while drilling, so enabling drilling to continue through weak formations and provide continuous lining of the wellbore. While the lining provided by the expanded sleeve may not be sufficiently strong to act as a permanent casing, longer, extended sections can be drilled before steel casing is required, so reducing the number of casing strings required and enabling smaller diameter wells to be drilled to the target zones. Alternatively, where there is little requirement for mechanical reinforcement, the expanded sleeve may be sufficient to act as a permanent liner.
As is described generally in relation to
This method of borehole lining is conveniently applied during the drilling phase, prior to placing cement into the annulus. The choice of polymer material is determined by the glass transition, or softening, temperature (Tg) being higher than the temperature likely to be experienced by the polymer liner during normal operation, both during well construction and production, but such that the polymer tube may readily be raised above this value during the expansion/lining phase. The temperature may be raised in a number of ways: by circulating hot fluid within the sleeve or outside the sleeve (see above), by electrical heating (either by use of a separate heater or by operation of embedded heating elements in the sleeve), by activating an exothermic chemical reaction in the liquid sitting within or surrounding the sleeve etc.
Suitable polymers are exemplified by, but not restricted to: polyolefins (polyethylene, polypropylene, polybutene . . . ), polyalkylmethacrylates (alkyl=methyl, propyl, butyl . . . ), polyvinyl chloride, polysulphones, polyketones, polyamides (such a nylon 6,6), polyesters such as polyalkylene terephalates, and fluorinated polymers (such as PTFE, which will provide low friction with the drillstring and/or casing and so give enhancements for long, extended deviated and horizontal wells) to name but a few. Copolymers and blends of these are also possible.
Composites of these polymers with solid inorganic materials (e.g. carbon black, silica and other minerals), or fibre composites (short fibres or continuous, woven mat) are also possible.
An alternative approach is to use a thermoset, rather than a thermoplastic, polymer material, wherein an uncrosslinked flexible resin sleeve (with or without fibre reinforcement) blended or impregnated with cross-linker (a ‘prepreg’) which crosslinks when the sleeve is expanded and its temperature raised sufficiently, so that it changes from a soft, deformable material to a hard, strong seal.
Other materials include those in powder or granular form, held in a bag or other flexible container, e.g. thermoplastic powder or granules in a thin fibre, metal foil or plastic annular sack which fuse against the wellbore wall on expansion and heating of the sleeve.
The sleeve can comprise pre-stressed liner which is prevented from expanding by a polymer below its Tg; on heating the polymer softens, enabling the pre-stressed liner to expand against the formation and form a seal.
Further changes may also be made while staying within the scope of the invention. For example, in the case of a sidetrack or lateral borehole drilled from a main borehole, the sleeve may be connected to the opening of the new borehole in the main borehole rather than at the surface. Also, expansion may be achieved by means of a mechanical device (former) which has a diameter similar to the borehole and can be pushed down the sleeve, or which can expand in the sleeve and be pushed or pulled along to expand the sleeve into contact with the borehole wall.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05292716.7 | Dec 2005 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/011808 | 12/6/2006 | WO | 00 | 11/13/2008 |
