GB2310018A - A liner for a well - Google Patents

Abstract

The liner (1) avoids collapse due to settlement loads by having tubular lining sections insertable one (2) inside another (3) with coupling means comprising an expanding ring (28) locating in a deeper groove (27) of the first section (2) during insertion, moving into shallower groove (25) to inhibit separation by abutting against a shoulder of groove (36) in the second section (3), but is compressible back into deeper groove (27) to allow telescoping. A limiting means such as shear-off pins or a welded ring element (60) limits initial insertion, the limiting means being overcome by longitudinal settlement loads applied to the liner.

Description

A LINER FOR A WELL The present invention relates to a liner used to keep open a well by inhibiting the collapse of surrounding material.

As an example, on a landfill or land raising site it is desired to monitor levels of methane and leachate (dirty water). This is achieved by providing one or more wells in the landfill material. Commonly, landfill sites are filled with a mixture of dry waste materials and are covered or interspersed with layers of soil. A tubular liner is inserted into a well shaft, or built up in sections with the layers of landfill material. The liner may be surrounded by an annulus of gravel or the like, to stabilise the liner and prevent landfill material making direct contact with the liner.

A typical prior art liner comprises a plurality of plastics material tubular sections. The sections are joined by means of male and female in-wall threads at either end of each section. The threads couple to give a flush butt joint. The liner is not usually desired to be liquid or gas tight, so some leakage or permeation at the joints is permissible.

Some sections, known as casing sections, have a continuous wall surface. Others, known as screen sections, have a plurality of apertures such as horizontal slots. Gas or liquid from the landfill material permeates the gravel annulus and enters the screen sections. The gas or liquid can be monitored, or extracted by pumping. The uppermost end of the liner may be coupled to a collection system or wellhead.

A problem arises in that, depending upon the type of material, landfill and land raising sites can settle by up to around 30 per cent. During settlement, skin friction between the landfill material and the well liner exerts a considerable vertical load on the liner. If this load cannot be accommodated, the liner will buckle and render the well unusable.

An aim of the present invention is to provide a liner which does not buckle in use during settlement of the surrounding material.

According to the present invention there is provided a liner for a well, comprising: a plurality of tubular lining sections, a first of said sections being insertable into a second of said sections; coupling means for coupling together said first and second sections, said coupling means comprising an expandable engagement ring operatively engaging an external circumferential groove in said inner first section and an internal circumferential groove in said outer second section, to thereby inhibit separation of said sections; and limiting means for limiting initial insertion of said first section into said second section to a predetermined amount, said limiting means configured or arranged so as to be overcome in response to longitudinal settlement loads applied to the liner and allow further insertion of said first section.

In the preferred embodiment, the coupling means comprises an expandable engagement ring which expands in use to inhibit separation of the sections. The ring is preferably located in an external circumferential groove around an inner section. The ring may be biassed to expand in use and engage with a corresponding internal circumferential groove within an overlapping coupling section. The internal groove ideally has a sloping portion which during relative linear movement of the sections in one direction forces the ring into a compressed state.

During installation, a first section is inserted into a second section by a predetermined amount. The sections are non-retractably coupled, so an upper section can support a lower section hanging therefrom such as when a liner string which is lowered down a well.

During settlement, an upper section may move vertically downward to increase overlap with a lower section (or vice versa). Since the well liner can move with the surrounding material during settlement, vertical buckling load is significantly reduced.

In the preferred embodiment, the first section is a casing or sleeve section provided at either end thereof with said coupling means. The casing or screen section is favourably of substantially constant external diameter.

An end of the casing or screen section is operatively inserted into a second section which is a coupling sleeve, also favourably of substantially constant internal diameter, and the liner is built up of a string of casing or screen sections interspersed with coupling sleeve sections. More sections can be added until the string is built up to the desired length.

Preferably, each casing or screen section is provided with said limiting means for limiting an initial overlap between one section and the next. During installation of the liner, the limiting means inhibits a casing or sleeve section from being inserted into a coupling sleeve by more than a predetermined amount. However, during settlement the loads on the liner are much larger and are sufficient to overcome the limiting means, thus allowing further insertion and overlap.

In a first embodiment, each casing or screen section is provided with one or more shear-off pin members at a predetermined distance from the end of the section. The shear strength of the pins is selected so as to be overcome by settlement loads, but not by loads imposed during installation of the liner.

In a second embodiment, the limiting means comprises a strip or a ring which is welded to a section with material of a known weld strength. Where the section is plastics material, a plastics weld can be selected using criteria which are familiar to the skilled person to give a weld strength which is overcome by settlement loads, but not by loads imposed during installation of the liner.

Preferred embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side view of a liner; Figs 2-6 are sectional views of a coupling arrangement; Fig. 7 is a schematic plan view of a ring; and Fig. 8 is a sectional side view of the coupling arrangement with insertion limiter.

Referring to Fig. 1, liner 1 comprises casing or screen sections 2 and coupling sleeves 3. The casing sections shown are coupled into the coupling sleeves to form a liner string. The string may built up section by section and lowered down a well shaft by the uppermost section. Each section supports the sections below in the string. Alternatively, the string may be built up with the surrounding material, so each section supports the ones above.

The liner is suitably made from plastics material, and preferably a thermoplastic material such as High Density Polyethylene (HPDE), Medium Density Polyethylene (MDPE), Polypropylene, or other polyolefin polymer.

The diameter of the liner sections and the wall thickness may be selected according to site requirements.

Typical dimensions would be in the range of 90mm to 1600mm outside diameter. Each casing or screen section is typically 2.3m long, and each coupling sleeve typically im long. Allowing for an initial assembly overlap of 150mm into each end of the coupling sleeve, the effective length of one section and one sleeve together is around 3m. These lengths can be altered, in particular according to the expected amount of settlement.

Referring now to Figures 2-8, the construction and operation of a preferred coupling arrangement is shown in detail.

The coupling arrangement comprises an expandable engagement ring 28 which expands in use to inhibit separation of the sections. The ring 28 is located in an external circumferential groove 24 around a casing or screen section 2. The ring expands in use to engage with a corresponding internal circumferential groove 34 within an overlapping coupling section 3.

The ring 28 is shown schematically in Fig. 7 and comprises a toriod of resilient material having a small gap, for example of around 5 to 10 degrees. The ring may be compressed to close the gap, and when not compressed springs back to an expanded state.

Unidirectional coupling is achieved by the profile of grooves. Groove 24 has a first portion 25 of a first depth, a second portion 27 of a second depth and an inclined portion 26 therebetween. The second depth is greater than the first depth, and substantially corresponds to the thickness A of the ring 28. Groove 34 has a first portion 36 with a sloping portion 35 to a main internal surface 32.

During assembly of a liner string, section 2 is presented to coupling sleeve 3 as in Fig. 2. Leading edges 21 and 31 are chamfered for ease of insertion. Ring 28 resides in groove 24 and may move freely along the groove. Ideally, the expanded internal diameter of the ring corresponds to the outside diameter of portion 25.

During insertion, ring 28 is compressed (assisted by chamfered edge 31) and pushed along into deeper portion 27.

The ring then has substantially the same external diameter as a main part of the section 2. In this position, shown in Fig. 5, relative movement of the sections is not inhibited.

Overlap is increased until, as shown in Fig. 3, ring 28 lies over groove 34 where it may expand into portion 36.

Insertion may be initially limited to this point by a limiting arrangement such as shear-off pins.

As shown in Fig. 4, further overlap (caused, for example, by settlement loads) pushes ring 28 along groove 34 and, with assistance from sloping section 35, into a compressed state in portion 27 of groove 24. Thus further overlap is not inhibited.

During installation, one section may support those below in the string so the sections are loaded towards decreasing overlap. From the position of Fig. 3, section 2 is moved out of coupling sleeve 3 and ring 28 passes from portion 27 over portion 26 to portion 25. This position is shown in Fig. 8, and further separation (decrease in overlap) is significantly inhibited by ring 28 between portion 25 and portion 36.

In a variation (not shown), groove 24 may comprise only portion 27. However, as shown in Fig. 8, portions 25 and 36 together are as deep as the thickness of ring 28, and compression of the ring is inhibited by portion 25.

Thus, failure of the coupling arrangement by forced compression of the ring is inhibited.

Fig. 8 shows a limiting strip or ring 60 of plastics material which is welded to section 2 by weld material 63 of known weld strength. This is selected to be overcome by expected settlement loads, but not by expected installation loads. An outside surface 61 of ring 60 may be chamfered, which directs material falling along the outside of the liner away from the coupling arrangement.

The telescopic coupling arrangement described herein has a further advantage. A lining section left protruding above ground level at the top of the well may be left telescoping inside a long coupling section. As the site settles, the top section may be brought progressively out of the coupling sleeve, maintaining connection with a well head and collection system arranged at a constant level over the site.

Whilst the coupling arrangement has been described with particular reference to a liner for a well, the skilled person will appreciate that the coupling arrangement is not limited to this application and may be employed in coupling any other tubular sections, such as pipework.

Reference is made to applicant's co-pending Application GB 9613956.3 (published as GB-A-2 304 165A) from which the present application is divided.

Claims (16)

CLAIM8

1. A liner for a well, comprising: a plurality of tubular lining sections, a first of said sections being insertable into a second of said sections; coupling means for coupling together said first and second sections, said coupling means comprising an expandable engagement ring operatively engaging an external circumferential groove in said inner first section and an internal circumferential groove in said outer second section, to thereby inhibit separation of said sections; and limiting means for limiting initial insertion of said first section into said second section to a predetermined amount, said limiting means configured or arranged so as to be overcome in response to longitudinal settlement loads applied to the liner and allow further insertion of said first section.

2. A liner as claimed in claim 1, wherein one of said grooves has a sloping portion which, during relative linear movement of said sections to increase insertion, compresses said ring into the other of said grooves.

3. A liner as claimed in claim 2, wherein said ring operatively lies within said external groove and is biassed to expand in use into said internal groove, said sloping portion being provided in said internal groove.

4. A liner as claimed in claim 2 or 3, wherein said external groove has a first portion of a first depth, a second portion of a second depth and an inclined portion therebetween, wherein the second depth is greater than the first depth and wherein the second depth substantially corresponds to a thickness of said ring.

5. A liner as claimed in claim 4, wherein said ring is compressible to lie within said second portion and have an external diameter substantially corresponding to that of said inner section.

6. A liner as claimed in claim 5, wherein said first portion and said internal groove together are dimensioned to substantially correspond to the thickness of said ring.

7. A liner as claimed in claim 6, wherein, after engagement of said ring with said grooves, separation of said sections moves said ring from said second portion of said external groove to said inclined portion and subsequently to said first portion where further separation is inhibited.

8. A liner as claimed in any preceding claims, wherein said ring comprises a toriod of resilient material having a gap.

9. A liner as claimed in any preceding claim, wherein, except for any groove, said first section has a substantially constant external diameter, and said second section has a substantially constant internal diameter.

10. A liner as claimed in any preceding claim, wherein said limiting means comprises a shear-off element that is welded to one of said first and second sections with a material of a known weld strength.

11. A liner as claimed in claim 10, wherein one or more of said shear-off elements are welded to an exterior surface of said first section.

12. A liner as claimed in claim 11, wherein the or each said shear-off element is a strip or ring element.

13. A liner as claimed in any preceding claim, comprising a string of sections wherein each inner one of said sections is a casing or screen section and each outer one of said sections is a coupling section.

14. A liner as claimed in claim 12, wherein each coupling section receives two casing or screen sections.

15. A liner as claimed in claim 13, wherein each coupling section is about 1m long, each casing or screen section is about 2.3m long, and initial insertion is limited to about 0.15m.

16. A liner substantially as hereinbefore described, with reference to the accompanying drawings.