GB2310019A - 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 such as barbs (4) for inhibiting separation during installation, and shear-off pins (6) for limiting initial insertion, the pins (6) being overcome in response to significant longitudinal settlement loads applied to the liner and thus allowing further insertion. The pins (6) are screwed into tapped holes. Alternative separation limiting means is an expandable ring initially in a deep portion of a groove in the section (2) and allowed to locate also in a groove in the section (3) upon section (2) insertion, the ring then seating in a shallower groove portion in the section (2).

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 over time 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 and operatively inhibiting longitudinal 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, said limiting means comprising a plurality of shear-off pin members of a known shear strength.

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. Each casing or screen section is provided with one or more of said shear-off pin members at a predetermined distance from the end of the section, to limit initial insertion into a coupling sleeve.

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. 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.

The coupling means may comprise means for engaging a surface, such as one or more barb members. A barb member of a relatively hard material such as metal is arranged to engage positively with a surface of a relatively soft material such as plastics material. Said engagement means may be provided on an exterior surface of a first section for engagement with an interior section of a second section, or vice versa. Alternate arrangements of the coupling means are envisaged, such as 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.

Preferred embodiments of the present invention will now be described, by way of example, with reference to Figs. 1-3 of the accompanying drawings, in which: Fig. 1 is a side view of a liner; Fig. 2 is a sectional side view of coupled sections, showing a first coupling arrangement; Fig. 3 is a side view of a barb member.

Figs 4-8 are sectional views of a second coupling arrangement; Fig. 9 is a schematic plan view of a ring; and Fig. 10 is a sectional side view of the second coupling arrangement.

Referring to Fig. 1, a 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 is 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.

As shown in Fig. 2, the end 21 of each casing or screen section 2 is provided with means for engaging a coupling sleeve 3. In one embodiment this is a plurality of circumferentially spaced apart barbs 4. The engagement means is arranged to allow the coupling sleeve 3 to slide over the section 2. In Fig. 2, the barbs 4 are mounted at an inclined angle. A moderate force trying to separate the coupling sleeve from the section is sufficient to effect positive engagement of the barbs 4 with the interior surface 32 of the coupling sleeve 3.

In a typical example, the barbs are able to support the weight of a liner string of around 30m to 50m in length. Four equally spaced barbs are shown, but the number can be varied to according to load requirements.

Referring also now to Fig. 3, each barb 4 is conveniently mounted with a base portion 41 inserted into a channel or groove 23 in section 2. An aperture 42 in the base 41 of each barb receives a plastics material band 5, such as a tie wrap, which runs in groove 23. Tightening the band 5 secures the barbs 4 in place.

This arrangement is simple and quick to manufacture and requires a minimum of labour and components. The recess 23 is easily machined into a plastics material pipe of casing section 2, and the barbs 4 and band 5 fitted.

Referring again to Fig. 2, insertion of casing section 2 into coupling sleeve 3 is limited by pin members 6. The pin members are conveniently screwed into tapped holes in the wall of section 2.

During settlement, the pin members are overcome to allow increasing overlap. Ideally, the pin members are of a brittle material such as nylon and shear off under the 2vertical load imposed on the well liner by the surrounding material. The number and strength of pin members 6 can be selected according to expected loading requirements.

This combination of barbs 4 and pin members 6 allows for a simple push-fit join, leading to easy and reliable assembly of the liner during installation. Also, the liner is self supporting during installation, i.e. whilst the annulus is being added. The liner is able to withstand loads imposed radially from the surrounding material. Since the join is covered by the coupling sleeve, there is unlikely to be interference from the annulus or surrounding material.

For ease of use when coupling sections together, the ends 31 of each coupling sleeve are chamfered. Also, the ends 21 of each coupling or sleeve section are internally and externally chamfered. This makes coupling easier because the ends are guided into position. It also makes movement of equipment along the inside of the liner easier, such as when lowering a pump down the well, since the risk of equipment catching is reduced.

The first embodiment is simple and effective but the loading capability of the barbs, whilst good, is limited.

For a very long or heavy liner string, greater load carrying capacity is desired. Also, the metal barbs are subject to decay and fatigue. Further, the limiting pins shear off over a relatively large range, so accurate prediction is sometimes difficult. The second embodiment, described below, addresses and improves on these features.

Referring now to Figures 4-10, the construction and operation of a second coupling arrangement is shown in detail. The arrangement of the sections is similar to the first embodiment described above and corresponding reference numerals are in general used for corresponding parts.

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. 9 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. 4. 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. 6, ring 28 lies over groove 34 where it may expand into portion 36.

Insertion is initially limited to this point by a limiting arrangement including shear-off pins (not shown).

As shown in Fig. 7, 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. 6, 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.

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-2304165A) from which the present application is divided.

Claims (10)

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 and operatively inhibiting longitudinal 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, said limiting means comprising a plurality of shear-off pin members of a known shear strength.

2. A liner as claimed in claim 1, said pin members extending radially externally of said first section at a predetermined distance from one end thereof.

3. A liner as claimed in claim 2, wherein each said pin member is located into a receiving aperture in a wall of said first section.

4. A liner as claimed in claim 3, wherein each said pin member is screwed into a tapped hole in said first section.

5. A liner as claimed in any preceding claim, wherein said coupling means comprises one or more barb members provided on an exterior surface of said first section for engagement with an interior surface of said second section, or vice versa.

6. A liner as claimed in any of claims 1-4, wherein said coupling means comprises an expandable engagement ring for 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.

7. 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.

8. A liner as claimed in claim 7, wherein each coupling section receives two casing or screen sections.

9. A liner as claimed in claim 8, wherein each coupling section is about lm long, each casing or screen section is about 2.3m long, and initial insertion is limited to about 0.15m.

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