WO2002075100A1

WO2002075100A1 - Apparatus and method for running down hole liners

Info

Publication number: WO2002075100A1
Application number: PCT/GB2002/001138
Authority: WO
Inventors: Paul Howlett; Mark Carmichael
Original assignee: Specialised Petroleum Services Group Ltd; SPS Afos Group Ltd
Current assignee: Schlumberger UK Holdings Ltd
Priority date: 2001-03-15
Filing date: 2002-03-13
Publication date: 2002-09-26
Anticipated expiration: 2003-09-15
Also published as: GB0106378D0

Abstract

A liner (10, 30) or liner assembly is disclosed which is prefabricated with a means for enlarging its outside diameter prior to it being run in a well bore (11). The enlarging means may be a coating, such as a cement coating or may be provided by the addition of an outer sleeve (20), in which case an annular space (21) between the liner (10, 30) and sleeve (20) may be filled with a buoyancy promoting fluid.

Description

APPARATUS AND METHOD FOR RUNNING DOWN HOLE LINERS

This invention rebates most particularly to liners used in well bores as may be typically required in oil or gas drilling operations. The invention also finds application in reduced diameter casings or casing sections.

It is considered desirable when drilling for oil or gas to line the well bore with a casing and, further downhole, a liner. Usually the liner is suspended from the casing by liner hanging apparatus, at least until it is cemented in place. Cementing the liner is a very important operation in the preparation of a well bore and involves the passing of cement down through the liner to the bottom and then back up the outside of the liner filling the annulc.r space between the liner exterior and the well bore.

As a result of the general size requirements of commonly used drilling equipment, the well bore may be substantially larger than the outside dimensions of the liner. The relatively large annular area between the liner and the well bore serves to cause low flow velocities of the cement and makes it more difficult for the cement to completely fill the gap evenly.

This can result in poor bonding of the cement to the exterior walls of the liner, which is most undesirable.

A constraint upon solving the problem is that it is considered advantageous to construct the work string with a constant internal diameter or monobore. Thus it is not generally suitable merely to increase the size, measured by the internal diameter, of the liner. Similarly, the problem is not satisfactorily solved by building the liner with much thicker metal walls than previously practised, in view of the additional weight that would result. Many wells now being drilled are horizontal at their extremity. For this reason a liner which has excessive weight can be most difficult to run, the liner having a tendency to fall to the lower wall of the well. Cementing around the liner can then also be difficult.

In the past some attempts have been made to improve the flow velocity and efficiency of the cement, including the use of centralisers which circumnavigate around the liner to hold it appropriately in position during the cementing operation. Also, bands have been placed around the liner in order to reduce the volume of the annular space to be filled with cement, the bands thereby serving to increase the flow velocity of the cement. However, such bands, made typically of rubber, diminish the integrity of the cement/liner bond.

An object of the present invention is to provide an improved means of increasing the flow velocity of the cement during a liner cementing operation. The present invention also recognises the importance of creating a strong bond between the liner wall and the cement. It is a further object of this invention to provide a means and method for improving the quality of the bond at the liner and cement interface.

According to a first aspect of the present invention there is provided a liner prefabricated with an enlarging means that serves to substantially increase the outside diameter of the liner prior to it being run in the well.

The enlarging means may be formed or shaped with a recess for containing components or tools on the liner. These may include, centralisers or stabilisers for example.

Preferably the enlarging means is a coating, such as cement. The cement may be provided with reinforcing.

The outer surface of the coating may incorporate means for improving its bond with cement or the like used to fix the liner in a well bore. For example, the outer surface may be roughened or include protruding steel reinforcement bars.

Alternatively, the enlarging means is a sleeve member sized to be positioned around the liner. Preferably, there is provided an annular space between the liner and the sleeve member adapted to be filled with a fluid of relatively low specific gravity to promote the buoyancy of the liner. The annular space would most suitably be sealed. According to a second aspect of the present invention there is provided a method of cementing a liner or liner assembly comprising the steps of:

a) enlarging the outside diameter of the liner or liner assembly prior to running the liner; b) running and hanging or otherwise suspending the liner; and c) circulating and setting cement or similar settable fluid to fill the space between the well bore and the said at least one layer.

The outside diameter of the liner may be enlarged by applying at least one layer of cement to the outer surface of the liner.

The first layer of cement would typically be applied to the liner in factory conditions. The liner would preferably be cleaned and prepared in factory conditions prior to the applr.cation of the at least one layer. This has the advantage of enabling an improved bond between the liner and the coating.

Typically, the coating may be applied to the liner with the use of a mould. Alternatively it may be hosed or sprayed to the liner surface.

In order to provide a better understanding of the invention, embodiments thereof will now be described, by way of example only, and with reference to the accompanying Figures, in which:

Figure 1 shov s a section of liner in a factory to which is being applied a first layer of cement; and Figure 2 illustrates an alternative liner hung from a casing in a well bore during a cementing operation.

Referring firstly to Figure 1, a liner, generally depicted at 10, is supported horizontally on plinths 2 in a factory. The outer surface of the liner 10 has been cleaned and prepared in factory conditions. Cleaning may be performed by washing or hosing the liner 10, and more rigorous preparation may include jet blasting the liner with sand, water or air.

If it is found desirable, the liner 10 may incorporate protruding lugs or like anchors 4 for the purpose of anchoring reinforcing 3, as shown in the drawing. The reinforcing 3 may be made from mild steel or any other appropriate material, most typically of ferrous metal.

Alternatively, the lugs 4 may be provided in plentiful fashion and serve to improve the bond of the coating to be applied to the liner 10.

Figure 1 shows a mould 5 which surrounds the liner 10 leaving an annular space 6 suitable for receiving a coating layer. The coating layer is most suitably cement, although it is realised in the present invention that other materials may be used. Indeed the ability to apply the coating under factory conditions provides an opportunity for a diverse range of materials to be employed, all having the desired effect of increasing the effective outside diameter of the liner. Additionally, materials having lower specific gravity could be chosen which would serve to increase the relative buoyancy of the liner or casing to which it was applied.

The mould 5 has a roughened inner surface which is related to the outer surface of the moulded coating.

Apparatus may be provided to rotate the liner 10 and mould 5 on the supporting plinths 2. Such controlled and slow rotation of the liner 10 during the application of the coating can be used to ensure the coating is applied evenly and continuously around the liner 10.

The mould 5 may be designed so as to shape the outer coating in a way which allows an external tool or component to be suitably housed on the liner. Such component may, for example, be a stabiliser. Depending upon the shape or cavity formed by the coating, once applied, a stabiliser may be allowed to move actually within predetermined limits set by the parameters of the coating material .

Rotation of the liner 10 during the application of the coating may also be desirable if the coating was applied in the form of a spray.

In Figure 2 an alternative liner 30 is shown suspended in a well bore 11. The liner 30 is circumnavigated by a sleeve 20 made of similar metallic material to the liner itself. The sleeve 20 is provided with suitable wall thickness for providing the liner assembly with ample strength prior to bonding with cement in the well. An annular compartment 21 is formed between the sleeve 20 and the liner 30, and sealed by seals 22. The compartment 21 is filled with air. Thus, although the sleeve 20 adds considerable mass to the liner assembly, the gas filled compartment 21 counters this during running of the liner, acting as a float by reason of the gas/air having far lower specific gravity than the drilling mud.

Cement 12 is circulated through the liner 30 and out the bottom of the liner 30 near the shoe of the well.

Thereafter the cement 12 is caused to flow up the annular space 13 between the outside of the liner 30 (and more specifically the outside of the sleeve 20) and the well bore 11.

As the sleeve 20 has effectively increased the outside diameter of the liner assembly, there is a reduced cross- sectional area in the annular space 13 and this in turn allows the cement 12 to have a greater flow velocity up the outside of the liner 10.

Neither the coating described herein with reference to Figure 1 or the sleeve 20 shown in Figure 2 prevent the perforation of the liner with the use of known explosive charges or devices.

The advantages of the present invention include the ability to improve the integrity of the bond between the liner wall and the cement, while also quickening the time required to fill the annular space outside the liner with cement during the liner cementing operation. The invention also provides opportunity for increasing the buoyancy of the liner when running the liner in the well. It should be understood that while reference is substantially made to liners in this specification, the invention may equally be applied to casings .

Further modifications and improvements may be incorporated without departing from the scope of the invention herein intended.

Claims

1. A liner for use in a well bore characterised in that the liner is prefabricated with an enlarging means that serves to substantially increase the outside diameter of the liner prior to it being run in the well.

2. A liner as claimed in Claim 1 wherein the enlarging means is formed with a recess for containing components or tools on the liner.

3. A liner as claimed in Claim 2 wherein a said component or tool is a centraliser.

4. A liner as claimed in Claim 2 wherein a said component or tool is a stabiliser.

5. A liner as claimed in any one of the preceding Claims, wherein the enlarging means is a coating.

6. A liner as claimed in Claim 5 wherein the coating is made of cement.

7. A liner as claimed in Claim 6 wherein the cement is reinforced.

8. A liner as claimed in any one of Claims 5 to 7, wherein the outer surface of the coating incorporates means for improving its bond with cement used to fix the liner in a well bore.

9. A liner as claimed in Claim 8 wherein the outer surface is roughened.

10. A liner as claimed in Claim 8 wherein the means includes protruding steel reinforcement bars.

11. A liner as claimed in any one of Claims 1 to 4 wherein the enlarging means is a sleeve member sized to be positioned around the liner.

12. A liner as claimed in Claim 11 wherein there is provided an annular space between the liner and the sleeve member adapted to be filled with a fluid of relatively low specific gravity to promote the buoyancy of the liner.

13. A liner as claimed in Claim 12 wherein the annular space is sealed.

14. A method of cementing a liner or liner assembly comprising the steps of:

a) enlarging the outside diameter of the liner or liner assembly prior to running the liner;

b) running and hanging or otherwise suspending the liner; and

c) circulating and setting cement or similar settable fluid to fill the space between the well bore and the said at least one layer.

15. A method as claimed in Claim 14 wherein the outside diameter of the liner is enlarged by applying at least one layer of cement to the outer surface of the liner.

16. A method as claimed in Claim 15 wherein a first layer of cement is applied to the liner in factory conditions.

17. A method as claimed in any one of Claims 14 to 16, wherein the cement is applied to the liner with the use of a mould.

18. A method as claimed in any one of Claims 14 to 16 wherein the cement is hosed or sprayed to the liner surface.

19. A method as claimed in Claim 4 wherein the outside diameter of the liner assembly is enlarged by adding a sleeve around the liner.

20. A method as claimed in Claim 19 wherein a buoyancy fluid is added to the liner assembly between the liner and the sleeve.