GB2509554A

GB2509554A - Method of plugging a well for permanent abandonment

Info

Publication number: GB2509554A
Application number: GB201300302A
Authority: GB
Inventors: Halvor Kjorholt; Gjermund Grimsbo; Gisle St Jern; P L Viggo Hemmingsen
Original assignee: Statoil Petroleum ASA
Current assignee: Equinor Energy AS
Priority date: 2013-01-08
Filing date: 2013-01-08
Publication date: 2014-07-09
Anticipated expiration: 2033-01-08
Also published as: WO2014108431A3; GB2509554B; WO2014108431A2; GB201300302D0

Abstract

A method of plugging a hydrocarbon well to facilitate permanent abandonment of the well, comprising expanding a section of inner or outer tubular 4 within the well such that the expanded section of the inner tubular comes into sealing contact with a casing 2 or wherein the expanded section of outer tubular comes into sealing contact with the formation 1. The expanded section of tubular is filled with material to form a sealing plug within the tubular. The material may be cement 12, and the expansion may be carried out by explosives, by hydraulics or by a cone forced against it. Sealant may be introduced between the tubular and the casing; the sealant may be cement, polymer composite or an epoxy resin. The inner tubular may be production tubing, inner casing or lining.

Description

A method for plugging a hydrocarbon well The present invention relates to a method for plugging a hydrocarbon well to facilitate permanent abandonment of the well.

Wells used in gas and oil recovery need to be satisfactorily plugged and sealed after the wells have reached their end-of life and it is not economically feasible to keep the wells in service. Oil and gas wells have in general three different purposes, as producers of hydrocarbons; injectors of water or gas for reservoir pressure support or for depositing purposes; or as exploration wells. Plugging of wells is performed in connection with permanent abandonment of wells due to decommissioning of fields or in connection with permanent abandonment of a section of well to construct a new wellbore (known as side tracking or slot recovery) with a new geological well target.

A well is constructed by a hole being drilled down into the reservoir using a drilling rig and then sections of steel pipe, casing or liner are placed in the hole to impart structural integrity to the wellbore. Cement is placed between the outside of the casing or liner and the bore hole and then tubing is inserted into the casing to connect the wellbore to the surface. Once the reservoir has been abandoned, a permanent well barrier must be established across the full cross-section of the well. This is generally achieved by removal of the inner tubulars from the well bore by means of a workover rig which pulls the tubulars to the surface. Well barriers are then established across the full cross-section of the well, in order to isolate the reservoir(s) and prevent flow of formation fluids between reservoirs or to the surface. It is necessary to remove the inner tubulars from the wellbore in order to set the cement plug against the outer casing or liner and to verify the casing or liner cement.

Improperly abandoned wells are a serious liability so it is important to ensure that the well is adequately plugged and sealed. However, the number of steps and equipment involved, such as a rig and drillpipe, results in this stage of the life of the well being costly and time-consuming, at a time when the well no longer generates revenue.

Attempts have been made to increase the efficiency of the method of abandonment.

For example, GB2407835 (Head) describes wellbore sealing wherein explosive charges are used to perforate a lower end of the tubing and then sealing fluid is then pumped through the perforations so as to plug the well around the bottom end of the tubing.

US2591807 (Greene) relates to an apparatus that uses relatively low and high velocity explosive charges spaced at opposing ends of a container full of cement for placing in a zone of a wellbore whereby upon ignition cement is forced downwardly and outwardly to release cement into the cavity between the tubing and formation. US2696258 and US2696259 (also to Greene) relate to an apparatus for depositing cement in a zone wherein the cement is contained within an elongated container and a gas generating charge is ignited to displace the cement through a lower outlet of the container into the zone. The charge expands the container into sealing contact with the casing, while at the same time rupturing the end of a tubular body to release cement into the wellbore.

It is an object of the present invention to provide an improved method for plugging an abandoned well that reduces the number of steps involved in the process and/or removes the need for a rig.

Accordingly, the present invention provides a method of plugging a hydrocarbon well to facilitate permanent abandonment of thewell, the method comprising: expanding a section of inner or outer tubular within the well wherein the expanded section of an inner tubular comes into sealing contact with a casing lining the well to at least partially seal the tubular to the casing or wherein the expanded section of the outer tubular comes into sealing contact with the formation; and filling the expanded section of tubular, in whole or in part, with a material so as to form a sealing plug within the tubular.

The present invention is particularly suitable for plugging of oil and gas wells, especially offshore wells.

In the context of this disclosure, the term tubular" refers generally to any kind of pipe contained within a well, including an inner or outer casing within the well, tubing, such as production tubing and liners.

Expansion of the tubular may be accomplished by any suitable means that causes the tubular to expand sufficiently for it to deform into sealing contact with the surrounding casing or formation of the well. Preferably, explosives are provided within the tubular, for example, attached to a wire line that is inserted into the tubular to deliver explosives to the section to be expanded against the casing or formation. In this embodiment of the invention, an appropriate detonator should also be provided. Explosives may be used to expand a section of the inner tubular to cause at least paitial fusion of the tubular with the outer casing.

Additional and/or alternative means may be used to effect expansion of the tubular, such as hydraulics or other mechanical means, for example a cone, provided said means generates enough force to expand the tubular against the casing or formation to fuse the two together to result in the forniation of a single barrier element Generally, the expanded section of the tubular will be filled with cement to form a permanent plug within the tubular. However, alternative sealing materials may be used.

It may be preferable to improve the seal between the casing and the tubular by the introduction of a sealant or adhesive between the casing and the tubulai. The sealant may comprise a polymer composite, such as epoxy resin, or cement.

Foi a bettei understanding of the piesent invention and to show more clearly how it may be carried into effect, iefeience will now be made by way of example only, to the accompanying drawings in which: Figure 1A is a schematic diagram of a well section; Figure 1 B is the well section of Figure 1 provided with a wiieline; Figure 1 C illustrates detonation of explosive charges along the wireline causing expansion of the tubular towards the casing; Figure 1D illustrates plugging of the expanded section using cement; and Figuie 2 is an illustrative flow chart showing the steps of a method of plugging a hydrocarbon well according to the present invention.

The present invention enables the establishment of permanent wellbore bariiers by the expansion of an inner tubing (or other tubular, such as an inner casing) causing it to fuse with an outer casing to allow for simplified plugging and abandonment of a well.

The method involves the expansion of the inner tubular of a production well towards the outer casing to form a single tubular steel pipe, as illustrated in Figures 1A to 1D of the accompanying drawings. This removes the need to remove the inner tubular by means of a rig prior to the formation of a barrier across the welibore. In the illustrated example, expansion is achieved using explosives. A well comprises a casing 2 lining a wellbore drilled through a formation 1. A tubular 4 extends through the casing 2. A cement bond 6 is provided between the steel casing and the welibore. When the well is to be abandoned and hence requires plugging and sealing, a wireline 8 with explosive charges 10 is fed down the tubular into a section of the well (see Fig. 1B).

The explosive charges are then detonated to cause expansion of the tubular 4 towards the casing. This must be carried out in such a manner as to ensure that the tubular 4 is welded into the casing 2 to form a single solid pipe section, as shown in Figure lD.

The creation of a single barrier element is achieved by metallurgically joining the two metal tubings by explosive welding, a well-known method for joining a wide variety of similar or dissimilar metals. The expanded section is then permanently plugged with cement 12. A squeeze operation may also be performed to establish a permanent seal behind the casing, if logging shows poor cement bond. This may be achieved by squeezing cement or other sealant into the annular space behind the casing.

It is to be appreciated that the type of explosive used in the procedure may comprise any chemical explosive that generates sufficient energy to accelerate the inner tubular 4 to collide at high velocity into the outer casing so that they are fused together. The tubular itself must be comprised of a material that allows for such expansion. In oil and gas wells, the tubular generally consist of various steel grades. Steel is a material that can be expanded by the application of stresses above the yield point and into a plastic region to create permanent deformation. Such steel pipes should be able to expand by 20-30% without fracturing.

Alternative methods for expansion of the tubular include hydraulic means, mechanically by a cone or any other means that generates the necessary force to expand the tubular against the outer casing. Explosives may be used in conjunction with the other expansion means whereby the need for high velocity explosives is reduced, making a broader selection of explosives available for selection.

The sealant may be injected into the annulus between the casing and the tubular before expansion using a punch-tool or annulus injection. The sealant consists of a material that is qualified as part of a permanent barrier element. For example, a polymer composite type material, such as epoxy.

Figure 2 of the accompanying drawings is an illustrative flow chart showing the steps of plugging a hydrcarbon well according to the present invention, comprising (a) expansion of an inner or outer tubular; (b) obtaining sealing contact of the expanded tubular with a casing or formation; and (c) filling the expanded section of tubular with a material to form a sealing plug.

The barrier element formed according to the process of the present invention should be tested for integrity. This may be carried out by perforating into the annulus below and above the expanded section of tubular and pressure testing across the barrier element.

It is clear that the present invention removes the need for a rig to remove the inner tubular and enables the use of light well intervention vessels or coiled-tubing vessels to perform permanent plug and abandonment of offshore wells, leading to a quicker and cheaper procedure.

Whilst the illustrated embodiment demonstrates the expansion of an inner tubular to fuse it to the outer casing followed by plugging of the tubular, an outer casing or liner may be expanded against the formation in order to achieve a permanent barrier. The inner casing/tubing may be pulled out by conventional means. This embodiment removes the need to mill out the casing from the well.

Claims

CLAIMS: 1. A method of plugging a hydrocarbon well to facilitate permanent abandonment of the well, the method comprising: expanding a section of an inner or outer tubular within the well wherein the expanded section of inner tubular comes into sealing contact with a casing lining the well to at least partially seal the tubular to the casing or wherein the expanded section of outer tubular comes into sealing contact with the formation; and filling the expanded section of tubular, in whole or in part, with a material so as to form a sealing plug within the tubular.
2. A method according to claim 1 wherein the inner tubular comprises a production tubing, inner casing or lining for coming into sealing contact with a casing lining the well.
3. A method according to claim 1 wherein the outer tubular comprises an outer casing or liner for coming into sealing contact with the formation.
4. A method according to claim 1, 2 or 3 wherein an explosive force causes expansion of a section of the tubular.
5. A method according to claim 4 wherein explosives are introduced into a section of the tubing on a wireline.
6. A method according to any one of claims 1 to 5 wherein hydraulics expand the tubular.
7. A method according to any one of claims 1 to 6 wherein a cone forced against a section of the tubular causes expansion of the tubular.
8. A method according to any one of the preceding claims wherein the expanded section of the tubular is filled with cement to form the sealing plug within the tubular.
9. A method according to any one of the preceding claims further comprising introducing a sealant between the tubular and the casing to enhance the seal therebetween.
10. A method according to claim 9 wherein the sealant is cement.
11. A method according to claim 9 wherein the sealant is a polymer composite.
12. A method according to claim 11 wherein the polymer composite is an epoxy resin.
13. A method according to any one of the preceding claims for use in the plugging of a production well, injector well or an exploration well.
14. A method according to any one of the preceding claims for use in the plugging of offshore wells.