WO2022171604A1

WO2022171604A1 - Method for abandoning a completed wellbore

Info

Publication number: WO2022171604A1
Application number: PCT/EP2022/052972
Authority: WO
Inventors: Walter STAM; Petrus Cornelis Kriesels
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2021-02-11
Filing date: 2022-02-08
Publication date: 2022-08-18

Abstract

A wellbore, which comprises a production tubing with a functional cable extending along a length on the exterior thereof, is plugged for abandonment. To plug the wellbore, an external cement barrier is placed, along a zone of interest, in an annulus directly surrounding the production tubing. The external cement barrier is in direct contact with the production tubing and the functional cable. After placing the external cement barrier is allowed to set, after which the functional cable can be subjected to an after-treatment to close any axial leak path associated with the functional cable. Finally, an internal barrier plug is formed within the production tubing, in the zone of interest, and while maintaining at least a portion of the external cement barrier in place.

Description

METHOD FOR ABANDONING A COMPLETED WELLBORE

FIELD OF THE INVENTION

The present invention relates to a method of plugging a wellbore for abandonment, wherein the wellbore comprises a production tubing with a functional cable extending along a length on the exterior thereof.

BACKGROUND TO THE INVENTION

There is an upcoming increase in plugging and abandonment (P&A) needs for oil and gas wells, especially in mature, offshore areas such as the North Sea and Gulf of Mexico, and deep-water wells in Brazil and west African waters.

In the course of constructing an oil or gas well, a borehole is drilled to a predetermined depth. The drilling string is then removed, and a metal tubular or casing is run into the well. When the casing reaches the bottom of the well, cement is pumped down the casing and displaced up the annulus between the casing and the original wellbore. The function of the cement is to secure the casing in position and ensure that the annulus around the casing is sealed. This process of drilling, running casing and cementing is repeated with successively smaller drilled holes and casing sizes until the well reaches its target depth.

At this point, a so-called production tubing is run into the well. The well may now be put on production, with hydrocarbon fluids flowing up the production tubing and gathered at surface. Hydrocarbon fluids are allowed to enter into the wellbore below the production packer, and hence find their way into the production tubing. Over time, which may be several decades, the production of hydrocarbons reduces until the production rate is no longer economically viable, at which point the well has reached the end of its productive life. The well now needs to be plugged and abandoned.

A commonly accepted method of abandonment plugging, would be to pull the production tubing, including any gauge cables and/or control lines that typically run along an exterior wall of the production tubing, out of the wellbore prior to setting one or more abandonment plugs. Notwithstanding, particularly in offshore areas, any downhole operation which requires rig time can incur significant cost. Significant time, and thus cost, can be saved if pulling of wellbore tubing, or milling of wellbore tubing, could be avoided. Reference WO 2019/122857 A1 describes a well abandonment procedure wherein control lines are at least partially removed from the wellbore before placing a cement plug. The reference recognizes that control lines cannot simply be cemented in place when abandoning a well, as they present a potential leak path through the cement plug. In order to remove the control lines from the wellbore, the production tubing is perforated at a location adjacent one or more control lines, and self-supporting settable composition is displaced through the perforations into the annulus to secure the one or more control lines in place. Subsequently, the production tubing and the one or more control lines are cut at the location of the self-supporting settable composition. The self-supporting settable composition is then washed away, and at least a portion of the one or more control lines is then removed from the wellbore.

There is still a need for a reliable method by which tight plugs can be placed across the caprock while any tubing and gauge cable and/or control line are left in place. A problem which occurs when the gauge cable and/or control line is left in place extending along a length of the production tubing, is that such cable forms a risk of providing an axial leak path through any barrier plug through which the cable traverses.

SUMMARY OF THE INVENTION

In accordance to one aspect of the present invention, there is provided a method of abandoning a wellbore that comprises a production tubing, with a functional cable extending along a length on the exterior thereof, comprising:

- placing an external cement barrier along a zone of interest in an annulus directly surrounding the production tubing, whereby the external cement barrier is in direct contact with the production tubing and the functional cable;

- allowing the external cement barrier to set;

- subsequently subjecting the functional cable to an after-treatment to close any axial leak path associated with the functional cable;

- subsequently forming an internal barrier plug within the production tubing in the zone of interest while maintaining at least a portion of the external cement barrier in place.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict one or more implementations in accordance with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.

Fig. 1 schematically shows a cross sectional view of a production tubing in a cased wellbore; and

Fig. 2 schematically shows the cased wellbore of Fig. 1 after arranging cement in the annulus around the production tubing;

Fig. 3 schematically shows the wellbore of Fig. 2, with an after-treatment tool disposed in the production tubing;

Fig. 4 schematically shows the wellbore of Fig. 2 after performing an after-treatment;

Fig. 5 schematically shows the wellbore of Fig. 4 after an internal barrier plug has been formed within the production tubing;

Fig. 6 schematically shows the wellbore of Fig. 2 after performing an alternative after-treatment;

Fig. 7 schematically shows the wellbore of Fig. 6 after the internal barrier plug has been formed within the production tubing;

Fig. 8 schematically shows the wellbore of Fig. 1 after arranging an optional cement base in the annulus;

Fig. 9 schematically shows the wellbore of Fig. 8 during placing of the external cement barrier;

Fig. 10 schematically shows the wellbore of Fig. 9 after placing the external cement barrier;

Fig. 11 schematically shows the wellbore of Fig. 1 with a local expander tool deployed within the production tubing; and

Fig. 12 schematically shows the wellbore of Fig. 1 after forming an alternative optional cement base in the annulus.

DETAILED DESCRIPTION OF THE INVENTION

The person skilled in the art will readily understand that, while the detailed description of the invention will be illustrated making reference to one or more embodiments, each having specific combinations of features and measures, many of those features and measures can be equally or similarly applied independently in other embodiments or combinations. In the context of the present disclosure, the term “functional cable” is broadly used to describe any type of cable or line that extends along the production tubing into a wellbore regardless of their intended purpose. Examples include gauge cables and control lines. Functional cables may comprise one or more of hydraulic conduits, optical fibers, and electric conductors used for transmitting data signals, control signals, and/or power.

Figure 1 schematically shows a wellbore comprising a production tubing 2 and a functional cable 4 extending along a length on the exterior of the production tubing 2. The wellbore typically further comprises a casing 6 which is cemented into position in the wellbore. The production tubing 2 is configured to provide an additional pressure barrier within the casing 6, but is not cemented in place. This is usual practice in the industry for production tubing 2, so as to facilitate potential remedial operations, such as removal and replacement of the tubing in the event that it becomes damaged or corroded.

Typically, the uncemented annulus 8 around the production tubing 8 is sealed off from exposure to the formation pressure by a production packer (not shown) at a lower end of the production tubing 2.

The next paragraphs will illustrate a method to create a tight abandonment plug in the wellbore, without removing or pulling the production tubing 2 and or the functional cable 4 from the wellbore.

The method involves placing an external cement barrier 10 along a zone of interest in the annulus 8 directly surrounding the production tubing 2. This is shown in Fig. 2. The external cement barrier 10 is in direct contact with the production tubing 2 and the functional cable 4. The external cement barrier 10 is allowed to set before continuing the method. Suitably, an expanding cement is selected for creating the cement barrier 10. The cement barrier 10 provides part of the ultimate abandonment seal. In addition, the cement barrier 10 provides a structural support for the functional cable 4, which facilitates an after- treatment operation which is carried out to close any axial leak path associated with the functional cable 4. Absent the cement barrier 10, the functional cable 4 could be deflected (pushed away) from the impact of any after-treatment tool which tries to interact with the functional cable 4. The after-treatment may include locally applying a force to the functional cable 4 at the location of the cement barrier 10, whereby the cement barrier 10 provides counterforce, which holds the functional cable 4 in place.

Various after-treatment operations are conceived, which will be illustrated herein. An after-treatment may involve locally excavating a local cavity 28 in the external cement barrier, and subsequently filling the cavity with a sealing material. Figs. 3 to 5, for example, illustrate an after-treatment which involves cutting the functional cable 4 in one or more locations and allowing a sealant to settle in the cuts. At least parts of the cement barrier 10 stay intact as well, to continue to function as a sealing barrier.

Suitably, the after-treatment is accomplished from within the production tubing 2, which may involve deploying and operating a tool 30 within the production tubing, which is capable (when activated) to cut through both the production tubing 2 and the functional cable 4. Full 360° circumference cutting is preferred, as this would for example obviate the need for cable localization. Also, a full circumference cut may address any other leak paths that may exist that are not related to the functional cable 4, such as micro-annuli between the cement barrier 10 and the production tubing 2.

Pipe and tubing cutters for wellbore tubulars are available in many variants, including mechanical cutters and energetic cutters. These may typically be deployable on wire line, e-line, a capillary string (such as micro coil) or standard coiled tubing. Figure 3, for example, illustrates an energetic cutting tool 30 disposed on a coiled tubing 32 within the production tubing 2. In this example the cutting tool 30 consists of multiple layers of shaped charges 34, similar as shown in e.g. International publication WO 2020/037267 Al, but for the present purpose the shaped charges may be lined as it is the intention to cut the tubing material. After detonating the charges, a radial cutting jet is penetrating through the production tubing 2 and functional cable 4, which is held in position by the cement barrier 10. Alternatively, single stage cutters may be used in several trips. Such energetic cutting tools can be commercially sourced, for instance through W.T.Bell International Inc..

Instead of physically cutting through the functional cable 4, it may also suffice to locally expand the production tubing 2 radially outward against the functional cable 4, and into the external cement barrier 10. In this manner the local cavities 38 (Fig. 6) are located within the production tubing 2, inside the dents which correspond to the locally expanded bands. This after-treatment may also be accomplished from within the production tubing 2, for example with a similar tool 30 as shown in Fig. 3, but with charges optimized cause a shock wave that can travel radially outward to impact the tubular and expand a portion of the wall of the tubular radially outward without perforating or cutting through the tubular. Herewith a protrusion of the production tubular 2 is formed at said the portion of the wall. The charges are typically not provided with liners, as taught in International publications WO 2020/37143 Al and WO 2020/037267 Al. Other tools 30 may be employed instead, including another energetic expansion tool disclosed in WO 2019/151870 Al, or for example an expanding blade tool (e.g. US patent No. 10,794,158), or an axial compression expander tools (e.g. US pre-grant publication US 2010/0319427 Al).

The local expansion may deform the functional cable 4 by locally compressing it, and thereby constricting axial leak paths associated with the functional cable 4. Such leak paths may be internal leak paths inside the functional cable 4, for example at interfaces between certain mantle layers within the cable, and/or external leak paths at the interface between the functional cable 4 and the external cement barrier 10. Experiments have shown that local expansion applied on a cemented cable can result in significant reduction of internal leak paths. Moreover, as taught in US patent No. 10,794,158 and publication WO 2020/016169 Al, a local expansion into the cement barrier 10 has been demonstrated to provide a remediating effect in the impacted zones 22, as a result of which certain leak paths and (micro-)cavities are sealed. Setting local expansion zones over full 360° circumference is therefore preferred also in these embodiments, as this would for example obviate the need for cable localization and address other leak paths that may exist that are not related to the functional cable 4, such as micro-annuli between the cement barrier 10 and the production tubing 2. It is envisaged that the mechanical properties of the external cement barrier 10 can be selected such that an optimum is achieved

After having formed the cavities 28 and/or 38, the after-treatment is completed by forming an internal barrier plug 40 within the production tubing 2 in the zone of interest. At least a portion of the external cement barrier 10 is maintained in place. Examples are shown in Figs. 5 and 7. Prior to forming said internal barrier plug 40, a plug base 36 may suitably be set within the production tubing 2. This facilitates forming of the internal barrier plug 40 by using a liquid plug material and allowing that to solidify by curing and/or cooling off. In certain embodiments, the plug material may be cast on top of the plug base 36. It is not in all instances necessary to set a separate plug base 36.

Particularly, in cases where the external barrier has been pumped into the annulus 8 via perforations 12 in the production tubing 2, a residual amount of cement in the production tubing 2, suitably kept in place by a cement retainer, may be used as the plug base 36 to support the internal barrier plug 40.

Preferably, the internal barrier plug 40 comprises an expanding material, which expands upon becoming solid. Bismuth is known to be such a material, as suggested for example in publication WO 02/099247 Al, and there are also expanding cements or resins available. There are other suitable metals known, besides bismuth, which have the desired properties for the purpose of forming the internal barrier plug 40, including bismuth containing alloys such as taught in for example US patent 6,923,263.

As shown in Fig. 5, the cavities 28 may suitably be filled in the same step as forming the internal barrier plug 40 and with the same plug material, thereby forming a plug that integrally extends into the cavities 28. The same result can be achieved for the cavities 38 in the embodiment of Figs. 6 and 7.

Finally, it is envisaged that a combination of cuts 28 and dents 38 is employed whereby the benefits of both options are enjoyed in the same abandonment method. This may conveniently be done using a hybrid tool which may for example contain alternating sections of lined charges for cutting and unlined charges for energetically expanding.

Referring now to Figs. 8 to 10, some optional specifics are illustrated which may be applied for the placement of the cement to introduce the external cement barrier 10. For example, the production tubing 2 may be perforated with one or more cementing perforations 12, prior to pumping the cement, to allow the passage of the fluid cement between production tubing internal space 14 and the annulus 8. Also, a specific cement base 16 may optionally be configured in the annulus 8 below the cementing perforations 12, to avoid sagging of the cement while it is still liquid. Alternatively, it may be possible to allow the cement to sag on the production packer (not shown) in which case a separate cement base 16 does not need to be provided. Furthermore, it may be useful to configure a bridge plug 24 within the production tubing internal space 14, below the cementing perforations 12, to block the cement from proceeding through production tubing 2, and steer the liquid cement to the cementing perforations 12 instead. As illustrated in Fig. 9, the placing of the external cement barrier 10 may involve pumping the cement through a cement retainer 46 via a cementing conduit 37. The cement retainer 46, which primarily serves to avoid “u-tubing” of the cement back into the production tubing 2 prior to setting of the cement, may stay in place after setting the external cement barrier 10, as shown in Fig. 10, and subsequently serve as the plug base 36 discussed hereinabove.

In addition to preventing sagging of the external cement barrier 10, the optional cement base 16 may be beneficial also as means to help centralization of the production tubing 2 within the surrounding casing 6. Centralization is sufficient when sufficient standoff between the production tubing 2 and the surrounding casing 6 is established, in order to guarantee there is sufficient access for the liquid cement to form a closed continuous seal around the entire circumference of the production tubing 2. Typically, a minimum clearance of 1 cm, preferably of 1.5 cm, is considered sufficient standoff clearance for creating a continuous external cement barrier 10.

Figs. 11 and 12 show an alternative method of creating the cement base 16, in this case by applying a local expansion to the production tubing 2 to create a radially outwardly expanded band 26 protruding into the uncemented annulus 8. The expanded band 26 may extend around the entire circumference of the production tubing 2. This automatically provides standoff, without necessarily creating a perforation. A local expander tool 18 may be lowered into the production tubing 2 and positioned below the zone of interest. The tool may be deployed on a wireline 20 (as shown in Fig. 11), an e-line, a capillary string (such as micro coil) or standard coiled tubing, or by any other suitable manner. Any suitable type expander tool may be employed. Various types of local expander tools exist which may be suitable or adapted for this purpose, including energetic expander tools (e.g. International publications WO 2020/37143 A1 and WO 2019/151870 Al), expanding blade tools (e.g. US patent No. 10,794,158), or axially compression expander tools (e.g.

US pre-grant publications US 2010/0319427 Al and US 2018/0363407 Al). It is one aspect of the present invention that any of these tools may advantageously be used for the application of providing standoff and/or cement base in the annulus 8 surrounding production tubing 2. The placing of the external cement barrier may be done in a similar manner as shown in Figs. 8 to 10.

In particular in slanted (inclined) wellbores, the production tubing 2 will tend to sag to the gravitationally lower side. In such cases, for example, a specially adapted oriented energetic expander tool may optionally be employed, which has selectively a higher dosage of explosives oriented in a lower side of the energetic expander tool than in an opposing side. The oriented tool may be self-orienting. Self-orientation may be induced by employing an off-axis center of mass, to force the heavier part to face downward. A swivel joint may be employed, which allows rotation of the charges about a longitudinal tool axis.

The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims.

Claims

1. A method of plugging a wellbore for abandonment, wherein the wellbore comprises a production tubing with a functional cable extending along a length on the exterior thereof, said method comprising:

- allowing the external cement barrier to set;

2. The method of claim 1, wherein prior to placing the external cement barrier:

- perforating the production tubing for allowing passage of fluids between production tubing internal and external spaces.

3. The method of claim 1 or 2, wherein prior to placing the external cement barrier:

- providing a cement base in the annulus below the zone of interest; and/or

- centralizing the production tubing in or in an adjacent vicinity of the zone of interest.

4. The method of claim 3, wherein said providing said cement base and/or centralizing said production tubing comprises locally expanding the production tubing radially outward into the annulus using an expander tool positioned within the production tubing.

5. The method of any one of the preceding claims, wherein prior to forming said internal barrier plug, a plug base is set within the production tubing, and wherein the internal barrier plug is formed by casting a plug material on top of said plug base.

6. The method of any one of the preceding claims, wherein forming the internal barrier plug comprises allowing a liquid material to become solid, wherein the internal barrier plug comprises an expanding material which expands upon becoming solid.

7. The method of any one of the preceding claims, wherein subjecting the functional cable to said after-treatment comprises positioning a tool within the production tubing and causing the tool to perform said after-treatment.

8. The method of any one of the preceding claims, wherein said after-treatment comprises locally excavating a local cavity in the external cement barrier whereby cutting through the production tubing and the functional cable, and subsequently filling the cavity with a sealing material.

9. The method of claim 8, wherein said filling of said cavity is performed in the same step as forming the internal barrier plug within the production tubing whereby the internal barrier plug integrally extends into the cavity.

10. The method of claim 8 or 9, wherein cutting said production tubing over 360° full circumference.

11. The method of any one of claims 8 to 10, wherein said cutting is performed by means of a lined charge energetic cutter.

12. The method of any one of the preceding claims, wherein said after-treatment comprises expanding the production tubing radially outward against the functional cable and into the external cement barrier.

13. The method of claim 12, wherein expanding the production tubing over a limited length and over 360° full circumference.

14. The method of claim 12 or 13, wherein said expanding is performed by means of an energetic expander tool.

15. The method of any one of claims 12 to 14, in combination with any one of claims 8 to 11, wherein said locally cutting and said expanding is performed using a multistage tool positioned within the production tubing and comprising a local expander stage and a local cutting stage united in one tool.