The present invention relates to a method of plugging a well. In particular embodiments, the method comprises installing a permanent fluid-tight barrier for well abandonment.
The NORSOK standard D-10 rev.3 which is the basis for well integrity in drilling and well operations on the Norwegian Continental Shelf, including plug and abandonment procedures, states that “Control cables and lines shall be removed from areas where permanent well barriers are installed, since they may create vertical leak paths through the well barrier.” The main problem relates specifically to the insulation material of the control cables, which may degrade, creating void space between the plug material and the cable. Another problem is hydraulic lines, which are hollow and therefore cannot be a part of a permanent barrier. If the location for a permanent barrier contains control cables and lines, the practice today is to remove these by pulling out the whole production tubing which the cables and lines are attached to. This requires a drill rig onsite. Problems associated with this procedure are high time demands and cost, and potential safety issues.
WO10088542 aims to address these problems by forming a well barrier with a cable passing through the barrier and though fluid-tight pressure tested connectors. Cementation is performed around the connector and the cable is run on the outside of the tubing into a passageway through the connector. Thus, although the cable passes through the barrier, it is sealingly located in a passageway with pressure rated connectors provided at either end of the passageway. Of course, failure of the connectors could result in a fluid flow path through the barrier so the integrity of this system relies on the integrity of the connectors.
It is an aim of the present invention to provide an alternative method of plugging a well which helps to address the afore-mentioned problems.
In accordance with a first aspect of the present invention there is provided a method of plugging a well comprising:
Embodiments of the invention therefore effectively employ barrier-approved external cables in pre-set locations so that the well can be abandoned without requiring the tubing (and associated cables) to be pulled out of the wellbore prior to formation of a plug. Consequently, the plugging of the well can be performed using lighter equipment such as coil tubing or wireline. Accordingly, the invention can be implemented to save time and cost associated with plug and abandonment procedures whilst also reducing safety risks related to the traditional step of pulling the tubing from the wellbore using a drill rig.
As the external cable itself is fluid-tight there is no need for additional connectors or a specially designed tubing section, thus reducing complexity and minimising the risk of fluid leak due to failure of a single critical component. In fact, due to the elongate nature of the external cable even a point failure along the length of the external cable would not be catastrophic as the remaining sections of fluid-tight external cabling would prevent a fluid flow path from being established through the well plug.
It will be understood that the fluid-tight external cable will be exposed to the annular space where the plug is to be provided and the plugging material (e.g. concrete) will be set within the annulus so as to encapsulate the external control cable section therein.
An advantage of placing the internal cable section inside the tubing is that it is readily accessible and can easily be removed during a plug or abandonment procedure.
The step of providing the tubing in the wellbore may be implemented during completion of a new well or during re-completion of an old well.
In embodiments where the tubing is provided with an external cable section placed outside of the tubing in said location for a well plug, the step of forming a plug in the well may comprise:
The fluid-tight external cable is ideally designed and manufactured in such a way that no internal voids exist in the cable. Additionally or alternatively, the step of forming a plug in the well may comprise sealing any interior cavities in the external cable. Furthermore, the fluid-tight external cable may have an external surface which will not degrade under wellbore conditions to cause a leak path through the well plug and that will readily seal with the material forming the plug. The external surface may be provided by a coating (e.g. insulating) layer. This may also be advantageous in reducing the risk of possible leakage paths developing during production, transportation or installation of the tubing.
The (or each) external cable may, for example, be configured as an electrical control cable, a hydraulic line, a fiber optic cable or a support cable (also known as a bumper cable). As is common in the field, the support cable may be configured to withstand loads that may otherwise damage or tear apart the other cables. The support cable may be made of braided wire and may, in particular, be used during the winter season when floating rigs tend to experience maximum movement due to high wind and/or waves.
In some embodiments, a plurality of external cables may be provided outside of the tubing, in the location for the well plug. In particular embodiments, all cables may be provided as external cables outside of the tubing, in the location for the well plug.
The method may comprise sealing all of the external cables provided outside of the tubing. This may be achieved by providing a fluid-tight exterior to each external cable and by filling any interior cavities with a sealing material. For example, a sealant may be pumped into a hydraulic line to fill the cavity therein.
In embodiments where the tubing is provided with a section of internal cable placed inside the tubing in said location for the well plug, the step of forming a plug in the well may comprise:
In some embodiments, a plurality of internal cables may be provided inside of the tubing, in the location for the well plug. In particular embodiments, all cables may be provided as internal cables inside of the tubing, in the location for the well plug.
The (or each) internal cable may, for example, be configured as an electrical control cable, a hydraulic line, a fiber optic cable or a support cable (also known as a bumper cable).
The step of removing the internal cable section inside the tubing may comprise cutting, milling, dissolving or otherwise destroying the internal cable section to ensure that there is no fluid flow path through the internal cable in the location for the well plug.
The step of providing a tubing in a wellbore with a section of internal cable placed inside the tubing in said location for the well plug may comprise providing a tubing having a further section of cable placed outside the tubing and a port through which the further section of cable transitions from the outside of the tubing to the inside of the tubing to connect with said section of cable placed inside the tubing. The port will be configured to form a fluid-tight seal with the tubing.
The step of forming the plug in the well may comprise creating a hole in the tubing in the location for the well plug and introducing plugging material into the wellbore and through the hole. Multiple holes (i.e. perforations) may be created in the tubing in the location for the well plug. The hole or holes may be conveniently located above a production packer. A temporary plug may be provided in the tubing below the location of the hole or holes so as to form a shelf or ledge on which the plugging material within the tubing may set.
The step of forming a fluid-tight seal may be performed by introducing cement (which will set as concrete plugging material) into the wellbore, which seals against the tubing and the external cable section.
The fluid-tight seal may be formed to meet the requirements of a permanent well barrier.
The method may comprise forming multiple plugs in the wellbore at a number of locations configured for such well plugs.
The tubing may be constituted by production tubing.
The fluid-tight external cable may comprise one or more of the following:
According to a second aspect of the invention, there is provided a method of performing a wellbore operation, comprising:
According to a third aspect of the invention, there is provided a wellbore apparatus comprising:
According to a fourth aspect of the invention, there is provided a fluid-tight external cable (e.g. a fluid-tight electrical cable) for use in a wellbore.
Specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which:
With reference to
In particular embodiments, the fluid-tight electrical cable 16 may have a length of between 60 m and 200 m. However, it be understood that the required length will depend upon the desired length of the well plug to be formed around the fluid-tight electrical cable 16 and the accuracy of the procedures for providing the fluid-tight electrical cable 16 in the location for the well plug. In other embodiments, the (standard) electrical control cables 14 may be replaced with fluid-tight electrical cable 16 so that a well plug can be placed at any location along the length of the tubing.
As illustrated, a production packer 18 is provided in an annulus 20 surrounding the tubing 10, at or close to a lowermost region of the location for the well plug. A hole 22 is milled in the tubing 10, above the production packer 18, and a plugging material 24 (e.g. comprising cement) is introduced through the tubing 10 so as to form a well plug 26 in the tubing 10 and the annulus 20, in the location for the well plug. Accordingly, the plugging material 24 will encapsulate and seal against the tubing 10 and the fluid-tight electrical cable 16 in the location for the well plug 26.
Although not shown, a temporary plug may be provided in the tubing 10 below the location of the hole 22 so as to form a shelf or ledge on which the plugging material 24 within the tubing 10 may set.
It will be understood that, in practice, the tubing 10 will be provided within one or more outer casings 28 which are cemented in place. It may therefore be necessary to check that the outer casing cement 30 is properly placed and verified as a permanent barrier.
a, b, c and d illustrate a method for plugging a well in accordance with a second embodiment of the present invention. This method is similar to that described above in relation to
As illustrated in
Once the fluid cable section 34 has been removed, the method proceeds as described above. This,
Aspects of the invention therefore relate to the installation of control cables and lines during completion of a new well or re-completion of an old well, which can form a part of a permanent barrier, thereby minimising the time, cost and safety concerns associated with traditional plug and abandonment techniques.
It will be appreciated by persons skilled in the art that various modifications may be made to the above-described embodiments without departing from the scope of the present invention, as defined by the claims.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/068035 | 8/30/2013 | WO | 00 |