The present invention relates to an apparatus and method for installing a barrier in a tubular conduit.

There is recognised demand for establishing an impenetrable fixed barrier internally within a constrained environment, and particularly inside various metal piping or other tubular sections of conduits. For example, such a barrier may be desired to isolate the conduit from the external environment, or separate sections within the same conduit from each other. Examples of such demands include the nuclear power generation industry, aviation industry and other highly technological industries.

Industries operating with subsurface installations have developed standard practice to seal sections of pipes or wellbores, which relies on setting cement plugs and permanent mechanical cast iron plugs (or bridge plugs) to provide an internal separation between lower and upper sections of the installation (for future isolated use of the upper section), or a bottom seal to isolate the whole length of the conduit from the external environment.

This practice has proved to be relatively cost effective and practical constraints have inhibited the development of other alternative methods. Procedures have remained substantially unchanged for many years, with the primary focus of investment and technology being the recovery of re-useable equipment. However, quality cementing is not always achievable due to associated costs or any number of highly possible complications in the course of the cementing procedure. Bridge plugs too often cannot ensure a quality seal against seeping gases and other substances impelled by pressure differentials. Even where all procedures are performed according to the highest standards, ageing cement and degrading bridge plugs allow micro-channels to develop and breach the seal Once started, the pace of seal damage is accelerated through contact with fluid or gases entering the network of the cracks, quickly eroding the effectiveness of the seal. This is a very serious risk issue in many of its current applications, in which a permanent seal is relied on to prevent contamination, environmental hazards, explosions or other risk to human life.

The international industry and national governing bodies are now becoming more aware of the risks associated with poorly abandoned oil and gas wells, especially as the oil companies are liable for any clean up and environmental damage. Yet, historically, attention to abandonment by oil companies has been low, seen as a cost to be minimised after the economic life of the well has ended. In the United States alone, there are over 2.5 million abandoned well bores with significant evidence that many of these are leaking to a greater or lesser extent, with a large backlog of wells awaiting permanent plugging and abandonment ('Ρ&Α'). Similarly, in the UK North Sea sector, it is anticipated that £1.2billion will be spent on well abandonment in the next four years (i.e. from early 2013). With the growth of the shale gas market, in the US and globally, and the relatively shorter well production lives (compared to traditional oil & gas wells), a reliable and cost-effective P&A method presents a major challenge and opportunity.

EP 1251241 Al discloses the repair of a downhole casing by depositing metal at the desired area from within the casing. The repair apparatus comprises an oxygen tank, a fuel tank and a metal depositing device for flame spraying, plasma spraying or welding. A steering head is provided to reciprocate and rotate the apparatus so that the metal depositing device may be directed to the desired area in the casing.

The present invention provides a welding apparatus for installing a welded barrier element in a tubular conduit, the welding apparatus comprising a longitudinal housing, a welding head at a first end of the housing, the welding head being oriented away from the first end, a rotary drive system for causing relative rotation of the welding head and the housing, a centraliser mechanism extending transversely out of the housing for centralising the welding apparatus within a tubular conduit, and a releasable holder at the first end for selectively holding or releasing a shaft of a barrier element to be welded in the tubular conduit.

Optionally, the welding head has a free end located longitudinal of the first end and transverse of a longitudinal centre of the welding apparatus.

Optionally, the welding head is configured whereby rotation of the welding head by the rotary drive system defines an annular welding line. Further optionally, the annular welding line defines an annulus having a cross-sectional area substantially corresponding to the transverse cross-sectional area of the welding apparatus.

Optionally, the releasable holder is fixed to the longitudinal housing and the rotary drive system is arranged to cause rotation about a longitudinal axis of the welding head relative to the releasable holder and the longitudinal housing. Further optionally, the longitudinal axis is a longitudinal axis of the welding apparatus. Optionally, the welding apparatus is hermetically sealed against liquid ingress to permit welding when submerged at a hydraulic pressure of greater than 1 bar, optionally to up to 50 bars or higher depending on operating depth and pressure.

Optionally, the welding apparatus further comprises at least one cable extending from a second end of the housing opposite to the first end, the at least one cable being connected to a power control system and a welding control system in the welding apparatus.

Optionally, the welding apparatus further comprises a barrier element to be welded in the tubular conduit, the barrier element including a shaft extending from a barrier plate, the shaft being releasably held in the releasable holder. Further optionally, the shaft extends from a centre of the barrier plate. The barrier plate typically has a cross-sectional area substantially corresponding to the transverse cross-sectional area of the welding apparatus. Optionally, the barrier plate has a circular peripheral edge which has a diameter substantially corresponding to a diameter of the locus of the end of the welding head. The barrier plate may typically have a concave, convex, part-spherical or substantially planar configuration.

Optionally, the welding apparatus further comprises a controllable actuator for switching the releasable holder from a hold mode to a release mode.

The present invention further provides a method of installing a barrier element in a tubular conduit by welding, the method comprising the steps of:

(a) providing a barrier element to be welded in the tubular conduit, the barrier element including a shaft extending from a barrier plate;

(b) releasably holding the shaft in a welding apparatus, the welding apparatus comprising a rotatable welding head;

(c) inserting into a tubular conduit the welding apparatus releasably holding the shaft and barrier plate;

(d) at a selected longitudinal position along the tubular conduit, actuating the welding head to perform a welding operation, and welding an annular peripheral edge of the barrier plate to an inside surface of the tubular conduit by rotating the welding head relative to the barrier element;

(e) releasing the shaft from the welding apparatus; and (f) removing the welding apparatus from the tubular conduit.

Typically, the tubular conduit is an oil or gas well, which is sealed by the barrier element.

Optionally, in step (b) the shaft is releasably held in a releasable holder located at a first end of the welding apparatus, the releasable holder selectively holding or releasing the shaft.

Optionally, the shaft extends from a centre of the barrier plate. The barrier plate typically has a cross-sectionai area substantially corresponding to the transverse cross-sectional area of the welding apparatus. The barrier plate typically has a cross-sectional area lower than the transverse internal cross-sectional area of the tubular conduit to permit the barrier plate to be slid along the tubular conduit to the selected longitudinal position. The barrier plate preferably has a circular peripheral edge which has a diameter substantially corresponding to a diameter of the locus of the end of the welding head. The barrier plate may typically have a concave, convex, part-spherical or substantially planar configuration.

Optionally, in step (d) a centraliser mechanism of the welding apparatus centralises the welding apparatus within the tubular conduit.

Optionally, the welding apparatus comprises a welding head which is oriented away from a first end of the welding apparatus, and a rotary drive system for causing relative rotation between the welding head and a releasable holder at the first end for selectively holding or releasing the shaft of the barrier element.

Optionally, in step (d) an annular welding line is formed between the annular peripheral edge of the barrier plate and the inside surface of the tubular conduit.

Optionally, the welding step (d) is carried out while the welding head and barrier plate are submerged at a hydraulic pressure of greater than 1 bar, optionally to up to 50 bars or higher depending on operating depth and pressure. Further optionally, the welding is carried out in the presence of a solvent which cleans the inside surface of the tubular conduit at the welding location. Typically, the solvent is propylene glycol.

The present invention has particular application in the installation of a welded barrier element in a tubular conduit, such as an oil or gas well, or borehole casing, or borehole heat exchanger, for sealing the conduit, as described further in detail hereinbeiow. The welded barrier element may be composed of the same metal as the conduit, permitting a high quality robust seal to be readily achieved. The preferred embodiments of the invention provide an apparatus and method to establish a permanent or semi-permanent internal barrier within a metal pipe using a metal plate, matched to the internal pipe cross-section, with a fully welded join to the internal pipe wall circumference preventing any transmission of material across the barrier plate.

Heretofore, certain engineering companies specialising in design of welding equipment have developed various known welding systems for welding in dry controllable conditions, mainly utilising TIG (Argon welding) method. Most of these known systems are mounted on a small ROV (Remote Operating Vehicle) to reach their target destination and are expensive for both manufacturing and operation.

The cost element associated with all such known systems together with the requirement for a controlled, dry and clean environment inside each tubular section has presented a fundamental hurdle for expansion of these systems to other applications which may require implementation under live operating conditions within various industrial processes (i.e., without system shutdown) or implementation offsite in field conditions.

In particular, there is an extensive range of such potential 'field applications' for internal welding within specialist conduits and heat exchangers of tubular geometry. These include such areas as water for drinking and irrigation, heap leaching and other mining activities, geothermal and other renewable energy systems, and oil and gas industries. All of these industries operate in external, remote, underwater, underground or other harsher environments than contained indoor operations, and each requires a more robust and cost effective solution for simple and reliable isolation of tubes and conduits from unwanted access - e.g., isolation from certain geological zones, bottom-hole sealing of wells and boreholes, permanent sealing of nuclear or decommissioning, plugging and abandonment ('Ρ&Α') of depleted or redundant exploration or production wells within the water, mining or oil & gas industries.

The nature of most subsurface installations in particular suggests the unavoidable presence of water, water-based fluids and other fluid substances. Therefore, there is no opportunity to even achieve the necessary pre-conditions for use of expensive welding equipment developed for indoor operation in controlled environments. Even if an underwater welding solution were considered, there are a number of other clear and fundamental technical hurdles to ensuring an effective welded seal in such conditions, including depth and pressures, unclean surfaces, restricted operating confines, effective conveyance and placement, weld targeting on circular and/or irregular surface, testing and quality assurance, low light and remote operation. Any possibility of a welding solution in such conditions is therefore ignored or summarily dismissed.

The preferred embodiments of the present invention overcome these problems with known apparatus and methods by providing a specifically designed barrier element, typically metal and of the same material as the tubular conduit to be sealed, releasably carried on a specifically designed welding apparatus which can remotely weld, even under extreme conditions such as full submergence at high hydraulic pressures, the barrier element to the inside surface of the wall of the tubular conduit, such as a wellbore, a pipe of a borehole casing. The barrier element is then released from the welding apparatus, leaving a secure and robust weld.

Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic perspective side view, partly cut away, of a welding apparatus in accordance with an embodiment of the invention in a tubular conduit for a welding operation. The welding operation installs a barrier element into the tubular conduit for sealing the tubular conduit.

Referring to Figure 1, there is shown a welding apparatus 2 for installing a welded barrier element 24 in a tubular conduit 6. Both the barrier element 24 and the tubular conduit 6 are composed of a metal, and the metals are weldable together and typically composed of the same metal, such as steel, so as to provide uniform metallurgical properties at the welded seal The welding apparatus 2 comprises a longitudinal housing 8. A welding head 10 is disposed at a first end 12 of the housing 8. The welding head 10 is oriented away from the first end 12. A rotary drive system 14 is provided for causing relative rotation of the welding head 10 and the housing 8. A centraliser mechanism 16 extends transversely out of the housing 8 for centralising the welding apparatus 2 within a tubular conduit 6.

The welding head 10 has a free end 18 located longitudinal of the first end 12 and transverse of a longitudinal centre L of the welding apparatus 2. The welding head 10 is configured whereby rotation of the welding head 10 by the rotary drive system 14 defines an annular welding line. The annular welding line defines an annulus having a cross-sectional area substantially corresponding to the transverse cross-sectional area of the welding apparatus 2. A reieasabie holder 20 at the first end 12 selectively holds or releases a shaft 22 of a barrier element 24 to be welded in the tubular conduit 6. The reieasabie holder 20 may comprise a mechanical catch mechanism or an electromechanical holder. The reieasabie holder 20 is fixed to the longitudinal housing 8 and the rotary drive system 14 is arranged to cause rotation about a longitudinal axis of the welding head 10 relative to the reieasabie holder 20 and the longitudinal housing 8. The longitudinal axis is a longitudinal axis of the welding apparatus 2.

The barrier element 24 includes the shaft 22 extending from a barrier plate 26. The shaft 22 is reieasably held in the reieasabie holder 20. The welding apparatus 2 further comprises a controllable actuator 28 for switching the reieasabie holder 20 from a hold mode to a release mode.

The shaft 22 extends from a centre of the barrier plate 26. The barrier plate 26 has a cross- sectional area substantially corresponding to the transverse cross-sectional area of the welding apparatus 2. The barrier plate 26 has a circular peripheral edge 30 which has a diameter substantially corresponding to a diameter of the locus of the end of the welding head 10. The barrier plate 26 may have a concave, convex, part-spherical or substantially planar configuration.

The welding apparatus 2 is hermetically sealed against liquid ingress to permit welding when submerged at a hydraulic pressure of greater than 1 bar, optionally to up to 50 bars or higher depending on operating depth and pressure.

The welding apparatus 2 further comprises at least one cable 32 extending from a second end 32 of the housing 8 opposite to the first end 12. The at least one cable 30 is connected to a power control system 34 and a welding control system 36 in the welding apparatus 2, or alternatively these systems are at the ground surface remote from the welding apparatus 2. The at least one cable 30 may be spooled and of sufficient length to ran the welding apparatus 2 to the target setting depth of a well to be sealed. A cable winch device (not shown) to control cable feed into and out of the borehole casing of the well is optionally provided.

The welding apparatus 2 is used in a method of installing a barrier element 24 in a tubular conduit 6 by welding. Typically, the tubular conduit 6 is an oil or gas well, which is sealed by the barrier element 24 above a cementing plug 40 which has been inserted into the tubular conduit 6 by known technology. The barrier element 24 may be in installed in a plugging and abandonment procedure.

A barrier element 24 to be welded in the tubular conduit 6 is provided and the shaft 22 is releasably held in the welding apparatus 2 by the releasable holder 20. The welding apparatus 2 releasably holding the shaft 22 and barrier plate 26 is inserted into a tubular conduit 6.

At a selected longitudinal position along the tubular conduit 6, the welding head 10 is actuated to perform a welding operation. The welding head 10 welds the annular peripheral edge 30 of the barrier plate 26 to an inside surface 38 of the tubular conduit 6 by rotating the welding head 10 relative to the barrier element 24.

During welding, the centraliser mechanism 16 of the welding apparatus 2 centralises the welding apparatus within the tubular conduit 6.

An annular welding line is formed between the annular peripheral edge 30 of the barrier plate 26 and the inside surface 38 of the tubular conduit 6. The welding step may be carried out while the welding head 2 and barrier plate 26 are submerged at a hydraulic pressure of greater than 1 bar, optionally to up to 50 bars or higher depending on operating depth and pressure. The welding may be carried out in the presence of a solvent which cleans the inside surface 38 of the tubular conduit 6 at the welding location. Typically, the solvent is propylene glycol.

After completion of the welding operation, the shaft 22 is released from the welding apparatus 2 and the welding apparatus 2 is removed from the tubular conduit 6.

The preferred embodiments of the invention therefore provide an automated submersible circumferential arc welding system ('ACW') designed for carrying a pre-set welding plate 26 attached on a special shaft 22 within a confined tubular volume to the designated depth of a well. The shaft 22 provides a central axis for orbital movement of the welding apparatus 2, with a pre-oriented welding head 10 being rotatable around the shaft 22. The welding apparatus 2 is equipped with a release mechanism 20 for release of the shaft 22 with its permanently attached plate 26 after the plate 26 has been welded in place.

In an embodiment, a surface control unit (not shown) is provided to control the welding parameters and the systems of the welding apparatus. The preferred embodiments of the invention therefore also provide a method in which a well can be remotely sealed by a welded barrier to provide a completely sealed internal barrier within a section of any tubular metal structure. The welding can be carried out in wet conditions, without removal of water and without requiring dry surfaces to be welded. The welding operation can utilise the safety benefits of welding in an aqueous environment, namely protection against ignition or explosion of associated gases while arc welding. The arc welding cane be carried out in a liquid medium comprising a batch of specialist fluid such as suitable solvents for dissolving oil, grease and other impurities residing on the inside surface of the conduit, without the need for washing and cleaning fluid circulation. In some embodiments, the welded barrier plate 26 may have a downhole surface which is convex, conical, part-spherical or flat. The material of the barrier element 24 may comprise steel of a similar grade and chemical composition to the material of the tubular conduit 6, such as a borehole casing. The use of a common material for the barrier element 24 and the tubular conduit 6 ensures weld strength without risk to the strength or integrity of the pipe or well casing.

The preferred embodiments of the invention therefore provide a sealed barrier within a pipe or well bore casing that does not rely on a chemical seal from a cement plug or mechanical seal from a mechanical plug. Installed in situ is a metal barrier plate securely welded to the inner circumference of the pipe or well bore casing. The barrier element may be shaped and dimensioned for use in standard plugging procedures for sealing tubular installations such as production wells or ground heat exchangers.

The preferred embodiments of the invention therefore also allow a substantial reduction of the long-term risks associated with cement-based isolation techniques. A welded metal plate or barrier can provide a permanent, robust and impenetrable sealed barrier inside the well or pipe. It is envisaged that the invention may be applied either as the primary sealing barrier or in conjunction with established cement plug techniques to add an extra level of long-term reliability and security that mechanical plugs cannot provide. Additionally, multiple plates could be installed at multiple points or depths to improve reliability at minimal extra cost.

Thus possible configurations include:

A complete welded seal above a cement plug set at the low end of a tubular installation to eliminate any pressure differential which could otherwise cause the development of micro-channels in the plug, while the upper hollow section of the installation can continue to be used on a long term basis without risk of leaks through an imperfect seal (e.g., through developing cracks) at the bottom of the installation.

- A complete welded seal above a cement plug set at the upper end of a tubular installation to eliminate any pressure differential which could otherwise cause the development of micro-channels in the plug and as an ultimate measure to prevent possible leaks to the outside environment.

- Ultimate sealing for harsh subsurface environments represented by two or more welded seals to encapsulate cemented section(s), which simultaneously prevents a cement plug from contact with any possible rise of contaminants beneath the lower seal and protects the cement plug from the top and optional intermediate welded seal.

The preferred embodiments of the invention therefore may reduce costs associated with relatively expensive bridge plugs which could be replaced with low cost cementing plugs in combination with welded isolation plates. Due to its design, the welding system can be inserted into a confined borehole casing through surface pressure control equipment such as blowout preventers, stuffing boxes and lubricators, and the system can be configured for use in a variety of pipework and casing sizes. If for any reason the barrier required removal for future use, as in the case of temporary P&A, then standard conventional oilfield milling techniques could be employed to remove the barrier plate.