Patent Description:
In the domain of oil and gas wells, an annular pressure buildup increases the pressure in the wellbore casing annulus. It is the pressure generated by the thermal expansion of trapped wellbore fluids as they are heated in the wellbore during production. Other terms are also used to describe this occurrence such as "trapped annular pressure" and "annular fluid expansion". The casing used to extract oil and gas is therefore submitted to extreme pressure and temperature conditions. The casing can collapse under pressure and cause the loss of the well.

Vacuum insulated tubing is a known device for use in such wells to mitigate the annular pressure buildup. Referring to <FIG>, shown is a prior art vacuum insulated tubing <NUM>.

Vacuum insulated tubing is a tubing component placed in a well, and connected to the production tubing such that production fluids like oil and gas flow through the tubing component. The vacuum insulated tubing <NUM> has a vacuum space <NUM> between the inner and the outer tubes <NUM> and <NUM> of the vacuum insulated tubing <NUM> to improve the thermic isolation between the inside of the inner tube and the outside of the outer tube <NUM>. The vacuum space <NUM> is formed with a fillet welding <NUM> between the end of the inner tube <NUM> and the outer tubes <NUM>. An example of such a vacuum insulated tubing is disclosed in the document <CIT>.

However, in some high pressure and high temperature wells, the pressure of the well can be so great that no known vacuum insulated tubing can meet design requirements for a sufficient strength. Moreover, the fillet weld between the inner and outer tubes of existing vacuum insulated tubing are highly prone to corrosion, oil or H<NUM>S being for example highly corrosive. Such damage is very problematic as it can result in the loss of vacuum in the space between the inner and outer tube of the tubing. A High-Velocity Oxygen Fuel coating over the fillet weld has been tempted to protect the fillet weld from the corrosion, although this solution does not meet design requirements for high pressure and high temperature wells. Attempts have also been made with laser cladding. However, laser cladding requires tight machining tolerance on the surface to be cladded, that is not compatible with current vacuum insulated tubing assembly techniques.

What is needed is a vacuum insulated tubing capable of resisting the corrosion and high pressures and temperatures without collapsing and without losing vacuum. Finally, what is needed is a way and a method to produce with high precision this vacuum insulated tubing.

In general, in one aspect, the disclosure relates to a tubing component including an outer tube and an inner tube within the outer tube, said tubes being so configured to create a space between each other over a specified length. Each end of the inner tube is secured to the internal surface of the outer tube by a frustoconical fillet weld so that said space is leak-tight. The inner tube has a first internal diameter along a first length starting from each end of said tube and a second, smaller internal diameter along a second length beyond the first length. The tubing component further includes a protective metallic layer extending at least over the fillet weld.

In another aspect, the disclosure relates to a method for producing a tubing component as described above. The method includes providing, before assembly, an inner tube with a first internal diameter along a first length starting from each end of said tube and a second, smaller internal diameter along a second length beyond the first length. It further includes positioning the inner tube within the outer tube, welding each end of the inner tube to the internal surface of the outer tube so as to produce a frustoconical fillet weld that secures the tubes to each other so that said space is leak-tight, and forming a protective metallic layer that extends at least over the weld.

These and other objects, features and advantages of the present invention will become better understood with reference to the following description, appended claims and accompanying drawings. The drawings are not considered limiting of the scope of the appended claims. Reference numerals designate like or corresponding, but not necessarily identical, elements. The drawings illustrate only example embodiments. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the example embodiments. Additionally, certain dimensions or positionings may be exaggerated to help visually convey such principles.

In one embodiment, a vacuum insulated tubing for mitigating annular pressure buildup in a wellbore casing annulus of an oil or gas well is provided having an ability to withstand high pressure and high temperature conditions and to resist to oil and H<NUM>S corrosion.

Referring to <FIG>, one example embodiment of one end of the vacuum insulated tubing <NUM> of the present disclosure is shown. The vacuum insulated tubing <NUM>, also referred to as the tubing component <NUM>, has an inner tube <NUM>, having a maximum outer diameter <NUM>, a minimum outer diameter <NUM> defining a vacuum space <NUM>.

The inner tube <NUM> has a first internal diameter ID along a first length <NUM> starting from each of the very end of said tube. The inner tube <NUM> has also a second, smaller internal diameter ID' along a second length <NUM> beyond the first length <NUM>. For example, the first length <NUM> has a length of <NUM>, the first internal diameter ID has a diameter of <NUM> and the second internal diameter ID' has a diameter of <NUM>. The inner tube <NUM> comprises a bevel <NUM> between said first and second length <NUM> and <NUM>. This bevel <NUM> makes for example an angle of <NUM>° with a transversal plane. For the bevel <NUM> to be long enough, the difference ID-ID' is larger than <NUM>. The bevel <NUM> is created during manufacturing of the inner tube <NUM>.

The tubing component <NUM> also has an outer tube <NUM>, having a constant inner diameter for its internal surface <NUM> and an outer diameter <NUM>. The outer tube <NUM> fits around the inner tube <NUM> such that the end of the outer tube <NUM> extends beyond the inner tube <NUM>. In one embodiment, the outer tube has an outer diameter of <NUM>. The inner tube can have a maximum outer diameter of <NUM>.

The outer tube <NUM> and the inner tube <NUM> can be made from a suitable material for providing the required strength. In one embodiment, the outer tube <NUM> and the inner tube <NUM> are made from an alloy having a yield strength of at least <NUM> ksi.

In one embodiment, the outer tube <NUM> and the inner tube <NUM> are made from a weldable chromium steel alloy comprising at least <NUM>% of chromium, also referred to as 13Cr steel.

The vacuum space <NUM> is formed between the outer tube <NUM> and the inner tube <NUM>, having a vacuum in between. The vacuum is created using any suitable technology employed in known vacuum insulated tubing manufacturing.

A weld, such as a frustoconical fillet weld <NUM>, is formed at the corner between the end of the inner tube <NUM> and the internal surface <NUM> of the outer tube <NUM>. It permits to join the inner and outer tubes <NUM> and <NUM> and to seal the vacuum of the vacuum space <NUM>. The fillet weld <NUM> is made from a suitable weld material compatible with the 15Cr tubing.

A protective metallic layer <NUM> completely covers the surface of the fillet weld <NUM>. The protective metallic layer <NUM> is an overlay weld obtained by Gas Tungsten Arc Welding or Tungsten Inert Gas welding, also referred to as cladding. The fillet weld <NUM> and the protective metallic layer <NUM> do not extend, i.e., protrude, beyond the first internal diameter ID of the inner tube <NUM>; therefore, the second internal diameter ID' of the tubing component is not impacted by the fillet weld <NUM> and the protective metallic layer <NUM>. In one embodiment, the protective metallic layer <NUM> has a thickness from about <NUM> to about <NUM>. For example, the thickness can be <NUM>. The protective metallic layer <NUM> can be formed by depositing the material in two passes. The protective metallic layer <NUM> material deposited in the two passes can have substantially the same thickness. For example, the thickness of each of the two passes can be <NUM>. In one embodiment, the surface of the fillet weld <NUM> is prepared prior to the deposition of the protective metallic layer <NUM> by beveling, modifying or polishing the fillet weld <NUM> to help ensure complete coverage and bonding of the fillet weld <NUM> by the overlay weld. The protective metallic layer <NUM> can extend beyond the edges of the fillet weld, e.g., <NUM> in the axial direction of the tubing component <NUM>, to also cover the adjacent internal surfaces of the inner tube <NUM> and of the outer tube <NUM>. For example, the first length <NUM> of the internal surface of the inner tube <NUM> can be overlaps, i.e. over a first specified distance FD for example of <NUM>. In one embodiment, the cladding of the protective metallic layer <NUM> is precisely done with respect to the bevel <NUM>. A second specified distance SD for example of <NUM> can be overlaps on the internal surface <NUM> of the outer tube <NUM>. In order not to protrude beyond the first internal diameter ID of the inner tube <NUM>, the thickness of the protective metallic layer <NUM> is equal or smaller than (ID-ID')/<NUM> over the first length <NUM>, wherein the difference ID - ID' is larger than <NUM>, preferably larger than <NUM>. The protective metallic layer <NUM> can be thicker over the internal surface <NUM> of the outer tube <NUM>.

The protective metallic layer <NUM> is made from a suitable overlay weld material for protecting the fillet weld <NUM> under the conditions the tubing component will experience in the field system. In one embodiment, the overlay weld material is made of a corrosion resistant nickel-based alloy such as an alloy including Nickel, Chromium and Molybdenum wherein Nickel amounts to more than <NUM>%. In one embodiment, the protective metallic layer <NUM> material is Inconel <NUM>, that permits an excellent bonding.

The dilution iron can be no more than <NUM>% to <NUM> % for corrosion resistance of the overlay weld. This is achieved by depositing the protective metallic layer <NUM> material in two passes by making a bottom layer and at least a top layer on top of the bottom layer in order to reduce dilution of iron near the free surface of the layer. The thickness of the protective metallic layer <NUM> is thus high. In order not to reduce the drift of the tubing component <NUM> because of this cladding, a first length <NUM> with a first internal diameter ID and the bevel <NUM> of the inner tube <NUM> have been designed, as described above. This first internal diameter ID is bigger than the second internal diameter ID' and permits to an existing design of tubing to house the cladding without reducing the drift. The first internal diameter ID is also small enough to allow the fillet weld to match with the tubing strength required and to facilitate the welding of the fillet weld <NUM>.

The outer tube <NUM> can have external threads <NUM> along a portion of length proximate the end of the outer tube for attaching a coupling (not represented) having an internal threaded profile for connecting two outer tubes thereby connecting two segments of vacuum insulated tubing.

The protective metallic layer <NUM> provides the tubing component weld integrity which prevents corrosion or cracking of the fillet weld <NUM>, thus protecting against loss of vacuum the vacuum space <NUM>.

The vacuum insulated tubing is able to withstand higher pressures than known vacuum insulated tubing are capable of withstanding without collapsing and without losing vacuum.

Following will be introduced the method for producing a tubing component as disclosed with reference to the <FIG>.

<FIG> illustrates the tubing component <NUM> after inserting an inner tube <NUM> inside an outer tube <NUM>, as described above.

<FIG> illustrates the tubing component <NUM> after welding each end of the inner tube <NUM> to the internal surface <NUM> of the outer tube <NUM> so as to produce a frustoconical fillet weld <NUM> that secures the tubes to each other so that the vacuum space <NUM> is leak-tight.

<FIG> illustrates the tubing component <NUM> after beveling the fillet weld <NUM>. In particular, the tow <NUM> of the fillet weld <NUM> is not beveled to avoid reducing wall of the outer tube <NUM>.

Referring to <FIG>, in step <NUM>, an inner tube <NUM> and an outer tube <NUM> are provided. In step <NUM>, the outer tube <NUM> is positioned around the inner tube <NUM> in such a way that a corner <NUM> is formed at the intersection between the inner tube <NUM> and the outer tube <NUM> as shown in <FIG> and described above. In step <NUM>, a fillet weld <NUM> is formed at the corner <NUM> as shown in <FIG> and described above. In step <NUM>, the weld surface of the fillet weld <NUM> is beveled to remove faults, surfaces oxides, and facilitate application of the protective metallic layer <NUM> onto the weld surface as shown in <FIG> and described above. The beveling is achieved in order to obtain an angle between <NUM>° and <NUM>° between the fillet weld <NUM> and a transversal plan. For example, the angle can be <NUM>°. The bevel <NUM> is used as a reference for depth control of the beveling step <NUM> and thus ensures that the weld remains strong enough. The bevel <NUM> being a reference for the production of the tubing component <NUM>, it provides positive evidence that the weld after machining still has enough section to provide for the required strength. In the cladding step <NUM>, the protective metallic layer <NUM> is formed over the fillet weld surface as shown in <FIG> and described above.

In step <NUM>, the fillet weld <NUM> and the protective metallic layer <NUM> can be simultaneously heat treated (tempered) at a temperature greater than <NUM> in a stress-relieve operation. In one embodiment, the Post Weld Heat Treatment is processed on a zone centered on the protective metallic layer <NUM>, and extending axially of <NUM> on each side of the protective metallic layer <NUM>. The stress relieve equipment uses a low frequency induction to limit the risk with non-magnetic material interface response.

It should be noted that only the components relevant to the disclosure are shown in the figures, and that other components normally part of a wellbore or vacuum insulated tubing may not be shown for simplicity.

For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims are to be understood as being modified in all instances by the term "about. " Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," include plural references unless expressly and unequivocally limited to one referent.

Claim 1:
A tubing component (<NUM>), suitable for use in oil and gas wells, comprising an outer tube (<NUM>) and an inner tube (<NUM>) within the outer tube (<NUM>), said outer tube (<NUM>) and said inner tube (<NUM>) being made of steel, said tubes (<NUM>, <NUM>) being so configured to create a space (<NUM>) between each other over a specified length, the tubing component (<NUM>) being characterized in that
a. Each end of the inner tube (<NUM>) is secured to an internal surface (<NUM>) of the outer tube (<NUM>) by a frustoconical fillet weld (<NUM>) so that said space (<NUM>) is leak-tight,
b. The inner tube (<NUM>) has
i. a first internal diameter (ID) along a first length (<NUM>) starting from each end of said tube,
ii. a second, smaller internal diameter (ID') along a second length (<NUM>) beyond the first length (<NUM>),
c. The tubing component (<NUM>) further includes a protective metallic layer (<NUM>) extending at least over the fillet weld (<NUM>).