The present invention relates to an annular barrier for being mounted as part of a well tubular metal structure for providing zonal isolation in a small diameter borehole downhole for isolating a first zone from a second zone. The present invention also relates to a well tubular metal structure having a plurality of tubular sections and at least one annular barrier according to the present invention, and to a completion method of preparing an annular barrier according to the present invention.

Annular barriers for providing a zone isolation, e.g. for isolating a hydrocarbon-containing zone from a water producing zone, is provided by arranging an isolating element, such as an expandable metal sleeve surrounding the base pipe, such as the casing or liner, and expanded by liquid from within the base pipe. However, in small diameter wells there is no room between the inner wall of the borehole and the base pipe for such annular barrier solutions, since then the inner diameter of the base pipe would be too small for an efficient production. In such small diameter wells other solutions, such as swellable material around the base pipe, are used to provide the annular barrier.

The swelling of the swellable material is dependent on fluid content and temperature in the well and, most importantly, the deployment time from entering the well and until arrival at the determined position. Sometimes during deployment, the casing or well tubular metal structure gets stuck or is just much more difficult to deploy, resulting in the deployment time being much longer than planned, and in these cases, the swelling may occur too early and the barrier is then set too early. In small diameter wells, the space between the base pipe and the borehole wall is very narrow in order to maximise the inner diameter of the base and thus the production volume. Thus, in such small diameter wells, the risk of the casing or well tubular metal structure getting stuck is even higher than in larger wells.

Thus, it is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved annular barrier for small diameter wells which does not set too early, i.e. before the barrier is in the intended position in the borehole.

The above objects, together with numerous other objects, advantages and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by an annular barrier for being mounted as part of a well tubular metal structure for providing zonal isolation in a small diameter borehole downhole for isolating a first zone from a second zone, comprising:

• an expandable metal sleeve having a first end and a second end and an outer face facing the borehole,
• a first end part having a first end connected to the first end of the expandable metal sleeve and a second end for being mounted as part of the well tubular structure, and
• a second end part having a first end connected to the second end of the expandable metal sleeve and a second end for being mounted as part of the well tubular structure,

The second end of the first end part may be provided with a female thread connection, and the second end of the second end part may be provided with a male thread connection.

Moreover, the first and second end parts may be connected to the first and second ends of the expandable metal sleeve by means of a standard connection, such as a stub acme thread connection.

Also, sealing elements may be arranged on the outer face of the expandable metal sleeve.

Further, the expandable metal sleeve may have:

• a first section having a first outer diameter and a first thickness, and
• at least two circumferential projections having a thickness which is larger than a first thickness and having a second outer diameter which is larger than the first outer diameter, so that when expanding the expandable metal sleeve, the first section bulges more radially outwards than the first section, resulting in the expandable metal sleeve being strengthened.

In addition, the expandable metal sleeve may have an outer sleeve diameter in an unexpanded state, the unexpanded outer sleeve diameter being equal to or smaller than an outer diameter of the first and second end parts.

Additionally, the sealing elements may be arranged in grooves in the outer face of the expandable metal sleeve.

The expandable metal sleeve may be made of a material which is more pliant than the material of the first and second end parts.

In order to determine if the material of the expandable metal sleeve is more pliant and thus easier to elongate than the material of the first and second end parts, the test standard ASTM D1457 Elongation can be used.

The annular barrier as described above may further comprise a split ring-shaped retaining element, the split ring-shaped retaining element forming a back-up for the sealing element.

Furthermore, the split ring-shaped retaining element may have more than one winding, so that when the expandable tubular is expanded from the first outer diameter to the second outer diameter, the split ring-shaped retaining element partly unwinds.

Also, the split ring-shaped retaining element may be arranged in an abutting manner to the sealing element.

Moreover, the first and second end parts may be tubular and may have a maximum wall thickness which is larger than a maximum wall thickness of the expandable metal sleeve.

Further, the expandable metal sleeve may be welded to the first and second end parts.

In addition, the expandable metal sleeve may have a length, and no tubular may be arranged within the expandable metal sleeve along the entire length of the expandable metal sleeve.

Said expandable metal sleeves may be expanded by an internal fluid pressure in the well tubular metal structure.

At least one of the tubular sections between the expandable metal sleeves may comprise an inflow section, a sensor section or a gas lift valve.

The present invention also relates to a well tubular metal structure having a plurality of tubular sections and at least one annular barrier according to the present invention; wherein the first and second end parts and the expandable metal sleeve is mounted in succession with the plurality of tubular sections, so that the first end part and the second end part are arranged between the expandable metal sleeve and the tubular sections along an axial extension of the well tubular metal structure.

Furthermore, the well tubular metal structure may have an inner face, and an inner face of the expandable metal sleeve may form part of the inner face of the well tubular metal structure.

Also, a second annular barrier according to present invention may be mounted as part of the well tubular metal structure, and a plurality of tubular sections may be mounted between the annular barriers.

Moreover, the first end part may create a first distance between the expandable metal sleeve and one of the plurality of tubular sections, and the second end part may create a second distance between the expandable metal sleeve and another one of the plurality of tubular sections.

In addition, the expandable metal sleeve does not overlap any of the plurality of tubular sections.

Further, the expandable metal sleeve may have an outer sleeve diameter in an unexpanded state, the unexpanded outer sleeve diameter being equal to or smaller than an outer diameter of the tubular sections forming the well tubular metal structure.

The well tubular metal structure may be a produciton casing or a velocity string.

The present invention also relates to a downhole system comprising the well tubular metal structure according to the present invention and an expansion tool for isolating a part of the well tubular metal structure opposite the expandable metal sleeve for pressurising that part in order to expand the expandable metal sleeve.

Furthermore, the present invention relates to a completion method of preparing an annular barrier according to the present invention before being mounted as part of the well tubular metal structure, said completion method comprising:

• providing the expandable metal sleeve,
• making a female thread in the first end part,
• making a male thread in the second end part, and
• mounting the first and second end part with the expandable metal sleeve.

Finally, the present invention relates to a completion method comprising:

• mounting an annular barrier according to the present invention as part of the well tubular metal structure,
• submerging the well tubular metal structure into the borehole,
• retracting the well tubular metal structure in the event that the well tubular metal structure cannot be submerged to a predetermined depth,
• dismounting the annular barrier and part of a plurality of tubular sections of the well tubular metal structure,
• replacing the first and second end parts with other first and second end parts having a smaller outer thread diameter,
• replacing the part of the plurality of tubular sections with other tubular sections having a smaller outer diameter,
• remounting the annular barrier having the other first and second end parts of a smaller outer thread diameter, and
• submerging the remounted well tubular metal structure.

The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which

• Fig. 1 shows a cross-sectional view of an annular barrier for mounting as part of well tubular metal structure in a small diameter borehole,
• Fig. 2 shows a cross-sectional view of another annular barrier for mounting as part of well tubular metal structure in a small diameter borehole,
• Fig. 3 shows a cross-sectional view of yet another annular barrier for mounting as part of well tubular metal structure in a small diameter borehole, and
• Fig. 4 shows a well tubular metal structure having several annular barriers for isolating production zones from other zones.

All the figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.

Fig. 1 shows an annular barrier 1 for being mounted as part of a well tubular metal structure 100 for providing zonal isolation in a borehole downhole for isolating a first zone 101, e.g. producing oil or gas, from a second zone 102, e.g. producing water, as seen in Fig. 4. Tubular sections of the well tubular metal structure are illustrated by dotted lines in Fig. 1. The annular barrier 1 comprises an expandable metal sleeve 2 having a first end 3 and a second end 4 and an outer face 5 facing the borehole. The expandable metal sleeve 2 is shown in its unexpanded condition, and in order to provide zonal isolation, the expandable metal sleeve is expanded to a larger outer diameter by a hydraulic pressure from within to deform the expandable metal sleeve until the outer face presses towards the wall of the borehole. The annular barrier 1 further comprises a first end part 6 having a first end 7 connected to the first end of the expandable metal sleeve and a second end 8 for being mounted as part of the well tubular structure, and a second end part 9 having a first end 10 connected to the second end of the expandable metal sleeve and a second end 11 for being mounted as part of the well tubular structure. The first end 7 of the first end part 6 is connected "end to end" to the first end 3 of the expandable metal sleeve, and the first end 10 of the second end part 9 is connected "end to end" to the second end 4 of the expandable metal sleeve, so that they form one tubular pipe. Thus, there is no base pipe within the expandable metal sleeve along an entire length L (shown in Fig. 3) of the expandable metal sleeve and the annular barrier is therefore "base-less". The second ends 8, 11 of the end parts are provided with an external thread (male thread connection) 20b or an internal thread (female thread connection) 20b for being mounted to corresponding external or internal threads of the well tubular metal structure.

By providing such base-less annular barrier, the well tubular metal structure can be made with a substantially smaller outer diameter and fit into small diameter wells than annular barriers with a base pipe and a surrounding sleeve. The expandable metal sleeve has a first section 26 having a first outer diameter OD₁ and a first thickness T₁, and circumferential projections 27 having a thickness T₂ which is larger than the first thickness T₁ and having a second outer diameter OD₂ which is larger than the first outer diameter, so that when expanding the expandable metal sleeve, the first section bulges more radially outwards than the first section, resulting in the expandable metal sleeve 2 being strengthened in the expanded condition.

In small diameter wells, the expandable metal sleeve does not need to expand as much as in larger diameter wells/boreholes, and therefore it is possible for the expandable metal sleeve of the "base-less" annular barrier to maintain the barrier function without the base pipe.

Furthermore, the circumferential projections 27 increase the strength of the expanded expandable metal sleeve 2 when the expandable metal sleeve is not expanded more than required in small diameter wells/boreholes, so that the expandable metal sleeve can serve as both the base pipe and the barrier.

In Fig. 1, the second end 8 of the first end part 6 is provided with a female thread connection, i.e. an internal thread, and the second end 11 of the second end part 9 is provided with a male thread connection, i.e. an external thread. When submerging the annular barrier 1 as part of the well tubular metal structure 100, the female thread part, i.e. the female thread connection 20a, is most often the thread being closest to the top. The first and second end parts 6, 9 are connected to the first and second ends 3, 4 of the expandable metal sleeve 2 by means of a standard connection 14, such as a stub acme thread connection as shown. The first and second ends 3, 4 of the expandable metal sleeve 2 are provided with external threads matching internal threads of the first end part and the second end part 9, the internal and external threads forming the stub acme thread connections. Other standard connections within the oil industry can be used. Sealing elements 15 are arranged in grooves 16 on the outer face of the expandable metal sleeve 2 for increasing the sealing ability to the wall of the borehole when expanded downhole. The grooves 16 may be provided by the circumferential projections 27, and when expanding the expandable metal sleeve, the first section between the projections bulges more radially outwards than the projections, forcing the sealing element radially outwards. The expandable metal sleeve 2 has an outer sleeve diameter Od_e in an unexpanded state, the unexpanded outer sleeve diameter being equal to or sligthly smaller than an outer diameter OD_P of the first and second end parts, so that the end parts protect the sealing elements while run in hole.

In Fig. 1, the well tubular metal structure 100 has a first outer diameter ODwi, and in Fig. 2 the well tubular metal structure 100 has a second outer diameter OD_W2 which is smaller than the first outer diameter. If during running the well tubular metal structure in the small diameter borehole, circulation of fluid is poor due to an unexpected narrowing of the borehole, the well tubular metal structure can then be retracted, and part of a plurality of tubular sections of the well tubular metal structure can be dismounted and replaced with tubular sections having a smaller outer diameter OD_W2, as shown in Fig. 2. This can easily be performed by replacing the first and second end parts 6, 9 of the annular barrier 1 with other first and second end parts of a smaller outer diameter at the thread connections, and mounting other tubular sections having a smaller outer diameter. Thus, by having disconnectable end parts 6, 9 of the annular barrier, the end parts 6, 9 can easily be replaced with other end parts matching smaller (or larger) outer diameter tubular sections, so that reducing the outer diameter of the well tubular metal structure at certain sections to increase circulation in a certain area is possible.

As shown in Fig. 2, the first and second end parts 6, 9 are tubular and have a maximum wall thickness T_P1 which is larger than a maximum wall thickness T₂ of the expandable metal sleeve 2. The expandable metal sleeve is made of a material which is more pliant than the material of the first and second end parts. In order to determine if the material of the expandable metal sleeve is more pliant and thus easier to elongate than the material of the first and second end parts, the test standard ASTM D1457 can be used.

In Fig. 3, the annular barrier 1 further comprises a split ring-shaped retaining element 17 forming a back-up for the sealing element 15. The split ring-shaped retaining element 17 has more than one winding, so that when the expandable tubular is expanded from the first outer diameter to the second outer diameter, the split ring-shaped retaining element partly unwinds. Thus, the split ring-shaped retaining element 17 may be arranged in an abutting manner to the sealing element, or an intermediate element 31 is arranged between the split ring-shaped retaining element 17 and the sealing element 15.

In Figs. 1 and 2, the expandable metal sleeve 2 is connected to the end parts 6, 9 without any welded connections; however, in Fig. 3 the expandable metal sleeve 2 is welded to the first and second end parts 6, 9, and a connection ring 29 is arranged outside and overlapping the end 3, 4 of the expandable metal sleeve and the first end 7, 10 of the end part 6, 9 and is threadingly connected thereto.

As shown in Fig. 4, the well tubular metal structure 100 may have a plurality of tubular sections 40 between two annular barriers 1, and the first and second end parts 6, 9 and the expandable metal sleeve 2 are mounted in succession with the plurality of tubular sections, so that the first end part 6 and the second end part 9 are arranged between the expandable metal sleeve 2 and the tubular sections along an axial extension 30 of the well tubular metal structure 2. The expandable metal sleeve 2, the end parts 6, 9 and the tubular sections 40 form one single walled pipe/tubular. Thus, an inner face 22 (shown in Figs. 1-3) of the expandable metal sleeve 2 forms part of the inner face 21 (shown in Figs. 1-3) of the well tubular metal structure. A flow section 60 is furthermore arranged between two annular barriers in the first zone. The flow section provides primary flow into the well tubular metal structure, when the annular barriers have been expanded, but may also be used for ejecting fluid into the annulus, e.g. for fracking the formation surrounding the well tubular metal structure 100.

As shown in Figs. 1 and 2, the first end part creates a first distance di between the expandable metal sleeve and one of the plurality of tubular sections, and the second end part creates a second distance d₂ between the expandable metal sleeve and another one of the plurality of tubular sections. Thus, the expandable metal sleeve does not overlap any of the plurality of tubular sections.

The expandable metal sleeves are expanded by an internal fluid pressure in the well tubular metal structure. In order to provide an internal pressure, the entire well tubular metal structure may be pressurised from within, or an expansion tool for isolating a part of the well tubular metal structure opposite the expandable metal sleeve may be introduced in the well tubular metal structure for pressurising that part and expand the expandable metal sleeves one by one. The well tubular metal structure may be submerged by means of a drill pipe, and the annular barriers may be expanded by pressuring the drill pipe and the well tubular metal structure before disconnecting the drill pipe from the well tubular metal structure.

Even though not shown, at least one of the tubular sections between the annular barrier may comprise an inflow section for letting fluid into the well tubular metal structure also called the production casing. One of the tubular sections may also comprise a sensor section for measuring a condition downhole, e.g. for controlling and optimise the production. One of the tubular sections further up the well may also comprise a gas lift valve for introducing gas to reduce the hydrostatic pressure in the fluid column.

The well tubular metal structure may be a production casing installed more permanently in the borehole, or the well tubular metal structure may be a velocity string used for early production. In the event that the early production shows a successful result, the velocity string is then used as the production casing.

By fluid or well fluid is meant any kind of fluid that may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By gas is meant any kind of gas composition present in a well, completion, or open hole, and by oil is meant any kind of oil composition, such as crude oil, an oil-containing fluid, etc. Gas, oil, and water fluids may thus all comprise other elements or substances than gas, oil, and/or water, respectively.

By a well tubular metal structure or casing is meant any kind of pipe, tubing, tubular, liner, string etc. used downhole in relation to oil or natural gas production.

In the event that the tool is not submergible all the way into the casing, a downhole tractor can be used to push the tool all the way into position in the well. The downhole tractor may have projectable arms having wheels, wherein the wheels contact the inner surface of the casing for propelling the tractor and the tool forward in the casing. A downhole tractor is any kind of driving tool capable of pushing or pulling tools in a well downhole, such as a Well Tractor®.

Although the invention has been described in the above in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.