SYSTEM AND METHOD FOR RAIALLY EXPANDING A TUBULAR ELEMENT COMPRISING AN EMERGENCY BLOW-OUT PREVENTER

Abstract

The invention provides a system for lining a wellbore, and a method for using said system. The system comprises: a drill string (20) for drilling the wellbore; an expandable tubular element (4) enclosing the drill string, wherein a lower end portion of a wall of the expandable tubular element is bent (14) radially outward and in axially reverse direction to define an expanded tubular section (10) extending around an unexpanded tubular section (8); a pushing device (50) for pushing the unexpanded section into the expanded tubular section; a blow-out preventer (302) for closing off the wellbore in case of an emergency. Herein the blow-out preventer encloses the unexpanded tubular section and comprises a cutter (320) for cutting the unexpanded tubular section and at least one closure device (324) for closing the wellbore.

Description

The present invention relates to a system for radially expanding a tubular element. The invention also relates to a method of using said system.

The technology of radially expanding tubular elements finds increasing application in the industry of oil and gas production from subterranean formations. Wellbores are generally provided with one or more casings or liners to provide stability to the wellbore wall, and/or to provide zonal isolation between different earth formation layers. The terms “casing” and “liner” refer to tubular elements for supporting and stabilising the wellbore wall. Typically, a casing extends from surface into the wellbore and a liner extends from a certain depth further into the wellbore. However, in the present context, the terms “casing” and “liner” are used interchangeably and without such intended distinction.

In conventional wellbore construction, several casings are set at different depth intervals, and in a nested arrangement. Herein, each subsequent casing is lowered through the previous casing and therefore has a smaller diameter than the previous casing. As a result, the cross-sectional area of the wellbore that is available for oil and gas production decreases with depth.

To alleviate this drawback, it is possible to radially expand one or more tubular elements at a desired depth in the wellbore, for example to form an expanded casing, expanded liner, or a clad against an existing casing or liner. Also, it has been proposed to radially expand each subsequent casing to substantially the same diameter as the previous casing to form a monodiameter wellbore. It is thus achieved that the available diameter of the wellbore remains substantially constant along (a section of) its depth as opposed to the conventional nested arrangement.

WO-2008/006841 discloses a wellbore system for radially expanding a tubular element in a wellbore. The wall of the tubular element is induced to bend radially outward and in axially reverse direction so as to form an expanded section extending around an unexpanded section of the tubular element. The length of the expanded tubular section is increased by moving, for instance by forcing or pushing, the unexpanded section into the expanded section. Herein the expanded section retains the expanded tubular shape. At its top end, the unexpanded section can, for instance, be extended by adding pipe sections or by unreeling, folding and welding a sheet of material into a tubular shape.

The present invention aims to improve the above referenced prior art system.

The present invention therefore provides a system for lining a wellbore, the system comprising:

• • a drill string for drilling the wellbore;
  • an expandable tubular element enclosing the drill string, wherein a lower end portion of the wall of the expandable tubular element is bent radially outward and in axially reverse direction to define an expanded tubular section extending around an unexpanded tubular section;
  • a pushing device for axially extending the expanded tubular section by forcing the unexpanded section to move relative to the expanded tubular section;
  • a blow-out preventer device (BOP) for closing an annular opening between the expandable tubular element and the drill string.

By moving the unexpanded tubular section downward relative to the expanded tubular section, the tubular element is effectively turned inside out. The tubular element is progressively expanded without an expander that is pushed, pulled or pumped through the tubular element. The expanded tubular section can form a casing or liner in the wellbore. The expanded tubular liner may have a collapse resistance which is adequate to stabilize or support the wellbore wall.

The BOP seals the opening at the upper end of the unexpanded tubular section, thus allowing fluid, such as drilling fluid, within the system to be pressurised. The BOP enables the drill string and/or sections of the expandable tubular liner to be disconnected safely, while ensuring that well control operations can be carried out in case of a kick or blow-out. Herein, a blow-out may indicate an uncontrolled flow of (reservoir) fluids into the wellbore, which may sometimes catastrophically rise to the surface. Said fluids may include salt water, oil, gas or a mixture of these. Blowouts may occur in all types of exploration and production operations, not just during drilling operations.

Preferably, the sealing capability of the BOP can withstand pressures that may be experienced during well control operations. The BOP is for instance designed to withstand pressures that may be expected in case of a blowout, for instance a maximum pressure in the range of 200 bar to about 1600 bar or more, for instance about 400 bar to 800 bar or more.

It is preferred that the wall of the tubular element includes a material that is plastically deformed during expansion. The expanded tubular section will retain an expanded shape due to the plastic deformation, i.e. permanent deformation, of the wall of the expandable tubular element. There is no need to apply an external force or pressure to maintain the expanded tubular section in its expanded form. If, for example, the expanded tubular section engages the wellbore wall, no additional radial force or pressure needs to be exerted to keep the expanded tubular section against the wellbore wall.

The wall of the tubular element may comprise a metal such as steel or any other ductile metal capable of being plastically deformed by eversion of the tubular element. The expanded tubular section preferably has adequate collapse resistance to support or stabilize the wellbore wall. Depending on the respective formation, the collapse resistance of the expanded tubular section may exceed, for example, 100 bar, 150 bar, or about 1500 bar or more.

Suitably the bending zone is induced to move in axial direction relative to the remaining tubular section by inducing the remaining tubular section to move in axial direction relative to the expanded tubular section. For example, the expanded tubular section is axially fixed at some location, while the unexpanded tubular section is moved in axial direction through the expanded tubular section to induce said bending of the wall.

In order to induce said movement of the remaining tubular section, the remaining tubular section is subjected to an axially compressive force acting to induces said movement. The axially compressive force preferably results at least partly from the weight of the remaining tubular section. A pushing device may supplement the weight of the unexpanded tubular section by applying an additional external force to the remaining tubular section to induce said movement. The additional force applied by the pushing device may be upward or downward. For instance, as the length and hence the weight of the unexpanded tubular section increases, an upward force may need to be applied to the unexpanded tubular section to maintain the total force applied to the unexpanded section within a predetermined range. Maintaining the total force within said range will prevent uncontrolled bending or buckling of the bending zone.

If the bending zone is located at a lower end of the tubular element, whereby the remaining tubular section is axially shortened at a lower end thereof due to said movement of the bending zone, it is preferred that the remaining tubular section is axially extended at an upper end thereof in correspondence with said axial shortening at the lower end thereof. The remaining tubular section gradually shortens at its lower end due to continued reverse bending of the wall. Therefore, by extending the remaining tubular section at its upper end to compensate for shortening at its lower end, the process of reverse bending the wall can be continued until a desired length of the expanded tubular section is reached. The remaining tubular section can be extended at its upper end, for example, by connecting a tubular portion to the upper end in any suitable manner such as by welding. Alternatively, the remaining tubular section can be provided as a coiled tubing which is unreeled from a reel and subsequently inserted into the wellbore.

Optionally the bending zone can be heated to promote bending of the tubular wall.

The invention will be described hereinafter in more detail and by way of example with reference to the accompanying drawings in which:

FIG. 1 shows a vertical cross section of a lower portion of a system for radially expanding a tubular element;

FIG. 2 shows a vertical cross section of an example of an upper portion of the system of FIG. 1;

FIG. 3 shows a vertical cross section of another example of an upper portion of the system of FIG. 1;

FIG. 4 shows a vertical cross section of an embodiment of the system of the present invention;

FIG. 5 shows a vertical cross section of another embodiment of the system of the present invention;

FIG. 6A shows a vertical cross section of an embodiment of the present invention in a first state of use;

FIG. 6B shows a plan sectional view of the system of FIG. 6A along the line B-B;

FIG. 6C shows a plan sectional view of the system of FIG. 6A along the line C-C;

FIG. 7A shows a vertical cross section of an embodiment of the present invention in a second state of use;

FIG. 7B shows a plan sectional view of the system of FIG. 7A along the line B-B;

FIG. 7C shows a plan sectional view of the system of FIG. 7A along the line C-C;

FIG. 8A shows a vertical cross section of an embodiment of the present invention in a third state of use;

FIG. 8B shows a plan sectional view of the system of FIG. 8A along the line B-B; and

FIG. 8C shows a plan sectional view of the system of FIG. 8A along the line C-C.

In the drawings and the description, like reference numerals relate to like components.

FIG. 1 shows a wellbore 1 formed in an earth formation 2. A radially expandable tubular element 4, for instance an expandable steel liner, extends from surface 6 down into the wellbore 1. The tubular element 4 comprises an unexpanded tubular section 8 and a radially expanded tubular section 10. The unexpanded section 8 extends within the expanded section 10. Preferably, an outer diameter of the expanded tubular section 10 is substantially equal to the diameter of the wellbore 1.

Although the wellbore shown in FIG. 1 extends vertically into the formation 2, the present invention is equally suitable for any other wellbore. For instance, the wellbore 1 may extend at least partially in horizontal direction. Herein below, upper end of the wellbore refers to the end at surface 6, and lower end refers to the end down hole.

At its lower end, the wall of the unexpanded section 8 bends radially outward and in axially reverse (in FIG. 1 the upward) direction so as to form a curved lower section 12, defining a bending zone 14 of the tubular element 4. The curved section 12 is U-shaped in cross-section and interconnects the unexpanded section 8 and the expanded section 10.

A drill string 20 may extend from surface through the unexpanded liner section 8 to the lower end of the wellbore 1. The lower end of the drill string 20 is provided with a drill bit 22. The drill bit comprises, for instance, a pilot bit 24 having an outer diameter which is slightly smaller than the internal diameter of the unexpanded liner section 8, and a reamer section 26 having an outer diameter adapted to drill the wellbore 1 to its nominal diameter. The reamer section 26 may be radially retractable to a smaller outer diameter, allowing it to pass through the unexpanded liner section 8, so that the drill bit 22 can be retrieved through the unexpanded liner section 8 to surface. The drill string 20 may comprise multiple drill pipe sections 28. The pipe sections 28 may be mutually connected at respective ends by male and female threaded connections 30. An annular space 32 between the drill string 20 and the unexpanded tubular section 8 is referred to as the drilling annulus 32.

The connections 30 are not shown in detail, but comprise for instance threaded, pin and box type connections. The connections 30 may comprise joints fabricated with male threads on each end, wherein short-length coupling members (not shown) with female threads are used to join the individual joints of drill string together, or joints with male threads on one end and female threads on the other. Said threaded connections may comprise connections which are standardized by the American Petroleum Institute (API).

FIG. 1 also shows a rig floor 40, which is elevated with respect to the surface 6 and encloses an upper end of the drill string 20 and of the unexpanded tubular section 8. The rig floor 40 is part of a drilling rig, which is however not shown in its entirety. A pipe pusher 42, which is for instance arranged below the rig floor, encloses the unexpanded section 8. The pipe pusher is for instance supported by base frame 44. The base frame 44 provides stability, and may for instance be connected to the drilling rig or be supported at surface 6. The pipe pusher may comprise one or more motors 46, which are arranged on the base frame, and one or more conveyer belts 48 which can be driven by the respective motors. Each conveyer belt 48 engages the outside of the unexpanded section 8. The conveyer belts 48 can exert force to said unexpanded section 8 to force the unexpanded section to move into the expanded section 10. Other embodiments of the pipe pusher 42 are conceivable, which will be able to exert downward or upward force to the unexpanded section.

A sealing device 50 can be connected to the upper end of the expanded liner section 10 to seal the unexpanded liner section 8 relative to the expanded liner section 10. Herein, the sealing device 50 enables the unexpanded liner section 8 to slide in axial direction relative to the sealing device 50. The sealing device comprises a conduit 52 which is connected to a pump (not shown) for pumping fluid into or out of a blind annulus 44, i.e. the annular space between the unexpanded liner section 8 and the expanded liner section 10. The annular space 44 is referred to as blind annulus as it is closed at the downhole end by the bending zone 14. The sealing device includes one, two or more annular seals 56, 58. The seals 56, 58 engage the outside of the unexpanded section 8 and prevent said fluid to exit the blind annulus. Preferably, the sealing device 50 comprises at least two seals 56, 58 to provide at least one additional seal to improve safety and reliability in case the first seal may fail.

The sealing device 50 can be regarded as a blind annulus blow out preventer (BABOP). Therefore, the seals 56, 58, the connection of the device 50 to the upper end of expanded section 10, and one or more valves (not shown) for closing conduit 52 will all be designed to at least withstand fluid pressures that may arise in a well control situation. Depending on specifics of the formation, the sealing device 50 is for instance designed to withstand pressures that may be expected in case of a blowout, for instance in the range of 200 bar to 1600 bar, for instance about 400 bar to 800 bar or more. Such pressures may for instance arise in the blind annulus 44 in case of a failure, for instance due to rupture, of the expandable tubular 4 in combination with a well control situation.

The expanded liner section 10 is axially fixed, by any suitable fixation means, to prevent axial movement. The expanded liner section 10 may be fixated at its upper end at surface. For instance, said upper end of the expanded section may be connected to a ring or flange 59, for instance by welding and/or screwing. Said ring can be attached to or incorporated in any suitable structure at surface, such as the sealing device 50. The inner diameter of said ring may be larger than the outer diameter of the expanded section. Optionally, the expanded section 10 may be fixed to the wellbore wall 12, for instance by virtue of frictional forces between the expanded liner section 10 and the wellbore wall 12 as a result of the expansion process. Alternatively, or in addition, the expanded liner section 10 can be anchored, for instance to the wellbore wall, by any suitable anchoring means.

At the interface indicated by the line II-II, the lower portion of the system shown in FIG. 1 can be connected to an upper portion as for instance shown in FIGS. 2 and 3.

FIG. 2 shows a top drive 60 connected to an upper end connection part 62, which is rotatable with respect to the top drive. Preferably, the upper end connection part comprises a flush pipe, having a smooth outer surface. The pipe end 64, which is remote from the top drive, is provided with a threaded connection 30 as described above. The threaded end 64 is connected to an additional drill string section 66. Typically, the additional drill string section 66 will be substantially equal to the drill string sections 28, shown in FIG. 1. At the interface indicated by line I-I, the additional drill pipe section 66 can be connected to the upper end of the drill string 20 shown in FIG. 1.

A drilling annulus sealing device 70 may cover the top end of the drilling annulus 32. The sealing device 70 comprises a housing 72, which encloses the connection part 62 and provides an internal space 74. At the top end, near the top drive 60, the housing comprises one, two or more seals 76, 78, which engage the outside of the pipe 62. Preferably, the seals 76, 78 enable the housing to slide along the pipe 62. At the opposite end, the housing may comprise one, two or more seals 80, 82 which engage the outside of an additional expandable pipe section 84. In addition to the seals, the housing may comprise grippers 106, which may engage the outside and/or the inside of the pipe section 84. An activation line 88 is connected to the housing for activating or releasing the seals 80, 82 and/or the grippers 86. A fluid conduit 90 is connected to the internal space 74 for supply or drainage of (drilling) fluid to or from the annular space 32.

The sealing device 70 may comprise an extending part or stinger 100. The stinger extends into the inside of the additional expandable pipe section 84. The stinger may comprise seals 102, 104 and/or grippers 106 to engage the upper end of the pipe section 84. The stinger may also comprise seals 108 to engage a lower end of the pipe section 84, and seals 110 to engage the inside of the upper end of the unexpanded tubular section 8 (shown in FIG. 1). A backing gas tool 192 may be integrated in the stinger between the seals 108, 110. The backing gas tool covers the inner interface between the additional expandable pipe section 84 and the unexpanded tubular section 8.

The stinger may be at least slightly longer than the pipe section 84 so that the stinger may extend into the unexpanded section 8, which will enable the stinger to function as an alignment tool for aligning the pipe section 84 and the unexpanded section 8.

In practice, the length of the pipe section 84 may be in the range of about 5-20 metres, for instance 10 metres. The stinger will for instance be about 2% to 10% longer, for instance 5% longer than the pipe section 84. An annular space 112 is provided between the stinger and the pipe 62 to provide a fluid connection from the annulus 32 to the space 74 and the conduit 90.

The sealing device 70 may be referred to as drilling annulus blow out preventer (DABOP) 70. The seals 76-82, the grippers 86, and one or more valves (not shown) for closing conduits 88 and 90 will all be designed to at least withstand fluid pressures that may arise in a well control situation. Depending on specifics of the formation and the expected maximum pore pressures, the DABOP 70 is for instance designed to withstand pressures in the range of about 200 bar to 800 bar or more, for instance about 400 bar.

The DABOP may comprise any number of seals. The DABOP 70 may comprise one seal 76 and one seal 80, or a plurality of seals. In a practical embodiment, two seals 76, 78 to seal with respect to the pipe 62 and two seals to seal with respect to the tubular section 84 will provide a balance between for instance fail-safety and reliability on one hand and costs on the other hand. For instance, the double barrier provided by the inner seals 102, 104, engaging the inside of the expandable pipe 84, and the outer seals 80, 82, engaging the outside of the expandable pipe 84, improves the reliability and leak-tightness of the sealing device 70.

FIG. 3 shows an upper portion of the system of FIG. 1. The unexpanded liner section 8 is at its upper end formed from a (metal) sheet 130 wound on a reel 132. The metal sheet 130 has opposite edges 133, 134. After unreeling from the reel 132, the metal sheet 130 is bent into a tubular shape and the edges 133, 134 are interconnected, for instance by welding, to form the unexpanded tubular section 8. Consequently, the expandable tubular element 4 may comprise a longitudinal weld 135.

A fluid conduit 136 extends from the interior of the unexpanded tubular section 8, to above the upper end of the unexpanded tubular section 8. The fluid conduit 136 may at its lower end be connected to, or integrally formed with, a tube 138 located in the unexpanded tubular section 8. A first annular seal 140 seals the tube 138 relative to the unexpanded liner section 8, and a second annular seal 142 seals the tube 138 relative to the drill string 20. The fluid conduit 136 is in fluid communication with the interior space of the tube 38 via an opening 144 provided in the wall of the tube 138. Furthermore the tube 138 is provided with gripper means 146 allowing upward sliding, and preventing downward sliding, of the tube 138 relative to the unexpanded liner section 8. The first annular seal 140 allows upward sliding of the tube 138 relative to the unexpanded liner section 8.

The upper portion shown in FIG. 3 can be combined with a lower portion shown in FIG. 1, wherein the unexpanded tubular section 8 is however continuously formed around the drill string 20. Herein, some of the features shown in FIG. 1 are omitted in FIG. 3 to improve the clarity of the latter figure, such as the sealing device 50, the pipe pusher 42 and drilling floor 40.

FIG. 4 shows the system 300 for radially expanding the expandable tubular element 4 by eversion thereof. As an example, the system 300 includes the upper section shown in FIG. 2, but the system may likewise include an upper section comparable to the upper section shown in FIG. 3.

The system 300 includes an emergency blow-out preventer 302 for blocking the drilling annulus in case of an emergency, such as an otherwise uncontrollable blow-out of the well. The emergency blow-out preventer comprises a housing 304 which encloses at least a part of the unexpanded tubular section 8. The housing is preferably located at surface to enable workers access to the device, but may also be located downhole or at the seabed in case of an offshore application.

The housing 304 may be attached to the sealing device 50. Herein, the sealing device 50 may function as a wellhead. Wellhead herein means the surface termination of the wellbore that may incorporate a means of hanging the production tubing and installing a Christmas tree and surface flow-control facilities in preparation for the production phase of the well.

Optionally, and as shown in FIGS. 4 and 5, the housing 304 comprises multiple housing parts 306, 308, 310. Each housing part may comprise a different device or provide a different functionality. Respective housing parts are for instance cylindrically shaped, comprising flanges 312 at opposite ends. Adjacent housing parts can be mutually connected by connecting their respective flanges to each other, for instance by bolt-nut assemblies 314. The inside of each housing part may optionally be provided with upper and lower seals 316, 318 respectively, wherein each seal is adapted to be able to engage the unexpanded liner section 8. Each seal 316, 318 may include one, two or more seals, depending on local conditions, expected pressures, etc. The seals 316, 318 are for instance comparable with, or similar to the seals 56, 58 of the sealing device or wellhead 50.

In an embodiment, shown in FIG. 4, the emergency blow-out preventer 302 comprises a cutter 320. The cutter is located in a lower part of the housing 304, for instance in first housing part 306. In addition the emergency blow-out preventer 302 comprises one or more ram-type preventers 322, 324 for closing off the annulus 32, which are arranged above the cutter 320. The ram type preventers for instance include a pipe ram 322 and a shear ram 324. The pipe ram can comprise two opposite ram blocks 226 which can close around the drill string 20. The shear ram can comprise two opposite shear ram blocks 228 which can cut through the drill string. The housing 304 may include one, two or more of each ram type preventer, to improve reliability and fail-safety.

In another embodiment, shown in FIG. 5, the emergency blow-out preventer 302 comprises a cutter 320. An annular preventer 330 is arranged above the cutter. The annular preventer comprises for instance one or more inflatable packer elements 332 that can close around the drill string 20. The packer elements can be inflated with pressurized fluid. The emergency blow-out preventer 302 also comprises the shear ram 324.

A fluid conduit or kill line 334 connects the drilling annulus 32 below the lowest ram type preventer with an external pump system (not shown). Fluid, typically mud or heavy drilling fluid, can be circulated via the drill string and the drilling annulus 32, indicated by arrows 336 and 338 respectively, and through the kill line 334, or vice versa.

The ram type preventers are devices that can be used to quickly seal the top of the wellbore in the event of a well control event, also known as a kick. The ram type preventer may comprise two halves of a cover for the well that are split down the middle. Said halves can be driven by hydraulic cylinders (not shown), which are normally retracted (FIG. 6A shows the ram blocks in their retracted position) and can force the two halves of the cover together in the middle to seal the wellbore (as shown in FIGS. 4 and 5). These covers are for instance constructed of steel for strength and may be fitted with elastomer components on the sealing surfaces. The halves of the covers, also called ram blocks, may have a variety of configurations.

In case of the pipe ram 322, the ram blocks 326 may have a circular cutout 340 in the middle that corresponds to the diameter of the pipe in the wellbore, for instance enabling them to seal around the drill pipe 20 (see FIG. 6C). Variable-bore rams (not shown) and inflatable packers 332 are designed to seal a wider range of pipe diameters. Shear ram blocks 328 are fitted with a cutting surface to enable the ram blocks to completely shear through the drill pipe 20 (as schematically shown in FIGS. 4 and 5), hang the drill string off on the ram blocks themselves and seal the wellbore. Shearing the drill string limits future options and is employed only as a last resort to regain pressure control of the wellbore.

The various ram blocks can be changed in the ram type preventers, enabling an operator to optimize the configuration of the emergency blow-out preventer 302 for the particular wellbore section or operation in progress.

In an exemplary embodiment, the cutter 320 comprises a guide ring 342 for enclosing the unexpanded section 8 and a cutting wheel 344 (FIG. 6A) which can rotate along said guide ring around the unexpanded tubular section. The cutting wheel herein can be moved from a first position wherein the cutting wheel is radially retracted (FIG. 6B) to a second position (FIG. 7B) wherein the cutting wheel touches the outside of the unexpanded tubular section 8.

In other embodiments, the cutter 320 may comprise a laser cutter and/or a blade which can be mounted on the guide ring 342. Other options may include a pressurized water cutter or a cutting rope which can engage the outer surface of the pipe.

Typically, and as shown in FIG. 6A, the emergency blow-out preventer 302 is placed above the sealing device 50 or similar wellhead device. The emergency blow-out preventer 302 is adapted to cut the unexpanded tubular section 8 and to subsequently seal the drilling annulus 32. In an inactive position (FIG. 6A), the cutter does not engage the unexpanded tubular section 8 (FIG. 6B) and all the ram blocks, such as ram blocks 326 shown in FIG. 6C, are in a retracted position.

When the emergency blow-out preventer 302 is activated, first a cutting action is achieved by activating the cutter 320. The cutting wheel 344 is moved from its radially retracted position to its cutting position wherein the cutting wheel touches the unexpanded tubular section 8 (FIG. 7B). Subsequently, the cutting wheel cuts the unexpanded tubular section 8, for instance by rotating around the tubular section 8 once, twice or as many times as required to sever a detached unexpanded section 350. During cutting, the ram blocks 326 remain in their retracted position (FIG. 7C).

After cutting, the detached unexpanded section 350 is lifted to create a space for the respective ram type preventers (FIG. 8A). Lifting can for instance be achieved by draw works or other lifting means (not shown) incorporated in the drilling rig.

In a subsequent step, one of the ram type preventers can be activated to seal the drilling annulus 32 (FIG. 8C). Typically, the operator will first activate either one of the pipe ram 322 or the annular preventer 330, both of which will maintain the drill string 20. Otherwise, the shear ram 324 can be activated, wherein the ram blocks 328 will shear the drill string 20, engage each other and seal the wellbore.

When the wellbore is closed, drilling fluid, having a predetermined density and weight, can be circulated via the drill string 20, the annulus 32 and through the kill line 334, as indicated by the arrows 336, 338 and 352, until regaining control of the wellbore.

In a practical embodiment, the diameter and/or wall thickness of the liner 4 can be selected such that the expanded liner section 10 is pressed against the wellbore wall 14 during the expansion process. The expanded liner 10 may thus seal against the wellbore wall and/or stabilize the wellbore wall.

The wall thickness of the liner 4 may be equal to or thicker than about 2 mm (0.08 inch). The wall of the liner 4 may be for instance more than 2.5 mm thick, for instance about 3 to 30 mm thick or about 3.2 to 10 mm. The outer diameter of the unexpanded section may be larger than 50 mm (2 inch), for instance in the range of about 50 to 400 mm (16 inch). The expanded section may have any outer diameter suitable for or commonly used in hydrocarbon production. Additionally, the wall of the liner may comprise a relatively strong material, such as a metal or preferably steel, or be made of solid metal or steel. Such steel may include low carbon steel, for instance comprising less than 0.3% carbon. Thus, the liner 4 can be designed to have adequate collapse strength to support a wellbore wall and/or to withstand internal or external pressures encountered when drilling for hydrocarbon reservoirs.

The length and hence the weight of the unexpanded liner section 8 will gradually increase during extension of the wellbore. Hence, the downward force exerted by the pushing device 50 can be gradually decreased in correspondence with the increasing weight of unexpanded liner section 8. As said weight increases, the downward force eventually may need to be replaced by an upward force to maintain the total force within a predetermined range. This may prevent buckling of liner section 8.

During drilling, the unexpanded liner section 8 proceeds into the wellbore while the drill string 20 also gradually proceeds into the wellbore 1. The unexpanded liner section 8 is moved downward at substantially the same speed as the drill string 20, so that the bending zone 14 remains at a relatively short distance above the drill bit 22. Herein, said short distance indicates the so-called open hole section L1 (see FIG. 1), i.e. the unlined section, of the wellbore 1. The method of the present invention enables an open hole section having a length L1 smaller than, for instance, about 100 or smaller than 50 metres at all times while drilling the wellbore.

The unexpanded liner section 8 may be supported by the drill string 20, for example by means of a bearing device (not shown) connected to the drill string, which supports the U-shaped lower section 12. In that case the upward force is suitably applied to the drill string 20, and then transmitted to the unexpanded liner section 8 through the bearing device. Furthermore, the weight of the unexpanded liner section 8 then can be transferred to the drill string and utilised to provide a thrust force to the drill bit 22.

Drilling fluid containing drill cuttings is discharged from the wellbore 1 via outlet conduit 90. Alternatively, drilling fluid may be circulated in reverse circulation mode wherein the drilling fluid is pumped into the wellbore via the conduit 90 and discharged from the wellbore via the drill string 20.

When it is required to retrieve the drill string 20 to surface, for example when the drill bit 22 is to be replaced or when drilling of the wellbore 1 is complete, the reamer section 26 can be collapsed to its radially retracted mode, wherein the radial diameter is smaller than the internal diameter of the unexpanded liner section 8. Subsequently, the drill string 20 can be retrieved through the unexpanded liner section 8 to surface.

With the wellbore system of the invention, it is achieved that the wellbore is progressively lined with the everted liner directly above the drill bit, during the drilling process. As a result, there is only a relatively short open-hole section L1 of the wellbore during the drilling process at all times. Advantages of a short open hole section include limited possibility of influx into the wellbore, which will minimize the resulting pressure increase and simplify well control. The advantages of such short open-hole section will be most pronounced during drilling into a hydrocarbon fluid containing layer of the earth formation. In view thereof, for many applications it will be sufficient if the process of liner eversion during drilling is applied only during drilling into the hydrocarbon fluid reservoir, while other sections of the wellbore are lined or cased in conventional manner. Alternatively, the process of liner eversion during drilling may be commenced at surface or at a selected downhole location, depending on circumstances.

In view of the short open-hole section during drilling, there is a significantly reduced risk that the wellbore fluid pressure gradient exceeds the fracture gradient of the rock formation, or that the wellbore fluid pressure gradient drops below the pore pressure gradient of the rock formation. Therefore, considerably longer intervals can be drilled at a single nominal diameter than in a conventional drilling practice wherein casings of stepwise decreasing diameter must be set at selected intervals.

Also, if the wellbore is drilled through a shale layer, such short open-hole section eliminates possible problems due to a heaving tendency of the shale.

After the wellbore has been drilled to the desired depth and the drill string has been removed from the wellbore, the length of unexpanded liner section that is still present in the wellbore can be left in the wellbore or it can be cut-off from the expanded liner section and retrieved to surface.

In case the length of unexpanded liner section is left in the wellbore, there are several options for completing the wellbore. These are, for example, as outlined below.

A) A fluid, for example brine, is pumped into the blind annulus 44 between the unexpanded and expanded liner sections so as to pressurise the annulus and increase the collapse resistance of the expanded liner section 10. Optionally one or more holes are provided in the U-shaped lower section 12 to allow the pumped fluid to be circulated.
B) A heavy fluid is pumped into the blind annulus 44 so as to support the expanded liner section 10 and increase its collapse resistance.
C) Cement is pumped into the blind annulus 44 in order to create, after hardening of the cement, a solid body between the unexpanded liner section 8 and the expanded liner section 10. The cement may expand upon hardening.
D) The unexpanded liner section is radially expanded (i.e. clad) against the expanded liner section, for example by pumping, pushing or pulling an expander through the unexpanded liner section.

In the above examples, expansion of the liner is started at surface or at a downhole location. In case of an offshore wellbore wherein an offshore platform is positioned above the wellbore, it may be advantageous to start the expansion process at the offshore platform, at or above the water surface. Herein, the bending zone moves from the offshore platform to the seabed and subsequently into the wellbore. Thus, the resulting expanded tubular element not only forms a liner in the wellbore, but also a riser extending from the offshore platform to the seabed. The need for a separate riser is thereby obviated.

Furthermore, conduits such as electric wires or optical fibres for communication with downhole equipment can be extended in the annulus between the expanded and unexpanded sections. Such conduits can be attached to the outer surface of the tubular element before expansion thereof. Also, the expanded and unexpanded liner sections can be used as electricity conductors to transfer data and/or power downhole.

Since any length of unexpanded liner section that is still present in the wellbore after completion of the eversion process, will be subjected to less stringent loading conditions than the expanded liner section, such length of unexpanded liner section may have a smaller wall thickness, or may be of lower quality or steel grade, than the expanded liner section. For example, it may be made of pipe having a relatively low yield strength or relatively low collapse rating.

Instead of leaving a length of unexpanded liner section in the wellbore after the expansion process, the entire liner can be expanded with the method described above so that no unexpanded liner section remains in the wellbore. In such case, an elongate member, for example a pipe string, can be used to exert the necessary downward force to the unexpanded liner section during the last phase of the expansion process.

In order to reduce friction forces between the unexpanded and expanded liner sections during the expansion process, a friction reducing layer, such as a Teflon layer, may be applied between the unexpanded and expanded liner sections. For example, a friction reducing coating can be applied to the outer surface of the unexpanded section 8. The friction reducing layer reduces the annular clearance between the unexpanded and expanded sections, reducing tendency of the unexpanded section to buckle. Instead of, or in addition to, the friction reducing layer, centralizing pads and/or rollers can be applied in the blind annulus between the unexpanded and expanded sections to reduce the friction and the annular clearance.

Instead of expanding the expanded liner section against the wellbore wall (as described), the expanded liner section can be expanded against the inner surface of another tubular element, e.g. casing or a liner, already present in the wellbore.

Although the embodiments of the invention have been described including a top drive, the present invention is likewise suitable for use with alternative drilling systems. The latter may include for instance a downhole motor instead of a top drive. Said downhole motor is a drilling tool comprised in the drill string directly above the bit. Activated by pressurized drilling fluid, it causes the bit to turn while the drill string remains fixed. Examples of the downhole motor include a positive-displacement motor and a downhole turbine motor.

The present invention is likewise suitable for directional drilling, i.e. drilling wherein the drilling direction can be adjusted. For instance, a downhole motor may be used as a deflection tool in directional drilling, where it is made up between the bit and a bent sub, or the housing of the motor itself may be bent.

The present invention is not limited to the above-described embodiments thereof, wherein various modifications are conceivable within the scope of the appended claims. For instance, features of respective embodiments may be combined.

Claims

1. A system for lining a wellbore, the system comprising:

a drill string for drilling the wellbore;

an expandable tubular element enclosing the drill string, wherein a lower end portion of a wall of the expandable tubular element is bent radially outward and in axially reverse direction to define an expanded tubular section extending around an unexpanded tubular section;

a pushing device for pushing the unexpanded section into the expanded tubular section;

a blow-out preventer for closing off the wellbore in case of an emergency, wherein the blow-out preventer encloses the unexpanded tubular section and comprises:

a cutter for cutting the unexpanded tubular section; and

at least one closure device for closing the wellbore.

2. The system of claim 1, comprising a wellhead device for closing an annular space between the unexpanded section and the expended section, wherein the blow-out preventer is connected to said wellhead device.

3. The system of claim 1, wherein the closure device comprises one or more of: a shear ram device, a pipe ram device, an annular preventer device.

4. The system of claim 1, wherein the cutter is arranged below the closure device.

5. The system of claim 1, wherein the blow-out preventer comprises a housing, which comprises at least one seal for sealing the housing with respect to the unexpanded tubular section, the at least one seal being arranged below the cutter.

6. The system of claim 1, wherein the cutter comprises:

a cutting wheel; and

a guiding ring for guiding the cutting wheel around the unexpanded tubular section.

7. The system of claim 1, wherein the cutter comprises a laser cutter for cutting the unexpanded tubular section.

8. The system of claim 1, wherein the expandable tubular element comprises a plurality of interconnected tubular sections.

9. The system of claim 1, wherein the expandable tubular element is provided with a longitudinal weld.

10. Blow-out preventer for a system for lining a wellbore using an expandable tubular element, wherein a lower end portion of a wall of the expandable tubular element is bent radially outward and in axially reverse direction to define an expanded tubular section extending around an unexpanded tubular section, the blow-out preventer comprising:

a housing for enclosing the unexpanded tubular section of the expandable tubular element;

a cutter, which is arranged in the housing, for cutting the unexpanded tubular section; and

at least one closure device for closing an annulus between a drill string and the unexpanded tubular section.

11. Method for lining a wellbore using the system of claim 1.