Tool and method for pulling tubing hanger and tubing string

Abstract

A tubing hanger retrieval tool (3) and a method for retrieving a tubing hanger (5) and a downhole production tubing string (25) from a subsea wellhead (7) or X-mas tree (9), without hydraulic umbilica

Description

[0001] TOOL AND METHOD FOR PULLING TUBING HANGER AND TUBING STRING

[0002] This invention concerns a device and a method for retrieving a tubing hanger (hereinafter also denoted TH) and a production tubing string from a subsea wellhead, or a subsea horizontal X-mas tree.

[0003] More specifically, the invention concerns a tool configured for operation without the need for hydraulic umbilical control / supply lines from the surface, and without hydraulic control valves for operating the tool. The invention further concerns a method for operating the tool by mechanical means: i.e. , deploying and latching it onto a tubing hanger, un-locking a tubing hanger from a subsea wellhead or X-mas tree, contingency un-latch of the tool if the tubing hanger is stuck and cannot be retrieved with the tool, and finally, separation of the tool from a tubing hanger, after successful retrieval to the surface.

[0004] Traditionally, subsea running and retrieval tools for well completion and well permanent plugging and abandonment (PP&A) have been operated from the surface, via hydraulic lines in a twisted hose bundle with an external, reinforced jacket. This is known in the subsea industry as a hydraulic umbilical. The umbilical is clamped to a work-string that is used to lower or hoist the tool, with or without equipment hanging from the tool, depending on the specific operation.

[0005] The traditional control system, providing the hydraulics, is known in the subsea industry as a workover control system (hereinafter denoted WOOS). The work-string, which may be made up of joined drill pipes or riser joints, will typically vary between an inner diameter of 75 mm (3") and 180 mm (7"). The dimension of the umbilical typically varies between an outer diameter of 70 and 100 mm.

[0006] During a well completion phase, the drilled subsea well is provided with production tubing, which is made up of tubular joints and lowered into the well from the drill floor of a drilling vessel. Completion equipment is lowered through a marine drilling riser, which is suspended from the vessel, and connected to a subsea blowout preventer (hereinafter denoted BOP) at the seabed. The BOP is locked to a wellhead, or on top of a X-mas tree that has been locked to a wellhead. The marine drilling riser, typically with an outer diameter of 535 mm (21"), projects up from a lower marine riser package (hereinafter denoted LMRP) on a lower BOP stack, to an underside of the drill floor of the vessel, and is filled with drilling or completion fluid, that constitutes a shared liquid volume with the well.

[0007] One of the final steps during the installation of a production tubing string in a subsea well, is to screw the TH, which is provided with a lower tubing pup joint, onto a top end of the production tubing string. The TH will be suspended from a bottom end of the workstring, with a tubing hanger running tool (THRT) locked onto a top end of the TH. Hydraulic lines for enabling control of a downhole valve in the production tubing string, from the production control system, are connected to a bottom end of the TH, before it is lowered into the marine drilling riser. Tubular joints are made up to the work-string, as the TH is lowered to land in a wellhead or a X-Mas Tree, depending on the configuration of the subsea production equipment.

[0008] Traditional configurations used for TH installation, or retrieval, are:

[0009] 1) a Simplified Landing String (hereinafter also denoted SLS), or 2) a Lower Landing String Assembly (hereinafter denoted LLSA).

[0010] Hydraulic control / supply lines from the WOCS are distributed to the tool system through a surface hose bundle, and a subsea umbilical. The SLS, or the LLSA, is deployed with a hydraulic control umbilical clamped to the work-string. The umbilical is stored on, and is spooled off an umbilical reel, and is clamped to the work-string, as new joints are added, while the equipment is lowered into the marine drilling riser. Finally, the tubing hanger is turned into landing position by means of orientation grooves, before it is fully landed and locked into an internal locking groove in the wellhead, or in a X-mas tree.

[0011] More specifically:

[0012] 1) A Simplified Landing String (SLS) is used at the lower end of the work-string when installing, or recovering, a tubing hanger and the associated production tubing string. In this case, the work-string is made up of drill pipe joints. The SLS typically comprises a drill pipe joint with hydraulic tubing from an umbilical termination point at a top end, clamped along the drill pipe to a slick-joint with inner bores for hydraulic communication past a sealing point of a closed BOP pipe ram. The slick joint will be placed opposite one of the BOP's pipe rams, which is configured for being actuated to clamp around the slick joint in a sealing manner. Hydraulic tubing from a bottom end of the slick joint is connected to the tubing hanger running tool, fitted at a bottom of the SLS.

[0013] 2) Since the late 1990s, after the SLS solution came into use, the Lower Landing String Assembly (LLSA) has almost exclusively been used if the well is to be flowed to a test separator on board the drilling vessel for cleaning of the well, after perforating the production casing liner. The work-string will in this case be a work-over riser, typically made up of casing joints. The Lower Landing String Assembly (LLSA) comprises well barrier and working valves, a slick-joint with inner bores, and a shear-sub that can be sheared with a shear ram of the BOP. Like the SLS, the LLSA interfaces the tubing hanger running and retrieval tool in the bottom end. The LLSA items will be spaced out to fit the BOP stack configuration.

[0014] For tool systems and well equipment being operated at depths down to 500 m, direct hydraulic actuation is commonly used, controlled with directional control valves and hydraulic fluid from the WOOS at the surface. In-riser subsea control modules provided with local hydraulic accumulation and directional control valves, have been developed for deep waters, to operate LLSA / tool systems with many functions, where fast response is also needed in emergency situations. The control module encircles the work-string in the marine riser, at a short distance above the LLSA / tool system.

[0015] Common hydraulic supply and return lines will then be used, instead of direct hydraulic lines in the umbilical. The solution thus provides an advantageous reduction of umbilical diameter and weight.

[0016] The umbilical and associated clamps along the work-string are exposed to damage inside the marine riser, in that they can be squeezed between the work-string and the inside of the marine riser when the vessel and the marine riser move due to external environmental loads, like waves and ocean currents. Potential damage to the umbilical, and the consequences of loose parts from damaged umbilical clamps falling through the drilling riser, to the BOP, constitute a significant risk of lost productive rig time. Problems and economic consequences of such incidents will magnify with increasing water depth.

[0017] Another negative aspect of deep and ultra-deep water is that time consumed for preparations, and for running and retrieval operations, with clamping and un-clamping of the umbilical to / from the work-string, will be significant.

[0018] Due to said and other disadvantages of clamping the umbilical to the work-string and advantages that a tool system without an umbilical will have, i.e. , reduced cost, space and weight of WOCS umbilical systems, increased efficiency, reduced damage potential for the completion string and personnel, lower equipment cost, etc. an alternative solution has been developed for tubing hanger (TH) installation that will be operable without hydraulic directional control valves and an umbilical from the surface. The solution is known in the patent literature from WO 2022 / 093033 A1 . Because this solution is exclusively intended for the installation of tubing hangers (TH) and associated production tubing through a specific construction and limited functionality, it cannot be used for TH retrieval.

[0019] In the coming years, there will be a significant increase in the number of subsea wells that shall be permanently plugged and abandoned, (PP&A). An alternative solution has thus been developed, which will be dedicated to the task of pulling tubing hangers and associated production tubing. The new solution is based on similar principles as the solution described in WO 2022 / 093033 A1 , but with a construction intended to enable the required functions and operational steps related to TH pulling, instead of TH installation.

[0020] Prior art for landing strings shows them being provided with a secondary system for operation of emergency functions. The secondary system comprises a module provided with hydraulic shuttle valves that are normally open for actuating the tool functions via a primary hydraulic system, but which, in an emergency, is configured for being switched to operation of selected tool functions with completion fluid as the control media. A closed-in annular space surrounding the secondary system in the BOP will in an emergency be pressurised from the surface via existing pipe connections to the BOP cavities. The connections are related to the choke and kill lines, (C&K lines), which are high pressure tubulars, integrated as part of the marine drilling riser. Burst disks that form part of the secondary system will crack in a predetermined sequence, as pressure is increased in the BOP annular space that surrounds the valve module. As the burst discs rupture, at different pressure levels, pressurized completion fluid flows through the open ports, and will activate the relevant tool functions, via the shuttle valves in the valve module.

[0021] The C&K lines are otherwise only used in well control situations. In case of a so-called “well kick” during conventional drilling, the BOP pipe rams are shut, and the only contact with the wellbore will be via the C&K lines and the drill string. To return the bottom-hole pressure (BHP) back to the mud window, drilling fluid with new properties is pumped down into the wellbore via the drill string, and thereby the kick fluid is circulated out of the well and to the surface via the choke line. In the extreme event that the drill-string is cut by the BOP shear-ram, the kill-line is instead used to inject drilling fluid into the wellbore.

[0022] From the patent literature, the following publications are cited as background art:

[0023] WO 2022 / 093033 A1 discloses a device and method for installation of a tubing hanger and associated production tubing in a subsea wellhead, or subsea horizontal X-mas tree, without the need for hydraulic operation of the functions from a traditional workover control system (WOCS). In addition to reduced damage potential, the solution contributes to increased efficiency. The prior art, umbilical less tubing hanger (TH) running tool, cannot be used for tubing hanger retrieval. This is because the functionality is limited to the specific task, since the operation is sequentially tied to inherent mechanical features, hydraulic ring-pistons, and shear-pin arrangement of the tool.

[0024] US2005217845A1 discloses a solution where completion fluid is pressurised in a closedin annular space in a BOP through kill / choke lines to the surface. Pressurised completion fluid is distributed as hydraulic supply to a subsea control module. The control module is provided with electrically activated directional control valves that via communication from the surface are commanded to pressurise hydraulic outlets of control lines that distribute fluid for actuating the tool functions of a lower landing string assembly (LLSA) and the associated tubing hanger running tool I tubing hanger. The tool system can thereby be of a standard type, i.e., hydraulically operated, corresponding to that which is operated from the surface via an umbilical. One difference is that completion fluid is used instead of pure hydraulic fluid, with the challenges that this entails.

[0025] US2013175045A1 discloses a closed hydraulic system with accumulators that supply hydraulic fluid to directional control valves in a control module. The pressure in the hydraulic system can be recharged when the supply pressure becomes too low to carry out further tool operations. At least one hydraulic piston pump charges the hydraulic accumulators. The pump is driven by pressurised completion fluid from a closed-in annular space in a BOP connected to the surface via kill / choke lines.

[0026] W02019004842A1 discloses a solution where a bladder functioning as a hydraulic reservoir is disposed in a closed-in annular space in a BOP. The annular space is connected to the surface via kill / choke lines. When the annular space in the BOP is pressurised, the bladder is squeezed, and will supply hydraulic fluid to a control module with directional control valves to actuate tool functions.

[0027] US2011 / 0247799A1 discloses a method for installing a production tubing and a tubing hanger in a subsea wellhead or X-mas tree wherein the apparatus comprises an upper transition pipe coupled to a work-string, a lower centre element with a through-going centre passage and several hydraulic channels, a housing that surrounds the upper part of the centre element, an expandable locking ring for locking the centre element to an internal groove in the tubing hanger, a ring ring-piston that surrounds the central part of the centre element and is arranged to expand the locking ring, and locking balls or gripping fingers that can engage with the lock sleeve when they are being radially displaced. Shearable locking pins arranged for locking movable components that surround the centre element are not described. Also not described herein is a housing that surrounds the lower part of the centre element and that is provided with threads that can engage with external threads on the centre element.

[0028] GB 2448262A discloses a tubing hanger running tool comprising an elongated body which includes a first end that is positioned adjacent the tubing hanger and a second end that is connected to a running string; at least first and second locking pistons which are each movably supported on the body; and an electrically operated actuator for moving each of the first and second locking pistons between respective first and second unlocked and first and second locked position.

[0029] The purpose of the invention is to eliminate the need for an umbilical from the surface for hydraulic supply and control of tool functions during tubing hanger and production tubing string retrieval, as well as the need for controlled directional control valves for hydraulic actuation of the tool functions.

[0030] The purpose is fulfilled by features specified in the description below and subsequent patent claims.

[0031] According to a first aspect of the invention, there is provided a tubing hanger retrieval tool for engaging a tubing hanger from a subsea wellhead or a subsea X-mas tree. The tubing hanger retrieval tool comprises:

[0032] - an upper body mandrel for operation by a work string, a lower body connected to the upper body mandrel, wherein the upper body mandrel is axially displaceable with respect to the lower body from a first position to a second position ;

[0033] - a latch ring-piston, an un-lock ring-piston, and a plurality of axially displaceable collet fingers movable together with the upper body mandrel from the first position to the second position, and releasably interconnected by means of shearable looking pins; wherein:

[0034] - a lower end portion of the latch ring-piston is configured to radially expand a split ring arranged on the lower body and, in a position of use of the tubing hanger retrieval tool, into engagement with an inner ring groove of a tubing hanger;

[0035] - the collet fingers extending from a retainer ring, wherein the collet fingers are configured for engaging a locking groove in a tubing hanger lock sleeve;

[0036] - the un-lock ring-piston has a portion configured for, in a position of use of the tubing hanger retrieval tool, being subject to an activation fluid having a first pressure, wherein the activation fluid is communicated from a closed-in annular space of a BOP to break shear pins initially connecting the un-lock ring-piston to the upper body mandrel, whereby the un-lock ring-piston is axial displaceable relative to the collet fingers to a position wherein a lower portion of the un-lock ring-piston abuts against the collet fingers, thereby preventing disengagement of the collet fingers from the tubing hanger lock sleeve; and - a ratchet latch, configured for engaging a groove in the retainer ring when the collet fingers are prevented from disengagement from the tubing hanger lock sleeve.

[0037] The tubing hanger lock sleeve will hereinafter also be denoted TH lock sleeve.

[0038] By means of the activation fluid communicated from a closed-in annular space of a BOP to break shear pins initially connecting the un-lock ring-piston to the upper body mandrel, the THRET is configured for being operated from surface without and umbilical control lines.

[0039] The upper body mandrel may be threadedly connected to the lower body so that the lower body is axially displaceable with respect to the lower body by rotating the upper body mandrel. Controlling an axial displacement of the upper body mandrel by means of rotation, provides a safe fully controllable position of the upper body mandrel with respect to the lower body, and thus the operation of the THRET.

[0040] In a preferred embodiment, the THRET comprises an internal ratchet latch configured for preventing back-rotation of the upper body mandrel, the ratchet latch comprising a first part arranged in a bottom of the upper body mandrel, and a mating second part arranged in a top portion of the lower body, wherein the first part is in engagement with the second part when the upper body mandrel is in the second position.

[0041] The retainer ring may be connected the un-lock ring-piston and the latch ring-piston by means of a plurality of shearable locking pins extending into respective slits in the un-lock ring-piston. The shearable locking pins may be designed to withstand the first pressure of the activation fluid, but break when subject to a second pressure being higher than the first pressure, wherein broken locking pins allow the un-lock ring-piston and the latch ringpiston to move to the first position, thereby disengaging the lower end portion of the latch ring-piston form the split ring, thereby allowing disengagement of the tubing hanger retrieval tool from a stuck tubing hanger.

[0042] In a second aspect of the invention, there is provided a method for connecting the tubing hanger retrieval tool according to the first aspect of the invention to a tubing hanger and associated production tubing string from a wellhead, or a X-mas tree. The method comprising the following steps: a) by means of a work string, lowering the tubing hanger retrieval tool with the upper body mandrel, the un-lock ring-piston, the latch ring-piston and the collet fingers being in the first position, and orienting and landing the tubing hanger retrieval tool in the tubing hanger; b) initiating latch of the tubing hanger retrieval tool to the tubing hanger, by rotating the work-string to break the shear pins so that the upper body mandrel, the un-lock ringpiston, the latch ring-piston, and the collet fingers are moved from the first position to the second position; whereby: the collet fingers spring into engagement with an internal, encircling locking groove in tubing hanger lock sleeve, and; the lower end of the latch ring-piston is wedged between the lower body and the split-ring, thereby expanding the split-ring so that it locks into a circumferential, inner locking ring groove in the upper part of the tubing hanger; c) pressurization of the BOP annular space via a supply-line, so that; the first pressure acts on the un-lock ring-piston and displaces it in an upwards stroke, and lower edge of slits in the un-lock ring-piston hits shear-pins, that extend into the slits from the retainer ring, and a relative movement of the unlock ring-piston with respect to the collet fingers which are connected to the retainer ring, stops, and; the lower portion of the un-lock ring-piston abuts a lower portion of the collet fingers, thereby preventing disengagement of the collet fingers from the tubing hanger lock sleeve during the further un-lock ring-piston movement towards the first position, and; the continued stroke of the un-lock ring-piston causes the upper body mandrel shear-pins to break, and; the combined vertical displacement of the un-lock ring-piston and the collet fingers pulls the tubing hanger lock sleeve out of locking engagement with locking segments of the tubing hanger, and further, into complete retraction; whereby spring-loaded locking bolts in the un-lock ring-piston engage a locking groove which encircles the upper body mandrel, and; the ratchet latch springs into locking engagement with the groove on the outside the retainer ring of the collet fingers, thereby keeping the tubing hanger lock sleeve in its fully retracted position.

[0043] The method may in a step d) further comprise pulling the tubing hanger retrieval tool, the released tubing hanger, and a production tubing string to the surface by means of the work-string. Thereafter, the method may further comprise disconnecting the tubing hanger retrieval tool from the tubing hanger by the following steps; e) removal of shear-pins connecting the latch ring-piston to the upper body mandrel; f) disengage the spring-loaded locking bolts in the un-lock ring-piston, from the circumferential locking groove in the upper body mandrel; g) temporarily install a jack pin, and jack the latch ring-piston so that the lower end of the latch ring-piston is pulled out of its wedged position between the lower body and the splitring, so that the split-ring disengages with the internal locking groove in the tubing hanger lock sleeve; and h) pressurize a vent side of the un-lock ring-piston with a pressure below a cracking pressure of a vent check valve, whereby a resulting un-lock ring-piston stroke causes the lower portion of the un-lock ring-piston to move past the lower portion of the collet fingers, which then bend inwards when they slide across an edge of the locking groove inside the tubing hanger lock sleeve during separation of the tubing hanger retrieval tool from the recovered tubing hanger.

[0044] In case of a stuck TH that cannot be retrieved, the method may comprise disconnecting the TH RET from the stuck tubing hanger by means of:

[0045] - increasing a pressure in the BOP annular space to a second pressure being higher than the first pressure, the second pressure being sufficient to break the shearable locking-pins extending into respective slits in the un-lock ring-piston, whereby:

[0046] - displacement of the un-lock ring-piston towards first position will carry the latch ring-piston with it, in that coupling pins, arranged between the un-lock ring-piston and the latch ring-piston, and extend from the un-lock ring-piston into slits in the latch ring-piston, abut against an upper slit edge, thereby also break shear-pins between the latch ringpiston and the upper body mandrel;

[0047] - the joint movement of the latch ring-piston and the un-lock ring-piston causes the lower portion of the latch ring-piston to be pulled out of its wedged position between the lower body and the split-ring, thereby releasing the tubing hanger retrieval tool from the stuck tubing hanger; and

[0048] - with the un-lock ring-piston displaced to its upper end position, the collet fingers are free to bend inwards, as the lower end portion of the collet fingers slide past an edge of the locking groove on the inside of the stuck tubing hanger lock sleeve, when the released tubing hanger retrieval tool is pulled out of the tubing hanger, and to the surface.

[0049] Thus, disclosed herein is a tubing hanger retrieval tool (TH RET) provided with mechanical features and function ring-pistons for latching onto a tubing hanger (TH) in a wellhead or horizontal X-mas tree, disconnecting a TH, as well as un-latching the TH RET from a stuck TH.

[0050] Disclosed herein is a method is provided for retrieving a tubing hanger and associated production tubing from a wellhead or X-mas tree, using the THRET as disclosed herein- and in one embodiment, use work-string rotation, combined with hydraulic operation with pressurised completion fluid in a closed-in annular space in a subsea BOP to perform the functions.

[0051] As disclosed herein, the method may also, as a contingency mode feature, comprise unlatching of the tubing hanger retrieval tool (THRET) from a stuck tubing hanger (TH).

[0052] As disclosed herein, the method may also comprise un-latching of the tubing hanger retrieval tool (THRET) from a recovered TH at the surface, prior to further THRET disassembly, refurbishment, and re-configuration of the tool for a new TH and tubing string retrieval operation.

[0053] Disclosed herein is a tubing hanger retrieval tool, (THRET), configured for recovering a tubing hanger and production tubing string from a subsea wellhead or a subsea X-mas tree. Such a THRET may comprise:

[0054] - an externally slick adapter that corresponds with a BOP set of sealing pipe rams, coupled to a work-string in the top end;

[0055] - shearable locking pins, arranged to hold in position movable ring-pistons, used for THRET latch to a TH, TH un-lock, as well as a contingency solution that may be used to release the THRET from a TH, if the TH cannot be released from a wellhead, alternatively a X-mas tree;

[0056] - a latch ring-piston for connection of the THRET to the TH, which can be operated to expand a split-ring on the THRET lower body, to engage a corresponding, inner ring groove in the TH; collet fingers that can be operated to engage an inner ring groove in the TH lock sleeve;

[0057] - an un-lock ring-piston for tubing hanger, hydraulically actuated with pressurized completion fluid in a closed-in annular space in the BOP, which can be operated to retract the TH lock sleeve, or with a higher pressure, un-latch the TH RET from a stuck TH;

[0058] - a TH RET lower body, with a threaded top end;

[0059] - a TH RET upper body, provided with an internal threaded portion, which is arranged to axially displace the TH un-lock ring-piston, the THRET latch ring-piston and the collet fingers, when it is screwed down on the lower THRET body;

[0060] - an internal ratchet latch designed to lock into engagement with each other when the upper body bottoms-out against the lower body. This prevents inadvertent back- rotation of the upper THRET body;

[0061] - an external ratchet latch, designed to hold the TH un-lock ring-piston, the collet fingers, and the retracted TH lock sleeve in the upper position, after successful TH lock sleeve retraction.

[0062] Disclosed herein is a method for retrieving a tubing hanger and tubing string from a wellhead or X-mas tree, using the tubing hanger retrieval tool (THRET), as disclosed herein. Before the tubing hanger is retrieved, the method comprises latching the THRET to the tubing hanger through the following steps: a) Prior to lowering the THRET through a marine drilling riser, it will have been configured to hold the TH un-lock ring-piston and the THRET latch ring-piston in an upper position, by means of shear-pins; b) lowering the THRET, until the THRET lower body enters the upper part of the tubing hanger, and is oriented so that anti-rotation elements line up with vertical slots in the tubing hanger, and the tool is subsequently landed in the TH; c) initiating latch of the THRET to the TH, with rotation of the work-string, whereby shearpins that have kept the ring-pistons in an upper position are first broken, and;

[0063] - the upper body is screwed, with continued rotation of the work-string, onto the THRET lower body. Thus, the TH un-lock ring-piston, the THRET latch ring-piston, and the collet fingers are vertically displaced, until the movement stops, with the internal ratchet lock in full engagement; - whereby the collet fingers spring into engagement with an internal, encircling locking groove in the TH lock sleeve, and;

[0064] - a tip of the THRET latch ring-piston is forced under and expands a split-ring on the lower THRET body, so that it locks into a circumferential, inner locking groove in the upper part of the tubing hanger; d) pressurization of the lower BOP annular space via a supply-line, so that;

[0065] - the pressure acts on the TH un-lock ring-piston and displaces it in an upwards stroke. As the lower edge of slits in the TH un-lock ring-piston hits shear-pins that extend into the slits from the retaining ring of the collet fingers, the relative movement of the TH un-lock ring-piston versus the, thus far, immobile collet fingers will stop, and;

[0066] - the tip of the TH un-lock ring-piston has now been positioned inside the tip of the collet fingers, and will ensure that these are kept in engagement with the internal, surrounding locking groove in the TH lock sleeve during the further TH un-lock ring-piston travel, and;

[0067] - the continued stroke of the TH un-lock ring-piston will initially cause the upper body shear-pins to break, and;

[0068] - the combined vertical displacement of the TH un-lock ring-piston and the collet fingers will pull the TH lock sleeve out of engagement inside the TH locking segments, and further, into complete retraction;

[0069] - whereby spring-loaded locking bolts in the TH un-lock ring-piston will engage a locking groove which encircles the upper THRET body, and;

[0070] - an external ratchet latch will spring into locking engagement with a groove on the outside the retainer ring of the collet fingers, thereby keeping the TH lock sleeve latched in its fully retracted position; e) the released tubing hanger, TH, connected with the THRET, as well as the production tubing string are then pulled to the surface by means of the work-string;

[0071] Disclosed herein is an alternative method for use if the TH is stuck and cannot be retrieved. Such a method for disconnecting the THRET from the tubing hanger may comprise the following steps: a) Increasing the pressure in the lower BOP annular space via the supply line, and letting the pressure act on the TH un-lock ring-piston, so that increased hydraulic force will break the shear-pins that extend into the slits in the TH un-lock ring-piston from the retainer ring of the collet fingers;

[0072] - whereby displacement of the TH un-lock ring-piston towards its end position will carry the TH RET latch ring-piston with it, in that the coupling pins between the TH un-lock ring-piston and the THRET latch ring-piston, that extend from the TH unlock ring-piston, into slits in the THRET latch ring-piston, will abut against the upper slit edge. This will also break the shear-pins between the latch ring-piston and the upper body, and;

[0073] - the joint movement of the TH un-lock ring-piston and the THRET latch ring-piston will cause the tip of the latch ring-piston to be pulled out of its wedged position behind the split-ring, thus releasing the THRET from the stuck TH, and;

[0074] - with the TH un-lock ring-piston displaced to its upper end position, the collet fingers will now be free to bend inwards, as the tip of the collet fingers will slide past the edge of the locking groove inside the stuck TH lock sleeve, when the released THRET is pulled out of the tubing hanger, and to the surface.

[0075] Disclosed herein is further steps for un-latching a THRET from a successfully recovered tubing hanger: a) Removal of the, in this case, intact shear-pins between the THRET latch ring-piston and the THRET upper body, and; b) by means of “tool-bolts”, screw back the spring-loaded locking bolts in the TH un-lock ring-piston from engagement with the circumferential locking groove around the upper THRET body, and; c) temporarily install a jack pin, and jack the THRET latch ring-piston so that the tip of the latch ring-piston will be pulled out of its wedged position behind the split-ring, so that it disengages with the internal locking groove in the tubing hanger, and; d) pressurize the vent side of the TH un-lock ring-piston to a pressure below the cracking pressure of the vent check valve. The resulting TH un-lock ring-piston stroke will cause the tip of the TH un-lock ring-piston to be moved past the tip of the collet fingers. They will then be free to bend inwards when they slide across the edge of the groove inside the TH lock sleeve, during separation of the THRET from the recovered TH. In the following, a device, and a method for tubing hanger retrieval from a wellhead or X- mas tree is described, wherein:

[0076] Fig. 1 A-C schematically illustrates a simplified example of a tubing hanger installed in a wellhead or X-mas tree, the BOP stack, the marine drilling riser, and the vessel. The figure also shows a simplified landing string with a tubing hanger retrieval tool, THRET, with the outline of closed BOP pipe-rams, and a closed-in BOP annular space.

[0077] Fig. 2 illustrates a subsea BOP stack with C&K lines, BOP rams, and a simplified landing string with a tubing hanger retrieval tool (THRET), connected to a tubing hanger (TH). The wellhead or X-mas tree is not shown.

[0078] Fig. 3 shows a cross-sectional view of a THRET, with the outline of closed BOP pipe-rams and a closed-in BOP annular space.

[0079] Fig. 4 A-C shows the steps of latching the THRET to a TH.

[0080] Fig. 5 A-C shows the THRET, latched onto the TH. A detailed view of the relevant components, prior to the un-lock sequence for the TH are shown in figure 5B. Fig. 5C shows dump of the swept TH un-lock ring-piston volume into the THRET centre bore, through a vent check valve.

[0081] Fig. 6 A-D shows cross-sectional views of a THRET and the upper part of a TH, illustrating the steps of un-locking of the TH from a wellhead or X-mas tree.

[0082] Fig. 7 A-C shows cross-sectional views of a THRET and a TH, illustrating a contingency THRET un-latch operation, in case the TH is stuck, and cannot be released with the THRET.

[0083] Fig. 8 A-F shows cross-sectional views of a THRET and the upper part of a TH, illustrating the steps of post TH retrieval separation of a THRET from a recovered TH.

[0084] Any positional indications refer to the position shown in the figures.

[0085] In the figures, same or corresponding elements are indicated by same reference numerals. For clarity reasons, some elements may in some of the figures be without reference numerals.

[0086] A person skilled in the art will understand that the figures are just principal drawings. The relative proportions of individual elements may also be distorted. In figure 1A, reference number 1 indicates in a simplified manner a landing string having a portion arranged inside a BOP 2 shown in for example fig. 1B. The landing string 1 is provided with a tubing hanger retrieval tool (THRET) 3, to be latched onto a tubing hanger 5 inside a wellhead 7, as illustrated in fig. 1 B, alternatively inside a horizontal X-mas tree 9, with a BOP 2 connected at the top, as illustrated in fig. 1C.

[0087] Fig. 1B illustrates installation of the THRET 3 from a vessel 11 through a marine drilling riser 13, exposed to open sea. A work-string 15 is arranged inside the drilling riser 13, with the THRT 3 extending into the BOP 2. The marine drilling riser 13 is shown as skewed, to illustrate external loads and bending. It is provided with so-called flex joints 17 and 19 in the upper and lower ends, respectively. The flex joints will unload the bending moment on the marine drilling riser 13. A bending of the drilling riser 13 will cause an internal umbilical (not shown), clamped to the work-string 15, to be particularly exposed to damage in the upper and lower ends of the riser. Other challenges are the marine drilling riser's 13 slip joint 21 and the opening in the drill floor 23, where the umbilical will be exposed to wear caused by movement. One measure to protect an umbilical would be to insert centralising clamps (not shown). However, such centralising clamps are exposed to loads that may cause damage to the centraliser clamps such that parts might come loose and drop down to the BOP 2. Loose parts from broken centralising clamps, or normal umbilical clamps (not shown) would have to be "fished out" with time-consuming methods, and specialised equipment that forms part of a so-called wireline operation. The consequence will be expensive delays in operations.

[0088] It is therefore preferable to introduce a new solution and method for installing and retrieving production tubing, to eliminate the umbilical for these operations. This will also increase the efficiency of the operations.

[0089] Fig. 1A shows in more detail an outside view of the THRET 3, with the outline of a closed set of pipe rams 29, and a closed-in BOP annular space 27, enclosing a portion of the THRET 3, when the THRET 3 has been fully landed onto a TH 5 in a wellhead 7 (see fig. 1 B), or a X-mas tree 9 (see fig.1 C).

[0090] Reference is now made to figure 2. The present invention is a solution based on a combination of work-string rotation, and hydraulic energy for operation of the THRET 3 functions for tubing hanger 5, and downhole production tubing string 25 recovery, being supplied through pressurisation from surface of the closed-in BOP annular space 27 below the pipe ram 29 in the BOP 2, through a fluid supply line 31. Reference is made to figure 3, showing a cross-section of the THRET 3, configured for deployment. A tubing hanger un-lock ring-piston 33 and a latch ring-piston 35 for THRET 3 latch onto a TH 5, (see figures 1 B and 1C) are kept in an upper, non-engaged position by means of shear-pins 37. The components are exposed to a confined pressure in the closed-in annular space 27 which will be formed when the pipe rams 29 of the BOP are clamped in a sealing manner around a landing string 1 adapter part 39.

[0091] Figure 4A shows a cross-section of the THRET 3 fully oriented and landed into the TH 5, but not yet latched to the TH 5.

[0092] Figure 4B shows in further detail an initial position of a tip of a plurality of collet fingers 41 (two shown) extending from a retainer ring 42, the TH un-lock ring-piston 33 and the latch ring-piston 35, prior to latch of the THRET 3 onto the TH 5. A lower body 43 of the THRET 3 is now inhibited from rotation, since the THRET 3 is fully landed in the TH 5, with TH orientation and anti-rotation elements 44 engaged with corresponding, vertical grooves 45 in the TH 5, as shown in fig. 1A.

[0093] The work-string 15 is turned, typically with three turns in the clockwise direction in the embodiment shown, whereby the THRET 3 upper body mandrel 46 is screwed down on a threaded section at a top end portion of the THRET lower body 43. This will break shearpins 37 that have initially kept the un-lock ring-pistons 33 and latch ring-piston 35 in a nonengaged position.

[0094] While figure 4B shows the initial position, fig. 4C shows the end-position of the THRET 3 when fully latched onto the TH 5. The TH un-lock ring-piston 33 and the THRET latch ringpiston 35, together with the collet fingers 41 of the THRET 3 have been moved along with the axial displacement of the THRET upper body mandrel 46, as it was screwed down onto the THRET lower body 43. In the position shown in fig. 4C, the tip of the collet fingers 41 are urged radially inwards as they slide along a groove edge inside the TH lock sleeve 47, before they spring back and engage a locking groove 49 on an inside of the TH lock sleeve 47. At the same time, a lower tip portion of the THRET latch ring-piston 35 is forced downwards and radially expands a split-ring 51 on the THRET lower body 43, so that it engages mating, inner ring grooves 53 of the TH 5. An internal ratchet latch 55 (shown in figures 4B and 4C) comprises a first part arranged in a bottom of the THRET upper body mandrel 46, and a mating second part arranged in a top portion of the THRET lower body 43, is engaged when the THRET upper body mandrel 46 has bottomed-out against the THRET lower body 43. The joined ratchet latch 55 is configured to prevent unintentional back-rotation of the upper body mandrel 46. The THRET 3 is subjected to an overpull test through the work-string 15, with a typical load of 50 Metric ton, to verify successful latch of the TH RET 3 to the TH 5.

[0095] Figure 5A shows the THRET 3 latched onto the TH 5. A detailed view of the relevant components, prior to the TH 5 un-lock operation sequence, is shown in figure 5B.

[0096] Reference is now made to figure 3. The pipe ram 29 is closed in a sealing manner around the slick adapter 39 of the landing string 1. The closed-in annular space 27 in the BOP 2 is pressurized from the surface, through a supply line 31 (see fig. 2), to stroke the TH unlock ring-piston 33 upwards, with an actuation pressure of typically maximum 250 Bar.

[0097] Fig. 5A, shows the starting point of the TH un-lock ring-piston 33 up-stroke, with a detail view of the main components in fig. 5B. A fluid within an annulus 57, defined by a top of the TH un-lock ring-piston 33, the THRT upper body mandrel 46, and the THRET upper body housing 48, is vented into a centre bore 59 of the THRET 3, via a vent check valve 61 , as shown in fig. 5C.

[0098] The further TH 5 un-lock sequence is shown in figures 6A, 6B and 6C. Figure 6A shows the starting point of the TH un-lock ring-piston 33 up-stroke. As shown in figure 6B, the TH 5 un-lock ring-piston 33 up-stroke, driven by the actuating pressure in the closed-in BOP annular space 27, will break shear-pins 63 of the THRET upper body mandrel 46.

[0099] With reference to the figures 6C and 6D, a plurality of shear-pins 65 is arranged through the retainer ring 42 of the collet fingers 41 , wherein each shear-pin 65 protrudes into a respective slit 67 and is configured to slide along the respective slit 67 at the start of the TH un-lock ring-piston 33 up-stroke, until a lower end of the slits 67 stop against the shear-pins 65 of the collet finger retainer ring 42.

[0100] As shown in figures 6B and 6C, during the up stroke of the TH 5 un-lock ring-piston 33, a lower tip portion of the TH 5 un-lock ring-piston 33 will now be positioned radially inwards of the tip of the collet fingers 41 , that engage the locking groove 49 inside the TH lock sleeve 47. The collet fingers 41 will thus be prevented from bending inwards and will be kept engaged with the locking groove 49 during the continued up-stroke, thereby pulling the TH lock sleeve 47 out of engagement inside the TH locking segments 69, as shown in fig. 5A.

[0101] When the TH lock sleeve 47 has been fully retracted, as shown in fig. 6C, a plurality of spring-loaded locking bolts 71 (one shown) in the TH 5 un-lock ring-piston 33 will spring into engagement with a locking groove 73 arranged circumferentially in the THRET upper body mandrel 46. When the TH lock sleeve 47 has been fully retracted, as shown in fig. 6C and 6D, an external ratchet latch 75 configured to I be bent radially outwards during the ring-piston 33 up-stroke, will spring into engagement with a groove 76 arranged circumferentially in the retainer ring 42 of the collet fingers 41. When being in engagement with the groove 76, the external ratchet latch 75 will keep the joined TH un-lock ring-piston 33, the collet fingers 41 , and the fully retracted TH lock sleeve 47, in the upper, TH un-lock position.

[0102] For normal TH retrieval operations, a plurality of coupling pins 77, one shown in fig. 6C, will protrude into, and slide along respective slits 79 in the THRET latch ring-piston 35, thereby allowing a limited upwards stroke of the tubing hanger un-lock ring-piston 33, which is required for TH 5 un-lock. Relative movement between the engaged THRET latch ring-piston 35 and the TH un-lock ring-piston 33, during the TH 5 un-lock operation, can be seen by comparing fig. 6A with fig. 6C.

[0103] With successful TH 5 un-lock and pull to surface of the production tubing hanger and downhole production tubing string 25, the joined THRET 3 and TH 5 will be disconnected from the work-string 15 and the production tubing string 25. The THRET 3 will subsequently be manually released from the TH 5.

[0104] If the TH lock sleeve 47 is stuck, and the TH 5 cannot be retrieved with the THRET 3, the tool must be unlatched from the TH 5 and recovered to the surface through a contingency operation. The starting position for this scenario is shown in figure 6B, i.e. , the TH lock sleeve 47 is connected to the tip of the collet fingers 41 which engage the circumferential locking groove 49, and the tip of the TH un-lock ring-piston 33 will keep the collet fingers 41 in place in the locking groove 49. As shown in detail in fig. 6D, the shear-pins 65 of the collet finger retainer ring 42 are now abutting against the lower end of the corresponding slits 67 in the un-lock ring-piston 33.

[0105] The THRET 3 is configured to facilitate a contingency mode operation, where the TH 5 un-lock ring-piston 33 will be subjected to a higher pressure which will break the shearpins 65, whereby the TH 5 un-lock ring-piston 33 will be fully stroked to its end-position. As shown in figures 7A and 7B, the TH 5 un-lock ring-piston 33 will carry the THRET latch ring-piston 35 upwards, so that the lower tip portion of the latch ring-piston 35 will be pulled out of its wedged position between the TH lower body 43 and the split-ring 51 , which wedged position locked the THRET 3 to the TH 5.

[0106] The contingency operation will be initiated with pressurization of the closed-in BOP annular space 27 to typically 330 Bar. The TH un-lock ring-piston 33 will then be stroked to its end position. The fluid within the annulus 57 will be vented into a bore 59 of the THRET 3, via a vent check valve 61 , as shown in fig. 7C. The TH un-lock ring-piston 33 up-stroke will break shear-pins 81 extending through the latch ring-piston 35and into engagement with the TH RET upper body mandrel 46, and also the collet finger retainer ring 42 shearpins 65 abutting against the lower end of the corresponding slits 67 in the TH un-lock ringpiston 33 shown in fig. 6D.

[0107] Reference is made to figure 7B. Each one of the plurality of coupling pins 77 protrude into and abut against an upper end of the respective slit 79 in the THRET 3 latch ring-piston 35. The TH un-lock ring-piston 33 up-stroke will thus carry the THRET latch ring-piston 35 upwards, so that the lower tip portion of the latch ring-piston 35 will be pulled out of its wedged position between the TH lower body 43 and the split-ring 51 .

[0108] When the split-ring 51 no longer engages the corresponding, inner, circumferential groove 53 of the TH 5, the TH RET 3 can be pulled out of the stuck TH 5. Since the TH 5 un-lock ring-piston 33 has been subject to a complete up-stroke, the collet fingers 41 will be free to bend radially inwards, as the tip of the collet fingers 41 will slide across the circumferential groove edge inside the stuck TH lock sleeve 47, as the un-latched THRET 3 is pulled out of its engagement with the TH 5 and hoisted to the surface with the work-string 15.

[0109] Reference is now made to the figures 8A-8F, showing the steps involved in separation of a THRET 3 from a TH 5, after a successful TH 5 retrieval operation. The joined THRET 3 and TH 5 will be disconnected from the production tubing string 25 and the work-string 15 at the drill-floor and moved to a suitable location for disassembly.

[0110] The figures 8A-8B show the initial step of removing the, in this case, intact shear-pins 81 of the THRET latch ring-piston 35 from the upper body mandrel 46. Figure 8A shows a cross section view of the THRET 3, and fig. 8B shows an outside detail view of the latch ring-piston shear-pin 81 to be removed.

[0111] Reference is now made to fig. 8C. Separate bolts 83, typically M6 x 60mm, with washer, are brought into engagement with the spring-loaded locking bolts 71 in the TH 5 un-lock ring-piston 33, so that locking bolts 71 are withdrawn from their engagement with the circumferential groove 73 in the THRET upper body mandrel 46.

[0112] Reference is now made to fig. 8D and 8E. With the latch ring-piston shear-pin 81 removed, an un-latch jack pin 85 is temporarily installed. The THRET latch ring-piston 35 is jacked back, to pull the tip of the ring-piston 35 out of its wedged position behind the splitring 51 , so that it will no longer engage the inner ring grooves 53 of the TH lock sleeve 47.

[0113] Reference is made to fig. 8F. The tubing hanger un-lock ring-piston 33 is pressurized on the vent side by a pressure being lower than a cracking pressure of the vent check valve 61. The resulting TH un-lock ring-piston 33 down-stroke causes the tip of the un-lock ringpiston 33 to be moved back, past the tip of the collet fingers 41 , so that they are free to bend inwards, as they slide across the circumferential groove edge inside the TH lock sleeve 47 when the THRET 3 is pulled-out of the recovered TH 5. The THRET 3 is now ready for further dis-assembly, refurbishment, and preparation for a new TH retrieval operation.

[0114] Necessary seals are not described but are known to a skilled person.

Claims

P a t e n t c l a i m s1. Tubing hanger retrieval tool (3) for engaging a tubing hanger (5) from a subsea wellhead (7) or a subsea X-mas tree (9), c h a r a c t e r i z e d i n that the tubing hanger retrieval tool (3) comprises:- an upper body mandrel (46) for operation by a work string (15), a lower body connected to the upper body mandrel (46), wherein the upper body mandrel (46) is axially displaceable with respect to the lower body (43) from a first position to a second position ;- a latch ring-piston (35), an un-lock ring-piston (33), and a plurality of axially displaceable collet fingers (41) movable together with the upper body mandrel (46) from the first position to the second position, and releasably interconnected by means of shearable looking pins (37, 63, 65, 81); wherein:- a lower end portion of the latch ring-piston (35) is configured to radially expand a split ring (51) arranged on the lower body (43) and, in a position of use of the tubing hanger retrieval tool (3), into engagement with an inner ring groove (53) of a tubing hanger (5);- the collet fingers (41) extending from a retainer ring (42), wherein the collet fingers (41) are configured for engaging a locking groove (49) in a tubing hanger lock sleeve (47);- the un-lock ring-piston (33) has a portion configured for, in a position of use of the tubing hanger retrieval tool (3), being subject to an activation fluid having a first pressure, wherein the activation fluid is communicated from a closed-in annular space (27) of a BOP (2) to break shear pins (63) initially connecting the un-lock ring-piston (33) to the upper body mandrel (46), whereby the un-lock ring-piston (33) is axial displaceable relative to the collet fingers (41) to a position wherein a lower portion of the un-lock ring-piston (33) abuts against the collet fingers (41), thereby preventing disengagement of the collet fingers (41) from the tubing hanger lock sleeve (47); and- a ratchet latch (75), configured for engaging a groove (76) in the retainer ring (42) when the collet fingers (41) are prevented from disengagement from the tubing hanger lock sleeve (47).

2. Tubing hanger retrieval tool (3) according to claim 1, wherein the upper body mandrel (46) is threadedly connected to the lower body (43) so that the lowerbody is axially displaceable with respect to the lower body (43) by rotating the upper body mandrel (46).

3. Tubing hanger retrieval tool (3) according to claim 2, further comprising an internal ratchet latch (55) configured for preventing back-rotation of the upper body mandrel (46), the ratchet latch (55) comprising a first part arranged in a bottom of the upper body mandrel (46), and a mating second part arranged in a top portion of the lower body (43), wherein the first part is in engagement with the second part when the upper body mandrel (46) is in the second position.

4. Tubing hanger retrieval tool (3) according to any one of the preceding claims, wherein the retainer ring (42) is connected the un-lock ring-piston (33) and the latch ring-piston (35) by means of a plurality of shearable locking pins (65) extending into respective slits (67) in the un-lock ring-piston (33), wherein the locking pins (65) are designed to withstand the first pressure of the activation fluid, but break when subjected to a second pressure being higher than the first pressure, wherein broken locking pins (65) allow the un-lock ring-piston (33) and the latch ring-piston (35) to move to the first position, thereby disengaging the lower end portion of the latch ring-piston (35) form the split ring (51), thereby allowing disengagement of the tubing hanger retrieval tool (3) from a stuck tubing hanger (5).

5. Method for connecting the tubing hanger retrieval tool (3) according to any one of the preceding claims, to a tubing hanger (5) and an associated production tubing string (25) from a wellhead (7), or a X-mas tree (9), c h a r a c t e r i z e d i n that the method comprising the following steps: a) by means of a work string (15), lowering the tubing hanger retrieval tool (3) with the upper body mandrel (46), the un-lock ring-piston (33), the latch ring-piston (35) and the collet fingers (41) being in the first position, and orienting and landing the tubing hanger retrieval tool (3) in the tubing hanger (5); b) initiating latch of the tubing hanger retrieval tool (3) to the tubing hanger (5), by rotating the work-string (15) to break the shear pins (37) so that the upper body mandrel (46), the un-lock ring-piston (33), the latch ring-piston (35), and the collet fingers (41) are moved from the first position to the second position;whereby the collet fingers (41) spring into engagement with an internal, encircling locking groove (49) in the tubing hanger lock sleeve (47), and; the lower end of the latch ring-piston (35) is wedged between the lower body (43) and the split-ring (51), thereby expanding the split-ring (51) so that it locks into a circumferential, inner locking ring groove (53) in the upper part of the tubing hanger (5); c) pressurization of the BOP annular space (27) via a supply-line (31), so that; the first pressure acts on the un-lock ring-piston (33) and displaces it in an upwards stroke, and lower edge of slits (67) in the un-lock ringpiston (33) hits shear-pins (65), that extend into the slits (67) from the retainer ring (42), and a relative movement of the un-lock ring-piston (33) with respect to the collet fingers (41) which are connected to the retainer ring (42), stops, and; the lower portion of the un-lock ring-piston (33) abuts a lower portion of the collet fingers (41), thereby preventing disengagement of the collet fingers (41) from the tubing hanger lock sleeve (47) during the further un-lock ring-piston (33) movement towards the first position, and; the continued stroke of the un-lock ring-piston (33) causes the upper body mandrel (46) shear-pins (63) to break, and; the combined vertical displacement of the un-lock ring-piston (33) and the collet fingers (41) pulls the tubing hanger lock sleeve (47) out of locking engagement with locking segments (69) of the tubing hanger (5), and further, into complete retraction;- whereby spring-loaded locking bolts (71) in the un-lock ring-piston (33) engage a locking groove (73) which encircles the upper body mandrel (46), and; the ratchet latch (75) springs into locking engagement with the groove (76) on the outside the retainer ring (42) of the collet fingers (41), thereby keeping the tubing hanger lock sleeve (47) in its fully retracted position.

6. The method according to claim 5, further comprising in a step d) pulling the tubing hanger retrieval tool (3), the released tubing hanger (5), and a production tubing string (25) to the surface by means of the work-string (15).

7. The method according to claim 6, further comprising disconnecting the tubing hanger retrieval tool (3) from the tubing hanger (5) at surface by the following steps; e) removal of shear-pins (81) connecting the latch ring-piston (35) to the upper body mandrel (46); f) disengage the spring-loaded locking bolts (71) in the un-lock ring-piston (33), from the circumferential locking groove (73) in the upper body mandrel (46); g) temporarily install a jack pin (85), and jack the latch ring-piston (35) so that the lower end of the latch ring-piston (35) is pulled out of its wedged position between the lower body (43) and the split-ring (51), so that the split-ring (51) disengages with the internal locking groove (49) in the tubing hanger lock sleeve (47); and h) pressurize a vent side of the un-lock ring-piston (33) with a pressure below a cracking pressure of a vent check valve (61), whereby a resulting un-lock ringpiston (33) stroke causes the lower portion of the un-lock ring-piston (33) to move past the lower portion of the collet fingers (41), which then bend inwards when they slide across an edge of the locking groove (49) inside the tubing hanger lock sleeve (47) during separation of the tubing hanger retrieval tool (3) from the recovered tubing hanger (5).

8. The method according to claim 5, further comprising disengaging the tubing hanger retrieval tool (3) from a stuck tubing hanger (5) by means of:- increasing a pressure in the BOP annular space (27) to a second pressure being higher than the first pressure, the second pressure being sufficient to break the shearable locking-pins (65) extending into respective slits (67) in the un-lock ring-piston (33), whereby:- whereby displacement of the un-lock ring-piston (33) towards first position will carry the latch ring-piston (35) with it, in that coupling pins (77), arranged between the un-lock ring-piston (33) and the latch ring-piston (35), and extend from the un-lock ring-piston (33) into slits (79) in the latch ring-piston(35), abut against an upper slit edge, thereby also break shear-pins (81) between the latch ring-piston (35) and the upper body mandrel (46);- the joint movement of the latch ring-piston (35) and the un-lock ringpiston (33) causes the lower portion of the latch ring-piston (35) to be pulled out of its wedged position between the lower body (43) and the split-ring (51), thereby releasing the tubing hanger retrieval tool (3) from the stuck tubing hanger (5); and- with the un-lock ring-piston (33) displaced to its upper end position, the collet fingers (41) are free to bend inwards, as the lower end portion of the col- let fingers (41) slide past an edge of the locking groove (49) on the inside of the stuck tubing hanger lock sleeve (47), when the released tubing hanger retrieval tool (3) is pulled out of the tubing hanger (5), and to the surface.

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