A system and a method for re-entering a previously abandoned offshore well

Abstract

A method and a system 100 for re-entering a previously abandoned offshore well. A seabed location is identified that is above the well to within a tolerance. A support frame 110 is lowered onto the seabed location. A guide 120 is moved into position relative to the support frame 110, until the guide 120 is directly centred above the well. Thus, the well can be re-entered using one or more tools (400 and 410), each of which can be received by the guide 120.

Description

[0001] A SYSTEM AND A METHOD FOR RE-ENTERING A PREVIOUSLY ABANDONED OFFSHORE WELL

[0002] Technical Field

[0003] This disclosure relates to well re-entry. In particular, this disclosure relates to a system and method for re-entering a previously abandoned offshore well. Disclosure is provided of a means and method of re-entering and securing a previously abandoned oil and gas well, in order to repurpose or use the formation(s) that the well enters or passes through, for example, to store carbon dioxide or hydrogen within the legacy oil and gas formation and / or the saline aquifer that may be present above or below the oil and gas formation.

[0004] Background

[0005] Access to a subsea oil and gas reserves is achieved by drilling and installing pipes subsurface, in order to drill one or more well(s), so that the oil and / or gas deposits can be explored, apprised or extracted. Once exploration, appraisal or production activities have been completed, the well(s) are typically closed up and abandoned. Often these abandonment activities have not or do not consider the future use of the oil and gas formation or saline aquifer that the well enters or passes through in regards to utilisation as a carbon dioxide (CO2) or hydrogen storage site.

[0006] The exploration, appraisal and production wells associated with oil and / or gas activities typically involves drilling a number of wells, in order to access the oil and gas reserve that lies in rock formations beneath the seabed. The wells may pass through multiple layers of cap rock and saline aquifer(s) and other zones, before the oil and gas reserve is reached. After the exploration, appraisal or production activities have ceased, the reservoir and other formations are typically plugged, so that the well can be permanently abandoned and the well mechanically or explosively cut just above, at or below the seabed with no means to vertically re-enter the now abandoned well. Legacy wells may introduce leak paths from the oil and gas formation or saline aquifer that the well enters or passes through, which should be addressed to prevent the legacy well from contaminating the environment with naturally present fluids or gases or where these formations are being utilisation as a carbon dioxide (CO2) or hydrogen storage site.

[0007] FIG. 1 illustrates a cross section through the earth’s crust, showing a legacy subsea well which has been abandoned once the oil & gas (O&G) reserve became depleted. The O&G reserve was accessed by passing through a layer of cap rock, a saline aquifer, and another layer of cap rock. This legacy well was abandoned leaving a pipe that was severed below the mudline.

[0008] The inset image in FIG. 1 illustrates a path for gas to escape from the legacy well. Problems are encountered on previously abandoned legacy wells as they can present a communication pathway and weak spot through subsurface formations, in particular;

[0009] • The formation that the legacy well enters or passes through is being used or assessed for use as a CO2 or hydrogen storage site as the zonal isolation and or the plugs may not have been designed to suit this application or seal off specific zones that may now be of interest as a CO2 or hydrogen storage formation.

[0010] • Assessment has determined that the risk of deterioration of zonal isolation, plugs or well bore elements such as cement and steel has or might be affected by corrosion or contact with CO2 or hydrogen or other drivers or degeneration of competence.

[0011] • A leak or subsurface communication or influx has been identified, either during injection or storage or as a result of a failure of the original abandonment where no injection or storage has been performed or planned.

[0012] A single legacy well that enters or passes through a potential CO2 or hydrogen storage formation target could mean that unless it is re-abandoned with suitable zonal isolation and / or suitable materials and plugs, the entire site may not be technically or commercially feasible. Alternative methodologies, such as intersect / relief well drilling can have technical limitations especially where the well location is unknown, or its subsurface trajectory is unknown or a shallow intersect is to be completed, above the area that requires re-abandonment, where the subsurface conditions may not support. Furthermore, alternative techniques can have economic constraints because such processes are extremely expensive.

[0013] Sealing the well before it is abandoned prevents pollution from leaking into the maritime environment above the well, although the quality of sealing these legacy wells depends upon the methods used, which have varied over time with advances in technology and changes to regulations. Further the materials used may not be suitable for contact with storage fluids and gases such as CO2 or Hydrogen for example and also may not have attempted or considered to isolate a particular zone (such as a saline aquifer) that is now of interest as a storage formation for CO2 or Hydrogen for example. The principles of carbon capture and storage (CCS) are well-proven, having been utilized for many years by oil and gas operators for EOR (enhanced oil recovery). Worldwide, the number of CCS projects starting up is increasing everyday as industry and governments drive forward the energy transition. The growing demand for preventing greenhouse gasses from being released into the atmosphere has increased the focus on CCS technology, in order to ensure compliance with the Paris agreement climate goals. A CCS solution is for CO2 to be stored away from the atmosphere in subsurface formations, for example, in legacy oil and gas formations and saline aquifers. Previous oil wells are well-known as having been able to store hydrocarbons for millions of years. Therefore, storing greenhouse gases in legacy oil and gas reservoirs or saline aquifers provides a CCS solution that is safe as well as reliable on a geological time frame.

[0014] The quality of the plugging of the legacy well(s) may not be sufficient, or the abandonment configuration may not be suitable for the change of usage of the existing reservoir or saline aquifer (e.g. existing legacy well plugs may not be located to stop leak paths of the CO2 and / or materials used may not be suitable for contact with Hydrogen or CO2). As a result, there is often a demand to reopen these legacy wells and then reseal them more securely, so that storage gases and fluids do not leak once they are injected into the CCS reservoir.

[0015] Legacy oil and gas fields are often considered good carbon storage locations. CO2 is seen as a waste product therefore cost is critical to making a storage site viable. Legacy production or exploration wells may compromise the security of the formation where CO2 will be stored, become a liability, and reduce the economics of a storage site. Challenges encountered in reabandoning legacy wells include:

[0016] • Legacy wells are not designed to be re-entered.

[0017] • Location of legacy wells may be uncertain or unknown.

[0018] • Location of well centre and depth to casing may not be known.

[0019] • Condition of casing / conductor is unknown and therefore should be isolated from various loads.

[0020] • Cement and casing pipe clean up are to be performed.

[0021] • There may be multiple cut points from successive explosive ordnances.

[0022] • Condition of external conductor or casing may be weak.

[0023] • Plug placement may be unknown. • Seabed stability may increase the likelihood of the legacy well being damaged, or becoming damaged if disturbed.

[0024] Summary

[0025] Aspects of the present invention are set out by the claims. Further aspects are also described.

[0026] According to a first aspect, disclosure is provided of a method for re-entering a previously abandoned offshore well. The method comprises identifying a seabed location that is above the well to within a tolerance, lowering a support frame onto the seabed location, moving a guide into position relative to the support frame and the well, and re-entering the well using a tool which is received by the guide.

[0027] An advantage of providing a guide that can be moved relative to the support frame is that a tolerance is available to correct location of the seabed onto which the support frame has been lowered, so that the guide is precisely positioned directly above the well. As a result, the support frame can be lowered into position before the location of the well has been precisely identified. Including this tolerance makes it more likely that the support frame will be positioned in the correct place, while ensuring that there is tolerance for re-entering the well at the correct location. Tools which may be received by the guide may include one or more of:

[0028] • A milling conduit which can be used to transfer load forces away from the well into the support frame. The milling conduit typically has a mule shoe which is used to bury the milling conduit into the seabed and guide tooling toward the legacy well centre. Note that it’s possible that the milling conduit is not needed in some applications.

[0029] • A muleshoe stinger, which serves to provide an environmental barrier, which allows circulation and isolation from the surrounding seawater. The muleshoe stinger also functions to prevent sediment and / or debris from re-entering the cleared well bore. Note that it’s possible that the muleshoe stinger is not needed in some applications.

[0030] • A BHA (Bottom Hole Assembly) which can be used to drill down to the legacy well among other downhole applications.

[0031] The milling conduit never enters the legacy well. It is intended to remain just above to provide support to milling and help guide the mule shoe stinger / environmental barrier into the legacy well. There are also scenarios where the milling conduit can pass over the top of the legacy well encompassing it for a distance, this is more feasible in wells which have been mechanically severed. Both the milling conduit and the environmental barrier are received by the guide.

[0032] There are multiple potential applications of this innovation, some examples are that the legacy well may be re-abandoned (e.g., removing the current abandonment configuration and replacing with another), turned into a monitoring well, or turned into an injection well or simply re-abandoning a previously abandoned well as it is leaking or has the potential to leak.

[0033] Optionally, the method further comprises substantially diverting re-abandonment operational loads away from the well and into the support frame and seabed. Advantageously, the support frame allows the well to be re-entered and re-abandoned while preventing operational loads from causing damage to the legacy well.

[0034] Optionally, the method further comprises re-configuring or enhancing the abandonment of the well to bring the well in line with selected specifications (e.g., current standards / codes / practices), and re-abandoning the well. An advantage of enhancing the abandonment / well barriers before it is subsequently re-abandoned is that leakages can be prevented. Thus, the structural integrity abandonment strength of the well can be enhanced, with a potential example application being that this facilitates the use of an aquifer or a reservoir that is below the seabed for the storage of fluids and gases such as CO2 and Hydrogen for example. Furthermore, enhancing the strength of the abandonment of the well may ensure that the well can be reabandoned so that it is in compliance with standards that have improved since the well was abandoned originally.

[0035] Optionally, the method further comprises re-configuring or enhancing the abandonment of the well to provide zonal isolation across formations that the well passes through or enters. Providing zonal isolation which was not included during the previous abandonment will allow isolation of the various formations from each other or back to the seabed or surface. An example of this is installing zonal isolation to facilitate use of the saline aquifer as a CO2 storage location, where previously the saline aquifer was not independently isolated.

[0036] Optionally, the method further comprises repurposing one or more formations that the well enters or passes through. Advantageously, the one or more formation can be repurposed for applications such as the storage of gases and fluids (e.g., carbon dioxide or hydrogen). Thus, a formation, such as an aquifer or a reservoir, may be used as a temporary or permanent store. According to a second aspect, disclosure is provided of a system for re-entering a previously abandoned offshore well. The system comprises support frame configured to be lowered onto a seabed location identified as being above the well to within a tolerance, and a guide configured to be moved into position relative to the support frame, before a tool for re-entering the well is received by the guide.

[0037] Advantageously, an apparatus is provided for re-entering a legacy well. Thus, disclosure is provided of apparatus which is configured to implement the above method. Typically, the guide and the support frame are integral to one another, forming a single system which can be lowered into position. The guide may also be referred to as a slot.

[0038] Optionally, the system further comprises a well marker configured to confirm the seabed location prior to deployment of the support frame. Advantageously, the well marker identifies the location of the well, so that it can be efficiently identified where the support frame should be lowered. The well marker typically is a jetted pipe that tags or enters or stops just above the well positioned concentrically. Once installed subsurface scans using, for example, sub bottom profiling or imaging can be utilised to confirm positional accuracy or if off centre facilitate the re-positioning of the well marker until confirmed within the circumference of the well pipe proximity.

[0039] Optionally, the guide is configured to transfer load forces away from the well via the support frame. Advantageously, the system functions during use to dissipate forces away from well, into the support frame, and through to the seabed. The condition of a legacy pipe of the well may have deteriorated, or be unknown, and so the system protects the legacy well from being damaged.

[0040] Optionally, the guide is configured to receive and retain a tool configured to transfer the load forces away from the well via the support frame. Advantageously, once installed, the tool serves to transfer load forces away from the well into the guide. These load forces are dissipated away from the legacy well, through to the support frame, and into the seabed. The guide has a dual purpose, such that firstly during installation the guide can be moved relative to the well to ensure that that guide is centrally positioned above the well, and secondly it helps to transfer the load away from the well via the support frame. Optionally, the system further comprises an alignment mechanism configured to move the guide relative to the support frame and the legacy well. Advantageously, an integrated system is provided which includes the support frame, the guide, and the alignment mechanism. This allows this system to be lowered into position in a single step. Once the system has been lowered into position, the alignment mechanism can be used to move the guide into a precise location that is directly above the well.

[0041] Optionally, the guide is configured to be moved laterally with respect to the support frame. Advantageously, a tolerance in the x-y position is available for precisely aligning the guide so that it is directly above the well.

[0042] Optionally, the system further comprises a measuring device configured to be retained within the well before the well is re-abandoned. Advantageously, the optional measuring devices (for example passive seismic measuring devices or gas monitoring sensors) can be used to monitor the well before and / or after the well is abandoned.

[0043] Optionally, the system is configured to be reusable. Advantageously, providing a reusable system ensures that the system can be used for re-entering a number of previously abandoned offshore wells. The reuse of apparatus enhances the environment and reduces costs by preventing wastage of materials. The apparatus is not discarded on the seabed after use, and so it does not present a hazard to marine life or vessels once the well has been re-abandoned. Accordingly, the system may be referred to as a recoverable abandonment frame (RAF) system.

[0044] Optionally, the system further comprises a plurality of pile guides, each of which is configured to receive and retain piles or ballast that secure the support frame to the seabed location. Advantageously, the pile guides allow the system to be securely attached to the seabed, so that forces can be dissipated away from the legacy pipe, and into the piles. This feature is optionally, because in some environmental conditions or locations, the system can act as a gravity based or ballasted structure, which removes any requirement for piling or additional ballast of the support frame into the seabed.

[0045] Optionally, the system further comprises a mudmat configured to serve as a base of the support frame once the support frame has been lowered onto the seabed location. Advantageously, the mudmat provides a surface for resting subsea equipment, so that it doesn’t sink into the mud. The mudmat also serves to provide stability to the system before pile installation. The mudmat and the primary frame can be lowered to the seabed together in a single lift. Providing a mudmat that is detachable provides the functionality that the mudmat can be secured in place before adding the weight of the support frame. The mudmat is typically detachable, so that it may be lowered onto the seabed location in separate lift, before the support frame is lowered onto the seabed location. The size and / or dimensions of the mudmat may be configurable for site specific requirements, and may have the ability to be installed with ballast.

[0046] Optionally, the mudmat is configured to be installed with a number of guide posts which during use guide the support frame into position on top of the mudmat. Further optionally, the guide posts can be locked to the support frame to allow the support frame and the mudmat to be installed or recovered as one unit. Advantageously, the guide posts are used to navigate the support frame onto the mudmat. The guide posts facilitate the lowering of the support frame into position. The mudmat has the facility to connect to the support frame for a single lift, and to detach should separate lifts be preferred. The mudmat can be detached from the seabed once the support frame is located in position. This detaching of the mudmat may be used for levelling of the support frame.

[0047] Optionally, the system further comprises a levelling device configured to allow the support frame to be levelled relative to the seabed to provide further alignment of the guide to the well. Further optionally, the levelling device is configured to allow the support frame to be levelled relative to the mudmat (where present). Advantageously, the levelling device ensures that the support frame instalment is level, which ensures that it functions optimally to allow access to the legacy well, and to transfer load forces away from the legacy well into the seabed.

[0048] Optionally, the system further comprises a cover configured to be lowered onto the frame. Advantageously, the cover serves to prevent dropped objects from becoming attached to the frame. In addition, the cover ensures that the system design is more fisher-friendly, by guarding potential internal snag points from fishing nets. Providing a cover that has a smooth surface prevents a fishing net from becoming tangled if it comes into contact with the system. The cover may have sloped sides, which deflect any dropped objects or nets away from the well.

[0049] Optionally, the system further comprises a number of hatches configured to provide access to the support frame. Advantageously, opening the hatches allow access to the interior of the system. Closing the hatches ensures that the system has a smooth exterior, preventing damage due to fishing nets becoming tangled. The cover allows the recoverable abandonment frame to be installed and left on the seabed for extended periods of time, for example, between well location identification and RAF installation to the point where a mobile offshore drilling unit is mobilised to the site. Optionally, the support frame is configured to accommodate the installation of subsea pressure control equipment. Advantageously, during use, the system is configured to support subsea equipment, such as a subsea wellhead. Accordingly, the system is compatible with a setup where a semi-submersible drilling rig is used. Accommodating this equipment may be achieved by mounting the pressure control equipment on the top of the slot or a flat top of the primary frame.

[0050] Optionally, the system further comprises one or more transponders configured to identify the location of the support frame, in order to ensure that the support frame is positioned accurately onto the seabed location and to facilitate moving of the guide into position relative to the support frame. Advantageously, the transponders allow the location of the system to be easily determined, which helps to ensure that the support frame is positioned in the correct location.

[0051] Optionally, the guide facilitates the deployment of a pipe (e.g., a temporary drill pipe) during initial well tagging or logging runs in order to provide final adjustment. This is using a drill pipe temporarily through the guide with cameras / tools / drill bits on the end. This will allow the well to be viewed or analysed to make sure the RAF is central prior to installing the milling conduit, etc. Advantageously, the guide facilitates the installation of the milling conduit, the environmental conduit, and the pressure retaining conduit

[0052] Optionally, the guide facilitates the installation of a milling conduit which is configured to provide a guide down to the well and provide support to milling and clean up tools.

[0053] Advantageously, the milling conduit helps to prevent seabed cave in when exposing the legacy well. Additionally, the milling conduit helps to centralise the BHA during milling operations, and re-distributes loads away from the legacy well into the seabed via the milling conduit, conductor slot, and Recoverable Abandonment Frame.

[0054] Optionally, the guide and milling conduit facilitate the installation of the environmental and pressure retaining barriers.

[0055] Advantageously, the guide and the milling conduit support the position environmental and pressure retaining barriers with the installation of various types of centralising devices. Additionally, the loads from the environmental / pressure retaining barriers are transferred away from the legacy well into the seabed via the milling conduit, guide slot, and Recoverable Abandonment Frame. Optionally, the environmental and / or pressure retaining barriers can be tied back to a Jack-up drilling rig, or to subsea pressure control equipment for a floating drilling rig.

[0056] Advantageously, establishing the environmental and / or pressure retaining barriers allows conduits to the drilling rig which work can be conducted through, such as the re-abandonment of the well. Additionally, the design allows for tieback to both fixed and floating drilling rigs which supports well re-entry for all different water depths with the respective drilling rig ranges.

[0057] Optionally, the system further comprises a tension table (which may function as a support frame guide), wherein when subsea pressure control equipment for a floating drilling rig is to be installed, the tension table utilises a wellhead termination of the pressure retaining conduit just above the guide that has tension applied below once tied back to the well in order to isolate the subsea pressure control equipment weight away from the well once the equipment is installed.

[0058] Advantageously, this facilitates the tie back to a floating drilling rig and isolates the loads away from the legacy well, ensuring the well does not become damaged through the installation and operation of the subsea pressure control equipment.

[0059] Optionally, the support frame has tethering lines attached to it and the conduits or subsea pressure control equipment to provide further lateral support and further reduction of loads.

[0060] Advantageously, this reduces loads when the pressure control equipment is tied back to the drilling rig, further reducing the risk of operational damage / problems.

[0061] Brief Description of the Drawings

[0062] Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0063] • FIG. 1 illustrates an offshore legacy well which has been severed below the mudline, with an inset showing a path for gas to leak out from the legacy well;

[0064] • FIGs. 2A-2C illustrate a well marker identifying the location of a legacy well, which is protected by a protective cover; • FIG. 3 illustrates a recoverable abandonment frame (RAF) being lowered from a vessel onto a seabed location that has been identified as being directly above a pipe of a legacy well within a tolerance.

[0065] • FIG. 4 illustrates piles being driven into the seabed to hold in place the RAF;

[0066] • FIG. 5 illustrates a milling conduit being received and retained by a guide of the recoverable abandonment frame, wherein the guide has been aligned with the pipe of the legacy well;

[0067] • FIG. 6 provides a cross section view of the RAF, held in place by the piles;

[0068] • FIG. 7 provides a cross section view of the RAF, illustrating a drill bit within the milling conduit;

[0069] • FIG. 8 provides a cross section view of the RAF, illustrating sensors being used to inspect the pipe of the legacy well;

[0070] • FIG. 9 provides a cross section view of the RAF, illustrating the environmental conduit or barrier inside the mule shoe, then continuing to be inserted into the casing of the legacy well;

[0071] • FIG. 10 provides a cross section view of the RAF, illustrating a milling operation; with optional mud and cuttings recovery system

[0072] • FIG. 11 provides a cross section view of the RAF, illustrating the final configuration where the legacy well is tied back to pressure control equipment on the Jack-up drilling rig;

[0073] • FIG. 12 provides a cross section view of the RAF, illustrating a dummy subsea wellhead attached to the pressure retaining conduit that is supported laterally and vertically via the RAF. Therefore compressive loading generated via the pressure control equipment or BOP are reacted down into the dummy wellhead and then away from the legacy well into the RAF;

[0074] • FIG. 13 provides a cross section view of the RAF, illustrating load forces from a blowout preventer (BOP) (or other pressure control equipment) being dissipated away from the pipe of the legacy well (Additional detail from FIG. 12 is provided highlighting that the support from the dummy wellhead into the RAF is via an adjustable tension table. In addition optional BOP stabilising tethering lines are shown that can help further reduce lateral loads away from the legacy well);

[0075] • FIG. 14 provides a cross section view of the RAF, illustrating a temporary abandonment state; • FIG. 15 provides a cross section view of the RAF, illustrating how to remove the piles and withdraw things such as the milling conduit;

[0076] • FIG. 16 provides a perspective view of an example of the RAF;

[0077] • FIGs. 17A-17D provide perspective views of parts of the RAF, wherein: o FIG. 17A shows an upper portion of the RAF; o FIG. 17B shows a top part of the RAF; o FIG. 17C shows a frame section of the RAF; and o FIG. 17D shows a mudmat of the RAF;

[0078] • FIG. 18 provides a top view of the RAF;

[0079] • FIGs. 19A-19C provide a schematic views of the RAF, wherein: o FIG. 19A illustrates how the slot can be moved laterally within the RAF, in order to align the slot with the pipe of the legacy well; o FIG. 19B illustrates the RAF dissipating load forces away from the legacy well; and o FIG. 19C illustrates the RAF held in place by piles, with a milling conduit configured to prevent cave-in and manage loads from the bottom hole assembly (BHA), a mule shoe stinger providing an environmental barrier, and a pressure retaining barrier;

[0080] • FIGs. 20-22 illustrate options for maintaining the RAF in position relative to the well, wherein: o FIG. 20 illustrates a first option of the weight of the RAF being used in order to maintain the position of the RAF relative to the well; o FIGs. 21 A-21B illustrate a second option of adding ballast to the RAF in order to maintain the position of the RAF relative to the well; and o FIGs. 22A-22E illustrate a third option of piles being used in order to maintain the position of the RAF relative to the well;

[0081] • FIG. 23 provides a perspective view of the RAF, installed with piles;

[0082] • FIG. 24 provides a cross section view of the RAF, showing the optional riserless mud recovery system being used to pump mud to the Jack-up;

[0083] • FIGs. 25A-25C provide cross section views of the RAF, wherein: o FIG. 25A shows the installation of the milling conduit; o FIG. 25B shows installation of the environmental barriers; and o FIG. 25C shows installation of the pressure retaining barrier; • FIG. 26 provide a cross section view of the RAF, showing an example of tie-back to the Jack-up rig once re-connected to the legacy well;

[0084] • FIGs. 27A-27B illustrate the recoverable abandonment frame installed on the seabed, with FIG. 27A providing a perspective view, and FIG. 27B providing a cross section view; and

[0085] • FIGs. 28A-28C illustrate installation of a mudmat and a frame, as a possible way of installing the recoverable abandonment frame, with FIG. 28A showing the mudmat installed on the seabed, FIG. 28B showing the frame being lowered onto the mudmat, and FIG. 28C showing the recoverable abandonment frame in position on the seabed.

[0086] Detailed Description

[0087] Innovation is to be found in the strengthening of legacy wells, so that depleted oil & gas reservoirs and / or saline aquifers can contribute to preventing climate change by storing CO2 or Hydrogen for example. Various exemplary embodiments, features, and aspects are described in detail below with reference to the drawings.

[0088] Records identifying the location of wells that have been abandoned may not be accurate, and so in order to locate the legacy well, surveys of the seabed are carried out. A legacy well may be located by performing a desktop study to identify the expected position of the well, followed by performing physical surveys in order to zone in on the exact location. Once the well has been located, a more detailed survey is carried out, in order to determine its position more precisely, as well as potentially assess its condition. Techniques for establishing the location of the well include:

[0089] • Side Scan Sonar: Used to produce an image of the seafloor to identify any debris, boulders, sediment changes, etc, that can help to locate the legacy well.

[0090] • Sub-Bottom Imager: Used to produce an initial picture of below the seabed to help to narrow down the location of the legacy well.

[0091] • Magnetometer: Used to produce a 2D image of the seafloor which, using magnetism, will detect variations beneath the seabed.

[0092] • Gradiometer: Used to measure the gradient of the magnetic field, allowing for even more precise measurements of magnetic variations. Marine magnetometer and gradiometer systems are typically towed behind a survey vessel and record data as the vessel moves over the seafloor. • Acoustic Corer: Used to produce a 3D cylindrical image below the seabed. This will provide a very accurate location of the legacy well.

[0093] A well-marker typically installed at the identified location of the legacy well, so that preparations can begin for the legacy well to be re-entered. Transponders are placed in the vicinity of the legacy well, in order to indicate its location. Transponders are used in conjunction with the location technology (e.g. Acoustic Corer) to ensure the well can be marked as accurately as possible. Once the well marker is in place the transponder is left on the well marker so that it can be easily located at a later date. Then the protective frame is placed over the marker. The process is designed so that the location and the marking of the well can be completed using lower cost vessels, with the Jack-up or Semi-submersible drilling rig being bought in once the process has been further progressed.

[0094] Once the legacy well has been located, several techniques are available to re-enter the well. Vertical well re-entry is deemed the lowest in cost and duration, and it is possible to re-use the primary equipment to further enhance cost effectiveness. Sometimes conductors (i.e., the well’s outer pipe) are found to be sticking up above the mudline. However, it’s more common for the top of a legacy pipe to be 3 to 10 metres below the mudline. Vertical re-entry is more difficult if the legacy pipe is submerged below the seabed, because determining the location and condition of the legacy pipe is more of a challenge, and then accessing the pipe should be done carefully to prevent any damage being caused to the legacy well. An option for accessing the legacy pipe is to excavate the seabed, although this is a large undertaking that has a high risk of damaging the legacy well. Excavation is high in cost and duration, with investment including the installation of supporting structures, which increases the complexity of the work. An alternative option is the drilling of a relief well, which intersects with the legacy well. However, this is a highly complex operation, making this the highest cost and duration of the methods available. Furthermore, the creation of a relief well risks introducing an additional leak path.

[0095] Opening of the well should be done carefully, to prevent damage. A subsea well is subject to high loads, including tidal forces, weather conditions, and the weight of offshore structures. It is important for these load forces to be dissipated away from the well itself, in order to prevent damage to the legacy well. Re-entry of the well is achieved by putting in place structural support that distributes the weight of the drilling, milling, conduits and environmental loads away from the legacy well, as well as stabilising the well for cleaning. The structural support also reacts the loads away from the riser string back to the mobile offshore drilling unit.. Before the well is entered, the milling conduit is installed to centralise and steady the BHA holding it in place regards to the legacy well as well as preventing seabed cave-in. Once the legacy well has been cleared up by the initial milling operation, the environmental barrier can be installed providing communication between surface, seabed and the legacy well for the first time since it was abandoned. The inside of the environmental barrier or conduit can now be cleaned up and displaced if desired to a conditioned drilling mud as a low pressure seal is now established between the legacy well and the environmental conduit lower mule shoe stinger. This barrier stops ingress of seawater / seabed, and also allows for the use of drilling fluid in the subsequent milling operations. Any environmental loading, via wave action for example, into the environmental conduit is distributed away from the legacy well via a centraliser system between the outside diameter of the environmental conduit and the inside diameter of the milling conduit into the RAF and away to the seabed.

[0096] The disclosed process for re-entering previously abandoned wells is repeatable, regardless of soil condition, or depth of well below mudline. Thus, a single repeatable methodology is provided for re-entering an abandoned well. This enhances efficiency, and also reduces costs by ensuring a reusable recoverable abandonment frame system can be used to mitigate the risks of re-entering a large number of legacy wells.

[0097] FIGs. 2A-2C illustrate a well marker 10 identifying the location of a legacy well, which is protected by a protective cover 20. FIG. 2A shows a cross section detail of the well, showing the well marker 10 inserted into the well. The well marker 10 emits a signal, so that the location of the well can be identified. FIG. 2B shows the protective cover 20 being lowered onto the seabed over the well marker, which can hold the well marker 10 in place, and prevents it from being damaged. FIG. 2C shows the protective cover 20 over the well marker 10. Accordingly, disclosure is provided of a way of locating the well, including marking the well and the adding of a protective structure.

[0098] FIGs. 3 to 15 show a possible way in which a recoverable abandonment frame (RAF) 100 can be installed onto the seabed over the legacy well. This entire process can be done in stages, whereby lower cost vessels can be used, as appropriate. FIGs. 16 to 19 illustrate the RAF 100 in detail, with FIG.18 providing a top view of the RAF system 100. The RAF system 100 includes a guide 120 (which is also referred to as a slot). The guide (slot) 120 is configured to be moved relative to a support frame 110 and legacy well. Once in position, the guide (slot) 120 can accommodate a tool which can be used to re-enter the legacy well. The RAF 100 is lowered into position from a vessel 300 once a seabed location is identified as being directly above the pipe 200 of the legacy well.

[0099] The RAF 100 includes a support frame 110 which supports pile guides 111 which are used for securing the RAF 100 to the seabed using piles 112. Adding the support frame 110 around the legacy well allows the dissipation of load forces away from the centre of the well, which prevents the pipe 200 from becoming damaged.

[0100] The RAF 100 further includes a guide (i.e., a slot) 120 through which the legacy well is opened up. The slot 120 can be moved relative to the rest of the support frame 110, providing a tolerance that allows the legacy well to be located with precision after the RAF 100 has been secured in place. A tolerance of 1 metre radially is achieved by allowing the slot 120 to be moved relative to the support frame 110.

[0101] In the example shown, the recoverable abandonment frame 100 includes four pile guides 111 at each corner, and a slot 120 that can be moved laterally relative to these pile guides 111. The slot 120 being movable within the support frame 110 ensures that the RAF 100 can be adjusted to account for the level and condition of the seabed. The slot 120 provides structural support, by holding the well centre, during the initial well clean up milling operation string. Thus, the RAF 100 structurally supports below mudline conduits and tie back strings. Furthermore, the RAF 100 support the riser system and pressure control equipment during jack up or semi sub operations.

[0102] The RAF 100 includes a mudmat 130, which provides stability of the RAF 100 before the pile installation. The mudmat 130 may act as a gravity base for the RAF. The mudmat 130 may be detached from the rest of the support frame 110, so that the mudmat 130 can be placed on the seabed before the support frame 110 is subsequently placed on top of the mudmat 130. The mudmat 130 is a structure that prevents the offshore structures from sinking into soft unconsolidated soil on the seabed. The mudmat serves as a seafloor support for subsea equipment, before the support frame 110 may be secured in place by the piles 112 if required. The mudmat 130 supports the subsea equipment by distributing load forces over a large area, preventing them from being pushed down into the surface due to their weight, as well as other load forces that are incurred due to conditions in the ocean environment, such as the weather and tidal forces. Often, the seabed is sufficiently robust to support the weight of the support frame 110, and so for the example shown in FIG. 3, the RAF 100 is placed on the seabed in a single step, with the mudmat 130 already being attached to the support frame 110. The RAF being supported via piles is considered a worst case. In some cases the seabed, mud mat and weight of the RAF alone will be suitable for project specific loading. In other cases additional ballast may need to be added inside the pile guides to overcome project specific load cases.

[0103] In FIGs. 3 to 15, the RAF 100 is shown installed with a cover 150, which prevents fishing nets from becoming tangled with the RAF 100. The cover 150 includes access hatches 151 which are opened during the operational phase to permit access to the interior of the support frame 110. Thus, the RAF protection frame 100 has a profile that is fishing friendly and slab sided. The structure 100 is designed such that all expected fishing gear interaction load cases, including temporary snagging, are considered. However, the structure 100 allows removal of snagged fishing gear by simple reversal or ‘backing-up’ of the fishing gear. Retrieval of fishing gear is also considered as a major load case. Thus, the cover 150 ensures that the RAF 100 is designed to be left for prolonged periods, offering protection against fishing and dropped object loads. Note that the cover 150 is optional. Furthermore, the hatched 151 are optional. Access using hatches 151 may be provided even in cases where no cover is present, in order to facilitate access to the interior of the RAF 100.

[0104] Transponders 160 of the RAF 100 identify the location of the RAF 100. The transponders 160 may also be used to transmit the location of the RAF 100. Thus, the location of the RAF 100 can easily be determined by operators of the vessel 300.

[0105] FIG. 4 illustrates piles 112 being driven into the seabed, to hold in place the recoverable abandonment frame 100 (see FIG. 23 for further details). This is achieved by the vessel 300 deploying a crane 310 which serves as a pile driver 310. The crane 310 is used to insert piles 112 through the pile guides 111 of the support frame 110 in order to securely attach the RAF 100 to the seabed. The piles 112 support the weight of the offshore equipment, so that not all of the load forces are transferred to the mudmat 130. Thus, the support frame 110 is configured to support the pipe 200 of the legacy well, by allowing load forces to be dissipated away from the pipe 200, preventing the legacy well from becoming damaged. The use of piles 112 is optional, with disclosure being provided of other ways of holding in place the RAF 100 (see FIGs. 20 to 22).

[0106] FIG. 5 illustrates a milling conduit 400 being received and retained by the slot 120 of the recoverable abandonment frame 100. The milling conduit 400 is installed above the well stub. The milling conduit 400 is installed to help support any loads from the drill string. Furthermore, the milling conduit 400 helps to centralise the drill string. Supports cave in of the seabed into the legacy well during initial phases. The slot 120 is shown having been aligned with the pipe 200 of the legacy well. Thus, the milling conduit 400 serves as a support that surrounds the pipe 200 of the legacy well.

[0107] The milling conduit 400 could potentially be installed via a vessel but more likely via the mobile offshore drilling unit (MODU) once on location to allow for additional services such as circulation or drilling out. The sloped sides of the RAF 100 may be replaced by a slab side style as highlighted in FIG.16 for example. The mud mat may be installed independently. Clump weight pulley lines may potentially be used to pull the RAF 100 accurately to the well centre. As an alternative to the RAF 100 having sloped sides, the RAF 100 be provided as a slab side unit.

[0108] An alignment mechanism (i.e., a coupling) 121 between the slot 120 and the frame 100 is configured for moving the slot 120 laterally within the support frame 110. During use, the coupling 121 transfers load forces away from legacy well, to the seabed via the support frame

[0109] 110. The coupling 121 may comprise rails 121 configured for moving the slot 120 relative to the support frame 110.

[0110] The support frame 110 of the RAF 100 is configured to divert all loads away from the legacy well 200, into the seabed. Load forces are transferred from the legacy pipe 200, to the milling conduit 400, to the slot 120, to the coupling 121, to the support frame 110, to the pile guides

[0111] 111. to the piles 112, and into the seabed. Thus, the load forces are transferred away from the pipe 200 into the seabed via the support frame 110 of the RAF system 100. For an arrangement where the piles 112 are not installed, the load forces can be dissipated via the support frame 110 into the mudmat 130, and from the mudmat 130 into the seabed.

[0112] FIG. 6 shows the recoverable abandonment frame 100 held in place on the seabed by the piles

[0113] 112. FIG. 7 shows a drill bit 405 inserted within the milling conduit 400. The drill bit 405 is used to mill out the outer casing, in preparation for installation of the environmental barrier 410. This procedure is referred to as milling, where the conductor bore is milled out smooth. FIG. 8 shows a sensor 406 (e.g., a camera) which is used for inspecting the pipe 200 of the legacy well. FIG. 9 shows a mule shoe stinger 410 inserted into the pipe 200 of the legacy well, in order to create an environmental barrier between the sea water and the Legacy Well.

[0114] FIG. 10 shows a milling activities, which are completed to take the target casing string to the required depth and to clean it to a condition ready for the installation of the pressure retaining barrier casing patch. During this further milling operation, the mule shoe 410 and environmental barrier / conduit prevents sea water from entering the pipe 200 or becoming contaminated with material that is removed from the pipe 200, as well as allowing the use of milling / drilling conditioned mud inside to aid operations. The milling operation optional uses a subsea pump module 500 to extract the material out of the pipe 200 and up to sea level (see FIG. 24 for further details). This is optional, and would be used during initial milling operations with the Milling Conduit installed only. Once the environmental barrier is installed (complete with Muleshoe on the end) 410 this will be tied back and used as the conduit to circulate mud and remove cuttings etc via the mobile offshore drilling units drilling fluids handling system. The RMR (Riserless Mud Recovery System) which includes the subsea pump module can be installed directly onto the conductor slot 120 of the RAF, then removed when the Environmental barrier 410 is installed but is optional as returns can be taken to seabed or a conduit installed back to the mobile offshore drilling units drilling fluids handling system. FIG. 11 shows the environmental barrier and pressure retaining barrier 420, from the drilling rig to the Legacy Well (pipe 200). Thus, a casing patch is installed, to provide a pressure retaining barrier 420. The pressure retaining barrier 420 sits inside the environmental barrier 410, and is pressure tested to confirm pressure integrity. There is also an option to tie back to multiple casing strings which would involve running another casing patch inside of the initial pressure retaining barrier 420. The final tie-back arrangement includes a riser from the legacy well, through the RAF, up to the Jack-up drilling rig 800. The load path indicates that during operation of the RAF 100, load forces are transferred away from the legacy well 200 to the support frame 110 of the RAF 100, and into the seabed (either via the mudmat or piles if installed).

[0115] See FIG. 25A for further details regarding the installation of the milling conduit 400 using a jetting tool 405. See FIG. 25B for further details regarding installation of the environmental barrier 410. See FIG. 25C for further details regarding installation of the pressure retaining barrier 420.

[0116] FIG. 12 shows the recoverable abandonment frame 100 supporting a dummy subsea wellhead 600 on the top of the conductor slot 120 or via a flat top tension table. The subsea pressure control equipment, e.g., the wellhead and BOP for example, will land on top of the conductor slot 120. The subsea wellhead 600 may be attached to the flat top of the RAF 100 using a lockdown device, in order to transfer lateral and vertical loads into the conductor slot 120, this is an adjustable device that can use screw jacks or hydraulic cylinders to engage the load. The loads are transferred via the frame, into the seabed.

[0117] FIG. 13 illustrates load forces from a blowout preventer (BOP) 610 being diverted away from the pipe 200 of the legacy well. This ensures that load forces can be dissipated via the piles 112 or just the mud mat in some cases, rather than risking damage to the pipe 200 of the legacy well. The use of piles 112 is not essential, because instead or in addition, the load forces can be dissipated via the frame and / or the mudmat.

[0118] The subsea pressure control equipment includes a wellhead and BOP. FIG. 13 shows the RAF 100 including an optional tension table frame guide 620 (e.g., hydraulic cylinders or ROV- operated screw jacks). Thus, the RAF 100 may include a tension table 620, which is located above the conductor slot 120. Once the rig has installed the casing patch to create a pressure retaining barrier, the Tension Table Frame Guide 620 is raised to meet the load shoulder of the wellhead and takes the weight which re-distributes loads away from the legacy well to the seabed via the support frame. The rig then lowers the BOP onto the wellhead, and the weight is again taken by the Tension Table Frame Guide 620 and re-distributed away from the legacy well to the seabed via the support frame.

[0119] The support frame 110 can have tethering lines attached between it and the pressure control equipment 600 to provide further lateral support and further reduction of loads.

[0120] The Tension Table (Frame Guide) 620 is installed in the Recoverable Abandonment Frame 100 slightly above the Conductor Slot 120. The following process is performed once the Milling Conduit 400 and Environmental Barrier (i.e., Muleshoe Stinger) 410 are installed. Both of these are hung off the conductor slot 120 and not involved in the below.

[0121] • Step 1. Rig lowers casing patch (Pressure retaining barrier) and wellhead to legacy well and engages patch, (e.g., Rig > drill pipe > wellhead > casing strings > casing patch).

[0122] • Step 2. Rig pulls slight tension to confirm patch has engaged correctly.

[0123] • Step 3. Tension Table (Frame Guide) is raised / jacked up to meet the wellhead load shoulder and take the weight.

[0124] • Step 4. Rig releases tension on the wellhead and released so the wellhead weight is taken completely by the Tension Table (Frame Guide). • Step 5. Rig lowers BOP onto wellhead and all load is taken by the Tension Table (Frame Guide) which means loads are distributed away from the well into the support frame and then seabed.

[0125] The support frame 110 can have tethering lines attached between it and the pressure control equipment 600 to provide further lateral support and further reduction of loads.

[0126] FIG. 14 illustrates a temporary abandonment state of the recoverable abandonment frame 100. Once the RAF 100 has been installed, it is possible that the legacy well 200 may be temporarily abandoned, for example, due to weather conditions. Access hatches 151 of the cover 150 are closed and secured. Temporary abandonment caps 152 may be placed over open bores. The transponders 160 identify the location of the RAF 100. The arrangement shown by FIG. 14 would be applicable to the semi-sub approach if the wellhead is mounted to the RAF 100.

[0127] FIG. 15 shows how recovery of the RAF 100 is completed. Thus, FIG. 15 demonstrates how re-abandonment of the legacy well can be performed.

[0128] FIG. 16 provides a perspective view of an example of the RAF 100, which is shown including the support frame 110, the pile guides 111, the guide 120, and the mudmat 130. The guide 120 is a slot which serves as a tool guide and is configured to receive tools which are used to reenter the well.

[0129] The RAF 100 may further includes a levelling device 170 configured to allow the support frame 110 to be levelled relative to the seabed to provide further alignment of the guide 120 to the well. If the mudmat 130 is present, then the levelling device 170 may be configured to allow the support frame 110 to be levelled relative to the mudmat 130. The levelling mechanisms 170 may form part of the main frame 100, as shown by the example in FIG. 16. The levelling device 170 may comprise posts on the main frame 110 that locate into the mudmat guides. The levelling device 170 may comprise cylinders which can be moved up and down to level the main frame 110 relative to the mudmat 130 and seabed.

[0130] FIGs. 17A-17D provide perspective views of parts of the RAF 100. A protective cover 115 of the RAF 100 is installed to protect the internal components of the RAF from damage.

[0131] FIG. 18 provides a top view of the RAF 100. Movement of the guide (slot) 120 is demonstrated, with solid lines showing the guide 120 in a first position, and dot-dashed lines showing the guide 120 in a second position. Thus, the guide (slot) 120 is configured to be moved laterally with respect to the support frame 110 and the Legacy Well. FIGs. 19A to 19C illustrate a guide 120 of the RAF 100 being moved into position, and once in position, the guide 120 accommodating tools which are used to re-enter the well. FIGs. 20 to 23 show ways in which the position of the RAF 100 can be maintained during use. FIG. 24 illustrates the RAF 100 in use, during which an optional riserless mud recovery system is used to pump mud out from the well, so that the well can be re-entered. FIGs. 25A-25C show installation of a milling conduit 400, environmental barriers 410, and a pressure retaining barrier 420.

[0132] FIGs. 19A-19C illustrates the functionality of the recoverable abandonment frame 100. FIG. 19A shows how the slot 120 can be moved laterally within the recoverable abandonment frame 100, in order to align the slot 120 with the pipe 200 of the legacy well. Adjusting the position of the slot 120 with the well centre ensures that the RAF 100 can accommodate for any locational and installation tolerances. FIG. 19B shows the recoverable abandonment frame 100 dissipating load forces away from the pipe 200 of the legacy well. By reacting the loads away from the legacy well, this prevents damage to the pipe, because the integrity of the existing casing is unknown, so applying loads to the pipe should be avoided.

[0133] FIG. 19C shows the recoverable abandonment frame 100 held in place by piles 112. The milling conduit 400 prevents cave in, and manages loads from the bottom hole assembly (BHA). The muleshoe stinger 410 serves to provide an environmental barrier 410, which allows circulation and isolation from the surrounding seawater. The muleshoe stinger 410 also functions to prevent sediment and / or debris from re-entering the cleared well bore. A pressure retaining barrier 420 provides a pressure seal to inner string(s). Multiple barriers can be established, in order to enables plugging and abandonment (P&A) activities to be completed. The pressure retaining barrier 420 maybe a Elastomer seal or could be a metal to metal patch. In some applications, where there is sufficient length of casing before the upper abandonment plug, this could be a grouted mule shoe stinger 410. Where sufficient depth is not available, a specialist low melting point metal to metal pipe seal can be used, potentially only just over 2m of length may be used to gain a significant pressure rated gas tight seal and mechanical connection dependent on the pressure rating and loading required.

[0134] Once the legacy well has been re-entered, the plugging and abandonment of the legacy well can be completed to regulatory standards, preventing the reservoir it enters or passes through from leaking, guarding against possible future leaks or where it is used as a permanent or temporary store for Hydrogen or CO2 for example, preventing these fluids or gases leaking into the environment. FIGs. 20-22 illustrate options for maintaining the RAF in position relative to the well. FIG. 20 illustrates the weight of the RAF 100 being used in order to maintain the position of the RAF 100 relative to the well. FIGs. 21 A-21B illustrate the adding ballast to the RAF 100 in order to maintain the position of the RAF 100 relative to the well. FIGs. 22A-22E illustrate piles being used in order to maintain the position of the RAF relative to the well.

[0135] FIG. 23 provides a perspective view of the RAF 100, installed with piles 112. Further details of how piles can be used to support the RAF 100 are provided by FIG. 4. The main support frame 110 of the RAF 100 is shown having four pile guides 111, which are configured to receive the piles 112. Each of the pile guides 111 can be fitted with a removable pile guide 113, which during installation helps to direct the piles 112 into the pile guide 111. The RAF 100 is shown fitted with a mudmat 130 as well as a removable lid 115.

[0136] FIG. 24 provides a cross section view of the RAF 100, showing the optional riserless mud recovery system 550 being used to pump mud to the Jack-up. The milling operation is shown using a subsea pump module 500 to extract material from the milling conduit 400 and up to sea level (see FIG. 10 for further details).

[0137] FIGs. 25A-25C provide cross section views of the RAF 100 during use. FIG. 25 A shows the installation of the milling conduit 400, within the guide 420 of the RAF 100 (see FIG. 5 to 7 for further details). FIG. 25B shows installation of the environmental barriers 410 (see FIGs. 6 to 9 for further details). The environmental barrier 410 comprises a pipe referred to as a mule shoe, which has a pointed end known as a mule shoe stinger which functions to bury the environmental barrier 410 into the seabed with the mule shoe stinger able to be jetted or rotated to provide alignment and access into the bore of the legacy well. Once the mule shoe stinger is in place inside the legacy well, elastomeric seals provide a low pressure environmental seal meaning that the connection between the legacy well, the mule shoe and the environmental conduit back to surface can hold a low pressure (500 PSI for example) to facilitate conditioned mud, well control and circulation FIG. 25C shows installation of the pressure retaining barrier 420 (see FIG. 10 & FIG. 24 for further details).

[0138] FIG. 26 provide a cross section view of the RAF, showing an example of tie-back to the Jackup drilling rig 800 once re-connected to the legacy well, (see FIG. 11 for further details). FIGs. 27A-27B illustrate the recoverable abandonment frame 100 installed on the seabed. FIGs. 28A-28C illustrate installation of the mudmat 130 and a support frame 110, as a possible way of installing the recoverable abandonment frame 100. FIG. 28 A shows the mudmat 130 installed on the seabed. Once the mudmat 130 has been lowered into place, it is fitted with removable guideposts 131. FIG. 28B shows the support frame 110 being lowered onto the mudmat 130, with the guideposts 131 being used for hardware guidance, in order to lower the support frame 110 into place on top of the mudmat 130. Once the support frame 110 has been lowered into place, a removable lid 115 may also be lowered into place on top of the support frame 110. FIG. 28C shows the recoverable abandonment frame 100 in position on the seabed. The procedure shown in FIGs. 28A-28C is an alternative to the procedure shown in FIG. 3, for which the RAF 100 is lowered onto the seabed in a single step, rather than the mudmat 130 and support frame 110 being lowered separately.

[0139] In summary, the following key factors contribute to the success of vertical re-entry once the well centre and depth below mudline is determined:

[0140] • Ability to mark the well centre and also provide radial adjustment to account for locationally, installation and general tolerance inaccuracy.

[0141] • Can be adjusted to account for seabed level and condition.

[0142] • Designed to be left for prolonged periods offering protection against fishing and dropped object loads.

[0143] • Structural support (holding well centre) during initial well clean up milling operation string.

[0144] • Structurally supports below mudline conduits and tie back strings.

[0145] • Support the riser system and pressure control equipment during jack up or semi sub operations.

[0146] • Provides a milling conduit that does not enter the well, provides an environmental conduit that does enter the well via a mule shoe stinger enabling a low pressure conduit and a pressure retaining conduit that is rated high enough to account for maximum expected shut in pressure during the re-abandonment operation to allow pressure control equipment or Blow Out Preventor (BOP) installation to facilitate well control measures.

[0147] • Divert all loads away from the legacy well, into the seabed. • Is repeatable regardless of soli condition, or depth of well below mudline (single repeatable methodology).

[0148] • Provides shallow hazard well control and fluids transportation.

[0149] • Ideally is installed, centred with confirmation (logged ID of well bore) before a mobile offshore drilling unit (MODU) on site.

[0150] The RAF system 100 includes the following core features, which can be achieved once the legacy well has been located:

[0151] • Provides an accurate well centre guide location once installed.

[0152] • Has modular initial lightweight well centre marker as well as lowering guide line tether winch for accurate vessel deployment.

[0153] • Oversize lateral and vertical load bearing slot which can be adjusted radially by approximately Im to account for locational and installation tolerances.

[0154] • Initial mud mat support and load bearing centre slot levelling device.

[0155] • Pin piles to suit seabed condition and required conduit, tieback string and pressure control equipment loading - length designed for specific location (see FIGs. 22A-22E). Alternatively, a gravity based structure is possible (see FIG. 20), and also a ballasted structure is possible (see FIGs. 21A-21B).

[0156] • Optional Riserless mud recovery interface to support shallow well control, milling and drilling operations.

[0157] • able to remain independently subsea for extended periods.

[0158] • Can support measurement, monitoring and verification (MMV) equipment (node location or monitor well).

[0159] After the well has been re-abandoned, the following may be performed:

[0160] • Reuse the well as a monitoring well: Install geophones and fibre optic cable for passive or even active spot light CCS subsurface monitoring.

[0161] • Full recovery and clean seabed: Piles can be cut and recovered or jetted out and fully recovered, the mudmat and RAF can be fully recovered leaving a clean seabed with all elements removed well below the mudline (10m + if required).

[0162] • All elements can be re-used: Even the cut piles if sufficient fatigue life remains as an extension section can be welded on if required to account for the cut section if not jet removed. For a wet subsea wellhead option, the pressure retaining barrier 420 may have a profile that terminates just above the RAF guide c / w a forged reaction load shoulder. Once the running tool has made the tieback connection the subsea wellhead will be at the correct height so that the RAF centre slot jacks (only required for subsea wellhead option) can jack up against the reaction load shoulder to place a small amount of tension on the tieback string (via screwjacks or hydraulic cylinders). Once the subsea BOP Pressure Control Equipment is then installed the vertical load and environmental loading will be diverted away from the legacy well into the RAF - mud mats or piles if applicable - seabed.

[0163] Although the disclosed subject matter has been described using specific terminology relating to apparatus features and / or method features, it is to be understood that the claimed subject matter is not necessarily limited to the examples disclosed. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. The advantages disclosed may relate to several of the examples that are disclosed.

Claims

Claims1. A method for re-entering a previously abandoned offshore well, the method comprising: identifying a seabed location that is above the well to within a tolerance; lowering a support frame (110) onto the seabed location; moving a guide (120) into position relative to the support frame (110) and the well; and re-entering the well using a tool (400, 410) which is received by the guide (120).

2. The method according to claim 1, further comprising: substantially diverting re-abandonment operational loads away from the well and into the support frame (110) and seabed.

3. The method according to claim 1 or claim 2, further comprising: re-configuring or enhancing the abandonment of the well to bring the well in line with selected specifications; and re-abandoning the well.

4. The method according to any preceding claim, further comprising: re-configuring or enhancing the abandonment of the well to provide zonal isolation across formations that the well passes through or enters5. The method according to any preceding claim, further comprising: repurposing one or more formations that the well enters or passes through.

6. A system (100) for re-entering a previously abandoned offshore well, the system (100) comprising: a support frame (110) configured to be lowered onto a seabed location identified as being above the well to within a tolerance; and a guide (120) configured to be moved into position relative to the support frame (110), before a tool (400, 410) for re-entering the well is received by the guide (120).

7. The system (100) according to claim 6, further comprising: a well marker (10) configured to confirm the seabed location prior to deployment of the support frame (110).

8. The system (100) according to claim 6 or claim 7, wherein the guide (120) is configured to transfer load forces away from the well via the support frame (110).

9. The system (100) according to any one of claims 6 to 8, wherein the guide (120) is configured to receive and retain a tool (400, 410) configured to transfer the load forces away from the well via the support frame (110).

10. The system (100) according to any one of claims 6 to 9, further comprising an alignment mechanism (121) configured to move the guide (120) relative to the support frame (110).

11. The system (100) according to any one of claims 6 to 10, wherein the guide (120) is configured to be moved laterally with respect to the support frame (110).

12. The system (100) according to any one of claims 6 to 11, further comprising a measuring device configured to be retained within the well before the well is re-abandoned.

13. The system (100) according to any one of claims 6 to 12, wherein the system (100) is configured to be reusable.

14. The system (100) according to any one of claims 6 to 13, further comprising a plurality of pile guides (111), each of which is configured to receive and retain piles (112) or ballast that secure the support frame (110) to the seabed location.

15. The system (100) according to any one of claims 6 to 14, further comprising a mudmat (130) configured to serve as a base of the support frame (110) once the support frame (110) has been lowered onto the seabed location.

16. The system (100) according to claim 15, wherein the mudmat (130) is configured to be installed with a number of guide posts (131) which during use guide the support frame (110) into position on top of the mudmat (130).

17. The system (100) according to claim 16, wherein the guide posts can be locked to the support frame (110) to allow the support frame (110) and the mudmat (130) to be installed or recovered as one unit.

18. The system (100) according to any one of claims 6 to 17, further comprising: a levelling device (170) configured to allow the support frame (110) to be levelled relative to the seabed to provide further alignment of the guide (120) to the well.

19. The system (100) according to claim 18, when further dependent upon any of claims 15 to claim 17, wherein the levelling device (170) is configured to allow the support frame (110) to be levelled relative to the mudmat (130).

20. The system (100) according to any one of claims 6 to 19, further comprising a cover (150) configured to be lowered onto the support frame (110).

21. The system (100) according to any one of claims 6 to 20, further comprising a number of hatches (151) configured to provide access to the support frame (110).

22. The system (100) according to any one of claims 6 to 21, wherein the support frame (110) is configured to accommodate the installation of subsea pressure control equipment.

23. The system (100) according to any one of claims 6 to 22, further comprising one or more transponders (160) configured to identify the location of the support frame (110), in order to ensure that the support frame (110) is positioned accurately onto the seabed location and to facilitate moving of the guide (120) into position relative to the support frame (110).

24. The system (100) according to any one of claims 6 to 23, wherein the guide (120) facilitates the deployment of a temporary drill pipe during initial well tagging or logging runs in order to provide final adjustment.

25. The system (100) according to any one of claims 6 to 24, wherein the guide (120) facilitates the installation of a milling conduit (400) which is configured to provide a guide down to the well and provide support to milling and clean up tools.

26. The system (100) according to claim 25, wherein the guide (120) and milling conduit (400) facilitate the installation of the environmental and pressure retaining barriers (410, 420).

27. The system (100) according to claim 26, wherein the environmental and pressure retaining barriers (420) can be tied back to a Jack-up drilling rig, or to subsea pressure control equipment for a floating drilling rig.

28. The system (100) according to any one of claims 6 to 27, further comprising a tension table (620), wherein when subsea pressure control equipment for a floating drilling rig is to be installed, the tension table (620) utilises a wellhead termination of the pressure retaining conduit (420) just above the guide (120) that has tension applied below once tied back to the well in order to isolate the subsea pressure control equipment weight away from the well once the equipment is installed.

29. The system (100) according to claim 28, wherein the support frame (110) has tethering lines attached to it and the conduits or subsea pressure control equipment (600) to provide further lateral support and further reduction of loads.

Images