Methods and tools for riserless and / or rigless plug and abandonment of a well

Abstract

The present invention relates to a method for riserless and / or rigless plug and abandonment, from within a production tubing, of subsea and platform wells, leaving all steel behind.

Description

[0001] Methods and tools for riserless and / or rigless plug and abandonment of a well

[0002] TECHNICAL FIELD

[0003] The present invention relates to plug and abandonment (P&A) of a wellbore which is a critical process in a lifecycle of any well I wellbore. This plug and abandonment method involves securely sealing a well / wellbore that is no longer productive or needed, to ensure that no hydrocarbons and / or other fluids and / or gases can escape into the surrounding environment.

[0004] BACKGROUND OF THE INVENTION

[0005] The main steps in a plug and abandonment process I method of a wellbore typically comprise the following:

[0006] 1 . Installing a blowout preventer (BOP), opening a closed-in well, running in hole and eventually installing a deep-set mechanical plug, punching and perforating the tubing to equalize pressure.

[0007] 2. Pulling the production tubing including the tubing hanger to the surface.

[0008] 3. Setting mechanical plugs, wherein the mechanical plugs are placed at various depths within the wellbore. Commonly used plugs include bridge plugs and / or cement retainers.

[0009] 4. Optionally are sections milled for wall-to-wall access. Establishing a primary barrier above the reservoir and establishing a secondary barrier where maximum anticipated pressure can be withstood. Cementing, wherein the cement is pumped into the wellbore above the mechanical plugs to create a solid and impermeable barrier. Multiple cement plugs might be set at various intervals to ensure complete isolation of different geological formations. These plugs act as physical barriers to prevent fluid and gas migration.

[0010] 5. Verification, wherein the integrity of the plugs and cement barriers is verified through pressure testing and logging tools to ensure that there are no pathways for fluid migration.

[0011] 6. Removing production equipment. The permanent plugs normally consist of Portland cement, however recently some new techniques and materials have been introduced involving:

[0012] Portland cement with additives, Low melting point metal alloys, Thermosetting polymers (resins), Unconsolidated sand slurries, Inorganic colloids Geopolymers, and

[0013] Thermic melting of casing, cement and formation.

[0014] The objective of the plug and abandonment process is to protect the environment by preventing the escape of hydrocarbons and / or other fluids and / or gases, thus ensuring that the well is safely and permanently abandoned.

[0015] On some occasions, rigs and risers are often used in the plug and abandonment process of a subsea wellbore, especially in offshore settings.

[0016] Drilling or workover rigs, with a drill string capacity, are used to provide a necessary platform and infrastructure for heavy equipment and personnel involved in the plug and abandonment process of wells.

[0017] Risers are used in offshore drilling, production, intervention and plug and abandonment-operations, typically on floating platforms or rigs, to connect the subsea wellhead or Christmas tree to the surface facility. They provide a conduit for circulating fluids (e.g., drilling mud, production fluids) and deploying tools and equipment (e.g., drill strings, wireline tools) into the well.

[0018] Some drawbacks of the known plug and abandonment method of subsea wells are high rig rates and personnel costs, time and energy consumption, operational complexity, weather dependency, etc. Generally, the use of a drilling string in a plug and abandonment process is time and energy consuming due to the need for mantling and dismantling of drill string joints and the practice of pulling the production tubing. Recently, some other alternative methods are being developed and tried in plug and abandonment operations of subsea wells.

[0019] Light well intervention vessels (LWIVs) can be used to perform some plug and abandonment tasks of subsea wells without any need for a full-scale drilling rig or riser, thus potentially reducing costs, time and energy consumption.

[0020] Riserless and / or rigless plug and abandonment techniques can be used, wherein a coiled tubing or wireline is deployed from a vessel to offer a more cost-effective and less complex solution for certain plug and abandonment operations.

[0021] Rigless refers to the absence of a drilling rig and a drill string. Riserless operations refer to subsea activities without the use of a marine riser, which is the conduit connection from the subsea wellhead to the surface facilities, for example a drilling rig or a production platform.

[0022] Exploring alternative methods that mitigate the above-mentioned rig and riser related issues can provide more efficient and cost-effective solutions for any well to be plugged and abandoned, especially subsea wells.

[0023] SUMMARY OF THE INVENTION

[0024] It is an object of the present invention to provide a more operational efficient and cost-effective solution for plug and abandonment operations.

[0025] Another object of the invention is to provide a better riserless and / or rigless plug and abandonment method than the recently used methods.

[0026] Yet another object of the invention is to provide a less labour-intensive process and enhanced safety of personnel and environmental protection due to more efficient operations. Yet another object of the invention is to minimize and / or reduce time and energy consuming in the plug and abandonment process.

[0027] Yet another object of the invention is to provide increased flexibility and adaptability of the plug and abandonment process.

[0028] Yet another object of the invention is leaving all steel behind after a well has been permanently plugged.

[0029] Yet another object of the invention is to isolate and seal off downhole control lines.

[0030] Yet another object of the invention is to verify the integrity of the placed barriers.

[0031] Yet another object of the invention is to establish an environmental barrier upon a subsea structure on the seabed.

[0032] According to a first aspect of the invention this is achieved with a method for riserless and / or rigless plug and abandonment of a wellbore.

[0033] The present invention concerns a method for riserless and / or rigless plug and abandonment of a wellbore, the method comprising, in a recommended order, the steps of: a) placing a pumping unit in close proximity to a wellhead of the wellbore; b) placing a coiled tubing injector stack on top of the wellhead or on top of a Christmas tree on the wellhead if any; c) connecting a source on the pumping unit, using a connection comprising a first hose, to a choke valve arranged on the coiled tubing injector stack by using the first hose; d) connecting the pumping unit to a pit or separator via a first umbilical or hose; e) removing any unnecessary plug on the way down for the coiled tubing or the wireline string by means of a stroker arranged at the operational end of the string; f) optionally perforating above production packer to equalize pressure and to accommodate for displacement of fluids / gases in the a-annulus; g) optionally scraping and washing a section of the wellbore to be plugged, by means of a scraper having high-pressure nozzles and brushes and using a washing fluid with solvents and anti-freeze agents. Furthermore, in this step g) and / or the next step h) a cleaning assembly 95a, 96 and possibly a well tractor 75, 75a can be dropped into the wellbore in order to save time. h) running a string into the wellbore, wherein the wireline or coiled tubing string, for each run-in-hole operation, equipped, at an operational end thereof and depending on the operation to be performed, with at least one of: a stroker configured for removing any unnecessary plug, a passive packer being unset under run-in-hole operation and configured to expand or set under use, and / or assemblies comprising at least one perforation gun and / or a milling tool, and a plug. Under use (e.g. under establishing of cross section barrier(s)) the expansion of the passive packer can for example be done by increasing pressure or flow over a predetermined level, or by inflation, or by hydraulics, or the like; i) milling and / or perforating the section of the wellbore to be plugged with its adjacent production tubing, other adjacent casing and / or adjacent formation by means of the milling tool and / or the at least one perforation gun respectively; j) optionally placing at least one packer and / or at least one plug above and / or below the section to be plugged, and / or using any existing packer and / or plug to isolate the section to be plugged; k) pumping barrier materials through the coiled tubing string into the section to be plugged and through perforations and / or milled slots to create a first barrier, wherein the passive packer at the operational end of the coiled tubing string is being activated and expanded under use and isolates the annular space between the coiled tubing string and the production tubing; and l) pulling out the coiled tubing string with the passive packer and wait for curing of the barrier material; m) optionally sealing off any control lines; n) optionally pressure testing and / or tagging the cured barrier.

[0034] The passive packer can be placed over the section to be plugged. Furthermore, it can also be placed over some of the perforations, while other perforations are located above / over the passive packer, wherein these other perforations are used for evacuation of displaced fluids and / or gases, as well as for circulation of barrier material(s) in the annuli, as well as for cross section pressure I under pressure tests. The passive packer can be pulled up while squeezing, according to calculated volumes and / or pressures. And when the activated packer is being lifted, barrier material is being squeezed to the upper parts of the barrier.

[0035] The connection to the pumping unit can be a Y-connection further comprising a second hose, and the source on the pumping unit can be connected to an annulus valve arranged on the possible Christmas tree or on the wellhead’s outlet valves by using the second hose to facilitate circulation to the surface, and / or pumping into production tubing and / or a-annulus.

[0036] The subsea pumping unit can be equipped with a seawater intake, inhibitor chemicals, and the option of either pumping high volumes or creating under pressure and assist pumping return fluids to surface by two sets of pumps.

[0037] The subsea pumping unit can be linked with a surface pump for better enabling fluid and gas displacement to the surface, injection into the reservoir, and delivery of seawater inhibitors.

[0038] The method for riserless and / or rigless plug and abandonment can further comprise the steps of: if a valve cannot be manually operated, placing a hydraulic power unit in close proximity to the wellhead; connecting the hydraulic power unit, having at least one tank for control line sealant barrier material, to a wellhead port via an external control line; optionally connecting an umbilical from the hydraulic power unit for the operation of the coiled tubing injector stack.

[0039] The method for riserless and / or rigless plug and abandonment can further comprise the steps of: curing the barrier material of the first barrier; and optionally pressure testing the first barrier; Means of pressure testing are:

[0040] 1 . Assessing barrier integrity while pumping barrier material against a foundation, and through perforations below and above the coiled tubing packer, while measuring pumped and displaced volumes, and pressure in a closed system.

[0041] 2. Increasing and measuring the pressure above a cured barrier, and eventually across full cross section through perforations above.

[0042] 3. Creating a negative pressure above the barrier, by activating the subsea pump, and eventually across full cross section, through perforations shot above.

[0043] 4. Placing a gas emitter with timer adjacent to perforations below the barrier and placing a gas-sensor in the wellhead, Christmas tree or in the subsea coiled tubing injector stack.

[0044] The method for riserless and / or rigless plug and abandonment can further comprise the step of: creating at least one second barrier above the first barrier using all or some of the steps a) - n).

[0045] Under steps f) and i) the displaced fluids / gases and / or barrier material can be circulated through the annuli, to the surface from the coiled tubing string placed inside the production tubing, and through the created perforations or slots placed below and / or above a packer or the coiled tubing packer. The displaced fluids / gases can eventually be bull headed into the reservoir.

[0046] The method for riserless and / or rigless plug and abandonment can further comprise the steps of: curing the barrier material of said at least one second barrier; and optionally pressure testing said at least one second barrier as described above. The curing process can be delayed or accelerated by placing colloidal silica dispersed in a freshwater pill, separated from exposure to cations, prior to being mixed at planned location.

[0047] The method for riserless and / or rigless plug and abandonment can further comprise the step of: bleeding off and sealing off downhole control lines.

[0048] The method for the riserless and / or rigless plug and abandonment can further comprise the steps of:

[0049] - leaving all steel behind, including the production tubing, all the casing strings, control lines (if any), wellhead and optionally the subsea Christmas tree.

[0050] - using the steel as reinforcement in the barriers;

[0051] - in an eternal perspective, the embedded and coated steel can remain as reinforcement while other metals will oxidize and erode.

[0052] The method for the riserless and / or rigless plug and abandonment can further comprise the steps of:

[0053] - permanently preventing inflow through control lines by establishing cross section barrier below, or adjacent to the downhole termination point; and

[0054] - permanently preventing leakage by coating the control lines with barrier material where the lines are unencapsulated and exposed, as the encapsulation is expected to degrade over time.

[0055] The method for riserless and / or rigless plug and abandonment can further comprise the step of: establishing an environmental plug upon the remaining subsea structure. This can be done if required; using a remotely operated vehicle to jet and clear sediments around the wellhead to provide for adhesion of cement; placing a cover plate with reinforcement elements on top of a wellhead; pouring cement on top of a wellhead with a cover plate; wherein the cement can be placed by a submersible cement bucket; if a Christmas tree is placed upon the wellhead, circulating barrier material through all bores, and embedding the Christmas tree in cement; avoiding trapped gas or water in the cement dome by use of vibration, e.g. a vibration rod mounted on a remotely operated vehicle.

[0056] The method for riserless and / or rigless plug and abandonment can be configured for plug and abandonment of a subsea well, wherein a light well intervention vessel and at least one remote operated vehicle, ROV, connected to the vessel and operated by at least one ROV umbilical can be used to perform some of the method steps.

[0057] Furthermore, the method for riserless and / or rigless plug and abandonment can be configured for plug and abandonment of a platform well, where any drilling facilities previously have been removed.

[0058] Finally, a tracer and / or a sensor can be used to track and / or verify the circulation of the barrier material.

[0059] The method for riserless and / or rigless plug and abandonment can further comprise the steps of: positioning a cover plate over the wellhead to enclose the wellhead; delivering a cement slurry upon the cover plate to embed the wellhead and outlet ports of the control line(s) and / or the wellhead; and applying vibration, for example by means of a vibration rod, within the cement slurry to remove any excess air and / or water, thereby forming a cement dome encapsulating the wellhead and the outlet ports of the control line(s) and / or the wellhead. The cement dome can be a void-free cement dome.

[0060] The main features of this invention are given in the independent claim. Additional features of the present invention are given in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] These and other aspects of the invention are apparent from and will be further elucidated, by way of example(s), with reference to the drawings, wherein:

[0062] Fig. 1 shows documentation of a well and / or nearby wells needed to be investigated by personnel to understand the plug and abandonment tasks.

[0063] Fig. 2 shows a process map separated into three main processes comprising: understanding P&A tasks, establishing barriers and verifying barriers.

[0064] Fig. 3 shows a light well intervention vessel equipped for the plug and abandonment process of a wellbore.

[0065] Fig. 4 shows a rig, fixed or floating, equipped with a coiled tubing and wireline string and necessary bottom hole assemblies, remote operated vehicles etc. for plug and abandonment of the wellbore.

[0066] Fig. 5 shows a subsea wellhead with a vertical Christmas, and a subsea injection stack, through which a coiled tubing string has accessed, having removed any unnecessary plugs by means of a stroker tool. To the left of the wellhead is a subsea pump with an actuated Y-connection, an umbilical to surface and a seawater-intake. To the right of the wellhead is a subsea hydraulic power unit, with a preheater for bleeding off and sealing off control lines. Two off remote operated vehicles are observing the operation.

[0067] Fig. 6 shows a subsea wellhead with a vertical Christmas, and a subsea injection stack, through which a wireline string has accessed, having removed any unnecessary plugs by means of a stroker tool. To the left of the wellhead is a subsea pump with an actuated Y-connection and a seawater intake. To the right of the wellhead is a subsea hydraulic power unit, with a preheater for bleeding off and sealing off control lines. Two off remote operated vehicles are observing the operation.

[0068] Fig. 7 shows a well with a plug placed adjacent to the production packer. A wireline string equipped with perforation guns and a well tractor, having perforated the production tubing above the production packer in order to equalize pressure, and allow for displacement of fluids / gases in the production tubing and a-annulus.

[0069] Fig. 8 shows a well with a coiled tubing string equipped with a washing and scraping tool and composed washing train inside. A plug is placed adjacent to the production packer and perforations are shot above. Fluid / gases are displaced to surface via a- annuli and through the subsea pumping unit and further to surface assisted by a surface pump.

[0070] Fig. 9 shows a well in which fluids / gases in production tubing and a-annuli is bull headed into the reservoir. This is obtained by pumping fluids through the coiled tubing string and through the subsea pumping unit with seawater intake. The coiled tubing string is equipped with a washing and scraping tool and composed washing train inside, and is to conduct cleaning, scraping and washing of the production tubing and chemical washing of a-annulus.

[0071] Fig. 10 shows a well with perforations into the reservoir and adjacent to the production liner shoe. A perforations gun and well tractor has been dropped. A coiled tubing string with packer and sensors, is ready to squeeze barrier material into the reservoir.

[0072] Fig. 11 shows filling of barrier material into the reservoir. The coiled tubing string is equipped with a packer and sensors and is being lifted while pumping according to calculated volumes and pressure.

[0073] Fig. 12 shows a coiled tubing string with a packer and sensors, being pulled up while pumping barrier material according to calculated volumes into the reservoir.

[0074] Displaced fluids are evacuated through perforations above.

[0075] Fig. 13 shows a cured primary barrier placed full cross section in the reservoir, and adjacent to the production liner shoe.

[0076] Fig. 14 shows a well with a plug placed in the top of the production liner, and perforations shot above. The coiled tubing string with a packer is located above the plug, ready to place a foundation. The primary barrier is placed below the termination point for the pressure and temperature gauge with a control line running to the wellhead.

[0077] Fig. 15 shows the coiled tubing string with a packer squeezing barrier material across full cross section below and adjacent to the production liner shoe. Displaced fluids are evacuated through perforations above.

[0078] Fig. 16 shows the coiled tubing string with a packer being lifted while barrier material is pumped according to calculated volumes. Fig. 17 shows a cured and tagged primary barrier, placed across full cross section below the termination point of the control line. The barrier is being pressure tested through increased pressure from above, and through perforations above the barrier. Fig. 18 shows a well with a plug placed adjacent to the production packer, with perforations shot above. Perforations are also shot below the intermediate casing shoe. A coiled tubing string with a packer has tagged the plug.

[0079] Fig. 19 shows the coiled tubing string with the packer squeezing barrier material across full cross section above the production packer and adjacent to the termination point of the control line, hence the control lines will be sealed off from below.

[0080] Fig. 20 shows the coiled tubing string being lifted while pumping according to calculated volumes. Evacuated fluids are handled through the subsea pump with Y- connection and flow meters. Barrier integrity is verified through measuring the pumped and displaced volume, and pressure development.

[0081] Fig. 21 shows a cured and tagged barrier being pressure tested across full cross section from above and through perforations shot above.

[0082] Fig. 22 shows a well with a plug placed below the intermediate casing shoe, and perforations shot above the plug and adjacent to the intermediate casing shoe. The coiled tubing string with packer and sensors is ready to place a two-component foundation.

[0083] Fig. 23 shows the coiled tubing string about to tag the cured foundation.

[0084] Fig. 24 shows the coiled tubing string with packer and sensors, gently placing barrier material across full cross section through perforations shot adjacent to the intermediate casing shoe. Evacuated fluids are displaced through perforations above and handled through the subsea pump with Y-connection and flow meter, hence barrier integrity can be assessed.

[0085] Fig. 25 shows an upper barrier section being squeezed across full cross section.

[0086] Fig. 26 shows a cured barrier placed adjacent to the intermediate casing shoe, failing pressure test due to cracks.

[0087] Fig. 27 shows the coiled tubing string with a packer placing low viscous barrier material, such as colloidal silica, through perforations above. The material is placed across full cross section, filling the cracks.

[0088] Fig. 28 shows waiting a certain amount of time for the colloidal silica to cure. Fig. 29 shows the barrier being pressure tested after repair. Fig. 30 shows a plug with a gas emitter with timer below, placed below the intermediate casing shoe. A foundation is placed on top of the plug. Perforations are shot below the plug, adjacent and above intermediate casing shoe, and perforations are also shot below the intermediate casing shoe.

[0089] Fig. 31 shows placement of a cross-section barrier. Barrier material is pumped through the coiled tubing string, consisting of inorganic colloids and relevant cations being placed across full cross section above the foundation. Displaced fluids are evacuated through perforations above.

[0090] Fig. 32 shows the coiled tubing string being lifted while measuring pumped and displaced volumes, and pressure, hence barrier integrity is assessed.

[0091] Fig. 33 shows a cured and tagged barrier which is being pressure tested. The gas emitter with timer, will eventually contribute to testing the barrier integrity from below. Fig. 34 shows a well with a plug and a foundation placed below the surface casing shoe. Perforations are shot adjacent to the surface casing shoe, and above. The coiled tubing string with a packer is ready to squeeze barrier material across full cross section.

[0092] Fig. 35 shows a coiled tubing string with a packer squeezing barrier material across all annuli. Displaced fluids are evacuated through perforations above. The integrity of the barrier can be verified by inflow test or by creating negative pressure through engagement of the subsea pumping unit with a Y-connector.

[0093] Fig. 36 shows a pressure test of a cured and tagged barrier, and through perforations above.

[0094] Fig. 37 shows a vertical Christmas tree placed on a wellhead with a subsea coiled tubing injector stack placed upon. The injector stack is closed by activating the annular preventor. The downhole control lines are being sealed off from above, by bleeding off and then squeezing preheated oil-soluble sealant material into the lines, through application of the module for bleeding off and sealing off control lines. A remote operated vehicle is assisting in connecting to the wellhead ports.

[0095] Fig. 38 shows a horizontal Christmas tree with a coiled tubing injector stack placed upon. A plug and a foundation are placed below the wellhead. Barrier material is pumped through the coiled tubing string and circulated through all bores. Circulation to surface is achieved by engagement of the subsea pump with a Y-connection, and a suction pump on surface. Fig. 39 shows all bores and cavities in the wellhead and in the Christmas tree filled with barrier material and the coiled tubing injector stack being lifted to surface.

[0096] Fig. 40 shows cured barrier material inside the wellhead and Christmas tree. The remote operated vehicle is jetting and clearing sediments around the base of the wellhead. A submersible cement bucket lowered by crane is placed above the structure.

[0097] Fig. 41 shows the submersible cement bucket emptying the content, creating an environmental plug embodied as a cement dome. The remote operated vehicle is equipped with a vibrating rod to remove excess air and water.

[0098] Fig. 42 shows a hoisting devise lowered by crane pulling the vertical Christmas tree to surface. One remote operated vehicle is observing the pulling operation, and another remote operated vehicle is removing sediments from the base of the wellhead to provide for adhesion for the cement dome.

[0099] Fig. 43 shows a hoisting device lowered by crane, pulling a horizontal Christmas tree to surface after the production tubing is cut below the wellhead. Two off remote operated vehicles of which one is observing, and the other is removing sediments from the base of the wellhead.

[0100] Fig. 44 shows a submersible cement bucket emptying its content above a wellhead covered by a plate with e.g. metal ribbons or elements for reinforcement, avoiding cement to enter the wellhead and wellbore. Debris have been removed around the base of the subsea structure, for adhesion. A remote operated vehicle equipped with a vibrating rod is removing excess air and water.

[0101] Fig. 45 shows a well with all steel left behind with three full cross sections of verified barriers, placed from below: Adjacent to the production- intermediate- and the surface casing shoe, and an environmental plug placed upon the wellhead.

[0102] Fig. 46 shows a plugged well in an eternal perspective. All metals not embedded and coated in barrier material is oxidized and eroded. Over the long term, the embedded steel within the barrier reinforces the barrier element, enhancing its structural integrity.

[0103] Fig. 47 shows a well in an eternal perspective with an embedded Christmas tree, both internally and externally, in a cement dome. All metals not embedded and coated in barrier material is oxidized and eroded. Over the long term, the embedded steel within the barrier reinforces the barrier element, enhancing its structural integrity.

[0104] Fig. 48 shows a well with a dry wellhead being permanently plugged from a platform with coiled tubing and wireline equipment. A primary barrier is placed above the production packer, using methods as previously described.

[0105] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0106] Figure 1 shows documentation (1 ) of a well to be permanently plugged and experiences from nearby wells, which is needed to be investigated by personnel (2) to understand the plug and abandonment tasks. Figure 1 also shows rooms with personnel (2) needed for team alignment and training as the permanent plugging operation, especially when conducted from a light vessel (6), is a rather complex process with a series of operations. On the right side of the figure there is a comparison of a P&A process using a rig (3) or a derrick (25) and a P&A process using a light vessel (6) with coiled tubing equipment (12) and eventually wireline equipment (12a) with regard to cost (4) and time (5) needed for permanent plugging of a well. It is clear that the P&A process using the drilling rig (3) and a derrick (25) is much more expensive and time consuming than the P&A process using the light well intervention vessel (6) with coiled tubing (12) and wireline (12a) strings.

[0107] Figure 2 shows a process map of a (permanent) plug and abandonment method separated into three main processes, comprising: understanding P&A tasks, establishing barriers and verifying barriers. As the process of (permanent) plug and abandonment, P&A (PP&A), from a light vessel is new, and as this P&A (PP&A) process requires multi-skilled personnel, early involvement and training is paramount. Continual improvement in the planning and execution is required. All main and necessary steps are shown and described on figure 2.

[0108] This P&A process shall be done according to requirements defined by relevant authorities. Figure 3 shows a light well intervention vessel (6) equipped with at least one remote operated vehicle, ROV (19, 20), a coiled tubing (12) and wireline (12a) strings and equipment (8-9, 11 ,13, 69), a remote operated vehicle control unit (18), barrier materials (85a-85h), a mixer (65) and a stirrer (66), pumps (69, 118), a pit or separator (26), chemicals and freshwater (61a-61 e) and a cement laboratory (17b). The vessel (6) is fully stacked with a selection of washing train components (61a-e), solvents and anti-freeze agents (95b), a cement laboratory (17b), optionally a derrick

[0109] (25), a coiled tubing pump unit (69) and a crane (98), helicopter deck (24), steering house (7), control cabin (10), a moonpool (23), and umbilicals to subsea equipment (14, 15, 21 , 22, 55a, 55b).

[0110] Figure 4 shows an offshore oil / gas facility (3) either fixed or floating, prepared for conducting a plug and abandonment operation according to this method. The offshore facility (3) can be equipped with helicopter deck (24), lifeboats (3b), living quarter (3a), control cabin (10), ROV control unit (18), cranes (98), a pit or separator

[0111] (26), coiled tubing string (12) and coiled tubing equipment (8-11 , 13, 118 / 69), wireline string (12a), pumps, cement laboratory (17b), a mixer (65), a stirrer (66), ROV (19, 20), barrier materials (85-85h), washing train components (61 a-e), solvents and antifreeze agents (95b), subsea and down hole equipment. The offshore oil / gas facility (3) can be further equipped with a mid-ship derrick (25) to ease mounting of bottomhole assemblies (68). Below the main hull are umbilicals for subsea equipment (14, 15, 21 , 22, 55a, 55b) located in the moonpool (23) area.

[0112] Figure 5 shows a well (79) with a coiled tubing string (12) placed inside a subsea coil tubing injector stack (58d) placed on top of a subsea vertical Christmas tree (78, 94), which is placed on top of a wellhead (51 ) The coiled tubing string (12) is removing any unnecessary plugs (71 , 72) by means of a stroker tool. Downhole communication is preferably used to enable independent operation of more than one tool in the bottomhole assembly (68).

[0113] The subsea coiled tubing injector stack (58a) may be equipped with a lubricator (58h), an annular preventor (113a) an injector (58d), shear-, pipe- and slip rams (58e-g), kill- and choke line valves (58b-c) and a control panel (94b). On the subsea vertical tree (78, 94) the production swab valve (34c), production upper master valve (34a) and production lower master valve (34a1 ) are open to provide access through the tree (78, 94) for the coiled tubing string (12).

[0114] On the left side of the wellhead (51 ) and the Christmas tree (78, 94) and subsea coiled tubing injector stack (58d), is a subsea pump (16b), equipped with a Y- connection (105) with functionality to select one or two sources, which is connected to an annulus isolation valve (37a) on the Christmas tree (78, 94) through a hose (104), and to the choke line entry port valve (58c), through the hose (108). An umbilical (14) is connected to the subsea pump (16b) from the rig (3) or vessel (6) further connected to a pit or separator (26). The subsea pumping unit (16b) also has a seawater intake (106) with inhibitor supply though the umbilical (14) as option.

[0115] On the right side of the wellhead (51 ) is subsea hydraulic power unit (17a) which is connected to surface with an umbilical (15). For controlling and powering the subsea coiled tubing injector stack (58a) an umbilical (15a) can be connected from the hydraulic power unit (17a). Another umbilical (15a1 ) is connected from the hydraulic power unit (17a) to the control panel (94a) on the Christmas tree (78, 94).

[0116] The hydraulic power unit (17a) also contains a module for bleeding off and sealing off control lines (93). This module includes at least one tank with pressurized sealing material (93a), with a preheater (30) and at least one low-pressure tank (93c) for bleeding off control lines. All tanks have associated arrangement of pumps (93b), valves and sensors. As some of the control lines may have residual hydrocarbons after being bled off, an appropriate sealing material for these lines is a mixture of oilbased glue and silicone (101 ). All downhole control lines (52) must be permanently sealed off.

[0117] On the right side are two off remotely operated vehicles (19, 20) which are controlled from a surface control unit (18) through the umbilicals (21 , 22), assisting and observing. Figure 6 shows a wellhead (51 ), a vertical Christmas tree (78), a subsea injector stack (58a), and subsea equipment as described in Figure 5. A wireline string (12a) is removing any unnecessary plug(s) (71 , 72) by means of a stroker tool. Downhole communication is preferably used to enable operation of the bottomhole assembly (68).

[0118] Figure 7 shows a well (79) with all steel remaining (130), including the production tubing (42), casing strings (43a, 44a, 45a, 46a) and any control lines (52). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or lack of cement (123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a).

[0119] A plug (71 , 72) is placed adjacent to the production packer (40). A wireline string (12a) equipped with a perforation gun (62b) and a well tractor (75a), having perforated the production tubing (42) above the production packer (40). The perforations are to equalize pressure and to allow for displacement of fluids through a-annuli (99b).

[0120] Figure 8 shows a well (79) with all steel remaining (130), including the production tubing (42), casing strings (43a, 44a, 45a, 46a) and any control lines (52). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or lack of cement (123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a).

[0121] A plug (71 , 72) is placed adjacent to the production packer (42), with perforations (89) shot above.

[0122] The horizontal Christmas tree (28), the coiled tubing subsea injector stack (58a), the subsea pump (16b) with Y-connection (105) to the left, and the subsea hydraulic pressure unit (17a) with a module (93) and associated hoses and umbilicals (15, 15a, 15a1 ) and lines (16a), are described in Figure 5. The subsea pump (16b) with the actuated Y-connection (105) is engaged to bleed off fluids from a-annulus (99b) through the wing valve (37d) on the Christmas tree (78, 94) and through the hose (104), and further to a pit or separator (26) on surface via the umbilical (14 / 110), eventually assisted be a surface pump.

[0123] The coiled tubing string (12) is equipped with a drifting, scraping and brushing tool (59), consisting of a cleaning and scraper tool (95a) and a rotating brushing tool (96), and a through tubing well tractor (75a), which may be required.

[0124] The coiled tubing string (12) contains a washing train (61 c) followed by heavy fluid or seawater (109) or salt brine (100). An example of the washing train (56) composition is constituted of: solvents and anti-freeze agents (95b), spacers (61 a), a washing pill (61 c) arranged between the spacers (61 a).

[0125] As the coiled tubing string (12) with the cleaning and scraper tool (95a, 96) is pushed down, the fluid train (56) and following fluid is pumped through the coiled tubing string (12), and any gas and existing fluids in the wellbore (79a) is displaced through the perforations (89) above the plug (71 , 72) and evacuated upwards through a- annuli (99b) by the subsea pumping unit (16b) to surface via the umbilical (14 / 1 10) assisted by the surface pump (16c), hence both the production tubing (42) and the a- annuli (99b) will be cleaned.

[0126] Displacement of fluids / gases to surface requires fluid and gas handling capacity on the vessel (6) or rig (3).

[0127] When using the cleaning and scraper tool (95a, 96) with solvents and anti-freeze agents (95b), the through tubing well tractor (75a) can be used to avoid buckling of the coiled tubing string (12) under each run-in-hole operation.

[0128] Figure 9 shows a well (79) as described in Figures 5 and 8, however no plug is placed in the production tubing. The coiled tubing string (12) is equipped with a cleaning and scraper tool (95a, 96) and contains a washing train (56) as described in Figure 8. The subsea pumping unit (16b) with seawater intake (106) and Y- connection (105) is pumping seawater (109), through the hose (108), via choke line entry port (58c) on the subsea coiled tubing injector stack (58a), and through the hose (104) to the production isolation valve (34b) on the Christmas tree (28, 94), which allows for pumping seawater (109) through both a-annulus (99b) and production tubing (42) simultaneously.

[0129] As fluids are pumped through the coiled tubing string (12) and through the hoses (104, 108) simultaneously, sufficient fluid volumes are pumped to overcome the migration velocity of gases, hence existing fluids / gases in a-annuli (99b) and production tubing (42) will be bull headed into the reservoir (50).

[0130] Figure 10 shows a well (79) with all steel remaining (130), including production tubing (42), casing strings (43a, 44a, 45a, 46a) and control lines (52). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or no cement (123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a). The subsea pump (16b) with a Y-connection (105) is optionally used to lower pressure (124) in a-annuli (99b) and / or within production tubing (42), and / or to obtain circulation of fluids to surface (110).

[0131] The coiled tubing string (12) with unset packer (60b) is placed in the reservoir (50), above a dropped perforation gun (62b) and well tractor (75). Deep perforations (89) are shot below, adjacent and above the production liner (43a) shoe (47) and into reservoir (50, 90). The coiled tubing string (12) with unset packer (60b) and sensors for pressure and temperature (112) below the packer, and sensors for tracer material (91a) above the packer, ready to pump a fluid train, if not pre-mixed on surface, from below consisting of: chlorides with relevant cations (100 / 100a) and a tracer (85f), a spacer (61 a), barrier material #1 (85a), which can be colloidal silica dispersed in a freshwater pill (85a1), a spacer (61 a), and chlorides with relevant cations (100 / 100a) and a tracer (85f), a spacer (61 a), chlorides with relevant cations (100 / 100a) and a tracer (85f), a spacer (61 a), barrier material #1 (85a), which can be colloidal silica dispersed in freshwater pill (85a1 ), a spacer (61 a), and chlorides with relevant cations (100 / 100a) and a tracer (85f), a spacer (61 a).

[0132] The purpose of using the barrier material #1 (85a), together with relevant cations (100a), in this sequence is to obtain a downhole mixing effect. The barrier material, which can be colloidal silica dispersed in freshwater pill (85a1 ), is as explained below:

[0133] The curing time of the barrier material (85a1 ) is being delayed by the freshwater.

[0134] Cations (100a) acts as curing agent for barrier material (85a) and hence the curing time can be managed, which also allows for pre-mixing of the barrier material (85a2).

[0135] The grain size of the barrier material (85a) is customized to match that of the reservoir and the formation, thus allowing it to penetrate micro-annuli. When the grain size in the receiving part matches the barrier material's grain size, this ensures proper binding, maximum surface contact and adhesion. Moreover, the best suited barrier material (86) shall be used.

[0136] When establishing a primary barrier in the reservoir (50), and adjacent to the production liner (43a) shoe (47), below the termination point for control lines (52), these will no longer have the capacity of migrating fluids / gases to surface, hence are sealed off from below. Figure 11 shows the well as described in Figure 10. The coiled tubing string (12), with a set packer (60a) is placed in the reservoir (50). Barrier material (85a1 ) is being squeezed and mixed with the chlorides / cations (100a) and tracer material (85f), providing for verification of circulation (110) of barrier material (86) in annuli (90) through perforations (88) below and above the coiled tubing packer (60a). The lower part of the primary barrier is placed by squeezing (111 ) barrier material (86) through perforations (90) into the reservoir (50) and into annuli (99) and micro-annuli (99a). When barrier material with the tracer (85f) is detected by sensor (91a) above the coiled tubing packer (60a) and the pressure and temperature sensor (112) below the packer (60a) reads a planned pressure development, the coiled tubing string (12) is pulled up while pumping (119c), the subsea pump (16b) and the Y-connection (105) is evacuating displaced fluids to surface through the artificial annuli (99) via the choke valve (58c) on the coiled tubing injector stack (58d) and via the hose (108) and to surface via umbilical (14), eventually assisted by the surface pump (118), (Figures 5 and 8).

[0137] Figure 12 shows the well as described in Figures 10 and 11 . The coiled tubing string (12) with set packer (60a) is placed above perforations in the reservoir (89, 90) and below perforations adjacent to the production liner (43a) shoe (47). The upper part of the primary barrier is being squeezed into the reservoir (111 ) and micro-annuli (99a). The integrity of the primary barrier, can be verified while squeezing, utilizing back pressure, and measuring pumped and displaced volumes and pressure (119b). The fluids are evacuated through perforations above (110c), and the tracer (85f), and the sensor (91 a) will indicate circulating of barrier material through perforations above. Then the coiled tubing string (12) is lifted up to avoid being embedded in the barrier material (86).

[0138] Figure 13 shows a well (79) as described in Figures 10, 11 and 12. The primary barrier is established across full cross section in the reservoir (50), and across full cross section adjacent to the production liner (43a) shoe (47). When establishing a primary barrier in the reservoir (50), the control lines (52) will no longer have the capacity of migrating fluids and gases. As all steel is left behind (130), in an eternal perspective (128) the embedded steel / reinforcement will remain intact and strengthen the barrier element (129).

[0139] Figure 14 shows a well (79) with all steel remaining (130), including production tubing (42), casing strings (43a, 44a, 45a, 46a) and control lines (52), running back to the wellhead (51 ) outlet ports (29, see Figure 8). A pressure and temperature (112) gauge is located above the production packer (40). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or no cement (120, 123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a). The subsea pump (16b) with a Y-connection (105) is optionally used to lower pressure (124) in a-annuli (99b) and / or within the production tubing (42), and / or to obtain circulation of fluids to surface (110).

[0140] The coiled tubing string (12), with a set packer (60a), is placed above a tagged (121 ) plug (64a, 71 , 72), which is placed in the production liner (43a), below the production casing (44a) shoe (47). Perforations (89) are shot through all annuli (99), above the plug (64a), and below the production casing (44a) shoe (47). Perforations (88) are also shot into a-annuli (99b) only, in the section adjacent and above the liner hanger packer (41 ) and below the production packer (40), with the aim of accommodating for evacuation of displaced fluids (92) through perforations above and into a-annuli (99a). The subsea pump (16b) with the Y-connection (105), is running to create a negative pressure (124), to ease the displacement and evacuation of fluids (Figures 5 and 8). The coiled tubing string (12) is ready to pump a foundation (85g) consisting of from below, a spacer (61 a), barrier material (86), and a spacer (61a).

[0141] When establishing a primary barrier below the production casing (44a) shoe (47), the control lines (52) terminated above, will no longer have the capacity of migrating fluids / gases to surface.

[0142] Figure 15 shows the well as described in Figure 14, in which the foundation (85g) has hardened (85h) across all annuli (99) above the plug (64a). The plug (64a) and foundation (85h) has been tagged (121 ) by the coiled tubing string (12), now placed adjacent to the production casing (44a) shoe (47), squeezing barrier material (86) across full cross section according to calculated volumes, through the perforations (89) below the production casing (44a) shoe (47). Displaced fluids are evacuated through perforations (88) (119c) above the packer (60a). By measuring pumped and displaced volumes, and pressure, and utilizing the back pressure of the fluid column above the packer (60a), the integrity of the primary barrier can be verified while pumping (119b). When calculated volumes are placed, the coiled tubing string (12) with a packer (60a) is being lifted to avoid embedding, and to allow for placing of upper section of the primary barrier.

[0143] Figure 16 shows the well as described in Figures 14 and 15), in which the coiled tubing string (12), with the set packer (60a), have been pulled up while pumping (119b), and placed adjacent to the liner hanger packer (41 ). Barrier material (86) is squeezed through the lower perforations (89) and displaced fluid is evacuated through perforations (88) above the coiled tubing (12) packer (60a). Hence the barrier integrity can be verified (119b, 119c), while establishing a full cross section primary barrier.

[0144] Figure 17 shows the well as described in Figures 14,15, 16, with a hardened (87b) and tagged (121 ) primary barrier. The integrity of the barrier was verified during pumping (119b, 122), however a new pressure test (119) can be conducted by pumping fluid through the coiled tubing string (12) and applying pressure against the plug (87b) and through the perforations (88) above the plug (87b). Alternatively, the integrity of the primary barrier, can be verified by applying negative pressure (119a, 124) above the plug (87b, 119), and by measuring pressure development. By installing a permanent plug in the production liner (43a) below the terminated control lines (52), the control lines are sealed off from below, preventing hydrocarbon ingress. Over the long term (128), the embedded steel within the barrier reinforces the barrier element (129), enhancing its structural integrity.

[0145] Figure 18 shows a well (79) with all steel remaining (130), including production tubing (42), casing strings (43a, 44a, 45a, 46a) and control lines (52), running back to the wellhead (51 ) outlet ports (29, see Figure 8). On Figure 18 is a pressure and temperature (112) gauge, located above the production packer (40). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or no cement (123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a). The subsea pump (16b) with a Y-connection (105) is optionally used to lower pressure (124) in a-annuli (99b) and / or within production tubing (42), and / or to obtain circulation of fluids to surface (110).

[0146] A plug (64a, 71 , 72) is placed and tagged (121 ) adjacent to the production packer (40), a temporary plugged well (81 ) might look like this. Perforations (88) are shot above the plug (64a, 71 , 72, 121 ). Perforations into a-annuli (99b) only (89, 92) are also shot below the intermediate casing (45a) shoe (47), which is for evacuation of displaced fluids, and for later use for a secondary plug. By establishing a primary barrier above the production packer (40), the production packer serves as a foundation for the barrier material (86) in a-annuli (99b).

[0147] Figure 19 shows the well as described in Figure 18. The coiled tubing string (12) with set packer (60a) is placed in the mid-section of the perforations, squeezing barrier material (86) across full cross section (111 ), according to pre-calculated volumes, through perforations shot between the production packer (40) and the plug (64a, 71 , 72, 121 ). Displaced fluids are evacuated through perforations above (89, 92).

[0148] Figure 20 shows a well as described in Figures 18 and 19. The coiled tubing string (12) with a set packer (60a) has been lifted while pumping (119c), and is now placed above the perforations (88) and below the perforations (89, 92) squeezing barrier material (86) through the perforations (89) and into annuli (99) and micro-annuli (99a) with the plug (64a, 71 , 72, 121 ) and the production packer (40) as a foundation. Displaced fluids are evacuated through the perforations (89, 92) below the intermediate casing (45a) shoe (47). As the coiled tubing packer (60a) is sealing of the artificial annuli (99c) above the packer (60a), the barrier material (86) rises in the a-annuli (99b) and fills up cavities towards formation (48) with missing cement (44b, 123). The integrity of the plug can be verified while pumping, by measuring pumped barrier material (86) and displaced volumes and pressure (119c).

[0149] Figure 21 shows a well as described in Figures 18-20. The coiled tubing string (12) has tagged (121 ) the cured barrier (87b) and is now placed above. The integrity of the barrier was verified by squeezing against back pressure, and through measuring pumped and displaced volumes and pressure (119b). As the perforations (89, 92) below the intermediate casing (45a) shoe (47) allows for cross section test, additional pressure test can be conducted from above (119), either by measuring pressure development during inflow test, or during a negative pressure test (119a, 124). As all steel is left behind in the well, the steel / iron will act as reinforcement for the barrier material (86), which may be cement (85c). Over the long term, the embedded steel within the barrier reinforces the barrier element (129), enhancing its structural integrity.

[0150] Figure 22 shows a well (79) with all steel remaining (130), including production tubing (42), casing strings (43a, 44a, 45a, 46a) and control lines (52). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or no cement (123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a). The subsea pump (16b) with a Y-connection (105) is optionally used to lower pressure (124) in a-annuli (99b) and within production tubing (42), and / or to obtain circulation of fluids to surface (110).

[0151] A plug (64a) is placed and tagged (121 ) inside the production tubing (42) in the production casing (44a) section below the intermediate casing (45a) shoe (47). Perforations (88, 89) are shot above the plug, adjacent to and above the intermediate casing (45a) shoe (47). The coiled tubing string (12), equipped with control line (91 b) and sensors (91 a) for detecting tracer material (85f) and reading of pressure and temperature (112), is about to place a two-component fast-setting foundation (85g), consisting of a base component (85g1 ) separated by a spacer (61a), a hardener (85g2), followed by a spacer (61 a), to be placed across full cross section above the plug (64a, 121 ).

[0152] Figure 23 shows the well as described in Figure 22. The foundation is hardened (85h) and tagged (121 ) by the coiled tubing string (12).

[0153] Figure 24 shows the well as described in Figures 22-23. The coiled tubing string (12) with a set packer (60a) is placed above the tagged (121 ) plug (64a) and the tagged foundation (85h, 121 ) in between the perforated section adjacent and above the intermediate casing (45a) shoe (47). The lower section of the permanent barrier is placed by hesitation pumping (125) of barrier material (86) with tracer (85f) above the tagged (121 ) foundation (85h). The sensor (91 a) for tracer (85f) will register any circulation through the perforations above (110c, 92) the packer (60a). The sensor for pressure and temperature (112) below the packer (60a) reads pressure development during pumping.

[0154] Figure 25 shows the well as described in Figures 22-24. After waiting a certain amount of time for the barrier material (86, 85f) to cure (87a), the lower section is tagged (121 ), and through the coiled tubing string (12), barrier material (86, 85f) is squeezed across full cross section through perforations (88). Over the long term (128), the embedded steel within the barrier reinforces the barrier element (129), enhancing its structural integrity.

[0155] Figure 26 shows a well as described in Figures 22-25. The barrier has been hardened and tagged (121 ), and a pressure test from above revealed a pressure drop, indicating leakage.

[0156] Figure 27 shows a well as described in Figure 26. Additional perforations (88, 92) are shot above the cured barrier (87a) for circulation in annuli (99) and evacuation of displaced fluids (119c) to be handled by the subsea pump unit (16b) with actuated Y- connection (105). Colloidal silica (85a) with a tracer (85f) dispersed in saltwater (61 d) is pumped according to calculated volumes and pressure through a coiled tubing string (12) with a packer (60a) and sensors for pressure and temperature (1 12) and tracer (91 a). The aim of the operation is to seal off any cracks which caused the pressure drop during the pressure test.

[0157] The barrier integrity is verified while pumping barrier material against a foundation, and through perforations below and above the coiled tubing packer, while measuring pumped and displaced volumes, and pressure in a closed system (119b).

[0158] Figure 28 shows a well as described in Figure 27. After waiting a certain amount of time for the colloidal silica (85a) and saltwater (61 d) to cure (87a) the repaired barrier can be pressure tested if deemed necessary.

[0159] Figure 29 shows a well with a cured (87a) and pressure tested (87b) barrier.

[0160] Figure 30 shows a well (79) with all steel remaining (130), including production tubing (42), casing strings (43a, 44a, 45a, 46a) and control lines (52). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or no cement (123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a). The subsea pump (16b) with a Y-connection (105) is optionally used to lower pressure (124) in a-annuli (99b) and / or within production tubing (42), and / or to obtain circulation of fluids to surface (1 10).

[0161] Perforations (88a) below the intermediate casing (45a) shoe (47) are shot prior to placing and tagging the plug (64a, 121 ) in the production casing (44a), to accommodate for verification of the barrier across full cross section by gas, emitted from gas emitter with timer (126), after the barrier has been established and cured (87a). A foundation (85h) for the barrier is placed across full cross section upon the plug (64a, 121 ). Multiple perforations (88) are shot above, adjacent and below the intermediate casing (45a) shoe (47). Perforations (89, 92) are also shot below the surface casing (46a) shoe (47), to accommodate for evacuation of displacement fluids, and to be used for establishment for a barrier. The gas emitter (126) is equipped with a timer, scheduled to emit gas when the barrier (87a) is cured. A sensor (127) for the specific gas from the gas emitter (126) can be placed in the coiled tubing injector stack(58a) (Figures 5, 6, 31 ) or on the Christmas tree (94). The coiled tubing string (12) with open packer (60b) is placed in the lower part of the intermediate casing (45a), above the plug (64a, 121 ) and foundation (85h, 121 ), in the perforated (88) section, ready to pump two subsequent sequences of relevant dispersed cations (100a) separated by a spacer (61 a) from colloidal silica dispersed in freshwater pill (85a1 ). The aim of this fluid train is to obtain optimal mixing of colloidal silica (85a1 ) and cations (100a) as described in Figures 10-13.

[0162] Figure 31 shows the well as described in Figure 30. The mixture of dispersed substances (85a1 , 100a) is being mixed (85a2) and squeezed across full cross section of the well (79) according to measured, calculated volumes and pressure. Displaced fluids are evacuated through perforations above the packer (60b) and to surface, through the Y-connection (105) with associated flowmeter (119c).

[0163] Figure 32 shows the well as described in Figures 30-31 . The coiled tubing string (12) with closed packer (60a) has been lifted while pumping (119c). The barrier material components (85a1 , 100a), separated by a spacer (61a), is being squeezed through perforations (89) below the packer (60b), and the displaced fluids are being evacuated through the perforations (89, 92) below the surface casing (46a) shoe (47) and through the Y-connection (105), with associated flowmeter, on the subsea pump (16b), to surface, optionally assisted by the surface pump (118), Figure 3, 4, 5 and 6. The barrier is pressure tested while the barrier material is being squeezed, by utilizing back pressure, measurement of pumped and displaced volumes, and pressure (119b).

[0164] Figure 33 shows the well as described in Figures 30-32. After waiting a certain amount of time for the barrier material (85a2) to cure (87a), the coiled tubing string (12) with a closed packer (60b) is placed above the barrier (87a, 85a2), and below the perforations (88, 92) shot below the surface casing (46a) shoe (47). By displacing fluids above the barrier (87a 85a2) a negative pressure test (119a, 124) across full cross section can be conducted, alternatively the integrity can be verified by conducting an inflow test (119). When the gas is emitted from the gas emitter with timer (126), the gas will flow through the perforations (89) below the plug (64a, 121 ), and eventually also through the plug (64a, 121 ) and through the barrier (87a, 85a2). Any leakage will be detected by the sensor (127) in the coiled tubing injector stack (58a), or on the Christmas tree (94). Over the long term (128), the embedded steel within the barrier reinforces the barrier element (129), enhancing its structural integrity.

[0165] Figure 34 shows a well (79) with all steel remaining (130), including production tubing (42), casing strings (43a, 44a, 45a, 46a) and control lines (52). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or no cement (120, 123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a). The subsea pump (16b) with a Y-connection (105) is optionally used to lower pressure (124) in a-annuli (99b) and / or within production tubing (42), and / or to obtain circulation of fluids to surface (110).

[0166] A plug (64a) is placed and tagged (121 ) in the production tubing (42), below the surface casing (46a) shoe (47). A foundation (85g) has been placed and hardened (85h) across full cross section above the plug (64a, 121 ). The foundation (85h) is tagged (121 ) by the coiled tubing string (12). Perforations (88, 89a) are shot below, adjacent and above the surface casing (46a) shoe (47). These perforations (88, 89a) are for placing a full cross section barrier. The upper perforations (89a, 92) are not perforating the surface casing (46a). These are for evacuation of displaced fluids and pressure test.

[0167] Figure 35 shows the well as described in Figure 34. The coiled tubing string (12) with expanded packer (60a), is placed above the perforations (88) and below perforations (89a, 92), squeezing barrier material (86) according to calculated and measured volumes and pressure, across all annuli (99), except outside the surface casing (46a), through the perforations (88, 89a). The displaced fluids are evacuated through perforations (89a, 92) above the coiled tubing string (12) packer (60a). A verification of the barrier integrity can be conducted while pumping by utilizing back pressure, and measuring pumped and displaced volumes, and pressure (119b).

[0168] Figure 36 shows the well as described in Figures 34-35. The coiled tubing string (12) has tagged (121 ) the cured barrier (87a). A pressure test is being conducted through the coiled tubing string (12) with expanded packer (60a). A fluid is pumped against the barrier and through the perforations (89, 92), above the barrier (119).

[0169] Alternatively, a negative pressure test (124) can be conducted by engaging the subsea pump (16b) with the Y-connection (105).

[0170] Figure 37 shows the subsea equipment as described in Figure 6. The control lines (52) can be sealed off by engaging the module for bleeding off and sealing off control lines (93), associated with the hydraulic pressure unit (17a) placed on the right side of the Christmas tree (94). The module for bleeding off and sealing off control lines (93) is operated from the control cabin (10) on the vessel (6) via the umbilical (15).

[0171] This operation can be conducted any suitable time after the hold open sleeve (39c) has been placed across the downhole safety valve (39a) sleeve. The remote operated vehicle (20) is engaged to switch between wellhead outlets ports (29). The reason why the downhole safety valve (39b) control line (52) can be sealed off, while the downhole safety valve (39b) is operated open, is that the downhole safety valve (39b) has no function as barrier in the long term. When a P&A operation is conducted according to the method described in this patent, the control lines are also sealed off from below. The following procedure is for operation of the module for bleeding and sealing off control lines from above:

[0172] - Preheater (30) is engaged to preheat control line (52) sealing material (101 ).

[0173] - The first wellhead outlet port (29) is connected to the module (93) through the hydraulic control line (16a).

[0174] - The valves to the first low pressure tank (93c) are opened, and the suction pump (93b) is engaged. - When calculated volume of fluids from the first wellhead outlet port (29) have been evacuated to the first low pressure tank (93c), the pump is stopped, and the valves are closed.

[0175] - Then the valves to the first and / or second tank with pressurized sealant material (93a, 101 ) are opened, and the pump (93b) for injection is engaged.

[0176] - The one or two-component sealing material (101 ) is pumped through a static mixer (31 ).

[0177] - When calculated volumes of sealant material (101 ) are pumped into the first control line (52) through first wellhead outlet port (29), the lines are flushed and the pump (93b) is stopped, and the valves are closed.

[0178] - A remote operated vehicle can assist in connecting to another wellhead outlet port (29).

[0179] Figure 38 shows the subsea equipment with full circulation to surface (110), with the aim of sealing off all cavities in the horizontal (28) Christmas tree (94), including the production bore (33) and the annulus bore (32). A plug (64a) is placed and tagged (121 ) in the upper section of the surface casing (46a). Perforations (89) into a- annulus are shot above, and a foundation (85g) is placed upon the plug (64a, 121 ). After waiting a certain amount of time for the foundation to cure (85h), barrier material (86) is pumped through the coiled tubing string (12). Fluid return to surface is achieved by engaging the subsea pump (16b), with a Y-connection (105) and a surface pump (118). See Figure 3, 4 and 5.

[0180] Figure 39 shows a well as described in fig. 38. The subsea pumping unit (16b) and the subsea hydraulic power unit (17a) has been removed, and all cavities in the horizontal Christmas tree (28, 78) is filled with barrier material, constituting an environmental plug, preventing any hydrocarbons from escaping. The subsea coiled tubing injection stack (58a) has been released and is being pulled to surface. A remotely operated vehicle ROV (20), operated through an umbilical (22), is surveying the lifting operation. This is an alternative to pulling a Christmas tree (94), especially relevant if the subsea Christmas tree (94) is horizontal (28), in which the production tubing (42) is hung off when installed. Figure 40 shows the well as described in Figure 39. All cavities in the Christmas tree (28, 94) are filled with cured barrier material (87a). A remotely operated vehicle ROV (20), operated through an umbilical (22), is jetting the base of the wellhead (51 ) area to remove sediments, to ensure adhesion for the cement dome which is to be placed upon the horizontal (28) Christmas tree (94) and eventually any remaining structure. The cement is placed upon the subsea structure by use of a submersible cement bucket (67), sized according to vessel (6) or rig (3) lifting capacity. Embedding the subsea structure in a cement dome (117) can be regarded as a specialized operation, hence be conducted by dedicated and relevantly equipped vessels (6) in later operations. The submersible bucket (67) has the following functionality: top hinged hatches (67a), opened by remote operated vehicle (20) prior to open bottom bucket plug, lifting ears (67b), sliding base plate (67c), and hooks (67d) and ROV hooks with locking mechanism (67f), for remote operated vehicles (19, 20), The top hinged hatches (67a), and the sliding base plate (67c) are in open position when returning to surface, which allows for seawater to flush through and clean the bucket inside. The cement can alternatively be pumped through a coiled tubing string (12); however, the required viscosity could be a challenge. Placing a coffer around the subsea structure is also an alternative which allows for more precise volume predictions; however, the dome structure has the advantage of not being an obstruction for other commercial interests such as bottom trawling.

[0181] Figure 41 shows the well as described in Figure 40. All cavities in the horizontal (28) Christmas tree (94) are filled with cured barrier material (87a). The remote operated vehicle (19) has opened the top hinged hatches (67a) prior to opening the sliding base plate (67c) by pulling the hook (67d) and shearing the locking split pin (67e). And cement is pouring out by force of gravity, embedding the subsea Christmas tree (28, 94).

[0182] A remote operated vehicle (20) with a vibration rod (20a) is removing trapped air and water from the cement.

[0183] By embedding the subsea horizontal (28) Christmas tree (94) in a cement (86, 85c) dome, the subsea structure will no longer be an obstacle for commercial interests, such as bottom trawling. The subsea control lines (52) are additionally sealed off by embedding the wellhead (51 ) outlet ports (29).

[0184] Figure 42 shows a vertical Christmas tree (78, 94) being pulled to surface by a crane and a wire with hoisting device (67g), leaving the wellhead (51 ). A remote operated vehicle (19) is surveying the lifting operation. Another remote operated vehicle (20) is jetting sediments away from the base of the wellhead (51 ) by means of a high- pressure cleaner (20b) to provide for adhesion for cement.

[0185] Figure 43 shows a horizontal Christmas tree (28, 94) being pulled to surface by a hoisting device (67g) and crane (98). As the production tubing (42) is hung off inside the horizontal Christmas tree (28), the tubing hanger (57) and a piece of the production tubing (42), follows up after the production tubing (42) has been cut below the wellhead (51 ). Another remote operated vehicle (20) is jetting sediments away from the base of the wellhead (51 ) by means of a high-pressure cleaner (20b) to provide for adhesion for cement.

[0186] Figure 44 shows placement of an environmental plug, on a wellhead (51 ) from which a subsea Christmas tree (94) has been removed and pulled to surface. A cover plate with e.g. metal ribbons or elements (107) for reinforcement is placed upon the wellhead, avoiding cement from entering the wellhead (51 ) and wellbore (79a).

[0187] Debris have been removed around the base of the subsea structure, for adhesion. Cement is poured from the submersible cement bucket (67) as described in Figures 40-41 . A remote operated vehicle (20) is equipped with a vibrating rod (20a) to remove excess air and water from the cement dome.

[0188] By embedding the subsea wellhead (51 ) in a cement (86, 85c) dome, the subsea structure will no longer be an obstacle for commercial interests, such as bottom trawling. The subsea control lines (52) are additionally sealed off by embedding the wellhead (51 ) outlet ports (29).

[0189] Figure 45 shows a well (79) with all steel remaining (130), including production tubing (42), casing strings (43a, 44a, 45a, 46a) and control lines (52). The cement outside the casing strings; production liner (43a) cement (43b), production casing (44a) cement (44b), intermediate casing (45a) cement (45b), surface casing (46a) cement (46b) is presented as diagonal lines, showing poor or no cement (123). This knowledge about the cement bond might have been obtained by use of a cement bond log tool (59a). The control lines (52) terminated above the barriers have been sealed off from below, and additionally bled off and sealed off, by employment of the module (93), see Figures 5, 6 and 37.

[0190] A primary plug is placed adjacent to the production casing (44a) shoe (47). A plug (64a) is placed inside the production tubing (42) below the production casing (44a) shoe (47). Above the plug (64a) is a foundation (85h) placed across full cross section. A full cross section permanent barrier is placed adjacent to the production casing (44a) shoe (47), above the foundation (85h). The barrier has been tagged (121 ) and pressure tested from above (119a1 , 87b) and / or from below (119a) by creating negative pressure (124) above the plug, while observing pressure development. By establishing a cross-section barrier below the termination point of the control lines, inflow through these lines (52) will be permanently prevented.

[0191] A secondary plug is established adjacent to the intermediate casing (45a) shoe (47). A plug (64a) is placed in the production tubing (42) and perforations (89) are shot above. A foundation (85h) is placed across full cross section above the plug. A full cross section permanent barrier is placed adjacent to the intermediate casing (45a) shoe (47), above the foundation (85h). The integrity of the plug was verified during the establishment of the barrier while squeezing (119b, 119c). The barrier is tagged (121 ) and pressure tested from above (119a1 ) and / or from ‘below’ (119a), by creating negative pressure (124) above the secondary plug and observations were made for any pressure increase.

[0192] A tertiary plug is placed adjacent to the surface casing (46a) shoe (47). A plug (64a) is placed in the production tubing (42) below the surface casing (45a) shoe (47). A foundation is placed across full cross section through perforations (89) above the tagged (121 ) plug (64a). A full cross section permanent barrier is placed adjacent to the intermediate casing (45a) shoe (47), above the foundation (85h). The integrity of the plug was verified during the establishment of the barrier while squeezing (111 , 119b). The barrier is tagged (121 ) and pressure tested from above (119a1 ) and / or from ‘below’ (119a), by creating negative pressure (124) above the plug and observations were made for any unexpected pressure changes.

[0193] An environmental plug is placed upon the wellhead, embodied in form of a cement dome, preventing all emissions of hydrocarbon to sea, including preventing any leakage through the control lines.

[0194] Figure 46 shows a well (79) as described in Figure 43, in an eternal perspective (128) I over the long term. Except from steel and other components embedded in, and coated by barrier material (86), has oxidized and finally eroded. The embedded steel within the barrier reinforces the barrier element (129), enhancing its structural integrity.

[0195] Figure 47 shows a well (79) as described in Figures 43-44, however as this Christmas tree is horizontal (28), and could not be pulled without cutting the production tubing, it is embedded, internally, including the annulus (32) and the production bores (33), and externally in a cement dome (117), which is placed upon the Christmas tree (28, 94) and the wellhead (51 ). The embedded steel within the barrier reinforces the barrier element (129), enhancing its structural integrity.

[0196] Figure 48 shows a well (79), from below: A perforated reservoir (50, 90), a plug (64a, 71 , 72) placed adjacent to the production packer (40). The perforations (88) are shot through the production tubing (42) and the production casing (44a) above the plug, and perforations (89, 92) through the production tubing are shot below the intermediate casing (45a) shoe (47). Through the coiled tubing string (12) with expanded packer (60a), a barrier material (86) is being squeezed (122). Displaced fluids are evacuated through upper perforations (89, 92). By measuring pumped and displaced volumes, and pressure, barrier integrity can be assessed while pumping (119b, 119c). The plug and abandonment operation is being conducted from a platform (3) with dry wellhead (115). A surface BOP (113) is placed on the wellhead (115). The platform (3) is not equipped with conventional drilling facilities. Coiled tubing equipment (9, 11 , 12, 13, 13b) and assorted barrels (61 a, 61 c, 61 e, 85a, 85b, 85c, 85d, 85e, 85f, 85g, 85g 1 , 85g2, 85h, 85a1 , 85a2, 26), pumps (16c, 93b, 118) and motor (9a), reel (8), etc, as described in Figure 3 and 4. The platform (3) is also equipped with a cement laboratory (17b) and control cabin (10).

[0197] On the left side of the wellhead (115), is a pump (16c) with a Y-connection (105) to the wellhead (115) ports (29) and to the surface BOP (113) choke valves (58c). On the right side of the wellhead (115) is a hydraulic pressure unit (17a) with a module for sealing off (93) control lines (52).

[0198] Additional modifications, alterations and adaptations of the present invention will suggest themselves to those skilled in the art without departing from the scope of the invention as defined in the following patent claims.

[0199]

[0200]

[0201]

[0202]

Claims

AMENDED CLAIMS received by the International Bureau on 17 September 2025 (17.09.2025).1 . A method for riserless and / or rigless plug and abandonment of a wellbore (79a), the method comprising, in a recommended order, the steps of: a) placing a pumping unit (16b) in close proximity to a wellhead (51 , 115) of the wellbore (79a); b) placing a coiled tubing injector stack (58a) on top of the wellhead (51 ) or on top of a Christmas tree (94) on the wellhead (51 ); c) connecting a source (105) on the pumping unit (16b), using a connection comprising a first hose (108), to a choke valve (58c) arranged on the coiled tubing injector stack (58a), by using the first hose (108); d) connecting the pumping unit (16b) to a pit or separator (26) via a first umbilical or hose (14); e) removing any unnecessary plug (71 , 72, 64a) on the way down by means of a stroker arranged at the operational end of a string; f) scraping and washing a section of the wellbore to be plugged by means of a scraper (95a) having high-pressure nozzles and brushes and using a washing fluid (61c) with solvents and anti-freeze agents (95b) if required, and displacing fluid (109), gases and / or particles from the wellbore to maintain well integrity, g) running a coiled tubing string (12) or wireline string (12a) into the wellbore, with all steel remaining, including the production tubing, wherein the coiled tubing string (12) or wireline string (12a) is, for each run-in-hole operation, equipped, at an operational end thereof and depending on the operation to be performed, with at least one of: the stroker configured for removing any unnecessary plug (71 , 72, 64a), a passive packer (60a) being unset under run-in-hole operation and configured to expand or set under use, and / or assemblies (68) comprising at least one perforation gun (62a, 88, 89) and / or a milling tool (102), and a plug (64a), and possibly a well tractor (75, 75a); h) milling and / or perforating the section of the wellbore to be plugged with its adjacent production tubing (42), other adjacent casing and / or adjacent formation, by means of the milling tool (102) and / or the at least one perforation gun (62a, 88, 89) respectively;i) perforating (88, 89, 92) above the section of the wellbore (79a) to be plugged (80) to accommodate for evacuation of displaced fluid, and for pressure test across full cross section, j) placing at least one packer and / or at least one plug (63a, 63b, 64a, 71 , 72) above and / or below the section to be plugged, and / or using any existing packer (40, 41) and / or plug (71) to isolate the section to be plugged; k) pumping barrier materials (86) through the coiled tubing string (12) into the section to be plugged and through perforations (88, 89, 92) and / or milled sections (103) to create a first barrier, wherein the passive packer (60a, 60b) at the operational end of the coiled tubing string (12) is being activated and expanded under use and isolates the annular space between the coiled tubing string (12) and the production tubing (42); and l) pulling out the coiled tubing string (12) with the passive packer (60a).

2. The method for riserless and / or rigless plug and abandonment according to claim 1 , wherein the connection is a Y-connection (105) further comprising a second hose (104), and the source on the pumping unit (16b) is being connected to an annulus valve (37a; 116) arranged on the Christmas tree (94) or on the wellhead (51 , 115) by using the second hose (104) to facilitate circulation to the surface (110) or bull heading a-annulus volumes.

3. The method for riserless and / or rigless plug and abandonment according to claim 1 or 2, further comprising the steps of: if a valve cannot be manually operated, placing a hydraulic power unit (17a) in close proximity to the wellhead (51 ); connecting the hydraulic power unit (17a) having at least one tank (93a, 93c, 93d) for control line sealant barrier material (101) and a static mixer (31 ) to a wellhead port (29) via an external control line (16a).

4. The method for riserless and / or rigless plug and abandonment according to any preceding claim, further comprising the steps of: curing the barrier material of the first barrier; and optionally pressure testing the first barrier.

5. The method for riserless and / or rigless plug and abandonment according to any preceding claim, further comprising the step of: creating at least one second barrier above the first barrier using all or some of the steps a) - 1).

6. The method for riserless and / or rigless plug and abandonment according to claim 1 or 5, wherein under step j) the barrier material (86) is being circulated through the annuli (99) to the surface (110) through the coiled tubing string (12) placed inside the production tubing (42) and through the created perforations (88, 92) or milled slots (103) placed below the passive coiled tubing packer (60a).

7. The method for riserless and / or rigless plug and abandonment according to claim 5, further comprising the steps of: curing the barrier material of said at least one second barrier; and optionally pressure testing said at least one second barrier.

8. The method for riserless and / or rigless plug and abandonment according to any preceding claim, further comprising the step of: pressure testing, from above, each barrier placed across full cross section of the wellbore.

9. The method for riserless and / or rigless plug and abandonment according to claim 4 or 7, where the curing process is being delayed by placing colloidal silica dispersed in a freshwater pill (85a, 85a1 ) prior to exposing the colloidal silica to seawater (61 d) or salt brine (100) in the formation (48) and / or the reservoir (50).

10. The method for riserless and / or rigless plug and abandonment according to any preceding claim, further comprising the steps of: bleeding off all downhole control lines (52); and sealing off the downhole control lines (52).

11. The method for riserless and / or rigless plug and abandonment according to any preceding claim, further comprising the step of: pouring cement (85c) on top of the wellhead (51 ) and / or the Christmas tree (94) to create a cement dome (117) over them.

12. The method for riserless and / or rigless plug and abandonment according to any preceding claim, the method being configured for plug and abandonment of a subsea well, wherein a light well intervention vessel (6) and at least one remote operated vehicle, ROV, (19, 20), connected to the vessel (6) and operated by at least one umbilical (21 , 22), are being used to perform some of the method steps.

13. The method for riserless and / or rigless plug and abandonment according to any one of claims 1-11 , wherein the method is configured for plug and abandonment of a surface or platform well.

14. The method for riserless and / or rigless plug and abandonment according to any preceding claim, wherein a tracer and / or a sensor (85f, 91a) is / are used to track and / or verify the circulation of the barrier material.

15. The method for riserless and / or rigless plug and abandonment according to any preceding claim, further comprising the step of: positioning a cover plate (107) over the wellhead (51 ) to enclose the wellhead (51 ); delivering a cement slurry upon the cover plate (107) to embed the wellhead (51 ) and outlet ports (29) of the control line(s) (52) and / or the wellhead (51 ); and applying vibration, for example by means of a vibration rod (20a), within the cement slurry to remove any excess air and / or water, thereby forming a cement dome (117) encapsulating the wellhead (51 ) and the outlet ports (29) of the control line(s) (52) and / or the wellhead (51 ).

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