Search

EP-4359638-B1 - DOWNHOLE MILLABLE PERMANENT PLUG AND METHOD FOR SETTING A DOWNHOLE MILLABLE PERMANENT PLUG

EP4359638B1EP 4359638 B1EP4359638 B1EP 4359638B1EP-4359638-B1

Inventors

  • HIORTH, ESPEN

Dates

Publication Date
20260506
Application Date
20220602

Claims (16)

  1. Downhole millable permanent plug (1) for permanently sealing of a downhole well (WE) , wherein the permanent plug (1) comprises: - a mandrel (10) having a longitudinal axis (I-I); - a first sealing element (20a) provided radially outside of the mandrel (10); - a second sealing element (20b) provided radially outside of the mandrel (10) at a distance from the first sealing element (20a); - a metal body (40) provided radially outside of the mandrel (10) between the first sealing element (20a) and the second sealing element (20b); wherein the permanent well plug (1) is configured to be in the following states: - a run state, in which the first sealing element (20a) and the second sealing element (20b) are radially retracted; - an intermediate state, in which the first sealing element (20a) and the second sealing element (20b) are radially expanded into contact with the well (WE); - a set state; characterized in that : - the permanent plug (1) comprises a setting system (50) comprising a heater (51) for melting the metal body (40); - in the set state, the metal body (40) has been melted by the heater (51) and subsequently solidified into contact with the well (WE); - the first sealing element (20a) is provided between a first wedging surface (55) and a second wedging surface (45) and wherein relative longitudinal displacement between the first wedging surface (55) and the second wedging surface (45) towards each other is radially expanding the first sealing element (20a); - the second sealing element (20b) is provided between a third wedging surface (46) and a fourth wedging surface (16), and wherein relative longitudinal displacement between the third wedging surface (46) and the fourth wedging surface (16) towards each other is radially expanding the second sealing element (20a).
  2. Downhole millable permanent plug (1) according to claim 1, wherein the setting system (50) comprises: - a first spring support (52) secured to the mandrel (10); - a second spring support (53) longitudinally displaceable relative to the mandrel (10); - a spring (55) for moving the second spring support (53) relative to the first spring support (52); wherein the second spring support (53) is releasably secured to the mandrel (10) in the run state; wherein the second spring support (53) is released in the intermediate state, causing the second spring support (53) to be longitudinally displaced a first distance (D1) from the first spring support (52) relative to the mandrel (10); wherein the first sealing element (20a) and the second sealing element (20b) are radially expanded into contact with the well (WE) by the longitudinal displacement of the second spring support (53).
  3. Downhole millable permanent plug (1) according to claim 2, wherein the second spring support (53) is allowed to be longitudinally displaced a second distance (D2) from the first spring support (52) relative to the mandrel (10) when the metal body (40) has been melted by the heater (51), wherein the second distance (D2) is longer than the first distance (D1).
  4. Downhole millable permanent plug (1) according to claim 1, wherein the first wedging surface (55) is provided on the second spring support (53) and wherein the second wedging surface (45) is provided on the metal body (40).
  5. Downhole millable permanent plug (1) according to claim 1, wherein the third wedging surface (46) is provided on the metal body (40), wherein the fourth wedging surface (16) is provided on the mandrel (10) and wherein the metal body (40) is longitudinally displaceable relative to the mandrel (10).
  6. Downhole millable permanent plug (1) according to claim 2, wherein the second spring support (53) is releasably secured to the mandrel (10) by means of a meltable locking element (56) in the run state.
  7. Downhole millable permanent plug (1) according to claim 6, wherein the setting system (50) comprises an auxiliary heater (57) for melting the meltable locking element (56).
  8. Downhole millable permanent plug (1) according to claim 7, wherein the auxiliary heater (57) is integrated in the mandrel (10).
  9. Downhole millable permanent plug (1) according to any one of the above claims, wherein the metal body (40) comprises a metal or metal alloy whose volume is larger when solidified than when molten.
  10. Downhole millable permanent plug (1) according to claim 9, wherein the metal is bismuth or the metal alloy is a bismuth alloy.
  11. Downhole millable permanent plug (1) according to any one of the above claims, wherein the metal body (40) comprises a metal having or metal alloy having a melting temperature lower than the melting temperature of the mandrel metal.
  12. Downhole millable permanent plug (1) according to any one of the above claims, wherein the first sealing element (20a) and/or the second sealing element (20b) comprise a plurality of thimble-shaped elements inserted into each other to form a torus.
  13. Downhole millable permanent plug (1) according to any one of the above claims, wherein the heater (51) is integrated in the mandrel (10).
  14. Method for setting a downhole millable permanent plug (1) in a downhole well (WE), wherein the method comprises the steps of: - lowering the plug (1) to a desired location in the downhole well (WE); - expanding a first sealing element (20a) of the plug (1) radially into contact with the well (WE) by relative longitudinal displacement of a first wedging surface (55) and a second wedging surface (45) towards each other; - expanding a second sealing element (20b) of the plug (1) radially into contact with the well (WE) at a longitudinal distance from the first sealing element (20a) by relative longitudinal displacement of a third wedging surface (46) and a fourth wedging surface (16) towards each other; - supplying molten metal in an compartment (CC) outside of a mandrel (10) of the plug (1) and longitudinally between the first sealing element (20a) and the second sealing element (20b); - allowing the molten metal to solidify.
  15. Method according to claim 14, wherein the step of supplying molten metal is comprising the steps of: - melting a metal body (40) provided radially outside of the mandrel (10) longitudinally between the first sealing element (20a) and the second sealing element (20b).
  16. Method according to claim 15, wherein the method further comprises the step of: - reducing the longitudinal distance between the first sealing element (20a) and the second sealing element (20b) when the molten metal is present in the compartment (CC) outside of the mandrel (10) of the plug (1) and longitudinally between the first sealing element (20a) and the second sealing element (20b).

Description

FIELD OF THE INVENTION The present invention relates to a downhole millable permanent plug for permanently sealing of a downhole well. The present invention also relates to a method for setting a downhole millable permanent plug in a downhole well. BACKGROUND OF THE INVENTION Different types of downhole plugs are known. Their purpose is typically to seal off a downhole bore (for example a casing or a production tubing) during a well operation. Some downhole plugs are retrievable, i.e. after a period of time, a retrieving tool are used to retrieve the plug to topside again. Other downhole plugs are permanent plugs. One permanent plug is disclosed in NO 334009. If there is a need to remove a permanent plug, a milling operation is required to mill the permanent plug into smaller fragments. A common problem with such a milling operation is that parts of the plug may start to rotate together with the milling tool, effectively preventing milling to take place. Another permanent plug is disclosed in NO 335473. Here, rotation of the inner mandrel in the set state, typically caused by the milling tool, is bringing a mandrel section of the mandrel to a locked state, in which further rotation of the inner mandrel is prevented. This plug must typically be made of steel, and therefore has a higher cost than other permanent plugs, which typically are made of cheaper materials such as cast iron, cast steel etc. In plugging and abandonment (P&A) operations, permanent plugs are initially set in the well. Then, molten bismuth may be supplied above the permanent plug. Bismuth has expanding properties, i.e. volume of the metal is larger when solidified than when molten. Hence, solidified bismuth serves as an additional barrier above the permanent plug. Typically, a relatively large amount of bismuth is required, which in turn require a relatively large heater in the well to melt the bismuth at the desired location in the well. According to the report "European Commission, Study on the EU's list of Critical Raw Materials - Final Report (2020)", bismuth is considered to be a critical raw material. Hence, one purpose of the present invention is to be able to reduce the amount of bismuth when providing a barrier in a well. US2020056444 describes a system for sealing a region of open hole gravel pack comprising a sealing patch and an installation tool is described. The sealing patch includes a tubular assembly including two expandable anchor/seals and two low melting temperature alloy elements positioned on outside surface of the tubular assembly above the anchor/seals. The system is deployed in desirable location in the well and the tool is operated to set anchor/seals in interference contact with sand-screen. Then the alloy elements are melted to seal the patch. The anchor/seals serve two purposes: they provide a hanging capacity to support the patch in the well and create a "bridge" preventing the molten alloy from freely flowing through the annulus between the tubular assembly and sand screen and focusing the molten alloy at the anchor/seals to flow in radial direction penetrating through the sand-screen and the surrounding proppant sand creating a complete seal. WO03083255 describes a method and apparatus for forming a plug in a passageway. The apparatus comprises a carrier which in use is lowered into the passageway, the carrier comprising an elongate body of a material resistant to creep which supports at least two spaced apart portions that are a sliding fit in the well such that a gap is formed between each of the potions and the passageway. A body of material the :melting point of which is higher than the temperature within the passageway and which expands as it solidifies is supported on the carrier. A heating device is provided for melting the body of material such that the melted material fills a space defined between the first and second portions. The carrier is cooled preferentially to ensure that the molten material solidifies rapidly adjacent the two spaced apart portions, thereby resisting flow of the material as it solidifies past the spaced apart portions. Means are provided to obstruct the gaps formed between the portions arid the passageway; the obstructing means being displaced into the gaps as a result of melting of the body of material or as a result of any creep of material after it has been melted and solidified. WO2019151870 describes a method, system and plug for providing a cross-sectional seal in a well comprising a pipe body and an annulus, the method comprising: lowering a pipe expansion device into the pipe body to a selected location; with the pipe expansion device, expanding a section of the pipe body until contact with a wellbore wall, thus forming an expanded pipe section closing the annulus; lowering a fusible solid material into the expanded pipe section; lowering a heating tool into the expanded pipe section; activating the heating tool and melting the fusible solid material and allowing a m