Apparatus for use in well abandonment

Abstract

A plug (1) for plugging wells, and in particular oil and gas wells, is provided. The plug (1) has a plug body formed from an outer metal tube (2) of a reduced thickness. The plug also has reinforcement means (4), attached to an inner surface of the outer tube (2), that give the plug a cross-sectional structural strength that is at least equivalent to that of a thicker metal tube. The plug has a central heater receiving void located along the axis of the plug to enable a plug deployment heater to be received therein. Also provided is a plug assembly (10) with a variable cross-sectional area in a plane perpendicular to the plane in which the assembly is deployed during the plugging of underground conduits.

Claims

1. A plug assembly with a variable cross-sectional area in a plane perpendicular to the plane in which the assembly is deployed during the plugging of underground conduits, said assembly comprising: a plug having a plug body with a first area having a first cross-sectional area corresponding to a minimum cross-sectional area of the assembly, wherein the first area contains eutectic alloy beads; at least one compressible plug portion, positioned below the first area, and that is resiliently biased to form a second cross-sectional area corresponding to a maximum cross-sectional area of the assembly; and, a plug deployment heater releasably engaged within the plug, and comprising eutectic alloy retaining means that retain the eutectic alloy beads in-line with the plug during deployment of the assembly within an underground conduit so as to enable the minimum cross-sectional area of the assembly to be achieved.

2. The assembly of claim 1, wherein the at least one compressible plug portion comprises an umbrella spring arrangement which is expandable to increase the cross-sectional area of the assembly and compressible to decrease the cross-sectional area of the assembly.

3. The assembly of claim 2, wherein the umbrella spring arrangement is formed from or coated in a material capable of withstanding high temperatures.

4. The assembly of claim 3, wherein the alloy retaining means comprise a dump bailer located on the same axis to and in-line with the plug.

5. The assembly of claim 4, wherein the dump bailer comprises a remote wireline release to discharge the alloy into the area adjacent to the plug.

6. The assembly of claim 5, wherein the dump bailer release means and the plug deployment heater are activated by a single signal in a two-stage process.

7. The assembly of claim 2, wherein the alloy retaining means comprises a dump bailer located on the same axis to and in-line with the plug.

8. The assembly of claim 7, wherein the dump bailer comprises a remote wireline release to discharge the alloy into the area adjacent to the plug.

9. The assembly of claim 8, wherein the dump bailer release means and the plug deployment heater are activated by a single signal in a two-stage process.

10. The assembly of claim 1, wherein the alloy retaining means comprise a dump bailer located on the same axis to and in-line with the plug.

11. The assembly of claim 10, wherein the dump bailer comprises a remote wireline release to discharge the alloy into the area adjacent to the plug.

12. The assembly of claim 11, wherein the dump bailer release and the deployment heater are activated by a single signal in a two stage process.

13. A plug assembly with a variable cross-sectional area in a plane perpendicular to the plane in which the assembly is deployed during the plugging of underground conduits, said assembly comprising: a plug having a plug body with a first area having a first cross-sectional area corresponding to a minimum cross-sectional area of the assembly, wherein the first area contains eutectic alloy beads; at least one compressible plug portion, positioned below the first area, and that is resiliently biased to form a second cross-sectional area corresponding to a maximum cross-sectional area of the assembly; wherein during deployment and plugging the compressible plug portion cross-sectional area is larger than the cross-sectional area of the first area, whereby the second cross-sectional area is configured to remain in contact with an inner surface of the borehole during deployment and plugging; and, a plug deployment chemical heater releasably engaged within the plug, and comprising eutectic alloy retaining means that retain the eutectic alloy beads in-line with the plug during deployment of the assembly within an underground conduit so as to enable the minimum cross-sectional area of the assembly to be achieved.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various aspects of the present invention will now be described with reference to the drawings, wherein:

(2) FIG. 1 shows a cut away side view of a plug according to the first aspect of the present invention;

(3) FIG. 2 shows an end view of a plug according to the first aspect of the present invention;

(4) FIG. 3 shows an exposed view of the plug assembly of the second aspect of the present invention;

(5) FIG. 4 shows the plug assembly of FIG. 3 in situ within a well casing.

DESCRIPTION OF THE VARIOUS ASPECTS OF THE PRESENT INVENTION

(6) It is envisaged that the various aspects of the present invention can be use alone or in combination with one another to provide real benefits in the plugging of underground conduits. In this regard it is envisaged that the present invention is particularly applicable in plugging both vertical and non-vertical wells (with or without well casings).

(7) The described aspects can also be used together with the methods and apparatus described in WO2011/151271 to facilitated the squeezing off and repairing of wells.

(8) Whilst the various aspects of the present invention are considered particularly applicable to the plugging of oil and gas wells it is envisaged that they would provide benefits when plugging other forms of underground conduits such as water pipes for example.

(9) FIGS. 1 and 2 show a plug according to the first aspect of the present invention. The plug is shown in a simplified view for the sake of clarity, however it should be assumed that other features (e.g. heater engaging means) required of plugs of the type described in this document and in WO2011/151271 can be adopted without departing from the concept of this aspect of the present invention.

(10) FIG. 1 shows a cut-away side view of the plug 1 from which the outer tube 2 and the inner tube 3 can be appreciated. The inner and outer tubes, which are preferably circular in cross-section but may have other shapes as required, are spaced apart by the reinforcement means 4 (not shown in FIG. 1).

(11) So that the plug has the required structural strength and resilience both the inner and outer tubes are made from a metal, preferably carbon steel, stainless steel or titanium or other metal alloys suitable for the down-hole conditions. The thickness of the tube walls is in the region of 2 to 3 mm, although wall thicknesses in the region of 1 mm are also contemplated. The two tubes would normally be of a similar thickness.

(12) The plug 1 is provided with a base 5 to which both the inner and outer tubes are connected, for example by welding. The feature is preferable in most embodiments of this aspect of the present invention.

(13) Although spaced apart, the inner 2 and outer 3 tubes are connected together to form a structurally sound plug by virtue of reinforcement means 4. The reinforcement means 4 take the form of corrugated metal (preferably steel or titanium) which is bent back and forth between the inner wall of the outer tube 2 and the outer wall of the inner tube 3.

(14) Wherever the reinforcement means 4 touch the walls of the tubes there is a connection. Preferably the connection is formed by welding or a mechanical fixing (e.g. bolts).

(15) The reinforcement means 4 serves to hold the inner and outer tubes together in such a way as to form a plug with the required level of structural strength. However it is envisaged that by replacing a single solid tube having a thick metal wallas is currently used in plug bodieswith two tubes with thinner metal walls makes it much easier to drill through the plug body. This provides a further option for removing an unwanted well plug when alternative methods of extraction are not possible.

(16) It is envisaged that alternative forms of reinforcement means could be adopted between the inner and outer tubes to provide the same benefits as the corrugated metal. Another possible example is considered to be a metal honeycomb mesh (not shown).

(17) FIGS. 3 and 4 relate to the plug deployment assembly 10 of the second aspect of the present invention. The assembly 10 shown in the figures comprises a plug body 11 (such as, but not necessarily, the one described above), a heater 12 and an igniter wire 13.

(18) The plug body 11 is provided with an umbrella spring arrangement 14 which is mounted to the leading end of the plug 11 so that, when the assembly 10 is delivered down an underground conduit (such as a well casing) it is the umbrella spring arrangement 14 that leads the way.

(19) The umbrella spring arrangement 14 is resiliently biased to an expanded state, as shown in the figures. In its expanded state the umbrella spring arrangement 14 serves to increase the effective width of the plug 11 and the assembly 10.

(20) However when the umbrella spring arrangement 14 meets with obstructions as it is delivered down a well it has the capability to compress, thereby enabling the effective width of the assembly to be minimised to the size of the plug body. Once past the obstruction the umbrella spring arrangement springs back to its expanded state.

(21) This arrangement enables the assembly 10 the present invention to be navigated down wells and other underground conduits that may be suffering from issues such as collapsed casing or may have other forms of obstacle (i.e. abandoned equipment) in them. It is also common practice to have to set plugs through production tubing to enable to get to the desired location; this also involves using a plug that can expand once it is through the tubing. This enables plugs to be deployed into wells in situations that previously might have been impossible, or at best a costly exercise.

(22) The heater 12 is releasably engaged within the plug body 11 so that the heater can be retrieved from the plug body once it has been fixed into a well and the eutectic alloy plug has formed.

(23) The heater 12, which is preferably a thermite based chemical reaction source heater, is provided with a heater core 15 and an igniter/initiator 16. The heater 12 is attached to the igniter wire 13 so that the assembly can be delivered down a well and then the heater can be subsequently retrieved. The igniter wire 13 is connected to a standard wireline connector 17 to facilitate the delivery of the assembly down a well.

(24) The igniter wire 13 is connected to the igniter/initiator 16 through the wireline connector 17 to enable the remote operation of the initiator 16 from ground level. Preferably, and as mentioned above, a twin stage activation of both the igniter and the dump bailer may be achieved by a single signal.

(25) It is envisaged that the igniter/initiator 16 might be alternatively initiated by a pressure pulse, radio wave, fibre optic cable, timers or other remote means. This enables the heater to be deployed using coiled tubing or even slick line, which are non-electrically conductive delivery mechanisms). This is particularly useful when using heaters with chemical source heaters rather than electrical heat sources, which require a constant supply of electrical current to power them.

(26) The assembly 10 is further provided with a dump bailer 18, within which the eutectic alloy (e.g. bismuth alloy) is transported down the well to the site where the plug is to be formed.

(27) In order to minimise the effective width of the assembly, and aid its delivery down a well, the dump bailer is located above but in-line with the heater/plug in the region adjacent to the wireline 13.

(28) The alloy is preferably provided in the form of shot or small beads 19 so that it can freely escape the dump bailer 18 via the release means 20. As with the initiator 16, the release means 20 can be operated remotely via the wireline connector 17 or other means (see above).

(29) Once the release means 20 are actuated gravity ensures that the alloy shot is ejected from the dump bailer into the region adjacent to the plug 11 and the heater 12. However it is envisaged that alternative means for ejecting the alloy from the dump bailed might be adopted without departing from the general concept of the invention.

(30) As will be appreciated from FIG. 4, the expanded umbrella spring arrangement 14 makes contact with the side walls of the underground conduit 21 so that the alloy shot 19 does not simply fall past the plug 11. Once collected adjacent the plug/heater the heater can be actuated to melt the alloy and form a molten alloy. The umbrella spring arrangement 14 is preferably made from, or coated in, a heat resistant material to ensure that the molten alloy does not melt through it.

(31) The molten alloy is then allowed to cool where upon it expands to secure the plug body 11 relative to the underground conduit 21. Once the alloy 19a has cooled (and the plug is secure) the heater 12 can be extracted using the wireline 13.

(32) Although not essential, it is envisaged that the alloy delivered by the assembly 10 might be a Germanium/Bismuth alloy, which has a higher melting temperature than other Bismuth based alloys. The higher melting temperatures of such alloys make them particularly suitable for plugging deeper underground where the subterranean environment is hotter.

(33) In such applications it is appreciated that a chemical heater is required due to the increased level of heat required to melt the alloy (e.g. 550 C.). In particular it is appreciated that a chemical reaction heat source with a fuel composition comprising a mix of thermite and a damping agent would be particularly preferable, with solid mixes of these fuel compositions being especially desirable.