Downhole well tools and methods of using such

1. A downhole tool for use in a gas or oil well, said tool comprising a length of tubing; wherein the tubing has an upper end and a lower end and defines an internal channel open to the well at both ends; the tubing having at least one annular sealing means mounted on the outer surface thereof and wherein said at least one annular sealing means is formed from a eutectic/bismuth based alloy, and comprises a pre-set configuration and a set configuration;

wherein the tubing defines a tubing outer diameter;

wherein the tubing comprises a weakened area, the weakened area removed from the upper end and located between the upper end and lower end;

wherein the sealing means has: (i) a first outer diameter, a first annular cross section, and a first length defined by the alloy in the pre-set configuration; (ii) a second outer diameter, a second annular cross section, and a second length defined by the set alloy in the set configuration;

wherein the second outer diameter is greater than the first outer diameter which is greater than the tubing outer diameter;

wherein the second cross sectional area is greater than the first cross sectional area;

wherein the first length is greater than the second length;

wherein in the pre-set configuration the sealing means covers the weakened area of the tubing, and wherein in the set configuration the sealing means does not cover the weakened area of the tubing, whereby the weakened area is configured to separate the tubing in the set configuration; and,

wherein in the set configuration the sealing means is adjacent to the tubing outer diameter.

2. The downhole tool of claim 1 , wherein the annular sealing means comprises one or more conduits in the annular sealing means and running substantially parallel to the tubing.

3. The downhole tool of claim 2 , wherein the one or more conduits are provided as channels in the inner and/or outer circumferential surface of the annular sealing means.

4. The downhole tool of claim 2 , wherein the one or more conduits are provided as through holes in the main body of the annular sealing means.

5. A well tool deployment adaptor comprising the downhole tool of claim 1 .

6. The downhole tools of claim 1 , further comprising tool engagement means located within the tubing.

7. A method of manufacturing a downhole tool for use in a gas or oil well, said method comprising:

providing a length of tubing, wherein the tubing has an upper end and a lower end and defines an internal channel open to the well at both ends;

mounting at least one eutectic/bismuth based annular sealing means on the outer surface of the tubing; wherein the sealing means comprises a pre-set configuration and a set configuration;

wherein the tubing defines a tubing outer diameter;

wherein the tubing comprises a weakened area, the weakened area removed from the upper end and located between the upper end and lower end;

wherein the sealing means has: (i) a first outer diameter, a first annular cross section, and a first length defined by the pre-set configuration; and, (ii) a second outer diameter, a second annular cross section, and second length defined by the set configuration;

wherein the second outer diameter is greater than the first outer diameter which is greater than the tubing outer diameter;

wherein the second cross sectional area is greater than the first cross sectional area;

wherein the first length is greater than the second length;

wherein in the pre-set configuration the sealing means covers the weakened area of the tubing, and wherein in the set configuration the sealing means does not cover the weakened area of the tubing, whereby the weakened area is configured to separate the tubing in the set configuration; and,

wherein in the set configuration the sealing means is adjacent to the tubing outer diameter.

8. The method of manufacturing a downhole tool of claim 7 , wherein the annular sealing means is provided in the form of multiple component parts and the step of mounting the annular sealing means to the tubing involves securing the component parts together around the circumference of the tubing to complete the annulus.

9. A downhole tool for use in a gas or oil well, said tool comprising:

a) a length of tubing having at least one annular sealing means mounted on the outer surface thereof; wherein the annular sealing means comprises a pre-set configuration and a set configuration; wherein the annular sealing means is formed from a eutectic/bismuth based alloy; and,

b) wherein the tubing further comprises a weak point that is covered by the annular sealing means in the pre-set configuration and not covered by the annular sealing means in the set configuration; whereby in use the weak point is just above a slump line of the set alloy; and wherein the slump line of the set alloy is adjacent to the outer surface of the tubing; and,

c) wherein the weak point separates the tubing in the set configuration.

10. A downhole tool for use in a gas or oil well, said tool comprising a length of tubing; wherein the tubing has an upper end and a lower end and defines an internal channel open to the well at both ends; the tubing having at least one annular sealing means mounted on the outer surface thereof and wherein said at least one annular sealing means is formed from a eutectic/bismuth based alloy, and comprises a pre-set configuration and a set configuration;

wherein the tubing defines a tubing outer diameter;

wherein the sealing means has: (i) a first outer diameter, a first annular cross section, and a first length defined by the alloy in the pre-set configuration; (ii) a second outer diameter, a second annular cross section, and a second length defined by the set alloy in the set configuration;

wherein the second outer diameter is greater than the first outer diameter which is greater than the tubing outer diameter;

wherein the second cross sectional area is greater than the first cross sectional area;

wherein the first length is greater than the second length;

wherein in the pre-set configuration the annular sealing means comprises one or more conduits in the annular sealing means and running substantially parallel to the tubing; and,

wherein in the set configuration the sealing means is adjacent to the tubing outer diameter and does not extend below the lower end of the tubing.

11. The downhole tools of claim 2 , 3 , or 4 , further comprising tool engagement means located within the tubing.

12. The downhole tool of any of the preceding claims, wherein said at least one annular sealing means comprises multiple component parts which are combinable to form the complete annulus when mounted on the tubing.

13. The downhole tools of claim 1 , 2 , 3 or 4 , further comprising tool engagement means located within the tubing; and, wherein the tool engagement means are located on the inner surface of the tubing that is proximate to the externally mounted annular sealing means.

14. The tubing of claim 1 , 2 , 3 , or 4 , further comprising: (i) tool engagement means located within the tubing; (ii) tool engagement means located on the inner surface of the tubing that is proximate to the externally mounted annular sealing means or both (i) and (ii).

15. A method of sealing a leak in a completed oil/gas well using the downhole tool according to any of claim 1 , 2 , 3 , or 4 by heating the eutectic/bismuth based annular sealing means in situ to melt the alloy and seal the leak.

16. The method of sealing a leak in a completed oil/gas well of claim 15 , wherein a heating tool is deployed down the well to apply heat to the annular sealing means and cause it to melt.

17. The method of sealing a leak in a completed oil/gas well of claim 15 , wherein the tubing further comprises heating means that can be activated remotely to melt the alloy.

18. The method of sealing a leak in a completed oil/gas well of claim 17 , wherein the heating means are provided by a chemical heat source.

19. The method of manufacturing a downhole tool of any of claim 7 or 8 , further comprising providing multiple conduits in said at least one annular sealing means.

20. The method of manufacturing a downhole tool of claim 7 or 11 , further comprising providing multiple conduits in said at least one annular sealing means; and, wherein the conduits are provided in the form of channels in the inner and outer surface of the annular sealing means.

21. The method of manufacturing a gas or oil well tubings of claim 7 or 8 , further comprising providing multiple conduits in said at least one annular sealing means; and, wherein the conduits are provided in the form of through holes running through the main body of the sealing means.