Bore sealing method and apparatus

1. A method of sealing a well bore nnulus between first and second well bore-lining tubulars, the method comprising:

providing a first well bore-lining tubular having a first volume of alloy, a retainer, and a fusible member thereon, the retainer having a retracted first configuration and a radially extended second configuration, the retainer being initially maintained in the retracted first configuration by the fusible member, and the fusible member being configured to retain structural integrity and maintain the retainer in the retracted first configuration at ambient well temperature;

running the first well bore-lining tubular into a well bore provided with a second well bore-lining tubular;

utilizing the fusible member to maintain the retainer in the retracted first configuration in the well bore;

activating a heater to heat the fusible member to above ambient well temperature whereby the fusible member loses structural integrity and the retainer assumes the radially extended second configuration and radially extends from the first well bore-lining tubular;

fluidising the alloy;

retaining the fluidised alloy above the extended retainer; and

allowing the alloy to solidify in an annulus between the first well bore-lining tubular and the second well bore-lining tubular and bond the first well-bore lining tubular to the second well bore-lining tubular.

2. The method of claim 1 , wherein the heater is an exothermic heater.

3. The method of claim 1 , wherein flux is incorporated with the alloy and the alloy is fluidised in the presence of flux.

4. The method of claim 1 , comprising centralising the first bore-lining tubing in the second bore-lining tubing with the first volume of alloy.

5. The method of claim 1 , wherein the alloy creates a seal between the first bore-lining tubular and the second bore-lining tubular.

6. The method of claim 1 , wherein at least one of the bore-lining tubulars is one of casing and a liner.

7. The method of claim 1 , comprising allowing the alloy to solidify above one of a packer and a liner hanger.

8. The method of claim 1 , comprising:

providing the second bore-lining tubular with a second volume of alloy thereon;

locating the first volume of alloy adjacent the second volume of alloy; and

heating the first volume of alloy and allowing the first volume of alloy to heat the second volume of alloy.

9. A downhole apparatus for location in a well bore, the apparatus comprising a volume of fusible alloy, a retainer and a fusible member, the retainer being initially maintained in a retracted position by the fusible member, the fusible member being configured to: (a) retain structural integrity at ambient well temperature, and (b) lose structural integrity when heated above ambient well temperature and permit the retainer to be activated and move to an extended position for maintaining fluidised alloy at a bonding location while the alloy solidifies, the alloy, the retainer and the fusible member being adapted for mounting on a first well bore-lining tubular for location within a second well bore-lining tubular.

10. The apparatus of claim 9 , further comprising a first bore-lining tubular for location within a second bore-lining tubular, the first bore-lining tubular having the volume of fusible alloy on an outer portion thereof.

11. The apparatus of claim 10 , further comprising a second bore-lining tubular with a second volume of alloy thereon, whereby the first bore-lining tubular is locatable within the second bore-lining tubular with the first volume of alloy adjacent the second volume of alloy.

12. The apparatus of claim 9 , wherein the fusible member at least one of: encircles the retainer, and is operatively associated with a retainer restraining arrangement and heating of the fusible member above ambient well temperature permits reconfiguration of the restraining arrangement and allows the retainer to move to the extended position.

13. The apparatus of claim 9 , wherein the retainer comprises an arrangement of metal petals.

14. The apparatus of claim 9 , wherein the volume of alloy comprises a collar for location on a bore-lining tubular and the apparatus further comprises at least one stop collar for retaining the alloy collar on a tubular.

15. The apparatus of claim 9 , wherein the alloy is provided in combination with a volume of flux, and the flux is incorporated with the alloy.

16. The apparatus of claim 9 , wherein the alloy is at least one of a tin-based alloy, a high tin alloy comprising at least one of copper, antimony and nickel, and an alloy comprising 2.5-8.5% copper, 4-16% antimony, and less than 1% nickel.

17. The apparatus of claim 9 , wherein the volume of alloy extends axially along the first bore-lining tubular and the composition of the alloy varies axially along the tubular.

18. A downhole apparatus comprising a volume of fusible alloy in combination and incorporated with a volume of flux, the alloy adapted for mounting on a first bore-lining tubular for location within a second bore-lining tubular, whereby the flux facilitates downhole bonding between the alloy and the bore-lining tubulars, wherein the flux is provided in cavities within the fusible alloy.