Downhole fishing tool

Abstract

An oil or gas well fishing tool (60). The downhole fishing tool (60) has a receptacle (61) that is open at one end. The tool also has deployment tool engaging means (62), located on the opposite end of the receptacle (61) to the one end. The tool further has a layer of an alloy (64) provided on the interior surface of the receptacle (61). The alloy is a eutectic alloy and/or a bismuth alloy. The tool further comprises heating means (65) to heat the alloy (64) so that it melts and can flow over any object received within the receptacle (61).

Claims

1. An oil or gas well fishing tool, said tool comprising: a receptacle for positioning in a well defining an opening at a first end and defining an interior, the interior having an interior surface; a second end of the receptacle for receiving a line; an alloy provided within the interior of the receptacle, wherein the alloy is a eutectic alloy, a bismuth alloy or both; wherein the alloy comprises a layer and the layer of the alloy is provided on the interior surface of the receptacle; and a heater, wherein the heater comprises an ignition element and a layer of a chemical heat source located between the receptacle and the alloy layer and the heater is associated with the allow to heat and thereby melt the alloy; thereby defining the oil and gas well fishing tool.

2. The fishing tool of claim 1, comprising a spear member.

3. The fishing tool of claim 1, comprising a spear member, wherein the spear member extends beyond the opening at the first end of the receptacle.

4. The fishing tool of any of claim 1, wherein the receptacle is substantially bell-shaped.

5. The fishing tool of claim 1, wherein the receptacle comprises a main body and a foot section.

6. The fishing tool of claim 5, wherein the heater and the alloy are provided within the main body.

7. The fishing tool of claim 5, wherein the foot section comprises a gripping means.

8. The fishing tool of claim 1, wherein the alloy has fragments of a second material embedded within the alloy, wherein a melting temperature of the second material is higher than a melting temperature of the alloy.

9. A method of retrieving an object lost down a gas or oil well, said method comprising: a) delivering a fishing tool down a well so that the fishing tool surrounds at least part of an object in the well, wherein the fishing tool comprises a receptacle; b) melting an alloy within the fishing tool and allowing the molten allow to flow onto the object, wherein the alloy comprises a layer and the layer of the alloy is provided on an interior surface of the receptacle and the melting the alloy comprises a heater with an ignition element and a layer of a chemical heat source located between the receptacle and the alloy layer; c) cooling the alloy to cool, thereby binding the object to the tool; and, d) retrieving the fishing tool and the bound object from the well.

10. The method of claim 9, further comprising the steps of assessing a property of the object and then selecting a foot portion based at least in part upon the assessed property of the object.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 shows a diagrammatic cross-sectional representation of an embodiment of the fishing tool provided by the present invention;

(3) FIGS. 2A, 2B and 2C show a diagrammatic representation of the key stages of the deployment and operation of the embodiment of the fishing tool of FIG. 1;

(4) FIG. 3 shows an alternative embodiment of the fishing tool provided by the present invention; and

(5) FIG. 4 shows a further alternative embodiment of the fishing tool provided by the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

(6) FIGS. 1 and 2 both show a first embodiment of the oil/gas well fishing tool 60 provided according to the present invention, whereas FIG. 3 shows an alternative embodiment of the fishing tool 70.

(7) As described above fishing tools, such as those shown, are employed to retrieve objects that either fall into a well or cannot be retrieved by using their normal retrieval method—for instance a tool attached to a snapped wire line or cable.

(8) As can be seen from the cross-sectional view of the tool 60 provided in FIG. 1, the tool comprises an open-ended receptacle 61 with means 62 for engaging a deployment tool, such as wire line 63, so that the fishing tool 60 can be deployed down a well. In the preferred embodiment the receptacle is substantially ‘bell-shaped’. However alternative open-end receptacle shapes, such as boxes and cylinders, could also be employed without departing from the scope of the present invention

(9) Located within the inside of the receptacle is a layer of an alloy 64. The alloy is preferably a eutectic alloy, although other non-eutectic alloys formed from bismuth are also considered applicable without departing from the general scope of the present invention.

(10) In order to heat the alloy when needed the tool is also provided with heating means, which in the shown embodiment comprise a layer of chemical heat source 65 (e.g. thermite) provided between the inner surface of the receptacle 61 and the layer of alloy 64. The tool is further provided with ignition means 66, which can be activated via the wire line 63 to trigger the chemical heater and melt the alloy.

(11) In order to further explain the operation of the fishing tool 60 reference is now made to FIG. 2, which show the key stages of the tool's operation.

(12) In the first stage the fishing tool 60 is delivered down a well 67 towards the stranded object (e.g. wrench 68) using, in this example, a wire line 63.

(13) Once the receptacle of the tool 60 has be positioned about at least a portion of the object 68 the heating means are activated for a short period of time to cause the alloy located within the receptacle to melt and sag. As the alloy melts it comes into contact with the object and flows around it. As the heat source has already started to cool the alloy is itself beginning to cool down and solidify.

(14) As the alloy returns to its solid form the object 68 becomes embedded within the solid alloy 64 and in doing so becomes one with the fishing tool 60. The merged fishing tool 60 and object 68 can then be extracted from the well using the wire line 63.

(15) Preferably, although not shown in the figures, the alloy 64 may have fragments of a second material embedded within it. Such material, which is preferably a metal, has a higher melting point that the alloy so that it remains in its solid state when the alloy flows. In this way the fragments, which might be in the form of fibres or chips, enhance the gripping of the object by the alloy as it solidifies.

(16) The fishing tool 70 shown in FIG. 3 is further enhanced by the addition of a spear member 73 which projects from within the open-ended receptacle 71. The spear member 73, which is provided with tines 74 for enhanced gripping, is considered particularly suitable for retrieving snapped wire line and cable from within a well.

(17) Once again the tool is provided with means 72 for engaging a deployment tool.

(18) FIG. 4 shows a further alternative embodiment of the fishing tool of the present invention. The fishing tool 150 is provided with a receptacle that is comprised of two parts, a main body 151 and a removable foot portion 152. The foot portion 152 can be connected to the main body 151 by a screw thread, although alternative means may also be used without departing from the claimed invention.

(19) The main body 151 of the receptacle is provided with means for engaging a deployment tool 153. In FIG. 4 a wire line 154, which attaches the fishing tool to a deployment tool (not shown) located above ground, is also shown in part.

(20) Located within the main body 151 of the receptacle is a heater 155, which is housed with a mandrel 156. The eutectic/bismuth alloy 157 is provided on the surface of the mandrel 156. It is been discovered that by providing clearance between the main body 151 and the alloy 157 it enables the down hole fluids to circulate within the receptacle, which aids the flow of the melted alloy.

(21) The mandrel 156, which in the shown embodiment is located concentric to and entirely within the main body 151, is made from a material with a higher melting point than the alloy 157, suitable examples of which include steel and aluminium. This is also the case for the main body 151 and the foot portion 152.

(22) The foot portion 152 is provided with gripping means 158, in the form of a threaded region. It is envisaged that alternative types of gripping means, such as a roughened surface or a plurality of projections, might be used instead without departing from the general scope of the present invention.

(23) One key feature of the embodiment shown in FIG. 4 is that the foot portion 152 of the receptacle is detachable from the main body 151 of the receptacle. It is envisaged that this facility allows for a range of different shaped foot portions to be attached to the main body to suit the shape/size of the stranded object 160.

(24) The present invention therefore also provide a method of assessing the size and shape of the stranded object in order to select a suitable foot portion for a particular task.

(25) It is appreciated that by having the main components of the fishing tool provided by a standard tool that is connectable to a variety of more tailored foot portions, it is possible to greatly reduce the costs involved in retrieving stranded objects from down a well.

(26) It is appreciated that some variants of the foot portion may be provided with one or more spear members similar to those shown in FIG. 3.