BISMUTH METHOD OF ABANDONING A WELL

Abstract

A well abandonment tool for deployment in a well tubing, comprising an upper section, including a connector to allow the tool to be deployed on slickline or wireline a housing including a chamber containing bismuth a receiver and processor, capable of receiving a signal from the surface to actuate a permanent sealing process a lower section, including a release means capable of releasing the upper section of the tool from a lower section of the tool a tubing cup seal capable to making a seal against the inside of the well tubing to contain moltenbismuth until it solidifies a tubing bridge plug or anchor capable of securing the tool inside the well tubing the tool also including a heat source capable of melting the bismuth to a flowable state, actuated by the receiver and processor such that when the tool has been secured in the well tubing, the bismuth melting process can be initiated, and the upper housing released from the lower housing to recover the upper housing, and bismuth being melted by the heating means and caused to flow into the well tubing above the tubing cup seal to form a plug.

Description

Over the past 20 years or so a large number of offshore structures have been constructed which are now or will soon be exhausted and will need to be abandoned. These offshore structures may comprise production platforms which are either steel or concrete structures resting on the sea bed or floating platforms. Numerous conduits are connected to these offshore structures to carry the various fluids being gas, oil or water etc., which are necessary for the production of oil and/or gas from the well.

In abandoning a well, consideration has to be given to the potential environmental threat from the abandoned well for many years in the future.

In the case of offshore structure there is usually no rig derrick in place which can be used to perform the required well abandonment procedure. Therefore it is typically necessary to install a new derrick or alternatively a mobile derrick can be positioned above the well. This requirement adds considerable expense to the task of abandoning the offshore well, compared to a land based well.

A typical production well will comprise a number of tubular conduits arranged concentrically with respect to each. The method of abandoning the well which is presently known in the art involves the separate sealing of each of the concentric conduits which requires a large number of sequential steps.

In the abandonment method known in the art the first step is to seal the first central conduit usually by means of cement or other suitable sealant. The first annular channel between the first and second conduits is then sealed and the first central conduit is then cut above the seal and the cut section is removed from the well.

The second annular channel between the second and third conduits is then sealed and the second conduit cut above the seal and the cut section is removed from the well.

This process is repeated until all the conduits are removed. The number of separate steps required is typically very large indeed and the number of separate operations is five times the number of conduits to be removed. This adds considerably to the cost of the well abandonment due to the time taken and the resources required at the well head.

It is the purpose of the present invention to provide a method of abandoning a well which avoids the disadvantageous and numerous operations which are required by the existing known methods. This will greatly reduce the costs of safely abandoning a well. It is a further objective of the invention to provide a method of abandoning a well without the requirement of a rig which involves significant expense particularly in subsea based wells.

It is a further advantage of the invention to form a metal seal inside the tubing inside the well.

According to the present invention there is provided a method of abandoning a well, by using a tool loaded with thermite to provide a heat source and bismuth alloy fill the annular space around the thermite heated tube.

According to another aspect of the present invention the ignitor is electrically based and initiates a thermal ignitor when it receives a coded acoustic signal from a transmitting tool

According to another aspect of the present invention multiple bismuth metal to metal seals can be placed on top of each other to make a metal to metal seal of unlimited length.

According to a further aspect of the invention the ignitor could include a secondary back up such as a timer in addition to the electrical wet connector.

According to a further aspect of the invention the ignitor could include a secondary back up such as a hydrostatic pressure switch in addition to the electrical wet connector.

According to a further aspect of the invention the ignitor could include a secondary low temperature alloy part which has to melt to operate a switch in addition to the electrical wet connector.

According to a further aspect of the invention the bismuth melting method could be an electric heating element

According to a further aspect of the invention, the bismuth in the retrievable running tool could provide the connecting means to the bridge plug, so when it melts the running tool is automatically released from the bridge plug.

According to a further aspect of the invention the bismuth forms a solid plug inside the tubing.

According to a further aspect of the invention multiple runs can be performed to make the plug as long as required

According to the present invention there is provided a method of in a single trip into the well, set a bridge plug, melt bismuth alloy, deposit the alloy on top of the bridge plug, release from the plug and return tool to surface.

According to a further aspect of the invention there the tool could be attached to the bridge plug by the low temperature alloy and when it is heated, the tool automatically releases itself from the bridge plug

According to a further aspect of the invention, there is provided a heating element to heat the convert the alloy from solid to liquid

According to a further aspect of the invention, a flux is released together with the molten bismuth to improve the bonding of the bismuth to the steel tubulars and the top of the bridge plug

According to a further aspect of the invention, bismuth beads are deposited on the heat source

According to a further aspect of the invention, bismuth beads are conveyed in a container above the heat source

According to a further aspect of the invention, bismuth beads are deposited from surface using gravity

According to a further aspect of the invention, bismuth is cast around the heating element.

According to a further aspect of the invention the heat source could be thermite

Thus by means of the method according to the invention a very long metal to metal seal can be placed in the well tubing or well casing.

References to bismuth include alloys of bismuth capable of being melted, flowing to seal a region, and solidifying to provide a permanent seal.

The following is a more detailed description of an embodiment according to invention by reference to the following drawings in which:

FIG. 1. is a section side view of a well showing the tubing inside the well, a tool deployed on slickline or wireline, the tool consisting a tubing anchor, a tubing cup seal, a thermite heat housing, a shear release, a bismuth store housing, an electronics circuit, a battery pack, an acoustic receiver and a connector to the wireline or slickline.

FIG. 2 is a view similar to FIG. 1, with the anchor set, the thermite heat tube activated, and the upper tool assembly sheared off and the bismuth falling by gravity into the annular space around the thermite heat tube.

FIG. 3 is a view similar to FIG. 2 with a new thermite heat housing, a shear release, a bismuth store housing, a electronics circuit, a battery pack, an acoustic receiver and a connector to the wireline or slickline to be latched onto the first thermite heat tube previously set in the well with the bismuth seal between the thermite housing and the well tubing.

FIG. 4 is a similar view to FIG. 4, with the second tool string latched onto the first tool string.

FIG. 5 is a view similar to FIG. 4, with the second thermite heat tube activated, and the second upper tool assembly sheared of and the bismuth falling by gravity into the annular space around the second thermite heat tube and on top of the first bismuth plug.

FIG. 6 is a section side view of a well with another embodiment of the invention, in its position to be activated

FIG. 7. is a similar view to FIG. 6 with the tool having a complete section side view of its internal components.

FIG. 8 is a section side view of a well with the tool in a second released position from the bridge plug.

FIG. 9 is a similar view to FIG. 8 with the tool having a complete section side view of its internal components.

FIG. 10 is a section side view of a well and tool assembly with a second embodiment of the invention, in its position to be activated

FIG. 11 is a section side view of a detail highlighted in FIG. 10

FIG. 12 is a similar view to FIG. 10 with the upper half of the tool separated from the lower half.

FIG. 13 is a similar view to FIG. 12, with all the low temperature alloy deposited on top of the bridge plug and the upper half of the tool returning to surface.

Referring to FIGS. 1 to 5, there is shown a well tubing 1. Inside the tubing is a tool assembly 2, consisting of a tubing anchor 3, a cup seal 4, a tubular housing 5 containing thermite 6 and an ignitor 7, two electrical cables 8 and connectors 9, a shear pin 10, a second housing 11 inside which is bismuth alloy pellets 12, two electrical cables 13 linking the connectors 9 to a relay 13, the relay being part of an electrical circuit 14 which consists of a pressure sensor which only allows the tool to operate below a pre-defined depth in the well, a set of lithium batteries 15 each 30 amps and 4.4 volts arranged in series and an acoustic transmitter/receiver, all attached to a slickline or wireline 16

In operation, the assembly would be lowered in the well, once at the required setting depth, the tubing stop 3 would be set by rapidly stopping the downward movement of the wireline. This is a well-established practice and well understood by a well operative skilled in deploying slickline tools. Once set the wireline would be pull tested to confirm that the anchor is set.

A signal would be transmitted down the wireline, or an acoustic signal would be transmitted from surface if deployed on slickline, there are four operating modes: standby, ready, arm, and fire.

The goal is for safety and security, the receiver must receive the proper commands in the proper sequence in order to initiate the burn.

Before it can do anything, the pressure switch safety interlock has to be activate. Once that happens, it goes to ready mode, it will receive anything it hears, but it is looking for specific commands and a preamble and post amble (framing bytes). Unless all these conditions are met, the processor of the electrical circuit causes the tool to ignore the transmission.

So first the Ready command is sent, then “arm”, then “fire”. On Fire, the relay 13 latches on, and applies power which comes from 3×4.4 volt 30 amp batteries 15 in series to the initiator 7 and the retarded thermite does a slow burn.

The entire housing 5 heats up to 600-1000C. A temperature sensor 17, sends a signal back to the circuit 18 and this transmits this information back to surface.

Tension would be applied to the wireline to shear the shear pin 10, or wireline jar (not shown) would apply the shock load to shear the shear pin. The tool housing 11 would come free 20, and the bismuth inside would fall out of the inside of the housing due to gravity and fall into the annular space 21 and form a solid metal to metal seal from the cup seal 4 to just below the top 22 of the tool remaining in the well, the disconnected upper half of the tool 23 can be recovered to surface.

Additional bismuth beads could be supplied from surface by feeding the beads 40 into tubing and letting them fall under gravity to land on top the thermite heater 6, if the housing 11 cannot transport sufficient beads to fully cover the thermite heater. Alternatively, all the bismuth to be used in the process could be supplied from the surface to fall onto the heating element of the deployed tool.

A second tool assembly 24 can be deployed to increase the length of the metal to metal seal. This tool assembly consists of a collet 30, a tubular housing 5 containing thermite 6 and an ignitor 7, two electrical cables 8 and connectors 9, a shear pin 10, a second housing 11 inside which is bismuth alloy pellets 12, two electrical cables 13 linking the connectors 9 to a relay 13, the relay being part of an electrical circuit 14 which consists of a pressure sensor which only allows the tool to operate below a pre-defined depth in the well, a set of lithium batteries 15 each 30 amps and 4.4 volts arranged in series and an acoustic transmitter/receiver, all attached to a slickline or wireline 16

The collet 30 latches onto the profile 31, and then the sequence of igniting the thermite and releasing the bismuth into the annular space is repeated, the new melted bismuth falls on top of the previous, now solidified bismuth 32 from the first run, now the bismuth seal is twice the original length 33. This could be repeated again to further increase the metal to metal seal to be as long as required.

Referring to FIGS. 6 to 9 there is shown a section side of an oil or gas well with internal surface of the production tubing 101 shown as a single line (for clarity).

The tool is conveyed on electric wireline 102, and consists of a conventional connector 103 incorporating a standard release joint. Inside the tool is a telemetry package 104 which also includes temperature sensors and casing collar locator for depth control. The upper housing 105 of the tool contains a heating element 106 and the void space around it inside the housing is filled with low temperature alloy 107

When the tool is at the required setting depth, it is rapidly stopped, this deceleration causes a weighted rod 108 to shear a pin and unlock the slips 109, which are spring loaded 110, resulting in the slips locking the bridge plug to the tubing ID. A cup seal 111 provides a pressure seal, and more importantly a place for the molten bismuth to rest.

After the bridge plug is set, the tool is jarred up to release if from a S type release tool 113. The heating element 6 is then turned on and molten bismuth flows out of ports 112 and comes to rest on top of the seal 111and around the lower half 114 of the S type release tool

Once all the bismuth has been discharged the upper half of the tool assembly is returned to surface.

Referring to FIGS. 10 to 13, there is shown another embodiment of the invention, in this version, there is no release tool, low temperature alloy 120 is used to lock the lower assembly 121 to the upper assembly 122. It is cast into a recess 123 on the lower assembly and 124 on the upper assembly. When the heating element 125 is turned on, it melts the low temperature alloy which results in the two halves of the tool 121,122 separating, the molten bismuth is immediately above the cup seal 126. As the heating element goes to the very bottom of the assembly 122 there is no risk of the assembly 122 getting stuck by solidified low temperature alloy. Once all the low temperature alloy is deposited 127 on top of the bridge plug 128, the upper tool assembly 122 is returned to surface.

Claims

1. A well abandonment tool for deployment in a well tubing, comprising:

an upper section, including, and a connector to allow the tool to be deployed on slickline or wireline, a housing including a chamber containing bismuth, and a receiver and processor, capable of receiving a signal from the surface to actuate a permanent sealing process; and

a lower section, including: a release means capable of releasing the upper section of the tool from a lower section of the tool, a tubing cup seal capable to making a seal against the inside of the well tubing to contain molten bismuth until it solidifies, and a tubing bridge plug or anchor capable of securing the tool inside the well tubing;

the tool also including a heat source capable of melting the bismuth to a flowable state, actuated by the receiver and processor;

such that when the tool has been secured in the well tubing, the bismuth melting process can be initiated, and the upper housing released from the lower housing to recover the upper housing, and bismuth being melted by the heating means and caused to flow into the well tubing above the tubing cup seal to form a plug.

2. A tool according to claim 1, wherein the receiver is an acoustic receiver capable of receiving a coded acoustic signal from a transmitting tool.

3. A tool according to claim 1, wherein the receiver receives electrical signals conducted by a wire connection from the surface.

4. A tool according to claim 1, wherein the heat source is a housing containing thermite, provided with a ignitor and a battery pack to initiate a thermite reaction.

5. A tool according to claim 1, wherein the heat source is an electric element.

6. A tool according to claim 1, wherein the ignitor includes a secondary back up such as a timer in addition to the electrical wet connector.

7. A tool according to claim 1, wherein the ignitor includes a secondary back up such as a hydrostatic pressure switch in addition to the electrical wet connector.

8. A tool according to claim 1, wherein the ignitor includes a secondary low temperature alloy part which has to melt to operate a switch in addition to the electrical wet connector.

9. A tool according to claim 1, wherein the bismuth in the retrievable running tool could provide the connecting means to the lower section, so when it melts the running tool is automatically released from the lower section.

10. A tool according to claim 1, wherein a flux is provided, releasable together with the molten bismuth to improve the bonding of the bismuth to the steel tubulars and the top of the lower section.

11. A tool according to claim 1, wherein bismuth beads are conveyed in a container above the heat source.

12. A tool according to claim 1, wherein bismuth is cast around the heat source for deployment.

13. A method of using a tool according to claim 1, including depositing bismuth beads on the heat source.

14. A method of using a tool according to claim 13, wherein bismuth beads are deposited from surface using gravity.

15. A method of operating in a well using a tool according to claim 1, including deploying multiple tools to produce multiple bismuth metal to metal seals placed on top of each other to make a metal to metal seal of unlimited length.