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 isolate all the conduits and annuli with no return of the well bore tubulars to the surface. Furthermore, the method of abandonment of the well will comply with all the regulatory guidelines for the isolation of a well.

According to the present invention there is provided a method of abandoning a well, by first installing a barrier or plug at a depth in the well, depositing a thermal insulation material on top of this, then depositing thermite and an ignitor and on top of this a thermal insulation barrier and then some weight such as steel or ceramic balls, when the thermite is ignited, the thermal barrier contains the energy generated by the thermite and directs it to sever the tubing just below the thermal barrier. When the tubing is severed it will collapse into the annular space of the casing around it, and the thermal barrier and the balls above it will drop into the annular space with the severed tubing. A window is created to access the next casing out, and there is no obstruction in the tubing, so the process can be repeated to sever the next casing out. This process can be repeated for any number of nested casings.

According to a further aspect to the invention the thermite is transported on a slickline or wireline tool in the form of a cartridge.

According to a further aspect to the invention the thermite initiator is transported on a slickline or wireline tool in the form of a cartridge. It will operate by wireless telemetry such as RFID, or listen for different tones and respond to confirm it has been activated.

According to a further aspect to the invention the thermite initiator may require a wire to connect it to a RFID receiver.

According to a further aspect to the invention the insulation material is transported on a slickline or wireline tool in the form of a cartridge.

According to a further aspect to the invention the weighting is transported on a slickline or wireline tool in the form of a cartridge. According to a further aspect to the invention the bismuth is transported on a slickline or wireline tool in the form of a cartridge.

According to a further aspect to the invention the thermite is transported on a slickline or wireline tool in the form of a long flexible hose or a string of sausages type structure. According to a further aspect of the invention the insulation material will be a combination of starch, sodium bicarbonate and a binder fluid.

According to a further aspect of the invention the insulation material will be a combination of starch, sodium bicarbonate, carbon black and a binder material.

According to a further aspect of the invention, the thermal insulation barrier can be deployed via the tubing as small beads and which can form a barrier in any of the tubing or casings.

According to a further aspect of the invention and thermal insulation material can be coated on the tools, to provide a thermal insulation barrier and enable the heat and energy generated by the thermite to be precisely directed to server the tubing or casing.

According to a further aspect of the invention the thermal insulation material can be deployed in sealed cartridges and either dropped or lowered into the well on slickline, wireline, jointed tubing or coiled tubing. According to a further aspect of this invention the thermal insulation material is made from three materials, in approx ratios 90% corn starch, 10% Sodium bicarbonate, finally, these two blended powders are made into a putty paste by adding Poly(vinyl acetate) According to a further aspect of the invention, the thermal insulation barrier is reactive to the heat and forms carbon bubbles which have high temperature resistance.

According to a further aspect of the invention, while the thermite and surround formation is still hot and above the natural formation temperature, a low melting point alloy (bismuth) can be deposited on top of the thermite, this alloy has a very low viscosity and flows into any crack, void or fissure. During cool down all the fissures and conductive passages are plugged by the then cooled down to ambient temperature solidified metal alloy. Thus the well is plugged well out into the natural rock formation away from the well in multiple zones and wellbore itself is permanently plugged by a magma mass.

According to a further aspect of the invention, the thermal barrier could be ceramic balls

According to a further aspect of the invention the thermal barrier could be tungsten carbide balls. According to a further aspect of the invention, the thermal barrier could be bauxite in a small mesh size as used for hydraulic fracturing.

Thus by means of the method according to the invention the number of operations required is greatly reduced, thus resulting in a considerable reduction in the cost of carrying out the well abandonment.

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

Figure 1 is section side view through a well with a casing and a severed production tubing, with a tubing bridge plug, thermite magma, insulation material and weight material, sealing the lower section from an earlier operation.

Figure 2 is a similar view to figure 1, showing a wireline or slickline tool lowered through the previous tubing, and the tool highlighted by a dotted line box.

Figure 3 is an enlarged side view of the tool highlighted above

Figure 4 is a similar view to figure 3, showing a subsequent stage in the process.

Figure 5 is a similar view to figure 2, showing a slickline tool which has deposited its payload into the well.

Figure 6 is a similar view to figure 5, with all the ingredients needed for the operation deployed in cartridges, and a tool deployed on slickline activating the thermite initiators.

Figure 7 is a similar view to figure 6, after the thermite has been activated and it is severing the casing.

Figure 8 is a section side view through a well with the resulting parted tubing by the tool operation in figure 7

Figure 9 is a side view of another embodiment of the invention being conveyed on a slickline or wireline tool

Figure 10 is a subsequent operation to figure 9 with hose assembly released from the slickline, and the hose forming a coil at a position of rest inside the casing (casing not shown)

Figure 11 is a side view of another embodiment of the invention being conveyed on a slickline or wireline tool

Figure 12 is a view of a string of sausages containing the required ingredients released from the deployment tool Figure 13, is a side of the released sausages shown in figure 12 coming to rest as a compact pile inside the casing (not shown)

Figure 14 is a section side view of the well with an alternative means of communicating with multiple RFID initiating cartridges.

Figure 15 is a similar view to figure 14, at a subsequent step in the process.

Figure 16 is a similar view to figure 15, at a subsequent step in the process.

Figure 17 is a similar view to figure 16, at a subsequent step in the process.

Figure 18 is a section side view of the well with another means of communicating with multiple RFID initiating cartridges.

Figure 19 is a similar view to figure 18, at a subsequent step in the process.

Figure 20 is a similar view to figure 19, at a subsequent step in the process.

Figure 21 is a similar view to figure 20, at a subsequent step in the process.

Figure 22 is a circuit diagram for an acoustic transmitter / receiver

Referring to figures 1-8, an objective of this process is to make an access window to the open hole.

Figure 1 shows a well where the tubing has been severed using a bridge plug 10, thermal insulation material such as sand or ceramics, reacted thermite 12, a second quantity of thermal insulation material 13 and weight in the form of steel ball bearing 14.

The next operation will be described in more detail, the objective of which is to sever the next casing outside the one already severed, and to let that casing drop thereby enabling access outside of it.

This is achieved using a slickline 21 (or wireline or coiled tubing, the term slickline will only be used from now on) to lower the slickline running tool 22 into the well. The running tool clamps 23 to the slickline, extending from the running tool is a thin hollow rod 24, on the end of which is a low temperature alloy end cap 25, mounted on the rod are cartridges 26, which consist of a hermetically sealed chamber 27, with an outer cylindrical wall 28, in inner very small inner cylindrical wall 29, and a top 30, and bottom 31 cap. Inside the chamber, could be any type of dry material or liquid chemicals such as thermite, bismuth, insulation, weighting materials, or instruments or sensors or telemetry such as a sonar Pinger, an acoustic transmitter receiver, or a RFID transmitter receiver, an ignitor to initiate the thermite reaction.

When the slickline tags the top of the previous plug 32 a heating element is powered up by current supplied by a cable inside the rod 24, the low temperature alloy end plug will melt and then the cartridges will slide down the rod and be deposited on top 33 of the previous plug 32, the empty slickline conveyance means 34 can now return to surface and make a repeat run. The length of the slickline tool is governed by the length of the lubricator at surface and the weight limitation of the slickline. This means of deploying cartridges enables unlimited quantities of the right materials to be deposited into the well, in a controlled way and with total quality control of the process.

Once the required quantities of low temperature thermite 35, wireless initiator 36, high temperature thermite 37, additional initiators 38, thermal insulation 39 and weighting materials 40 have been installed, a master activation tool 41 is conveyed on the slickline and at the required time, it transmits an acoustic signal to activate the different initiators, and the different initiators transmit back different hand shake to confirm they have received the correct command and have been switched on. The initiators can either be turned on at the same time or different times if a different warm up profile of the thermite is preferred or required. For example, it may be better to ignite the low temperature thermite 36 using a signal A 120 so that it softens the steel casing, which is confirmed by the initiator sending back signal B 121 to the wireless transceiver 41, and then igniting the high temperature thermite 37 using signal C 122 which confirms initiation by returning signal D 123, so that it can more easily sever 42 the softened casing. Ideally this will occur just below the insulation 43. The insulation provides a thermal barrier for the weighting material 44, so the weighting material does not fuse or melt and free fall with the insulation material and the severed casing 45.

Referring to figures 9 to 13, there is shown other means of conveying long flexible modules of different materials into the well on a mono conductor wireline conveyance system.

The system consists of a mono conductor wireline 50, attached to which is a grapple connector 51. A shear pin assembly 52 is part of the assembly to enable a clean separation in the event of getting stuck. Termination of the conductor is in a heating element inside a low temperature alloy block 53 which connects the payload 54 to the lower part of the connector 55.

The payload is a long flexible tube, fitted with a rounded nose piece 56. Inside the flexible tube would be any of the previously described materials that are required for an operation in the well for example those shown in figure 3 and 4.

When electrical power is applied to the electrical conductor, the heating element is energised and this in turn melts the low temperature alloy which in turn disconnects the payload from the mono conductor running tool.

The payload comes to rest and coils 57 into a compact form in the casing (not shown) below it. As in the previous system this can be repeated as often as required until the required quantity of material is placed into the well.

Referring to figures 11 to 13, an alternative arrangement is to have the payload made up made like a string of sausages 64, the connecting members 60 being held tight in the sausage 64’ nearest the release mechanism 61, when the release mechanism is activated the connecting members comes free and allows the sausage containers to separate 62 and when they land in the bottom of the well they fill the space, so forming a bigger diameter and shorter length 63. As above, the sausage skin could be plastic, thin steel or composite. Inside the sausage skin would be the desired material as described in figure 1-8, and this would be hermetically sealed

Referring to figures 14 to 17 there is shown an alternative method of initiating the thermite ignitors. RFID (Radio Frequency ID) is now a well-established method of both transmitting and receiving data. An RF module (radio frequency module) is a small electronic device used to transmit and/or receive radio signals between two devices. It is often desirable to communicate with another device wirelessly. For in well applications the wireless communication is best accomplished radio frequency (RF) communication. In well RFID has a proven typical range of between 3-5 meters. In our application, an RFID initiator may be used for the thermite further away from the transmitter than this.

To overcome this limitation, the initiator is fitted with an RFID receiver / transmitter, connected via a long cable to the cartridge. In practice the deployment process would be as follows;

The cartridge initiator 70, would be lowered into the well as previously described, it would be adjacent to the running tool 71. At setting depth, an arm 72 would be activated which would deploy a magnet to attach itself to the casing 73, on the magnet will be a RFID transmitter / receiver, and a coiled cable 74 connecting it to the electronics inside the initiator cartridge 70. A solenoid 75 on the running tool would be energised and it would shear a pin 76 on the thin central rod 77 and the cartridges would fall into the bottom of the well. The initiator cartridge 70 would be buried with the rest of the thermite cartridges 78, and connected via the cable 74 to the receiver / transmitter 73.

When ah the required cartridges have been deposited, a tool 79 is deployed on the mono conductor and it transmits 80 to ah the RFID devices with their respective unique signals to arm them, they respond confirming they have been armed and then initiate the thermite reaction according to how they have been programmed.

Referring to figures 18 to 21, there is shown a further embodiment of the invention, showing multiple wireless RFID initiator cartridges 70, which talk to each other in a daisy chain manner exclusively using wireless communication. The signal to the lowest initiator is achieved via multiple RFID transmitter / receivers, because the cost is relatively low, they could be in every cartridge, resulting in multiple redundancy for signals in both directions, and also provide a quality assurance, as each cartridge is activated it could transmit that information before being vaporised. The other hermetically sealed cartridges would contain dry materials such as low temperature thermite 84, slow burning thermite 81, high temperature thermite or liquid propellant 82, weighting material 83

Referring to figure 22, there is shown a circuit diagram for a possible embodiment of the one of the acoustic transmitter / receivers for the initiators 38 of the invention. Once all the required tool assembly has been installed into the well, in order to activate the thermite reaction or some similar operation, an acoustic coded signal is transmitted from surface, or from a wireline or slickline deployed tool. A number of features to minimise premature activation are included. Prior to the on-board electronics 100 activating the device, the pressure safety switch 101 interlock has to be activate, and a certain temperature 99 must be achieved, both of these ensure that the device is at a certain depth in the well. Once these conditions have been met, the circuit board 100 goes to ready mode and is receptive to signals. When the circuit receives a command, it is checks for a specific command construction which may include a preamble and postamble (framing bytes), or some other identifier code. If the identifier code is incorrect, it ignores the transmission.

The assembly may also act to transmit and receive data to and from below it, so it forms a daisy chain.

First a Ready command is sent, then “arm”, then “fire”. On Fire, the relay 102 latches on, and applies power which comes from 3 x 4.4 volt 30 amp batteries 103 connected in series to the initiator 104. This all happens to all the acoustically activated switches that are to be initiated together simultaneously.

The acoustic transmitters / receiver’s 105 are specifically tuned to under water performance. When sound travels through medium that has different acoustic impedance, the reflection coefficient R (when energy propagates through mediums) can be calculated as: where Zl, Z2 represent the acoustic impedance value of medium 1 and medium 2. If we like to achieve 100% transmission rate, we like to have R=0 (no energy is reflected)

In transducers case, the model can be simplified to

1. Piezo ceramics composite (Zl) to air (Z2air, 0.000429 kg/s g/cm3),

2. Piezo ceramics composite (Zl) to water (Z2water, 1.5 kg/s g/cm3)

When an air transducer is to be used, the goal would be to achieve Zl as close as to the impedance of air of 0.000429, to minimize the R coefficient. By adding composite, we can achieve Zl close to 0.00085. In this case, the R coefficient is 10.8%, which means almost 89.2% of the energy is transmitted.

However, if the same air transducer is used in water, the second medium immediate has 10,000 times of change in acoustic impedance. And therefore, R = 99.99%, which means no energy can escape/transmit through the surface. For this reason, the transducer must to be specifically designed for underwater use, rather than employing an air transducer without modification.