Note: Descriptions are shown in the official language in which they were submitted.
WO 2021/038254
PCT/GB2020/052090
Method of Abandoning a Well
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 all 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.
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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
5 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 bather. When the tubing is severed it will collapse
into
20 the annular space of the casing around it, and the thermal bather 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
30 transported on a slickline or wireline tool in the form of a cartridge.
It will
operate by wireless telemetry such as RF1D, 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
35 require a wire to connect it to a REID 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.
40 According to a further aspect to the invention the weighting is
transported on
a slickline or wireline tool in the form of a cartridge.
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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.
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During cool down all the fissures and conductive passages are plugged by the
then cooled down to ambient temperature solidified metal alloy.
5 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
10 ceramic balls
According to a further aspect of the invention the thermal barrier could be
tungsten carbide balls.
15 According to a further aspect of the invention, the thermal bather 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
20 reduction in the cost of carrying out the well abandonment.
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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
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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 REID 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
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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
5 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
10 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
15 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
20 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
RFlD transmitter receiver, an ignitor to initiate the thermite reaction.
25 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
30 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.
35 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 lime, it transmits an
acoustic
signal to activate the different initiators, and the different initiators
transmit
40 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
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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
5 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.
15 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.
30 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
35 payload made up made like a string of sausages 64, the connecting
members
60 being held fight 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
40 63.
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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
5 Referring to figures 14 to 17 there is shown an alternative method of
initiating
the thermite ignitors. REID (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 RPM has a proven typical range of between 3-5 meters. In our
application, an REID 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 REID transmitter / receiver, and a coiled
cable 74 connecting it to the electronics inside the initiator cartridge 70. A
25 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 all the required cartridges have been deposited, a tool 79 is deployed on
the mono conductor and it transmits 80 to all 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
35 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
REID transmitter / receivers, because the cost is relatively low, they could
be
in every cartridge, resulting in multiple redundancy for signals in both
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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 thennite
5 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 thennite 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
15 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:
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21 txt Z
R .sa i
is + Zi
where Z1, 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
5 (no energy is reflected)
In transducers case, the model can be simplified to
1. Piezo ceramics composite (Z1) to air (Z2air, 0.000429 kg/s g/cm3),
2. Piezo ceramics composite (Z1) to water (Z2water, 1.5 kg/s g/cm3)
When an air transducer is to be used, the goal would be to achieve Z1 as close
as to the impedance of air of 0.000429, to minimize the R coefficient. By
adding composite, we can achieve Z1 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
20 use, rather than employing an air transducer without modification.
Acoustic
impedance
Z1 0.00085
Z2 air 0.000429
Z2 water 1.5
R of piezo to air 10.8%
R of piezo to water 100%
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