Note: Descriptions are shown in the official language in which they were submitted.
WO 2021/250404
PCT/GB2021/051434
Bismuth 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 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.
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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 he 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.
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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
tuhulars and the top of the bridge plug
According to a further aspect of the invention, bismuth beads are deposited on
the heat source
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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.
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The following is a more detailed description of an embodiment according to
invention by reference to the following drawings in which:
Figure 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.
Figure 2 is a view similar to figure 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.
Figure 3 is a view similar to figure 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.
Figure 4 is a similar view to figure 4, with the second tool string latched
onto
the first tool string.
Figure 5 is a view similar to figure 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.
Figure 6 is a section side view of a well with another embodiment of the
invention, in its position to he activated
Figure 7. is a similar view to figure 6 with the tool having a complete
section
side view of its internal components.
Figure 8 is a section side view of a well with the tool in a second released
position from the bridge plug.
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Figure 9 is a similar view to figure 8 with the tool having a complete section
side view of its internal components.
Figure 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
Figure 11 is a section side view of a detail highlighted in figure 10
Figure 12 is a similar view to figure 10 with the upper half of the tool
separated from the lower half.
Figure 13 is a similar view to figure 12, with all the low temperature alloy
deposited on top of the bridge plug and the upper half of the tool returning
to
surface.
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Referring to figures 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 x 4.4 volt 30 amp
batteries 15 in series to the initiator 7 and the retarded thermite does a
slow
burn.
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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.
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Referring to figure 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 figures 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
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deposited 127 on top of the bridge plug 128, the upper tool assembly 122 is
returned to surface.
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