U.S. patent application number 13/405571 was filed with the patent office on 2012-08-30 for activation device for use in a downhole well.
Invention is credited to Philippe Cravatte, Mathew John Kennedy.
Application Number | 20120217021 13/405571 |
Document ID | / |
Family ID | 43904213 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120217021 |
Kind Code |
A1 |
Cravatte; Philippe ; et
al. |
August 30, 2012 |
ACTIVATION DEVICE FOR USE IN A DOWNHOLE WELL
Abstract
An activation device for use in a downhole well for activation
of a downhole tool in the well. The downhole tool has a seat
adapted to engage the activation device. The activation device can
travel through a borehole of the downhole well to reach the seat.
The activation device has an outer layer and a core. The material
of the outer layer resists erosion by drilling fluid when the
activation device is in the borehole. The material of the core is
eroded by drilling fluid when the activation device is engaged in
the seat. The activation device is then able to pass through the
seat. There is also described a method of operating a downhole tool
having a seat for engaging an activation device. The method
includes the step of eroding at least a portion of the activation
device with drilling fluid until it can pass through the seat.
Inventors: |
Cravatte; Philippe;
(Malmedy, BE) ; Kennedy; Mathew John; (Mawson
Lakes, AU) |
Family ID: |
43904213 |
Appl. No.: |
13/405571 |
Filed: |
February 27, 2012 |
Current U.S.
Class: |
166/373 ;
166/318 |
Current CPC
Class: |
E21B 34/14 20130101;
E21B 23/00 20130101 |
Class at
Publication: |
166/373 ;
166/318 |
International
Class: |
E21B 34/06 20060101
E21B034/06; E21B 34/00 20060101 E21B034/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2011 |
GB |
1103295.0 |
Claims
1. An activation device for use in a downhole well for activation
of a downhole tool in the well, the downhole tool having a seat
adapted to engage the activation device whereby engagement of the
activation device in the seat changes the activation status of the
downhole tool, the activation device being adapted for passage
through the borehole of the well and being adapted to engage the
seat of the downhole tool in the well to change the activation
status of the downhole tool, the activation device comprising an
outer layer and a core housed within the outer layer, and wherein
the material of the outer layer is adapted to resist erosion during
passage of the activation device through the borehole of the well
in normal operating conditions, and wherein the material of the
outer layer and the core are adapted to be eroded by drilling fluid
when the activation device is engaged in the seat in the downhole
tool, whereby the drilling fluid erodes the seated activation
device such that the activation device is able to pass through the
seat.
2. An activation device according to claim 1 wherein the activation
device comprises a substantially spherical ball.
3. An activation device according to claim 1 wherein the core has a
compressive strength from 10 to 140 MPa.
4. An activation device according to claim 1 wherein the material
of the outer layer is selected from the group consisting of cement,
concrete, epoxy resin, ceramic, MOLYKOTE.RTM., ester,
flourosilicone, mineral oil, polyalkyleneglycol; polyalphaolephin,
perflouropolyether, silicone, and siloxane grease.
5. An activation device according to claim 1 wherein the material
of the core is selected from the group consisting of wax, salt, and
sand.
6. An activation device according to claim 1 wherein the activation
device is adapted to be eroded by the flow of drilling fluid past
the seated activation device.
7. An activation device according to claim 1 wherein the core
comprises a material adapted to change state from solid to liquid
when exposed to normal temperatures in the environment of the
seat.
8. An activation device according to claim 1 wherein the core
comprises a material that is more susceptible to erosion than the
material of the outer layer.
9. An activation device according to claim 1 wherein the material
of the outer layer is epoxy resin, the material of the core is a
salt and wherein the core has a compressive strength from 10 to 140
MPa.
10. A method of operating a downhole tool in a borehole of an oil
or gas well, the downhole tool having a seat for engaging an
activation device, the method comprising the steps of: providing an
activation device adapted to pass through at least a part of the
borehole and engage the seat, the activation device comprising a
core and an outer layer of material housing the core; transporting
the activation device in a flow of drilling fluid through the
borehole from an insertion point in the borehole to the seat of the
downhole tool, whereby the activation device engages in the seat of
the downhole tool; changing the state of activation of the downhole
tool when the activation device engages with the seat, and eroding
at least a portion of the activation device with drilling fluid
until the activation device can pass through the seat.
11. A method according to claim 10 wherein the activation device is
eroded by flowing the drilling fluid past the activation device
when the activation device is in the seat of the downhole tool.
12. A method according to claim 10 wherein the core comprises a
material that is more susceptible to erosion than the material of
the outer layer, whereby erosion of the outer layer to expose the
core takes more time than the subsequent erosion of the core.
13. A method according to claim 10 wherein the activation device is
eroded after the step of changing the activation status of the
downhole tool.
14. A method according to claim 10 wherein the eroded activation
device passes through the seat and is washed away from the downhole
tool by the drilling fluid.
15. A method according to claim 10 wherein the activation device
erodes over a period of between 10 seconds and 20 minutes when
located on the seat member.
16. A method according to claim 10 wherein the velocity of the
drilling fluid is between 5 and 45 metres per second.
17. A method according to claim 10 wherein the activation device is
eroded by particles of solids transported in the drilling
fluid.
18. A method according to claim 10 wherein the activation status of
the downhole tool is changed a second time by a second activation
device, the method comprising the further steps of: providing a
second activation device adapted to pass through at least a part of
the borehole and engage the seat, the second activation device
comprising a core and an outer layer of material housing the core;
transporting the second activation device in the flow of drilling
fluid through the borehole to the seat of the downhole tool,
whereby the second activation device engages in the seat of the
downhole tool; changing the state of activation of the downhole
tool when the second activation device engages with the seat, and
eroding at least a portion of the second activation device with
drilling fluid until the second activation device can pass through
the seat.
19. An activation device for use in a downhole well for activation
of a downhole tool in the well, the downhole tool having a seat
adapted to engage the activation device whereby engagement of the
activation device in the seat changes the activation status of the
downhole tool, the activation device being adapted for passage
through the borehole of the well and being adapted to engage the
seat of the downhole tool in the well to change the activation
status of the downhole tool, the activation device comprising an
outer layer and a core housed within the outer layer, wherein the
core has a compressive strength from 10 to 140 MPa and wherein the
material of the outer layer is adapted to resist erosion during
passage of the activation device through the borehole of the well
in normal operating conditions, and wherein the material of the
outer layer and the core are adapted to be eroded by drilling fluid
when the activation device is engaged in the seat in the downhole
tool, whereby the drilling fluid erodes the seated activation
device such that the activation device is able to pass through the
seat.
20. An activation device according to claim 19, wherein the
material of the outer layer is selected from the group consisting
of cement, concrete, epoxy resin, ceramic, MOLYKOTE.RTM., ester,
flourosilicone, mineral oil, polyalkyleneglycol; polyalphaolephin,
perflouropolyether, silicone, and siloxane grease.
21. An activation device according to claim 19, wherein the
material of the core is selected from the group consisting of wax,
salt, and sand.
Description
[0001] The present invention relates to an activation device such
as an activation ball for controlling the operation of a downhole
tool, particularly for use in an oil or gas well. Many different
kinds of downhole tool are known to be controlled using activation
balls; typical examples are tools used in drill strings and/or
tools used in production strings used to transport production
fluids through the borehole.
[0002] Known activation balls are normally substantially spherical
and are dropped into the wellbore from an insertion point at the
surface and travel through the wellbore to the downhole tool. The
activation ball may be carried by drilling mud or another fluid
that is pumped through the wellbore. The fluid may be contained in
a wellbore tubular or another structure of the wellbore.
[0003] When the activation ball reaches the downhole tool the ball
lands on a seat of the downhole tool allowing fluid and/or
hydraulic pressure to be applied to the ball on the seat. The fluid
pressure is generally applied from the surface and the force
resulting from the pressure is used to operate the downhole tool,
typically by moving the ball and the seat, or some mechanism
connected to it to change the activation status of the downhole
tool, for example to activate or de-activate it.
[0004] It is known to use a deformable activation ball or
deformable seat that deforms under increased fluid pressure such
that the ball is forced past the seat and out of the downhole tool
when the hydraulic pressure is increased beyond a threshold. This
has the advantage that a succession of activation balls can be sent
downhole from the surface to activate and deactivate a downhole
tool.
[0005] Deformable activation balls and a deformable seat on the
downhole tool address the problem of how to activate and then
deactivate or reactivate a downhole tool. Previously if the first
activation ball sent downhole did not activate the downhole tool,
then often the downhole tool and associated equipment would have to
be raised back to surface so that the activation ball could be
retrieved, before the tool was lowered downhole once more.
[0006] Deformable activation balls and seats however have
significant design problems. They require very precise
manufacturing tolerances to provide adequate resistance to
increased fluid pressure acting on the ball and therefore
facilitate operation of the downhole tool, whilst retaining the
required amount of deformability to allow the ball to be forced
past the seat and out of the downhole tool at the required higher
pressure.
[0007] According to a first aspect of the present invention there
is provided an activation device for use in a downhole well for
activation of a downhole tool in the well, the downhole tool having
a seat adapted to engage the activation device whereby engagement
of the activation device in the seat changes the activation status
of the downhole tool, the activation device being adapted for
passage through the borehole of the well and being adapted to
engage the seat of the downhole tool in the well to change the
activation status of the downhole tool, the activation device
comprising an outer layer and a core housed within the outer layer,
and wherein the material of the outer layer is adapted to resist
erosion during passage of the activation device through the
borehole of the well in normal operating conditions, and wherein
the material of the outer layer and the core are adapted to be
eroded by drilling fluid when the activation device is engaged in
the seat in the downhole tool, whereby the drilling fluid erodes
the seated activation device such that the activation device is
able to pass through the seat.
[0008] The activation device may comprise a substantially spherical
ball or may be cylindrical in shape. The seat of most downhole
tools is adapted to receive a substantially spherical ball. A
spherical activation device obviates the need to control the
orientation of the activation device relative to the seat and/or
tool and therefore optimises contact between the ball and the seat.
The activation device may be a drop ball.
[0009] The core may have a compressive strength from 10 to 140 MPa.
Optionally the core has a compressive strength of between 60 and
100 MPa. Optionally the core has a compressive strength of between
70 and 90 MPa. The core may have a compressive strength of 80 MPa.
The core may provide structural strength to the activation device.
The core can provide the required structural strength if the
compressive strength of the core is sufficient to withstand impact
of the activation device against the sides of the borehole during
passage of the activation device through the borehole of the well,
the impact of the activation device on the seat and the force
applied to the activation device through the drilling fluid to
activate the downhole tool. The core may have a compressive
strength such that the shape and size of the activation device
remain substantially constant at least during passage of the
activation device through the borehole of the well and change of
the activation status of the downhole tool.
[0010] The material of the outer layer may be one or more of
cement; concrete; epoxy resin; ceramic; and MOLYKOTE.RTM. as
supplied by Dow Corning Corporation. The outer layer may be a
protective layer that surrounds the core and protects the core from
erosion by the drilling fluid until the activation device is on the
seat. The outer layer may be resistant to dissolution in the
drilling fluid, and may form a barrier between the drilling fluid
and the core, preventing access to the core by the drilling fluid
until erosion of the outer layer when the activation device is
seated.
[0011] The material of the core may be one or more of wax; salt;
and sand. The core may be more susceptible to erosion by the
drilling fluid than the outer layer. This may reduce the time taken
for the activation device, including the outer layer and core, to
be eroded and subsequently pass through the seat, thereby clearing
the downhole tool for further unimpeded operation of the downhole
tool or a further change in the activation status of the downhole
tool to be affected by a second activation device. The outer layer
may therefore remain intact until the activation status of the
downhole tool has been changed.
[0012] The compressive strength of the salt core may be between 20
and 60 MPa. The compressive strength of the epoxy outer layer may
be between 80 and 120 MPa. The compressive strength of the concrete
outer layer may be between 80 and 100 MPa.
[0013] The core may have a coating disposed between the core and
the outer layer, the coating comprising a wax. The coating may
provide a barrier that separates the core from the outer layer, and
may reduce or prevent contact of the outer layer by the core
material. Such contact may for example prevent the outer layer from
forming during manufacture of the activation device and/or cause
premature degradation of the outer layer.
[0014] The activation device may be adapted to be eroded by the
flow of drilling fluid when the activation device is located in the
seat. When located in the seat, the activation device may reduce
the available flow path past the seat, but normally does not close
the flow path past the seat entirely, and normally the flow of
drilling fluid past the activation device may be possible because
the seat has slots, apertures or other suitable forms of bypass
channels that always remain open.
[0015] The core may comprise a material adapted to change state
from solid to liquid when exposed to normal temperatures in the
environment of the seat. The core may comprise a wax. The
compressive strength of the activation device may be reduced when
the wax has melted and is in liquid form. This may help to promote
fragmentation of the activation device after it has engaged the
seat and the activation status of the of the downhole tool has been
changed.
[0016] The core may comprise an inner core and an outer core. If
the activation device has more than one core then the compressive
strength of the core can be adapted and varied to suit a particular
application. A crust on the activation device may also be used to
adapt the overall compressive strength of the activation device.
There may be one or more layers between the core and the outer
layer, these one or more layers may also be used to adapt the
overall compressive strength of the activation device.
[0017] The activation device may have an external or outer diameter
of between 10 and 100 mm; optionally between 30 and 70 mm; and
normally 54 mm. These external or outer diameters mean that the
activation device is small enough to pass through the borehole of a
downhole well and big enough to engage with a typical seat of a
typical downhole tool to activate and/or deactivate the tool.
[0018] The core may have a diameter of between 9 and 99 mm;
optionally between 29 and 69 mm; and normally between 52 and 53 mm.
These core dimensions are normally sufficient to provide the
activation device with an outer layer of sufficient thickness to
provide the resistance to erosion by the drilling fluid the
activation device requires before and/or during passage of the
activation device through the borehole of the well to the downhole
tool.
[0019] According to a second aspect of the present invention there
is provided a method of operating a downhole tool in a borehole of
an oil or gas well, the downhole tool having a seat for engaging an
activation device, the method comprising the steps of:
[0020] providing an activation device adapted to pass through at
least a part of the borehole and engage the seat, the activation
device comprising a core and an outer layer of material housing the
core;
[0021] transporting the activation device in a flow of drilling
fluid through the borehole from an insertion point in the borehole
to the seat of the downhole tool, whereby the activation device
engages in the seat of the downhole tool;
[0022] changing the state of activation of the downhole tool when
the activation device engages with the seat, and
[0023] eroding at least a portion of the activation device with
drilling fluid until the activation device can pass through the
seat.
[0024] The downhole tool can be activated and then deactivated or
reactivated using two or more activation devices of substantially
the same external dimensions. Using the method of the second aspect
of the present invention negates the need to use objects of
increasing size or increasing external dimensions to subsequently
deactivate or reactivate the downhole tool. The activation device
of the present invention is particularly suited for repeatedly
operating a downhole tool.
[0025] Adapted to erode means the materials of the core and outer
layer can one or more of wear away; partially disintegrate;
disintegrate; deteriorate; and decay. The step of eroding the
activation device may include the steps of eroding the material of
the outer layer and then subsequently eroding the material of the
core.
[0026] The outer layer may be eroded by the action of the downhole
fluid in contact with the activation device. The activation device
may be eroded by flowing the drilling fluid past the activation
device when the activation device is in the seat of the downhole
tool. This means that the activation device can be added to the
borehole, pass through at least a part of the borehole and engage
the seat of the downhole tool, change the state of activation of
the downhole tool and then be effectively removed from the seat to
allow further unimpeded operation of the downhole tool or a further
change in the activation status of the downhole tool to be affected
by a second activation device.
[0027] The method may therefore further comprise the steps of:
[0028] providing a second activation device adapted to pass through
at least a part of the borehole and engage the seat, the second
activation device comprising a core and an outer layer of material
housing the core;
[0029] transporting the second activation device in the flow of
drilling fluid through the borehole to the seat of the downhole
device, whereby the second activation device engages in the seat of
the downhole tool;
[0030] changing the state of activation of the downhole device when
the second activation device engages with the seat, and
[0031] eroding at least a portion of the second activation device
with drilling fluid until the second activation device can pass
through the seat.
[0032] The susceptibility to erosion of the second material of the
core by the drilling fluid may be greater than that of the material
of the outer layer. Erosion of the outer layer to expose the core
may take more time that the subsequent erosion of the core. The
susceptibility to erosion of the material of the core and material
of the outer layer of the activation device by the drilling fluid
may be adapted so that the activation device remains in
substantially its original condition and having its original shape
and/or size until after the activation device has contacted a
downhole tool and the downhole tool has been activated, deactivated
or reactivated.
[0033] The activation device may be sufficiently rigid and the
outer layer or core have sufficient compressive strength to provide
adequate resistance to drilling fluid pressure in the downhole
well. The activation device is therefore able to facilitate
operation of the downhole tool. When the outer layer is eroded to
expose the chamber or core, the activation device may disintegrate
and may pass through the seat and be washed away from the downhole
tool by the drilling fluid in the downhole well. The activation
device may be eroded after the step of changing the activation
status of the downhole tool. The method of operating a downhole
tool may therefore be particularly suited for repeat operation of a
downhole tool.
[0034] The activation device may erode over a period of between 10
seconds and 20 minutes, optionally over a period of between 10
seconds and 15 minutes, normally over a period of between 10
seconds and 15 minutes and may be over a period of between 10 and
30 seconds when located in the seat member.
[0035] The method of operating a downhole tool may include
activating the tool using a first activation device. From this
activated configuration the downhole tool may be deactivated using
a second activation device that is substantially identical to the
first activation device.
[0036] The method of operating the downhole tool may include the
step of dropping the activation device into the borehole of the
downhole well. This is typically the way of introducing an
activation device into the borehole and has the advantage it does
not require or rely on any additional equipment or tools for the
deployment of the activation device. This reduces the dependence on
specific tools and therefore the risk of downtime casued by tool
failure.
[0037] The drilling fluid may be pumped through the borehole. The
drilling fluid may be pumped down the borehole of the downhole
well. Pumping is typically the method used to move the drilling
fluid in the borehole and can be used to control the velocity and
pressure of drilling fluid in the borehole. The drilling fluid may
be drilling mud.
[0038] The velocity of the drilling fluid may be between 5 and 45
metres per second and normally slower than 20 metres per second.
The velocity of the drilling mud is intended to be high enough to
erode at least a portion of the activation device but not too high
that the drilling fluid damages the and/or other downhole tools. If
the velocity of the drilling fluid is not high enough, then at
least a portion of the activation device will not be eroded or
eroded sufficiently quickly for efficient operation of downhole
tool and further unimpeded operation of the downhole tool. At least
a portion of the activation device may be eroded with drilling
fluid and the activation device passes through the seat up to 5
minutes after the activation device has engaged in the seat.
[0039] Erosion of the outer layer of the activation device may be
caused by friction. The erosion by friction may be abrasion, caused
by particles of solids transported in the drilling fluid contacting
the material of the outer layer and/or second material of the core
of the activation device. The particles of solids may scratch,
scrape and/or wear down the surface of the material of the outer
layer and/or the second material of the core of the activation
device. The particles of solid may be suspended in the drilling
fluid. Erosion of the activation device by particles of solids
transported in the drilling fluid does not require the use of
further downhole tools or for example special chemicals to be added
to drilling fluid. These solids are typically present in drilling
fluid during normal use.
[0040] The activation device may be erodible such that it will
collapse or implode. When the activation device is hollow, it does
not need to be eroded completely but rather to an extent that the
drilling fluid pressure is sufficient to crush the activation
device.
[0041] An erodible activation device can be slowly eroded such that
the activation device will not be substantially eroded on its way
through the downhole well (borehole) or string even though it is in
contact with the drilling fluid. Otherwise the activation device
would be substantially eroded and therefore relatively useless by
the time it reached the downhole tool, it not being able to
activate, deactivate or reactivate the downhole tool.
[0042] The second material of the core may be dissolvable.
Dissolvable means the material can one or more of pass into
solution in the drilling fluid; disperse; and disintegrate. The
material of the outer layer and/or second material of the core may
be corroded by the drilling fluid.
[0043] The preferred features of the first aspect of the invention
can be incorporated into the second aspect of the invention and
vice versa.
[0044] There is also herein described an activation device for use
in a downhole well for activation of a downhole tool in the well,
the downhole tool having a seat adapted to engage the activation
device whereby engagement of the activation device in the seat
changes the activation status of the downhole tool, the activation
device being adapted for passage through the borehole of the well
and being adapted to engage the seat of the downhole tool in the
well to change the activation status of the downhole tool, the
activation device comprising a body with at least one chamber at
least partially housed within the body, and wherein the material of
the body is adapted to resist erosion during passage of the
activation device through the borehole of the well in normal
operating conditions, and wherein the material of the body is
adapted to be eroded by drilling fluid when the activation device
is engaged in the seat in the downhole tool, whereby the drilling
fluid erodes the seated activation device such that the activation
device is able to pass through the seat.
[0045] The at least one chamber at least partially housed in the
body may be in the centre of the activation device and may be a
void, such that the activation device is hollow. The void may
comprise a vacuum. If the at least one chamber is a void, then when
the activation device is sufficiently eroded, it may collapse
generating fragments of the activation device that are able to pass
through the seat. The void means that only fragments of the body
need to pass through the seat. The vacuum may make it more likely
that the activation device collapses because there is a tendency
for the activation device to implode.
[0046] The at least one chamber at least partially housed in the
body may be at least one channel that extends from an outer surface
towards the centre of the activation device. The at least one
channel may extend across the activation device from one outer
surface to another outer surface of the activation device. The at
least one channel may provide fluid communication into or through
the body of the activation device. The at least one channel may
therefore provide a path for the flow of drilling fluid. The
material of the body is adapted to be eroded by drilling fluid and
so the at least one channel increases the surface area of the body
that is susceptible to erosion and therefore may reduce the time
taken for the activation device to be eroded and pass through the
seat.
[0047] A portion of the body of the activation device may be
weighted to control the orientation of the activation device in the
borehole and/or on the seat. This may help to control the flow of
fluid through the at least one channel and so also erosion of the
activation device.
[0048] The at least one chamber may alternatively contain a fluid.
The fluid may be one or more of air; an inert gas; a liquid; oil;
and water. The fluid may be at a pre-determined pressure or if the
fluid is air it may be at atmospheric pressure. The fluid may
affect the compressive strength of the body and/or activation
device and this may be used to help promote or hinder fragmentation
of the activation device after it has engaged the seat and the
activation status of the of the downhole tool has been changed.
[0049] The at least one chamber may be sealed from the environment
outside of the activation device and is optionally sealed by the
outer layer. By sealing the at least one chamber, and if
appropriate the fluid in the chamber from the environment outside
of the activation device, the composition of the fluid or contents
of the at least one chamber can be controlled and therefore also
the compressive strength of the body and/or activation device can
be controlled.
[0050] The body may have a compressive strength from 10 to 140 MPa.
Optionally the body has a compressive strength of between 60 and
100 MPa. The body may have a compressive strength of between 70 and
90 MPa. Normally the body has a compressive strength of 80 MPa. The
body may provide structural strength to the activation device. The
body can provide the required structural strength if the
compressive strength of the body is sufficient to withstand impact
of the activation device against the sides of the borehole during
passage of the activation device through the borehole of the well,
the impact of the activation device on the seat and the force
applied to the activation device through the drilling fluid to
activate the downhole tool. The body may have a compressive
strength such that the shape and size of the activation device
remain substantially constant at least during passage of the
activation device through the borehole of the well.
[0051] The material of the body may be one or more of cement;
concrete; epoxy resin, ceramic, chipboard and medium-density
fibreboard. The material of the body may be chosen to provide the
activation device with the required structural strength. The
material of the body may be impermeable to the drilling fluid and
so will only be eroded by the drilling fluid. This may allow the
user to control when the activation device is able to pass through
the seat and/or disintegration of the activation device.
[0052] The compressive strength of the body typically depends on
the material of the body. The compressive strength of a body
comprising concrete may be between 80 and 100 MPa. The compressive
strength of a body comprising epoxy resin may be between 80 and 120
MPa.
[0053] The activation device may comprise a substantially spherical
ball or may be cylindrical in shape. The seat of most downhole
tools is adapted to receive a substantially spherical ball. This
obviates the need to control the orientation of the activation
device relative to the seat and/or tool and therefore optimises
contact between the ball and the seat. The activation device may be
a drop ball.
[0054] The activation device may have an external or outer diameter
of between 10 and 100 mm; optionally between 30 and 70 mm; and
normally 54 mm. These external or outer diameters mean that the
activation device is small enough to pass through the borehole of a
downhole well and big enough to engage with a typical seat of a
typical downhole tool to activate and/or deactivate the tool.
[0055] The at least one chamber may be in the centre of the
activation and may have a diameter of between 2 and 80 mm; normally
between 6 and 49 mm. These dimensions are sufficient to provide the
activation device with a body of sufficient thickness to provide
the resistance to erosion by the drilling fluid the activation
device requires before and/or during passage of the activation
device through the borehole of the well to the downhole tool.
[0056] The preferred features of the first and second aspects of
the invention can be incorporated into the activation device
described above and vice versa.
[0057] Embodiments of the present invention will now be described,
by way of example, with reference to the accompanying drawings, in
which:
[0058] FIG. 1 is a cross-sectional perspective view of an
activation device according to an embodiment of the present
invention;
[0059] FIG. 2 is a cross-sectional perspective view of an
activation device according to an alternative embodiment of the
present invention;
[0060] FIG. 3 is a part cross-sectional perspective view of an
activation device;
[0061] FIGS. 4 to 6 are cross-sectional perspective views of an
activation device;
[0062] FIG. 7 is a plan view of a mould for the core of an
activation device;
[0063] FIG. 8 is an exploded perspective view of a mould for an
activation device;
[0064] FIG. 9 is an exploded perspective view of an alternative
mould for an activation device; and
[0065] FIG. 10 is a cross-sectional view of part of downhole tool
with a seat; an activation device according to an embodiment of the
present invention is engaged in the seat.
[0066] FIG. 1 shows an activation device in the form of a ball 10
with an outer layer 12 made of concrete and a core 14 made of wax.
The outer layer 12 of the ball 10 is erodible by, but impermeable
to, drilling mud. The ball 10 is generally spherical.
[0067] In use the impermeable outer layer 12 prevents the drilling
mud from coming into contact with the core 14 of wax when the ball
10 is being transported by the drilling mud from the surface to the
downhole tool (not shown). As the temperature of the drilling mud
increases the wax is heated and melts. The outer layer 12 contains
the core 14 of melted wax as the ball 10 is transported from the
surface to the downhole tool (not shown). The outer layer 12 may
insulate the core 14 of wax from the heat of the drilling mud
thereby delaying the melting of the core 14 of wax.
[0068] The compressive strength of the ball 10 is reduced or
weakened when the wax of core 14 has melted and is in liquid
form.
[0069] When the ball 10 is seated on the downhole tool the pressure
of drilling mud acting on the ball 10 activates the downhole tool.
With the ball 10 now stationary, the drilling mud erodes the outer
layer 12 of the ball 10, exposing the core 14 of wax. When the
thickness of the ball 10 is reduced sufficiently, the ball 10
typically disintegrates and the fragments of the outer layer 12 and
core 14 of wax are flushed into the drilling mud.
[0070] The wax (of core 14) is typically a hydrocarbon wax, and
usually a paraffin wax of a mixture of alkanes having the general
chemical formula of C.sub.nH.sub.2n+2 with a value of n between 20
and 40.
[0071] The ball 10 in this example has an external diameter of 54
mm; the core 14 has a diameter of 40 mm. The core 14 may have a
diameter of between 25 and 48 mm.
[0072] The outer layer 12 may be made only of cement. The concrete
described above typically contains cement, sand and/or gravel. The
cement binds the sand and/or gravel together to form concrete. The
cement may include one or more of the chemical elements aluminium;
calcium; iron; and silicon. The cement may incorporate
limestone.
[0073] The outer layer 12 of the ball 10 is made from a material
that can be eroded by drilling mud and is alternatively made of one
or more of epoxy resin; ceramic; and MOLYKOTE.RTM. as supplied by
Dow Corning Corporation.
[0074] The core 14 of the ball 10 may alternatively be made of
sand; the sand may be compacted. In use, the external outer layer
12 of the ball 10 provides the ball with a defined structure whilst
the ball is transported downhole and seated on the downhole tool.
As soon as the outer layer 12 of cement has been eroded enough to
expose the sand of the core 14 to the drilling mud, the sand is
then flushed into the mud system including the drilling mud. The
remaining outer layer 12 is then an empty shell that easily
fragments under the force applied by the drilling fluid flowing
past the seat and is also flushed into the mud system.
[0075] Alternatively, the core 14 of ball 10 is hollow.
[0076] Examples of a downhole tool that could be operated using an
activation ball according to an aspect of the present invention
include hole-enlargers; activation devices in a core barrel
assembly; inflatable packers; circulating subs and multi-activation
subs.
[0077] FIG. 2 shows a ball 20 with an outer layer 22 made of
concrete and a core 24 made of salt. The salt is typically sodium
chloride (NaCl). During manufacture, the core 24 is typically
covered in a layer 26 of wax to protect the concrete from the salt.
The wax is typically a hydrocarbon wax but may be any coating that
provides the necessary protection to the outer layer from the core
and does not affect the compressive strength of the ball or
erodibility of the core. In an alternative embodiment the outer
layer 22 of concrete contacts the salt core 24 and there is no
layer 26 of wax.
[0078] The ball 20 having a core 24 of salt typically has an
impermeable outer layer 22 or coating made of concrete. In use, the
outer layer 22 prevents the core 24 from being eroded or dissolved
when the ball 20 is submerged in the drilling mud. When the outer
layer 22 of concrete has been eroded enough to expose the salt of
the core 24 to the drilling mud, the salt is easily dissolved
and/or eroded by the drilling mud and fragments of the salt core 24
pass into the mud system. Any remaining fragments of the outer
layer 22 are also flushed through the downhole tool and into the
mud system.
[0079] The ball 20 has an external diameter of 54 mm; the core 24
has a diameter of 52 mm.
[0080] Alternatively, the outer layer 22 of the ball 20 is made
from epoxy resin, or ceramic. Alternatively, the outer layer 22 of
the ball 20 is made from one or more of an ester; fluorinated;
flourosilicone; mineral oil; polyalkyleneglycol; polyalphaolephin;
perflouropolyether; silicone; synthetic blend; and siloxane grease.
The outer layer may be MOLYKOTE.RTM. as supplied by Dow Corning
Corporation.
[0081] The epoxy resin outer layer 22 is typically resistant to
attack by chemicals and/or heat. The epoxy resin outer layer 22
provides the salt core 24 with good mechanical protection.
[0082] The concrete described above contains cement, sand and/or
gravel. The cement binds the sand and/or gravel together to form
concrete. The cement may include one or more of the chemical
elements aluminium; calcium; iron; and silicon. The cement may
incorporate limestone. The outer layer 22 provides the ball 20 with
a defined shape and size whilst the ball is transported
downhole.
[0083] Alternatively the core 24 is made of sand; the sand may be
compacted.
[0084] In use the impermeable outer layer 22 prevents the drilling
mud from coming into contact with the core 24 of salt when the ball
20 is being transported by the drilling mud from the surface to the
downhole tool (not shown). The outer layer 22 makes the ball 20
resistant to erosion by the drilling mud when it is travelling
downhole towards the tool (not shown). The outer layer 22 may also
protect the ball 20 from damage caused by the ball contacting the
sides of the borehole and/or other obstacles in the flow path of
the drilling mud between the surface and the downhole tool.
[0085] When the ball 20 is seated in the downhole tool the pressure
of drilling mud acting on the ball 20 is used to activate the
downhole tool. With the ball 20 now stationary, the ball 20 is
susceptible to erosion and the drilling mud erodes the outer layer
22 of the ball 20, exposing the core 24 of salt.
[0086] Erosion of the outer layer 22 and core 24 of the ball 20 by
the drilling fluid when it is seated in the downhole tool reduces
the diameter of the ball 20. When the diameter of the ball 20 has
been sufficiently reduced, the ball 20 is able to pass through the
seat of the downhole tool. The ball 20 now only comprises the salt
core 24 because the outer layer 22 has already been eroded away by
the drilling fluid. Further erosion of the salt core 24 by the
drilling mud is now possible as what remains of the salt core 24
passes through the seat and into the borehole below the tool. At
this stage the core 24 of the ball 20 is not protected by the outer
layer 22 and is susceptible to erosion by the drilling mud.
[0087] Usually up to 5 minutes after the ball 20 has first
contacted the downhole tool, the outer layer 22 and core 24 of the
ball 20 have been eroded and fragments of the ball 20 washed into
the drilling mud. These fragments are small enough so that they do
not interfere with the operation of other downhole tools and can be
carried or suspended in the drilling mud and therefore washed out
of the borehole by the drilling mud.
[0088] The velocity of the drilling mud moving past the ball 20 on
the seat of the downhole tool (not shown) is normally between 5 and
45 metres per second, optionally less than 20 metres per
second.
[0089] FIG. 10 shows a ball 100 in a downhole tool 101. The ball
100 has passed through a central bore 102 of the downhole tool 101
and is engaged in the seat 103. The seat 103 has slots 104 that
allow fluid to flow past the ball 100 in the direction of the
arrows 105a and 105b.
[0090] The outer layer of the activation ball 20 comprises a
material that remains substantially intact when travelling down the
borehole to the downhole tool. The outer layer of concrete, epoxy
resin or ceramic is therefore not eroded, such that the salt core
is not exposed, until the ball is on the seat.
[0091] Examples of a downhole tool that could be operated using the
activation ball 20 include hole-enlargers; activation devices in a
core barrel assembly; inflatable packers; circulating subs and
multi-activation subs.
[0092] In use, the ball 20 travels through the borehole until it
reaches the seat of the downhole tool. The seat catches the ball
20, the ball 20 substantially blocking the throughbore of the
downhole tool. The seat normally has slots, apertures or other
suitable forms of bypass channels that remain open to allow
drilling fluid to continue to flow past the ball 20 when it is in
the seat. The flow of drilling fluid past the ball on the seat is
typically reduced compared to the flow of drilling fluid through a
central channel of the downhole tool that is possible when the seat
is empty.
[0093] When the activation ball 20 is in the seat, the pressure of
the drilling fluid in the borehole increases. The increased force
acting on the ball 20 is used to operate the downhole tool, pushing
at least part of the downhole tool downwards in a downstream
direction.
[0094] The ball is eroded by the action of the drilling mud and/or
components of the drilling mud that pass the ball when it is in the
seat and the drilling mud is flowing through the slots in the
seat.
[0095] FIG. 3 shows a ball 30 made of concrete 32. The ball 30 has
three hollow channels 37a, 37b and 37c that extend from the outer
surface 35 of the ball 30 to the centre 38. The hollow channels
37a, 37b and 37c have an opening 33 on the outer surface of the
ball 30 and converge at the centre 38 of the ball 30 to produce a
chamber 39. The hollow channels 37a, 37b and 37c provide a flow
path for drilling mud and therefore promote erosion of the ball 30.
On break up of the ball 30 the pieces of cement 32 are relatively
small and easily pass through the downhole tool (not shown) carried
by the drilling mud.
[0096] The ball 30 has an external diameter of 54 mm; the hollow
channels 37a, 37b and 37c have an internal diameter of 8 mm. The
hollow channels 37a, 37b and 37c may have an internal diameter of
between 8 and 10 mm.
[0097] Alternatively, the concrete 32 of the ball 30 is a mixture
of cement and pebbles. The pebbles range in size from 1 to 2 mm in
diameter. The material of the ball is a conglomerate. Hollow
channels 37a, 37b and 37c are drilled in the concrete and pebble
mixture as described above.
[0098] Again alternatively, the concrete 32 of the ball 30 is a
mixture of cement and particles of lead. The particles of lead
range in size from 2 to 3 mm in diameter. The particles of lead add
to the mass of the ball 30 and thereby can help promote delivery of
the ball. Hollow channels 37a, 37b and 37c are drilled in the
concrete as described above.
[0099] In an alternative embodiment there may be more than three
hollow channels 37a, 37b and 37c.
[0100] FIGS. 4, 5 and 6 show a ball 40 referred to as a "dart
ball". The ball 40 is made of concrete 42. The ball 40 has radial
hollow channels 41 a and 41 b that extend from the outer surface 45
of the ball 40 to a central hollow channel 49. The hollow channels
41a and 41b have an opening 43 on the outer surface of the ball 40
and converge in, and are in fluid communication with, the central
hollow channel 49. The hollow channel 49 passes through the ball
40, as shown in FIG. 5. The ball 40 also has hollow conduits 50a-f
that extend from the outer surface 45 of the ball 40 towards, but
are not in fluid communication with, the central hollow channel 49.
The hollow channels 41a and 41b have an opening 43 on the outer
surface of the ball 40 and converge in, and are in fluid
communication with, the central hollow channel 49. There are other
radial hollow channels and hollow conduits in the ball 40; these
are shown in FIGS. 5 and 6. In use, the hollow channels 41a and 41b
act like the fins and help the ball 40 to "fly" through the
drilling mud or water column as appropriate. In use, the hollow
conduits 50a-f have a dead-end as described above and act as "worm
holes", increasing the surface area of the ball at which erosion
can occur. As erosion of the ball continues, the hollow conduits
50a-f will increase in length and penetrate the central hollow
channel 49, further helping the erosion process and subsequent
breakup of the ball.
[0101] The ball 40 is flattened at the ends of the central hollow
channel 49. The concrete 42 of the lower third (1/3) of the ball
40, indicated by the hatching 51, includes lead shot (not shown).
The lead shot has a diameter in the range of 2 to 3 mm and in use,
helps to weight and orientate the ball 40 in the downhole well (not
shown). In use, the drilling mud passes through the central hollow
channel 49 also helping to orientate the ball 40.
[0102] The ball 40 has an external diameter of 54 mm; the central
hollow channel 49 has an internal diameter of 12 mm; the angled
radial hollow channels 41a and 41b have an internal diameter of 5
mm; the hollow conduits 50a-f have an internal diameter of 8
mm.
[0103] The ball 40 shown in FIG. 6 further includes further hollow
conduits 60a-f that extend at right angles to the hollow conduits
50a-f shown in FIGS. 4 and 5. Like the hollow conduits 50a-f, the
hollow conduits 60a-f extend from the outer surface 45 towards the
centre of the ball 40.
[0104] FIG. 7 shows a mould for the manufacture of the core 14 of
the ball 10 shown in FIG. 1. The mould 70 is made of silicone and
has hemispherical depressions 71 spaced across a panel 72. In use,
sand (not shown) is poured into the mould 70 and a glue (not shown)
is added to fill the pores in the sand. Excess sand is removed to
produce a half ball or hemisphere. Once the glue has dried, the
half balls are taken out of the mould 70 and the two half balls
glued together to make a ball or sphere. The hemispheres have a
diameter of 25 mm. In an alternative embodiment the hemispheres
have a diameter of between 40 and 45 mm.
[0105] FIGS. 8 and 9 show a two types of mould for the manufacture
of the balls 10, 20, 30 and 40 shown in FIGS. 1, 2, 3 and 4-6
respectively. The moulds 80 and 90 are made of steel. Using the
mould shown in FIG. 8, it can sometimes be difficult to remove the
ball from the mould without damaging the ball. The mould shown in
FIG. 9 is easier to separate and remove the ball from and therefore
it is less likely that the ball is damaged when being removed from
the mould 90.
[0106] The following materials are used: sand; high resistance
cement (80 MPa); salt; glue (light glue); epoxy laminating resin;
wax; and petroleum jelly.
[0107] The following equipment is used: silicon mould (diameter of
hollows 25 & 40 mm); water drilling machine; concrete drill (8
& 10 mm drill bit); hammer; wrench; and glass ball.
[0108] There is herein described a method of manufacturing the ball
10 shown in FIG. 1, the ball having a hollow core 14. It is
difficult to manufacture the ball shown in FIG. 1 because the ball
must have a hollow centre that is concentric with the external
surface of the concrete ball. To produce a hollow centre to the
concrete ball a glass ball, typically a glass ball is used as an
object about which the concrete is poured. Using the mould 80 shown
in FIG. 8, the screws 81 and pins 82 are inserted into the mould 80
and the glass ball is laid on top of the pins 82 and screws 81. It
is important that the pins 82 and screws 81 are inserted into the
mould at the correct length to obtain the required concentricity.
The internal faces of the mould are lubricated with petroleum
jelly. Other suitable lubricants including molybdenum-based
lubricants and silicone-based lubricants could be used.
[0109] One mould half 85 of the mould 80 can be pre-filled with
concrete before inserting the glass ball (not shown). This makes it
easier to ensure that concrete fully surrounds the glass ball. The
other mould half 86 is then offered up to the mould half 85 and the
two mould halves 85 and 86 are connected together using the screws
87. Concrete can then be poured into the mould through the filling
hole 88 located in the mould half 85. Care is taken not to crush
the glass ball when filling the mould 80 with concrete.
[0110] It is important to minimise as much as possible air pockets
trapped inside the cement. A rubber hammer is used to gently tap
the mould so that air is driven from the cement and escapes the
mould. A vibrating plate could be used instead.
[0111] With the mould 80 filled with concrete, the concrete is
allowed to dry and after 20 minutes the two halves of the mould are
carefully separated. At this stage the concrete is not completely
dry but the ball (not shown in FIG. 8) is strong enough to be
manipulated. The concrete can be allowed to dry for between 30 and
40 minutes. It is important however that the concrete is removed
from the mould before the concrete sticks to the face of the mould
making the removal of the ball difficult without breaking the
ball.
[0112] When the ball is removed from the mould 80 there are holes
in the outer wall of the ball caused by the screws 81 and pins 82
that penetrate the inside of the mould. These holes are now filled
with fresh concrete and the ball is left to dry for 21 days to
ensure the concrete obtains its best resistance.
[0113] The mould 90 shown in FIG. 9 is used in the same way as the
mould 80 shown in FIG. 8. The difference between the moulds is that
the two mould halves 85 and 86 of mould 80 have been further split
into quarters 95a, 95b and 96a, 96b. Screws 99 are used to hold
together quarters 95a and 95b and screws 100 are used to hold
together quarters 96a and 96b.
[0114] The method of manufacturing the other balls 10, 20, 30 and
40 shown in FIGS. 1 to 6 is similar to that described above. The
differences are outlined below.
[0115] There is herein described a method of manufacturing the ball
10 shown in FIG. 1, the ball having a core 24 of wax. The first
step is to manufacture a wax ball (not shown). A glass ball is
used; the glass ball is filled with wax. The glass ball is
pre-heated to avoid thermic shock and also to make sure the wax
remains in a liquid state during the filling. This minimises the
chance of air pockets forming in the wax as it solidifies. A
venting hole is provided in the glass ball so that air can escape
during filling. The wax ball is then allowed to cool and harden and
then placed in the mould 80 and concrete added to the mould as
described above; the wax ball replaces the glass ball described
above with reference to the ball 10 of FIG. 1 with a hollow core
24.
[0116] There is herein described a method of manufacturing the ball
10 shown in FIG. 1, the ball having a core 24 of sand. The first
step is to manufacture the sand ball (not shown). The sand ball is
sufficiently consolidated to withstand the manufacturing process
but also soft enough to be washed away by drilling mud when the
concrete shell has been eroded and abraded to reveal the core 24 of
sand. Glue is used as a binding agent to bind or bond together the
grains of sand. The glue can be starch; methylcellulose; clay
and/or dextrin based. The glue must have a low viscosity and
relatively low adhesive strength.
[0117] There is herein described a method of manufacturing the ball
20 shown in FIG. 2, the ball having a core 24 of salt. The first
step is to manufacture a salt ball (not shown) having an external
diameter of 45 mm. The salt ball is milled using a computer
numerical control (CNC) milling machine. Salt is corrosive and
therefore to avoid problems caused by small particles of salt
produced by the CNC machine coming into contact with surrounding
equipment, the salt ball is dipped in oil before the ball is
milled.
[0118] After milling an impermeable protective layer or coating 26
of wax is applied to the salt ball to protect the salt from
environmental conditions and the surrounding environment from the
salt. The protective layer also reduces the chance of the salt
contaminating the concrete. Such contamination would prevent the
cement from drying.
[0119] The ball 20 shown in FIG. 2 also has an outer layer 22 made
of concrete. The outer layer 22 prevents water and other liquids in
the drilling mud reacting with and/or eroding the core 24 of the
salt when the ball 20 is added to the drilling mud or other fluid
in a borehole of a downhole well.
[0120] In an alternative embodiment, the core 24 of salt has an
outer layer of epoxy resin; or ceramic instead of concrete as
described above.
[0121] The epoxy resin is a two-part epoxy laminating resin. The
first component is the resin and the second component is a
hardener. The resin comprises epichlorohydrin and bisphenol-A. The
hardner comprises triethylenetetramine (TETA).
[0122] The proportions used are two doses resin and one dose
hardener. It is important to mix the resin and hardener slowly to
avoid the formation of air bubbles. When the components have been
mixed the mixture must be used within 50 minutes.
[0123] The resin is poured onto the ball until the ball is fully
covered with a uniform layer of resin. It is important to minimise
the contact points on which the ball rests and/or sits. The resin
is then dried at a temperature of 25.degree. C. for between 8 and
14 hours.
[0124] Alternatively the core 24 of the ball 20 has an outer layer
of ceramic. The core 24 of salt is covered with a ceramic powder
and then placed in an oven. The temperature is raised until the
powder melts. When cooling, the powder solidifies providing the
protective outer layer.
[0125] Alternatively the core 24 of the ball 20 has an outer layer
of grease and/or oil. The outer layer is allowed to dry before the
activation ball is used or brought into contact with the drilling
fluid.
[0126] There is herein described a method of manufacturing the ball
30 shown in FIG. 3, the ball 30 being made of concrete 32 and
having three hollow channels 37a, 37b and 37c. Either of the moulds
shown in FIG. 8 or 9 can be used to make this ball but using the
mould shown in FIG. 8 makes it easier to subsequently drill holes
in the ball. This is because the screws 81 and pins 82 generate
holes in the ball that can be used as pilot holes when subsequently
drilling the channels 37a, 37b and 37c in the ball.
[0127] The channels 37a, 37b and 37c are drilled when the concrete
has been dried for at least one week. A small hole with a diameter
of 4 mm (+/-1 mm) is drilled first and then the channels 37a, 37b
and 37c are drilled at a diameter of 8 mm. It is important to stop
drilling in the middle of the ball, otherwise there is a risk of
damaging the ball when the drill exits the other side of the
ball.
[0128] Modifications and improvements can be incorporated without
departing from the scope of the invention. Certain embodiments of
the invention avoid the need for ball catcher devices to catch the
activation device when it passes through the downhole tool, freeing
the tool from design constraints related to the limited capacity of
the catcher device for activation balls.
[0129] Certain embodiments of the invention allow an activation
ball to be eroded and then move thorough a seat of a first tool,
and onto the seat of a second tool further down the borehole to
activate the second tool.
[0130] Certain embodiments of the invention allow relaxation of
manufacturing tolerances for the ball which merely needs to occlude
the seat and then be eroded. Also, activation devices according to
the invention do not require the same precise pressure increase in
the activation regime as is the case with deformable balls, so
permit easier and more accurate activation and de-activation with
lower specifications of equipment and training.
* * * * *