U.S. patent application number 11/787090 was filed with the patent office on 2008-10-16 for method of cementing an off bottom liner.
Invention is credited to Peter Lumbye.
Application Number | 20080251253 11/787090 |
Document ID | / |
Family ID | 39852667 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080251253 |
Kind Code |
A1 |
Lumbye; Peter |
October 16, 2008 |
Method of cementing an off bottom liner
Abstract
A method of cementing an off bottom liner including the steps of
establishing a first flow blockage in the liner at a location
down-hole of a cementing valve located in the side wall of the
liner, opening the cementing valve which exposes openings in the
sidewall of the liner, pumping cement down the liner and out
through the openings in the sidewall of the liner, establishing a
second flow blockage up-hole of the cementing valve, closing the
cementing valve, opening the second flow blockage to establish
fluid communication through the second flow blockage, and opening
the first flow blockage to establish fluid communication through
the first flow blockage. The steps of opening the first and second
flow blockages are achieved by increasing the pressure in the liner
above the blockages. In this way, it is possible to cement an off
bottom liner and regain fluid communication to the wellbore below
the liner without the need for any drilling operations.
Inventors: |
Lumbye; Peter; (Malov,
DK) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Family ID: |
39852667 |
Appl. No.: |
11/787090 |
Filed: |
April 13, 2007 |
Current U.S.
Class: |
166/285 ;
166/317; 166/75.11 |
Current CPC
Class: |
E21B 33/16 20130101 |
Class at
Publication: |
166/285 ;
166/317; 166/75.11 |
International
Class: |
E21B 33/13 20060101
E21B033/13; E21B 33/16 20060101 E21B033/16 |
Claims
1. A method of cementing an off bottom liner comprising the steps
of: establishing a first flow blockage in the liner at a location
down-hole of a cementing valve located in the side wall of the
liner; opening the cementing valve to expose openings in the
sidewall of the liner; pumping cement down the liner and out
through the openings in the sidewall of the liner; establishing a
second flow blockage up-hole of the openings in the cementing
valve; closing the cementing valve; opening the second flow
blockage to establish fluid communication through the second flow
blockage; and opening the first flow blockage to establish fluid
communication through the first flow blockage; wherein the steps of
opening the first and second flow blockages are achieved by
increasing the pressure in the liner above the blockages.
2. A method according to claim 1, wherein the step of establishing
a blockage at a location down hole of a cementing valve comprises
the steps of pumping a wiper plug down the liner until it engages a
collar located down hole of the cementing valve.
3. A method according to claim 1, wherein the step of establishing
a blockage at a location up hole of the openings in a cementing
valve comprises the steps of pumping a wiper plug down the liner
until it engages a collar located up hole of the openings in the
cementing valve.
4. A method according to claim 2, wherein the step of establishing
a blockage at a location up hole of the openings in a cementing
valve comprises the steps of pumping a wiper plug down the liner
until it engages a collar located up hole of the openings in the
cementing valve.
5. A method according to claim 1 wherein the method further
comprises the step of establishing a seal below the cementing valve
in order to separate the volume in the wellbore below the seal and
the volume in the wellbore above the seal.
6. A method according to claim 2 wherein the method further
comprises the step of establishing a seal below the cementing valve
in order to separate the volume in the wellbore below the seal and
the volume in the wellbore above the seal.
7. A method according to claim 3 wherein the method further
comprises the step of establishing a seal below the cementing valve
in order to separate the volume in the wellbore below the seal and
the volume in the wellbore above the seal.
8. A method according to claim 4 wherein the method further
comprises the step of establishing a seal below the cementing valve
in order to separate the volume in the wellbore below the seal and
the volume in the wellbore above the seal.
9. A method according to claim 1, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
10. A method according to claim 2, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
11. A method according to claim 3, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
12. A method according to claim 4, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
13. A method according to claim 5, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
14. A method according to claim 6, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
15. A method according to claim 7, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
16. A method according to claim 8, wherein the method further
comprises the step of disabling a one-way valve located at the
bottom of the liner.
17. A wiper plug comprising an outer wiper part and an inner hollow
sleeve, and where the inner hollow sleeve is slideably arranged
within the outer wiper part and is held in place by a release
mechanism, wherein the inner hollow sleeve is formed with through
going openings which are exposed when the release mechanism
releases and the inner hollow sleeve extends out the end of the
wiper part.
18. A wiper plug according to claim 17, wherein the wiper plug
further comprises a restraining mechanism which locks the inner
hollow sleeve once it is extended into its extended position.
19. A wiper plug according to claim 17, wherein the wiper plug
further comprises a ratchet mechanism between the inner hollow
sleeve and the outer part.
20. A wiper plug according to claim 18, wherein the wiper plug
further comprises a ratchet mechanism between the inner hollow
sleeve and the outer part.
21. An assembly comprising a liner, a liner hanger running tool, a
top wiper plug suspended at the end of the liner hanger running
tool, a sidewall cementing valve, a top collar arranged up hole of
the openings in the cementing valve, a bottom plug arranged below
the cementing valve, and where the top collar is arranged such that
the top wiper plug engages the top collar when the top wiper plug
is pumped down the liner, wherein the top wiper plug and the bottom
plug are of the type which can be opened by applying pressure up
hole of the plug.
22. An assembly comprising a liner, a liner hanger running tool, a
top wiper plug suspended at the end of the liner hanger running
tool, a bottom wiper plug suspended below the top wiper plug, a
sidewall cementing valve, a top collar arranged up hole of the
openings in the cementing valve, a bottom collar arranged below the
cementing valve, and where the top collar is arranged such that the
top wiper plug sealingly engages the top collar when the top wiper
plug is pumped down the liner and lets the bottom wiper plug pass
the top collar when the bottom wiper plug is pumped down the liner
and where the bottom collar is arranged to sealingly engage the
bottom wiper plug when the bottom wiper plug is pumped down the
liner.
23. An assembly according to claim 22, wherein the inner diameter
of the top collar is larger than the outer diameter of the bottom
wiper plug and where the inner diameter of the bottom collar is
less than the outer diameter of the bottom wiper plug and where the
inner diameter of the top collar is smaller than the outer diameter
of the top wiper plug.
24. An assembly according to claim 22, wherein the top and bottom
wiper plugs are of the kind which can be opened by increasing the
pressure upstream of the wiper plug.
25. An assembly according to claim 23, wherein the top and bottom
wiper plugs are of the kind which can be opened by increasing the
pressure upstream of the wiper plug.
Description
FIELD OF THE INVENTION
[0001] The current invention relates to a method for cementing an
off bottom liner comprising the steps of establishing a first flow
blockage in the liner at a location down-hole of a cementing valve
located in the side wall of the liner, opening the cementing valve
which exposes openings in the sidewall of the liner, pumping cement
down the liner and out through the openings in the sidewall of the
liner, establishing a second flow blockage up-hole of the openings
in the cementing valve, closing the cementing valve, opening the
second flow blockage to establish fluid communication through the
second flow blockage, and opening the first flow blockage to
establish fluid communication through the first flow blockage. Off
bottom liners are used in wellbores where the end of the liner does
not reach the end of the wellbore. Off bottom liners can also be
used in wellbores which are not purely vertical. Some wellbores can
even be arranged horizontally.
BACKGROUND
[0002] During the creation of a well, liners are inserted into a
wellbore to line the wellbore. The liners are typically anchored to
the wellbore via cement which is pumped out the bottom of the
liner. The cement flows into the annulus between the wellbore and
the liner. When it hardens the liner is firmly cemented within the
wellbore. In other cases cement is pumped out through a cementing
valve which is arranged as part of the liner and which comprises
ports which allow the cement to flow out through the sidewall of
the liner. For an example of the first case, see U.S. Pat. No.
5,829,523, U.S. Pat. No. 6,318,472 and US 2003/0164237. For an
example of the second case, see GB 688,727.
[0003] When cementing an off bottom liner, the second method is
typically used since it is usually not desired to introduce cement
into the portion of the well below the end of the liner. In many
cases where off-bottom liners are used, the bottom of the well
could be hundreds to thousands of meters below the end of the
liner. Therefore, pumping cement out the bottom of the liner would
be unproductive.
[0004] A typical cementing procedure starts with the liner being
run to installation depth via a liner hanger running tool. A
one-way valve is located at the end of the liner to prevent fluid
flow into the liner, but which allows fluid flow out of the end of
the liner. Two wiper plugs are suspended at the end of the liner
hanger running tool. Once the liner has been run to the correct
depth, the liner is hung off the inside of the casing 2 via the
liner hanger, the bottom wiper plug is released from the running
tool and pumped down the well until it engages a landing collar
located near the bottom of the liner. The wiper plug is typically
released by pumping a pump down dart into the wiper plug,
increasing the pressure up hole of the wiper plug and causing shear
pins to break and a release mechanism to trigger that releases the
wiper plug.
[0005] When the bottom wiper plug engages the landing collar, the
end of the liner becomes plugged and the pressure in the liner can
be increased. By increasing the pressure in the liner, down hole
equipment such as an open hole packer can be activated. The open
hole packer is arranged on the outside of the liner and inflates
when activated. The open hole packer inflates such that it presses
out against the wellbore. In this way, a seal is created between
the volume located above the open hole packer and the volume
located below the open hole packer. Increased pressure is also used
to open a cementing valve which is located near the bottom of the
liner, but above the open hole packer. By opening the cementing
valve, a port in the side of the liner is opened. Cement can then
be pumped down the liner, out through the cementing valve and into
the annulus surrounding the liner. Due to the seal created by the
open hole packer, cement is only pumped into the annulus above the
open hole packer.
[0006] When enough cement has been pumped into the annulus, a top
wiper plug is released from the running tool and pumped down the
liner until it engages a suitable collar located at the cementing
valve. As with the bottom wiper plug, the top wiper plug is
released by pumping a pump down dart into the wiper plug, raising
the pressure in the liner and breaking shear pins that allows the
wiper plug to be released from the liner running tool.
[0007] Once the top wiper plug lands in the collar near or inside
the cementing valve, the pressure in the liner is increased again
in order to close the cementing valve. Excess cement is then
circulated out of the casing 2 on top of the liner and the liner
hanger running tool is removed from the well after setting a liner
hanger packer. When the cement has hardened, a drill string is
introduced into the liner and is used to drill the top wiper plug,
top collar, bottom wiper plug, bottom collar and one-way valve out
with a drill bit in order to open the plugs and establish fluid
communication with the wellbore beyond the bottom of the liner.
Once fluid communication is re-established through the bottom of
the liner, the drill string is removed from the liner.
[0008] However, one of the drawbacks of the method described above,
is that the step of drilling the plugs out is time consuming. A
drill string needs to be assembled and run down the well. When the
drilling is complete, the drill string needs to be removed from the
well and disassembled. Another drawback is that the drilling will
leave debris in the well that could interfere with production
equipment later in the well's life.
SUMMARY OF THE INVENTION
[0009] One aspect of the current invention is therefore to provide
a method of cementing an off bottom liner where it is not necessary
to drill the plugs out at the end of the procedure in order to
regain fluid communication to the wellbore below the liner.
[0010] This aspect is solved by a method as mentioned in the
introductory paragraph where the steps of opening the first and
second flow blockages are achieved by increasing the pressure in
the liner above the blockages. By using blockages which open when
the pressure is increased to a certain predefined level, it is not
necessary to drill out the plugs.
[0011] In one embodiment of the method, the step of establishing a
blockage at a location down hole of a cementing valve could
comprise the step of pumping a wiper plug down the liner until it
engages a collar located down hole of the cementing valve.
[0012] Once the first blockage has been established, the step of
establishing a second blockage at a location up hole of the
openings in a cementing valve could comprise the step of pumping a
wiper plug down the liner until it engages a collar located up hole
of the openings in the cementing valve.
[0013] In order to prevent cement from being filled into the end of
the wellbore, the method could further comprise the step of
establishing a seal in the annular space between the liner and the
wellbore below the cementing valve in order to separate the volume
in the wellbore below the seal and the volume in the wellbore above
the seal. The seal could for example be formed with an open hole
packer.
[0014] In one embodiment of the method, the liner comprises a
one-way valve located at the end of the liner. In this case, the
method could further comprise the step of disabling the one-way
valve. In this way, fluid can be pumped up the liner at the end of
the procedure.
[0015] In an advantageous form of a wiper plug, the wiper plug
could comprise an outer wiper part and an inner hollow sleeve, and
where the inner hollow sleeve is slideably arranged within the
outer wiper part and is held in place by a release mechanism. In
one embodiment, the inner hollow sleeve could be formed with
through going openings which are exposed when the release mechanism
releases and the inner hollow sleeve extends out the end of the
wiper part. By arranging the through going openings in the hollow
sleeve and exposing them when the sleeve slides forward, a large
flow can be achieved through the plug. The openings can be formed
as slots in the side of the sleeve which allow the openings to
achieve a very large area, thereby reducing the flow resistance of
the plug.
[0016] The wiper plug could further comprise a restraining
mechanism which locks the inner hollow sleeve once it is extended
into its extended position. In this way, the inner sleeve is
prevented from closing once it has been opened. This is beneficial
during the production of oil, since it would be detrimental to the
well if the well was blocked accidentally.
[0017] The wiper plug could also comprise a ratchet mechanism
between the inner hollow sleeve and the outer part that would
prevent the sleeve from closing. This is useful in the case where
the sleeve only opens partially. In this case, a potential
restraining mechanism hasn't engaged yet.
[0018] In one method according to the invention, an assembly can be
used which comprises a liner, a liner hanger, a liner hanger
running tool, a top wiper plug suspended at the end of the liner
hanger running tool, a sidewall cementing valve comprising openings
through the sidewall of the liner, a top collar arranged up hole of
the openings in the cementing valve, a bottom plug arranged below
the cementing valve, and where the top collar is arranged such that
the top wiper plug engages the top collar when the top wiper plug
is pumped down the liner and where the top wiper plug and the
bottom plug are of the type which can be opened by applying
pressure up hole of the plug.
[0019] In another method according to the invention, an assembly
can be used which comprises a liner, a liner hanger, a liner hanger
running tool, a top wiper plug suspended at the end of the liner
hanger running tool, a bottom wiper plug suspended below the top
wiper plug, a sidewall cementing valve comprising openings through
the sidewall of the liner, a top collar arranged up hole of the
openings in the cementing valve, a bottom collar arranged below the
cementing valve, and where the top collar is arranged such that the
top wiper plug sealingly engages the top collar when the top wiper
plug is pumped down the liner and lets the bottom wiper plug pass
the top collar when the bottom wiper plug is pumped down the liner
and where the bottom collar is arranged to sealingly engage the
bottom wiper plug when the bottom wiper plug is pumped down the
liner.
[0020] In one embodiment of this assembly, the inner diameter of
the top collar could be larger than the outer diameter of the
bottom wiper plug and the inner diameter of the bottom collar could
be less than the outer diameter of the bottom wiper plug and the
inner diameter of the top collar could be smaller than the outer
diameter of the top wiper plug.
[0021] The assembly could be arranged such that the top and bottom
wiper plugs are of the kind which can be opened by increasing the
pressure upstream of the wiper plug.
[0022] It should be emphasized that the term "comprises/comprising"
when used in this specification is taken to specify the presence of
stated features, integers, steps or components but does not
preclude the presence or addition of one or more other features,
integers, steps, components or groups thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In the following, the invention will be described in greater
detail with reference to the embodiments shown by the enclosed
Figures. It should be emphasized that the embodiments shown are
used for example purposes only and should not be used to limit the
scope of the invention.
[0024] FIGS. 1a-1e schematically show five steps according to one
embodiment of a method according to the current invention.
[0025] FIG. 1f shows the liner at the end of the cementing
operation with the cement shown.
[0026] FIGS. 2a-2e schematically show five steps according to a
second embodiment of a method according to the current
invention.
[0027] FIGS. 3a-3f schematically show six steps according to a
third embodiment of a method according to the current
invention.
[0028] FIGS. 4a-4d show more detailed cross section views of one
embodiment of a top wiper plug which can be used in a method
according to the current invention.
[0029] FIG. 5 shows the top wiper plug of FIGS. 4b and 4c in more
detail.
[0030] FIG. 6 shows the top wiper plug of FIG. 4d in more
detail.
[0031] FIGS. 7a-7c show cross section views of a first embodiment
of a bottom plug which can be used in a method according to the
current invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0032] One embodiment of the method according to the current
invention can be described with reference to FIGS. 1a-1e. The Figs.
show a wellbore 1, a casing 2, a liner 3, a liner hanger running
tool 4, a top wiper plug 5, a cementing valve 6, an open hole
packer 7 and a bottom plug 8. It should be noted that in the Figs.,
the wellbore is shown without a bottom. This is to show that the
current technique can be used in wells where the liner 3 does not
reach the bottom of the well.
[0033] As can be seen from the Figs., the casing 2 is suspended in
the wellbore 2 by cement 22. The liner 3 is run into the well bore
and suspended near the end of the casing 2 by the liner hanger
running tool 4. The liner 3 is then hung off the end of the casing
2 by a liner hanger (not shown). The liner hanger allows flow past
the liner hanger and in this way allows flow from the outside of
the liner 3 to flow up into the casing 2. At the end of the
procedure a liner hanger packer (9) is expanded to seal the opening
between the liner 3 and the casing 2 and to secure the top of the
liner 3 to the casing 2.
[0034] The top wiper plug 5 is suspended near the top of the liner
3 at the end of the liner hanger running tool 4. The top wiper plug
5 is attached to the liner hanger running tool 4 by a release
mechanism (not shown) which usually comprises a number of shear
pins. However, the person skilled in the art will be familiar with
other release mechanisms suitable for this use.
[0035] The cementing valve 6 is arranged near the bottom of the
liner 3 and comprises two sliding sleeves 10a, 10b and a number of
openings 11 through the side walls of the liner 3. The open hole
packer 7 is arranged below the cementing valve 6 and is of the kind
which when exposed to a pressure of a certain level, inflates such
that it presses out against the sides of the wellbore 1, thereby
establishing a seal between the volume of the wellbore 1 above the
open hole packer 7 and the volume of the wellbore 1 below the open
hole packer 7.
[0036] The bottom plug 8 is arranged at the bottom of the liner 3.
The bottom plug 8 comprises a check valve 12 which allows flow out
the end of the liner 3, but does not permit flow back up through
the liner 3. In many cases, it is desired to be able to flush fluid
out the bottom of the liner 3 in order to ease the insertion of the
liner 3.
[0037] The top wiper plug 5 and the bottom plug 8, both comprise an
outer part 5a, 8a and an inner sliding sleeve 5b, 8b, respectively.
The inner sliding sleeves 5b, 8b both comprise openings 14, 15
which are covered by the outer part 5a, 8a. The inner sliding
sleeve is held in place in the outer part by a release mechanism,
for example shear pins. The outer part 5a of the top wiper plug 5
further comprises wiper blades such as are known from other wiper
plugs in the industry.
[0038] At the start of the procedure the liner 3 is run into the
well until it is in a position as shown in FIG. 1a. When it is
desired to start the cementing operation, a ball 16 is dropped into
the liner 3. The ball has a diameter which is small enough so that
it can pass through the top wiper plug 5, but large enough so that
it is caught by the bottom plug 8. The ball 16 is made of a
material which is not too heavy. In many cases off bottom liners
are used in horizontal wells, where a heavy ball would not reach
the bottom plug. When the ball is made from a material which is not
too heavy, the ball almost floats on the well fluid and can be
pumped to the end of the liner 3, even if the liner 3 is
horizontal.
[0039] As shown in FIG. 1b, when the ball 16 is caught in the
bottom plug 8, a blockage is established by the bottom plug 8 at
the bottom of the liner 3. Fluid is therefore prevented from
leaving the liner 3. The pressure in the liner 3 can therefore be
raised. The bottom plug 8 also comprises a retaining mechanism (not
shown) such that once the ball 16 is caught in the plug, it cannot
leave the plug.
[0040] When the pressure is raised above a predefined level, a port
in the open hole packer 7 opens and the open hole packer inflates
until it presses out against the wellbore. The pressure can then be
raised again until the bottom sleeve 10b of the cementing valve 6
opens. This is shown in FIG. 1b. At this point, cement can be
pumped out of the liner 3 through the openings 11 in the sidewalls
of the liner 3 as shown by the arrows 17 in FIG. 1b. Note the
cement is not shown in FIGS. 1a-1e in order to simplify the Figs.
However, the cement 23 is shown in FIG. 1f.
[0041] As shown in FIG. 1c, when the desired amount of cement has
been pumped out of the openings in the side walls of the liner 3, a
pump down dart 18 is dropped into the well. The dart 18 is pumped
down the well until it reaches the top wiper plug 5 where it is
caught by the inner sliding sleeve 5b and locked into the sleeve.
Once the dart 18 is caught, fluid flow is prevented from passing
the top wiper plug 5. The pressure above the wiper plug 5 can then
be increased until the release mechanism which holds the wiper plug
5 to the liner hanger running tool is broken. The top wiper plug 5
can then be pumped down the liner 3 until it reaches a landing
collar 19 located at or inside the cementing valve 6. The pressure
behind the top wiper plug 5 can then be further increased until the
top sleeve 10a of the cementing valve 6 slides down and closes the
openings 11 in the cementing valve 6.
[0042] As shown in FIG. 1d, at this point, the pressure behind the
top wiper plug 5 can be increased, causing the release mechanism
(not shown) between the inner sleeve 5b and the outer part 5a of
the top wiper plug 5 to release, thereby allowing the inner sleeve
5b to slide down and expose the openings 14 in the inner sleeve 5b.
Fluid communication is therefore established again to the liner 3
below the top wiper plug 5.
[0043] The pressure behind the bottom plug 8 can then be raised,
causing the release mechanism between the inner sleeve 8b and the
outer part 8a of the bottom plug 8 to release. The inner sleeve 8b
then slides down to expose the openings 15 in the inner sleeve of
the bottom plug 8. At this point, fluid communication is
re-established with the wellbore below the bottom plug 8.
[0044] The production of hydrocarbons or the injection of liquids
and/or gasses can now start as shown in FIG. 1e by the arrows 21,
without the need for any drilling operations. The top wiper plug 5
and the bottom plug 8 can be left in the liner 3 since flow through
them is not prevented.
[0045] It should be mentioned that the top wiper plug 5 and the
bottom wiper plug 8 are formed such that once the inner sleeves
have been released and put into their free flow positions, the
sleeves cannot move back into their closed positions. This could be
with the help of a ratchet mechanism and/or some other form of
locking mechanism. An example of a top wiper plug and bottom plug
suitable for this method will be described in more detail later on
in this specification.
[0046] FIGS. 2a-2e show some of the steps of a second embodiment of
a method of cementing an off bottom liner according to the current
invention. In this case, the steps are almost identical, with the
exception of the bottom plug 30. The other elements are therefore
given the same reference numerals as in the first embodiment. In
addition, the process need not be described in detail, as the
process steps are almost identical.
[0047] In the second embodiment, the bottom plug 30 is of the kind
which is commonly called a "disappearing plug". Plugs of this kind
are well known in the industry and can, for example, comprise a
plug 31 made of a hard packed material which dissolves when exposed
to a high pressure. The plug 31 is arranged in an outer part 32.
One example of such a plug is the "Mirage".TM. plug manufactured by
Halliburton.
[0048] The advantage of using a disappearing plug is that a simpler
system is achieved. However, the disadvantage of using a
disappearing plug is that during the running in of the liner 3, the
bottom of the liner 3 is blocked and it is not possible to flush
fluid out of the end of the liner 3. Not being able to flush out
the end of the liner 3 is acceptable in cases where the well
parameters are well known and there is little risk in the liner 3
installation. Therefore the solution with the disappearing plug is
not always suitable.
[0049] The rest of the procedure is the same as the first
embodiment, the only difference being that no ball is necessary to
block the bottom plug 30. When it is desired to open the bottom
plug 30, the pressure inside the liner 3 is raised above the
predefined pressure point of the disappearing plug 30 and the plug
30 opens.
[0050] It should be mentioned, that instead of using a disappearing
plug 30, a mechanical plug which is similar to the bottom plug 8 of
the first embodiment can be used but which is already blocked at
the start of the procedure. In this way, it is not necessary to
drop a ball 16 into the well. However, as with the disappearing
plug, it is not possible to flush fluid out of the end of the liner
3 during the running of the liner 3 when the liner 3 is equipped
with this type of bottom plug.
[0051] FIGS. 3a-3f show some steps of a third embodiment of a
process for cementing an off-bottom liner. Most of the steps are
the same as the previous methods, and the same elements have been
given the same reference numerals.
[0052] In this embodiment, the difference is that two wiper plugs
5, 40 are suspended from the end of the liner hanger running tool
4. The two plugs are a top wiper plug 5 which is identical to the
one used in the first and second embodiments and a bottom wiper
plug 40 which is similar to the top wiper plug 5. The bottom wiper
plug 40 is attached to the top wiper plug 5 with a release
mechanism such as shear pins (not shown). The wiper plugs are of
the kind which permit fluid flow through them until they are
blocked by a plug 18, 41 which is pumped down the well or dropped
into the well. These types of plugs 7, 8 are known in the industry
and need not be described in more detail. The plugs which block the
wiper plugs are typically in the form of a ball or a wiper dart. In
the current embodiment, a wiper dart is used. Again, this
technology is well known to the person skilled in the art and need
not be discussed further here.
[0053] The wiper plugs 5, 40 are furthermore of the type which
comprise means for re-establishing fluid flow through them at a
time after they have been blocked by a plug. Plugs of this kind are
known to the person skilled in the art from other cementing
procedures. See for example the references in the introduction of
this specification. However, the plugs of this kind have not been
used in a method according to this invention before. Furthermore,
while the known plugs can be used in a method according to the
current invention, they are not optimal. An example of a plug
designed for use in this method is described later on in this
specification.
[0054] A bottom collar 42 is located near the bottom of the liner
3. The bottom collar 42 is designed such that when the bottom wiper
plug 40 is pumped down the liner 3, the bottom wiper plug 40 will
engage the bottom collar 42 and not be able to pass the bottom
collar 42. A check valve 43 is arranged at the bottom of the liner
3. The top collar 19 is designed such that when the bottom wiper
plug 40 is pumped down the liner 3, the bottom wiper plug 40 does
not engage the top collar 19 and is able to pass the top collar 19.
However, the top collar 19 is also dimensioned such that when the
top wiper plug 5 is pumped down the liner 3, it engages the top
collar 19 and is not allowed to pass it.
[0055] This could be arranged by ensuring that the outer diameter
of the bottom wiper plug 40 was smaller than the inner diameter of
the top collar 19 and greater than the inner diameter of the bottom
collar 42. The top wiper plug 5 can be arranged such that its
diameter is greater than the inner diameter of the top collar
19.
[0056] As can be seen from FIG. 3a, at the start of the procedure,
the top 5 and bottom 40 wiper plugs are attached to the liner
hanger running tool and there is free fluid flow through the wiper
plugs and out the end of the liner 3. When it is desired to start
the cementing operation, a dart 41 is dropped into the well. The
dart 41 has an outer diameter which is greater than the inner
diameter of the outlet 44 of the bottom wiper plug 40. The dart 41
therefore blocks the outlet of the bottom wiper plug 40 and blocks
fluid flow through the bottom wiper plug 40. By increasing the
pressure in the running tool, force is applied to the bottom wiper
plug 40 and the shear pins between the top and bottom wiper plugs
are sheared thereby releasing the bottom wiper plug 40. It should
be mentioned that there are many release mechanisms available in
the prior art which ensure that the bottom wiper plug 40 is
released before the top wiper plug 5. The person skilled in the art
will be familiar with these release mechanisms so details of
different types of release mechanisms will not be presented
here.
[0057] The bottom wiper plug is pumped down the liner 3, past the
top collar 19 and past the cementing valve 6 until it reaches the
bottom collar 42 as shown in FIG. 3b. The bottom wiper plug 40
engages the bottom collar 42 and blocks the end of the liner 3. It
should be noted that when the bottom wiper plug 40 engages the
bottom collar 42, the bottom wiper plug 40 is arranged to press the
one-way valve 43 open. In this way, once the bottom wiper plug 40
is arranged in the bottom collar, the one-way valve is fixed in the
open position.
[0058] The pressure can then be increased in the liner 3. The
increased pressure first causes the open hole packer 7 to inflate
and then causes the cementing valve 6 to open. This is shown in
FIG. 3c. It should be noted that cementing valves 6 and open hole
packers 7 of the type discussed here are known to the person
skilled in the art. These devices have therefore been shown very
schematically.
[0059] Once the cementing valve 6 has opened, cement can be pumped
out through the ports 11 in the cementing valve 6 and into the
annulus between the wellbore 1 and the liner 3. The flow of cement
is shown in FIG. 3c by the arrows 17. When enough cement has been
pumped into the annulus, a second dart 18 is dropped into the well.
The outer diameter of the second dart 18 is larger than the
diameter of the outlet 20 of the top wiper plug. The second dart 18
therefore plugs the outlet of the top wiper plug 5. Pressure can
then be raised again in the running tool 4 causing force to be
applied to the top wiper plug 5 which shears the shear pins between
the top wiper plug 5 and the running tool 4. This releases the top
wiper plug 5 which can be pumped down the liner 3 until it engages
the top collar 19.
[0060] When the top wiper plug 5 engages the top collar 19, fluid
flow is again blocked which allows the pressure in the liner 3 to
be raised again. By raising the pressure, the cementing valve 6 is
forced closed by sliding the top sleeve 10a of the cementing valve
over the ports 11. This is shown in FIG. 3d.
[0061] As shown in FIG. 3e, the fluid flow through the liner 3 is
now blocked completely. However, by increasing the pressure in the
liner 3 further, the top wiper plug 5 can be forced open due to the
design of the top wiper plug 5. The release mechanism between the
inner sleeve 5b and the outer part 5a of the plug is released and
the inner sleeve 5b slides down, exposing the openings 14 in the
inner sleeve. This re-establishes fluid communication through the
top wiper plug 5.
[0062] Once the top wiper plug 5 is open, pressure can be applied
to the bottom wiper plug 40 which can also be opened in the same
manner as the top wiper plug 5. By increasing the pressure, force
can be applied to the inner sleeve 40b of the bottom wiper plug 40.
This causes a release mechanism arranged between the outer part 40a
of the bottom wiper plug and the inner sleeve 40b of the bottom
wiper plug to release, thereby allowing the inner sleeve 40b to
slide downwardly, causing the openings 45 to be exposed. This
establishes fluid communication through the bottom wiper plug
40.
[0063] Once the bottom wiper plug 40 is opened, fluid communication
is established through the entire liner 3. Excess cement is also
flushed from the top of the liner 3 whereafter the liner hanger
packer (9) is set. Once excess cement is circulated out,
hydrocarbon production, as shown by the arrows 21 in FIG. 3f, or
liquid and/or gas injection can be started.
[0064] In this way, fluid communication through the liner 3 is
established without the need for any drilling operations. This
means that a significant amount of time can be saved during the
establishment of the well.
[0065] FIGS. 4a-4d show more detailed cross section views of one
embodiment of a top wiper plug which could be used with the above
described methods.
[0066] FIG. 4a shows the wiper plug 5 suspended at the end of the
liner hanger running tool 4 and arranged inside the liner 3. In the
Fig., the dart 18 is shown on its way into the wiper plug 5. FIG.
4b shows the wiper plug 5 on its way down the liner 3 after it has
been released from the liner hanger running tool 4. The dart 18 is
fully engaged with the end of the wiper plug 5 thereby blocking the
outlet 20 of the wiper plug 5. FIG. 4c shows the wiper plug engaged
with the top collar 19 of the cementing valve 6. FIG. 4d shows the
wiper plug 5 after the inner sleeve 5b has been released from the
outer part 5a and the openings 14 in the inner sleeve 5b have been
exposed. The wiper plug 5 is now open for free flow through the
plug 5. It should be noted that in the open position, the sleeve is
locked by a locking mechanism to prevent it from returning to its
closed state.
[0067] FIG. 5 shows the top wiper plug 5 in its closed flow
position in more detail and FIG. 6 shows the top wiper plug 5 in
its open flow position in more detail. The wiper plug 5 comprises
an inner sleeve 5b, an outer part 5a and a dart 18 which has been
pumped down the well and into the plug 5 such that it blocks the
outlet 20 of the inner sleeve. The dart 18 is equipped with a
locking ring 60 which locks the dart 18 in the inner sleeve 5b once
the dart is fully inserted in the sleeve.
[0068] The inner sleeve 5b is fastened to the outer part 5a with
two independent release mechanisms. The first release mechanism 61
comprises shear pins arranged around the circumference of the inner
sleeve. When the force between the inner sleeve 5b and the outer
part 5a is great enough, these pins shear and release the inner
sleeve 5b from the outer sleeve 5a. The second release mechanism 62
comprises a slideable pin 63 arranged in a slot in the outer part
and a bendable hook 64 attached to the inner sleeve 5b. When the
wiper plug 5 is on its way down the liner 3, the hook is engaged
with the slot in the outer part 5a. When the wiper plug 5 lands in
the collar 19, the pin 63 is pressed in thereby displacing the hook
64 inwardly. The hook 64 thereby releases the slot in the outer
part 5a and releases the inner sleeve 5b from the outer part 5a. In
this way, the inner sleeve 5b cannot be released until it is
sitting properly on the collar 19. This ensures that the wiper plug
5 does not accidentally open on its way down the liner 3 if the
pressure in the liner 3 were to increase above the shearing force
of the shear pins. This could for example occur if the wiper plug 5
where to meet an obstruction at a position above the top collar
19.
[0069] The wiper plug 5 further comprises a locking mechanism 65
which engages when the inner sleeve 5b has been fully extended. The
locking mechanism 65 comprises a spring biased split ring or c-ring
connected to the inner sleeve which engages a recess 66 in the
outer part near the end of the outer part 5a. The locking mechanism
65 ensures that once the sleeve has been fully opened, it cannot
accidentally close again.
[0070] The wiper plug can furthermore comprise a ratchet mechanism
(not shown) between the inner sleeve and outer part in order to
prevent the sleeve from closing again if the sleeve does not open
enough to engage the locking mechanism.
[0071] The wiper plug also comprises a second locking ring 67 which
locks the wiper plug in the collar 19 when the wiper plug is
engaged with the collar.
[0072] An end stop 68 is furthermore arranged at the end of the
inner sleeve 5b which prevents the sleeve from sliding completely
out of the outer part 5a. Seals 69 are arranged between the inner
sleeve and the outer sleeve. Additional seals 70 are arranged on
the outer part which establish a seal between the outer part and
the collar 19.
[0073] It should also be noted that the openings 14 in the inner
sleeve are arranged as slots. In this way, it is possible to
provide a very large opening area through the plug thereby reducing
the flow resistance of the plug.
[0074] FIGS. 7a-7c show an embodiment of a bottom plug 8 in
different modes. The bottom plug 8 shown in the Figs. is suitable
for use in a method which is similar to the method described in
FIGS. 1a-1e. The bottom plug 8 is fixed to the liner 3 at a
position near the end of the liner 3 before the liner 3 is run into
position. The plug 8 has a one way valve 12 at its outlet which
ensures that fluid can flow out of the liner 3, but not into the
liner 3.
[0075] FIG. 7a shows the plug 8 in the state it is in when the
liner 3 is being run into position. The plug 8 has an inner sleeve
8b which is fastened to an outer part 8a with shear pins 80. There
is free flow through the plug 8 out of the liner 3. The bottom plug
8 also comprises seals 82 located between the inner sleeve 8b and
the outer part 8a.
[0076] FIG. 7b shows the plug 8 after a ball 16 has been dropped
into the plug 8. The ball 16 is held in place by the pressure in
the tube. However, in case that the pressure should fall, a
retaining mechanism 81 is arranged in the plug 8 to hold the ball
16 in place. Once the ball 16 is in place, the outlet of the bottom
plug 8 is blocked.
[0077] FIG. 7c shows the plug 8 after the pressure in the liner 3
has been increased. The shear pins 80 have broken and the inner
sleeve 8b has been displaced forward with respect to the outer part
8a. In this position, the openings 15 in the inner sleeve 8b which
were previously blocked by the outer part 8a are now exposed and
fluid is free to flow either way through the bottom plug 8.
[0078] It is to be noted that the Figures and the above description
have shown the example embodiments in a simple and schematic
manner. The internal details have not been shown since the person
skilled in the art should be familiar with these details and they
would just unnecessarily complicate this description and the Figs.
For example, the details of open hole packers, liner hanger running
tools, liner hangers, liner hanger packers, cementing values, etc
have not been disclosed in great detail since the person skilled in
the art will be familiar with these items. Furthermore, the methods
have been discussed rather superficially since many of the steps
will be familiar to the person skilled in the art.
[0079] Furthermore it should be noted that the above mentioned
embodiments have only shown a limited number of embodiments of the
method and the devices used in the methods. The person skilled in
the art should be able to use the teachings of the current
specification to develop other embodiments of methods and devices
which are included in the scope of the current invention, but which
are not explicitly disclosed herein.
[0080] Furthermore, a number of terms are used in this
specification which should be understood more broadly than their
literal meaning. For example, the current specification mentions
the word "cement" quite often. However, the person skilled in the
art should understand that cement is typically used to fasten off
bottom liners in a well-bore. However, there are other materials
for example polymer systems or other forms of concrete which would
also fulfill the demands of the fastening material. Therefore, the
person skilled in the art should interpret the term "cement" more
broadly than its pure literal meaning, thereby including the other
suitable materials within the definition of the term cement in the
context of this specification.
* * * * *