U.S. patent number 3,559,739 [Application Number 04/835,268] was granted by the patent office on 1971-02-02 for method and apparatus for providing continuous foam circulation in wells.
This patent grant is currently assigned to Chevron Research Company. Invention is credited to Stanley O. Hutchison.
United States Patent |
3,559,739 |
Hutchison |
February 2, 1971 |
METHOD AND APPARATUS FOR PROVIDING CONTINUOUS FOAM CIRCULATION IN
WELLS
Abstract
A method and apparatus is disclosed for maintaining continuous
circulation of foam in a well through a segmented tubing string
while the tubing string is being made up or broken up. A chamber
having a foam entry port is formed around the tubing string above
the wellhead. A valve is provided above the foam entry port to
close off the upper portion of the chamber when the tubing string
is broken and the upper portion thereof raised above such valve.
When it is desired to add or remove a tubing section from the
tubing string, the tubing string is held by slips with its open end
in the lower portion of the chamber. The upper tubing section is
lifted in the chamber to above the valve. The valve is closed and
foam is circulated in the chamber through the foam entry port to
provide for continuous foam circulation while another section of
tubing is added or removed from the tubing string.
Inventors: |
Hutchison; Stanley O.
(Bakersfield, CA) |
Assignee: |
Chevron Research Company (San
Francisco, CA)
|
Family
ID: |
25269078 |
Appl.
No.: |
04/835,268 |
Filed: |
June 20, 1969 |
Current U.S.
Class: |
166/311; 175/69;
166/81.1; 166/380; 175/207 |
Current CPC
Class: |
E21B
37/00 (20130101); E21B 19/16 (20130101); E21B
21/02 (20130101); E21B 21/14 (20130101); E21B
33/068 (20130101) |
Current International
Class: |
E21B
21/00 (20060101); E21B 19/16 (20060101); E21B
21/02 (20060101); E21B 33/068 (20060101); E21B
21/14 (20060101); E21B 33/03 (20060101); E21B
19/00 (20060101); E21B 37/00 (20060101); E21b
033/02 (); E21b 021/00 () |
Field of
Search: |
;166/77,75,77.5,84,81,311,315,312 ;175/214,57,69,71,65,207,215 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
vail et al., "New Developments in air-gas drilling and
completions,"World Oil, Gulf Publishing Co., Houston, Texas,
Reprint from Nov. and Dec., 1963. Copy in 175-69.
|
Primary Examiner: Novosad; Stephen J.
Claims
I claim:
1. A method of providing continuous circulation of fluids in a
segmented tubing string during makeup of such string comprising
flowing fluid in or out of a well through a tubing string, forming
a fluid-tight chamber about the upper end of said tubing string,
providing a port in said chamber for flow of fluid in the same mode
as the fluid flowing in said tubing string, opening said tubing
string in said chamber, flowing fluid through said port and the
open end of said tubing string to maintain circulation of fluid in
said tubing string, adding another section of tubing to said tubing
string and flowing fluid through said tubing string including the
section added thereto.
2. A method of maintaining continuous circulation in a segmented
tubing string and well annulus system comprising the steps of
connecting a foam source to the upper end of a tubing string,
injecting foam from said foam source down said tubing string and
into a well, flowing foam up the well annulus between the tubing
string and the well wall and exhausting the foam at the earth's
surface, forming a foam-tight chamber about the upper end of said
tubing string, injecting foam from said foam source into the lower
portion of said chamber while continuing to inject foam from said
foam source down said tubing string, positioning said tubing string
so that the connection between said foam source and said tubing
string is positioned in said chamber, hanging said tubing string
below said connection in tension in the well, disconnecting said
connection in said chamber to open the upper end of the tubing
string and the lower end of said foam source in said chamber,
raising the lower end of said foam source to near the upper part of
said chamber, closing off said chamber to flow between the lower
end of said foam source and the entry for foam into the lower
portion of said chamber, stopping foam flow through the lower end
of said foam source, removing the lower end of said foam source
from said chamber while continuing to maintain foam flow into the
lower portion of said chamber and into the open end of said tubing
string for injection down said well, connecting a new section of
tubing to the lower end of said foam source, inserting said newly
connected section of tubing into said chamber, connecting said
newly connected section of tubing with the open end of said tubing
string in said chamber and injecting foam from said foam source
through said tubing string into said well.
3. A method of maintaining continuous circulation in a segmented
tubing string and well annulus system comprising the steps of
injecting foam down a well annulus, flowing foam up a tubing string
located in the well and exhausting the foam through a foam exhaust
connected to such tubing string, forming a foam-tight chamber about
the upper end of said tubing string, positioning said tubing string
so that a connection between the foam exhaust and said tubing
string is positioned in said chamber, hanging said tubing string
below said connection in tension in the well, providing a port for
exit of foam from said chamber, disconnecting said connection in
said chamber to open the upper end of said tubing string in said
chamber, raising the lower end of the foam exhaust to the upper
portion of said chamber, closing off said chamber to flow between
the lower end of said foam exhaust and the exit for foam from said
chamber to cause foam from said tubing string to be exhausted from
said chamber, through said port, removing the lower end of said
foam exhaust from said chamber, connecting a new section of tubing
to the lower end of said foam exhaust, inserting said newly
connected section of tubing into said chamber, connecting said
newly connected section of tubing with the opened end of said
tubing string in said chamber and exhausting foam from said well
through said newly connected section.
4. A method of refluxing foam in a well annulus formed between a
well wall and a tubing string located therein comprising
establishing a foam source at the earth's surface, forming a
fluid-tight chamber about the upper end of a tubing string
extending down a well providing a port in said chamber for flow of
foam thereto, connecting said port with said foam source,
connecting the well annulus with said foam source and alternately
injecting foam down said tubing string and up said well annulus and
injecting foam down said well annulus and up said tubing
string.
5. Apparatus for use in a foam circulating system comprising a
tubular shell of greater diameter than a tubing string to be used
therewith, said tubular shell having an open upper end and an open
lower end and a port for foam injection into the interior thereof
or foam exhaust from the interior thereof, stripper rubber means in
both the upper end and the lower end of said tubular shell, said
stripper rubber means adapted to slidably engage tubing inserted
through the ends of said tubular shell in a flow-tight manner to
form with said shell a chamber about a tubing so inserted, valve
means on said shell for closing off said shell to foam flow above
said foam entry port and means for connecting said tubular shell in
vertically spaced apart alignment with a wellhead.
6. Apparatus for use on a wellhead to provide continuous
circulation in a tubing string extending into a well and the
annulus formed between the exterior of the tubing string and the
well casing comprising a tubing string, means for running said
tubing string in a well, a foam source, conduit means for
connecting said foam source to the upper end of said tubing string,
a tubular shell arranged about the upper part of said tubing string
and having a diameter greater than the diameter of said tubing
string, said tubular shell having an open upper end and an open
lower end, resilient stripper means fixedly connected in the ends
of said tubular shell slidably engaged against the tubing string
contained therein to cooperate with said tubing string to close off
the ends of said tubular shell to form a closed annular chamber,
means for flowing foam from said foam source into the lower portion
of said annular chamber, valve means in said annular chamber above
said foam entry means for closing off said annular chamber to
longitudinal flow in the absence of a tubing section located
adjacent thereto, a wellhead having tubing string hanging means and
means for fixedly connecting said tubular shell to said wellhead in
axially aligned, spaced apart relationship with the entry for the
tubing string into said wellhead.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The present invention is related to the field of inventions in
copending U.S. Pat. application Ser. No. 704,832, filed Feb. 12,
1968, now U.S. Pat. No. 3,463,231, Ser. No. 720,977, filed Apr. 12,
1968, now U.S. Pat. No. 3,486,560 and Ser. No. 807,766, filed Mar.
13, 1969, on all of which I am either an inventor or a
coinventor.
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for providing
continuous foam circulation in a well during drilling or workover
operations and, more particularly, this invention provides for
maintaining continuous circulation in a segmented tubing string and
the annulus between the tubing string and the well wall during
makeup or breakup of the tubing string as it is lowered or raised
in the well to accomplish well cleanout, drilling or the like.
Well cleanout, which includes the removal of drill chips, sand or
other unconsolidated materials and fluids from a well has long been
a problem. Thus the removal from a well of drilled solids produced
while penetrating a formation with a drilling string and also the
removal of the solids which flow into the well during oil
production have both continued to be a problem to the oil industry.
This is particularly true when formations penetrated during
drilling or from which fluids are produced, are unconsolidated
low-pressure formations. Various techniques, including the use of
wire line bailers and various circulating fluids have heretofore
been suggested for removing such material from wells.
One such circulating fluid found successful in such operations is a
stable, low density foam. Foam of this type has proven quite
successful in removing solids and fluids from wells. However, it
has been found that certain techniques must be utilized to overcome
problems encountered in the use of foam as a circulating fluid for
removing sand and the like from a well. One such technique is
disclosed and claimed in the above noted application Ser. No.
807,766. In this technique, the foam in the tubing string is
maintained for a period of time in a dynamic condition by certain
one-way valve means provided in the tubing string. This method has
proven successful. However, it has also been found that where
delays may be encountered in changing tubing or if downtime is
likely to occur it is desirable to provide for continuous
circulation of foam during makeup or breakup of the tubing
string.
One prior art technique for providing continuous circulation is
disclosed in an article entitled "New Developments in Air-Gas
Drilling and Completions" in WORLD OIL, Nov.--Dec. 1963. The
procedure disclosed in this article used a special sub in each
tubing joint having a hinged disc to provide for continuous
circulation during tubing string makeup. The obvious problem with
this procedure is that a special sub is required in each tubing
section to obtain circulation.
The reason for the need for such special techniques required in the
application of foam to wells will be better understood when it is
realized that in a typical well cleanout operation utilizing foam
as the circulating medium, a segmented tubing string is used to
inject foam down a well to the position in the well from where it
is desired to remove sand and/or produced fluids. The foam picks up
the sand or fluids and carries them out of the well via the
tubing-well wall annulus. A tubing string is made up of a plurality
of individual pipe sections coupled together. A rig or hoist is
used to lower each successive pipe section into the well to
approximately its full length. After the pipe section has been
lowered to such a position, it is gripped near its upper end by
various means such as slips to suspend it in the well. The hoist is
then released from the pipe section and a second pipe section is
connected to the first section. The hoist is then connected to the
second pipe section and the slips released from the hanging tubing
string and it is lowered further into the well to near the full
extent of the second pipe section when the slips are again applied
and the above sequence repeated. As this sequence is repeated,
successive pipe sections form a tubing string which progressively
goes deeper and deeper into the well. Once the lower end of the
tubing string has reached a level from where it is desired to
remove sand or liquid a flexible tube is connected onto the top
pipe section and foam is injected into the tubing string and
circulated down the string out the bottom end and up the annulus
between the tubing string and the well wall or well casing to the
surface. As foam is circulated, it carries up the fluids and/or
sand and chips from the well. The tubing string during this foaming
period is progressively lowered deeper into the well. This
necessitates, of course, adding additional pipe sections to the
tubing string at the wellhead. When such pipe sections are added,
the flexible foam tube must be disconnected from the top pipe
section forming the uppermost joint of the tubing string and
reconnected to the top of the newly connected pipe section. Thus
for a short time foam circulation down the tubing is stopped. It
has been found necessary, however, to prevent backflow of foam up
the tubing string and consequent collapse of foam in the tubing
string-casing annulus. If foam is allowed to backflow up the
tubing, uncomfortable and dangerous conditions will exist at the
wellhead. Even more seriously, if foam is allowed to collapse in
the annulus, solids will settle out of the foam and bridge against
the tubing string causing it to become stuck in the well. As noted
above, the special techniques directed at preventing this have not
been entirely satisfactory. The present invention is directed to
solving these problems.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for
continuously circulating foam in a well through a segmented tubing
string while the tubing string is being made up or broken up. The
invention permits maintaining continuous circulation during such
makeup or breakup--normal circulation down the tubing string and up
the well annulus or reverse circulation down the well annulus and
up the tubing string. A foam source is provided with a conduit
connecting it to a tubing string through an appropriate coupling
known as a pup joint. A chamber is formed around the tubing string
above the wellhead and is provided with a port through which foam
can be injected into the chamber or, if circulation is reversed,
from which foam can be removed from the chamber. The ends of the
chamber permit sliding movement of the tubing string therethrough
while preventing escape of foam from the chamber. The joint that is
desired to disconnect is opened in the chamber while in the case of
normal circulation foam is also injected into the chamber through
the port provided for such purpose and then into the open end of
the tubing string and then down the tubing string. For reverse
circulation operation the port is opened to provide flow of foam
from the chamber. The pup joint is lifted up the chamber above the
valve means and the lower half of the chamber is then isolated. In
reverse circulation operation the foam is flowed out of the chamber
through the port until the new tubing section is connected. In
normal circulation foam injection is stopped from said foam source
through the pup joint and the pup joint is removed from the
chamber. Meanwhile foam is continuously circulated through the foam
entry port into the chamber and then into the open end of the
tubing string and down the string into the well. A new section of
tubing is connected to the pup joint and is inserted into the upper
half of the chamber and foam is injected therein. The valve means
is then opened to open the chamber and the new tubing is inserted
and connected to the tubing string. After such connection is made,
foam injection through the port in the chamber is stopped, the
slips are released from the tubing and the tubing string is run
further into the hole.
BRIEF DESCRIPTION OF THE INVENTION
Briefly, the present invention provides for maintaining continuous
foam circulation while connecting or disconnecting a pipe section
to the tubing string. A chamber is formed above the wellhead around
the tubing string and the ends of the chamber are provided with
resilient means which allow passage of the tubing string in both an
up and down direction therethrough. The resilient means, however,
frictionally engage against the tubing in a manner to prevent flow
of foam from the chamber. The chamber is provided with a foam port
and a valve is provided for closing off the chamber to flow above
such port. The connection to be broken is positioned in the chamber
below such valve and foam is injected through the foam entry port
into the chamber at least the injection pressure of the foam
circulating down the tubing. The connection is then broken by
suitable means such as a power swivel or power tongs, and the top
section of pipe is raised up to above the valve. The valve is
closed to close off the upper portion of the chamber and foam
injection through the top section of pipe is stopped. This top
section may then be removed from the chamber and a new pipe section
added thereto. Meanwhile foam is continuously circulated from the
chamber down the tubing. As noted above, if reverse circulation is
desired the foam leaves the chamber through the entry port while
the tubing section is being made up. When the new section of pipe
is connected to the top section, its lower end is inserted into the
chamber and foam is injected therethrough. The valve is opened to
open the chamber and the new pipe section is lowered and connected
into the tubing string. After such connection is made, foam
injection into the chamber is stopped and the tubing string is
lowered further into the hole while foam injection continues down
the tubing.
The apparatus of the present invention provides continuous
circulation through a tubing string extending into a well and the
annulus formed between the exterior of the tubing string and the
well casing during makeup of the tubing string. The apparatus
includes a tubular shell having a diameter greater than the
diameter of tubing run in the well. The tubular shell has an open
upper end and an open lower end. Resilient stripper means are
fixedly connected in the ends of the tubular shell to slidably
engage against the tubing string contained therein to cooperate
with said tubing to close off the ends of said tubular shell to
form a closed annular chamber. Means for flowing foam into or out
of the lower portion of the annular chamber are provided. Gate
valve means are located in the annular chamber above the foam entry
means for closing off the annular chamber to longitudinal flow in
the absence of tubing therein. A wellhead having tubing hanging
means and means for fixedly connecting the tubular shell to the
wellhead in axially aligned, spaced apart relationship with the
entry for tubing into said wellhead are also provided in accordance
with the invention.
OBJECTS OF THE INVENTION
A particular object of the present invention is to provide for
continuous circulation of foam in a well during foam cleanout or
the like while a tubing string is being made up or broken up.
Further objects and advantages of the present invention will become
apparent from the following detailed description read in light of
the accompanying drawings which are made a part of this
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view, with parts broken away for clarity of
presentation, of the preferred embodiment of apparatus assembled in
accordance with the invention in which foam is injected through a
tubing string into a well, and FIG. 2 is a view, with parts broken
away for clarity of presentation, of the preferred embodiment of
apparatus in which foam is injected into the foam chamber and
thence into the tubing string while a new section of tubing is
being added.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Refer now to the drawings and to FIG. 1 in particular where the
preferred embodiment of apparatus assembled in accordance with the
present invention is illustrated. The preferred embodiment is
described with regard to maintaining normal circulation in the
well. As noted, normal circulation exists when fluid is injected
down the tubing string and up the well annulus. As shown, foam is
being injected from a foam source 18 down a string of tubing 20 to
a location in a well indicated generally by a number 22 from where
it is desired to remove produced fluids and/or solids. This might
be desirable, for example, in a well cleanout operation. The
circulating medium such as foam is circulated down the segmented
tubing string 20 and up the well annulus 24 formed between the
outside of the tubing string 20 and the well casing 26. The foam
carries the solids and fluids up the well annulus and out blooie
line 28 to a suitable sump (not shown) at the surface. A valve 30
is located on the blooie line 28 and is normally left open.
The wellhead 32 includes a suitable tubing head 34 having a collar
36 which contains a suitable fitting 38 for the blooie line and a
fitting 40 for an emergency foam line 42 which is connected through
valve 44. The emergency foam line is located below the wellhead
equipment and is intended for emergency use such as might be caused
by a downhole fire. A wellhead base plate 46 having a central
opening for the tubing string therethrough is connected to the top
of the collar 36. A stripper rubber 48 is located in the collar 36
to frictionally engage the tubing string therein in a liquid-tight
manner to prevent flow of foam through the wellhead collar past the
tubing string. Tubing hanging slips 50 are arranged around the
tubing string 20 above the base plate 46. The tubing slips are used
to hang the tubing on the wellhead while it is disconnected from
the pup joint 70 and the power swivel. A chamber is formed about
the tubing string 20 above the wellhead by a tubular shell 52 which
is larger in diameter than the tubing string 20. The shell 52 is
positioned around the tubing string and located above the slips 50
on the wellhead. The tubular shell 52 thus forms a chamber around
the tubing string above the wellhead. The ends 53 and 55 of the
tubular shell 52 contain stripper rubbers 54 and 56 which slidably
engage the tubing string so as to prevent foam from leaving the
chamber by passing along the outside of the tubing string. Thus a
fluid-tight chamber is formed about the tubing string by the
cooperation of the shell and the sealed ends. A foam entry is
provided into the chamber by port 58 in the shell 52. The entry
port 58 is located near the lower end portion of the tubular shell
52. A valve indicated generally by the number 60 is arranged
intermediate the ends of the tubular shell 52 and has the
capability of closing off flow up the chamber in the absence of the
tubing string. The chamber may thus be divided into two separate
compartments. The foam entry port 58 is connected to the foam
source 18 by means of a suitable conduit 64. Valve 66 controls flow
of foam from the foam source 18 through line 64 to foam entry port
58. By controlling the valves foam may be injected as desired into
the chamber formed about the tubing string.
The wellhead 32 and the tubular shell 52 which forms the chamber
about the tubing string are connected in vertically aligned, spaced
apart relationship by suitable means such as a plurality of
centralizing and supporting arms 68. The tubular shell 52 must be
securely anchored in position while foam is injected therein under
high pressure. The centralizing and supporting arms 68 serve to
align and to support the tubular shell 52 in such a manner by
connecting the supporting arms 68 to the wellhead. In this mode the
weight of the tubing string 20 hanging from the wellhead serves as
an anchor for the tubular shell 52. It is usually preferred to have
three spaced apart supporting arms 68 to connect the tubular shell
to the wellhead.
In accordance with the invention foam is provided for injection
down tubing string 20 by a suitable foam source 18. The foam source
18 is connected to a pup joint 70 located in power swivel 72 by
means of a suitable flexible conduit 74. Valve 75 controls foam
flow through conduit 74. A bleed down line 76 having valve 78 is
provided on the conduit 74. In the embodiment shown in FIG. 1 the
foam in injected from the foam source 18 into the tubing string 20
down the well and up the annulus to the surface. As noted above,
the tubing string 20 is progressively lowered into the well as the
cleanout goes on to a point where the upper end of the tubing
string 20 which is connected to the pup joint 70 at connection 80
is located in the lower portion of tubular shell 52. Obviously this
connection 80 was at one time located well above the upper end 53
of the shell 52 and as the tubing string 20 was lowered by lowering
the power swivel 72 the connection 80 was lowered to its present
position. When the connection 80 has reached such a position, it is
time to disconnect the pup joint 70 from the tubing string and to
add a new joint of tubing to the up pup joint 70 for connection to
the top of the tubing string 20. As is evident, however, foam
injection through the pup joint and thence into the tubing string
20 during this period must be stopped. Utilizing the apparatus of
the present invention, however, foam injection through the tubing
string 20 need not be halted during this period.
As indicated above, the connection 80 is now located in the shell
80 in a position where it should be broken. However, before
breaking the connection 70 foam under pressure must be supplied to
the chamber formed by shell 52 about the upper end of the tubing
string. To accomplish this the bleed down valve 82 on the alternate
foam conduit 64 is closed. Then alternate foam valve 66 is opened
to cause foam to flow from foam source 18 through conduit 64 and
entry port 58 into the chamber formed by shell 58 about the tubing
string 20. Bleed valve 84 on chamber bleed line 86 is also closed
at this time. The tubing hang slips 50 are set so as to be ready to
hang the tubing string 20 on the wellhead when it is disconnected
from the power swivel and hoist. The connection 80 between the
upper end of tubing string 20 and the lower end of the pup joint 70
is now broken by suitable means such as reversing the power swivel
to rotate the pup joint and unscrew the connection. The power
swivel 72 is then raised by a hoist means to lift the bottom of the
pup joint 70 up the chamber to a position above gate valve 60. This
position is illustrated in FIG. 2. The end of the pup joint 70 is
maintained in the chamber between gate valve 60 and the stripper
rubber 54 in the upper end of tubular shell 52. Valve 60 is now
closed as indicated in FIG. 2 to close off the upper part of the
chamber to the flow of foam. Foam circulation in the well is
maintained through the upper end of the tubing string 20 by the
foam entering shell 52 through line 64. At this time valve 75 is
closed to stop foam flow in the main foam line and pressure is bled
from the pup joint system 70 through lines 76 and 86 by opening
valves 78 and 84. The dual bleed lines give additional assurance
that complete bleed down will occur. The pup joint 70 is now
removed from the chamber formed by shell 52 and a new joint of
tubing is connected to the lower end of the pup joint. The lower
end of this new joint of tubing is then inserted through the upper
stripper rubber 54 into the upper portion of the chamber formed by
shell 52. Bleed valves 78 and 84 are closed and main foam valve 75
is opened to inject foam into the upper portion of the chamber to
equalized the pressure across gate valve 60. After the pressure has
been so equalized, gate valve 60, opened and the new lower end of
the tubing joint is lowered to contact the open upper end of the
tubing string 20 and the power swivel is rotated to connect the new
tubing joint into the tubing string. As this connection is made
foam again flows down the tubing string 20 directly from the foam
source. At this time foam injection through the alternate foam
injection line 64 is stopped by closing valve 66. Pressure is bled
from the alternate foam conduit by opening valve 82. The slips 50
are now released and the tubing string 20 is run another joint down
into the well to continue circulating undesired debris
therefrom.
The apparatus of the present invention is also effective in
providing continuous circulation when the mode of operation
requires reverse circulation. Reverse circulation requires that
foam be injected down the well annulus and up the tubing. Thus with
respect to FIGS. 1 and 2 foam is injected in line 42 through valve
44 and down well annulus 24 to the lower end 22 of tubing string
20. The foam then goes up tubing string 20 through pup joint 70 and
is exhausted through conduit 74 which serves as the blooie line.
Obviously the foam source 18 and the valving therefore would be
connected to line 42 and the blooie line 28 for normal circulation
would be closed. When it is desired to add a section of tubing to
the tubing string the connection 80 which is to be broken is
positioned as shown in the lower portion of shell 52 and the tubing
slips 50 are set to hang the tubing string 20 on the wellhead 32.
Valve 82 is opened and the connection 80 is then broken and the pup
joint lifted above the gate valve 60. When gate valve 60 is closed,
foam is exhausted from shell 52 via line 64. A new tubing section
is added to the pup joint and it is inserted back into the top of
shell 52. The gate valve is opened and the new tubing section is
connected into the tubing string and operations are resumed.
As is also evident, circulation may be sequentially changed or
refluxed from normal to reversed while the open tubing string is
being held in the lower portion of the shell 52 by the tubing
slips. Thus by the manipulation of the exhaust and injection valves
circulation may be refluxed. Refluxing of the foam is useful for
many purposes. It is particularly useful when cleaning a well liner
with a cleaning fluid such as solvent, acid or the like. A slug of
such a cleaning fluid is positioned in the well adjacent a liner
and a column of foam is established in both the annulus and the
tubing on both sides of the slug. The tubing string 20 is hung in
the shell 52 forming the closed chamber as shown in FIG. 2. By
alternatively injecting foam down the tubing string 20 and bleeding
it from the well annulus 24 and injecting foam down the annulus 24
and bleeding it from the tubing string 20, the cleaning slug is
reciprocated up and down the well liner to provide a more thorough
cleaning action. This operation is accomplished by injecting foam
from the foam source 18 through valve 66 and line 64 into the shell
52 and then down the open tubing string 20 to the annulus 24. The
foam in the annulus 24 above the cleaning slug is removed from the
annulus through blooie line 28. When it is desired to reflux the
cleaning slug valve 30 on conduit 28 is closed as is valve 66 on
the conduit from the foam source to the shell. Valve 82 is opened
to provide a vent to atmosphere through conduit 64. Valve 44 on
conduit 42 which is connected to the foam source is opened to cause
foam to be injected down the well annulus 24 to reflux the cleaning
slug while the foam which moves up the tubing string 20 is bled
from shell 52 through conduit 64 and valve 82.
While preferred embodiments of the invention have been shown and
described, it is evident that modifications thereof can be made by
one skilled in the art without departing from the scope of the
invention.
* * * * *