Note: Descriptions are shown in the official language in which they were submitted.
~31 1681
This invention relates to a cleanout method for
oil wells, in particular wells producing heavy oil. Such
wells incorporate features to prevent the entry of
particulate matter such as sand, but do not entirely
eliminate such matter, which tends to accumulate at the
lower end of the well casing, eventually requiring a time
consuming cleanout operation.
Wells producing heavy oil typically comprise an
outer production casing, which is cemented into place from
the surface to just below the oil producing horizon. This
casing is perforated, generally by means of explosive
charges, to allow oil to enter. A liner, generally having
a welded closed bottom (known as a bullnose), is suspended
in the lower portion of the casing, from a liner hanger.
The liner itself has perforations such as slots, to permit
the entry of oil, and to restrict the entry of sand or
similar matter.
When the liner is in place, a service rig is used
to lower an open ended production tubing within the
production casing and within the liner, where it is set
with the bottom of the tubing about three meters above the
bullnosed bottom of the liner. This distance of about
three metres facilitates the accumulation and retention of
any sand which does enter the liner, rather than permitting
it to be drawn into the pump, which is located adjacent to
the bottom of the tubing, seated by a seating m~ans.
After the production tubing is set in place, the
service rig can be removed, and an operating rig, known as
a Co-rod* rig, is moved onto the well, to lower into place
a continuous steel rod, at the lower end of which is
attached the pump~ The co-rod rig itself is then removed
to be replaced by a pump jack for operating the pump to
remove the oil.
Despite the design of the liner and the production
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1 31 1 681
tubing, eventually sand and similar matter accumulates to
such an extent as to impede the operation of the pump,
ultimately causing seizure. At this point, the sand must
be cleaned out. The present method involves the re-
installation of the co-rod rig to remove the co-rod and the
pump from the well, and thereafter, removal of the co-rod
rig and installation of the service rig back onto the well
to pick up the tubing. For this operation, extra tubing
may be added to reach the accumulated matter in the
bullnose. Fluid is then pumped into the production tubing,
to wash the accumulated matter up to the surface in the
annulus between the production tubing and the production
casing.
In addition, if the well is under pressure, this
pressure must be killed before the extra tubing is added
and the cleaning fluid pumped into the well. This is
achieved either by the use of known heavy killing fluids,
or by the use of a known snubbing unit.
When the accumulated matter has been removed, the
extra tubing can be removed, the service rig moved off the
well and the co-rod rig is used once again to replace the
co-rod and pump. The co-rod rig is in turn replaced by the
pump jack for the resumption of the pumping operation.
The present system of cleaning such oil wells
suffers from several disadvantages. In particular, there
is considerable downtime for production from the well by
reason of the time taken to remove the co-rod rig, rod and
pump from the vicinity of the well, and to enable the
installation of the service rig and extra tubingO During
this downtime, pressure problems may arise. In addition,
;there is an inherent increased safety risk involved each
time the rigs are exchanged.
; The present invention therefore provides a
cleanout method to overcome these disadvantages, by
utilizing a simple cleanout tool which requires reduced
downtime for the operation of the well, by use only of the
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co-rod rig, and not necessitating the use of a service rig.
Efficiency and safety are thereby considerably enhanced.
In addition, the tool can include means for enabling the
reverse flow of the cleaning fluid, where
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desirable.
This invention therefore provides a method for
particulate matter cleanout for an oil well having a
production casing, an inner production tubing and pumping
means connected to a continuous rod mounted on a co-rod
rig, comprising the following steps, withdrawal of the
pumping means to the land surface, connection to the rod
of a cleanout tool of predetermined length and comprising
a perforated tubular upper section, a central tubular
section to which is attached pack-off means to restrict
fluid circulation within ~he production tubing adjacent
the outside of the tool, and a lower tubular section, tha
tubular sections having an external diameter less than the
internal diameter of the production tubing, insertion of
the tool into the production tubing, pumping a cleanout
fluid through the production tubing, and thereby forcing
the fluid through the perforations and downwards through
the central and lower tubular sections into accumulated
particulate matter in a lower portion of the production
casing, and forcing the fluid and particulate matter
upwards in an annulus within the production casing and
surrounding the production tubing.
There is also provided in accordance with
another aspect o the present invention a cleanout tool
for use in an oil well having a production casing, an
inner production tubing and a continuous rod extending
through the production tubing, the cleanout tool
comprising a tubular upper section adapted for connection
to a lower end of the continuous rod and having at least
one perforation formed therein, a central tubular section
to which is attached pack-off means for fluid-tight
sealing against the inner surface of the production
tubing, and a lower tubular section, each of the tubular
sections having an external diameter less than the
internal diameter of the production tubing to form an
annulus therebetween.
Preferred embodiments of the present inventi.on
will now be described in greater detail and will be better
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understood from the following description with reference
to the accompanying drawings, in which:
Figure 1 is a vertical cross-sectional view of a
well casing with a first embodiment of the cleanout too]
in place; and
Figure 2 is a cross-sectional view of the
central section of a second embodiment of the cleanout
tool.
ReEerring to Figure 1, an oil well casing 12 is
cemented in place and perforated for oil production,
having a-t its lower end adjacent the oil producing zone a
slotted liner 13 attached by hanging means 17. The lower
end of the liner 13 is w~lded closed to form a bullnose
14. A production tubing 10 is suspended within the casing
12 and liner 13, having an open end 11 typically set
approximately three metres above the bullnose 14. An
annulus 15 surrounding the production tubing 10 is defined
by the outer wall of the production tubing 10 and the
inner wall of the casing 12.
During active operation of the well, a pump ~not
shown) is suspended by means of a co-rod 9 within the
tubing 10, seated by seating nipple 28 at an appropriate
height above the open end 11 of the tubing. Particulate
matter 18 which enters the liner 13 despite the
configuration of the slots (not shown) in the liner will
tend to accumulate in the bullnose 14, and will eventually
rise to the level of the pump to impede the flow of oil
through the pump, often causing the pump to seize and
re~uiring a cleanout operation.
For cleanout by the method of the present
invention, co-rod 9 is removed from the well and the pump
detached therefrom, and a tool 1 is attached in its place
by any suitable means, such as screwing or a sucker rod
pin, to the lower end of co-rod 9. The co-rod with tool 1
attached is then run into the well. An upper section 2 of
the tool is of tubular configuration and has perforations
5 along at least part o~ its surface, which may take the
form of longitudinal slots. To the upper section 2 is
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threadedly attached a central section 3. A pack-off cup 6
made of, for e~ample, carboxyenated nitrile rubber,
surrounds the central section 3, 50 as to form a seal
between the outer surface of tool 1 and the inside wall of
production tubing 10. Pack-off cup 6 is seated on -the
central section 3 by means of a suitable seating means
such as a cup seat 7, mounted above a tubing drift 16.
The central section 3 is also of tubular configuration.
The lower end of the central section 3 is attached by any
suitable means such as a collar union 20 to a lower
section 4. The lower end 8 of the lower section 4 is
open, and the lower section ~ is of tubular conEiguration.
In the embodiment shown in Figure 1, lower
section 4 consists of a swedge 31 screw-threaded between
collar 20 and a lower collar 29. The lower end of collar
29 is internally threaded for connection to one or more
lengths of hollow tubing 30 which together comprise a
"stinger", the length of which is chosen so that the
distance between the lower end of the stinger and the
bottom of tubing drift 16 slightly exceeds the calculated
distance from the bullnose to the top of pump seating
nipple 28.
The tool is constructed of any suitable material
such as high strength steel, and the external diameters of
the tubular sections 2, 3 and 4 must be less than the
internal diameter oE the production tubing 10 and pump
seating nipple 28, sufficient to provide adequate
clearance for insertion, removal and flow of cleaning
fluid.
When the tool 1 is in place, the cleaning fluid,
which is usually water, can be pumped into the upper
portion of the production tubing 10, down to a level
adjacent to the upper section 2 of the tool 1. The pack-
off cup 6 prevents the fluid from passing therebelow, and
the fluid is consequently forced into the upper section 2
through the perforations 5 and thence down the inside of
the tubular central section 3 to the open-ended stinger 4.
The fluid passes out through the open end 8 of the
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stinger, and thence removes the accumulated particulatematter 18 as it is washed upwards through the annulus 15
between the production tubing 10 and the casing 12, to be
removed at the well head. The direction of flow of the
cleaning fluid is shown by the arrows A.
Referring now to Figure 2, an alternative
embodiment of the central section 3 of the tool 1 is
shown, which enables the reverse flow of cleaning fluid
for the cleanout operation. For this purpose, it is
necessary to impede the flow of cleaning fluid in an
upwards direction from the lower portion of the production
tubing 10. In the embodiment shown, reverse flow is
opposite to the normal flow direction shown in Figure 1,
and indicated therein by the arrows A. This reverse flow
direction is indicated in Figure 2 by arrows B.
To achieve this reverse flow direction, the tool
1 is additionally provided with a lower pack-off cup 23 in
combination with the upper pack-off cup 2i. The two pack-
offs 23 and 21 are seated respectively on a lower seat 24
and an upper seat 22, which may be separated by a tubing
drift 25.
When reverse flow cleanout is desired, the
cleaning fluid is pumped down the annulus 15, to the lower
end of the casing 12, to remove accumulated particulate
matter 18 from the bullnose 14. The fluid is then forced
upwards into the production tubing 10 through the open end
11, or directly into the stinger 4 of the tool 1. The
upwards flow of the fluid and particulate matter within
the production tubing 10 is restricted by the lower pack-
off means 23. All the remaining fluid therefore passesinto and travels upward through the tool 1 to the well
head, as indicated by arrow B. As will be appreciated,
; the length of the stinger for this configuration is
shortened by the length of pack-off 23 and its associa-ted
seat 24.
~ here the well is pressured, the effects of the
pressure must be counteracted before the cleanout
operation begins. For this purpose, a known snubbing
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t31 16~1
stack (not shown) is used, which enables the pressure to
be contained, while the use of a known lubricator enables
the insertion of the open-ended tool into the pressured
well. After the cleanout tool of the invention has been
S lubricated into the upper end of the production tubing,
through the snubbing stack, the method of use of the tool
is as described above for a non-pressured well. Thus, the
method of the invention saves the costs tradi-tionally
required Eor killing fluids, and overcomes the
disadvantages of the traditional use of tubing-snubbing
units.
The method of the invention is particularly
suitable as part of a preventative maintenance program, in
which it can be used for cleanout for example each time a
pump is changed. The regular use of the method can avoid
damage to the lower portion of the production tubing, by
accumulated particulate matter, and damage to the pump.
Where the performance of the cleanout operation is time-
consuming, cumbersome or hazardous, there is a tendency
for the operator to avoid such regular maintenance, and to
perform the cleanout only when the pump has seized, which
can result in greater damage to the components. The
advantages of the present invention in increased
efficiency, reduced time loss, increased safety and
economy provide an incentive to implement a beneficial
program to maximize those advantages.
The tool 1 for use with the method of the
; invention can be of any suitable size according to the
type of well for which it is required. As the pack-off
means 6, 21 and 23 are designed to be adapted for use in
standard diameters of production tubing lO, the method and
the tool 1 are suitable for use in any well having the
typical features described above.
Further modification of the method and the tool
1 can be made without departing from the spirit of the
invention.
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