Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED OIL RECOVERY METHODS,
WELL CASING SEALING METHODS, AND
SEALING DEVICES FOR CASING ASSEMBLIES
BACKGROUND OF T_E_INVENTI_N
The present invention relates to improved sealing
devices and methods for sealing oil and gas well casings in
place, and to improved methods for recovering oil and gas.
Generally speaking, oil and gas wells are formed ln a
two-step procedure. First, a borehole is drilled from the
surface into the desired payzone, and then the borehole is
lined with a casing assembly which may include a pump column
for raising petroleum products from the payzone to the
surface. One conventional approach to casing a borehole is
to lower a string of casing to a point near the bottom of
the borehole, and then to pump cement into the casing under
pressure, forcing it up the borellole annulus between the
casing and the borehole. The concrete is then allowed to
set up for a considerable period of time in order to optimize
chances that the cement will form a water and oil imperme-
able bond between the casing and the borehole wall. Oncethe cement has hardened, a perforating tool is then lowered
into the casing. This perforating tool is used to fire
projectiles into the wall of the casing at what is believed
to be the depth of the payzone. These projectiles may or
may not penetrate the casing completely. The perforating
tool is then removed and acid is placed inside the casing
under pressure. The acid passes through the holes made by
the perforating tool projectiles in the casing, and it
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dissolves concrete in the borehole annulus adjacent these
holes. In this way, concrete is selectively removed from
the borehole annulus at the level of the payzone, thereby
allowing oil and gas to pass from the payzone through the
perforations in the casing into the casing string.
This prior art approach to sealing a casing string
inside a borehole is characterized by a number of important
disadvantages. On occasion, the concrete may not form an
effective, watertight seal between the casing string and the
borehole, thereby allowing contaminants such as saltwater to
flow from adjacent strata into the casing string at the
payzone. Such saltwater contamination can represent a
significant problem. In addition, the available penetrating
tools are not completely reliable and conse~uently the
projectiles do not all penetrate the casing as intended.
This can result in uneven perforation of the well casing
such that it is possible for all the perforations to be in
either the upper or lower area of the payzone. Furthermore,
acid is difficult or impossible to control once it has
escaped out of the casing string. It is possible for the
acid to dissolve more of the concrete than desired, thereby
destroying whatever seal exists between the payzone and
adjacent zones which may include saltwater.
In addition, the conventional well casing technique
described above relies on natural pressures to cause petro-
leum to travel from the payzone into the perforated casing.
In many cases, such pressure is inadequate to recover
petroleum products from low pressure payzones effectively.
SUMMARY OF THE IMVENTIO~
__ _ _ ._
The present invention is directed to improved oil
recovery methods, improved well casing methods, as well as
improved sealing devices for casing assemblies. The method
and sealing devices of this invention to a large extent
overcome the aforementioned disadvantages of the prior art.
According to a first aspect of this invention, an
improved method for recovering oil from a payzone by means
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of a borehole which passes through the payzone comprises thestep of positioning a casing assembly in the borehole. This
casing assembly includes a casing string and a pump column
disposed within the casing string. Once the casing assembly
has been properly positioned, the borehole annulus is then
sealed off between the borehole and the casing assembly,
both above and below the payzone. The annular passageway
between the pump column and the casing string is also sealed
off by means of a casing seal at a point above the payzone.
Fluids are then pumped from the interior of the casing assembly
below the casing seal in order to reduce the pressure in the
borehole annulus in the p~yzone below that of at Ieast a portion
of the payzone, thereby materially increasing the flow of oil
and gàs from the payzone into the casing assembly.
This first aspect of the invention provides a method
for creating an effective seal such that when fluids are
pumped from the interior of the casing assembly via the pump
column, fluid pressures are reduced in the payzone adjacent
the casing assembl~. This reduction in pressure in the
payzone provides a driving force which promotes the flow of
fluids in the payzone toward the casing assembly. In this
way oil can be efficiently recovered from a low pressure
payzone at low capital cost without the need for more
expensive measures such as heating or using surface mounted
vacuum pumps. This method can be used either with existing
wells or with newly drilled wells, and a wide range of
hardware can be used to create the necessary seals.
According to a second aspect of this invention, a
casing assembly is sealed within a borehole adjacent either
side of a payzone. The first step in this method is to
provide a casing assembly which comprises a lower borehole
packer, an upper borehole packer, and a length of perforated
tubing coupled between the upper and lower packers. Typic-
ally, both of the packers and the perforated tubing will be
situated near the end of a casing string, àlso included in
the casing assembly. The casing assembly is then positioned
in the borehole with the lower packer situated below the
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payzone, the perforated tubing situa-ted ln the payzone, and
the upper packer situated above the payzone, such that the
upper and lower packers operate to seal the borehole annulus
above and below the payzone in a reversible manner, thereby
substantially preventing the flow of contaminants into the
payzone via the borehole annulus.
Preferably, both the upper and lower packers comprise a
respective elastomeric sleeve and means for selectively and
reversibly applying a compressive force to the sleeve to
reduce the length of the sleeve in order selectively to
increase the outside diameter of the sleeve. Once the
casing assembly has been positioned in the borehole with the
lower packer situated below the payzone and the upper packer
situated above the payzone, the means for applying com-
pressive forces to the sleeves of the upper and lowerpackers are then operated to increase the outside diameter
of the sleeves of the upper and lower packers, thereby
sealing the borehole annulus at the upper and lower packers
in order to isolate the payzone from the borehole annulus
above the upper packer and below the lower packer. Pre-
ferably, the means for applying compressive forces to the
respective sleeves each comprises means for transmitting the
weight of at least a portion of the casing assembly to the
respective sleeve in order to reduce the length and increase
the diameter of the respective sleeve.
The method of this invention for sealing a casing
assembly provides the important advantage that the casing
assembly need not be cemented in place in the borehole in
all applications. Rather, it is often possible simply to
use the packers to create the necessary seals around the
payzone. As explained, the packers are reversibly operated
such that the casing assembly can be installed in place, the
packers can then be activated to create the desired seals,
and then the packers can be de-activated to release the seal
if it becomes deslrable to remove the entire casing assembly
from the borehole.
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The sealing method of this invention provides the
further advantage in that in many applications it eliminates
the need for cement, perforating tools, and acid. The
packers of this method provide improved and precise control
over the location of the perforated portion of the casing
assembly in order to obtain a good match between the posi-
tion of the payzone and the position of the packers.
Furthermore, the packers of this method provide a good seal
against the borehole walls, thereby substantially eliminat-
ing saltwater contamination. The methods of this inventionare particularly useful in connection with casings designed
for use on multiple payzones, each separated in elevation
from the other.
Accordiny to a third aspect of this invention, a
sealing device is provided which can, for example, be used
for the casing seal or the borehole packers described above.
This sealing device comprises a tube having a first and a
second end, and an elastomeric sleeve disposed around the
tube. First means are provided for securing the first end
of the tube to a first portion of a casing assembly, and
second means are provided for securing the second end of the
tube to a second portion of the casing assembly. In addi-
tion, means are provided for selectively applying compres-
sive forces to the sleeve in a direction parallel to the
length of the tube to reduce the length of the sleeve,
thereby increasing the diameter of the sleeve to cause the
sleeve to create a seal between the tube and a sealing
surface situated around and adjacent to the outside of the
sleeve.
In the preferred embodiments described in detail below,
the means for selectively applying compressive forces acts
to apply the weight of at least a portion of the casing
assembly to achieve the desired deformation of the elasto-
meric sleeve. When this sealing device is positioned on the
outside of the casing assembly, it can be used to create an
effective seal between the casing assembly and the borehole
wall. Similarly, when this sealing device is placed within
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the casing assembly between the pump column and the casing
string, it creates an effective seal within the casing
assembly.
The sealing device of this invention provides the
important advantage that is a reversible seal. That is, it
can be lowered in place in the borehole without sealing, and
can then be activated once it has been properly positioned
in the borehole to create an effective seal. Furthermore,
preferred embodiments of this sealing device utilize the
static weight of the casing assembly to provide large forces
tending to shorten the elastomeric sleeve and to deform it
into the sealing position. By using the static weight of
the casing assembly itself, the need for complex or actively
powered means for compressing the elastomeric sleeve is
avoided.
The present invention, together with further objects
and attendant advantages, will best be understood by refer-
ence to the following detailed description taken in conjunc-
tion with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRA~INGS
FIGURE 1 is an elevational view in partial cutaway of a
casing assembly which incorporates preferred embodiments of
the sealing device of this invention and is suitable for
practicing preferred embodiments of the methods of this
invention.
FIGURE 2 is a partial sectional view of the casing
sealing device of the embodiment of FIG. 1.
FIGURE 3 is a sectional view taken along line 3-3 of
FIG. 2.
FIGURE 4 is a partial sectional view of the upper
packer included in the embodiment of FIG. 1.
FIGURE 5 is a partial sectional view of the lower
packer included in the embodiment of FIG. 1.
FIGURE 6 is a sectional view of a pump suitable for use
with the oil recovery method of this invention.
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DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
Turning now to the drawings, FIG. 1 shows an eleva-
tional view in partial cutaway of a casing assembly 20 which
incorporates preferred embodlments of the sealing devices of
this invention. As shown in FIG. 1, this casing assembly 20
is positioned in place in a borehole 10 which passes through
a plurality of earth formations. One of these formations,
the payzone 12, is an oil and gas bearing zone. The refer-
ence numeral 14 is used to indicate the lowermost end of the
borehole 10 and the reference numeral 16 indicates the
borehole annulus, an annular space between the casing
assembly 20 and the wall of the borehole 10. The bore-
hole 10 can be formed by any conventional drilling method,
and the formation of the borehole 10 does not form part of
the present invention.
The casing assembly 20 is made up of a number of
separate components which will be described in detail below.
Proceeding from the upper to the lower end of the casing
assembly 20, it comprises a casing string 30, a pump
column 40, a casing seal 50 which serves to create a seal
between the pump column 40 and the casing string 30, an
upper packer 70, a perforated tube 110, a lower packer 70',
and a spacer tube 120.
As shown in FIG. 2, the casing string 30 is made up of
cylindrical tubular elements. In this preferred embodiment
the borehole is about 7-1/2 inches in diameter and the
casing string is about 4-1/2 inches in outside diameter.
This casing string 20 extends upwardly from its lowermost
end 32 to the surface and is formed of lengths of conven-
tional casing. Mounted within the casing string 30 is thepump column 40 which terminates at a lowermost end 42. The
pump column 40 serves as a conduit through which oil and gas
are pumped upwardly from the payzone 12 to the surface. The
casing string 30 is well known to those skilled in the art
and will not therefore be described in detail here. The
lower end of the pump column 40 is shown in detail in
FIGURE 6.
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As shown ln FIG. 2, the casing seal 50 comprises an
upper ring 52 which is annular in cross-section and is
secured to a coupling member 54. This coupling member 54 is
provided with a threaded connection to receive the threaded
lowermost end 42 of the pump column 40. In addition, the
coupling member 54 is firmly secured, as by welding for
example, to the uppermost end of a collection tube 60. The
upper ring 52 is sized substantially to fill the annular
volume between the collection tube 60 and the casing
string 30. The upper ring 52 is secured, as by welding for
example, to the coupling member 54 such that the upper
ring 52 is held substantially immobile with respect to the
collection tube 60 and the pump column 40.
An elastomeric sleeve 56 is disposed immediately below
the upper ring 52. This elastomeric sleeve is sized to fit
between the collection tube 60 and tlle casing string 30 and
is preferably between 3 inches and 1 foot in lenyth. In
this preferred embodiment the collection tube 60 has an
outer diameter of about 2-3/8 inches and therefore the
central opening in the elastomeric sleeve 56 is somewhat
greater than this amount. The elastomeric sleeve 56 is
preferably formed of a hard, oil resistant, elastomeric
material such as die shoe rubber or polyurethane. A lower
ring 58 is situated immediately below the elastomeric
sleeve 56 and is shaped to rest on the upper end 76 of an
upper packer tube 72. Thus, the lower ring 58 is held
securely in place by the lower packer tube 72, and is not
free to move axially with the pump column 40. Preferably,
the elastomeric sleeve 56 is bonded at one end to the upper
ring 52 and at the other end to the lower ring 58 such that
the entire casing seal 50 forms a single integral unit. In
its rest state, as shown in FIG. 2, the elastomeric sleeve 56
is small enough to allow the entire casing seal 50 to slide
within the casing string 30 so as to facilitate positioning
of the casing seal 50.
Immediately below the casing seal 50 is the upper
packer 70, which is shown in cross-sectional views in
5~
g
FIGS. 2, 3 and 4. In general terms, the upper packer 70
comprises the packer tube 72, an upper collar 80, a lower
collar 100, and an elastomeric sleeve 90 positioned between
the upper and lower collars 80,100, respectively. The upper
collar 80 is threadedly connected to the lowermost end 32 of
the casing string 30. This upper collar 80 defines a
recessed annular contact surface 82 immediately adjacent the
outer edge of the packer tube 72, and a total of four
radially extending pins 84. The pins 84 each engage a
complementary slot 74 defined in the packer tube 72. The
upper collar 80 is not secured to the packer tube 72 other
than by the cooperation of the pins 84 and the slots 74.
Thus, the packer tube 72 is free to slide within a limited
axial range inside the upper collar 80. The lower collar 100
of the upper packer 70 defines a recessed, annular contact
surface 102 adjacent the elastomeric sleeve 90. This lower
collar 100 is securely fastened, by welding for example, to
the lowermost end of the packer tube 72, and is threadedly
connected at its lower end 106 to a perforated tube 110.
The elastomeric sleeve 90 of this preferred embodiment
is about seven inches in outer diameter and about twenty-
four inches in length in its rest state. The upper and
lower contact surfaces 82,102 of the upper and lower
collars 80,100, respectively, serve to confine the axial
length of the elastomeric sleeve 90. When the upper
collar 80 slides toward the lower collar 100 guided by the
pins 84 and the slots 74, the axial length of the sleeve 90
is reduced, causing an increase in the outer diameter of the
sleeve 90.
The perforatèd tube 110 of this preferred embodiment is
formed of a length of about ten feet of casing similar to
the casing of the casing string 20. This perforated tube 110
provides a plurality of about a dozen perforations 112, each
of which is about 5~8 of an inch in diameter. These perfora-
tions 112 are evenly spaced along the length of the perforated
tube 110.
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The lowermost end 114 of the perforated tube 110 is
threadedly connected to a lower packer 70'. This lower
packer 70' is substantially identical to the upper packer
70, and comparable elements of the lower packer 70' and the
upper packer 70 are indicated by the same reference numerals,
except the reference numerals for the lower packer 70'
include a prime. The si.ngle difference between the lower
packer 70' and the upper packer 70 is that the lower packer
70' includes a plug 108' welded iIl place in the lower
collar 100'. The plucJ 108' forms an oil and watertight seal
preventing the loss of fluids from the lower packer tube 72'
downwardly into the spacer tube 120.
The lowermost element of the casing assembly 20 is the
space tube 120, which is threadedly connected at its upper-
most end 122 to the lower packer 70'. The spacer tube 120
defines a lowermost end 124 which rests on the bottom 14 of
the borehole 10. In this preferred embodiment, the spacer
tube 120 is formed of conventional casing, similar to the
casing used in the casing string 30.
The packers 70,70' and the casing seal 50 provide a
particularly effective system for sealing the casing assembly
adjacent the payzone 12 and for facilitating the recovery of
oil from the payzone 12. In preparation for the sealing and
oil recovery methods of this invention, the first step is to
drill the borehole 10 and to log the well in order to
determine the total depth of the borehole 10, and the depth
and thickness of the payzone 12. Once these parameters have
been determined, the appropriate length for both the spacer
tube 120 and the perforated tube 110 are determined in order
to position the upper and lower pa-kers 70,70' properly
adjacent the upper and lower boundaries of the payzone 12.
Then a spacer tube 120 of the calculated length is assembled
with the lower packer 70', a perforated tube 110 of the
appropriate length, and the upper packer 70. The casing
string 30 is then built up above the upper packer 70.
Finally, the entire casing assembly 20 is allowed to rest
with the lowermost end 124 of the spacer tube 120 at the
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bottom of the borehole 10. As the spacer tube 120 comes to
support the compressive load of the weight of the casing
string 30, the upper collars 80,80~ move towards the lower
collars 100,100', respectively. This movement shortens the
elastomeric sleeves 90,90', thereby increasing the outer
diameter of the sleeves 90,90'. The rest diameter of the
sleeves 90,90' should be chosen such that the sleeves 90,90'
can swell out and come into firm, sealing engagement with
the borehole 10, substantially without rupturing or tearing
the sleeves 90,90'. Thus, the weight of the casing string 30
is used to automatically and reversibly deform the sleeves
90,90' such that it is the weight of the casing string 30
which creates an effective, fluid-tight seal between the
casing assembly 20 and the borehole 10. This arrangement is
particularly advantayeous in that it allows for automatic
deployment of the packers 70,70', and it permits ready
removal of the casing assembly 20 from the borehole 10.
Merely by lifting the casing assembly 20 off the bottom 14
of the borehole 10, the weight of the casing string 30 can
be removed from the sleeves 90,90'. When this happens, the
sleeves 90,90' resume their rest state, thereby effectively
disengaging the packers 70,70' from the borehole 10 to
permit the casing assembly 20 to be lifted to the surface
for reuse.
The casing seal 50 operates in a somewhat similar
manner. The elastomeric sleeve 56 of the casing seal 50
extends between the upper ring 52, which moves in unison
with the pump column 40, and the lower ring 56, which moves
in unison with the packer tube 72. At least a portion of
the weight of the pump column 40 is supported by the upper
ring 52. This weight is in turn supported by the elasto-
meric sleeve 56 and the lower ring 58. The weight of the
pump column 40 causes the upper ring 52 to move toward the
lower ring 58, thereby shortening the overall length of the
elastomeric sleeve 56 and increasing its outer diameter. In
this way, the elastomeric sleeve 56 is orced against the
collection tube 60 on the inside and the casing string 30 on
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the outside such that an effective, gas and airtight seal is
created. Similarly, when the weight of the pump column 40
is removed from the upper ring 52, the elastomeric sleeve 56
tends to return to its rest state to facilitate removal of
the casing seal 50 from the casing string 30.
The casing seal 50 cooperates with the packers 70,70'
and the plug 108' to permit an efficient method of oil
recovery from the payzone 12. As explained above, once the
casing assembly 20 has been fully assembled such that the
packers 70,70' have been expanded against the borehole and
the casing seal 50 has been expanded to seal the annular
space between the casing string 30 and the collection
tube 60, a substantially gas and airtight chamber adjacent
the payzone is created. The upper and lower packers 70,70'
prevent the movement of fluids via the borehole annulus 16
into the payzone 12; the plug 108' prevents the movement of
fluids from the spacer tube 120 into the payzone 12; and the
casing seal 50 prevents the flow of fluids down the annular
passageway between the pump column 40 and the casing string
30 into the payzone 12. Thus, the payzone 12 is completely
sealed except for the passageway provided by the interior of
the pump column 40 to the surface.
In use, a pump such as that shown in FIGURE 6 contained
within the pump column 40 is used to move fluids up out of
the perforated tube 110 to the surface. FIG. 6 shows the
lowermost end of the pump column 40, including the threaded
end 42. As shown in FIG. 6, the pump column 40 contains a
cylinder 150 at its lower end. The cylinder 150 includes
cylinder cap 154 which cooperates with a number of upper
valve ports 152 to make up an upper check valve. A cylinder
tail pipe 159 is mounted to the lower end of the cylinder
150, and it defines a lower valve port 156 and a number of
entry ports 160. A spherical valve ball 158 is positioned
inside the cylinder 150 above the lower valve port 156 to
form a lower check valve, and sealing rings 162 are provided
between the tail pipe 159 and the pump column 40.
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A pump rod 180 extends down the centerline of the pump
column 40, through an opening in the cap 154, into the
cylinder 150, where it is secured to a plunger cap 175,
which is in turn secured to a plunger 170. The plunger cap
5 175 defines a number of ports 174 which extend between the
upper end of the cylinder 150 and an interior space 178
between the plunger cap 175 and the plunger 170. This
interior space 178 is connected via a passageway 172 with
the lower end of the cylinder 150, and a check valve ball
176 restricts downward flow of fluid into the passageway
172.
In operation, the pump rod 180 is reciprocated to cause
the plunger 170 to move between the upper and lower ends of
the cylinder 150. The check valves formed by the cap 154
15 and the balls 176, 158 cause the reciprocating plunger 170
to lift fluids from the collection tube 60 (FIG. 2) into the
pump column 40 above the cylinder 150, and then to push
fluid upward to the surface. The upward flow of fluids
through the collection tube 60 and the pump column 40 serves
to reduce the pressure inside the perforated tube 110 and
therefore in the payzone 12 adjacent to the perforated
tube 110. This reduced pressure tends to enhance the flow
of petroleum products out of the payzone 12 into the per-
forated tube 110. Thus, the packers 70,70', the plug 108'
and the casing seal 50 cooperate to provide a substantially
airtight seal around the payzone 12 which can be used to
facilitate oil recovery from low pressure payzones. In many
applications, the method of this invention can increase the
flow of oil into the pump column by a factor of 1-1/2, 2, or
even more.
From the foregoing, it should be apparent that a number
of advantageous features for a casing assembly and its
method for use have been described. In particular, packers
have been described which act to seal a casing assembly
reliably in place above and below a payzone, while allowing
the casing assembly to be withdrawn for reuse when desired.
In this way, the need for cement as a sealing means, with
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the disadvantages described above, can be avoided. In
addition, an effective casing seal has been described which
utilizes the weight of a portion of the casing assembly to
create an effective, airtight seal between a pump column and
a casing string included in the casing assembly. The
packers and the casing seal of this invention can be ad-
vantageously used in the casing sealing methods described
above. Furthermore, these packers and casing seals can also
be used in the oil recovery methods described above which
substantially seal the payzone off from other strata and the
surface in order that the pumping of fluids up from the
payzone to the surface serves to create a low pressure zone
in the payzone, thereby facilitating the flow of oil and its
recovery.
Though the oil recovery method of this invention can be
implemented with the packers and seals described above, it
should be clearly understood that the method is not to be
limited to this particular structure. Rather, the oil
recovery method can be implemented with the widest range of
means for creating seals between the casing and the strata
adjacent the payzone, and between the casing and the lower
end of the pump column. For example, the oil recovery
method of this invention can be used to enhance the flow of
oil from existing wells, which may include conventionally
cemented in place casing strings, for example. In this
case, packers such as the packers 90,90' described above
would of course not be needed. In addition, pump column
packers such as those sold by Arrow Packer tools of Tulsa,
Oklahoma, for example, can be used to seal off the annular
space around the pump column.
Of course, it should be understood that various changes
and modifications to the preferred embodiments described
above will be apparent to those skilled in the art. For
example, the packers and the casing seal of this invention
can readily be adapted to other sized boreholes and to other
geometries. Therefore the dimensions listed above are in
particular intended merely as illustrative of one presently
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preferred embodiment. In addition, the oil recovery method
of this invention can be practiced with other means than the
packer 70 for sealing the borehole annulus above and below
the payzone, and with other means than the casing seal 50
for sealing the annular passageway inside the casing string.
Also, the pluy 108' can be deleted and the spacer tube 120
can simply be capped to seal the payzone. It is therefore
intended that the foregoing detailed description be regarded
as illustrative of the presently preferred embodiments and
not as limiting. It is the following claims, including all
equivalents, which are intended to define the scope of this
invention.
