CA1179250A - Oil recovery methods, well casing sealing methods and sealing devices for casing assemblies - Google Patents

Abstract

ABSTRACT
An oil well casing assembly includes a perforated tube and upper and lower packers coupled to the upper and lower ends of the tube. The lower packer is in turn coupled to a spacer tube and the upper packer is connected to a casing string. Each packer includes an elastomeric sleeve bounded by upper and lower collars. The packers are so arranged that when the casing assembly is lowered into the borehole and comes to rest at the bottom of the borehole, the weight of the casing assembly is used to cause the elastomeric sleeves to swell out against the borehole surface, thereby sealing the casing assembly above and below the payzone. In addition, a casing seal is provided which comprises an elasto-meric sleeve positioned between upper and lower rings around a pump column included in the casing assembly. The upper and lower rings are so mounted that the weight of the pump column causes the elastomeric sleeve to shorten axially and to swell out against the inside of the casing string, there-by providing an effective, airtight seal between the pump column and the casing string. The packers and casing seal of this invention can be used in a method for sealing a cas-ing in place such that the casing can be removed when neces-sary. Furthermore, the normal pumping action of the pump inside the pump column serves to remove oil from the payzone area and, because of the seals provided by the casing seal, to reduce pressure in the payzone, thereby promoting the flow of oil into the perforated tube. This method can be used with other types of seals between the casing and the borehole and between the pump column and the casing.

Description

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 .63~S~

-2-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 ~79~

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 1:~'7~S~

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 ~ 7~

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

3~5~:3 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 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.

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 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 ~7~0 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.

Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for recovering fluids from a payzone via a borehole passing through the payzone, said method com-prising:
(a) positioning a casing assembly in the bore-hole, said casing assembly comprising a casing string and a pump column disposed therein;
(b) sealing off the borehole annulus between the borehole and the casing assembly above and below the pay-zone;
(c) sealing off the annular passageway between the pump column and the casing string with a casing seal at a point above the payzone; and then (d) pumping fluids from the interior of the cas-ing assembly below the casing seal through the pump column in order to reduce the pressure in the borehole annulus in the payzone below that of at least a portion of the payzone, thereby promoting the flow of fluids from the payzone into the casing assembly.

2. A method for recovering oil from a payzone via a casing assembly positioned in a borehole which passes through the payzone, wherein the borehole annulus between the casing assembly and the borehole is sealed above and below the pay-zone, and wherein the casing assembly comprises a casing string, a perforated region of the casing string in the pay-zone, a pump column positioned within the casing string and extending from a point at least as low as about the level of the payzone to the surface, and a pump included in the pump column, the method comprising the following steps:
(a) forming a seal between the casing string and the pump column near the perforated region of the casing string to seal the interior of the perforated region such that the payzone near the borehole is in fluid communication only with the interior of the pump column; and then (b) operating the pump to move fluids out of the payzone up the pump column to reduce the pressure in the perforated region of the casing in order to promote the flow of fluids from the payzone into the casing.

3. A method for recovering oil from a payzone via a borehole passing through the payzone, said method compris-ing:
(a) positioning a casing assembly in the bore-hole, said casing assembly comprising a lower packer posi-tioned below the payzone, an upper packer positioned above the payzone, a perforated tube disposed between the upper and lower packers in the payzone, a casing string coupled to the upper packer, a pump column extending down the casing string at least as far as the payzone, a casing plug posi-tioned to close off the casing assembly below the payzone, and a casing seal disposed between the pump column and the casing string above the payzone, said upper and lower packers sealing off the borehole annulus above and below the bore-hole, said casing seal sealing off the annular passageway between the pump column and the casing string; and then (b) pumping fluids from the interior of the cas-ing assembly below the casing seal through the pump column in order to reduce the pressure in the borehole annulus in the payzone, thereby promoting the flow of oil from the pay-zone into the casing assembly.

4. The invention of claim 3 wherein each of the upper and lower packers comprises:
a respective elastomeric sleeve; and means for selectively and reversibly applying com-pressive forces to the respective sleeves to reduce the length and increase the outside diameter of the respective sleeves in order to form a seal between the respective sleeves and the borehole.

5. The invention of claim 3 wherein the casing seal comprises:

an elastomeric casing seal sleeve disposed between the pump column and the casing string; and means for selectively and reversibly applying com-pressive forces to the casing seal sleeve to reduce the length and increase the outside diameter of the casing seal sleeve to form a seal between the pump column and the casing string.

6. The invention of claim 4 wherein the casing seal comprises:
an elastomeric casing seal sleeve disposed between the pump column and the casing string; and means for selectively and reversibly applying com-pressive forces to the casing seal sleeve to reduce the length and increase the outside diameter of the casing seal sleeve to form a seal between the pump column and the casing string.

7. The invention of claim 4 wherein each of the means for applying compressive forces to the respective sleeves comprises means for transmitting the weight of at least a portion of the casing assembly to the respective sleeve to reduce the length and increase the diameter of the respective sleeve.

8. The invention of claim 5 or Claim 6 wherein the means for applying compressive forces to the casing seal sleeve comprises means for transmitting the weight of at least a portion of the casing assembly to the casing seal sleeve to reduce the length and increase the diameter of the casing seal sleeve.

9. The invention of claim 3 wherein the pump column comprises a cylinder positioned in the pump column, a plunger positioned in the cylinder, a pump rod extending between the plunger and the surface, and at least two check valves, one at either end of the cylinder; and wherein the pumping step comprises the step of reciprocating the pump rod to raise fluids from the interior of the casing assembly below the casing seal into the pump column.

10. A method for sealing a casing assembly to a bore-hole adjacent either side of a payzone, said method compris-ing:
(a) providing a casing assembly comprising a lower borehole packer, an upper borehole packer, and a length of perforated tubing coupled between the upper and lower packers, each of said packers comprising an elastomeric sleeve and means for selectively and reversibly applying compressive forces to the sleeve to reduce the length of the sleeve to selectively increase the outside diameter of the sleeve to form a seal between the sleeve and a borehole;
(b) positioning the casing assembly in the bore-hole with the lower packer situated below the payzone, the perforated tubing situated in the payzone, and the upper packer situated above the payzone; and then (c) causing the means for applying compressive forces to the sleeves of the upper and lower packers to in-crease the outside diameters of the sleeves of the upper and lower packers, respectively, 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.

11. The invention of claim 10 wherein each of the means for applying compressive forces to the respective sleeves comprises means for transmitting the weight of at least a portion of the casing assembly to the respective sleeve to reduce the length and increase the diameter of the respective sleeve.

12. A casing assembly sealing device comprising:
a tube having a first end and a second end;
an elastomeric sleeve disposed around the tube;
first means for securing the first end of the tube to a first portion of a casing assembly;
second means for securing the second end of the tube to a second portion of the casing assembly;
means for selectively applying compressive 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.

13. A casing assembly sealing device comprising:
a tube;
an elastomeric sleeve disposed around the tube and having a first end and a second end;
a first collar disposed around the tube adjacent a first portion of the sleeve, said first collar defining a first surface positioned to abut the first end of the sleeve;
a second collar disposed around the tube adjacent a second portion of the sleeve, said second collar defining a second surface positioned to abut the second end of the sleeve;
means for mounting the first and second collars to the tube such that the sleeve is captured between the first and second surfaces and at least one of the collars is free to slide along the tube to reduce the length of the sleeve;
and means for applying the weight of at least a portion of a casing assembly to the mounting means to cause the at least one collar to slide along the tube so as to shorten the length and increase the diameter of the elastomeric sleeve.

14. A casing assembly packer comprising:
a tube having a first end and a second end;
an elastomeric sleeve disposed around the tube and having a first end and a second end;
first means for attaching the first end of the tube to a first portion of a casing assembly, said first attaching means defining a first surface positioned to abut the first end of the sleeve;
second means for attaching the second end of the tube to a second portion of the casing assembly, said second attaching means comprising a collar which defines a second surface positioned to abut the second end of the sleeve, and means for slidably mounting the collar to the tube such that an axial force tending to move the collar toward the first attaching means causes the collar to compress the sleeve between the first and second surfaces, thereby increasing the diameter of the sleeve so as to cause the sleeve to create a seal between the tube and an adjacent borehole surface.

15. A sealing device for creating a seal between an outer tube included in a casing assembly and an inner tube included in the casing assembly, said sealing device compris-ing:
an elastomeric sleeve disposed around the inner tube and having a first and a second end;
a first ring disposed around the inner tube within the outer tube adjacent the first end of the sleeve;
means for supporting the first ring on the outer tube;
a second ring disposed around the inner tube with-in the outer tube adjacent the second end of the sleeve;
means for supporting the second ring on the inner tube;
said sleeve dimensioned such that the weight of a pump column, when applied to the inner tube, causes the second ring to move toward the first ring, thereby reducing the length of the sleeve so as to increase the diameter of the sleeve in order to create a seal between the outer tube and the inner tube.

16. The invention of Claim 1 or Claim 3 wherein the pumping step is performed with a pump situated within the pump column near the casing seal.

17. The invention of Claim 2 wherein the pump is situated near the casing seal.