WO2011060493A1

WO2011060493A1 - External casing packer

Info

Publication number: WO2011060493A1
Application number: PCT/AU2010/001548
Authority: WO
Inventors: Ian Gray
Original assignee: Ian Gray
Priority date: 2009-11-19
Filing date: 2010-11-19
Publication date: 2011-05-26
Also published as: AU2010321679A1; ZA201203565B; CN102741497A; WO2011060495A1; CA2781001A1

Abstract

A method and apparatus for cementing a zone of borehole casing using an external casing packer (ECP). The method involves sealing the base of the ECP with a ball dropped in a seat, and then pressurising the casing to inflate an elastomeric packer sleeve through a one-way valve. When a design differential pressure is reached across the casing and elastomeric sleeve, a grout valve In the upper part of the packer opens to limit the sleeve inflation pressure and to provide a one-way valve through which cement grout passes to permit grouting of the annulυs between the casing and the borehole.

Description

EXTERNAL CASING PACKER

Related Patent Application

This PCT application claims the benefit of two Australian provisional applications, both filed on 19 November 2009, and accorded respective application numbers 2009905659 and 2009905660. The disclosures of the Australian provisional patent applications are incorporated herein by reference.

Technical Field of the Invention

The present invention relates in general to the field of completing hydrocarbon or water wells, and more particularly to methods and apparatus for manufacturing inflatable packers, and sealing the base of a casing by cement grouting the annulus above the packer, while not damaging the underlying borehole with grout. Background of the Invention

The conventional process to install a casing in a borehole is to first drill a borehole, install a casing therein, and cement the casing in place. The borehole can then be extended beyond the bottom of the casing by drilling a smaller size hole, which usually occurs in the production zone. The cementing process usually involves pumping cement through the casing and out of the bottom thereof, and up into the annulus between the casing and the borehole. The cement is displaced downwardly and out of the casing by pumping a drilling fluid or water into the top of the casing. A cement displacement plug is normally used to separate the water from the cement in the casing. Sometimes a float shoe (one way valve) is attached to the bottom of the casing so as to avoid the need to hold pressure within the casing while the cement in the annulus sets. An alternative process is to drill the borehole to final gauge and depth, and then run the casing with an external packer attached in the casing string or to the end thereof into the borehole. A port at the base of the external casing packer is closed and the casing is pressurised to set the packer. Cementing ports are then opened above the packer, cement is pumped through the casing ports and into the annulus to cement the casing in place. At the end of the cementing process a displacement plug is run down the casing and the cement is displaced out of the casing and into the annulus. The cementing ports are then closed. The casing is then free of cement and the annulus is cemented within the borehole. The normal process is then to run a drill string and drill bit back into the casing to drill out any cement remaining in the packer, drill out the cement displacement plug and the bottom port to clean out the borehole below the packer. In existing external casing packers, the bottom port is usually blocked by a ball dropped into the casing. The cementing ports are actuated by either rotating, raising or lowering the casing or by dropping balls or darts of different sizes into the casing to move sliding annular seals.

Summary of the Invention

The external casing packer according to the various embodiments described herein is referred to at times as '"ECP." The operation of the ECP is however simpler than existing packer systems. The manufacture is also simpler and more cost effective than other packer devices currently available. The external casing packer, according to the invention, is attached to the outer cylindrical surface of the casing, with the casing extending above and in some cases below the ECP. A non-return valve is fitted in the base of the ECP, which permits fluid to enter the casing from the borehole during lowering of the casing into the borehole, but prevents the reverse flow of liquids from the casing down into the borehole. In its simplest form, the non-return valve is a port formed or installed in the base of the ECP, and is sealed by a ball that is dropped into the casing from surface. The ball seats in the port in a conventional manner in the base of the ECP. Such a system enables flow in and out of the casing until the ball is dropped. Alternative non-return valve arrangements may be used, such as a wire line retrievable plug, or a one-way valve such as a float shoe.

Once the one-way valve in the base of the ECP is actuated, the casing is pressurised to inflate an elastomeric sleeve of the ECP. The inflation of the sleeve is achieved by use of a non-return inflation valve system located between the casing and the ECP sleeve. As the pressure in the casing is raised, an elastomeric sleeve of the ECP inflates to expand and engage the annular wall of the borehole. At a preset pressure in the casing, frangible grout valves constructed within the mandrel of the ECP are actuated to open and to subsequently allow a cement grout mixture to be pumped through the grout valves to the portion of the annulus located above the ECP. The grout valves are constructed to function as a combination of a burst or shear disk, and a non-return check valve. With the -failure of the burst or shear disk in the grout valve during the sleeve infl.atJ.on process, the pressure inside the casing drops so that the ECP sleeve no longer inflates through the non-return inflation valve, as the pressure in the ECP sleeve exceeds that in the casing. The fracturing and the opening of the grout valves thus functions as a relief valve to prevent over-inflation of the elastomcric sleeve. Thus, the preset pressure to which the casing is pressurised is relative to the point at which the frangible grout valve discs break, and to the desired pressure to be maintained in the elastomeric sleeve. At this stage of the process, the inflation valve is closed and the grout valve of the ECP is activated and opened, whereupon a cement grout mixture is pumped down through the casing. The cement grout mixture flows down the casing and pushes the grout valves open. The cement grout then flows through the grout valves and into the annulus between the casing and the wall of the borehole, in the annulus area above the ECP. When the required volume of cement grout has been pumped down the casing, a cement displacement plug is introduced into the top of the casing. A liquid is then pumped down the casing to force the displacement plug downwards to the ECP. This is continued until the displacement plug reaches a location just beyond the grout valves, whereupon further downward movement of the displacement plug is halted, because a hydraulic lock forms between the cement displacement plug and the closed non-return valve in the base of the ECP. There is generally no further need to pressurise the casing to support the cement grout, as the grout valves are one-way check valve devices which prevent the backflow of cement grout from the annulus back into the casing. The grout valves also permit breaks or interruptions in the cement grout pumping process without the backflow of the grout from the annulus back into the casing. At the completion of the cementing operation a drill string can be run into the casing to drill out the cement displacement plug and the bottom non-return valve arrangement, along with any residual cement grout which has hardened in the drill path, Various features of the invention include the grout valves, the inflation valves and the manufacture process which can be incorporated into a single elastomer layer bonding operation. The one-way grout valves each comprise a chamfered valve member which is preferably a seal disc that scats in a chamfered port formed in the ECP mandrel above the packer sleeve. The valve or seal members are attached to respective burst or shear discs. The discs are preferably constructed of a frangible material having a well defined shear failure stress such as some plastics, metals or ceramics. The chamfered valve member is attached to an elastomeric grout valve sleeve which surrounds the mandrel. In the absence of pressure in the casing, the elastomeric nature of the grout valve sleeve retains the chamfered valve member and ensures a seal with the chamfered seat of the mandrel on closure. Preferably, the elastomeric grout valve sleeve is bonded to the top of the chamfered valve member aad forms part of the inflatable ECP sleeve situated around the mandrel.

The inflation valve comprises a flap of an elastomeric material situated on the inflatable elastomeric sleeve side of the mandrel. The inflation valves each co ver a small port formed in the mandrel. Fluid can therefore flow through the inflation ports in one direction and displace the flap outwardly to inflate the elastomeric sleeve of the ECP. On cessation of the fluid flow to. inflate the ECP sleeve (when the grout valve discs shear and open), the inflation ports are closed by the respective flaps, which prevents the packer sleeve from deflating. The inflation flap preferably comprises part of the ECP sleeve construction to simplify the manufacturing process.

The inflation valves and the grout valves are both operated in a sequence during the process of inflating the elastomeric sleeve to set the packer and casing in the borehole. The inflated sleeve provides an obstruction in the borehole annulus so that the annulus area above the obstructing sleeve can be filled with a cement grout -Mixture. To that end, the casing and ECP attached thereto arc lowered at the desired location in the borehole. The open one-way valve in the bottom of the ECP allows air and any liquid in the lower part of the borehole to equilise during lowering of the casing and ECP therein, as the ball has not been dropped down the casing. A ball is then dropped down the casing to scat with the one-way valve in the bottom of the ECP, thereby plugging said valve. The casing is then pressurised with a liquid to inflate the elastomeric sleeve via the inflation valves. As the sleeve is inflated and engages the sidewall of the borehole, the pressure of the inflation liquid increases, whereupon the shear point of the grout valves is reached and such valves arc actuated and opened. When the grout valves burst open, the inflation valves automatically close due to the reverse differential pressure across the inflation valves. The closed inflation valves leave the sleeve pressurised and compressed against die wall of the borehole. The cement grout mixture can then be pumped down the casing and out of the opened grout valves into the annulus area above the inflated sleeve.

The sealing system between the packer sleeve and mandrel comprises the packer sleeve being bonded directly to the packer mandrel at one end of the mandrel. At the other end of the packer there is a seal which moves axially along the outer surface of the mandrel and accommodates shortening of the packer sleeve as it expands radially outwardly during inflation. In most packers this takes the form of a sliding elastomeric hydraulic seal between the sleeve and the mandrel, Such a hydraulic seal requires a substantial housing to contain it. In the preferred embodiment of the invention, the sliding hydraulic seal is replaced by a sealing sleeve of elastomer that is bonded at one end to the packer sleeve at a position below a packer retaining ring, and to the packer mandrel at the other end. Thus, as the packer sleeve is inflated and shortens in a longitudinal direction, the sealing sleeve compresses longitudinally but maintains a seal to the mandrel. The sealing sleeve is pressed via inflation pressure against the mandrel and is prevented from being torn from the packer sleeve by the packer retaining ring which maintains an outer diameter and confines the seal. In one embodiment, the packer sealing sleeve is reinforced by an open mesh interlayer which is placed on the bias to the packer axis to permit longitudinal changes in sealing sleeve dimension, and to reinforce the elastomeric sleeve against tears by preventing excessive local strain.

The bonded sleeve system is used to transfer load between the packer sleeve reinforcement and the packer retaining ring. In a packer where the sleeve is reinforced with flexible cords or straps of low inextensibility, the reinforcing carries tensile load. The tensile load is retained against expansion by the packer retaining ring. The loading force on the packer retaining ring comprises the component perpendicular to the retaining ring which is restrained by the packer retaining ring operating as hoop reinforcement. There is also an axial component which tends to slide the packer retaining ring axially away from the inflated portion of the packer sleeve. Thus, the retaining ring tends to be pushed over the packer sleeve reinforcement contained in the elastomeric sleeve. By bonding a stiff or rigid sleeve, which is in contact with the packer retaining ring, to the elastomeric sleeve, which is in turn bonded to the reinforcing, shear is transferred between the packer retaining ring and the reinforcement via the rigid sleeve and the elastomer. The rigid sleeve may advantageously be made in a longitudinally split form to permit the easy assembly and bonding to the underlying elastomer while relieving the manufacture of close tolerance issues. The sleeve system is therefore of low cost to fabricate and rapidly incorporated into the packer construction.

The overall design of the packer, can therefore include one or more features which are easily incorporated into the manufacture of a packer by layers of elastomer to be cured and bonded, or specifically not bonded together, according to the design. The elastomer may be derived from natural or synthetic sources, and is usually bonded together in a process involving pressure and heat. This is known for natural rubber systems as the process of vulcanisation. It is thus possible to achieve very strong bonding between layers of elastomer and between the elastomer and the mandrel (especially to steel) by the use of the correct surface preparation of the metal.

According to one embodiment of the invention, disclosed is a method of cement grouting a borehole using an inflatable packer system. The method includes placing a casing with an external casing packer attached thereto at a location in a borehole for cement grouting a portion of the borehole annulus that is located above the externa) casing packer. Also included is the inflation of an inflatable elastomeric sleeve of the external casing packer to block the annulus of the borehole by pressurising the casing with an inflation fluid, which opens a one-way inflation valve in the external casing packer and inflates the inflatable sleeve to a preset pressure. The preset pressure is determined by a pressure relief valve located between the external casing packer and the annulus which opens at the preset pressure and then becomes a one-way grout valve. A liquefied cement grout mixture is pumped down through the casing via the open one-way grout valve which is located in the external casing packer above a portion of the inflated inflatable sleeve. The grout valve is biased to a closed position using an elastomeric member attached to the packer, whereby when the pressure of the cement grout mixture is reduced in the casing, the elastomeric member causes the grout valve to close and prevent backflow of the cement grout mixture from the annulus back into the casing! According to another embodiment of the invention, disclosed is a method of setting an external casing packer in an annulus of a borehole to fix a casing therein. The method includes sealing a base of the packer, and pressurising the packer to inflate an inflatable elastomeric sleeve surrounding a portion of a packer mandrel by passing a pressurised fluid through a one^:way inflation valve into the inflatable sleeve. The inflation pressure of the inflatable sleeve is limited by using a pressure relief valve in the packer which relieves the pressure in the packer to the outside of the casing when a design differential pressure is reached. The pressure relief valve is used as a one-way valve to permit a grout material to flow therethrough to the annulus of the borehole. The pressure relief valve is closed to prevent a backflow of the grout material from the annulus back into the packer.

According to yet another embodiment of the invention, disclosed Is a method of cement grouting a borehole using an inflatable packer system. The method includes lowering into a borehole a casing with the inflatable packer system attached thereto. The casing is pressurised with a fluid so that the pressurised fluid enters one or more one-way inflation valves in the packer system to inflate a sleeve and obstruct an annulus of the borehole. The pressure of the fluid in the casing is increased until one or more one-way frangible grout valves rupture to allow the pressurised fluid to enter the borehole annulus above the packer system, whereby the pressure of the casing drops and the one-way inflation valves close and maintain the sleeve inflated in the borehole annulus. A cement grout is pumped down the casing and through the ruptured one-way grout valves and into the portion of the borehole annulus located above the packer system.

With regard to yet another embodiment of the invention, disclosed is an inflatable packer system for grouting a borehole annulus. The packer system includes a mandrel forming a body of the packer system, where the mandrel is adapted for attachment to a casing, and the mandrel has formed therein one or more ports for respective grout valves, and one or more ports for respective inflation valves. A seat is formed in a bottom part of the mandrel, where the seat is adapted to be blocked by a ball dropped down through the casing. An elastomeric sleeve is formed around the mandrel and around the inflation valve ports. An anchor seal is formed at a top portion of the elastomeric sleeve around the mandrel above the inflation valve ports and below the grout valve ports. A sliding seal is formed at a bottom portion of the elastomeric sleeve along the mandrel. One or more one- way inflation valves are provided, where each one-way inflation valve is located over one of the inflation valve ports, and each one-way inflation valve is adapted for allowing an inflation fluid to pass through the inflation valve port and into the elastomeric sleeve, but not in the reverse direction. One or more one-way grout valves are provided, wheTe each one-way grout valve is located over one of the grout valve ports, and each one-way grout valve is adapted for allowing a cement grout to pass through the grout valve port and into the borehole annulus, but not in the reverse direction. Each one-way grout valve is formed with a frangible member which breaks in response to a predetermined inflation fluid pressure, whereby when the elastomeric sleeve is inflated to the predetermined fluid pressure the frangible members break to enable operation of the one-way grout valves. The one-way inflation valves then close to allow the elastomeric sleeve to maintain the predetermined inflation fluid pressure.

Brief Description of the Drawings

Further features and advantages will become apparent from the following and more particular descriptions of the preferred and other embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters generally refer to the same parts, functions or elements throughout the views, and in which:

Fig. 1A-1F schematically illustrate the sequence of steps for installing the external casing packer in a borehole;

Fig. 2 is a cross-sectional view illustrating the external casing packer according to an embodiment of the invention;

Fig. 3 is a cross-sectional view illustrating the grout valve according to an embodiment of the invention, in a closed condition;

Fig. 4 is a cross-sectional view of the grout valve of Fig. 3, but in an open condition;

Fig. 5 illustrates in a one-quarter longitudinal section view the upper end of the packer with the inflation valve, according to an embodiment of the invention, in an open condition; and

Fig. 6 illustrates In a one-quarter longitudinal section view the lower sliding end of the packer and the construction of the scaling sleeve according to an embodiinent of the invention. Detailed Description of the Invention

Fig. 1A illustrates the external casing packer enclosing a casing 2 which has been lowered into a borehole 1. The portion of the casing 2 above the ECP extends to the surface, and the casing portion 3 below the ECP is optionally perforated, as shown. The body of the packer is constructed using a metal mandrel 5. The ECP includes an inflatable reinforced elastomeric sleeve 4 which encircles the mandrel 5. The grout valve at the upper end of the casing packer is shown as numeral 6. The packer seat 8 of the non-return valve is located in the lower portion of the mandrel 5, and is a cone of material, usually concrete. The inflation valve 7 is adapted for use in inflating the elastomeric sleeve 4 to obstruct or otherwise block the annulus of the borehole 1 ,

Fig. IB illustrates a cementing system attached to the top end of the casing 2. The cementing system includes a top casing section 10 which contains a cement displacement plug 15 therein. Also included are grout and inflation valves 11 and 13 which are connected to the top casing section 10. Once the casing 2 is situated at a desired location in the borehole 1, a ball 16 is dropped down through the casing 2 and into contact with the valve seat 8 to seal the bottom end of the packer. The elastomeric sleeve 4 of the ECP is then inflated by pumping a fluid into the top section 10 of the casing 2 via port 14 and valve 13. The pressurisation of the casing 2 causes the flap of the one-way inflation valve 7 in the packer mandrel 5 to open and permit the pressurised fluid to enter the space between the mandrel 5 and the packer sleeve 4, thereby inflating and expanding the elastomeric sleeve 4 into contact with the borehole I. Fig. 1C illustrates the elastomeric sleeve 4 of the ECP fully expanded and in contact with the wall of the borehole I. Eventually, the differential of the fluid pressure across the expanded elastomeric sleeve 4 exceeds a designed threshold, whereupon the frangible grout valve 6 is activated to open and initially allow fluid to flow from the casing 2 into the annulus between casing 2 and borehole 1. As noted above, when the grout valves 6 open, the pressure in the casing 2 drops and closes the inflation valves. Fig. ID illustrates the process of pumping the cement grout 17 into the casing top section 10 via port 14 of grout valve 13. The cement grout 17 passes down through the casing 2 and out of the opened grout valve 6 to fill that part of the annulus above the packer and between the casing 2 and the borehole 1. The cement grout 17 also flows down through the mandrel 5 of the ECP, to the ball 16 and closed valve seat 8.

View IE shows a fluid being pumped into port 12 through inflation valve 1 1 while grout valve 13 is closed. This fluid pushes the cement displacement plug 15 down into the casing 2 and into the top of the mandrel 5 until the cement displacement plug 15 forms a seal below the grout valve 6. At this point, a hydraulic lock forms between the cement displacement plug 15 and the ball 16 in the valve seat 8.

Fig. IF illustrates the use of a conventional drill bit 19 attached to the end of a drill string 18 to drill out the cement grout displacement plug 15 (shown already drilled out), as well as drill out the cement grout 17 within the remainder of the casing 2, the mandrel 5, and the ball 16 and valve seat 8. When drilled in the manner noted, the production zone below the packer is coupled to the casing 2 above the packer.

Fig. 2 illustrates the structural details of the ECP.^' As noted above, in the embodiment shown the ECP comprises a mandrel 5 partially covered or encircled with a reinforced elastomcric sleeve 4. The sleeve 4 is constructed of various layers of material to cany out the functions described herein. The elastomeric sleeve 4 is multilayered and would normally be constructed of a natural or synthetic rubber. The sleeve 4 is bonded to the mandrel 5 at the top of the packer beneath outer rigid sleeve layer 23, but is not bonded to the mandrel 5 over the remainder of sleeve 4 length. Between the packer retaining rings 20 and 21 the packer sleeve 4 may expand outwardly in response to internal, pressure to form a seal in the annulus of the borehole. The packer retaining rings 20 and 21 are manufactured from high tensile steel and are bonded to the elastomeric sleeve 4, and restrained by upper and lower rigid outer sleeves 22 and 23 which are also bonded to the sleeve 4. The rigid outer sleeves 22 and 23 can be constructed of a rigid material or metal, such as steel. The mandrel 5 is shown with threaded connections at the top 26 and bottom 27 to permit attachment to casing sections located above and below the packer. The absence of bonding between the reinforced elastomeric sleeve 4 and mandrel 5 at the lower end of the packer allows the lower end of the sleeve 4 to slide up the mandrel 5 as the sleeve 4 becomes inflated. It is realised that when the reinforced elastomeric sleeve 4 is inflated, the natural tendency is for the overall length to become shortened. The other alternative is for the material of the elastomeric sleeve 4 to stretch during inflation, but with the reinforced construction of the sleeve 4, stretching of the sleeve material is not preferred. The seal between the sleeve 4 and the mandrel 5 is described in more detail in below. The lower end of the mandrel 5 contains a cone-shaped valve scat 8 which forms a non-return valve when the ball 16 is dropped down the casing 2 and rests on the conical-shaped seal 8. The cone- shaped element 8 can be cast in concrete or other suitable materials to lower manufacture cost. The non-return inflation valve 7 and the grout valves 6 described above are also illustrated. The grout valves 6 described in more detail below are covered by an elastomeric grout valve sleeve 25.

Fig. 3 illustrates the details of the grout valve 6 in a closed position. As noted above, the grout valve 6 is constructed with a chamfered port 30 formed in the sidewall of the mandrel 5. Seated in the port 30 is a chamfered valve member 31 which in its preferred embodiment is made of metal and which is attached to a frangible shear disc 32. The shear disc 32 is preferably made of a material having a well-defined shear strength such as a plastic, metal or ceramic. The force exerted by the pressure of fluid in the casing during the sleeve inflating proce$$ is sufficient to fully inflate the sleeve, and shortly thereafter shear the shear disc 32. The shear disc 32 is connected to the valve member 31 via a fastener 33, shown as a screw. The elastomeric grout valve sleeve 25 encircles the mandrel 5 and is bonded to the outer surface of the grout valve member 31, but not to that part of the mandrel 5 shown to the right of the grout valve 6 in the drawing. The elastomeric grout valve sleeve 25 is, however, bonded to the mandrel 5 at the location to the left of the grout valve 6.

In operation, when the differential pressure across the grout valve 6 exceeds a specified design value during inflation of the elastomeric sleeve, the peripheral rim of the frangible burst disc 32 undergoes stress and eventually shears, whereupon the chamfered grout valve member 31 is activated and moves out from its seated position to thereby allow fluid to flow through the opened grout valve 6. As will be described below, during inflation of the large elastomeric sleeve through the open inflation valves, a point is reached where the • elastomeric sleeve is fully inflated in the annulus and the grout valves 6 then rupture and open. At this time, the pressure in the casing drops abruptly, whereupon the inflation valves close. To that end, the opening of the grout valves 6 function as a relief valve for the inflation of the elastomeric sleeve. When the grout valves 6 are forced open, the elastomeric grout valve sleeve 25 is forced to expand outwardly, as shown in Fig. 4. After the casing is set by the inflated sleeve, the cement grout can be pumped down the casing. The force of the liquefied cement grout on the grout valves 6 causes them to open and allow flow in the direction of the arrow. Once a specified volume of the cement grout mixture is pumped through the grout valves 6 and into the borehole annulus, the cement grout pumping operation is halted. The expanded elastomeric grout valve sleeve 25 then contracts, which action returns the chamfered valve member 31 and the remaining part of the shear disc 32 back into a seated condition with the chamfered port 30 of the mandrel 5. Once the grout valve 6 returns to its seated condition due to the contraction of the elastomeric grout valve sleeve 25 around the mandrel 5, a seal is provided between the chamfered grout valve member 31 and the chamfered port 30 of the mandrel 5.

Fig. 4 illustrates the grout valve 6 in an open position, as noted above. The frangible shear disc 32 is shown with its peripheral edge sheared off following its failure at the design inflation pressure of the ECP. The elastomeric grout valve sleeve 25 positions the chamfered valve member 31 during fluid flow, including that of cement grout, so that when the fluid flow ceases, the chamfered valve member 31 returns to the seated condition in the chamfered valve port 30. The registration of the grout valve member 31 and the valve port 30 is achieved by bonding the elastomeric grout valve sleeve 25 to the outer surface of the chancered valve member 31 and to the mandrel 5 at location 34. The elastomeric grout valve sleeve 25 can be manufactured as part of an extension of the packer sleeve, but this is not a necessity.

Fig. 5 illustrates the upper zone of the packer sleeve 4, the inflation valve 7, the retaining ring 21 and the bonded elastomeric sleeve 4. The reinforced elastomeric sleeve 4 is of multi-layered construction, including an outer elastomer layer 40, a reinforcing layer 41, (depicted here as a single layer for diagrammatic convenience, but could be made of layers of steel cord or steel strips embedded in the elastomer) and an inner elastomer layer 42. The layered elastomeric sleeve 4 is bonded over surface area 43 to the outer cylindrical surface of the mandrel 5. The outer elastomer layer 40 of the reinforced sleeve 4 is bonded to the rigid outer sleeve 23.which bears against the packer retaining ring 21 at location 44. The retaining ring 21 has acting on it the loads from the sleeve reinforcing layer 41. This would tend to move the retaining ring 21 axially to the right in the drawing. The rigid outer sleeve 23 however restrains the retaining ring 21 from being moved to the right because it is bonded to the elastomer layer 40 which is in turn bonded to the reinforcing layer 41. The radial component of the load on the packer retaining ring 21 is contained by hoop stress within the retaining ring 21. The axial component of the load on the retaining ring 21 is transferred to the rigid sleeve 23 via the contact surface at location 44. The axial load imparted on the retaining ring 21 is transferred through shear stress in the elastomer layer 40 back to the reinforcing layer 41. The contact surface 44 is shown as an acute angled abutment so that the rigid sleeve 23 does not disengage under load from the packer retaining ring 21. The inflation valve system which permits fluid to expand the packer sleeve 4 is fitted in a concentric recess in the mandrel 5 at location 48. Although one inflation valve 7 is illustrated, it is to be understood that a number of such valves are formed around die packer mandrel 5. At the location 48, a port 47 is drilled in the mandrel 5 to provide an inflation fluid entry point. Movement of the inflation valve 7 is provided by an elastomeric annular flap 46 which is bonded over the outside surface of the mandrel 5 at location 45. The bonding of the annular end of the elastomeric annular flap 46 to the mandrel 5 is under the metal retaining ring 21 to maintain the annular edge of the flap 46 anchored to the mandrel 5. During inflation of the packer sleeve 4, the inflation fluid forces the elastomeric annular flap 46 open, as shown in the drawing. When pumping the packer inflation fluid to a specified pressure, the grout valves rupture and open, whereupon the pressure in the casing drops, thereby causing the elastomeric annular flap 46 to close the respective ports 47. The inflation valve 7 is held in the closed state by fluid pressure contained between the packer sleeve 4 and the mandrel 5. The force exerted on the inside of the closed elastomeric annular flap 46 by the inflated packer sleeve 4 is greater than the fluid force exerted on the other side of the inflation flapper 46 by the cement grout forced down the casing during the grouting process. Accordingly, the cement grout does not force the flapper valve 46 open during the grouting process. Otherwise, the cement grout would enter between the packer sleeve 4 and the mandrel 5. The rigid outer sleeve 23 is advantageously made in longitudinally split form so as to facilitate assembly of the packer while minimising the need for precise tolerance in diameter between the rigid outer sleeve 23 and the elastomer layer 40. During assembly, the rigid split sleeve 23 is clamped into place to the underlying elastomer layer 40 to permit the formation of a bond therebetween. It should be appreciated by those skilled in the art of elastomer construction that various bond and de-bonded sections of layers are advantageous to produce the ECP. Fig. 6 illustrates the structural details of the lower end of the packer sleeve 4 as shortened during inflation. The lower end of the packer sleeve 4 includes the sliding seal 55, the retaining ring 20 and the outer sleeve layer 40. The arrangement of the packer sleeve 4 at the lower end thereof includes the inner elastomer layer 42, the reinforcing layer 41, the outer elastomer layer 40, the retaining ring 20, and the rigid outer sleeve 22, all of which are similar in construction to that described above in connection with the upper end of the packer in Fig. 5. The major difference is that the inner elastomer layer 42 is manufactured so that it can slide over the mandrel 5 in an axial direction at surface area 53 as the packer sleeve 4 shortens during inflation. Unlike most packers which have a form of sliding hydraulic seal, the packer disclosed herein utilises an annular sleeve seal 55 made of an elastomer which is preferably of a similar elastomer construction as the sleeve 4. The annular sleeve seal 55 is contained in an annular external groove 54 formed in the mandrel 5. The annular sleeve seal 55 is bonded to the outside of the mandrel 5 over surface area 58, and to the inside of the packer inner elastomer layer 42 over surface area 57. The sleeve seal 55 is otherwise not bonded, but is free to slide axially on the mandrel 5 within the external groove 54. In the drawing the packer sleeve 4 is shown in an inflated state, engaged in contact with the borehole 1. In the inflated state the sleeve seal 55 is longitudinally compressed from its original position where it occupies the entire length of the external groove 54. The distance by which the sleeve seal 55 becomes compressed is shown as the dimension G. The sleeve seal 55 is shown in the drawing as having been manufactured with a reinforcing layer 56. This would preferably be an open weave mesh laid on the bias so that it can compress axially. The reinforcing mesh 56 would be bonded into the elastomer and prevent uneven strain of the sleeve seal 55, which could otherwise lead to tears within the material of the sleeve seal 55. The sleeve seal 55 is held against the mandrel 5 within groove 54 by fluid pressure in the expanded sleeve 4 and is prevented from being torn from the inner elastomer 42 of the sleeve 4 by the tight annular restraint of the packer retaining ring 20. While the preferred and other embodiments of the invention have been disclosed with reference to a specific external casing packer, and associated methods of use and manufacture thereof, it is to be understood that many changes in detail may be made as a matter of engineering choices without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method of cement grouting an annulus between a casing and a borehole using an inflatable packer system, comprising:

placing a casing with an externa] casing packer attached thereto at a location in a borehole for cement grouting a portion of the borehole annulus that is located above the external casing packer;

inflating an inflatable elastomeric sleeve of the external casing packer to block the annulus of the borehole by pressurising the casing with an inflation fluid, which opens a one-way inflation valve in the external casing packer with the pressurised inflation fluid and inflates the inflatable sleeve to a preset pressure;

detennining the preset pressure by a pressure relief valve located between the external casing packer and the annulus which opens at the preset pressure and then becomes a one-way grout valve;

pumping a liquefied cement grout mixture down through the casing via the open one-way grout valve which is located in the external casing packer above a portion of the inflated inflatable sleeve; and

biasing the grout valve to a closed position using an elastomeric member attached to the packer, whereby when the pressure of the cement grout mixture is reduced in the casing, the elastomeric member causes the grout valve to close and prevent backflow of the cement grout mixture from the annulus back into the casing.

.

2. The method of Claim 1, further including rupturing or shearing a portion of the grout valve at a given pressure to open the grout valve and permit a pressure drop in the casing.

3. The method of Claim 2, ftuther including using the pressure drop in the casing to maintain closure of the sleeve inflation valve.

4. The method of Claim 1, further including pressurising the casing to open the one-way inflation valve and inflate the inflatable sleeve, and using the pressurised casing to shear an element of the grout valve to allow the grout valve to open when the inflatable sleeve is inflated,

5. The method of Claim 1, further including biasing the grout valve to a closed condition by the elastomeric member, by using an elastomeric sleeve member which both encircles the packer and is attached to a movable part of the grout valve.

6. The method of Claim 1 , further including fabricating the elastomeric sleeve of the grout valve as part of the inflatable elastomeric sleeve, whereby when the grout valve is opened the elastomeric sleeve member stretches radially outwardly.

7. The method of Claim 5, further including bonding a portion of the elastomeric sleeve of the grout valve to a mandrel of the packer and bonding the elastomeric sleeve of the grout valve to a chamfered grout valve member, which is the movable member of the grout valve.

8. The method of Claim 5, further including forming the elastomeric sleeve member as a unitary part of the inflatable elastomeric sleeve during one manufacturing process.

9. The method of Claim 1, further including using a sleeve of an elastomeric material as a flap member of the non-return inflation valve, and bonding one annular edge of the elastomeric flap member sleeve to the mandrel of the packer, allowing another annular edge of the sleeve of elastomer material to be free for lifting off of respective ports in the mandrel to permit one-way fluid flow.

10. A method of setting an external casing packer in an annulus of a borehole to fix a casing therein, comprising:

sealing a base of the packer;

pressurising the packer to inflate an inflatable elastomeric sleeve surrounding a portion of a packer mandrel by passing a pressurised fluid through a one-way inflation valve into the inflatable sleeve;

limiting the inflation pressure of the inflatable sleeve by using a pressure relief valve in the packer which relieves the pressure in the packer to the outside of the casing when a design differential pressure is reached; using the pressure relief valve as a one-way valve to permit a grout material to flow therethrough to the annulus of the borehole; and

closing the pressure relief valve to prevent a backfiow of the grout material from the annulus back into the packer.

11. A method according to claim 10 whereby the base of the packer is sealed by dropping a ball into a seat located in the base of the packer.

12. A method of cement grouting a borehole using an inflatable packer system, comprising:

lowering into a borehole a casing with the inflatable packer system attached thereto;

pressurising the casing with a fluid so that the pressurised fluid enters one or more one-way inflation valves in the packer system to inflate a sleeve and obstruct an annulus of the borehole;

increasing the pressure of the fluid in the casing until one or more one-way frangible grout valves rupture to allow pressurised fluid to enter the borehole annul us above the packer system, whereby the pressure of the casing drops and the one-way inflation valves close and maintain the inflation of the sleeve in the borehole annulus; pumping cement grout down through the casing and through the ruptured one-way grout valves into the portion of the borehole annulus located above the packer system.

13. The method of Claim 12, further including pumping a predetermined volume of the cement grout down the casing and into the borehole annulus, and then stopping the pumping of the cement grout, whereby the one-way grout valves close and prevent a backfiow of the cement grout from the annulus back into the casing.

14. The method of Claim 12, further including sealing the base of the packer system before pumping the cement grout down tlte casing to prevent the cement grout from passing into a perforated portion of the casing below the packer system

15. The method of Claim 13, further including forcing a plug down through the casing after the predetermined volume of cement grout has been pumped down the casing, to clear at least a portion of the cement grout from the casing and force the same through the one-way grout valves and into the borehole annulus.

16. The method of Claim 15, further including drilling the portion of the cement grout that has set in the packer system to provide a flow path of production fluid from the bottom of the borehole to the top of the casing.

17. The method of Claim 12, further including forming an elastomeric sleeve around a mandrel body of the packer system, where an annular top portion of the sleeve is anchored and scaled to the mandrel, and a bottom portion of the sleeve is slideable along and sealed to the mandrel as the sleeve is inflated.

18. The method of Claim 17, further including forming a portion of the elastomeric sleeve over the one-way grout valves so that elasticity of the sleeve moves the one-way grout valves into closed positions in respective ports formed in the mandrel.

19. The method of Claim 17, further including anchoring the top portion of the sleeve to the mandrel using a retaining ring which clamps the sleeve around the mandrel, and forming the one-way inflation valves by using an elastomeric flapper which covers respective ports formed in the mandrel, where the flappers are anchored at one end thereof to the mandrel under the retaining ring.

20. An inflatable packer system for grouting a borehole annulus, said packer system comprising:

a mandrel forming a body of the packer system, said mandrel adapted for attachment to a casing, said mandrel having formed therein one or more ports for respective grout valves, and one or more ports for respective inflation valves;

a seat formed in a bottom part of said mandrel, said seat adapted for being blocked by a ball dropped down the casing;

an elastomeric sleeve formed around the mandrel and around the inflation valve ports; an anchor seal formed at a top portion of the elastomcric sleeve around the mandrel above the inflation valve ports and below the grout valve ports;

a sliding seal formed at a bottom portion of the elastomeric sleeve along said mandrel;

one or more one-way inflation valves, each said one-way inflation valve located over one said Inflation valve port, each said one-way inflation valve adapted for allowing an inflation fluid to pass through the inflation valve port and into the elastomeric sleeve, but not in a reverse direction;

one or more one-way grout valves, each said one-way grout valve located over one said grout valve port, each said one-way grout valve adapted for allowing a cement grout to pass through the grout valve port and into the borehole annulus, but not in a reverse direction; and

each said one-way grout valve formed with a frangible member which breaks in response to a pr^etennined inflation fluid pressure, whereby when said elastomeric sleeve is inflated to the predetermined fluid pressure the frangible members break to enable operation of the one-way grout valves, and the one-way inflation valves close to allow the elastomeric sleeve to maintain the predetermined inflation fluid pressure.