Patent Publication Number: US-10329869-B2

Title: Well abandonment tool and method of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Canadian Patent Application No. 2,913,933 filed Dec. 4, 2015, the entirety of which is incorporated herein by reference. 
     FIELD 
     The present disclosure is directed to a tool and method of using the tool useful for plugging wellbores. They particularly find application in the procedure practiced in abandoning the cased bore of a well. 
     BACKGROUND 
     Oil and gas reservoirs are accessed with a well casing extending downhole to a subterranean formation, and traversing various strata therealong. In the completion process, an annulus is formed between the casing and the formation. The annulus is filled with cement to seal the annulus, blocking cross-strata fluid communication and communication to surface. At the end of the commercial life of the well the well is abandoned. 
     The Alberta Energy Regulator currently requires that a “bridge plug” be installed as the first step in well abandonment. The bridge plug comprises a mechanical tool having a body carrying slips to grip the casing and an expandable, elastomeric seal ring to seal against the casing&#39;s inner surface. The tool can be operated by a tubing string extending down from surface. The body and seal ring thereby combine to permanently close and seal the cased bore. 
     During a conventional abandonment procedure the bridge plug is positioned and set at a pre-determined depth in the bore of the casing. A hydraulic pressure test is then carried out to determine if the bridge plug and casing are competent to hold pressure. The pressure test is currently performed by filling the casing bore with water and applying pressure at 1000 psi for 10 minutes. After it has been determined that both the bridge plug and the casing above the bridge plug are competent, a column of cement (typically 25 feet in length) is deposited in the bore immediately above the bridge plug. Finally, the top end of the steel casing is cut off at a point below ground level and a steel plate or vented cap is welded on the upper end of the casing. 
     However, problems can commonly arise over time with this system for plugging and abandoning wells. For example, the elastomeric element of the bridge plug may develop surface cracks or otherwise deteriorate and allow fluid to leak thereby. 
     Further, in the instance where the casing-to-cement and cement-to-formation seal fails, unacceptable hydrocarbon flow can occur to surface. Minute cracks may also develop in the cement column, including shrinkage of the cement sheath around the outside of the casing forming a micro-annulus where the cement abuts the inside surface of the casing. One or more of these defects can result in natural gas or other fluid leaking either up through the cased bore or along the outside surface of the casing to surface. Such leakage indicates that the abandonment process has failed. This failure is commonly identified when vegetation surrounding the well at ground surface begins to die from hydrocarbon exposure. 
     Presently there are thousands of wells in Alberta that have been abandoned. Many have been identified as leaking fluid to ground surface. Therefore, there is a need in the industry for an abandonment tool and method for closing and sealing wells which addresses the limitations of the current methods. 
     SUMMARY 
     A well abandonment tool is provided for emplacement using a tubular string of pipe lowered into the casing bore of a well. The tool functions to permanently block and seal the bore on its own, or in combination above other known forms of casing plugs. 
     In one embodiment, a tool is located in the well casing forming a tool annulus thereabout, affixed to the casing at a sealing location, and the tool annulus is flooded with hot asphalt which seals the tool to the casing bore and blocks the passage of fluids thereby. In an embodiment, the tool blocks the casing uphole of the tool from the uphole passage of fluids, such hydrocarbons emanating from downhole of the tool. 
     In another embodiment, the tool further acts to expand the casing for closing any local presence of a micro annulus between the outside the casing and structure outside the casing. Typically the structure outside the casing is the formation or cement in the casing annulus. Accordingly, both the inside and the outside of the casing can be sealed for remediation of the well abandonment. 
     In one aspect, a tool is located in the bore of the casing and forming a tool annulus between the tool and the casing. The tool has an axial stack of annular pleated rings slidably mounted about a mandrel. Pleated rings have an outer diameter less than that in their less or unpleated state. An example of an unpleated ring is a flat washer. The stack of pleated rings is axially compressible on the mandrel. Within the stack, pleated rings flatten, expanding radially to engage the casing and impart an expanding hoop stress thereinto for local expansion of the casing. The stack of pleated rings is sandwiched between a stop or first slip that can be fixed axially and a second stop that can be moved towards the first slip. As disclosed, the tool has a first slip for anchoring one axial extent of the pleated rings. The mandrel, fit with the second stop, is manipulated to actuate the pleated rings against the first slip, compressing the rings. Once the desired radial expansion of the rings is achieved, a second slip is set to lock the stack of pleated rings in compression for securing the tool in the casing. 
     In an embodiment, each pleated ring is an annular ring that undulates about its circumference between peaks and valleys. Like a wave spring, each ring elastically resists axial force. When compressed axially to reduce its height, each spring expands radially, increasing its diameter. For predictability and uniformity of ring compression along the stack, one or more rings can be separated from one another by a flat washer. The peaks and valleys engage the flat washer during compression. 
     When the axial stack is actuated for compression from one end, the individual rings can vary in spring constant or like-rings along the stack are supplemented with variable concentrations of compressible pleat spacers distributed about the ring circumference. Higher concentrations of spacers are provided adjacent the actuation end of the stack to manage compression therealong. Copper tubing is suitable as are elastomeric rods such as those of nitrile. 
     In another aspect, while the tool is mechanically coupled to the casing, tool can further sealed to the casing with sealant distributed at the tool for sealing between the tool and the casing. A flow of fluid elastomer can be delivered to the bore and tool annulus for providing a permanent and reliable seal at the tool location. In an embodiment, a sealant is a heated, flowable asphalt. 
     In one embodiment, the mandrel has a through passage or tool bore for delivery of the sealant to the casing bore below the tool. Blocked from flowing downhole, sealant flows back uphole into the tool annulus. A pre-determined measured volume or charge is conveyed in a container with the tool downhole for deployment one the tool is located in the casing. The container can be a cylinder having storage area for the sealant charge within. Hydraulic actuation of a piston in the cylinder enables the storage area to be discharged from the tool. 
     In an embodiment, the pre-determined measured volume or charge of sealant is conveyed in a heated state. In the instance of asphalt or like sealant that is flowable when heated, the charge is stored in an insulated container, filled hot at surface and remaining hot enough during conveyance and operation to flow when needed. The insulated container is fluidly connected to the mandrel and supplies the charge of hot liquid sealant through bore of the mandrel. The mandrel is fluidly connected to the bore of the casing. 
     In another aspect, a method of abandoning a well is provided for sealing the casing bore of said well. A tool as described above is conveyed downhole into the bore of the casing on a tubing string. The tool is run-in-hole to a strategic blocking location in the casing for isolating the surface uphole thereof from well fluids downhole thereof. The tool is anchored in the casing such as with a first slip. The charge of sealant is released to flow out of the mandrel and about the stack of pleated rings in their uncompressed stage. The mandrel is actuated to compress the sealant-imbued rings and expand into the casing, displacing and distributing sealant about the compressed rings and along at least a portion of the axial extent of the tool. The ring compression is locked in, such as with a second slip, to permanently retain the rings in the axially compressed and radially expanded condition. The tubing string is separated from the tool, leaving the tool downhole to seal the bore of the casing. In an embodiment, the sealant is fluid when heated and solidifies at well temperatures. Accordingly, the sealant is conveyed and released hot, and when cooled to well temperatures, the sealant solidifies about the tool to seal the bore of the casing. 
     In one embodiment, an abandonment tool is provided having a central tubular mandrel having a longitudinal bore and connected to a conveyance string from surface. A stack of pleated rings is slidably mounted on the mandrel and sandwiched between first and second radially expandable locking assemblies such as slips. The first locking assembly is slidably mounted on the mandrel and releasably secured thereto. A first compression plate is slidably mounted on the mandrel between the first locking assembly and a first end of the stack. The second locking assembly is mounted to the mandrel at the other or second end of the mandrel. A second compression plate is mounted on the mandrel between the second locking assembly and the other end of the stack. The first locking assembly is actuable for locking engagement of first end of the stack to the casing. The mandrel and second locking assembly are axially actuable to compress the second end stack towards the first end. In an embodiment, the second locking assembly and second compression plate move axially as a compression unit with the mandrel when pulled by the pipe string to compress the stack. 
     Upon the stack reaching the design compression, the second locking assembly actuates into locking engagement with the casing to axially lock the compression in the stack of rings. One or both of the locking assemblies can be slips. In an embodiment, frangible means such as shear pins are provided to release one or more of the slips into locking engagement with the casing. The first slip can be released such as at a first force when the tool is located at the sealing location. The second slip can be released at a second force when the stack has been compressed to seal the bore. Release force, for separating the conveyance tubing string from the tool, can be applied by applying a torque or a pulling force to the mandrel. 
     In a further embodiment, the bore of the mandrel is fit with container of sealant. A one way valve is fit to the mandrel bore at a downhole end and, when opened, is fluid communication with bore of the casing below the tool. The tool can also be equipped with a casing plug downhole of the one way valve so as to block or limited the extent of sealant flow downhole thereof and to urge sealant uphole about the stack of rings. In another embodiment, an independent casing plug, such as previously placed bridge plug or older failed plug, can be utilized in combination with the tool, being located downhole of the tool prior to running in of the tool. The casing plug blocks sealant flow downhole of the tool. 
     The tool can be run in and positioned downhole and is actuated by means such as the tubular pipe string extending from a rig at ground surface. 
     The locking assemblies can be slip assemblies for locking the stack to the casing. The first slip assembly is actuated by rotation of the mandrel to axially drive a cone ramp surface radially inward of circumferentially spaced first slips to drive the slips radially outwardly and to the casing. The first slips can be supported on a collet and held axially by drag blocks. The second slip assembly is actuated by axial movement of the mandrel. The axial actuation of the mandrel can axially drive a cone ramp surface radially inward of circumferentially spaced second slips to drive the slips radially outwardly and to the casing. 
     Therefore the slip assemblies can be selectively actuated at separate stages of the emplacement. Typically the first slip assembly and first compression plate are located at the upper end of the ring stack and the second compression plate and second slip assembly are located at the lower end. Therefore the first slip assembly can initially be expanded by mandrel rotation, overcoming first shear pins in the cone, to lock the upper end of the stack in place. Subsequently the mandrel can be pulled upwardly to cause the lower compression plate to compress the stack against the fixed upper compression plate. These steps are performed by manipulating the pipe string which is connected with the mandrel. The second slip assembly is locked, such as by second shear pins to the mandrel, and remains non-expanding through most of the compression step until the extent of axial pull on the mandrel causes the second shear pins to release so as to allow the cone to engage the second slip to expand and engage the casing. 
     The container assembly preferably comprises a thermally insulated container having a chamber containing a piston at its upper end and closed at its bottom end by a frangible disc. The container is connected between the pipe string and the mandrel. Fluid pressure applied through the bore of the pipe string is used to bias the piston downwardly, pressurizing the container and rupturing the disc to discharge the contained charge of hot liquid sealant from the chamber through the bore of the mandrel. The sealant preferably is asphaltic in nature. It melts when heated sufficiently and solidifies when it cools to seal against surfaces with which it is in contact. The mandrel and rings are normally formed of steel. Preferably, flat washers are provided between the pleated rings. 
     In another aspect, in use, the tool as described above can be run in hole to the sealing location and operated for releasing and expanding the first locking assembly to engage the casing and thereby positionally fix the first compression plate and the upper end of the stack. The container assembly is activated to discharge a charge of hot liquid sealant through the mandrel bore, filling the stack and the annular space between the stack and the casing with hot sealant. Further, heat is thereby transferred from the sealant to the adjacent surrounding casing. The mandrel is actuated to pull the mandrel and bottom compression unit upwardly so that the stack is compressed against the fixed upper compression plate, flattening the pleated rings to expand radially to engage the adjacent heated casing section, expanding the casing into the casing annulus. One continues to pull the mandrel until the second locking assembly is released and expanded to engage the casing and thereby positionally fix the lower end of the stack. Thereafter, the pipe string is disengaged and removing from the well. The sealant cools and solidifies into an impermeable mass having sealing engagement with surfaces of the rings, mandrel and casing. 
     In another embodiment, the sealing location for the tool can be aligned with existing perforations in the casing, perforations can be created, or the casing can be cut about all or a portion of its girth to access the casing annulus thereout. Accordingly, when the tool is actuated, the sealant is not only discharged about the tool annulus, but is also discharged through the access ports formed in the casing and into the casing annulus. As the casing annulus is typically cement, the remediation of the cement is two-fold: by mechanical expansion of the casing itself, and sealant flowing into and along any defects in the cement. 
     From the foregoing it will be observed that the present system involves the following actions and potential results. One contacts the tool with an adjacent section of steel casing with hot liquid sealant which causes the casing wall to thermally expand radially a small amount and makes the casing more pliable and receptive to expansion. Axial compression of the stack radially expands the pleated steel rings to press against the heated casing wall, interlock with it and effect a metal-to-metal circumferential engagement with it. The tool frictionally engages the casing with the top and bottom slips to thereby permanently maintain the stack in a compressed and expanded condition. The expanded stack can sufficient expand the casing that provides closure of micro-annular spaces in the casing annulus to block fluid communication therealong. The tool forms an impermeable mass of cooled and solidified sealant that provides closure of the casing bore and seals against the surfaces of the stack, the mandrel, and the inner surface of the casing. The radial compression is significant and should a cement annulus shrink over time, the rings continue to can continue to expand the casing to close any micro annulus that could otherwise form. 
     The system is characterized by the following attributes: the steel rings and the asphaltic sealant combine to formulate a plug that is highly resistive to shrinkage, cracking and degradation in the downhole environment and therefore may better resist failure over time when compared to cement and elastomer; the rings, washers and mandrel combine to form a frame or skeleton that reinforces and stabilizes the mass of sealant; the dual effects of heating and radial force application applied to the casing wall section opposite to the tool tend to radially expand the casing wall a small amount, which may result in closing cracks in the surrounding exterior casing sheath and thereby potentially lead to reduction or elimination of substantial fluid leakage up the well annulus; and the stack of pleated rings, locked in a compressed expanded state, should continue to indefinitely interlock with and press against the surrounding casing wall, thereby maintaining the wall in an expanded condition. 
     In an independent aspect of the invention, a component assembly is provided having a stack of pleated steel rings, separated or bracketed by flat annular washers, which is slidably mounted on a mandrel between flat compression plates. The washers serve to distribute compressive force evenly to the pleated rings and cause diametral expansion thereon. The rings are dimensioned and configured so that they are insertable in the casing bore and yet, when compressed a suitable amount (e.g. 50% of their axial pleat height), they are operative to expand radially sufficiently to press against the casing wall and provide a circumferential frictional interlock or engagement with the casing. 
     In a further preferred feature, compression-modifying or resistant spacers may be positioned in varying density amongst the pleats and between the washers, so as to provide a characteristic of increasing resistance to compression of the individual pleated rings from the fixed compression plate to the actuated compression plate. Thus the pleated rings that are sliding along the mandrel and relative to the casing, from the actuated compression plate towards the fixed compression plate, are the last to be compressed. The pleated rings therefore expand in sequence to control the drag of the expanding rings as they are axially compressed. 
     In summary, the fully operational or complete well abandonment tool is characterized by capabilities for effecting: the application of metal-to-metal circumferential radial force and frictional engagement of the rings with the well casing; heating of the casing wall at the point of radial force application; and fluid tight closure and sealing of stack, mandrel and internal casing section surfaces. 
     In still another aspect the invention comprises the previously described method for establishing a plug downhole in the course of well abandonment. 
     In still another aspect the invention comprises a product or plug which closes and seals the bore of a string of casing in a well. The plug comprises a steel skeleton supporting a mass of asphaltic sealant. It is positioned downhole to prevent upward migration of fluid through the casing bore. The plug comprises a central mandrel; a stack of axially compressed pleated rings mounted on the mandrel and circumferentially and frictionally engaging the casing; expanded locking assemblies connected with the mandrel and located at top and bottom of the stack, said locking assemblies frictionally engaging the casing so as to be positionally fixed to thereby maintain the pleated rings in the compressed condition; and a mass of impermeable solidified asphaltic material sealing against surfaces of the mandrel, stack and casing and providing closure of the casing bore. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a side view of an embodiment of the abandonment tool with its components broken apart; 
         FIG. 2A  is a side view of the tool in a cross-section of casing, the stack of pleated rings having an increasing density of compression modifiers closer to the actuating end of the stack; 
         FIG. 2B  is a close up view of adjacent pleated rings, the stack cut away above and below to illustrate the pleated rings separated by flat washers, having adjacent peaks and troughs misaligned, one spacer being illustrated in exploded view separate from the pleated rings, and a mandrel passing therethrough; 
         FIG. 2C  is a close up view of adjacent pleated rings, according to  FIG. 2B , with adjacent pleat peaks and troughs aligned; 
         FIG. 3  is an exploded and cross-sectional side view of the tool, a sealant container and uphole pipe separation components; 
         FIG. 4  is a cross-sectional assembled view of the conveyed tool according to  FIG. 3 ; 
         FIG. 5A  is a cross-sectional view of the sealant container, filled with sealant and with frangible disc intact; 
         FIG. 5B  is a cross-sectional view of the sealant container of  FIG. 5A , after actuation with the frangible disc ruptured and the sealant discharged from the container; 
         FIGS. 6A through 6G  illustrate a cross-section of a well to be abandoned having a casing plug previously set therein and various steps of the deployment and operation of the tool above the casing plug, namely 
         FIG. 6A  illustrates the tool and conveyance string of pipe run in hole to the sealing location; 
         FIG. 6B  illustrates actuation of the uphole slip; 
         FIG. 6C  illustrates discharge of the sealant; 
         FIG. 6D  illustrates compression of the stack of rings to seal the casing. 
         FIG. 6E  illustrates actuation of the downhole slip; 
         FIG. 6F  illustrates separation of the pipe string between the sealant container and the engaged stack of rings; 
         FIG. 6G  illustrates the sealed tool in the well; 
         FIG. 7A  is a side cross-sectional view of a tool fit with a packer cup casing plug below the stack of rings for effecting a well bore plug downhole of the tool, the pleated rings being omitted to illustrate an embodiment of a stack support sleeves; 
         FIG. 7B  is a rolled-out flat view of interlocking finger, stack-support sleeves about the mandrel; 
         FIG. 8A  is a side cross-sectional view of the tool and a side elevation view of a casing packer shoe below the stack of rings for effecting a casing plug downhole of the tool; 
         FIG. 8B, 9A through 9C  are cross-sectional views of tool&#39;s stack of pleated rings of  FIG. 8A , shown actuated in sequence, namely; 
         FIG. 8B  illustrates the stack of pleated rings in run in mode; 
         FIG. 9A  illustrates the stack of rings with the first slip actuated to engage the casing, the casing not shown; 
         FIG. 9B  illustrates the stack of rings with the mandrel actuated to compress the stack; 
         FIG. 9C  illustrates the stack of rings with the second slip set to locing in the compression and fix the tool to the casing; 
         FIGS. 10A, 10B and 10C  are the components of an upper slip shown in cross-section, the form of slips having a rotational actuation and a mandrel ratchet along the inner bore, more particularly,  FIG. 10A  illustrating the collet mounted, circumferentially arranged slips,  FIG. 10B  illustrating an axially split threaded ring, and  FIG. 10C  illustrating the conical expander, actuated axially by mandrel rotation of the threaded ring therein to engage the slips; 
         FIGS. 11A through 11F  illustrate a cross-section of a well to be abandoned having a casing plug previously set therein and various steps of an alternated form of deployment and operation of the tool at casing cut above the casing plug, namely 
         FIG. 11A  illustrates a first conveyance string and abrasive tool, at the sealing location, for cutting perforations in the casing or cutting the entire girth of the casing; 
         FIG. 11B  illustrates the casing cut at the sealing location and the abrasive tool pulled out of hole; 
         FIG. 11C  illustrates the abandonment tool and conveyance string of pipe run in hole to the cut casing at the sealing location; 
         FIG. 11D  illustrates actuation of the uphole slip; 
         FIG. 11E  illustrates discharge of the sealant; and 
         FIG. 11F  illustrates compression of the stack of rings to seal the casing and actuation of the downhole slip. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Having reference to  FIG. 1 , an embodiment of a well abandonment tool  10  is provided for conveyance downhole into the cased bore of a well. The tool generally comprises a downhole tool  12  for positioning and abandonment downhole, a container assembly  14  for conveying sealant downhole, and a separation sub  16  or snap latch connector for separation of the container assembly from the tool  12 . The tool itself has upper and lower slips,  20 ,  22  and a stack of pleated rings  24 . The container assembly  14  has a separation sub, a rupture disc sub  28 , a sealant filling sub  30 , a sealant chamber  32 , a piston sub  34 . A quick connecter  36  couple the container assembly  14  to a string of conveyance tubing or pipe. 
     Having reference to  FIG. 2A , the downhole tool  12  comprises a central tubular mandrel  38 . The mandrel  38  serves to convey, downhole and to support, the stack  24  of pleated metal rings  40 . The pleated rings  40  are formed of rings having an inner and an outer diameter. The rings  40  are crimped along radials to undulate up and down about the rings circumference. The inner diameter of each ring  40  is slidable on the mandrel  38 . The pleated rings  40  are separated apart by flat, annular rings or washers  42 . First and second compression plates  44 ,  46  bracket the stack  24  at its upper and lower ends respectively. The compression plates  44 ,  46  are axial stops that extend annularly about the mandrel  38  and engage the stack  24  of pleated rings at their opposing ends. 
     A first or upper slip assembly  48  is supported by the mandrel  38  above the upper compression plate  44 . In this embodiment, the upper compression plate  44  becomes fixed axially when actuated, such as supported by the mandrel  38  or the upper slip assembly  48 . The lower compression plate  46 , washers  42  and stock  24  of pleated rings  40  are slidably mounted on the mandrel  38 . 
     A second or lower slip assembly  50  is disengagably secured to the mandrel  38  below the lower compression plate  46 . The lower compression plate is slidable upwardly along the mandrel to engage downhole end  45  of the stop and compress the pleated stack  24  against the upper compression plate  44 . The lower slip assembly  50  can be disengaged from the mandrel  38  to axially fix the lower compression  46  plate as described in greater detail later. 
     With reference to  FIG. 3 , the abandonment tool  10  further includes the container assembly  14  fluidly connected to the mandrel  38 . 
     The chamber  32  is actuated by a piston  60  initially housed in piston sub  34 . The bore  62  of the piston sub  34  is in fluid communication with the bore  64  of conveyance tubing string of pipe through inlet  65  at its upper end. The conveyance tubing string of pipe extends uphole to ground surface for administration of fluid and fluid pressure control to actuate the piston  60 . Chamber  32  has a bottom outlet  66  which communicates with the bore  68  of the mandrel  38 . The chamber outlet  66  is initially closed by the rupture disc sub  28  at a frangible disc  22 . A threshold pressure applied to the piston  60 , pressurizes the sealant and ruptures the rupture disc  70  to flow sealant to the mandrel  38 . 
     As shown in  FIG. 5A , for filling the chamber, and located between the frangible disc and the piston, is a filling sub, having a one way valve for filling or refilling the chamber. Typically, the piston is initially lowered (such has shown in the emptied position in  FIG. 5B ) or fluidly driven to its lowest position, physically stopped against the filling sub. Accordingly, sealant can be injected under pressure into the chamber, displacing the piston upwardly to stop against the upper end of the chamber. Alternately, the filling port can be connected to a passive reservoir of sealant and the piston physically pulled up to draw sealant into the chamber. The piston can be equipped with an eyebolt connection or other connector for this purpose. 
     The mandrel  38  is formed of steel suitable for downhole use and is adapted for coupling at, at least, its upper end for connection to the container assembly  14 . Referring to  FIG. 2A , the pleated rings  40  are formed of corrosion—resistant material, such as stainless steel. Each pleated ring  40  is sized for a sliding fit on the mandrel  38  and are dimensioned and configured so that they are insertable in bore  72  the casing  74  in their normal, pleated condition but, when compressed axially, for example partly compressed to about ½ of their axial height, they are capable of extending out radially sufficiently so as to reach the inside surface  76  of the bore  72  and to press firmly against it, thereby frictionally engaging it and slightly expanding the wall casing  74 . 
     With reference to  FIGS. 2A and 2B , the stack  24  comprises flat annular washers  42  positioned between each adjacent pair of rings  40 . The rings  40  can be oriented with their facing peaks  80  misaligned or aligned. As shown in  FIG. 2B , if the peaks  80  of adjacent, facing pleated rings are misaligned, the intermediate flat washer is unsupported, and can be subject to deformation. As shown in  FIG. 2C , if the peaks  80  of adjacent, facing pleated rings  40  are aligned, the intermediate flat washer  42  is supported between acting peaks and all the axially compressive force is transferred through the pleated rings. The flat washer can be a steel or an elastomeric including Durometer 90 nitrile rubber. 
     As shown in  FIGS. 2A and 2B , the stack  24  further includes compression-modifying or resistant spacers  82  positioned between pleats and the flat washers  7 . The spacers  82  are distributed in varying concentrations or density that diminishes upwardly from the lower compression plate  46  to the upper compression plate  44 . The concentrations and distributions are selected so as to facilitate the desired sequential compression of the rings  40  from the stack&#39;s fixed end  84  downwards. The spacers  82  can be formed of short lengths of copper tubing  82 T. The compression spacers  82  provide a characteristic of increasing resistance to compression of the individual pleated rings from the fixed compression plate to the actuated compression plate. Thus the pleated rings  40  that are sliding along the mandrel  38  and relative to the casing  74 , from the actuated compression plate  46  towards the fixed compression plate  44 , are the last to be compressed. The pleated rings  40  therefore expand in sequence to control the drag of the expanding rings as they are axially compressed. 
     Table 1 as follows sets forth relevant dimensional, material and compression data from a test in which a stack  24  of pleated rings  40 , as shown in  FIG. 2A  was mounted on a mandrel  38  and axially compressed within a 60″ length of oilfield 4.5″ steel casing  74  using a press. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 mandrel outside diameter-2.5″ 
                 Each ring pleat height-0.375″ 
               
               
                 casing inside diameter-3.826″ 
                 ring material-410 stainless steel 
               
               
                 casing wall thickness-0.337″ 
                 ring wall thickness-0.025″ 
               
               
                 casing outside diameter-4.5″ 
                 Pleat spacers (copper tubing), 0.375″ 
               
               
                 number of pleated rings-10″ 
                 diameter and wall thickness-0.0625″ 
               
               
                 inside ring diameter-2.5″ 
                 flat steel washer thickness-0.125″ 
               
               
                 outside ring diameter prior to compression-3.750″ 
                 compressive force applied-~27,000 lb/ft 
               
               
                 outside ring diameter (unconstrained) 
                 extent of stack length reduction-about 40% 
               
               
                 after compression-3.834″ (Δ0.084″) 
                 Result: Casing expansion-about 0.008″. 
               
               
                   
               
            
           
         
       
     
     With reference to  FIGS. 5A and 5B , the container assembly  14  comprise a vacuum-insulated, double-walled tube having a chamber  32  within for storing sealant  15 A. The chamber  32  contains the movable piston  35  at the upper inlet  65 . The upper inlet  65  communicates with the bore of the tubing string. An upper end of the chamber  32  is closed by the piston  35 . At its lower end of the assembly  14 , the outlet is closed by a frangible shear disc  70 . In an embodiment, the chamber  32  contains a charge of hot molten asphaltic sealant  15 A. Plastomers are used to improve the high temperature properties of modified asphaltic materials. Low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) are examples of plastomers used in asphalt modification. 
     The charge of sealant  15 A, loaded into the container chamber  32 , is a molten thermo-settable asphaltic liquid, typically heated to a temperature of about 200° C. A suitable sealant  15 A is polymer-modified asphalt available from Husky Energy™ under the designation PG70-28. It melts at about 60° C. and solidifies at about 35° C. The hot asphaltic liquid can be filled at 200° C. and remain hot for up to about 8 hours, being available for discharge at about 190° C. Enough hot sealant can be stored on site for multiple wells. 
     The volumes of the container chamber  32  and the charge of sealant  15 A are selected so as to enable filling of an annular space or annulus  90  between the tool  12  and the well casing  7 A and an overage amount to accommodate excess volumes below the mandrel and above a casing plug  92 . 
     With reference to  FIGS. 6A through 6G , actuation of the abandonment tool  10  is carried out by manipulating the tubing string  94 , the container assembly  14 , and the mandrel  38  so that they together form a unit. As shown in  FIG. 6A , the tool  10  is conveyed downhole to a sealing location, in this case above the casing plug  92 . A conventional casing or bridge plug is already in place or set at depth and the casing above it is pressure tested to establish that the casing and the plug itself is competent. 
     In  FIG. 6B , the tubing string  94  is rotated to shear frangible pins associated with the conventional upper slip assembly  48 . An upper cone or expander  100  of the upper slip assembly  48  threadably ascends the mandrel  38  and biases the upper slips  102  into locking engagement with the adjacent casing  74 . The upper slip assembly  48  axially fixes the upper compression plate  44  of the stack. 
     In  FIG. 6C  and  FIG. 5B , fluid pressure from surface, such as water, drives the piston  35  into the chamber  32 , pressurizing the sealant  15 A and rupturing the frangible disc  70  to dispense sealant out of the downhole end of the tool. Sealant encounters the casing plug  92  and flows up about the pleated rings  40  of the tool  12  and into the tool annulus  90 . The stack  24  of rings has an uncompressed height of L 0 . 
     In the embodiment in which the sealant is hot asphaltic sealant, the sealant rises within the annular space, floods the stack and also transfers heat to the adjacent section of casing wall. 
     With reference to  FIG. 6D , upward movement of the mandrel  38 , actuated by pulling up on the tubing string  94  drives the lower compression plate  46  uphole, compressing the stack  24 . The lower slip assembly  50  and compression plate  46 , moving with the mandrel unit, compress the stack  24  sufficiently so as to cause the pleated rings  40  to partly flatten, expand radially, and press against the adjacent casing wall to effect a metal-to-metal circumferential compression and frictional engagement with the casing  74 . The mandrel  38  is forcibly moved uphole through the fixed uphole slips  102 . 
     As shown in  FIG. 6E , as the axial pull is increased, and the stack of  24  pleated rings  40  compresses to a axial threshold compression, frangible pins of the lower slip assembly shear allowing the mandrel  38  to move uphole a further increment so that the lower slip assembly  50  can ascend a lower cone or expander  104 , and expand so that the lower slips  106  are biased into locking engagement with the casing  74 . The stack of pleated rings is fixed in a compressed state with a stack height of L 1 . 
     Later in the process, at  FIGS. 6F and 6G , further pulling or rotation of the tubing/string mandrel unit causes a separation shear pin associated with the unit to part at  FIG. 6F , allowing the container assembly  14  and tubing string  94  to separate from the mandrel  38  and be pulled out of hole. After the conveyance tubing string  94  is removed from the well, the tool  12  of compressed rings  40  and sealant  15 A seal the casing in the abandoned well. 
     Turning more detail to the tool structure, and with reference to  FIGS. 7A and 8A , the mandrel  38  can be fluidly connected to a casing plug  92 . The casing plug  92  can be conveyed downhole with the tool  12  rather than relying on any pre-existing plug. The casing plug  92  can comprise a housing  110  connected to a downhole end  112  of the mandrel  38 , the housing  110  having a plug bore  114 , contiguous with that of the mandrel, and external packer cups  116  for sealing to the casing. The plug housing  110  has one or more ports  118  for fluid communication between the plug bore  114  and the tool annulus  90 . In operation, the sealant is discharged through the bore of the mandrel, and through a one way flapper valve. The bore of the casing plug fills with sealant, which then overflows to the casing bore and uphole into stack of pleated rings and tool annulus. An alternate form of packer cup plug  92 , such as a casing packer shoe, is illustrated on  FIG. 8A  in elevation view. 
     Once the sealant has been discharged, the flapper valve closes to prevent post-discharge backflow up the mandrel. The sealant sets and ensures the flapper valve is permanently sealed. 
     As shown in  FIGS. 7A  (with the rings omitted) and  7 B, the mandrel  38  can be fit with a pair of sleeves  120  to add variability in mandrel diameter to accommodate various casing sizes. The sleeves can also aid in movement of the rings axially along the mandrel during compression. The pair of sleeves are fit with circumferentially-spaced interlocking fingers  122 . The fingers of upper sleeve  122 T are circumferentially and alternating interspersed with the fingers of lower sleeve  122 B. The lower sleeve  122 B can slide or shift uphole with the lower portion of the rings in the stack  24  as they are driven uphole along the mandrel  38 . 
     Turing to  FIGS. 8B through 9C , illustrating the steps of fixing the tool  12  in the casing (NOT shown) and actuating the stack  24  of pleated rings  40 , the tool is shown in four stages of operation, the sealant container assembly and casing plug omitted. With reference to  FIG. 8B , the tool  12  is in run-in-mode, with the upper slip  102  disengaged and the expander cone  100  releasably secured to the mandrel  38 . In  FIG. 9A , the mandrel  38  is rotated, shearing the frangible pin  126 , and the expander cone  100  is threadably-driven uphole, the cone&#39;s ramp engaging the slips  102  and driving them outwardly to engage the casing and fix the tool at the desired sealing location. Depending on any preload in the pleated rings  40 , an axial gap g can open between the expander cone  100  and the stack  24 . A downhole face  128  of the cone  100  also serves as the upper stop or compression plate  44  currently idle. 
     In  FIG. 9B , the mandrel  38  is actuated to be pulled uphole. The lower expander cone  104  is releasably secured to the mandrel and follows the mandrel uphole. An uphole face  130  of the lower cone  104  also serves as the lower stop or lower compression plate  46  for the stack  24 . As the mandrel  38  is pulled uphole, the lower compression plate  46  compresses the stack  24  of rings  40  against the upper compression plate  44 , shortening the height of the stack  24  and expanding them radically outwards to the casing. The mandrel  38  drags through a ratcheting mandrel-to-expander interface  132 , the components for which are shown in  FIGS. 10A, 10B and 10C . 
     In  FIG. 9C , when the resistance of the stack compression reaches a threshold, the force on the lower compression plate  46 , the expander cone  104  in this embodiment, overwhelms a first lower frangible pin  134 , and the mandrel is axially released therefrom. The mandrel drags the lower slips  106  uphole onto the expander  104 . The slips  106  are axially secured to the mandrel and axially movable therewith, as illustrated, such as by engaging a sub box end  136  threaded to the downhole end of the mandrel. The lower slips  106  are forcibly driven axially uphole to engage the lower cone&#39;s ramp, driving them outwardly to engage the casing and fix the stack compression. A secondary lower frangible pin  138  is provided that can release the mandrel from the lower slip assembly  50  in its entirely in an emergency. So that the secondary lower pin  138  can survive the shearing of the first lower pin  134 , the second pin is secured in a slot  140  in the mandrel to permit the mandrel axial movement to set the lower slips  106 , but remain engaged with the mandrel  38 . 
     As discussed above, in the illustrated embodiment, and shown in  FIGS. 10A, 10B and 10C , the upper slips  102  are actuated via threaded interface. 
       FIG. 10B  illustrates an axially split threaded ring  142 , and  FIG. 10C  illustrates the conical expander  100 , actuated axially by mandrel rotation of the threaded ring  142  therein to engage the slips  102 . 
     With reference to  FIG. 10A , finger slips are collet mounted, circumferentially arranged slips that extend downhole from a ring base  138  and are supported on a tubular sub on or above the mandrel  38 . The slips  102  can resist axial movement during actuation such as by conventional drag blocks, not shown. In  FIG. 10B , the axially split, dual threaded sleeve  142  is provided between the expander  100  cone of  FIG. 10C  and the mandrel  38 . An outer coarse-threaded portion  144  is threadably engaged with an internal thread  146  of the expander cone  100 . Rotation of the expander cone  100  relative to the threaded sleeve  142  drives the cone ramps  148  uphole into the slips  102 . The internal threads  150  are fine, asymmetrical threads that frictionally engage the mandrel. The mandrel need not be fit with complementary threads. The fine threads  150  have an uphole cant, also acting as a ratchet to enable a one-way uphole movement of the mandrel when actuated. 
     During actuation of the upper slip  102 , rotation of the mandrel  38  rotates the threaded sleeve  142 , and drives the expander cone  100  upwardly. The fine internal threads  150  of the sleeve may or may not rotate, but a reverse thread also enables uphole movement of the threaded sleeve, albeit at a slower rate due to the fine pitch. A rotation of about 6 turns can actuate the slips  102 . 
     With reference to  FIGS. 11A through 11F , in another embodiment, the casing  74  may have perforations therethrough to the annulus, or as illustrated, access to the annulus can be created. The sealing location for the tool can be aligned with existing perforations in the casing, perforations can be created, or the casing can be cut about all or a portion of its girth to access the casing annulus  162  thereout. 
     As shown in  FIG. 11A , a cutting tool  164  can be run in to depth and the casing cut. As shown, an abrasive cutting tool can be run in on a conveyance string  94  to the sealing location. Fluid with abrasives therein can be jetted out towards the casing  74 . In an embodiment, the cutting tool or the conveyance string  94  can be rotated to perforate or cut access ports  160  about a portion or the entirety of the casing about its girth at the sealing location. As shown in  FIG. 11B , the cutting tool  164  is pulled out of hole, with the annulus  162  outside the casing accessed through the access ports  160 . 
     Turning to  FIG. 11C , an embodiment of the current abandonment tool  10  can be run in to the sealing location. If a casing plug  92  was not already in place below the sealing location, the tool  12  could be fit with a casing plug shoe. At  FIG. 11D , the upper locking assembly  48  of the tool is locked to casing  74  with the tool adjacent the cut, or straddling the cut or access ports  160  as shown. As shown in  FIG. 11E , sealant  15 A is discharged to the casing bore  72 . The sealant is not only discharged about the tool annulus, but is also discharged through the access ports  160  formed in the casing and into the casing annulus. 
     In  FIG. 11F , the tool  12  is actuated and the stack  24  of pleated rings is compressed. Accordingly, as the casing annulus  162  is typically cement  166 , the remediation of any fluid leak paths is two-fold: by mechanical expansion of the casing itself, and sealant flowing into and along any defects in the cement.