Abstract:
An apparatus and method for generating a drive force in a downhole environment includes chambers of a reactant and a catalyst, respectively, that are maintained separate until selectively exposed to one another. Once exposed, the reactant and catalyst produce expanding fluid pressure and sometimes heat. The products of the reaction are directed to a drive member to carry out a desired operation in the downhole environment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.K. Patent Application No. 0509465.1, filed May 10, 2005, which is incorporated by reference in its entirety.  
       BACKGROUND  
       [0002]     The present invention relates to a downhole tool for, and a method of, generating a drive force in a downhole environment. In particular, but not exclusively, the present invention relates to downhole tools for generating rotary and axial drive forces in a downhole environment.  
         [0003]     Tools for generating a drive force in a downhole environment are known in the oil/gas industry. These include downhole motors, turbines and setting tools. Turbines are fluid driven and are run on a string of tubing, with associated fluid circulation apparatus at surface. Whilst this is an effective procedure for most drilling applications, it is time-consuming and expensive for secondary drilling applications, such as removing an obstruction in a borehole or de-scaling and hydrate removal procedures.  
         [0004]     Setting tools are used to generate a force to set tools such as plugs, packers and the like, which are initiated by a tensile/compressive load. One known setting tool is the pyrotechnic setting tool which generates high forces by ignition/detonation of a pyrotechnic charge. The pyrotechnic charge is housed in a pressure-tight piston chamber, and detonation generates a controlled burn, releasing gases which generate significant pressure in the chamber. This pressure acts on a piston which “strokes”, generating a high force, similar to a hydraulic ram, and this force is applied directly to the tool to be set. There are many disadvantages associated with pyrotechnic tools. For example, pyrotechnic charges are require delicate handling under very stringent regulations. Export/import of explosives into and out of certain regions of the world is prohibited. Use of the tool involves significant risks to personnel and structures. An electrical charge is required to ignite or detonate the charge and this limits use of the tool mainly to electric wireline applications. In such applications, radio silence must be enforced in the vicinity of the setting tool during deployment. If the setting tool is deployed on slick wireline, a battery operated trigger or detonator is required which operates on a timer basis, limiting its uses. Finally, failure of the charge to properly detonate creates a significant handling problem.  
       SUMMARY  
       [0005]     According to a first aspect of the present invention, there is provided a downhole tool for generating a drive force in a downhole environment, the tool including: a chamber for storing a reactant; activating means for activating the reactant; and isolation means for isolating the activating means from the reactant, and for selectively exposing the activating means to the reactant to activate the reactant and generate a drive medium for driving a drive member to generate the drive force.  
         [0006]     Advantageously, this provides a downhole tool which may be used to generate a drive force when required, by exposing the activating means to the reactant. The tool may therefore be located downhole before activating the reactant to generate the drive force, for carrying out a desired downhole procedure. Furthermore, the tool can be easily pulled out of hole for replenishment of the reactant or replacement of the activating means.  
         [0007]     The downhole tool may be, for example, a setting tool; a fishing tool; a cutting tool such as a casing or tubing cutter, a mill, a drill, or a tubing/casing clean-up or de-scaling and hydrate removal tool; a wireline or coiled tubing tractor; or an artificial lift tool for driving a pump.  
         [0008]     Preferably, at least part of the isolation means is movable to expose the activating means to the reactant. In particular, at least part of the isolation means may be moveable between at least an isolation position where a barrier is defined between the activating means and the reactant, and an exposed position, where the activating means is exposed to the reactant. The isolation means may include a movable member and may further include a seal for isolating the activating means from the reactant. The seal may be fixed relative to a body of the tool and the activating means may be coupled to the movable member for moving the activating means into the reactant chamber. Alternatively, the seal may be movable relative to the movable member and the movable member may be movable to release the seal and expose the activating means to the reactant.  
         [0009]     Conveniently, the downhole tool is a one-shot tool for use downhole and subsequent return to surface for replenishment of the reactant and/or the activating means. Alternatively, the downhole tool may be a multi-shot tool; this may allow a number of downhole procedures to be carried out before the tool is required to be returned to surface for replenishment. It will be understood that this may be achieved by selectively isolating and exposing the activating means a number of times downhole.  
         [0010]     Preferably, the downhole tool includes the drive member. The drive member may comprise a rotatable drive member or a member for generating an axial force such as a piston. The rotatable member may in particular comprise a turbine rotor, or a rotor of a motor, such as a positive displacement motor (PDM). Alternatively, the drive member may be separate from the downhole tool, and may form part of a secondary tool.  
         [0011]     Preferably, the reactant comprises a chemical reactant such as an oxidising agent, in particular hydrogen peroxide (H 2 O 2 ), and the activating means comprises catalyst means such as a copper, iron or other metal based catalyst. In particular, the catalyst means may comprise copper or iron sulphate. Thus when the copper/iron based catalyst is exposed to the hydrogen peroxide, the drive medium generated comprises oxygen, and water in the form of steam as the reaction is exothermic. Accordingly, the generated drive medium may comprise a fluid, in particular a gas, liquid, or vapour.  
         [0012]     The movable part of the isolation means may be moveable in response to an applied external force, which may be generally axially directed. The movable part of the isolation means may be directly or indirectly moveable; in particular, it may be adapted to be moved relative to a body of the tool by a force exerted directly on the moveable part. Alternatively, the movable part may be adapted to be moved relative to the body by a force exerted on the tool body. The drive member itself may define the moveable part of the isolation means, and the activating means may be coupled to the drive member, such that movement of the drive member moveable exposes the activating means to the reactant. Alternatively, the moveable part of the isolation means may be moveable by application of a fluid pressure force.  
         [0013]     The tool may be adapted to be run on, in particular, wireline or coil tubing for ease and speed of deployment. However, the tool may be adapted to be run on any suitable means such as drill or completion tubing or the like.  
         [0014]     The downhole tool may include a vent for venting spent drive medium out of the tool. The downhole tool may further comprise a pressure relief valve for controlling the venting of spent drive medium from the downhole tool in the event of the pressure of the drive medium reaching a determined threshold value.  
         [0015]     According to a second aspect of the present invention, there is provided a downhole tool for generating a rotary drive force, the tool having: a chamber for storing a reactant; activating means for activating the reactant; isolation means for isolating the activating means from the reactant, and for selectively exposing the activating means to the reactant to activate the reactant and generate a drive medium; and a rotatable drive member adapted to be driven by the drive medium to generate the rotary drive force.  
         [0016]     Preferably, the downhole tool is a turbine or a motor, such as a positive displacement motor (PDM). Advantageously, the invention provides a turbine or motor, which does not require a motive fluid to be supplied from surface. Instead, the turbine/motor can be located downhole and the activating means exposed to the reactant, to generate the drive medium downhole for driving the rotatable drive member. The downhole tool may in particular comprise or form part of, for example, a setting tool; a cutting tool such as a casing/tubing cutter, a milling tool, a drilling tool, a tubing/casing clean-up or de-scaling and hydrate removal tool; a linear propulsion tool such as a wireline or coiled tubing tractor; and an artificial lift tool.  
         [0017]     Preferably, the rotatable drive member comprises a rotor. The tool may include a tool body defining the reactant chamber. At least part of the isolation means may be moveable relative to a body of the tool to expose the activating means to the reactant. The movable part of the isolation means may comprise a support member and the activating means may be coupled to the support member for moving the activating means into the reactant chamber. The isolation means may further comprise a seal for isolating the activating means from the reactant. The seal may be located in a wall of the reactant chamber and the activating means may be moveable from an isolated position outside the chamber to an exposed position inside the chamber.  
         [0018]     The downhole tool may include a tool connection member through which a force may be exerted on the moveable part of the isolation means, to expose the activating means to the reactant. The connection member may be coupled to the body of the tool and the may be initially restrained from movement with respect to the body until a determined release force is exerted thereon. The connection member may be initially restrained by shearable restraints, such as release screws or pins which may be adapted to shear at the determined release force.  
         [0019]     The downhole tool may further include a fluid medium outlet for directing generated fluid medium to exit the reactant chamber to impinge on and drive the rotatable drive member. The outlet may be closed by the activating means and/or the movable support member when the activating means is isolated from the reactant and may be open when the activating means is exposed to the reactant. Thus a rotary drive force may be generated, and through a suitable coupling with a secondary tool, such as a drill bit, a desired downhole procedure may be carried out. The downhole tool may further include at least one vent for venting spent drive medium from the tool.  
         [0020]     According to a third aspect of the present invention, there is provided a downhole tool for generating a force in a downhole environment, the tool having:a chamber for storing a reactant; activating means for activating the reactant; isolation means for isolating the activating means from the reactant, and for selectively exposing the activating means to the reactant to activate the reactant and generate a drive medium; and a piston member adapted to be driven by the drive medium to generate the force.  
         [0021]     Preferably, the downhole tool is a setting tool or an impact hammer. However, the tool may be, for example, a fishing tool; or a cutting tool such as a tubing or casing cutter, wireline sidewall cutter, crimper or the like. The tool may be for generating an axial force and thus the piston member is preferably axially movable. The generated force may be a compressive or tensile force. In use, the downhole tool may advantageously be latched to a secondary tool such as a plug, packer, gauge hanger, anchor or any other similar device, before the activating means is exposed to the reactant. This generates the drive medium, to drive the piston member and exert a setting or jarring force on the secondary tool.  
         [0022]     At least part of the isolation means may be moveable relative to a body of the tool to expose the activating means to the reactant. Preferably, the piston member defines the moveable part of the isolation means, and the activating means may be mounted on or in the piston member. Alternatively, the piston member may be separate from the isolation means. The piston member may be movable in a first direction to at least partly expose the activating means to the reactant. The downhole tool may include a tool connection member coupled to the body of the tool for exerting a force on the tool to relatively move the piston member in the first direction, to initiate the reaction. The piston member may also be moveable in a second direction opposite said first direction under the force of the generated drive medium acting on the piston, to generate the force. The reaction causes rapid movement of the piston relative to the tool body in said second direction, to generate a relatively large compressive or tensile force. The downhole tool may include at least first and second couplings for coupling the tool to a secondary tool, for exerting a force on the secondary tool directed between the respective couplings. The piston member may include or define one of the first and second couplings and the tool body may define the other coupling.  
         [0023]     The isolation means may further include an activation sleeve which may be movable relative to the activating means, for selectively isolating the activating means from the reactant. The activation sleeve may be at least partly restrained against movement with the piston member in said first direction to at least partly expose the activating means to the reactant. The isolation means may also comprise a reactant release sleeve defining a primary barrier to isolate the activating means from the reactant. The release sleeve may be moveable to expose the activating means to the reactant following movement of the piston member in said first direction. The tool may further have a vent for allowing movement of the piston member in said second direction, the vent preventing hydraulic lock-up. The tool may also have a reactant filling port for reactant replenishment. The filling port may include a pressure release valve for allowing venting of spent drive medium from the chamber in the event of the tool experiencing over-pressure during the reaction. Further features of the reactant and the activating means of the second and third aspects are defined above in relation to the first aspect of the present invention.  
         [0024]     According to a fourth aspect of the present invention, there is provided a downhole tool assembly comprising the downhole tool of any one of the first to third aspects of the present invention.  
         [0025]     Further features of the downhole tool are defined above with reference to the first to third aspects of the invention.  
         [0026]     According to a fifth aspect of the present invention, there is provided a method of generating a drive force in a downhole environment, the method comprising the steps of: providing a downhole tool having a reactant and activating means for activating the reactant; isolating the activating means from the reactant to initially prevent the activating means from activating the reactant; locating the tool in a downhole environment; exposing the activating means to the reactant to activate the reactant and generate a drive medium; and directing the generated drive medium to drive a drive member and generate the drive force.  
         [0027]     The downhole tool is preferably charged with reactant at surface and the reactant is isolated from the activating means by sealing the activating means with respect to the reactant. The method may be implemented in a one-shot operation, including the step of removing the downhole tool from the downhole environment after exposure of the activating means to the reactant and optionally recharging the downhole tool with reactant for subsequent further use. Alternatively, the method may further include the step of re-isolating the activating means from the reactant in the downhole environment, to prevent further reaction. Thus the method may further be used in a multi-shot operation which may also include the step of re-exposing the activating means to the reactant, to re-activate the reactant. This may allow further downhole procedures to be carried out before the tool is removed from the downhole environment.  
         [0028]     The activating means may be exposed to the reactant by applying an external force to the downhole tool. The activating means may be coupled to a moveable member of the tool and a force may be exerted on the moveable member to expose the activating means to the reactant. The downhole tool may be suspended from a tool connection member coupled to the moveable member, and a force may be exerted on the tool connection member and thus on the moveable member to move the activating means to expose it to the reactant. The method may further include the step of exerting a determined force on the support member to expose the activating means to the reactant, to overcome a restraining force exerted on the tool connection.  
         [0029]     Alternatively, the method may further include the step of coupling the activating means to the drive member and moving the drive member in a first direction, to expose the activating member to the reactant, to activate the reactant. The generated drive medium may move the drive member in a second, opposite direction to generate the drive force. The drive force may be exerted on a secondary tool coupled to the downhole tool and may be a compressive or tensile load. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0030]     Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0031]      FIG. 1  is a schematic illustration of a downhole tool assembly including a downhole tool in accordance with a first embodiment of the present invention, shown in a downhole environment;  
         [0032]      FIGS. 2A and 2B  are enlarged, longitudinal sectional and sectioned perspective views, respectively, of the downhole tool of  FIG. 1 , shown in a run-in-hole (RIH) position;  
         [0033]      FIGS. 3A and 3B  are views similar to  FIGS. 2A and 2B , but showing the downhole tool in an in-use position;  
         [0034]      FIG. 4  is a longitudinal sectional view of a downhole tool in accordance with an alternative embodiment of the present invention, and shown in a RIH position;  
         [0035]      FIG. 5  is a view of the downhole tool of  FIG. 4  in an activated position; and  
         [0036]      FIG. 6  is a view of the downhole tool of  FIG. 4 , in a fully stroked position, following activation as shown in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION  
       [0037]     Turning firstly to  FIG. 1 , there is shown a schematic illustration of a downhole tool assembly, in the form of a drilling assembly indicated generally by reference numeral  10 . The drilling assembly  10  includes a downhole tool  12  in accordance with a first embodiment of the present invention, which in  FIG. 1  is a downhole tool for generating a rotational drive force, in the form of a turbine. The turbine  12  is located in a borehole  14  which has been lined at  16  and cemented at  18 , in a fashion known in the art. The turbine  12  is run into the borehole  14  on coiled tubing  20 , and a drill bit  22  is coupled to and driven by the turbine  12 . The drilling assembly  10  has particular uses in removing obstructions within the lined borehole  14  and in de-scaling/hydrate removal.  
         [0038]     Turning now to  FIGS. 2A and 2B , there are shown enlarged longitudinal sectional and sectioned perspective views, respectively, of the turbine  12  of  FIG. 1 , shown in a RIH position. The turbine  12  generally comprises a chamber  22  for storing a chemical reactant  23 , activating means in the form of catalyst means  24  for activating the reactant, isolation means indicated generally by reference numeral  26  and a drive member  28 . The isolation means initially isolates the catalyst means  24  from the reactant  23 , but also allows the catalyst means  24  to be selectively exposed to the reactant  23 . This activates the reactant  23 , generating a drive medium for driving the drive member  28 , to in-turn generate a drive force.  
         [0039]     In more detail, the turbine  12  has an outer body  30  which defines the chamber  22 . The isolation means includes a floating piston  32 , a fixed seal  34  and a movable member in the form of a support rod  36 . The body  30  has a male pin end  38 , by which the turbine  12  is coupled to the coiled tubing  20 , and a tool connection member  40  extends through the end  38  and is secured to the support rod  36 . The tool connection member  40  is initially restrained from movement by shearable release screws  42  which secure it to the outer body  30 .  
         [0040]     At a lower end of the tool (to the right in  FIGS. 2A and 2B ), the drive member  28 , which takes the form of a turbine rotor, is mounted in a rotor housing  44 . A lip  46  of the seal  34  is held between the body  30  and rotor housing  44 , to hold the seal  34  in place. The rotor  28  has a lower male pin end  48  for coupling to the drill bit  21 . A number of vent ports  50  are spaced around a circumference of the rotor housing  44  (two shown in FIGS.  2 A/ 2 B), and these allow venting of spent drive medium from the turbine  12 .  
         [0041]     The reactant  23  in the chamber  22  is an oxidising agent, in particular hydrogen peroxide (H 2 O 2 ), whilst the catalyst means  24  typically takes the form of an iron or copper catalyst, such as iron or copper sulphate. In the RIH position of FIGS.  2 A/ 2 B, the catalyst  24  is isolated from the reactant  23  by the fixed seal  34 , through which the support rod  36  protrudes, and an O-ring  52  seals the outer surface of the rod  36 . The turbine  12  is maintained in this configuration until the drilling assembly  10  has been run into the borehole  14  to the desired location, where it is required to carry out a drilling operation.  
         [0042]     To activate the turbine  12 , the tool connection  40  is engaged and pulled to shear the release screws  42 , as shown in  FIGS. 3A and 3B . This draws the catalyst  24  into the chamber  22 , where it is exposed to the H 2 O 2  reactant  23 . A collar  54  on the support rod  36  abuts an end face  56  of the chamber  22 , to restrain the rod  36  against further movement. As the support rod  36  moves, the floating seal  32  is carried with it, urged against the collar  54  by the pressure of the generated drive medium. Hydraulic lock of the floating piston  32  is prevented by the provision of bleed ports  58  in the outer body  30 , which allow bleed of fluid from the region  60  of the chamber  22  to annulus.  
         [0043]     When the catalyst  24  is exposed to the H 2 O 2 , an exothermic reaction takes place and the H 2 O 2  decomposes into oxygen and steam, constituting the drive medium. The generated drive medium is directed through an outlet passage  62  in the fixed seal  34 , which has been opened by movement of the rod  36 , and is thus jetted onto the rotor blades  64  of the rotor  28 , which is rotated to in-turn drive the drill bit  21 . Spent drive fluid discharges through the vent ports  50  to annulus, as indicated by the arrows A in  FIG. 3A . When the supply of H 2 O 2  has been used, the reaction ceases such that no further drive fluid is generated and the rotor  28  stops rotating. Accordingly, the chamber  22  is sized to contain sufficient H 2 O 2  to carry out the desired drilling operation, as specified above. The downhole tool assembly  10  is then pulled out of hole (POOH) for replenishment of the H 2 O 2  reactant  23 .  
         [0044]     Turning now to  FIGS. 4-6 ,  FIG. 4  shows a longitudinal sectional view of a downhole tool in accordance with an alternative embodiment of the present invention, shown in a RIH position, the tool indicated generally by reference numeral  112 . The tool  112  is suitable for generating a force in a downhole environment, in particular an axial force. Like components of the tool  112  with the tool  12  of  FIGS. 2A-3B  share the same reference numerals, incremented by  100 . The setting tool  112  is run on a string of coiled tubing or wireline, in a similar fashion to the turbine  12 . The tool  112  takes the form of a setting tool for exerting a setting force on a secondary tool, such as a plug or packer, or for locking gauge hanger anchors or any other downhole tool requiring a relatively high compressive or tensile load to set. The setting tool  112  includes a chamber  122  for storing H 2 O 2  reactant  123  and a catalyst  124 . Isolation means  126  isolates the catalyst  124  from the H 2 O 2    123 , in a similar fashion to the turbine  12 . A piston member  66  is driven by drive medium generated when the catalyst  124  is exposed to the reactant  123 , to generate an axially directed force.  
         [0045]     In more detail, the setting tool  112  has an outer body  130  and a tool connection  140  coupled to the body  130  by a threaded joint  68 . The piston member  66  is movably mounted in the casing  130  and defines a moveable member of the isolation means  126 . A lower end (right side in  FIG. 4 ) of the body  130  carries a male threaded coupling  70  for connecting the setting tool  112  to a secondary tool to be set. Similarly, the piston member  66  includes a coupling  72  for coupling the piston  66  to the secondary tool at a second location. As will be described below, this allows a force to be exerted between the two couplings  70  and  72 , to exert a tensile (or compressive) setting force upon the secondary tool.  
         [0046]     An upper end (left hand side in  FIG. 4 ) of the piston  66  carries a sliding O-ring seal  74  and the body  130  includes a number of circumferentially spaced bleed ports  158 , to prevent hydraulic lock of the piston  66 . The catalyst  124  comprise a ring located in a groove  76  in the piston  66 . O-ring seals  78  and  80  straddle the catalyst  124 , sealing against an activation sleeve  82  of the isolation means  126 . The isolation means  126  also includes a reactant release sleeve  84  which, in the RIH position of  FIG. 4 , acts as a primary barrier to isolate the catalyst  124  from the reactant  123 , by sealing against a shoulder  86  in the body  130  through an O-ring seal  88 . The body  130  also includes a reactant filling port  90  in which a pressure relief valve  92  is mounted. This both allows the reactant  123  to be replenished when the tool is POOH after the downhole procedure has been completed, and allows bleed of reactant  123  and/or generated drive medium in the event of over-pressure during the reaction. The setting tool  112  is secured through the couplings  70  and  72  to the secondary tool to be set.  
         [0047]     The reaction is initiated by exerting a pull on the body  130 , as shown in  FIG. 5 . This causes a movement of the piston  66  relative to the casing  130  in a first direction indicated by the arrow B. During this movement, the activation sleeve  82  is restrained against movement with the piston  66  by the shoulder  86 , and this uncovers the catalyst  124 . In addition, the reactant release sleeve  84  is carried out of sealing engagement with the shoulder  86  by a shoulder  87  of the piston  66 , and the catalyst  124  is then fully exposed to the reactant  123 , to initiate the reaction.  
         [0048]     As shown in the fully activated position of  FIG. 6 , this causes the piston  66  to move rapidly upwardly in the direction of the arrow C, under the forcing action of the generated drive medium. During this movement, the piston  66  expels fluid from the region  160  in the body  130  through the bleed ports  158 . Thus, a high tensile setting force is exerted on the secondary tool as the distance between the first and second couplings  70  and  72  is rapidly shortened. This sets the secondary tool and the setting tool  112  is then disconnected and POOH. The H 2 O 2  reactant  123  may then be replenished through the filling port  90  for subsequent further use of the setting tool.  
         [0049]     Various modifications may be made to the foregoing within the scope of the present invention. For example, the tool  12  has uses in other downhole tool assemblies, such as cutting tools. These cutting tools include milling tools and tubing cutters, where centrifugal blades are fitted to the turbine  12  and are rotated to expand outwards to effect a circular cutting motion, used to cut or profile a wellbore tubular. The turbine  12  may also be used as a setting tool, for setting secondary downhole tools, as an artificial lift tool, or as a linear propulsion tool, fitted to a tractor device for propelling tools, gauges and the like along deviated or horizontal sections of wellbore.  
         [0050]     The tool  112  may be used to retrieve tools lodged in a borehole by exerting a high pulling or impact force on the tool. Also, attachments may be provided such as tubing cutters, wireline sidewall cutters, crimpers or the like activated by the axial force generated by the tool.  
         [0051]     The downhole tools may thus be used for displacing tools lodged in boreholes, or for the removal of sedimentary deposits or any other obstruction, through associated cutting/impact assemblies.