Abstract:
The present invention generally relates to an apparatus and method of jarring with an overpull generator. In one aspect, a method of dislodging an object stuck in a wellbore is provided. The method includes the step of running an assembly into the wellbore on a conveyance member and attaching the assembly to the object, wherein the assembly comprises an overpull generator and a delay force release device. The method also includes the step of generating an overpull force in the wellbore by selectively activating the overpull generator. Additionally, the method includes the step of applying an impact force to the object by activating the delay force release device and releasing the generated overpull force, thereby dislodging the object stuck in the wellbore. In a further aspect, an assembly for dislodging an object stuck in a wellbore is provided. In yet a further aspect, an overpull generator for use in generating an overpull force in a wellbore is provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to an apparatus and methods for generating a downhole overpull force. More specifically, the present invention relates to jarring with a downhole overpull generator. 
     2. Description of the Related Art 
     In a conventional downhole fishing operation, a bottom hole assembly is lowered into a wellbore on a drill string. The bottom hole assembly typically includes a slinger, a jar, and a fishing tool (such as an overshot) that are connected via drill collars and drill pipe. A jar is a device that is used downhole to deliver an impact load to another downhole component, especially when that object is stuck in the wellbore. The jar generally includes a device for storing energy (e.g. a spring or a pressure chamber) and a triggering device that is configured to activate the jar at a predetermined instant, thereby allowing the jar to deliver the impact load. 
     During the fishing operation, the bottom hole assembly is lowered into the wellbore and attached to the object stuck in the wellbore by utilizing the fishing tool. Thereafter, a rig at the surface of the wellbore is used to pull up on the drill string, imparting a force on the drill string and storing the created energy in the slinger and the drill string. At a predetermined pull force and/or time, the triggering device in the jar activates the jar, thereby causing the jar to deliver the impact load to the object stuck in the wellbore. 
     The use of a bottom hole assembly in a conventional fishing operation may be effective in dislodging an object stuck in a vertical wellbore since the rig is able to pull up on the drill string and generate the energy for use with the jar. However, a problem arises when the same bottom hole assembly is used in a deviated wellbore. In this situation, the rig is not fully pulling up on the drill string and generating the energy for use with the jar due to the curvature and the associated friction between the drill string and the wall of the wellbore. 
     Therefore, there is a need for a device and a method of generating a overpull force downhole. There is a further need for a device and a method of fishing with a downhole overpull generator. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to an apparatus and method of fishing with an overpull generator. In one aspect, a method of impacting an object in a wellbore is provided. The method includes the step of running an assembly into the wellbore on a conveyance member and attaching the assembly to the object, wherein the assembly comprises an overpull generator and a delay force release device. The method also includes the step of generating an overpull force in the wellbore by selectively activating the overpull generator. Additionally, the method includes the step of applying an impact force to the object by activating the delay force release device and releasing the generated overpull force, thereby dislodging the object stuck in the wellbore. 
     In another aspect, a method of freeing an object stuck in a wellbore is provided. The method includes the steps of generating an overpull force downhole and storing the overpull force downhole. The method also includes the step of selectively releasing the overpull force in the wellbore and applying a force to the object to free the stuck object. 
     In a further aspect, an assembly for dislodging an object stuck in a wellbore is provided. The assembly includes an overpull generator configured to generate an overpull force in the wellbore. The assembly also includes a delay force release device configured to selectively release the overpull force and apply an impact force. Additionally, the assembly includes a coupling member configured to attach to the object stuck in the wellbore. 
     In yet a further aspect, an overpull generator for use in generating an overpull force in a wellbore is provided. The overpull generator includes a housing having a section configured to transmit torque. The overpull generator further includes a series of fluid actuated pistons disposed in the housing. The overpull generator also includes a piston rod movable in the housing between a first position and a second position by utilizing the series of fluid actuated pistons, the piston rod having a section configured to transmit torque. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a view illustrating a bottom hole assembly disposed in a wellbore with a piston rod in an overpull generator in an extended position. 
         FIG. 2  is a view illustrating the bottom hole assembly disposed in the wellbore with the piston rod in the overpull generator in a retracted position. 
         FIG. 3  is a view illustrating the bottom hole assembly disposed in the wellbore after an object in the wellbore has been dislodged. 
         FIG. 4  is a sectional view of the overpull generator. 
         FIG. 5  is a cross-sectional view taken along line  5 - 5  in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention generally relates to an apparatus and method of jarring with an overpull generator. More specifically, the invention relates to a bottom hole assembly that includes an overpull generator that works in conjunction with a delay force release device to dislodge an object stuck in the wellbore. It is to be noted, however, that even though the overpull generator will be described in relation to the delay force release device, the present invention is not limited to a delay force release device, but is equally applicable to other types of downhole tools. Additionally, the present invention will be described as it relates to a deviated wellbore. However, it should be understood that the present invention may be employed in a vertical or a non-deviated wellbore without departing from the principles of the present invention. To better understand the novelty of the apparatus of the present invention and the methods of use thereof, reference is hereafter made to the accompanying drawings. 
       FIG. 1  is a view illustrating a bottom hole assembly  200  disposed in a wellbore  10  with an overpull generator  100  in an extended position. The bottom hole assembly  200  is generally used to dislodge an object  20  that is stuck in the wellbore  10 . As will be described herein, the bottom hole assembly  200  includes the overpull generator  100  configured to apply a force, a slinger  160  configured to store the energy, a delay force release device  150  configured to release the stored energy, and a coupling member  175  configured to grip the object  20 . The bottom hole assembly  200  may also include an optional anchor device  170  that is configured to secure the bottom hole assembly  200  in the wellbore  10 . 
     It should be noted that the overpull generator  100  is positioned in the bottom hole assembly  200  proximate the delay force release device  150 . This arrangement minimizes pulling force loss due to wellbore friction relative to the conventional fishing operation. In other words, in the conventional fishing operation, the drill string is pulled at the surface to create an overpull, however, this arrangement results in a relatively lower tension at the bottom hole assembly due to an interface  75  with the wellbore  10 . Furthermore, due to wellbore friction at the interface  75 , it may be hard to determine how much force is actually experienced at the bottom hole assembly in the conventional fishing operation which may reduce the effectiveness of the operation. Additionally, there is typically a limit to how much tension can be applied by some rigs/hoists, and a limit to the tensile rating of the drill string (or another type of conveyance member). However, by using the overpull generator  100  in the wellbore  10 , the overpull generator  100  enables these limitations to be circumvented by ensuring the necessary load is applied directly to the bottom assembly  200 . Additionally, not only is it possible to generate a higher load, but a known load can be applied based upon the known piston characteristics of the overpull generator  100 . Further, when the overpull generator  100  is used in combination with downhole instrumentation and optional data communication (e.g. wires, EM, mud pulse), the operational characteristics can be determined and then tailored to suit the situation in the wellbore  10 . 
     The overpull generator  100  is configured to create a force which is used by the other components in the bottom hole assembly  200  to dislodge the object  20 . The energy is generated by moving a piston rod  110  of the overpull generator  100  between an extended position and a retracted position, as shown in  FIGS. 1-3 . Although the bottom hole assembly  200  in  FIGS. 1-3  shows the overpull generator  100  in a downward position, the overpull generator  100  may be in an upward position, thereby reversing the direction of the actuation force and the release force without departing from principles of the present invention. Generally, the overpull generator  100  includes a plurality of pistons  125  that activate due to a pressure drop in the bottom hole assembly  200 . The overpull generator  100  will be described in greater detail in  FIGS. 3 and 4 . 
     The slinger  160  is configured to store energy that is generated by the overpull generator  100 . Generally, the slinger  160  is a tool that is used in conjunction with the delay force release device  150  to store energy that comes from the overpull generator  100 . An example of a slinger is set forth in U.S. Pat. No. 6,328,101, which is herein incorporated by reference in its entirety. The energy, once released by the slinger  160 , provides an impact force that operates associated downhole tools to help the release of the object  20  stuck in the wellbore  10 . The energy may be stored in the slinger  160  by any means known in the art, such as by a mechanical spring or a compressible fluid. 
     The delay force release device  150  is generally a device that releases energy after a certain period of time. The delay force release device  150  may be any type of device known in the art that is configured to release energy, such as a jar. An example of a jar is set forth in U.S. Pat. No. 6,202,767, which is herein incorporated by reference in its entirety. As known in the art, a jar is a device that is used downhole to deliver an impact load to another downhole component, especially when that component is stuck. The delay force release device  150  may be hydraulically activated by using a timer comprising a viscous flow meter, whereby at a predetermined over pull force generated by the overpull generator  100  a detent releases thereby allowing the delay force release device  150  to release. Alternatively, the delay force release device  150  may be mechanically activated by using a mechanical timer, whereby at a predetermined overpull force generated by the overpull generator  100  the mechanical timer allows the delay force release device  150  to release. Even though the respective designs may be different, each device uses energy that is stored in the slinger  160  and is suddenly released by the delay force release device  150  when it fires. 
     The delay force release device  150  can be designed to strike up, down, or both. In the case of jarring up above the stuck object  20 , as shown in  FIG. 1 , the slinger  160  and a plurality of drill collars  190 ,  195  are pulled upward by the overpull generator  100  but the stuck object does not move. Since the slinger  160  and the drill collars  190 ,  195  are moving up, this means that the slinger  160  and the drill collars  190 ,  195  are stretching and storing energy. When the delay force release device  150  reaches a predetermined overpull force, the delay force release device  150  suddenly allows one section of the delay force release device  150  to move axially relative to a second section, being pulled up rapidly in much the same way that one end of a stretched spring moves when released. After a few inches of movement, this moving section slams into a steel shoulder in the delay force release device  150 , imparting an impact load on the stuck object  20 . 
     The coupling means  175  is a tool that is capable of connecting to the object  20  in the wellbore  10 , such as an overshot. The coupling means  175  may be configured to engage on the outside surface of the object  20  stuck in the wellbore  10 . Typically, the coupling device  175  includes a grapple or similar slip mechanism that grips the object  20  such that a force and jarring action may be applied to the object  20 . If the object  20  cannot be removed, a release system within the coupling device  175  allows the coupling means  175  to be disengaged and retrieved. 
     The bottom hole assembly  200  optionally may include the anchor device  170 . The anchor device  170  may be positioned in the bottom hole assembly  200  above the overpull generator  100 . The anchor device  170  may include a slip mechanism that is configured to grip the walls of the wellbore  10  in order to secure the bottom hole assembly  200  in the wellbore  10 . In another embodiment, the anchor device may be part of the overpull generator  100 . 
     The bottom hole assembly  200  optionally may also include a vibration member (not shown). An example of a vibration member is set forth in U.S. Pat. No. 6,164,393, which is herein incorporated by reference in its entirety. The vibration member is used to generate vibration that works in conjunction with the impact force of the delay force release device  150  to dislodge the object  20  stuck in the wellbore  10 . The vibration member may generate the vibration by any suitable means known in the art, such as oscillating a moving mass, creating a cyclic restriction to fluid flowing through the bottom hole assembly  200 , an electromagnetic oscillator, creating pressure pulses in a fluid, or injecting gas, a liquid, or a combination thereof into fluid operatively associated with the device in the bottom hole assembly  200 . 
     The bottom hole assembly  200  may include a hydraulic or mechanical disconnect device (not shown) to allow the operator to disconnect from the object  20  and retry the downhole operation. An example of a disconnect device is described in U.S. patent application Ser. No. 11/842,837, which is herein incorporated by reference in its entirety. The use of the disconnect device allows the operator to disconnect and reconnect to the object  20  multiple times. 
     The bottom hole assembly  200  may include a sensing member (not shown) that is configured to measure a downhole parameter. In one embodiment, the sensing member may be configured to measure the impact force applied by the delay force release device  150  to the object  20 . In a further embodiment, the sensing member may be configured to measure the amount of force (i.e. energy) generated by the overpull generator  100 . In another embodiment, the sensing member may be configured to measure a torque, a direction of rotation and a rate of rotation of a component in the bottom hole assembly  200 . The sensing member may send the measured data to the surface via a communication line in the conveyance member  50 . Alternatively, the sensing member may send the measured data to a memory device in the bottom hole assembly  200  which is capable of storing the measured data until the data is retrieved when the bottom hole assembly  200  is removed from the wellbore  10 . Further, the sensing member may send the measured data to the surface via EM or mud pulse devices. The measured data may be used by an operator to effectively perform the downhole operation. For instance, the operator may use the data to tailor the downhole operation (or subsequent attempts) to dislodge the object  20  stuck in the wellbore  10 . 
     The bottom hole assembly  200  is disposed in the wellbore  10  on a conveyance member  50 . The conveyance member  50  may be any type of member that is capable of positioning the bottom hole assembly  200  in the wellbore  10 , such as a drill string, coiled tubing, Corod®, etc. 
     In operation, the bottom hole assembly  200  is positioned in the wellbore  10  to allow the coupling member  175  to attach to the stuck object  20 . Thereafter, the conveyance member  50  is pulled upward to remove any slack that may be in the in the conveyance member  50 . Next, the piston rod  110  is moved to the extended position by further pulling up on the conveyance member  50 . Alternatively, the bottom hole assembly  200  may be lowered into the wellbore  10  with the piston rod  110  in the extended position. In either case, the overpull generator  100  is in the extended position in order to generate the energy to be used by the delay force release device  150 . Subsequently, fluid is pumped down the conveyance member  50  into the overpull generator  100  to create a pressure differential which causes the pistons  125  in the overpull generator  100  to retract the piston rod  110 . The movement of the piston rod  110  from the extended position to the retracted position generates an overpull force (i.e. energy) that is stored in the slinger  160  and will be used to dislodge the object  20  stuck in the wellbore  10 . At a predetermined overpull force, the delay force release device  150  fires thereby releasing the energy stored in the slinger  160  and imparting an impact load on the stuck object  20 . The impact load may be 3 to 5 times the initial overpull force. Further, if the anchor member  170  is part of the bottom hole assembly  200 , then the anchor device  170  is set prior to the movement of the piston rod  110  from the extended position to the retracted position in order to support the overpull force generated by the overpull generator  100 . Additionally, if there is a vibrator in the bottom hole assembly  200 , then the vibrator may be activated when the fluid is pumped down the conveyance member  50  to create the pressure differential that activates the overpull generator  100 . 
     The movement of the piston rod  110  of the overpull generator  100  from the extended position to the retracted position generates an overpull force (i.e. energy) that will be used to dislodge the object  20  stuck in the wellbore  10 . The overpull generator  100  is activated by a pressure differential between the inside the overpull generator  100  and the outside the overpull generator  100 . The pressure differential causes the plurality of pistons  125  in the overpull generator  100  to retract the piston rod  110 . The pressure differential may be generated by regulating the flow rate through the overpull generator  100  or by using a restriction in the overpull generator  100 . If the pressure drop across the overpull generator  100  is not sufficient with the existing bottom hole assembly  200 , then an orifice sub (not shown) may be included in the bottom hole assembly  200 , and positioned below the overpull generator  100  in order to create the pressure differential required to activate the overpull generator  100  and move the piston rod  110  from the extended position to the retracted position. In one embodiment, the overpull generator  100  is activated at a predetermined threshold pressure differential. In this embodiment, the overpull generator  100  may include a frangible member (not shown), such as a shear screw, between components of the overpull generator  100 , wherein the frangible member is configured to shear (or break apart) at a predetermined pressure differential thereby allowing the pistons  125  to retract the piston rod  110 . Alternatively, the overpull generator  100  may include a biasing member (not shown), such as a spring, that is configured to bias the rod  110 , wherein at a predetermined pressure differential the biasing force of the biasing member is overcome thereby allowing the pistons  125  to retract the piston rod  110 . Further, the overpull generator  100  may include a combination of frangible members and biasing members. 
     Although the bottom hole assembly  200  in  FIGS. 1 and 2  illustrate a single overpull generator  100  attached to the delay force release device  150 , it should be understood, however, that any number of overpull generators  100  may be employed in the bottom hole assembly  200 , without departing from principles of the present invention. The use of more than one overpull generator  100  with the delay force release device  150  may be beneficial if there is a need for additional energy to activate the delay force release device  150  or if there is a need for additional stroke in the assembly  200 . In another embodiment, a first overpull generator  100  may be positioned in the bottom hole assembly  200  to activate the delay force release device  150  and a second overpull generator  150  may be positioned in the bottom hole assembly  200  between the delay force release device  150  and the coupling device  175  to push against the object  20  to create a push/pull effect. In a further embodiment, the bottom hole assembly  200  may include multiple delay force release devices  150  working in conjunction with multiple overpull generators  100 . In the embodiments with multiple overpull generators  100 , each overpull generator  100  may have a separate orifice sub to active the overpull generator  100  or a single orifice sub may be moved through the bottom hole assembly  200  to selectively activate each overpull generator  100  at a specified time. In a further embodiment, the overpull generator  100  may be configured to be electrically activated. In this embodiment, the piston rod  110  is movable between the extended position and the retracted position due to an electrical signal. The electrical signal may be communicated from the surface via the conveyance member  50 , such as wireline, wired drill pipe, wired coiled tubing, wired Corod®, or wireline run with the drill string. 
       FIG. 3  is a view illustrating the bottom hole assembly disposed in the wellbore after the object  20  in the wellbore  10  has been dislodged. As illustrated, the piston rod  110  of the overpull generator  100  is in the retracted position and the slinger  160  is deactivated. After the object  20  has been dislodged, the bottom hole assembly  200  may be used to remove the object  20  from the wellbore  10 . 
       FIG. 4  is a cross-sectional view of the overpull generator  100 . Generally, the overpull generator  100  converts wellbore fluid energy into mechanical energy. As illustrated, the overpull generator  100  includes a top sub  105 , the plurality of pistons  125  connected in series, and the piston rod  110 . For clarity purposes, the overpull generator  100  is shown in  FIG. 4  with the piston rod  110  in a retracted position. As discussed herein, the piston rod  110  of the overpull generator  100  is movable between the extended position and the retracted position to generate the overpull force (i.e. energy) that is used by the other components in the bottom hole assembly  200 . As also discussed herein, the pistons  125  cause the piston rod  110  of the overpull generator  100  to move from the extended position to the retracted position. The pistons  125  are operated by a pressure differential that is created between the outside and the inside of the overpull generator  100 . If the pressure drop across the overpull generator  100  proximate the bottom sub  110  is not sufficient, then the orifice sub (not shown) may be lowered into the bottom hole assembly. The orifice sub may be positioned below the overpull generator  100  in order to create the pressure differential required to activate the overpull generator  100  and move the piston rod  110  from the extended position to the retracted position. It should be noted that the orifice sub may function as an actuation switch, whereby the overpull generator  100  is selectively activated at a predetermined time. 
     As illustrated in  FIG. 4 , the overpull generator  100  includes a bore  120  formed therein. The bore  120  has an enlarged inner diameter. The bore  120  is used to pump fluid through the overpull generator  100 . Additionally, the bore  120  may be used to run downhole tools, such as wireline tools, a plasma cutting torch, logging tools such as a freepoint indicator, backoff explosives, a camera, or a string shot, through the overpull generator  100  to perform other downhole wellbore operations. Additionally, darts or balls could be pumped through the bore  120  of the overpull generator  100  to activate a tool below the overpull generator  100 . 
       FIG. 5  is a cross-sectional view taken along line  5 - 5  in  FIG. 4 . The overpull generator  100  may also be configured to transmit torque through the overpull generator  100 . As shown in  FIG. 5 , a spline arrangement  115  is formed between the piston rod  110  and a housing  130 . A rotational force (i.e. torque) that is generated above the overpull generator  100  may be transferred through the overpull generator  100  via the spline arrangement  115  to a point below the overpull generator  100 . The transfer of the rotational force may be useful in dislodging the object stuck in the wellbore or for performing another downhole operation. It should be noted that the overpull generator  100  may transmit the rotational force when the piston rod  110  is in the extended position and the retracted position. In another embodiment, a hexed arrangement, a keyed arrangement or any other torque transmitting arrangement may be formed between the piston rod  110  and the housing  130  that is configured to transmit torque through the overpull generator  100 . 
     As described herein, the overpull generator  100  and the delay force release device  150  has been used in a bottom hole assembly  200  that is configured to dislodge a previously stuck object in the wellbore  10 . In another embodiment, the overpull generator  100  and the delay force release device  150  may be part of a drill string assembly (not shown) having a drill bit at a lower end thereof. In this embodiment, if the drill bit becomes stuck during the drilling operation, then the overpull generator  100  may be activated by creating a pressure differential in the drill string assembly. In similar manner as described herein, the overpull generator  100  generates an overpull force that is used by the delay force release device  150  to dislodge the stuck drill bit. In a further embodiment, the overpull generator  100  may be used with the drill bit without the delay force release device  150 . 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.