Patent Publication Number: US-9428980-B2

Title: Hydraulic/mechanical tight hole jar

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. §371 national stage application of PCT/US2010/062499 filed Dec. 30, 2010, which is hereby incorporated herein by reference in its entirety for all purposes. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     1. Field of the Invention 
     The invention relates generally to downhole tools. More particularly, the invention relates to jars for applying an axial impact force to a downhole assembly. 
     2. Background of the Technology 
     In oil and gas well operations, it is frequently necessary to apply an axial blow to a tool or tool string that is positioned downhole. For example, application of axial force to a downhole string may be desirable to dislodge drilling or production equipment that is stuck in a wellbore. Another circumstance involves the retrieval of a tool or string downhole that has been separated from its pipe or tubing string. The separation between the pipe or tubing and the stranded tool or “fish” may be the result of structural failure or a deliberate disconnection initiated from the surface. 
     Jars have been used in petroleum well operations for several decades to enable operators to deliver axial impacts to stuck or stranded tools and strings. “Drilling jars” are frequently employed when either drilling or production equipment gets stuck in the well bore. The drilling jar is normally placed in the pipe string in the region of the stuck object and allows an operator at the surface to deliver a series of impact blows to the drill string via manipulation of the drill string. These impact blows are intended to dislodge the stuck object, thereby enabling continued downhole operations. “Fishing jars” are inserted into the well bore to retrieve a stranded tool or fish. Fishing jars are provided with a mechanism that is designed to firmly grasp the fish so that the fishing jar and the fish may be lifted together from the well. Many fishing jars are also provided with the capability to deliver axial blows to the fish to facilitate retrieval. 
     Conventional jars typically include an inner mandrel disposed in an outer housing. The mandrel is permitted to move axially relative to the housing and has a hammer formed thereon, while the housing includes an anvil positioned adjacent to the mandrel hammer. By impacting the anvil with the hammer at a relatively high velocity, a substantial jarring force is imparted to the stuck drill string. If the jarring force is sufficient, the stuck string will be dislodged and freed. 
     There are four basic types of jars: purely hydraulic jars, purely mechanical jars, bumper jars, and mechanical-hydraulic jars. Bumper jars are primarily used to provide a downward jarring force. The bumper jar usually contains a splined joint with sufficient axial travel to allow a pipe to be lifted and dropped, causing the impact surfaces inside the bumper jar to come together to deliver a downward jarring force to the string. 
     Mechanical, hydraulic, and mechanical-hydraulic jars differ from the bumper jar in that each contains a triggering mechanism which prevents impacting each other until a sufficient axial strain, either tensile or compressive, has been applied to the jar. To provide an upward jarring force, the drill pipe is stretched by an axial tensile load applied at the surface. This tensile force is resisted by the triggering mechanism of the jar long enough to allow the string to stretch and store potential energy. When the jar triggers, this stored energy is converted to kinetic energy causing the impact surfaces of the jar to move together at a relatively high velocity. To provide a downward jarring force, the pipe weight is slacked off at the surface and, and in some cases, additional compressive force is applied, to place the string in compression. This compressive force is resisted by the triggering mechanism of the jar to allow the string to compress and store potential energy. When the jar triggers, the potential energy is converted to kinetic energy causing the impact surfaces of the jar to come together at a relatively high velocity. 
     The triggering mechanism in most mechanical jars consists of a friction sleeve coupled to the mandrel which prevents movement of the mandrel relative to the housing until the load applied to the mandrel exceeds a preselected amount, often referred to as the “triggering load.” The triggering mechanism in most hydraulic jars consists of one or more pistons which pressurize fluid in a chamber in response to movement by the mandrel relative to the housing. The compressed fluid resists movement of the mandrel. The pressurized fluid is ordinarily allowed to bleed off at a preselected rate. As the fluid bleeds off, the mandrel slowly translates relative to the housing, eventually reaching a point in the jar where the chamber seal is opened, and the compressed fluid is allowed to rush past the piston, thereby allowing the mandrel to move rapidly. 
     Mechanical-hydraulic jars ordinarily combine some features of both purely mechanical and purely hydraulic jars. For example, one design utilizes both a slowly metered fluid and a mechanical spring element to resist relative axial movement of the mandrel and the housing. Another design utilizes a combination of a slowly metered fluid and a mechanical brake to retard the relative movement between the mandrel and the housing. In this design, drilling mud is used as the hydraulic medium. Therefore, the string must be pressurized before the jar will operate. This pressurization step will ordinarily require a work stoppage and the insertion of a ball into the work string to act as a sealing device. After the jar is triggered, the ball must be retrieved before normal operations can continue. 
     In many wireline retrieval operations, particularly tight hole operations, it is often desirable to applying a tensile load on the wireline in an attempt to free the stuck downhole object without firing the jar. For example, the operator may slowly increase tension on the wireline, and then hold the tension for an extended period of time to try and dislodge the downhole assembly without the need for triggering the jar. In some cases, the operator may choose apply an overload tension in excess of the triggering load of the jar to try and dislodge the downhole assembly, but not want to fire the jar. However, with most conventional jars, application of a tensile load over a long period of time and application of an overload tension are likely to cause the jar to inadvertently fire or be very near the point of firing. 
     Accordingly, there remains a need in the art for downhole jars and associated devices that allow the jar triggering load to be exceeded for a finite period of time without causing the jar to fire. Such jars and associated devices would be particularly well-received if they provided the operator the option of reducing the line tension shortly after the overpull to avoid jarring, or maintaining the overpull to fire the jar. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     These and other needs in the art are addressed in one embodiment by a jar having a longitudinal axis. In an embodiment, the jar comprises a housing including an anvil. In addition, the jar comprises a mandrel telescopically disposed within the housing and including a hammer. Further, the jar comprises an annular chamber radially positioned between the mandrel and the housing. Still further, the jar comprises an actuation assembly disposed in the annular chamber. The actuation assembly includes a first collet disposed about the mandrel and adapted to releasably engage the mandrel. The first collet is axially moveable between a neutral position engaging the mandrel and a triggered position disengaged from the mandrel. The actuation assembly also includes a first trigger sleeve disposed about the first collet and adapted to releasably engage the first collet. Still further, the actuation assembly includes a first biasing member adapted to exert an axial force on the mandrel upon compression of the first biasing member by movement of the mandrel in a first axial direction relative to the housing when the first collet is in the neutral position. Moreover, the jar comprises a lock assembly disposed in the annular chamber. The lock assembly includes a second collet disposed about the mandrel and adapted to releasably engage the mandrel. The second collet is axially moveable between a neutral position engaging the mandrel and a triggered position disengaged from the mandrel. The lock assembly also includes a second trigger sleeve disposed about the second collet and adapted to releasably engage the second collet. Further, the lock assembly includes a second biasing member adapted to exert an axial force on the mandrel upon compression of the second biasing member by movement of the mandrel in the first axial direction relative to the housing when the second collet is in the neutral position. The lock assembly is adapted to release the mandrel, and the actuation assembly is adapted to release the mandrel and allow to the hammer to axially impact the anvil. 
     These and other needs in the art are addressed in another embodiment by a jar having a longitudinal axis. In an embodiment, the jar comprises a housing including an anvil surface. In addition, the jar comprises a mandrel telescopically disposed within the housing and including a hammer surface. Further, the jar comprises a seal assembly radially disposed between the housing and the mandrel. Still further, the jar comprises an annular hydraulic chamber radially positioned between the mandrel and the housing and extending axially from the seal assembly to an annular balancing piston disposed about the mandrel. Moreover, the jar comprises an annular actuation piston disposed in the hydraulic chamber and axially positioned between the seal assembly and the balance piston. The jar also includes a first biasing member disposed in the hydraulic chamber and axially positioned between the actuation piston and a first annular shoulder on the housing. The first biasing member biases the actuation piston in a first axial direction. In addition, the jar includes a first trigger sleeve disposed in the hydraulic chamber about the mandrel. Further, the jar includes a first collet disposed in the hydraulic chamber about the mandrel. The first collet has a first position positively engaging the mandrel and the second position positively engaging the first trigger sleeve. The first collet and the actuation piston are adapted to move with the mandrel relative to the housing and the first trigger sleeve when the first collet is in the first position, and the mandrel is adapted to move relative to the first collet and the actuation piston when the first collet is in the second position. Still further, the jar includes a second trigger sleeve disposed in the hydraulic chamber about the mandrel. Moreover, the jar includes a second collet disposed in the hydraulic chamber about the mandrel. The second collet has a first position positively engaging the mandrel and the second position positively engaging the second trigger sleeve. The jar also includes a second biasing member axially positioned between a second annular shoulder on the housing and the second collet. The second collet is adapted to move with the mandrel relative to the housing and the second trigger sleeve when the second collet is in the first position, and the mandrel is adapted to move relative to the second collet when the second collet is in the second position. 
     These and other needs in the art are addressed in another embodiment by a method of operating a downhole jar. The jar including a housing with a longitudinal axis and a mandrel telescopically disposed within the housing. In an embodiment, the method comprises (a) applying a tensile load to the jar so as to move the mandrel relative to the housing in a first axial direction. In addition, the method comprises (b) compressing a first biasing member that biases the mandrel in a second axial direction that is opposite the first axial direction with a first biasing force. Further, the method comprises (c) removing the first biasing force from the mandrel after sufficient axial movement of the mandrel relative to the housing. Still further, the method comprises (d) continuing to apply a tensile load to the jar so as to move the mandrel relative to the housing after (c). Moreover, the method comprises (e) compressing a second biasing member that biasing the mandrel in the second axial direction with a second biasing force during (d). 
     Thus, embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a schematic view of a downhole assembly including an embodiment of a jar in accordance with the principles described herein; 
         FIGS. 2A-2D  are cross-sectional views of successive portions of the jar of  FIG. 1  in its neutral position; 
         FIG. 3  is an enlarged view of the jar of  FIGS. 2A-2D  taken within section  3 - 3  of  FIG. 2B ; 
         FIG. 4  is an enlarged view of the jar of  FIGS. 2A-2D  taken within section  4 - 4  of  FIG. 2C ; 
         FIG. 5  is a cross-sectional view of the jar of  FIG. 1  taken along section  5 - 5  of  FIG. 2A ; 
         FIG. 6  is an upper, end view of the actuating piston of  FIG. 2B ; 
         FIG. 7  is a perspective view of one of the collets of the jar of  FIGS. 2A-2D ; and 
         FIGS. 8A-8D  are cross-sectional views of successive portions of the jar of  FIG. 1  in its fired position. 
     
    
    
     DETAILED DESCRIPTION OF SOME OF THE PREFERRED EMBODIMENTS 
     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
     Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. 
     Referring now to  FIG. 1 , a downhole assembly  10  is shown disposed in a borehole  11  extending through an earthen formation. Borehole  11  includes casing  14  that extends downhole from the surface. In this embodiment, assembly  10  is lowered downhole with a wireline tool string  20  extending through casing  14 . However, in general, the downhole assembly (e.g., assembly  10 ) may be run downhole by any suitable means including, without limitation, a pipe string, a drill string, a sucker rod, or other suitable device. Assembly  10  includes one or more downhole tools  30  for performing downhole operations. In general, tools  30  may include any suitable tool(s) for performing downhole operations including, without limitation, formation testing tools, perforation equipment, fracturing tools, fishing tools, etc. 
     As may be necessary to traverse particular producing formations, borehole  11  may include generally straight sections and curved sections. In reality, both straight and curved sections may include various kinks and twists, which generally increase the probability of assembly  10  becoming stuck downhole. Consequently, in this embodiment, a jar  100  is included in assembly  10 . As will be described in more detail below, in the event assembly  10  becomes stuck in borehole  11 , jar  100  may be triggered or fired to provide an abrupt, axial force sufficient to dislodge assembly  10 . Although  FIG. 1  shows jar  100  suspended in borehole  10  with wireline  20 , in general, jar  100  may be inserted into a well borehole by any suitable means including, without limitation, via a pipestring, tubing string, drillstring, or cable string as desired. 
     Referring now to  FIGS. 2A-2D , an exemplary embodiment of jar  100  is shown. Due to the length of jar  100 , it is illustrated in four longitudinally broken sectional views, vis-à-vis  FIGS. 2A, 2B, 2C and 2D . The sections are arranged in sequential order moving along jar  100  from  FIG. 2A  to  FIG. 2D .  FIGS. 2A-2D  show jar  100  is a neutral or unfired position.  FIGS. 8A-8D , which will be discussed in more detail below, show jar  100  in the fired position. 
     Jar  100  has a central or longitudinal axis  105 , a first or upper end  100   a , and a second or lower end  100   b  opposite end  100   a . As indicated by the relative terms “upper” and “lower,” jar  100  is configured to be positioned in the borehole with end  100   a  uphole of end  100   b . In this embodiment, jar  100  includes a radially inner tubular mandrel  110  telescopically disposed within a radially outer tubular housing  210 . Mandrel  110  and housing  210  are coaxially aligned such that each has a central axis coincident with jar axis  105 . 
     Referring still to  FIGS. 2A-2D , mandrel  110  has a first or upper end  110   a  defining jar end  100   a  ( FIG. 2A ), and a second or lower end  110   b  opposite end  110   a  and disposed within housing  210  proximal jar lower end  100   b  ( FIG. 2D ). In addition, mandrel  110  has a longitudinal throughbore  112  extending axially between ends  110   a, b . One or more electrical conducts (e.g., cables, wires, etc.) may extend through bore  112  to provide power and/or communicate signals across jar  100 . In this embodiment, mandrel  110  is formed from a plurality of tubular segments joined together end-to-end with mating box-pin end threaded connections. In particular, moving axially from upper end  110   a  to lower end  110   b , mandrel  110  includes an upper tubular member  120  ( FIG. 2A ), a first intermediate tubular member  130  threadably coupled to upper tubular member  120  ( FIGS. 2A and 2B ), a second intermediate tubular member  140  threadably coupled to first intermediate tubular member  130  ( FIGS. 2B and 2C ), and a lower tubular member  150  threadably coupled to second intermediate tubular member  140  ( FIGS. 2C and 2D ). 
     As best shown in  FIG. 2A , upper tubular member  120  has a first or upper end  120   a  defining jar upper end  100   a , and a second or lower end  120   b  disposed within housing  210 . In this embodiment, upper end  120   a  comprises a pin end that is threadably received by a mating box end (not shown) of a connector sub or other downhole tool, coupling, or fitting, and lower end  120   b  comprises a box end that receives first intermediate tubular member  130 . Upper tubular member  120  may be divided into three axial sections based on its outer diameter. Specifically, upper tubular member  120  includes a first reduced outer diameter portion  121  extending axially from end  120   a , a second reduced outer diameter portion  122  extending axially from end  120   b , and an enlarged outer diameter portion  123  axially disposed between portions  121 ,  122 . As a result, the radially outer surface of upper tubular member  120  includes an annular hammer shoulder or surface  124  at the intersection of portions  121 ,  123 , and an annular seating shoulder or surface  125  at the intersection of portions  122 ,  123 . As will be described in more detail below, when jar  100  is triggered to fire, mandrel  110  moves axially upward relative to housing  210  at a relatively high velocity and hammer shoulder  124  impacts a mating surface in housing  110  to provide a substantial upward axial jarring force; and when jar  100  is in the neutral, unfired position, seating shoulder  125  is seated against a mating surface in housing  110 . 
     Referring now to  FIGS. 2A and 2B , first intermediate tubular member  130  has a first or upper end  130   a  and a second or lower end  130   b  opposite upper end  130   a . In this embodiment, upper end  130   a  comprises a pin end coaxially received by box end  120   b  of upper tubular member  120 , and lower end  130   b  comprises a pin end coaxially received by second intermediate tubular member  140 . In addition, the radially outer surface of first intermediate tubular member  130  includes an annular shoulder  131  as best shown in  FIG. 2A , and as best shown in  FIGS. 2B and 3 , a plurality of axially spaced annular recesses or grooves  132  defining a plurality of annular flanges  133 —one flange  133  is axially disposed between each pair of axially adjacent grooves  132 . 
     Referring now to  FIGS. 2B and 2C , second intermediate tubular member  140  has a first or upper end  140   a  and a second or lower end  140   b  opposite end  140   a . In this embodiment, upper end  140   a  comprises a box end that receives pin end  130   b , and lower end  140   b  comprises a pin end coaxially received by lower tubular member  150 . As best shown in  FIGS. 2C and 4 , the radially outer surface of second intermediate tubular member  140  includes a plurality of axially spaced annular recesses or grooves  141  defining a plurality of annular flanges  142 —one flange  142  is axially disposed between each pair of axially adjacent grooves  141 . 
     Moving now to  FIGS. 2C and 2D , lower tubular member  150  has a first or upper end  150   a  and a second or lower end  150   b  opposite end  150   a . In this embodiment, upper end  150   a  comprises a box end that receives pin end  140   b , and lower end  150   b  is a free end disposed within housing  210 . In addition, the radially outer surface of lower tubular member  150  includes an annular flange  151  that is employed to prevent jar  100  from “gas locking.” Methods for preventing jars from gas locking with use of an annular flange such as flange  151  are disclosed in U.S. Pat. No. 7,290,604, which is hereby incorporated herein by reference in its entirety for all purposes. 
     Referring again to  FIGS. 2A-2D , housing  210  has a first or upper end  210   a  disposed about mandrel  110  proximal jar upper end  100   a  ( FIG. 2A ) and a second or lower end  210   b  defining jar lower end  100   b  ( FIG. 2D ). Housing upper end  210   a  is axially spaced below mandrel upper end  110   a  and housing lower end  210   b  is axially spaced below mandrel lower end  110   b . In addition, housing  210  has a longitudinal throughbore  212  extending axially between ends  210   a, b.    
     Similar to mandrel  110 , housing  210  is formed from a plurality of tubular segments joined together end-to-end with mating box-pin end threaded connections. In particular, moving axially from housing upper end  210   a  to housing lower end  210   b , housing  210  includes an upper tubular member  215  ( FIG. 2A ), a first intermediate tubular member  220  threadably coupled to upper tubular member  215  ( FIG. 2A ), a second intermediate tubular member  225  threadably coupled to first intermediate tubular member  220  ( FIG. 2A ), a preload adjustment tubular mandrel  230  threadably coupled to tubular member  225  ( FIG. 2A ), a third intermediate tubular member  240  threadably coupled to tubular mandrel  230  ( FIGS. 2A and 2B ), a fourth intermediate tubular member  245  threadably coupled to tubular member  240  ( FIG. 2B ), a fifth intermediate tubular member  250  threadably coupled to tubular member  245  ( FIGS. 2B and 2C ), a metering adjustment tubular mandrel  255  threadably coupled to tubular member  250  ( FIG. 2C ), a sixth intermediate tubular member  265  threadably coupled to tubular mandrel  255  ( FIG. 2C ), a seventh intermediate tubular member  270  threadably coupled to tubular member  265  ( FIGS. 2C and 2D ), and a bottom tubular member  275  threadably coupled to tubular member  270  ( FIG. 2D ). 
     Referring now to  FIG. 2A , upper tubular member  215  has a first or upper end  215   a  and a second or lower end  215   b  opposite end  215   a . In this embodiment, lower end  215   b  comprises a pin end that is coaxially received by first intermediate tubular member  220 . In addition, upper tubular member  215  includes a reduced outer diameter portion  216  extending axially from end  215   b  and a counterbore  217  extending axially from end  215   b.    
     Housing upper tubular member  215  sealingly engages mandrel  110 . In particular, tubular member  215  includes a seal assembly  218  that forms dynamic seals with mandrel upper tubular member  120 . Seal assembly  218  is radially disposed between tubular members  120 ,  215 , and in this embodiment, comprises a loaded lip seal  218   a  and an O-ring seal  218   b  positioned axially below lip seal  218 . 
     Referring still to  FIG. 2A , first intermediate tubular member  220  has a first or upper end  220   a  and a second or lower end  220   b  opposite end  220   a . In this embodiment, upper end  220   a  comprises a box end that receives pin end  215   b  and lower end  220   b  comprises a box end that receives second intermediate tubular member  225 . The radially inner surface of first intermediate tubular member  220  includes an annular shoulder  221  proximal upper end  220   a  and a radially inner shoulder  222  proximal lower end  220   b.    
     An anvil sleeve  300  is disposed about mandrel upper tubular member  120  and extends coaxially into counterbore  217 . Specifically, sleeve  300  has a first or upper end  300   a  and a second or lower end  300   b  opposite upper end  300   a . In this embodiment, sleeve  300  includes a cylindrical portion  301  extending axially from upper end  300   a  and an annular flange  202  extending radially outward from cylindrical portion  301  at end  300   b . Cylindrical portion  301  is disposed in counterbore  217  and flange  302  extends radially outward along lower end  215   b . In particular, flange  302  is axially disposed between and engages lower end  215   b  and shoulder  221 . Thus, lower end  215   b  and shoulder  221  restrict sleeve  300  from moving axially relative to housing  210 . Anvil sleeve flange  302  defines a downwardly facing annular anvil surface  303  that is impacted by hammer surface  124  of mandrel upper tubular member  120  to generate an upward axial jarring force when jar  100  is fired. 
     Referring briefly to  FIGS. 2A and 5 , the radially inner surface of intermediate tubular member  220  is provided with a plurality of circumferentially spaced flats  223  extending axially between shoulders  221 ,  222 . Flats  223  slidingly engage a plurality of mating external flats  126  on the radially outer surface of mandrel enlarged outer diameter portion  123 . Flats  126 ,  223  permit mandrel  110  to move axially relative to housing  210 , but prevent mandrel  110  from rotating about axis  105  relative to housing  210 . A plurality of elongate recesses  127  are formed in one or more mandrel flats  126 . Each recess  127  extends axially between mandrel shoulders  124 ,  125 , and forms a flow passage that allows fluid to move axially across mandrel enlarged outer diameter portion  123 . 
     Referring again to  FIG. 2A , second intermediate tubular member  225  has a first or upper end  225   a  and a second or lower end  225   b  opposite end  225   a . In this embodiment, upper end  225   a  comprises a pin end received by first intermediate tubular member  220  and lower end  225   b  comprises a box end that receives tubular mandrel  230 . Upper end  225   a  defines an annular seating shoulder  226  on the radially inner surface of housing  210  against which mandrel seating shoulder  125  of enlarged diameter portion  123  seats when jar  100  is in the neutral position shown in  FIGS. 2A-2D . Engagement of shoulders  125 ,  226  determines the lower limit of downward axial movement of mandrel  110  relative to housing  210 . Further, the radially inner surface of second intermediate tubular member  225  includes an annular shoulder  227 . 
     Referring still to  FIG. 2A , preload adjustment tubular mandrel  230  has a first or upper end  230   a  and a second or lower end  230   b  opposite end  230   a . In this embodiment, upper end  230   a  comprises a pin end received by box end  225   b , and lower end  230   b  comprises a pin end received by third intermediate tubular member  240 . The radially outer surface of mandrel  230  includes external threads  231  proximal upper end  230   a , external threads  232  proximal lower end  230   b , and an elongate recess or slot  233  axially positioned between threads  231 ,  231 . Slot  233  is oriented parallel to axis  105 . In other words, slot  233  extends axially along mandrel  230 . In this embodiment, threads  231 ,  232  are oppositely threaded, and thus, if threads  231  are right-hand threads, then threads  232  are left-hand threads, and if threads  231  are left-hand threads, then threads  232  are right-hand threads. An adjustment ring  234  is disposed about mandrel  230  and over slot  233 . The radially inner surface of ring  234  includes an elongate recess or slot  235  circumferentially aligned with mandrel slot  233 . A key  236  is radially disposed between mandrel  230  and ring  234 , and slidingly engages both axially extending slots  233 ,  235 . Key  236  has an axial length less than the axial length of each slot  233 ,  235 . Thus, key  236  allows mandrel  230  to move axially relative to ring  234 , but prevents mandrel  230  from moving rotationally about axis  105  relative to ring  234 . Accordingly, rotation of ring  234  about axis  105  results in the rotation of mandrel  230  about axis  105  in the same direction. Since external threads  231 ,  232  are oppositely threaded, rotation of ring  234  and mandrel  230  about axis  105  in a first direction results in the axial translation of mandrel  230  relative to ring  234 , second intermediate tubular member  225 , and third intermediate tubular member  240 . 
     Referring now to  FIGS. 2A and 2B , third intermediate tubular member  240  has a first or upper end  240   a  and a second or lower end  240   b  opposite end  240   a . In this embodiment, upper end  240   a  comprises a box end that receives pin end  230   b  and lower end  240   b  comprises a box end that receives fourth intermediate tubular member  245 . The radially inner surface of third intermediate tubular member  240  includes an annular shoulder  241  proximal lower end  240   b  and an annular shoulder  242  axially positioned between shoulder  241  and end  240   b.    
     Referring to  FIGS. 2B and 3 , fourth intermediate tubular member  245  has a first or upper end  245   a  and a second or lower end  245   b  opposite end  245   a . In this embodiment, upper end  245   a  comprises a pin end received by box end  240   b  and lower end  245   b  comprises a pin end received by fourth intermediate tubular member  250 . Further, the radially outer surface of tubular member  245  includes an annular groove or recess  246  extending axially from end  245   a.    
     Referring now to  FIGS. 2B, 2C, and 3 , fifth intermediate tubular member  250  has a first or upper end  250   a  and a second or lower end  250   b  opposite end  250   a . In this embodiment, upper end  250   a  comprises a box end that receives pin end  245   b  and lower end  250   b  comprises a box end that receives tubular mandrel  255 . The radially inner surface of tubular member  250  includes an annular shoulder  251  proximal lower end  250   b  and an annular shoulder  252  axially disposed between shoulder  251  and end  250   b.    
     Referring now to  FIGS. 2C and 4 , tubular mandrel  255  has a first or upper end  255   a  and a second or lower end  255   b  opposite end  255   a . Further, upper end  255   a  comprises a pin end received by box end  250   b , and lower end  255   b  comprises a pin end received by sixth intermediate tubular member  265 . The radially outer surface of mandrel  255  includes external threads  256  proximal upper end  255   a , external threads  257  proximal lower end  255   b , an annular recess  258  extending axially from end  255   a , an annular recess or groove  259  axially disposed between threads  256  and end  255   a , and an elongate recess or slot  260  axially positioned between threads  256 ,  257 . Slot  260  is oriented parallel to axis  105 . In other words, slot  260  extends axially along mandrel  255 . Threads  256 ,  257  are oppositely threaded, and thus, if threads  256  are right-hand threads, then threads  257  are left-hand threads, and if threads  256  are left-hand threads, then threads  257  are right-hand threads. An adjustment ring  261  is disposed about mandrel  255  and over slot  260 . The radially inner surface of ring  261  includes an elongate recess or slot  262  circumferentially aligned with mandrel slot  260 . A key  263  is radially disposed between mandrel  255  and ring  261 , and slidingly engages both axially extending slots  260 ,  262 . Key  263  has an axial length less than the axial length of each slot  260 ,  262 . Thus, key  263  allows mandrel  255  to move axially relative to ring  261 , but prevents mandrel  255  from moving rotationally about axis  105  relative to ring  261 . Accordingly, rotation of ring  261  about axis  105  results in the rotation of mandrel  255  about axis  105  in the same direction. Since external threads  256 ,  257  are oppositely threaded, rotation of ring  258  and mandrel  255  about axis  105  in a first direction results in the axial translation of mandrel  255  relative to ring  261 , fifth intermediate tubular member  250 , and sixth intermediate tubular member  265 . 
     Referring to  FIGS. 2C and 2D , sixth intermediate tubular member  265  has a first or upper end  265   a  and a second or lower end  265   b  opposite end  265   a . In this embodiment, upper end  265   a  comprises a box end that receives pin end  255   b  and lower end  265   b  comprises a pin end received by seventh intermediate tubular member  270 . Seventh intermediate tubular member  270  has a first or upper end  270   a  and a second or lower end  270   b  opposite end  270   a . In this embodiment, upper end  270   a  comprises a box end that receives pin end  265   b  and lower end  270   b  comprises a box end that receives bottom tubular member  275 . A plurality of ports  271  extend radially through tubular member  270  proximal lower end  270   b.    
     Referring to  FIG. 2D , bottom tubular member  275  has a first or upper end  275   a  and a second or lower end  275   b  opposite end  275   a . In this embodiment, upper end  275   a  comprises a pin end received by box end  270   b  and lower end  275   b  comprises a pin end that is threadably received by a mating box end (not shown) of a connector sub or other downhole tool, coupling, or fitting. Housing bottom tubular member  275  sealingly engages mandrel  110 . In particular, tubular member  275  includes a seal assembly  277  that forms dynamic seals with mandrel lower tubular member  150 . Seal assembly  277  is radially disposed between tubular members  150 ,  275 , and in this embodiment, comprises a loaded lip seal  278  and an O-ring seal  279  positioned axially below lip seal  278 . 
     Referring again to  FIGS. 2A-2D , housing upper tubular member  215  and housing lower tubular member  275  each sealingly engage mandrel  110 . However, axially between seal assemblies  218 ,  277 , housing  210  is radially spaced apart from mandrel  110 . In particular, an annulus  160  is generally defined by the open internal spaces radially disposed between mandrel  110  and housing  210 . As best shown in  FIG. 2D , an annular pressure equalizing or balance piston  320  is disposed in annulus  160  and divides annulus  160  into an annular operating or working fluid chamber  161  extending axially from upper seal assembly  218  to piston  320  and an annular fluid chamber  162  extending axially from lower seal assembly  277  to piston  320 . Fluid chamber  161  above piston  320  is filled with operating or working fluid and is generally permitted to flow axially back and forth within chamber  161  between and around the various components disposed within chamber  161 . The working fluid is preferably a hydraulic fluid, light oil or the like. Fluid chamber  162  below the piston  320  is vented to the wellbore annulus by ports  271  in housing intermediate tubular member  270 . 
     Piston  320  is designed to ensure that the pressure of the operating fluid within chamber  161  is substantially the same as the fluid pressure in the wellbore annulus, while simultaneously restricting and/or preventing fluid communication between chambers  161 ,  162 . Accordingly, piston  320  includes a radially inner seal assembly  321  that sealingly engages mandrel  110  and a radially outer seal assembly  322  that sealingly engages housing  210 . In this embodiment, inner seal assembly  321  includes an O-ring seal  323  and a loaded lip seal  324  axially spaced below O-ring seal  323 , and similarly, outer seal assembly  322  includes an O-ring seal  325  and a loaded lip seal  326  axially spaced below O-ring seal  325 . Thus, housing seal assembly  218  and piston seal assemblies  321 ,  322  restrict and/or prevent mud and other debris in the wellbore annulus from contaminating the operating fluid (e.g., hydraulic fluid) within chamber  161 , and restrict and/or prevent the loss of operating fluid from chamber  161  into the wellbore annulus. 
     Referring still to  FIGS. 2A-2D and 3 , working fluid may be added or removed from chamber  161  via one or more fill ports  290  provided in housing  210 . A fluid plug  291  is removably disposed within and closes off each fill port  290 . Access to chamber  161  may be achieved by removing any fluid plug  291  from its corresponding fill port  290 . In this embodiment, each fluid plug  281  comprises an externally threaded hex nut  292  that compresses a sealed disk  293  provided with an O-ring seal  294 . 
     As will be described in more detail below and is shown in  FIG. 8A , when jar  100  is triggered, mandrel  110  moves axially upward relative to housing  210  at a relatively high velocity until mandrel hammer surface  124  impacts anvil surface  303  to generate an upward axial jarring force. To reset jar  100  such that it may be fired again (i.e., to transition jar  100  from the fired position shown in  FIGS. 8A-8D  to the neutral position shown in  FIGS. 2A-2D ), mandrel  110  is moved axially downward relative to housing  210  until mandrel seating shoulder  125  axially abuts housing seating shoulder  226 . To aid in resetting jar  100 , particularly in highly deviated boreholes or situations with high wall drag, jar  100  includes a recocking assembly  330  disposed in chamber  161  and axially positioned between housing annular shoulder  227  and mandrel annular shoulder  131 . As best shown in  FIG. 2A , in this embodiment, recocking assembly  330  includes a washer  331  and a recocking spring  332 . Washer  331  is disposed about mandrel  110  and axially abuts housing shoulder  227 . Washer  331  is held in engagement with housing shoulder  227  by spring  332 , which extends axially between washer  331  and mandrel shoulder  131 . Specifically, spring  332  is compressed between washer  331  and mandrel shoulder  131 , and thus, urges washer  331  into engagement with housing shoulder  227 , urges mandrel shoulder  227  axially away from housing shoulder  227 , and urges mandrel seating shoulder  125  into engagement with housing seating shoulder  226 . Washer  331  includes a plurality of circumferentially spaced bores  333  extending axially through washer  331 . Bores  333  allow working fluid in chamber  161  to flow freely across washer  331 . 
     Referring now to  FIGS. 2A and 2B , in this embodiment, jar  100  includes a firing section  101  and a releasable lock section  102 . Firing section  101  is generally disposed between jar upper end  100   a  and housing intermediate tubular member  245 , and lock section  102  is generally disposed between jar lower end  100   b  and housing intermediate tubular member  245 . As will be described in more detail below, firing section  101  is the portion of jar  100  that, when triggered, generates an axial impact force to dislodge a stuck downhole assembly. Lock section  102  is the portion of jar  100  that prevents firing section  101  from firing until lock section  102  has first been actuated. 
     Referring now to  FIGS. 2B and 3 , jar firing section  101  includes a jar actuation assembly  340  disposed within chamber  161  and axially positioned between lower end  230   b  of housing mandrel  230  and upper end  245   a  of housing tubular member  245 . In this embodiment, jar actuation assembly  340  includes a biasing member  341 , an annular actuation piston  345 , a spacer or compression ring  350 , a trigger sleeve  351 , a trigger sleeve biasing member  355 , and an annular collet  360 . 
     Biasing member  341  is axially positioned between lower end  230   b  of housing mandrel  230  and actuation piston  345 . In particular, biasing member  341  has a first or upper end  341   a  that bears against lower end  230   b  and a second or lower end  341   b  that bears against piston  345 . In this embodiment, biasing member  341  comprises a stack of Bellville springs formed by a plurality of individual Bellville springs arranged one-adjacent-the other (e.g., one-above-the-other) to form an elongate “stack.” However, in other embodiments, the piston biasing member (e.g., biasing member  341 ) may comprise other types of spring arrangements including, without limitation, coil springs. Biasing member  341  is configured such that it provides minimal resistance to the axial flow of working fluid. For example, biasing member  341  may be radially spaced from housing  210 , radially spaced from mandrel  110 , include one or more axial throughbores or flow passages, or combinations thereof. 
     Biasing member  341  is axially compressed between end  230   b  and piston  345 , and thus, urges piston  345  axially downward and away from end  230   b . Thus, the biasing member  341  resists upward axial movement of actuating piston  345  and seeks to seat actuating piston  345  against housing annular shoulder  241  as shown in  FIG. 2B . As will be described in more detail below, biasing member  341  is compressed when jar  100  is in the neutral position, thereby providing firing section  101  with a preload that enables the operator to apply an upward axial force on mandrel  110  without necessarily firing jar  100 . For example, biasing member  341  may be configured to apply a 1,000 lb. downward force on piston  345  with the jar  100  in the neutral position shown in  FIGS. 2A-2D . So long as the upward axial force applied to piston  345  does not exceed this preload, firing section  101  will not fire. The amount of preload may be adjusted by varying the compression of biasing member  341  with housing tubular mandrel  230 . Specifically, adjustment ring  234  and mandrel  230  may be rotated about axis  105  in a first direction to move mandrel  230  axially downward towards shoulder  241  and piston  345 , thereby increasing the preload and axial compression of biasing member  341 . Alternatively, adjustment ring  234  and mandrel  230  may be rotated about axis  105  in the opposite direction to move mandrel  230  axially upward away from shoulder  241  and piston  345 , thereby decreasing the preload and axial compression of biasing member  341 . 
     Referring now to  FIG. 2B , actuating piston  345  is axially positioned between biasing member  341  and housing annular shoulder  241 . As previously described, biasing member  341  urges piston  345  into engagement with shoulder  241 . Piston  345  slidably engages mandrel  110  and housing  110 . Thus, piston  345  may move axially within chamber  161  relative to mandrel  110  and/or housing  210 . However, housing shoulder  241  defines the lower limit of axially downward movement of piston  345  within chamber  161 , and as will be described in more detail below, the positive engagement of trigger sleeve  351  and collet  360  defines the upper limit of axially upward movement of piston  345  within chamber  161 . 
     As best shown in  FIG. 3 , piston  345  includes a radially inner seal assembly  346  that sealingly engages mandrel  110  and a radially outer seal assembly  347  that sealingly engages housing  210 . Seal assembly  346  restricts and/or prevents working fluid in chamber  161  from flowing axially between piston  345  and mandrel  110 , and seal assembly  347  restricts and/or prevents working fluid in chamber  161  from flowing axially between piston  345  and housing  210 . In this embodiment, each seal assembly  346 ,  347  comprises an O-ring seal. 
     Referring now to  FIGS. 3 and 6 , actuating piston  345  includes a first flow passage  348  and a second flow passage  349 , each flow passage  348 ,  349  extends axially through piston  345 . First flow passage  348  is designed to permit the restrictive flow of fluid axially downward through piston  345  to permit the build up of working fluid pressure in the portion of chamber  161  between seal assembly  218  and piston  345  while simultaneously permitting actuating piston  345  to move axially upwards through chamber  161  until jar  100  triggers as described more fully below. In this regard, first flow passage  348  includes a conventional flow restriction orifice  348   a . In general, any suitable flow restriction device may be used. One example of a suitable flow restriction device is the Ø 0.187 in. (outer diameter) Visco Jet available from The Lee Company of Westbrook, Conn. 
     Second flow passage  349  includes a one-way check valve  349   a  that restricts and/or prevents working fluid from flowing through passage  349  when piston  345  moves axially upward within chamber  161 , but allows working fluid to flow through passage  349  when piston moves axially downward within chamber  161 . In general, the check valve may comprise any suitable check valve that allows one-way fluid flow. One example of a suitable check valve is the Ø 0.187 in. (outer diameter) Lee Chek check valve available from The Lee Company of Westbrook, Conn. 
     Actuating piston  345  divides jar working fluid chamber  161  into a first or upper portion  161   a  extending axially from seal assembly  218  to piston  345  and a second or lower portion  161   b  extending axially from piston  345  to piston  320 . Since piston  345  sealingly engages mandrel  110  and housing  210 , flow restriction orifice  348   a  in flow passage  348  restricts working fluid flow therethrough, and check valve  349   a  in flow passage  349  prevents working fluid flow therethrough, piston  345  substantially restricts working fluid in upper chamber portion  161   a  from flowing into lower chamber portion  161   b . Thus, as piston  345  moves axially upward within chamber  161 , the pressure of working fluid in chamber upper portion  161  increases. Such an increase in the working fluid pressure in chamber upper portion  161  resists the upward movement of piston  345 . That is, upward relative movement of piston  345  relative to the housing  210  reduces the volume of chamber upper portion  161   a , thereby causing a significant increase in the working fluid pressure within chamber upper portion  161   a  that generates an axial force that resist the upward movement of piston  345  relative to housing  210 . This resistance to relative movement of piston  345  allows a large buildup of potential energy. However, over time, flow restrictor  348   a  slowly allows working fluid to flow through piston  345  from chamber upper portion  161   a  to chamber lower portion  161   b , and thereby allows piston  345  to creep upward within chamber  161  relative to housing  210 . It is this bleeding of working fluid across piston  345  as piston  345  is urged axially upward within chamber  161  that defines the hydraulic delay portion of the firing cycle of jar  100  and firing section  101 . As previously described, biasing member  355  also exerts and axial force on piston  345  that resists upward movement of piston  345  relative to housing  210 . 
     Referring to  FIGS. 2B and 3 , tubular trigger sleeve  351  is radially positioned between housing  210  and collet  360 , and axially positioned between housing shoulder  242  and end  245   a  of housing tubular member  245 . Trigger sleeve  351  slidingly engages housing  210 , and thus, is generally free to move axially between shoulder  242  and tubular member end  245   a . However, biasing member  355  is axially positioned between trigger sleeve  351  and end  245   a . In particular, biasing member  355  has a first or upper end  355   a  that axially abuts trigger sleeve  351  and a second or lower end  355   b  that engages housing tubular member  245  and is seated in recess  246 . Biasing member  355  is axially compressed between trigger sleeve  351  and end  245   a , and thus, urges trigger sleeve  351  into engagement with housing shoulder  242 . In this embodiment, biasing member  355  is a coil spring, however, in general, the trigger sleeve biasing member (e.g., biasing member  355 ) may comprise any suitable biasing device such as a wave spring. 
     Trigger sleeve  351  has a radially outer cylindrical surface that slidingly engages housing  210  and a radially inner surface that includes a plurality of annular recesses  352  defining a plurality of radially inwardly projecting annular flanges  353 —one flange  353  is axially disposed between each pair of axially adjacent recesses  352 . As will be described in more detail below, recesses  352  and flanges  353  are sized and configured to releasably engage a plurality of mating flanges and recesses, respectively, provided on the radially outer surface of collet  360  when jar  100  is fired. 
     Referring now to  FIGS. 2B and 5 , collet  360  is radially disposed between mandrel  110  and trigger sleeve  351 , and has a first or upper end  360   a  and a second or lower end  360   b  opposite end  360   a . In addition, collet  360  has a generally tubular body  361  including a plurality of circumferentially spaced slots  362   a  extending axially from end  360   a  and a plurality of circumferentially spaced slots  362   b  extending axially from end  360   b . One slot  362   a  is circumferentially disposed between each pair of circumferentially adjacent slots  362   b . Slots  362   a  divide body  361  into a plurality of elongate circumferentially spaced fingers or segments  363  extending axially from ends  360   a, b . During the operation of jar  100 , segments  363  are subjected to bending forces and stresses. Accordingly, in this embodiment, the end of each slot  362   a, b  is rounded to avoid stress concentrations. 
     The radially outer surface of each axially extending segment  363  includes a primary flange  364  and a plurality of secondary flanges  365  positioned between lower end  360   b  and primary flange  364 . Flanges  364 ,  365  define a plurality of recesses or grooves  366  on the radially outer surface of each segment  363 —one groove  366  is axially positioned between each pair of axially adjacent flanges  364 ,  365 . Each flange  364 ,  365  extends circumferentially across its respective segment  363  and projects radially outward from body  361 . On each segment  363 , primary flange  364  is positioned axially above secondary flanges  365 , and further, primary flange  364  has a greater axial width than each secondary flange  365 . Collet flanges  364 ,  365  and recesses  366  are sized and configured to releasably mesh with and engage trigger sleeve recesses  352  and flanges  353 , respectively. When collet flanges  364 ,  365  and recesses  366  positively engage trigger sleeve recesses  352  and flanges  353 , respectively, collet  360  is fixed relative to trigger sleeve  351  (i.e., collet  360  does not move axially relative to trigger sleeve  351 ). 
     The radially inner surface of each axially extending segment  363  also includes a primary flange  367  and a plurality of secondary flanges  368  positioned between lower end  360   b  and primary flange  367 . Flanges  367 ,  368  define a plurality of recesses or grooves  369  on the radially inner surface of each segment  363 —one groove  369  is axially positioned between each pair of axially adjacent flanges  367 ,  368 . Each flange  367 ,  368  extends circumferentially across its respective segment  363  and projects radially inward from body  361 . On each segment  363 , primary flange  367  is positioned axially above secondary flanges  368 , and further, primary flange  367  has a greater axial width than each secondary flange  368 . Collet flanges  367 ,  368  and recesses  369  are sized and configured to releasably mesh with and engage mandrel recesses  132  and flanges  133 , respectively. When collet flanges  367 ,  368  and recesses  369  positively engage mandrel recesses  132  and flanges  133 , respectively, collet  360  is fixed relative to mandrel  110  (i.e., collet  360  does not move axially relative to mandrel  110 ). 
     As previously described, collet flanges  367 ,  368  and recesses  369  releasably engage mandrel recesses  132  and flanges  133 , respectively, and collet flanges  364 ,  365  and recesses  366  releasably engage trigger sleeve recesses  352  and flanges  353 , respectively. When collet flanges  367 ,  368  and recesses  369  positively engage mandrel recesses  132  and flanges  133 , respectively, collet  360  is secured to mandrel  110  and moves axially along with mandrel  110 . However, when collet flanges  364 ,  365  and recesses  366  positively engage trigger sleeve recesses  352  and flanges  353 , respectively, collet  360  is secured to trigger sleeve  351  and mandrel  110  is free to move axially relative to collet  360 . Thus, collet  360  of actuation assembly  340  may be described as having a first position secured to mandrel  110  and a second position secured to trigger sleeve  351 . Collet  360  transitions from the first position to the second position as collet flanges  364 ,  365  and recesses  366  come into alignment with trigger sleeve recesses  352  and flanges  353 , respectively, and simultaneously move into positive engagement with trigger sleeve recesses  352  and flanges  353 , respectively, and out of engagement with mandrel recesses  132  and flanges  133 , respectively. Further, collet  360  transitions from the second position to the first position as collet flanges  364 ,  365  and recesses  366  come into alignment with mandrel recesses  132  and flanges  133 , respectively, and simultaneously move into positive engagement with mandrel recesses  132  and flanges  133 , respectively, and out of engagement with trigger sleeve recesses  352  and flanges  353 , respectively. 
     As best shown in  FIG. 2B , compression ring  350  is axially positioned between collet  360  and piston  345  and transfers axial forces therebetween. So long as flanges  367 ,  368  and recesses  369  positively engage mandrel recesses  132  and flanges  133 , respectively, axial forces applied to mandrel  110  are transmitted through collet  360  to compression ring  350  and actuating piston  345 . Compression ring  350  does not sealingly engage mandrel  110  or housing  210  and allows working fluid in chamber  161  to pass axially thereacross as ring  350  moves axially through chamber  161 . In particular, there is a sufficient OD clearance between compression ring  350  and housing  210  to allow working fluid to bypass ring  350  with little restriction. 
     Referring now to  FIGS. 2B, 2C, and 4 , jar lock section  102  includes a lock assembly  370  disposed within chamber  161  and axially positioned between lower end  245   b  of housing tubular member  245  and upper end  255   a  of housing tubular mandrel  255 . In this embodiment, lock assembly  370  includes a biasing member  371 , a spacer or compression ring  375 , a trigger sleeve  381 , a trigger sleeve biasing member  385 , and a collet  360 ′. Thus, in this embodiment, lock assembly  370  includes substantially the same components as actuation assembly  340  previously described, except that lock assembly  370  does not include a piston (e.g., actuation piston  345 ). Collet  360 ′ of lock assembly  370  is substantially the same as collet  360  of actuation assembly  340  previously described and shown in  FIG. 5 , except that collet  360 ′ has a smaller ID than collet  360  since collets  360 ,  360 ′ are configured to mate with mandrel tubular members  130 ,  140 , respectively, which have different ODs. For purposes of clarity and further explanation, collet  360 ′ of lock assembly  370  has been denoted with a “′”. 
     Biasing member  371  is axially positioned between lower end  245   b  of housing tubular member  245  and compression ring  375 . In particular, biasing member  371  has a first or upper end  371   a  that bears against lower end  245   b  and a second or lower end  371   b  that bears against compression ring  375 . Biasing member  371  is configured such that it provides minimal resistance to the axial flow of working fluid. For example, biasing member  371  may be radially spaced from housing  210 , radially spaced from mandrel  110 , include one or more axial throughbores or flow passages, or combinations thereof. In this embodiment, biasing member  371  comprises a stack of Bellville springs. As previously described, a “stack” of Bellville springs refers to a plurality of Bellville springs positioned one adjacent the other (e.g., one-above-the-other) to form an elongate “stack.” In other embodiments, the piston biasing member (e.g., biasing member  371 ) may comprise other types of spring arrangements including, without limitation, coil springs. 
     Biasing member  371  is axially compressed between end  245   b  and ring  375 , and thus, urges ring  375  axially downward and away from end  245   b . Thus, the biasing member  371  resists upward axial movement of compression ring  375  and seeks to seat ring  375  against housing annular shoulder  251  as shown in  FIGS. 2C and 4 . As will be described in more detail below, biasing member  341  is compressed when jar  100  is in the neutral position, thereby providing lock section  102  with a preload that enables the operator to apply an upward axial force on mandrel  110  without necessarily actuating lock section  102 . For example, biasing member  371  may be configured to apply a 5,000 lb. downward force on ring  375  and mandrel  110  with the jar  100  in the neutral position shown in  FIGS. 2A-2D . So long as the upward axial force applied to compression ring  375  does not exceed this preload, lock section  102  remains in the locked position engaging mandrel  110 . The amount of preload provided by biasing member  371  may be adjusted by varying the compression of biasing member  371 . For example, additional Bellville springs may be added to the stack or the axial width of compression ring  375  may be increased. 
     The preload (e.g., lbs.) provided by each biasing member  341 ,  371  may be varied depending on the application and generally depends on the axial travel required to trigger collets  360 ,  360 ′, respectively. In this embodiment, sections  101 ,  102  are configured such that biasing member  371  provides a larger preload than biasing member  341 . This may be achieved, for example, by including Bellville springs in biasing member  371  with a greater axial thickness than the Bellville springs in biasing member  341  as shown in  FIGS. 2A-2C , compressing biasing member  371  greater than biasing member  341  in the neutral position, or combinations thereof. In this exemplary embodiment, the preload of biasing member  341  is about 20% the preload of  371 . 
     Referring now to  FIG. 2C , compression ring  375  is axially positioned between biasing member  371  and housing annular shoulder  251 . As previously described, biasing member  371  urges ring  375  into engagement with shoulder  251 . Ring  375  slidingly engages housing  210  but is radially spaced from mandrel  110 . Thus, ring  375  is generally free to move axially through chamber  181  relative to housing  210  and/or mandrel  110 . However, housing shoulder  251  defines the lower limit of axially downward movement of ring  375  within chamber  181 , and as will be described in more detail below, the positive engagement of trigger sleeve  381  and collet  360 ′ defines the upper limit of axially upward movement of ring  375  within chamber  181 . 
     Unlike piston  345  previously described, ring  375  does not sealingly engage housing  210  or mandrel  110 . Thus, working fluid in chamber  161  is generally free to move around ring  375  (e.g., between ring  375  and mandrel  210  and between ring  375  and housing  210 ) as ring  375  moves axially through chamber  161 . Since ring  375  is axially spaced from mandrel  110 , working fluid around ring  375  will pass through the annulus between ring  375  and mandrel  110 . In addition, there is a sufficient OD clearance between compression ring  375  and housing  210  to allow working fluid to flow between ring  375  and housing  210  with little restriction. 
     Referring to  FIGS. 2C and 4 , tubular trigger sleeve  381  is radially positioned between housing  210  and collet  360 ′, and axially positioned between housing shoulder  252  and end  255   a  of housing tubular mandrel  255 . Trigger sleeve  381  slidingly engages housing  210 , and thus, is generally free to move axially between shoulder  252  and end  255   a . However, biasing member  385  is axially positioned between trigger sleeve  381  and end  255   a . In particular, biasing member  385  has a first or upper end  385   a  that axially abuts trigger sleeve  381  and a second or lower end  385   b  that engages housing tubular mandrel  255  and is seated in recess  258 . Biasing member  385  is axially compressed between trigger sleeve  381  and end  255   a , and thus, urges trigger sleeve  381  into engagement with housing shoulder  252 . In this embodiment, biasing member  385  is a coil spring, however, in general, the trigger sleeve biasing member (e.g., biasing member  385 ) may comprise any suitable biasing device such as a wave spring. 
     Trigger sleeve  381  has a first or upper end  381   a  and a second or lower end  381   b  opposite end  381   a . In addition, trigger sleeve  381  has a radially outer surface including a cylindrical portion  382  extending from end  381   a  and an annular recess  383  axially positioned between cylindrical portion  382  and end  381   b . Recess  383  is proximal to, but does not extend to end  381   b , and therefore, defines an annular shoulder  384  along the outer surface of trigger sleeve  381 . The radially inner surface of trigger sleeve  381  includes a plurality of annular recesses  385  defining a plurality of radially inwardly projecting annular flanges  386 —one flange  386  is axially disposed between each pair of axially adjacent recesses  385 . Recesses  385  and flanges  386  are sized and configured to releasably engage mating flanges  364 ,  365  and recesses  366 , respectively, provided on the radially outer surface of collet  360 ′ as described in more detail below. 
     An annular split ring  387  couples trigger sleeve  381  to housing tubular mandrel  255 . Split ring  387  has a radially outer cylindrical surface that slidingly engages housing  210  and a radially inner surface include an annular recess  388  that defines annular flanges  389   a ,  389   b  at the upper and lower ends, respectively, of split ring  387 . Flanges  389   a ,  389   b  extend radially inward and engage recesses  383 ,  259 , respectively, of trigger sleeve  381  and housing tubular mandrel  255 , respectively. Together, adjustment ring  261 , housing mandrel  255 , and split ring  387  allow for the adjustment of the axial position of trigger sleeve  381  relative to collet  360 ′ in the neutral position. Specifically, adjustment ring  261  and mandrel  255  may be rotated about axis  105  in a first direction to move mandrel  255  and trigger sleeve  381  coupled thereto with split ring  387  axially downward. Alternatively, adjustment ring  261  and mandrel  255  may be rotated about axis  105  in the opposite direction to move mandrel  255  and trigger sleeve  381  coupled thereto with split ring  387  axially upward. It should be appreciated that housing shoulder  252  limits the extent of upward movement of trigger sleeve  381  relative to collet  360 ′. 
     Referring now to  FIGS. 2C, 4, and 7 , collet  360 ′ of lock assembly  370  is radially disposed between mandrel  110  and trigger sleeve  381 . As previously described, collet  360 ′ is substantially the same as collet  360  of actuation assembly  340  previously described and shown in  FIG. 5 . However, flanges  367 ,  368  and recesses  369  of collet  360 ′ of lock assembly  370  are sized and configured to releasably mesh with and engage mandrel recesses  141  and flanges  142 , respectively, and flanges  364 ,  365  are sized and configured to releasably mesh with and engage recesses  385  and flanges  386 , respectively, of trigger sleeve  381 . 
     When collet flanges  367 ,  368  and recesses  369  positively engage mandrel recesses  141  and flanges  142 , respectively, collet  360 ′ is secured to mandrel  110  and moves axially along with mandrel  110 . However, when collet flanges  364 ,  365  and recesses  366  positively engage trigger sleeve recesses  385  and flanges  386 , respectively, collet  360 ′ is secured to trigger sleeve  381  and mandrel  110  is free to move axially relative to lock assembly collet  360 . Thus, collet  360 ′ of lock assembly  370  may be described as having a first position secured to mandrel  110  and a second position secured to trigger sleeve  381 . Collet  360 ′ transitions from the first position to the second position as collet flanges  364 ,  365  and recesses  366  come into alignment with trigger sleeve recesses  385  and flanges  386 , respectively, and simultaneously move into positive engagement with trigger sleeve recesses  385  and flanges  386 , respectively, and out of engagement with mandrel recesses  141  and flanges  142 , respectively. Further, collet  360 ′ transitions from the second position to the first position as collet flanges  364 ,  365  and recesses  366  come into alignment with mandrel recesses  141  and flanges  142 , respectively, and simultaneously move into positive engagement with mandrel recesses  141  and flanges  142 , respectively, and out of engagement with trigger sleeve recesses  385  and flanges  386 , respectively. 
     The jarring movement of jar  100  may be understood by referring to  FIGS. 2A-2D  and  FIGS. 8A-8D .  FIGS. 2A-2D  show jar  100  in the unloaded, neutral, unfired position, whereas  FIGS. 8A-8D  show jar  100  in the fired position with hammer surface  124  engaging anvil surface  303 . 
     As best shown in  FIGS. 2B and 2C , with jar  100  in the neutral position, collet  360  of actuation assembly  340  and collet  360 ′ of lock assembly  370  each positively engage mandrel  110 . Namely, collet flanges  367 ,  368  and recesses  369  of collet  360  positively engage mandrel recesses  132  and flanges  133 , respectively, and collet flanges  367 ,  368  of collet  360 ′ positive engage mandrel recesses  141  and flanges  142 , respectively. Thus, both collets  360 ,  360 ′ move axially along with mandrel  110  relative to housing  210  and trigger sleeves  351 ,  381 . 
     When jar  100  or downhole component coupled to jar  100  (e.g., tool  30 ) becomes stuck downhole, the operator applies a lifting force to jar  100  from the surface in an attempt to dislodge the stuck component. As a result, jar  100  is placed in tension—upper end  100   a  and mandrel  110  are pulled upward (e.g., by wireline  20 ) relative to lower end  100   b  and housing  210 , which are stuck or connected to a stuck downhole component. In general, the range of permissible magnitudes of tensile loads, and thus the imparted upward jarring force, is limited only by the structural limits of jar  100  and the seals therein and by the string or wireline (e.g., wireline  20 ) that is supporting jar  100 . When jar  100  is placed in tension in the neutral position, mandrel  110  and both collets  360 ,  360 ′, which positively engaging mandrel  110 , are urged axially upward relative to housing  210  and trigger sleeves  351 ,  381 , which axially abut housing shoulders  242 ,  252 , respectively. 
     The axial upward force applied to collet  360  by mandrel  110  is transferred to biasing member  341  by compression ring  350  and piston  345 , and the axial force applied to collet  360 ′ by mandrel  110  is transferred to biasing member  371  by compression ring  375 . However, biasing members  341 ,  371  are compressed and preloaded in the neutral position such that each exerts an axial downward force on mandrel  110 —biasing member  341  exerts an axial downward force on mandrel  110  via piston  345 , compression ring  350  and collet  360 , and biasing member  371  exerts an axial downward force on mandrel  110  via compression ring  375  and collet  360 ′. Both collets  360 ,  360 ′ are secured to mandrel  110 , and thus, mandrel  110  and collets  360 ,  360 ′ do not move in response to tension applied to jar  100  unless and until the tensile force applied to jar  100  exceeds the total preload provided by biasing members  341 ,  371  (i.e., the sum of the preloads provided by biasing members  341 ,  371 ). In other words, biasing members  341 ,  371  share the tensile loads applied to jar  100 . As previously described, in this embodiment, the preload of biasing member  371  is greater than the preload of biasing member  341 . However, in other embodiments, the preload of the actuation assembly biasing member (e.g., biasing member  341 ) may be greater than the preload of the lock assembly biasing member (e.g., biasing member  381 ). 
     When the tension applied to jar  100  is sufficient to overcome the total preload of both biasing members  341 ,  371 , mandrel  110  and collets  360 ,  360 ′ secured thereto will begin to slowly move axially upward relative to housing  210  and trigger sleeves  351 ,  381 . As biasing members  341 ,  371  are axially compressed, each generates an increasing spring force that resists continued axial upward movement of collets  360 ,  360 ′ and mandrel  110 . In addition, working fluid pressure in chamber upper portion  161   a  resist the axial upward movement of collets  360 ,  360 ′ and mandrel  110  as piston  345  moves axially upward in chamber  161 . That is, upward axial movement of piston  345  relative to the housing  210  reduces the volume of chamber upper portion  161   a  causing a significant increase in the working fluid pressure within portion  161   a , thereby generating an axial hydraulic force that resist this relative movement. The hydraulic resistance to movement of piston  345  relative to housing  210  and the mechanical resistance to movement of piston  345  and compression ring  375  by biasing members  341 ,  371 , respectively, allows a large buildup of potential energy in the working string when a tensile load is placed on jar  100  from the surface. With regard to the hydraulic resistance, it should be appreciated that over time, flow restrictor  348   a  allows working fluid to flow through piston  345  from chamber upper portion  161   a  to chamber lower portion  161   b , thereby slowly relieving the pressure in chamber upper portion  161   a  and allowing piston  345  to move slowly upward within chamber  161  relative to housing  210 . 
     If the tension applied to jar  100  is maintained at a level sufficient to overcome both biasing members  341 ,  371  (i.e., the preloads of both biasing members  341 ,  371  as well as the added spring forces from the additional compression of both biasing members  341 ,  371 ), mandrel  110  and collets  360 ,  360 ′ secured thereto will continue to move axially upward relative to housing  210  and trigger sleeves  351 ,  381 . Collets  360 ,  360 ′ and trigger sleeves  351 ,  381 , respectively, are sized and positioned such that flanges  364 ,  365  and recesses  366  of collet  360 ′ come into alignment with mating recesses  385  and flanges  386 , respectively, of trigger sleeve  381  before flanges  364 ,  365  and recesses  366  of collet  360  come into alignment with mating recesses  352  and flanges  353 , respectively, of trigger sleeve  351  as collets  360 ,  360 ′ and mandrel  110  move axially upward relative to housing  210  and trigger sleeves  351 ,  381 . 
     As best shown in  FIG. 8C , when the primary outwardly facing flange  364  of collet  360 ′ just clears the uppermost flange  386  of trigger sleeve  381 , outwardly projecting flanges  365  come into substantial alignment with mating recesses  385  of trigger sleeve  381 , and fingers  363  of collet  360 ′ are cammed radially outward until flanges  364 ,  365  seat in mating recesses  385  of trigger sleeve  381 . In particular, once radial clearance is provided for flanges  364 ,  365 , sliding engagement of angled surfaces of mandrel flanges  142  and collet recesses  369 , and sliding engagement of angled surfaces of mandrel recesses  141  and collet flanges  368  urge fingers  363  radially outward. At that point, outwardly projecting mandrel flanges  142  radially clear inwardly projecting flanges  368 , collet  360 ′ fully disengages mandrel  110 , and mandrel  110  is released from the retarding action of lock assembly biasing member  371 . In other words, once collet  360 ′ moves out of engagement with mandrel  110  and into engagement with trigger sleeve  381 , the spring force generated by biasing member  371  is no longer transferred to mandrel  110 . 
     Once collet  360 ′ of lock assembly  370  moves out of engagement with mandrel  110 , the tensile load applied to jar  100  is substantially or entirely carried by actuation assembly  340 . If that applied tensile load is sufficient to overcome biasing member  341  (i.e., the tensile load is greater than the sum of the preload of biasing member  341  as well as the added spring force from the additional compression of biasing members  341 ), mandrel  110  and collet  360  secured thereto will continue to be urged axially upward. As previously described, compression of the hydraulic fluid in chamber upper portion  161   a  by piston  345  hydraulically resists movement of piston  345 , collet  360 , and mandrel  110  relative to housing  210 . However, over a period of time referred to as the “hydraulic delay” of firing section  101 , flow restrictor  348   a  allows working fluid to flow through piston  345  from chamber upper portion  161   a  to chamber lower portion  161   b , and thereby allows piston  345  to creep slowly upward within chamber  161  relative to housing  210 . In this manner, piston  345  and flow restrictor  348   a  enable a significant overpull to be applied to mandrel  110  followed by a gradual bleed off of fluid pressure through the piston  345  and eventual triggering of the jar  100 . In general, the hydraulic delay may be controllably adjusted by varying the relative axial positions of trigger sleeve  351  and collet  360  in the neutral position (i.e., the short the axial distance collet  360  must move to align flanges  364 ,  365  and recesses  366  with mating recesses  352  and flanges  353  of trigger sleeve  351 , the shorter the hydraulic delay of firing section  101 ). 
     With sufficient tension applied to jar  100 , piston  345 , mandrel  110 , and collet  360  moves axially upward relative to housing  210  and trigger sleeve  351 . As best shown in  FIG. 8B , when the primary outwardly facing flange  364  of collet  360  just clears the uppermost flange  353  of trigger sleeve  351 , outwardly projecting flanges  365  will be in substantial alignment with mating recesses  352  of trigger sleeve  351 , and fingers  363  of collet  360  are cammed radially outward until flanges  364 ,  365  seat in mating recesses  352  of trigger sleeve  351 . In particular, once radial clearance is provided for flanges  364 ,  365 , sliding engagement of angled surfaces of mandrel flanges  133  and collet recesses  369 , and sliding engagement of angled surfaces of mandrel recesses  132  and collet flanges  368  urge fingers  363  radially outward. At that point, outwardly projecting mandrel flanges  133  radially clear inwardly projecting flanges  368 , collet  360  fully disengages mandrel  110 . Without the resistance provided by biasing member  341 , mandrel  110  accelerates upward rapidly propelling hammer surface  124  into anvil surface  303 , thereby generating the upward impact and jarring load to jar  100  and components coupled thereto, as shown in  FIG. 8A . 
     If tension on mandrel  110  is released subsequent to firing jar  100 , recocking biasing member  332  urges mandrel  110  axially downward to the position shown in  FIG. 1B . In addition, biasing members  341 ,  381  urge collets  360 ,  360 ′, respectively, axially downward. As mandrel flanges  133  come into alignment with mating recesses  369  of collet  360 , the downward axial force provided by biasing member  341  will cause fingers  363  to cam radially inward and urge collet flanges  367 ,  368  into positive engagement with mandrel recesses  132 . Similarly as mandrel flanges  142  come into alignment with mating recesses  369  of collet  360 ′, the downward axial force provided by biasing member  371  will cause fingers  363  to cam radially inward and urge collet flanges  367 ,  368  into positive engagement with mandrel recesses  141 . As each collet  360 ,  360 ′ positively engages mandrel  110  and disengages trigger sleeves  351 ,  381 , respectively, biasing members  355 ,  385  urge trigger sleeves  351 ,  381 , respectively, back to the position shown in  FIGS. 2B and 2C . The downward movement of piston  345  relative to housing  210  is accompanied by a flow of working fluid up through piston  345 . 
     Collet  360  of actuation assembly  340  provides for relatively short firing or metering stroke. The metering stroke is defined approximately by the distance between primary flanges  364  and the lowermost secondary flanges  365 . This relatively short metering stroke minimizes bleed off or lost potential energy and minimizes the amount of working fluid that must pass through piston  345 , thereby reducing heat buildup on the fluid. 
     As previously described, each collet  360 ,  360 ′ is provided with a plurality of principal outwardly projecting flanges  364  that are axially wider than recesses  352 ,  385  in sleeves  351 ,  381 , respectively. This deliberate mismatch in dimensions is designed to prevent one or more of secondary outwardly projecting collet flanges  365  from prematurely engaging and locking into one of lower recesses  352 ,  385 . Such a premature engagement between the outwardly projecting secondary flanges  365  and recesses  352 ,  385  might prevent the additional axial movement of the mandrel  110  or result in a premature release of mandrel  110  and thus insufficient application of upward jarring force. 
     In general, the components of embodiments of jars described herein (e.g., jar  100 ) may be made from any suitable material(s) including, without limitation, metals and metal alloys (e.g., steel, aluminum, etc.), non-metals (e.g., polymers, ceramics, etc.), composites, or combinations thereof. For harsh downhole conditions, the components are preferably made from rigid, durable materials such as mild and alloy steels, stainless steels or the like. Wear surfaces, such as the exterior of the mandrel (e.g., mandrel  110 ), may be carbonized to provided a harder surface. 
     In the manner described, embodiments of jar  100  described herein allow the triggering load of jar firing section  101  to be exceeded for a period of time before triggering jar  100  to fire. Specifically, both biasing members  341 ,  371  provide preload and axial forces resisting upward movement of mandrel  110  and collets  360 ,  360 ′ when jar  100  is placed in tension. If the applied tension is sufficient to overcome both biasing members  341 ,  371 , and is maintained for a sufficient period of time, collet  360 ′ of lock assembly  370  will disengage mandrel  110 , and only then does firing section  101  begin its firing cycle. Even if collet  360 ′ disengages mandrel  110  and the applied tension is maintained at a level sufficient to overcome biasing member  341 , the hydraulic delay required for piston  345  to move through chamber  161  provides the operate added time to decide whether to reduce line tension and avoid jarring, or allow jarring to proceed. 
     While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.