Patent Publication Number: US-11028660-B2

Title: Downhole impact apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. patent application Ser. No. 15/803,799, titled “DOWNHOLE IMPACT APPARATUS,” filed on Nov. 5, 2017, now U.S. Pat. No. 10,480,270, which claims priority to and the benefit of U.S. Provisional Patent Application No. 62/508,905, titled “DOWNHOLE IMPACT APPARATUS,” filed on May 19, 2017, the entire disclosures of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Drilling operations have become increasingly expensive as the need to drill deeper, in harsher environments, and through more difficult materials has become a reality. In addition, testing and evaluation of completed and partially finished wellbores has become commonplace, such as to increase well production and return on investment. Consequently, in working with deeper and more complex wellbores, it becomes more likely that tools, tool strings, and/or other downhole equipment may become stuck within the wellbore. 
     A downhole impact or jarring tool may be utilized to dislodge stuck downhole equipment. The impact or jarring tool (hereafter collectively referred to as “an impact tool”) may be included as part of a tool string and deployed downhole along with the downhole equipment, or the impact tool may be deployed downhole after equipment already downhole becomes stuck. Tension may be applied from a wellsite surface to the deployed tool string via a conveyance means to store elastic energy in the tool string and the conveyance means. After sufficient tension is applied to the impact tool, the impact tool may be triggered to release the elastic energy in the impact tool and the conveyance means, thereby delivering an impact intended to dislodge the stuck downhole tool or to break a shear pin to disconnect a portion of the tool string from the stuck downhole tool. 
     However, in some downhole applications, such as in deviated wellbores or when multiple bends are present along the wellbore, friction between a sidewall of the wellbore and the conveyance means may reduce or prevent adequate tension from being applied to the impact tool. In such situations, the impact tool may be unable to produce an impact that is sufficient to dislodge the stuck downhole tool or break the shear pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a schematic view of at least a portion of an example implementation of apparatus according to one or more aspects of the present disclosure. 
         FIG. 2  is a schematic view of at least a portion of an example implementation of apparatus according to one or more aspects of the present disclosure. 
         FIG. 3  is a schematic view of the apparatus shown in  FIG. 2  at a different stage of operation. 
         FIG. 4  is a schematic view of the apparatus shown in  FIGS. 2 and 3  at a different stage of operation. 
         FIG. 5  is an enlarged view of a portion of the apparatus shown in  FIG. 2 . 
         FIG. 6  is an enlarged view of another portion of the apparatus shown in  FIG. 2 . 
         FIG. 7  is a schematic view of a portion of an example implementation of apparatus according to one or more aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the following disclosure provides many different implementations, or examples, for implementing different features of various implementations. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for simplicity and clarity, and does not in itself dictate a relationship between the various implementations described below. Moreover, in the description below, the formation of a first feature over or on a second feature may include implementations in which the first and second features are formed in direct contact, and may also include implementations in which one or more additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. 
     Existing impact tools included in downhole tool strings are operable to impart an impact (i.e., a force) to the tool string when the tool string is stuck in a wellbore. Energy for performing the impact may be stored (e.g., during jarring operations) within the impact tool, and perhaps also within the conveyance means used to convey the tool string into the wellbore. When the tool string gets stuck in the wellbore, the conveyance means is pulled from the wellsite surface in an uphole direction to build up tension and, thus, store elastic energy in the impact tool and the stretched conveyance means. The stored energy is released by triggering the impact tool at a predetermined time or situation. 
     Downhole impact tools within the scope of the present disclosure, however, are operable to store energy in the form of a pressure differential between ambient wellbore pressure external to the downhole impact tool and an internal pressure of the downhole impact tool. The pressure differential may be released or otherwise utilized to cause an impact between portions of the impact tool, such as to free a stuck portion of the tool string, and/or to break a shear pin to release a portion of the tool string for conveyance to the wellsite surface. 
     The downhole impact tool may comprise a housing, a chamber within the housing that is open to a space external to the housing, and a movable piston and shaft assembly fluidly isolating a portion of the chamber from the space external to the housing. The chamber may contain air or another gas at a predetermined pressure, such as atmospheric pressure (i.e., surface pressure) or another pressure. Thus, one side of a piston of the piston and shaft assembly may be exposed to the isolated portion of the chamber and, thus, the chamber pressure, while an opposing side of the piston may be exposed to a portion of the chamber exposed to the space external to the impact tool and, thus, hydrostatic wellbore pressure. 
     The downhole impact tool may be coupled along the tool string and conveyed downhole with the tool string. During downhole conveyance, the piston and shaft assembly may be locked or otherwise maintained in a predetermined position with respect to the housing or body of the impact tool, thus preventing relative movement between the piston and shaft assembly and the housing. Accordingly, the pressure within the isolated portion of the chamber may be maintained substantially lower than the pressure within the portion of the chamber open to the space external to the housing. As the downhole impact tool is conveyed deeper within the wellbore and the pressure within the wellbore increases, an increasing pressure differential is formed across the piston, storing an increasing amount of energy. The energy stored by or within the isolated portion of the chamber and the piston may be proportional or otherwise related to the hydrostatic wellbore pressure around the impact tool. 
     Releasing or freeing the piston and shaft assembly from or with respect to the housing may permit the pressure differential to cause relative movement between the piston and shaft assembly and the housing, accelerating the portion of the tool string that is not stuck. The relative movement between the piston and shaft assembly and the housing may terminate when the piston and shaft assembly, the housing, and/or other portions of the impact tool contact or impact each other to suddenly stop or decelerate the moving portion of the impact tool and the tool string, causing an impact force to be imparted through the impact tool to the stuck portion of the tool string. The impact may be utilized to free a stuck portion of a tool string, or to break a shear pin to release a portion of the tool string for conveyance to the wellsite surface. 
       FIG. 1  is a schematic view of at least a portion of a wellsite system  100  showing an example environment comprising or utilized in conjunction with a downhole tool string  110  comprising an impact tool  116  according to one or more aspects of the present disclosure. The tool string  110  may be suspended within a wellbore  102  that extends from a wellsite surface  104  into one or more subterranean formations  106 . The wellbore  102  may be a cased-hole implementation comprising a casing  108  secured by cement  109 . However, one or more aspects of the present disclosure are also applicable to and/or readily adaptable for open-hole implementations lacking the casing  108  and cement  109 . The tool string  110  may be suspended within the wellbore  102  via a conveyance means  120  operably coupled with a tensioning device  130  and/or other surface equipment  140  disposed at the wellsite surface  104 , including a power and control system  150 . 
     The tensioning device  130  may apply an adjustable tensile force to the tool string  110  via the conveyance means  120  to convey the tool string  110  along the wellbore  102 . The tensioning device  130  may be, comprise, or form at least a portion of a crane, a winch, a draw-works, a top drive, and/or another lifting device coupled to the tool string  110  by the conveyance means  120 . The conveyance means  120  may be or comprise a wireline, a slickline, an e-line, coiled tubing, drill pipe, production tubing, and/or other conveyance means, and may comprise and/or be operable in conjunction with means for communication between the tool string  110 , the tensioning device  130 , and/or one or more other portions of the surface equipment  140 , including the power and control system  150 . The conveyance means  120  may comprise a plurality of conductors, including electrical and/or optical conductors, extending between the tool string  110  and the surface equipment  140 . The power and control system  150  may include a source of electrical power  152 , a memory device  154 , and a controller  156  operable to receive and process electrical and/or optical signals from the tool string  110  and/or commands from a surface operator. The controller  156  may also be operable to transmit signals downhole to the tool string  110 , such as via the conveyance means  120 . 
     The tool string  110  is shown positioned in a non-vertical portion  107  of the wellbore  102  resulting in the conveyance means  120  coming into contact with a sidewall  103  of the wellbore  102  along a bend or deviation  105  in the wellbore  102 . The contact causes friction between the conveyance means  120  and the sidewall  103 , such as may impede or reduce the tension being applied to the tool string  110  and the impact tool  116  by the tensioning device  130 . However, the tool string  110  and the impact tool  116  may also be utilized within a substantially vertical well or well portion  111  of the wellbore  102 . 
     The tool string  110  may comprise an uphole portion  112 , a downhole portion  114 , and the impact tool  116  coupled between the uphole portion  112  and the downhole portion  114 . The uphole portion  112  of the tool string  110  may comprise at least one electrical conductor  113  in electrical communication with at least one component of the surface equipment  140 . The downhole portion  114  of the tool string  110  may also comprise at least one electrical conductor  115  in electrical communication with at least one component of the surface equipment  140 , wherein the electrical conductor  113  and the electrical conductor  115  may be in electrical communication via at least one electrical conductor  117  of the impact tool  116 . Thus, the electrical conductors  113 ,  115 ,  117  may connect with and/or form a portion of the conveyance means  120 , and may include various electrical connectors and/or interfaces along such path, including as described below. Although the conductors  113 ,  115 ,  117  are described as electrical conductors, the conductors  113 ,  115 ,  117  may also or instead be or comprise optical conductors. 
     Each of the electrical conductors  113 ,  115 ,  117  may comprise a plurality of individual conductors, such as may facilitate electrical communication of the uphole portion  112  of the tool string  110 , the impact tool  116 , and the downhole portion  114  of the tool string  110  with at least one component of the surface equipment  140 , such as the power and control system  150 . For example, the conveyance means  120  and the electrical conductors  113 ,  115 ,  117  may transmit and/or receive electrical power, data, and/or control signals between the power and control system  150  and one or more of the uphole portion  112 , the impact tool  116 , and the downhole portion  114 . The electrical conductors  113 ,  115 ,  117  may further facilitate electrical communication between two or more of the uphole portion  112 , the impact tool  116 , and the downhole portion  114 . Each of the uphole portion  112 , the downhole portion  114 , the impact tool  116 , and/or portions thereof may comprise one or more electrical connectors, such as may electrically connect the electrical conductors  113 ,  115 ,  117 . 
     The uphole and downhole portions  112 ,  114  of the tool string  110  may each be or comprise at least a portion of one or more downhole tools, modules, and/or other apparatus operable in wireline, while-drilling, coiled tubing, completion, production, and/or other operations. For example, the uphole and downhole portions  112 ,  114  may each be or comprise at least a portion of an acoustic tool, a centralizer, a cutting tool, a density tool, a directional tool, an electromagnetic (EM) tool, a formation evaluation, logging, and/or measurement tool, a gravity tool, a magnetic resonance tool, a mechanical interface tool, a monitoring tool, a neutron tool, a nuclear tool, an orientation tool, a perforating tool, a photoelectric factor tool, a plug, a plug setting tool, a porosity tool, a release tool, a reservoir characterization tool, a resistivity tool, a sampling tool, a seismic tool, a standoff, a surveying tool, and/or combinations thereof, among other examples also within the scope of the present disclosure. One or both of the uphole and downhole portions  112 ,  114  may comprise inclination sensors and/or other position sensors, such as one or more accelerometers, gyroscopic sensors (e.g., micro-electro-mechanical system (MEMS) gyros), magnetometers, and/or other sensors for utilization in determining the orientation of the tool string  110  (or a portion thereof) relative to the wellbore  102 . 
     One or both of the uphole and downhole portions  112 ,  114  may comprise a correlation tool, such as a casing collar locator (CCL) for detecting ends of casing collars by sensing a magnetic irregularity caused by the relatively high mass of an end of a collar of the casing  108 . The uphole and downhole portions  112 ,  114  may also or instead be or comprise a gamma ray (GR) tool that may be utilized for depth correlation. The CCL and/or GR tools may transmit signals in real-time to the wellsite surface equipment  140 , such as the power and control system  150 , via the conveyance means  120 . The CCL and/or GR signals may be utilized to determine the position of the tool string  110  or portions thereof, such as with respect to known casing collar numbers and/or positions within the wellbore  102 . Therefore, the CCL and/or GR tools may be utilized to detect and/or log the location of the tool string  110  within the wellbore  102 , such as during intervention operations. 
     Although  FIG. 1  depicts the tool string  110  comprising a single impact tool  116  directly coupled between two tool string portions  112 ,  114 , the tool string  110  may include two, three, four, or more impact tools  116 , which may be coupled together or separated from each other along the tool string  110  by the tool string portions  112 ,  114 . The tool string  110  may also comprise additional tool string portions  112 ,  114  directly and/or indirectly coupled with the impact tool(s)  116 . The impact tool  116  may be coupled elsewhere along the tool string  110  (relative to the location depicted in  FIG. 1 ), whether in an uphole or downhole direction with respect to the uphole and downhole portions  112 ,  114  of the tool string  110 . 
       FIGS. 2-4  are schematic views of at least a portion of an example implementation of the impact tool  116  shown in  FIG. 1  according to one or more aspects of the present disclosure, designated in  FIGS. 2-4  by reference numeral  200 .  FIGS. 2-4  show the impact tool  200  at different stages of impact operations. The following description refers to  FIGS. 1-4 , collectively. 
     The impact tool  200  comprises a housing  202  defining or otherwise encompassing a plurality of internal spaces or volumes containing various components of the impact tool  200 . Although the housing  202  is depicted in  FIGS. 2-4  as a single unitary member, the housing  202  may be or comprise a plurality of housing sections coupled together to form the housing  202 . 
     An uphole end  206  of the impact tool  200  may include a mechanical interface, a sub, and/or other interface means  208  for mechanically coupling the impact tool  200  with a corresponding interface means (not shown) of the uphole portion  112  of the tool string  110 . The interface means  208  may be integrally formed with or coupled to the housing  202 , such as via a threaded connection. A downhole end  210  of the impact tool  200  may include a mechanical interface, a sub, and/or other interface means  212  for mechanically coupling with a corresponding interface means (not shown) of the downhole portion  114  of the tool string  110 . The interface means  212  may be integrally formed with or coupled to the impact tool  200 , such as via a threaded connection. The interface means  208 ,  212  may be or comprise threaded connectors, fasteners, box couplings, pin couplings, and/or other mechanical coupling means. Although the interface means  208 ,  212  are depicted in  FIGS. 2-4  as being a box connector, one or both of the interface means  208 ,  212  may be implemented as pin connector. 
     The uphole interface means  208  and/or other portion of the uphole end  206  of the impact tool  200  may further include an electrical interface  209  comprising means for electrically coupling an electrical conductor  205  extending along the impact tool  200  with a corresponding electrical interface (not shown) of the uphole portion  112  of the tool string  110 , whereby the corresponding electrical interface of the uphole portion  112  may be in electrical connection with the electrical conductor  113 . The downhole interface means  212  and/or other portion of the downhole end  210  of the impact tool  200  may include an electrical interface  213  comprising means for electrically coupling with a corresponding interface (not shown) of the downhole portion  114  of the tool string  110 , whereby the corresponding electrical interface of the downhole tool string portion  114  may be in electrical connection with the electrical conductor  115 . The electrical interfaces  209 ,  213  may each comprise electrical connectors, plugs, pins, receptacles, terminals, conduit boxes, and/or other electrical coupling means. 
     The impact tool  200  may comprise chambers  214 ,  216  within the housing  202  and a tandem piston and shaft assembly  220  (hereinafter referred to as a “piston assembly”) slidably or otherwise movingly disposed within the housing  202 . The piston assembly  220  may comprise a piston  222  slidably disposed within the chamber  214  and dividing the chamber  214  into opposing chamber volumes  224 ,  226 . The piston  222  may sealingly engage an inner surface of the chamber  214  to fluidly separate the chamber volumes  224 ,  226 . The piston  222  may carry fluid seals  225  that may fluidly seal against the inner surface of the chamber  214  to prevent fluids located on either side of the piston  222  from leaking between the chamber volumes  224 ,  226 . The chamber  216  may include chamber portions  234 ,  236  having different inner diameters  235 ,  237 , wherein the inner diameter  235  of the chamber portion  234  may be substantially smaller than the inner diameter  237  of the chamber portion  236 . 
     The piston assembly  220  may further comprise a piston  232  movably disposed within the chamber  216 . When the piston  232  is positioned within the chamber portion  234 , the piston  242  may sealingly engage an inner surface of the chamber portion  234  to fluidly separate the chamber portions  234 ,  236 . The piston  232  may carry fluid seals  233  that may fluidly seal against the inner surface of the chamber portion  234  to prevent fluids located on either side of the piston  242  from leaking between the chamber portions  234 ,  236 . However, when the piston  232  moves out of the chamber portion  234  into the chamber portion  236 , the fluid seals  233  or other portions of the piston  232  may not engage and seal against an inner surface of the chamber portion  236 , thus permitting fluid within the chamber portion  236  to move around or past the piston  232 . 
     A rod or shaft  228  may extend between the pistons  222 ,  232  through a bore or pathway extending through the housing  202  between the chambers  214 ,  216 . The shaft  228  may connect the pistons  222 ,  232  such that the pistons  222 ,  232  move in unison. Fluid seals  229  may be disposed between the housing  202  and the shaft  228  to prevent or reduce fluid communication between the chamber volume  224  of the chamber  214  and the chamber portion  236  of the chamber  216 . 
     The piston assembly  220  may further comprise a rod or shaft  230  connected with the piston  222  opposite the shaft  228 . The shaft  230  may be axially movable within the chamber  214  and into and out of the housing  202  at a downhole end of the housing  202 . A stop section  240  of the housing  202  may retain the piston  222  within the chamber  214  and fluidly seal against the shaft  230  to isolate the chamber volume  226  from the space external to the housing  202 . The stop section  240  may comprise a central opening to permit the shaft  230  to axially move into and out of the housing  202 , and a fluid seal  242  to fluidly seal against the shaft  230  to prevent fluid located external to the housing  202  from leaking into the chamber volume  226 . A downhole end of the shaft  230  may be fixedly coupled with the downhole mechanical interface  212 . Accordingly, the piston assembly  220  connects the housing  202  and the uphole mechanical interface  208  with the downhole mechanical interface  212 . 
     The chamber volume  224  may be open to space external to the housing  202 , and the chamber volume  226  may be fluidly isolated from the space external to the housing  202  by the piston  222 . Thus, the piston  222  and shaft  230  may collectively function as a sealing member or device operable to fluidly isolate the chamber volume  226  from pressure and wellbore fluid in the space external to (i.e., surrounding) the impact tool  200 . A face area  221  of the piston  222  may be exposed to the pressure within the space external to the housing  202 , and an opposing face area  223  may be exposed to pressure within the chamber volume  226 . The chamber volume  224  may be open to or in fluid communication with the space external to the housing  202  via one or more ports  238  or other openings extending through a wall  204  of the housing  202  at or near an uphole end of the chamber  214 . Accordingly, when the impact tool  200  is conveyed downhole, the one or more ports  238  may permit wellbore fluid located within the wellbore  102  to be in communication with the chamber volume  224 , such that the pressure within the chamber volume  224  is substantially equal to the hydrostatic pressure within the wellbore  102  external to the housing  202 . 
     However, while the impact tool  200  is being conveyed downhole, the piston assembly  220  and, thus, the piston  222  may be maintained in a substantially fixed position such that the pressure within the chamber volume  226  is maintained substantially constant or otherwise substantially lower (e.g., at atmospheric pressure) than the hydrostatic wellbore pressure external to the housing  202 . Accordingly, a pressure differential across the piston  222  may be formed as the impact tool  200  is conveyed downhole, imparting a downhole force to the piston  222  and an uphole force to the housing  202  to urge relative movement (i.e., expansion) between the piston assembly  220  and the housing  202 . The downhole and uphole forces formed by the pressure differential across the piston  222  may be collectively referred to hereinafter as an “expansion force.” Although the present disclosure may describe the piston assembly  220  as the moving component of the impact tool  200 , it is done so for clarity and ease of understanding. It is to be understood that the expansion force may cause the housing  202  to move with respect to the piston assembly  220 , for example, when the uphole tool string portion  112  coupled with the housing  202  via the interface means  208  is free and the downhole tool string portion  114  coupled with the interface means  212  is stuck within the wellbore  102 . 
     The impact tool  200  may further comprise an impact feature  244  operable to impact or collide with a corresponding impact feature  246  to bring the relative motion between the piston assembly  220  and the housing  202  to a sudden stop to generate the impact. The impact feature  244  may be implemented as an outwardly extending radial surface, shoulder, boss, flange, and/or another impact member integral to or otherwise carried by the piston assembly  220 , and the corresponding impact feature  246  may be implemented as an inwardly extending radial shoulder, boss, flange, and/or another impact member integral to or otherwise carried by the housing  202 . For example, the impact feature  244  may be integral to or carried by a downhole portion or end of the piston  222 , and the impact feature  246  may be integral to or carried by an uphole portion of the stop section  240  of the housing  202 . However, the impact features  244 ,  246  may be integral to or carried by other portions of the impact tool  200 . For example, the impact feature  244  may be integral to or carried by the shaft  230 , and the impact feature  246  may be integral to or carried by other portions of the housing  202  defining the chamber  214 . The impact feature  244  may also be integral to or carried by the shaft  228  or piston  232 , and the impact feature  246  may be integral to or carried by a portion of the housing  202  defining the chamber portion  236 . 
     The piston assembly  220  and the housing  202  may be selectively locked or held in a substantially constant relative position resisting the expansion force generated by the pressure differential across the piston  222 . For example, hydraulic or another substantially incompressible fluid (e.g., distilled water) may be introduced and fluidly sealed within the chamber portion  236  of the chamber  216  prior to the impact tool  200  being conveyed downhole. Such fluid may be operable to prevent the piston  232  from moving out of the chamber portion  234  and into the chamber portion  236 . Although the piston  232  may drift slightly into the chamber portion  236  during downhole conveyance, the piston assembly  220  may be maintained in a substantially constant position with respect to the housing  202  while the pressure within the chamber volume  224  increases as the impact tool  200  is conveyed downhole. A piston assembly release mechanism  250  (i.e., a triggering mechanism) may be provided within the housing  202  or another portion of the impact tool  200  to selectively release the piston  232  to permit the expansion force to move the piston assembly  220  and the housing  202  relative to each other. The operation of the piston assembly  220  and the release mechanism  250  is described in additional detail below. 
       FIG. 2  depicts the impact tool  200  in a contracted or untriggered position, in which the impact tool  200  has a minimum overall length measured between the uphole and downhole ends  206 ,  210 . In such position, which is referred to hereinafter as a first impact tool position, the piston  222  may be located at the uphole end of the chamber  214 , the piston  232  may be fully disposed within the chamber portion  234 , and the shaft  230  may be retracted into the housing  202 . The release mechanism  250  may be operable to maintain the piston assembly  220  and the housing  202  in the first position until the release mechanism  250  is operated or triggered to permit relative motion between the piston assembly  220  and housing  202  and, thus, permit the impact features  244 ,  246  to collide. 
     An example release mechanism  250  may include a fluid control device  252  and a switch  254  operable to electrically operate the fluid control device  252 . One or more portions of the release mechanism  250  may be disposed within a chamber  256  within the housing  202 . The chamber  256  may be fluidly connected with the chamber portion  234  of the chamber  216  via a fluid pathway  258 . As the chamber  256  and the chamber portion  234  are fluidly connected by the fluid pathway  258 , the chamber  256 , the chamber portion  234 , and the fluid pathway  258  may be collectively considered a single continuous space or chamber. The chamber  256  may be fluidly connected with the chamber portion  236  of the chamber  216  via a fluid pathway  260 . The fluid control device  252  may be installed along or otherwise in association with the fluid pathway  260 , and may be operable to block fluid flow through the fluid pathway  260  to fluidly isolate the chamber  256  and chamber portion  234  from the chamber portion  236 . The fluid control device  252  may be or comprise a fluid blocking device, such as a plug  262 , disposed within a cavity  264  at an end of the fluid pathway  260 . The plug  262  may be fixedly maintained within the cavity  264 , such as via corresponding threads. Fluid seals  266  may be disposed between the plug  262  and inner surface of the cavity  264  to prevent fluid leakage around or past the plug  262 . The bolt  262  may contain therein an explosive charge  268  operable to breach, pierce, or open the bolt  262  or otherwise form a fluid pathway through, around, or past the bolt  262  to permit fluid flow from the chamber portion  236  into the chamber  256  and the chamber portion  234 . The switch  254  may be electrically connected with the fluid control device  252  via a conductor  272 , and may be operable to detonate the explosive charge  268  and, thus, trigger the impact tool  200 . 
     However, instead of comprising the plug  262  having the explosive charge  268  therein, the fluid control device  252  may be or comprise a hydraulic valve operable to selectively permit fluid flow therethrough. Such valve may be sealingly disposed within the cavity  264  or otherwise along the fluid pathway  260  between the chamber  256  and the chamber portion  234 . The hydraulic valve may comprise a fluid blocking member, such as a needle, a ball, a spool, or a plunger operable to move between closed flow and open flow positions. The hydraulic valve may be or comprise a cartridge valve, a spool valve, a globe valve, or another valve operable at high pressures associated with downhole operations to shift between closed and open flow positions to selectively permit fluid flow therethrough. The hydraulic valve may be actuated by an electrical actuator (not shown), such as a solenoid or an electrical motor, a hydraulic actuator, such as a hydraulic cylinder or motor, and/or by other means. The valve actuator may be electrically connected to the switch  254  via the electrical conductor  272 , such as may permit the hydraulic valve to be actuated via the switch  254 . 
     The switch  254  may be an addressable switch connected with or along the electrical conductor  205 , such as may permit the switch  254  to be operated from the wellsite surface  104  by the power and control system  150  via the electrical conductors  113 ,  205  and other conductors extending between the power and control system  150  and the switch  254 . If multiple impact tools  200  are included within the tool string  110  for creating multiple impacts, multiple addressable switches  254  may permit each of the impact tools  200  to be triggered sequentially or independently. The switch  254  may also be or comprise a timer, such as may activate or trigger the release mechanism  250  at a predetermined time. The switch  254  may be battery powered to permit the release mechanism  250  to be triggered without utilizing the electrical conductors  113 ,  205  extending to the wellsite surface  104 . Although the switch  254  is shown and described above as being configured for wired communication, it is to be understood that the switch  254  may be configured for wireless communication with a corresponding wireless device located at the wellsite surface  104  or another portion of the tool string  110 . Such wireless switch may permit the release mechanism  250  to be triggered from the wellsite surface  104  without utilizing the electrical conductors  113 ,  205  extending to the wellsite surface  104 . 
     The cavity  264  and perhaps a portion of the fluid pathway  260  may be located within or extend through a support member or block  270 . The support block  270  may be separate and distinct from the housing  202  and may be disposed within the chamber  256 . The support block  270  may be a sacrificial member operable to absorb energy of the detonation of the explosive charge  268 . The support block  270  may be replaced, such as if damaged by the detonation of the explosive charge  268 , without having to replace one or more portions of the housing  202 . One or more fluid seals  271  may be disposed between inner surface of the chamber  256  and the support block  270  around the fluid pathway  260  to prevent or reduce fluid communication between the fluid pathway  260  and the chamber  256 . 
     The impact tool  200  may further comprise a continuous bore or pathway  280  extending longitudinally through various components of the impact tool  200 , such as the chamber  256 , the housing  202 , the pistons  222 ,  232 , and the shafts  228 ,  230 . At least a portion of the electrical conductor  205  extending between electrical interfaces  209 ,  213  may extend through the pathway  280 . One or more portions of the electrical conductor  205  may be coiled  207  within the pathway  280  and/or the chamber  256 , such as may permit the electrical conductor  205  to expand in length as the length of the impact tool  200  expands during the impact operations. A portion of the pathway  280  may be defined by a tubular member  282  (i.e., a shaft comprising an axial bore) connected with the piston  232  opposite the shaft  228  and extending through the fluid pathway  258 . The tubular member  282  may protect the electrical conductor  205  from the pressure wave and/or high velocity particles caused by the detonation of the explosive charge  268 . The tubular member  282  may also maintain the electrical conductor  205  within the pathway  280  while the housing  202  and the piston assembly  220  move with respect to each other during and/or after the impact operations. For example, the tubular member  282  may prevent the electrical conductor  205  from coiling up within the chamber portion  234  when the piston assembly  220  is retracted after the impact operations. 
     Prior to being conveyed into the wellbore  102 , the impact tool  200  may be configured to the first position such that the chamber volume  226  is formed and isolated from the space external to the housing  202 . The pressure within the chamber volume  226  may be equalized with the atmospheric pressure at the wellsite surface  104 . 
     However, if additional impact force is intended to be delivered by the impact tool  200 , air may be drawn or evacuated from the chamber volume  226  to reduce the pressure within the chamber volume  226 , resulting in a larger pressure differential across the piston  222  and, thus, an increase in the amount of stored energy when the impact tool  200  is conveyed downhole. Similarly, if a smaller impact force is intended to be delivered by the impact tool  200 , air may be pumped into the chamber volume  226  to increase the pressure within the chamber volume  226 , resulting in a smaller pressure differential across the piston  222  and, thus, a decrease in the amount of stored energy when the impact tool  200  is conveyed downhole. Prior to being conveyed into the wellbore  102 , the chamber portion  236  may also be filled with the hydraulic fluid or another substantially incompressible fluid. The uphole end  206  of the impact tool  200  may then be connected with the uphole portion  112  of the tool string  110 , and the downhole end  210  may be connected with the downhole portion  114  of the tool string  110 . After the impact tool  200  is configured and coupled to the tool string  110 , the tool string  110  may be conveyed into the wellbore  102  to a predetermined depth or position to perform the intended wellbore operations. 
     While the tool string  110  is conveyed downhole, the hydrostatic pressure in the wellbore  102  external to the housing  202  of the impact tool  200  increases. However, because the chamber volume  226  remains substantially unchanged and is fluidly isolated from the wellbore fluid within the chamber volume  224 , the pressure within the chamber volume  226  remains substantially constant or otherwise substantially lower than the ambient wellbore pressure throughout the downhole conveyance of the tool sting  110 . Similarly to the chamber volume  226 , the chamber  256  and the chamber portion  234  may also be fluidly isolated from the chamber  214  and the wellbore  102  to maintain a substantially constant or otherwise substantially lower pressure within the chamber  256  and the chamber portion  234  while the tool string  110  is conveyed downhole. Accordingly, when the tool string  110  reaches the predetermined depth or position within the wellbore  102 , the pressure within the chamber volume  224  may be substantially greater than the pressures within the chamber volume  226 , the chamber  256 , and the chamber portion  234 . As described above, the pressure differential formed across the piston  222  results in the expansion force urging opposing movement (i.e., expansion) between the piston assembly  220  and the housing  202 . Relative position between the piston assembly  220  and the housing  202  may be maintained substantially constant by the hydraulic fluid within the chamber portion  236 , which prevents movement of the piston  232  into the chamber portion  236 . Because the hydraulic fluid is fluidly sealed within the chamber portion  236 , the pressure of the hydraulic fluid increases, thereby resisting movement of the piston  232  into the chamber portion  236  and, thus, resisting movement between the piston assembly  220  and the housing  202 . 
     The net expansion force urging relative movement between the piston assembly  220  and the housing  202  may be substantially determined based on the pressure differential across the piston assembly  220 . The expansion force (i.e., the force urging expansion of the shaft  230  and the housing  202 ) may be determined by multiplying the pressure within the chamber volume  224  by the uphole face area  221  of the piston  222 , and by multiplying the pressure within the chamber  256  and chamber portion  234  by a cross-sectional area (not numbered) of the shaft  228 . The contraction force (i.e., the force urging contraction of the shaft  230  and the housing  202 ) may be determined by multiplying the pressure within the chamber volume  226  by the downhole face area  223  of the piston  222 , and by multiplying the pressure within the wellbore  102  by a cross-sectional area (not numbered) of the shaft  230 . Calculating the difference between the expansion and contraction forces may substantially determine the net expansion force urging expansion (e.g., downhole movement of the piston assembly  220  with respect to the housing  202 , uphole movement of the housing  202  with respect to the piston assembly  220 ) of the piston assembly  220  and the housing  202 . 
     If the tool string  110  becomes stuck in the wellbore  102 , such that it is intended to deliver an impact to the tool string  110 , the impact tool  200  may be triggered, such as by operating the release mechanism  250 , to impart the impact to the tool string  110  and in attempt to dislodge the tool string  110 . The impact tool  200  may progress though a sequence of operational stages or positions to release the energy stored in the impact tool  200  and impart the impact to the tool string  110 .  FIGS. 3 and 4  are schematic views of the impact tool  200  shown in  FIG. 2  in subsequent stages of impact operations according to one or more aspects of the present disclosure. 
       FIG. 3  depicts the impact tool  200  shortly after the release mechanism  250  was triggered to detonate the explosive charge  268  to form a fluid pathway  274  through or around the bolt  262  and, thus, trigger the impact operation. After the fluid pathway  274  is formed, the pressurized hydraulic fluid within the chamber portion  236  is permitted to flow through the fluid pathway  260  and the cavity  264  into the chamber  256  and the chamber portion  234 , as indicated by arrows  276 . Evacuation of the hydraulic fluid out of the chamber portion  236  permits the piston  232  to enter the chamber portion  236  and, thus, permits relative motion between the housing  202  and the piston assembly  220 . If the stuck portion of the tool string  110  is the uphole portion  112  of the tool string  110  or another portion located uphole from the impact tool  200 , then the piston assembly  220  and the downhole portion  114  of the tool string  110  will move in the downhole direction with respect to the housing  202  and the stuck uphole portion  112  of the tool string  110 . However, if the stuck portion of the tool string  110  is the downhole portion  114  or another portion of the tool string  110  located downhole from the impact tool  200 , then the housing  202  and the uphole portion  112  of the tool string  110  will move in the uphole direction with respect to the piston assembly  220  and the stuck downhole portion  114  of the tool string  110 . 
     The piston assembly  220  and the housing  202  will continue to move with respect to each other until the piston  232  exits the chamber portion  234 , at which point the chamber portions  234 ,  236  are no longer fluidly isolated. In such position, the hydraulic fluid within the chamber portion  236  is free to flow around the piston  232 , permitting unobstructed movement of the piston  232  within the chamber portion  236  and, thus, permitting free relative movement between the piston assembly  220  and the housing  202 . The expansion force generated by the wellbore fluid pressure within the chamber volume  224  may then increase relative velocity between the piston assembly  220  and the housing  202 . The position of the impact tool  200  shown in  FIG. 3  is referred to hereinafter as a second impact tool position. 
     The wellbore fluid may continue to flow into the chamber  214  via the port  238 , as indicated by arrow  239 , increasing the chamber volume  224  while decreasing the chamber volume  226 . The piston assembly  220  and the housing  202  may continue to move with respect to each other until the impact features  244 ,  246  impact or collide together to suddenly decelerate the moving portions of the impact tool  200  and the tool string  110 , imparting the impact to the stuck portion of the tool string  110 .  FIG. 4  shows the impact tool  200  in an impact position, referred to hereinafter as a third impact tool position, in which the impact features  244 ,  246  come into contact. 
     The impact tool  200  may be adjustable to control the magnitude of the impact generated by the impact tool  200 . Wellbores may have different pressures, and the same wellbore may have different pressures at different depths. The energy available for creating the impact is proportional or otherwise directly related to the wellbore pressure in the space around the impact tool  200 , and the impact tool  200  may comprise means for varying the speed of the relative motion between the housing  202  and piston assembly  220  in order to impart the intended impact force. Accordingly, a flow restrictor  248  may be disposed within the port  238  to reduce or otherwise control the rate of fluid flow from the space external to the housing  202  into the chamber portion  224  through the port  238 . Although  FIGS. 2-4  show a single port  238  extending through the housing wall  204 , the housing  202  may comprise a plurality of ports  238  or other openings distributed circumferentially around the housing  202  at or near the uphole end of the chamber  214  to fluidly connect the space external to the housing  202  with the chamber volume  224 . Each or some of the plurality of ports  238  may have a corresponding flow restrictor  248  disposed therein. 
       FIGS. 5 and 6  are enlarged and side views, respectively, of a portion of the impact tool  200  shown in  FIG. 2 , depicting an example implementation of the flow restrictor  248  disposed within the port  238  according to one or more aspects of the present disclosure. For example, the flow restrictor  248  may comprise a needle valve, a metering valve, a ball valve, or a flow limiter, such as may contain one or more orifices  310  extending therethrough. The flow restrictor  248  may comprise a body  312  having a substantially cylindrical configuration and external threads  314 , such as may threadedly engage with corresponding internal threads  316  of the housing port  238 . The flow restrictor  248  may also comprise a slot  318  or a shaped cavity partially extending into the body  312 , such as may be operable in conjunction with a hand-tool, wrench, and/or other tool to rotate and threadedly engage the flow restrictor  248  within the port  238 . The orifice  310  may have a diameter  320  or cross-sectional area that is substantially smaller than a diameter  322  or cross-sectional area of the port  238 . 
     The orifice  310  may have a predetermined cross-sectional area or an adjustable cross-sectional area. For example, the flow restrictor  248  may comprise an adjustable plunger or a needle (not shown) extending along or into the orifice  310 , wherein the needle or the plunger may progressively open and close the cross-sectional area of the orifice  310 . The flow restrictor  248  may comprise a single orifice  310  or multiple orifices (not shown), which may permit an increased flow rate through the flow restrictor  248 . The orifice  310  may also comprise a different cross-sectional shape, such as a circle, an oval, a rectangle, or another shape. The flow restrictor  248  may by fixedly disposed within or about the port  238  by means other than threaded engagement. For example, the flow restrictor  248  may comprise or be utilized in conjunction with a flange or plate (not shown), such as may permit the flow restrictor  248  to be bolted to the housing  202  about the port  238 . The flow restrictor  248  may also comprise or be utilized in conjunction with a filter or a permeable material (not shown) disposed within or about the orifice  310 , such as may filter or otherwise prevent contaminants from flowing into the chamber volume  224 . 
     Before or after being coupled to the tool string  110 , the impact tool  200  may be configured to generate and/or impart a predetermined impact force to the tool string  110  based on, for example, depth of the tool string  110  within the wellbore  102 , weight of the tool string  110 , and wellbore fluid properties, such as viscosity. The magnitude of the intended impact may also depend on the structural strength or resiliency of the tool string  110  to withstand the impact force. Knowing such operational parameters may permit a surface operator to predict the velocity of the piston assembly  220  and, thus, adjust the one or more flow restrictors  248  to adjust the velocity of the piston assembly  220 . For example, the impact tool  200  may be configured by selecting and installing one or more flow restrictors  248 , such as may cause the impact tool  200  to generate and deliver the predetermined impact force. Flow rate through an opening is proportional to a diameter and/or cross-sectional area of such opening, such that the rate at which the wellbore fluid flows into the chamber volume  224  may be controlled by selecting an appropriate orifice diameter  320  of the flow restrictor  248 . The wellbore fluid is substantially incompressible, such that reducing the rate of flow of the wellbore fluid into the impact tool  200  may reduce the rate of speed at which the piston assembly  220  and the housing  202  move with respect to each other, which in turn, may reduce the magnitude of the impact to the tool string  110 . 
     The magnitude of the impact force may be configured, for example, by selecting and installing flow restrictors  248  having orifice sizes based on the operational parameters described above. Flow restrictors  248  having predetermined orifice diameters  320  and/or cross-sectional areas may be utilized interchangeably to control the magnitude of the impact. For example, the diameter  320  of the orifice  310  of one or more of the flow restrictors  248  may be about 1/16 inch (in) (about 1.6 millimeters (mm)), about ⅛ in (about 3.2 mm), about ¼ in (about 6.4 mm), or about ⅜ in (about 9.5 mm), and the cross-sectional area of the orifice  310  may be about 0.003 in 2  (about 1.98 mm 2 ), about 0.012 in 2  (about 7.92 mm 2 ), about 0.049 in 2  (about 31.7 mm 2 ), or about 0.110 in 2  (about 71.2 mm 2 ). However, other dimensions are also within the scope of the present disclosure. 
     Instead of or in addition to utilizing the flow restrictors  248 , the flow rate at which the wellbore fluid enters the chamber volume  224  may be controlled by closing some of the ports  238  to prevent flow through the closed ports  238  in order to control a cumulative flow area (i.e., open area) of the ports  238 . For example, one or more of the ports  238  may be blocked or closed off by one or more plugs (not shown) threadedly engaged or otherwise disposed within one or more of the ports  238 . Furthermore, if multiple impact tools  200  are included within the tool string  110  for creating multiple impacts, the magnitude of the impact force imparted by each impact tool  200  may be controlled or adjusted independently. For example, the flow restrictors  248  or plugs may be utilized to set an increasing impact force schedule, wherein each subsequent impact force imparted by each subsequent impact tool  200  increases until the tool string  110  is set free. 
     In addition to utilizing one or more flow restrictors  248  or plugs, the magnitude of the impact may also be controlled by adjusting the cumulative uphole and downhole areas of the piston assembly  220 . For example, the net expansion force generated by the impact tool  200  may be controlled by adjusting the diameters of the pistons  222 ,  232  and/or the diameters of the shafts  228 ,  230 . The magnitude of the impact may also be controlled by adjusting travel distance (i.e., the stroke distance) of the piston assembly  220  to adjust the distance over which the piston  220  assembly accelerates. 
       FIG. 7  is an enlarged view of a portion of an example implementation of an impact tool  300  according to one or more aspects of the present disclosure. The impact tool  300  is depicted in the third impact tool position, and may comprise one or more similar features of the impact tool  200 , including where indicated by like reference numbers, except as described below. The following description refers to  FIGS. 1, 4, and 7 , collectively. 
     The impact tool  300  may comprise a piston assembly  332  comprising a piston  334  slidably disposed within the chamber  214 . The piston  334  may comprise fluid seals  225  sealingly engaging inner surface of the chamber  214 . The impact tool  300  may further comprise means for locking or otherwise maintaining the piston assembly  332  and a housing  336  of the impact tool  300  in a locked or otherwise constant relative position, such as the third impact tool position. The locking means may include one or more latches  338  disposed within corresponding cavities  340  or other spaces extending radially into the piston  334 . Each latch  338  may be radially movable within the corresponding cavity  340  and biased in a radially outward direction by a corresponding biasing member  342  disposed within the cavity  340  and against the latch  338 . The biasing members  342  may comprise coil springs, leaf springs, gas springs, wave springs, spring washers, torsion springs, and/or other biasing means. 
     During impact operations of the impact tool  300 , while the piston  334  and the housing  336  move with respect to each other, the latches  338  may be maintained at least partially retracted within the cavities  340  by an inner surface of the housing defining the chamber  214 . When the impact features  244 ,  246  approach each other, the latches  338  may extend radially outwards into corresponding cavities  344  or other spaces extending radially into a wall  346  of the housing  336  at or near a downhole end of the chamber  214 . After the latches  308  are inserted within the corresponding cavities  344 , the piston  334  and the housing  336  may be locked in a relative position, such as may prevent the shaft  230  from retracting or collapsing into the housing  336  if the impact tool  300  is axially compressed during subsequent impact or other downhole operations. For example, if additional impact tools  300  are included within the tool string  110  for creating additional impacts, locking the piston assembly  332  and housing  336  may permit a subsequent impact force to be transmitted through the locked impact tool  300  to a stuck portion of the tool string  110 . However, if the piston assembly  332  and the housing  236  of the triggered impact tool  300  are permitted to move relative to each other, the triggered impact tool  300  may absorb at least a portion of the subsequent impact force (e.g., similarly to a spring or shock absorber) and/or not transfer all of the impact force to the stuck portion of the tool string  110 . 
     The impact tools  200 ,  300  described herein and shown in  FIGS. 2-4 and 7  are oriented such that the shaft  230  extends from the housing  202  in the downhole direction. However, the orientation of the impact tools  200 ,  300  within the tool string  110  may be reversed, such that the impact tool end  210  is coupled with the uphole portion  112  of the tool string  110  and the impact tool end  206  is coupled with the downhole portion  114  of the tool string  110 , without affecting the operation of the impact tools  200 ,  300 . 
     The foregoing outlines features of several implementations so that a person having ordinary skill in the art may better understand the aspects of the present disclosure. A person having ordinary skill in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the implementations introduced herein. A person having ordinary skill in the art should also realize that such equivalent constructions do not depart from the scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. 
     The Abstract at the end of this disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.