US20180283123A1 - Pressure actuated jarring device for use in a wellbore - Google Patents

Abstract

A pressure actuated jarring apparatus includes a tubular housing, a piston, a spring element, and a seat. The tubular housing has a passage therethrough extending from an upper end to a lower end. The piston is disposed within the central bore and is movable axially between an inactivated state and an activated state. The spring element is configured to store energy to drive the piston from the activated state. The seat is coupled to the piston such that when a plug is seated in an orifice of the seat fluid is prevented from flowing through the orifice. The jarring device is fired by increasing pressure in the passage until the plug is forced through the seat, thereby releasing the energy in the spring element and driving the piston from the activated state so that it impacts an abutment and generates a jarring force.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims priority to U.S. Provisional Application No. 62/480,135, filed Mar. 31, 2017, the entirety of which is incorporated herein by reference.
BACKGROUND
• During the drilling, work over, or plug and abandonment of oil and gas producing wellbores, a variety of downhole tools may be attached to a pipe (often referred as a drillstring) or coiled tubing string and utilized to perform various functions within the wellbore. Occasionally, these downhole tools become lodged or stuck in the wellbore. When this situation occurs, a fishing assembly can be deployed in the wellbore to attempt to free or dislodge the stuck object. In general, fishing assemblies employ a jarring or impact device that can deliver repeated blows to the stuck tool in an operation that is referred to as a “fish”.
SUMMARY
• Embodiments described herein are directed to a pressure actuated jarring apparatus for use in a wellbore. According to an embodiment, a jarring apparatus comprises a tubular housing, a piston, a spring element, and a seat. The tubular housing has a passage therethrough extending from an upper end to a lower end. The piston is disposed within the passage of the tubular housing and is movable axially within the passage between an inactivated state and an activated state. The spring element is disposed within the tubular housing to store energy to drive the piston from the activated state. The seat is coupled to the piston and has an orifice, such that when a plug is seated in the seat the orifice is blocked and fluid is prevented from flowing through the orifice. When the orifice is blocked and the piston is in the activated state, the pressure actuated jarring device is fired by increasing pressure in the passage until the plug is forced through the seat, thereby opening the orifice, releasing the energy in the spring element and driving the piston from the activated state so that it impacts an abutment and generates a jarring force.
• Embodiments described herein are also directed to a pressure actuated jarring apparatus comprising a tubular housing, an upper piston, a lower piston, a compressible element, and a seat. The tubular housing has a passage therethrough extending from an upper end to a lower end. The upper piston is disposed within the passage of the tubular housing and is movable axially within the passage between an inactivated state and an activated state. The upper piston has one or more ports through a sidewall of the upper piston. The lower piston is coupled to the upper piston and has a top face and an elongation. An annular cavity is formed between the elongation and the tubular housing and the annular cavity at least partially filled with a compressible fluid. The spring element is disposed within the annular cavity to store energy to drive the upper piston and the lower piston from the activated state. The seat is coupled to the upper piston or the lower piston and has an orifice, such that when a plug is seated in the seat, the orifice is blocked and fluid is prevented from flowing through the orifice. When the orifice is blocked and the first and lower pistons are in the activated state, the pressure actuated jarring device is fired by increasing pressure in the passage until the plug is forced through the orifice, thereby opening the orifice, releasing the energy in the spring element and driving the first and lower pistons from the activated state so that the upper piston impacts an abutment and generates a jarring force.
• Embodiments described herein are also directed to a method of generating a jarring force to free a stuck object in a wellbore. The method comprises deploying a plug through a coiled tubing or workstring until the plug engages a seat of a jarring apparatus and blocks flow through an orifice of the seat. The method also includes pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move a piston of the jarring apparatus from an inactivated state to an activated state against a force imparted on the piston by a spring element. The method also includes increasing the pressure of the fluid to force the plug through the orifice of the seat, thereby releasing the pressure on the piston and allowing the piston to be moved by the spring element to the inactivated state.
BRIEF DESCRIPTION OF THE DRAWINGS
• The features of the embodiments described herein will be more fully disclosed in the following detailed description, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein:
• FIG. 1 is a side cross-sectional view of a pressure actuated jarring apparatus in an inactivated state, according to an embodiment.
• FIG. 2 is a side cross-sectional view of the pressure actuated jarring apparatus ofFIG. 1 in an activated state, according to an embodiment.
• FIG. 3 is a side cross-sectional view of the lower piston of a pressure actuated jarring apparatus, according to one embodiment.
• FIG. 4 is a side cross-sectional view of a seat, according to an embodiment, in a first position with a plug engaged with the seat.
• FIG. 5 is a side cross-sectional view of the seat ofFIG. 4 in a second configuration.
• FIG. 6 is a side cross-sectional view of a piston with two seats, according to an embodiment.
• FIG. 7 is an elevation view of the pressure actuated jarring apparatus ofFIG. 1 deployed in a wellbore.
DETAILED DESCRIPTION
• This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship.
• Objects, such as tools, can often become stuck in a wellbore. When this situation occurs, a fishing assembly that is coupled to coiled tubing, a workstring, or drillstring in the wellbore can be used to attempt to dislodge the object. In general, a fishing assembly includes a jarring device that, when fired, delivers an upward impact or jarring force to dislodge the stuck object. Two common types of jarring devices are known. The first type is a hydraulic jar that operates based on tension or compression. The second type of jarring device is fluid actuated.
• To deliver an upward impact with a hydraulic jarring device, the drillstring or coiled tubing first provides a downward force for a given period of time to “cock” the jarring device. A tensile force is then applied and held for some period of time, generally about 1½ to 2 minutes, until the jarring device fires (i.e., delivers an impact or jarring force). However, because the drillstring or coiled tubing applies both compressive and tensile forces for each jarring cycle, fatigue results, particularly in the coiled tubing. Consequently, only a limited number of impacts can be delivered before the coiled tubing string must be exited from the wellbore so that the fatigued length of coil can be removed. Exiting the wellbore not only is time consuming, but the removal of the length of coiled tubing then places any future fatigue-inducing stresses into a different location on the coiled tubing string. Moreover, further time is consumed by the wait time that is required between impacts. If many impacts are needed to dislodge the object, the amount of time to dislodge a stuck object can be substantial.
• Hydraulic jarring device also typically do not function well (or at all) in horizontal well applications due to the inability to set down enough weight to cock the jarring device. This inability is caused by the frictional forces between the drillstring and the wellbore. The weight transfer from the drillstring to the jarring device diminishes as the length of the horizontal portion of the well increases.
• Known fluid actuated jarring devices likewise can have disadvantages. For example, many such devices again require the application of tensile or compressive forces to actuate the tool. The amount of tensile or compressive forces must correlate precisely with the fluid flowrate that is applied. If the amount of tension is too great, the fishing assembly will stall. If the amount of tension is too little, the jarring device will not produce impacts. Therefore, fluid actuated jarring devices can present challenges with their successful operation.
• Moreover, many fluid actuated jarring devices do not have the ability to transmit torque through the tool, which is an attribute often required in fishing operations. Yet further, the magnitude of the impacts delivered by many fluid actuated jarring devices can be limited. The magnitude of the impact is a function of momentum, which, by definition, is the mathematical product of velocity and the mass of the moving object (which in this case is an anvil (e.g., a piston)). Generally, the velocity is provided via a compression spring having a known spring force. However, the spring force is limited by the physical dimensions and properties of available springs and the tool itself. The mass of the anvil is a function of its physical dimensions and the density of the material from which it is made. In general, fluid actuated jarring devices offer no means to increase the impact force beyond that delivered by the spring nor any means of increasing the mass of the anvil.
• Accordingly, embodiments described herein are directed to a pressure actuated jarring apparatus that is part of a fishing assembly that is deployed in a wellbore to dislodge a stuck object or tool. The pressure actuated jarring apparatus can be coupled to coiled tubing and deployed in the wellbore when an object becomes stuck, or it can be utilized in daily downhole operations, such as drilling or other types of remedial work, as a preventative measure in the event that a drillstring or workstring does become stuck in the wellbore. In embodiments described herein, when not being used in a fishing operation, fluid can flow unobstructed through a central passageway of the jarring apparatus. When a fishing operation is initiated, the jarring apparatus is operated by restricting fluid flow through the jarring apparatus, such as by dropping a ball or other plugging device to obstruct the fluid passageway. Restriction of the fluid flow causes one or more pistons to shift from an inactivated state to an activated state in which a compressive element (e.g., a spring) stores potential energy. The fluid pressure applied to the plug can then be increased until the plug is dislodged, at which point the potential energy is released and the jarring device is fired. When fired, the released energy drives the one or more pistons from the cocked position and into contact with an abutment. The impact between the piston and the abutment creates a jarring force that helps to dislodge the stuck object.
• In one embodiment, as shown inFIGS. 1, 2 and 7, a pressure actuatedjarring apparatus5 that is part of a fishing assembly includes atop sub20, abottom sub25, a tubular housing30 (made up ofportions30a,30b), a piston40 (made up ofpistons40a,40b), aseat50, and aspring element60. Theapparatus5 is configured for engagement to a workstring or coiled tubing (“WS,” shown inFIG. 7) on itsupper end10 and to a fishing or latching tool (“F,” shown inFIG. 7) on itslower end15. Thetop sub20 can be coupled to the workstring WS in any appropriate manner. In the embodiment shown inFIGS. 1, 2 and 7, thetop sub20 contains athread22 for engagement to the workstring WS. Similarly, thebottom sub25 can be coupled to the fishing or latching tool F in any appropriate manner. In the embodiment shown inFIGS. 1 and 2, thebottom sub25 includes athread27 for engagement to the fishing or latching tool F.
• As can be seen inFIGS. 1 and 2, thetop sub20 defines acentral bore200 and thebottom sub25 defines acentral bore230. The tubular housing30 extends from anupper end31 to alower end32 and defines apassage34 between theupper end31 and thelower end32. Theupper end31 is configured to couple to thetop sub20 and thelower end32 is configured to couple to thebottom sub25. The tubular housing30 can be coupled to thetop sub20 in any appropriate manner, such as via a threadedconnection65. The tubular housing30 can be coupled to thebottom sub25 in any appropriate manner, such as via a threadedconnection80.
• In embodiments, the tubular housing30 can be manufactured as two independent housings for ease of machining, such as an uppertubular housing30aand a lowertubular housing30b(referred to collectively as tubular housing30). The uppertubular housing30aand the lowertubular housing30bcan be joined in any appropriate manner, such as via a threadedconnection70.
• Thepiston40 is disposed within thepassage34 of the tubular housing30 and is movable axially within thepassage34 between an inactivated state (shown inFIG. 1) and an activated state (shown inFIG. 2). Thepiston40 can be constructed of any appropriate material. For example, in one embodiment, thepiston40 is constructed of a material having a density higher than that of steel, such as tungsten (which has a density approximately 2½ times that of steel), to maximize its mass and, thereby, increase the jarring force created by thejarring apparatus5 when it is fired.
• Thepiston40 can include anupper piston40aand alower piston40b(referred to collectively as piston40). Theupper piston40aand thelower piston40bare coupled such that they move together from the inactivated state to the activated state. Thepistons40a,40bcan be coupled using any appropriate method. For example, in an embodiment, theupper piston40aand thelower piston40bare connected via threadedengagement75. Although the illustrated embodiment uses anupper piston40aand alower piston40b, any number of pistons can be used, including one piston, three pistons, four pistons, five pistons, or more. The addition of pistons increases the overall mass of the piston assembly and thus increases the jarring force generated by theapparatus5 when it is fired.
• Theupper piston40adefines acentral bore210 and thelower piston40bdefines acentral bore220. Theupper piston40acontains aseal element85 and thelower piston40bcontains aseal element95. Theseal elements85,95 create a seal between thepiston40 and the tubular housing30. Further, tubular housing30 can include aseal element90 configured to engage the outside of thepiston40. As a result, fluid is blocked from flowing around the outside of thepistons40a,40bso that fluid flow is directed instead through the pressure actuatedjarring apparatus5 via thecentral bores200,210,220, and230. The seal elements can be elastomeric elements, such as, for example, o-rings. Thelower piston40bcan also include aretainer55 for retaining thelower piston40bwith respect to thebottom sub25 and to retain thespring element60 during assembly. For example, theretainer55 can be a snap ring.
• In an embodiment, theupper piston40aincludes port(s)105 through ashaft42 of theupper piston40a. Fluid is allowed to pass through the port(s)105 into acavity110 formed between theupper piston40a, thelower piston40b, and the tubular housing30. As a result, the fluid is able to exert pressure on multiple portions of thepiston40. Hence, by providing the port(s)105, the addition of pistons increases the force applied to thespring element60 for a given amount of fluid pressure, thereby increasing the potential energy of thejarring apparatus5 when in the activated state.
• Thepiston40 includes anexternal shoulder130 and the tubular housing30 includes aninternal shoulder135. As shown inFIG. 2, when thepiston40 is in the activated state, theexternal shoulder130 contacts theinternal shoulder135. This contact limits the travel of theupper piston40. The positions of theexternal shoulder130 and theinternal shoulder135 can be configured to limit the travel of thepiston40 at the desired location when in the activated state to provide the desired jarring force.
• Thespring element60 is disposed within thepassage34 of the tubular housing30 and is configured to store energy to drive thepiston40 from the activated state toward the inactivated state. The upper end of thespring element60 is in contact with thepiston40 and the lower end of thespring element60 is in contact with thebottom sub25. The spring element may comprise any of a variety of resilient materials, such as a compression spring(s), Belleville washers, elastomeric springs, and/or compressible fluid. The spring element also can comprise a combination of materials. For example, a compressible fluid can be used in conjunction with, for example, a compression spring.
• In one embodiment, a sealedannulus44 is formed between thepiston40, the tubular housing30, and thebottom sub25. The sealedannulus44 can be, at least partially, filled with a compressible fluid to increase the force applied on thepiston40 when in the activated state. This compressible fluid is used as a fluid compression spring to maximize piston velocities during the jarring procedure. The combination of a physical spring, such as a compression spring, with a fluid spring exerts a large upward force on thepiston40. These features, in combination with the high density of thepiston40, create a jarring device capable of delivering high magnitude impacts.
• Theseat50 is coupled to thepiston40. Theseat50 has anorifice122 aligned with the central bore of thepiston40. Theorifice122 has a diameter that is less than the diameter of the central bore of thepiston40. Hence, theseat50 is configured to receive a plug in theorifice122 such that the plug blocks fluid from passing through thecentral bore220 of thelower piston40band/or thecentral bore210 of theupper piston40awhen theapparatus5 is in the activated state. The plug can engage ashoulder125 of theseat50. In an embodiment, theseat50 and thepiston40 are manufactured as a single component. Alternatively, theseat50 can be joined to thepiston40 through any appropriate means including welding, bonding, thread engagement, and press-fit. Thepiston40 can include aseal element100 configured to engage theseat50 to prevent fluid from flowing around theseat50.
• Theplug120 can be any appropriate object that can block the flow of fluid through the orifice. For example, the plug can be a spherical ball commonly used in the downhole drilling industry. In one embodiment, theseat50 is intended for use with a deformable ball.
• In other embodiments, the seat is expandable from a first configuration to a second configuration so that it can be used with non-deformable plugs, such as plugs made of steel. For example, theseat50 can be made of a deformable material. In another embodiment, anexpandable seat160 is used. In one example, as shown inFIGS. 4 and 5, theexpandable seat160 includes one or more splits orgrooves165 that allow theexpandable seat160 to flex.FIG. 4 shows anexpandable seat160 in a first configuration with aplug120 engaged with ashoulder180 of theseat160. With theplug120 in this position, fluid is prevented from flowing through theexpandable seat160. Theexpandable seat160 is maintained in this position by a biasingmember150 disposed between theexpandable seat160 and thepiston40. Theexpandable seat160 is able to move axially within apiston bore175 formed in thepiston40, from a first position to a second position. In the first configuration, as shown inFIG. 4, theseat160 is substantially restricted within thebore175 and is held in place via the biasingmember150. As pressure increases, the seat travels downward to a second position in which the seat is disposed in anenlarged bore170. In this position, theseat160 can expand to the second configuration and theplug120 is allowed to travel through theseat160, as illustrated inFIG. 5. The pressure actuatedjarring apparatus5 fires precisely at the moment theplug120 travels through theseat160, creating an upward impact and pressure pulse. Theseat160 can include aseal element155 configured to engage thepiston40 to prevent fluid from flowing around theseat160.
• FIG. 6 illustrateslower piston40bcomprising twoseats50. The twoseats50 can be manufactured as one piece. Alternatively, the twoseats50 can be separate components. Pressure actuatedjarring apparatus5 can be configured to operate with any number ofseats50, which can be made of various materials, and have any configuration oforifice122 sizes. Theseseats50 can be configured in any appropriate manner suitable for the operating pressures in the particular application in which thejarring apparatus5 is employed.
• In operation, the operator can use the pressure actuatedjarring apparatus5 to dislodge a tool that is stuck in a wellbore. The operator can select anappropriate plug120 to provide a desired jarring impact. Theplug120 can then be pumped from the surface through the workstring until it engages theseat50,160. Optionally, the operator can apply a tensile load to the fishing assembly via the toolstring or workstring. Fluid pressure in the central bore can then be slowly increased until the pressure required to force theplug120 to pass through theseat50 is achieved, at which point the pressure actuatedjarring apparatus5 fires. Thepiston40 is driven upward until thepiston40 impacts anabutment145 within the jarring apparatus. In the embodiment shown, theabutment145 is the bottom face of the top sub20 (shown inFIG. 2). In another embodiment, the abutment is provided by an internal stop, shoulder or abutment in the central bore of the tubular housing30. In the embodiment shown, theupper face140 of theupper piston40ais configured to contact theabutment145. In other embodiments, a flange or shoulder of theupper piston40aor thelower piston40bis configured to contact theabutment145. The mechanical impact between thepiston40 and theabutment145 creates a jarring force. In addition, when thejarring apparatus5 is coupled to coiled tubing, the release of pressure that occurs when the plug passes through the seat can result in a pressure pulse that causes the coiled tubing to spring upward and, thus, further enhance the jarring force that is created. If the stuck object does not come free, this process can be repeated.
• The amount of stroke of thepiston40 and the resulting impact forces is partially dictated by the spring constant, or stiffness, of the spring element(s)60 used. The magnitude of the impact is also dictated by the amount of pressure that is needed to force theplug120 through theseat50. This force is based on the size and material of theplug120. Generally, as the plug diameter or size increases, so does the amount of force needed to drive theplug120 through theseat50. The material from which theplug120 is constructed also can affect the force required for theplug120 to pass through theseat50. Providing a range ofplugs120 of various sizes and/or physical properties allows an operator to fire the pressure actuatedjarring apparatus5 at a range of pressures. For example, the operator can begin firing the pressure actuatedjarring apparatus5 at a low pressure then slowly increase the pressure until the stuck object is free.
• As shown inFIG. 3, thelower piston40bcan include acavity182. After theplug120 passes through theseat50,160, theplug120 may be captured in thecavity182. In another embodiment, theplug120 may be captured in an additional sub (not shown) below thejarring apparatus5. Thelower piston40bmay contain drain holes185 to allow fluid to exit thecavity182.
• FIG. 7 illustrates the pressure actuatedjarring apparatus5 attached to a workstring WS inside a wellbore WB and attached to a latching or fishing tool F. A shock sub (not shown) can be attached above the pressure actuatedjarring apparatus5. The shock sub allows the fishing assembly to travel upwards with each impact ofjarring apparatus5 without having to move the entire workstring, which could be several thousand feet long. A shock sub thus can allow for the stuck object to be more easily dislodged and removed from the wellbore.
• In another embodiment, a method of generating a jarring force to free a stuck object in a wellbore is provided. The method includes pumping aplug120 through a coiled tubing or workstring until theplug120 engages aseat50,160 of a jarring apparatus and blocks flow through anorifice122,162 of theseat50,160. The method also includes pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move apiston40 of the jarring apparatus from an inactivated state to an activated state against a force imparted on thepiston40 by aspring element60. The method also includes increasing the pressure of the fluid to force theplug120 through theorifice122,162 of theseat50,160, thereby releasing the pressure on thepiston40 and allowing thepiston40 to be moved by thespring element60 toward the inactivated state.
• The method can also include pumping asecond plug120 through the coiled tubing or workstring until the second plug engages theseat50,160 of the jarring apparatus and blocks flow through theorifice122,162 of theseat50,160, wherein the second plug has a larger diameter than the first plug. The method can also include pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move thepiston40 of the jarring apparatus from the inactivated state toward the activated state against a force imparted on thepiston40 by thespring element60. The method can also include increasing the pressure of the fluid to force the second plug through theorifice122,162 of theseat50,160, thereby releasing the pressure on thepiston40 and allowing thepiston40 to be moved by thespring element60 toward the inactivated state.
• Although the devices, kits, systems, and methods have been described in terms of exemplary embodiments, they are not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the devices, kits, systems, and methods, which may be made by those skilled in the art without departing from the scope and range of equivalents of the devices, kits, systems, and methods.

Claims (18)

What is claimed is:

1. A pressure actuated jarring apparatus for use in a wellbore, comprising:

a tubular housing having a passage therethrough extending from an upper end to a lower end;

a piston disposed within the passage of the tubular housing and movable axially within the passage between an inactivated state and an activated state;

a spring element disposed within the tubular housing to store energy to drive the piston from the activated state; and

a seat coupled to the piston and having an orifice, such that when a plug is seated in the seat the orifice is blocked and fluid is prevented from flowing through the orifice,

wherein, when the orifice is blocked and the piston is in the activated state, the pressure actuated jarring apparatus is fired by increasing fluid pressure in the passage until the plug is forced through the seat, thereby opening the orifice, releasing the energy in the spring element and driving the piston from the activated state so that it impacts an abutment and generates a jarring force.

2. The pressure actuated jarring apparatus ofclaim 1, wherein the tubular housing includes an upper tubular housing and a lower tubular housing.

3. The pressure actuated jarring apparatus ofclaim 1, wherein the piston includes an upper piston and a lower piston disposed within the tubular housing and movable axially within the passage between the inactivated state and the activated state.

4. The pressure actuated jarring apparatus ofclaim 3, wherein the upper piston includes one or more ports through a shaft of the upper piston configured to allow fluid traveling through the pressure actuated jarring apparatus to pass through the one or more ports and into a cavity formed between the shaft of the upper piston, the tubular housing, and a top face of the lower piston.

5. The pressure actuated jarring apparatus ofclaim 1, wherein a sealed annulus is formed between the piston and the tubular housing and the spring element is disposed within the sealed annulus and wherein the sealed annulus is at least partially filled with a compressible fluid.

6. The pressure actuated jarring apparatus ofclaim 1, wherein the piston defines a cavity configured to receive and retain the plug after the plug passes through the orifice of the seat.

7. The pressure actuated jarring apparatus ofclaim 1, wherein the orifice of the seat is expandable from a first configuration to a second configuration, and wherein the plug is unable to pass through the orifice when in the first configuration and is able to pass through the orifice when in the second configuration.

8. The pressure actuated jarring apparatus ofclaim 7, wherein the seat is axially movable relative to the piston from a first position to a second position, and wherein the orifice is restricted from expanding when the seat is in the first position and is able to expand when the seat is in the second position.

9. The pressure actuated jarring apparatus ofclaim 8, further comprising a biasing member disposed between the seat and the piston, the biasing member configured to bias the seat toward the first position.

10. The pressure actuated jarring apparatus ofclaim 1, further comprising a second seat.

11. A pressure actuated jarring apparatus for use in a wellbore, comprising:

a tubular housing having a passage therethrough extending from an upper end to a lower end, wherein the upper end is configured to couple to a workstring or coiled tubing sub and the lower end is configured to couple to a fishing tool;

an upper piston disposed within the passage of the tubular housing and movable axially within the passage between an inactivated state and an activated state, the upper piston having one or more ports through a sidewall of the upper piston;

a lower piston coupled to the upper piston, the lower piston having a top face and an elongation, wherein an annular cavity is formed between the elongation and the tubular housing, the annular cavity at least partially filled with a compressible fluid;

a compressible element disposed within the annular cavity to store energy to drive the upper piston and the lower piston from the activated state; and

a seat coupled to the upper piston or the lower piston and having an orifice, such that when a plug is seated in the seat, the orifice is blocked and fluid is prevented from flowing through the orifice,

wherein, when the orifice is blocked and the first and lower pistons are in the activated state, the pressure actuated jarring apparatus is fired by increasing pressure in the passage until the plug is forced through the orifice, thereby opening the central bore, releasing the energy in the compressible element and driving the first and lower pistons from the activated state so that the upper piston impacts an abutment and generates a jarring force.

12. The pressure actuated jarring apparatus ofclaim 1, wherein the tubular housing includes an upper tubular housing and a lower tubular housing.

13. The pressure actuated jarring apparatus ofclaim 11, wherein the lower piston defines a cavity configured to receive and retain the plug after the plug passes through the orifice of the seat.

14. The pressure actuated jarring apparatus ofclaim 11, wherein the orifice of the seat is expandable from a first configuration to a second configuration, and wherein the plug is unable to pass through the orifice when in the first configuration and is able to pass through the orifice when in the second configuration.

15. The pressure actuated jarring apparatus ofclaim 14, wherein the seat is axially movable relative to the first and lower pistons from a first position to a second position, and wherein the orifice is restricted from expanding when in the first position and is able to expend when in the second position.

16. The pressure actuated jarring apparatus ofclaim 15, further comprising a biasing member disposed between the seat and the lower piston, the biasing member configured to bias the seat toward the first position.

17. A method of generating a jarring force to free a stuck object in a wellbore, comprising:

deploying a first plug through a coiled tubing or workstring until the first plug engages a seat of a jarring apparatus and blocks flow through an orifice of the seat;

pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move a piston of the jarring apparatus from an inactivated state to an activated state against a force imparted on the piston by a spring element; and

increasing the pressure of the fluid to force the first plug through the orifice of the seat, thereby releasing the pressure on the piston and allowing the piston to be moved by the spring element to the inactivated state.

18. The method ofclaim 17, further comprising:

deploying a second plug through the coiled tubing or workstring until the second plug engages the seat of the jarring apparatus and blocks flow through the orifice of the seat, wherein the second plug has a larger diameter than the first plug;

pumping a fluid through the coiled tubing or workstring at a pressure sufficient to axially move the piston of the jarring apparatus from the inactivated state to the activated state against a force imparted on the piston by the spring element; and

increasing the pressure of the fluid to force the second plug through the orifice of the seat, thereby releasing the pressure on the piston and allowing the piston to be moved by the spring element to the inactivated state.

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