Dual acting locking jar

A double action locking jar is operable to provide a jarring force in an upward or downward direction. A pair of pressure pistons form a pressure chamber in which a Belleville spring stack is located. A metering orifice in one of the pistons serves to provide a delay mechanism for release of a mandrel within the housing. Two collets are located within the housing for mechanically releasing the mandrel when a tension or compression force is applied to the mandrel. The jar may be mechanically actuated only by allowing the pistons to freely move within the housing without hydraulic resistance.

BACKGROUND OF INVENTION

1. Field of Invention

This invention is directed to a work string jar which is capable of applying an upward or downward jarring force on a work string used in oil or gas wells.

2. Description of Related Art

Double acting jars are known in the prior art however they have certain drawbacks. A known double acting jar is disclosed in U.S. Pat. No. 5,624,001. This jar requires two sets of Belleville spring stacks which add to the complexity and length of the jar. The high pressure seals within the tool are exposed to the drilling mud which can cause premature failure due to the corrosive and abrasive nature of the drilling mud. Furthermore each of the pressure pistons requires an orifice and a check valve. Also this prior art jar does not include a trigger sleeve which reduces wear on the collet and release mechanism.

SUMMARY OF THE INVENTION

A sealed double acting jar with a floating piston to balance the interior fluid with hydrostatic pressure, and a hammer and anvil surface is disclosed. The jarring mechanism includes two pressure pistons which oppose each other to form a substantially sealed pressure chamber. A spring is positioned between the pressure pistons such that when one piston is moved toward the other piston, the spring creates a mechanical resistance at the same time as the compression of the fluid between the pistons creates a pressure, both of which resists movement of the piston. By requiring the piston to move a given distance the minimum load at the trigger point of the jar can be controlled by the compression of the Belleville spring stack. The actual load at the trigger point is a result of the tensile or compressive load placed on the jar by the work string and is balanced by the pressure differential across the piston acting on the cross sectional area of the piston. At least one pressure piston has a first flow passage or an orifice device to control the time delay and at least one pressure piston has a second flow passage or a check valve to allow the fluid to return to the pressure chamber. The jar has separate trigger mechanisms for jarring in tension or compression, however each is a mirror of the other. Each consists of a compression sleeve to transfer the jar load from the collet to the pressure piston, a trigger sleeve to allow the collet to release the inner mandrels after the specified travel has occurred and a coil spring to allow the trigger sleeve to move axially with respect to the collet to prevent damage to the load bearing surfaces. When jarring in either direction the non load bearing collet remains attached to and moves with the mandrel. The pressure pistons slide and seal on a flow sleeve. A fluid passageway is provided which allow the portions of the fluid chambers above and below the pressure pistons to communicate so that the fluid surrounding the chamber defined by the pressure pistons is maintained at hydrostatic pressure.

This configuration has many advantages over the existing art. The spring can be configured to define a minimum jarring load. This prevents the tool from inadvertently jarring on the surface and eliminates the need to use a safety clamp when racking the tool with drill collars. All of the high pressure is confined to the area between the pressure pistons so that all the seals that are exposed to well bore fluid are balanced with hydrostatic pressure. The collets and spring give a well defined neutral position. This configuration only requires one spring. This design has a hydraulic time delay but triggers mechanically.

According to another embodiment of the invention, the jar may be mechanically triggered only without the hydraulic time delay by allowing for free movement of the pistons within the housing.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1A-5A, an embodiment of the invention includes an outer housing comprising several portions. These include a sealing cap14, a proximal portion16, a first filling sub28, a proximal trigger sleeve housing37, spring housing68, distal trigger sleeve housing99, a second filling sub120, a floating balance piston housing125and distal portion127which includes threads129for connection to a distal portion of the work string.

The various portions of the housing are secured together by any known method. In one embodiment, the portions are secured together by male and female threaded segments for example7,8for the sealing cap14and proximal portion16of the housing. The first filling sub housing portion28has externally threaded stubs27and28that receive internally threaded portions5and6of proximal portion16and trigger sleeve housing portion37. Trigger sleeve housing portion37is externally threaded at66to receive an internally threaded portion67of spring housing68. The distal portion of spring housing68is internally threaded at98to receive externally threaded portion90of distal trigger sleeve housing99. Second filling sub housing120has externally threaded stubs121and122that connect to internally threaded portion119of distal trigger sleeve housing99and internally threaded portion124of floating balance piston housing125. The distal portion126of floating balance piston housing125is internally threaded to receive externally threaded portion128of distal housing portion127. Suitable seals3,4,35,36,76,96,97,140,133, and144are provided between the treaded portions.

Located within the housing for axial movement in both directions from a neutral position is a mandrel2which also comprises several sections. A mandrel work string connector portion12is threadly connected to a work string connection11. A seal13is provided between the connecting portions. The distal portion17of the work string connection portion is internally threaded to receive an upper mandrel portion21which in turn is internally threaded at62to receive an externally threaded portion63of central mandrel portion64. Central mandrel portion64is externally threaded at107to receive internally threaded portion103of distal mandrel portion113. Distal mandrel portion113is externally threaded at142to receive internally threaded portion141of lower end mandrel portion160. Suitable seals9,10,106, and143are located at the threaded connections. The mandrel has an internal fluid passageway150that extends throughout its length.

Mandrel connecting portion12has an enlarged section17that includes a plurality of splines18that slide within grooves19provided in the inner surface of housing portion16. An annular fluid filled chamber20is located between mandrel portion21and housing portion16. A trigger sleeve39is positioned within proximal trigger sleeve housing37and includes a plurality of grooves51on its inner surface. Trigger sleeve39includes a shoulder40and a reduced diameter portion41as shown inFIG. 2A. A coil spring38is captured between stub28of first filing sub25and the shoulder40. A first collet46is mounted on upper mandrel portion21between the mandrel and the trigger sleeve39. The exterior surface of upper mandrel portion includes a plurality of grooves50which interact with a plurality of ribs52on the interior of the fingers49of collet46in a manner to be explained below. Collet46also includes a plurality of ribs47on the outside of the fingers of the collet that interact with grooves51located on the interior surface of the proximal trigger sleeve39in a manner to also be described.

A first compression sleeve54surrounds the mandrel and is located between the first collet46and a first pressure piston69. Pressure piston69is mounted on a flow sleeve65which surrounds central mandrel portion64and is provided with a seal71. The piston includes a first flow passage or flow control orifice78and a second flow passage or a check valve79. A plurality of flow channels70are formed either in the outer surface of central mandrel portion64or on the inner surface of flow sleeve65to allow for fluid communication between the chamber or either side of pressure chamber82.

A second pressure piston93is mounted on the flow sleeve65downhole of the first pressure piston69and may include a flow control orifice80and a check valve81or first and second flow passages. Pressure pistons69and93are also provided with a flow passage91that extend from the metering orifices and check valves to the rear of the pistons as shown inFIG. 3A. A Belleville spring stack79surrounds the flow sleeve and extends between pressure pistons69and91and is confined between them. Although a Belleville spring stack is illustrated, any known spring such as a coil spring may be utilized. Flow sleeve65is captured between portion62of upper mandrel portion21and portion103of lower mandrel portion113. Downhole of the second pressure piston is a second compression sleeve101and collet112arrangement similar to that of compression sleeve54and collet46. Also a second trigger sleeve110surrounds collet112and includes a plurality of grooves116on its inner surface which interact with a plurality of ribs111on the outer surface of the collet fingers. Also distal mandrel portion113has a plurality of grooves152that interact with a plurality of ribs114on the inner surface of the collet fingers. Trigger sleeve110includes a shoulder161at its distal end and a reduced diameter portion117. A coil spring118abuts shoulder161at one and rests on a shoulder of the sub housing120at its other end as shown inFIG. 4A. Pressure pistons69and93along with the metering orifice and check valve or first and second flow passages, serve as an hydraulic delay mechanism for triggering the jar. However, it is within the scope of this invention to allow the pistons to move freely within the housing without causing any hydraulic resistance so that the jar is mechanically actuated only. This can easily be accomplished, for example, by allowing sufficient clearance between the pistons and the housing for unrestricted fluid flow. In this situation the pistons would merely function as spring abutment members.

A floating balance piston130having exterior and interior seals131,132floats on lower end mandrel portion160in a distal pressure chamber134formed between the lower portion160of the mandrel and housing portion125. The distal portion of the pressure chamber134is in fluid communication with the fluid passageway150in the mandrel, and the proximal portion135of pressure chamber134is in fluid communication with the interior portion of the tool between the housing and mandrel.

FIG. 6-8illustrates the details of collet46which is structurally identical to collet112. Collet46includes a plurality of alternating finger portions203,204that are joined at their top looking atFIG. 6by arcuate solid portions200. At their bottom, the finger portions are joined to a different finger portion by solid arcuate portions201thus forming a interconnects series of finger portions with slots205open at the top and slots202open at the bottom of the collet. The outer surface of each finger portions203,204of the collet is provided with a plurality of ribs47, the lowermost ribs49having a greater width than that of ribs47. In a similar fashion the inner surface of each finger portion203and204are provided with a plurality of ribs52and the lowermost rib206has a greater width than that of ribs52.

Operation of the jar is as follows. For jarring in the upward mode, an upward force is applied to the mandrel through work string connector11. Upward movement of the mandrel is resisted by Belleville spring stack79through collet112, compression sleeve101and pressure piston93. Upward movement of the mandrel is also resisted by the fluid within the pressure chamber82bounded by the two pressure pistons69and93. Fluid is allowed to escape from the pressure chamber by the metering orifice80provided in one of the pressure pistons. This arrangement acts as a hydraulic time delay to prevent premature triggering of the jar. As the mandrel continues to move upwardly as shown inFIG. 4Bribs111on the collet112will come into registry with grooves116provided in the inner surface of trigger sleeve110. The proximal ribs on the collet112has a width greater than that of the distal ribs and the proximal groove in the trigger sleeve has a width greater than that of the distal grooves to avoid jamming or release of the collet prematurely in a manner known in the art. Once ribs111and grooves116are in alignment the collet finger expands outwardly and the mandrel is released. This drives hammer portion152of enlarged portion17of the mandrel against anvil portion151of sealing cap14, as shown inFIG. 1B.

At this point the Belleville spring stack will act to move trigger sleeve110to the right looking atFIG. 4Bthrough pressure piston93and compression sleeve101. This in turn compresses coil spring118. To reset the jar, the upward force on the mandrel is relaxed. The mandrel returns to a neutral position shown inFIGS. 1A-5Aand ribs114on the inner surface of collet112engage grooves152on the outer surface of mandrel portion113. The width of the grooves152and the ribs114are formed in the manner of grooves116and ribs111. Compressed coil spring118now moves trigger sleeve to the left looking atFIG. 4Bto its neutral position inFIG. 4A. During the upward jarring sequence, collet46remains engaged with mandrel portion21.

Downward jarring is achieved by applying a downward force on the mandrel. Collet46, compression sleeve54, pressure piston69and Belleville spring stack all operate in a manner similar to upward jarring. Downward movement of the mandrel with respect to the housing causes collet46to release mandrel portion21after compressing Belleville spring stack79and moving pressure piston69to the right as seen inFIG. 3C. As the ribs47on collet46register with grooves51in trigger sleeve39, collet46disengages from proximal mandrel portion21. This will cause hammer surface153of enlarged portion17of mandrel portion12to strike anvil surface154provided on the proximal portion of filling sub housing25as shown inFIG. 26. This will also compress coil spring38.

To reset the jar, downward force on the mandrel is relaxed and the mandrel will move upwardly with respect to the housing. This will bring grooves50on mandrel portion21back and into alignment with ribs52on the inner surface of the collet46. At this point compressed coil spring38will move trigger sleeve39back to its neutral position.

An additional aspect of the invention involves providing a flow path70between mandrel portion64and flow sleeve65. This can be accomplished by providing flow channels either on the external surface of the mandrel or on the internal surface of the flow sleeve. These flow channels allow the portions of the fluid chambers distal and proximal to pressure chamber82to communicate so that the fluid surrounding chamber82is maintained at hydrostatic pressure.