Method and apparatus for decreasing drag force of trigger mechanism

Method and apparatus for decreasing drag force in a mechanism for releasing a mandrel is provided. The mandrel is released by a collet, which is controlled by a trigger sleeve. Most of the axial force on the collet is relieved, thereby decreasing the frictional force exerted by the collet on the mandrel after it is released.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention relates to tools that may be used in wells. More particularly, method and apparatus are provided for decreasing drag force in the trigger mechanism (a collet, mandrel, sleeve combination) of a jar used for releasing stuck objects in a well.

2. Description of Related Art

Jars are tools that are widely applied in wells for releasing an object stuck in the well. Mechanical jars store potential energy in a support above the jar and use a release mechanism to apply the energy as an impact force on the housing of the jar. One form of release mechanism is a collet that is adapted to release a mandrel when a sleeve disengages, allowing a hammer on the mandrel to impact an anvil on the housing. Examples of jars employing a collet, collar and mandrel as a release mechanism are described in U.S. Pat. Nos. 6,290,004; 6,481,495; 6,988,551; and U.S. Patent Application No. 2006/0169456, all having common inventorship with the present disclosure.

Frictional forces decrease the efficiency of mechanical devices such as collet-and-mandrel combinations. The frictional force created by relative motion of the collet and mandrel can have a great effect on the operation of such apparatus. In a jar, frictional force can significantly affect the mechanical impulse applied to the equipment that is stuck. Frictional force can also retard the actions necessary to reset the device. Therefore, there is need for means to decrease frictional drag in devices employing a collet mechanism to restrain a mandrel and release it at a selected position.

Methods used to decrease frictional force include use of lubricating coatings on surfaces and immersing surfaces in lubricating fluids. A further way to decrease frictional drag between surfaces is to decrease the contact force between the surfaces. There is a need for method and apparatus for decreasing the contact force between a collet and a mandrel in apparatus, such as a jar, in which the collet is used to release the mandrel at a selected position.

BRIEF SUMMARY OF THE INVENTION

Method and apparatus are provided for decreasing drag force between a collet and a mandrel when the collet is used with the mandrel that moves to store mechanical energy and is then released from the collet to apply an impact force to a surrounding housing.

The same numerical designations in each figure refer to the same part.

DETAILED DESCRIPTION OF THE INVENTION

The basic mechanisms of the jars to which the invention is applicable are described in U.S. Pat. Nos. 6,290,004; 6,481,495; 6,988,551; and U.S. Patent Application No. 2006/0169456. All of these patents and the published patent application are hereby incorporated by reference herein.

The mechanisms described generally include a mandrel in a housing positioned concentrically about the mandrel and a collet locked to the mandrel when the jar is ready to begin a cycle of storing and releasing potential energy. The collet moves from a first to a second position as force is applied to the mandrel by the support for the jar, normally a wire line. The cylindrical body of the jar is normally held by an object that is stuck in a well and is to be “jarred” free, A main spring in the jar is compressed a selected distance, the main spring displacement d, by applying a force to the wire line, causing movement of the mandrel, until a “trigger mechanism” suddenly releases the mandrel from the collet, allowing the mandrel to move rapidly to a third position. This sudden release allows the jar to “fire,” when a surface on the mandrel (the “hammer”) impacts a surface on the housing of the jar (the “anvil”). Then force on the wire line is decreased and the mandrel returns to a position where it is again Socked into the collet and is prepared for returning to the first position for another stroke. Both the firing and the resetting of the mandrel require relative movement between the mandrel and the collet. The purpose of the methods and apparatus described herein is to decrease the frictional drag that occurs between the collet and the mandrel during both the firing and the resetting stages of the jar.

Referring toFIGS. 1A,1B, and1C, the upper section of jar10is shown. Head12is shown at three different positions, but housing22is at the same position in each FIG. InFIG. 1A, jar10is in a no-load position—mechanical energy has not been stored in the jar and mandrel20is at a first position. InFIG. 1B, head12and attached mandrel20have been pulled upward to a second position, while compressing a main spring and storing mechanical energy in the support for the jar, but the jar has not tired to release the energy. Mandrel20may contain conductor21for electrical signal or power transmission through jar10. InFIG. 1C, the jar has fired, which means that mandrel20has been released to move to position three, where shoulder30(the “hammer”) on mandrel20impacts shoulder32(the “anvil”) in housing22. To reset the jar, force on head12is decreased and mandrel20is allowed to drop back to where it can be reset in the release mechanism for another stroke. Under some conditions of use of jar10, the weight available to lower mandrel20and reset the mandrel is small. Under these conditions the force resisting downward movement of the mandrel is preferably minimized so as to allow faster resetting.

Now referring toFIGS. 2A,2B and2C, a lower segment of jar10is shown, which contains springs and the inventive trigger mechanism. Housing22of the jar is in the same position in each figure and is continuous with the housings shown inFIGS. 1A,1B and1C. This lower segment contains main spring40for resisting movement of mandrel20as it moves toward the release position. The force required to compress main spring40determines the amount of potential energy stored in the support for the jar. Main spring40may be a stack of Belleville springs. InFIG. 2A, main spring40of the jar has not been compressed beyond its initial load and mandrel20is in position1. Main spring40is restrained at its lower end by piston42and piston42is resting on shoulder44. Therefore, compression ring46and collet48are not under a compressive pre-load of main spring40, if such load exists. Grooves47on the outside surface of mandrel20are engaged with or in registration with the cylindrical protuberances and grooves on the inside of collet48. External cylindrical protuberances and grooves of collet48are not in registration with the cylindrical protuberances and grooves on the inside of trigger sleeve50. This condition provides an inward, radial force from trigger sleeve50to overcome an outward radial force from collet48to maintain the cylindrical protuberances and grooves of collet48and the grooves of mandrel20in registration. Jar10is now set for application of upward force at head12to store energy in the support above the jar. Mandrel20and collet48are in their first position.

InFIG. 2B, upward force has been applied to head12of jar10to store mechanical energy in the support above the jar. This force may be applied by electric wireline, slick wireline, coil tubing or other means, while housing22of the jar is fixed to an object to be released. Jar10has not fired. Mandrel20has been moved upward to its second position, and it has moved with it collet48, since the cylindrical protrusions and grooves on the inside of collet48are in registration with the grooves of mandrel20. Collet48, now in its second position, has driven compression ring46, actuating piston42and the bottom of main spring40upward, moving the bottom of actuating piston42off shoulder44by the displacement, d, of main spring40, shown inFIG. 2B. At this point the total force of main spring40is applied downwardly on collet48. The outside flanges and grooves of collet48have been moved upward, while trigger sleeve50has been restrained from upward movement by shoulder49. When the outside cylindrical protrusions and grooves of collet48are moved enough to come in registration with the grooves of trigger sleeve50, collet48expands, releasing the grooves on mandrel20and allowing mandrel20to move upward very rapidly to its third position, which is shown inFIG. 2C. This is the “firing” of the jar. Before mandrel20has moved very far upward after collet48expands, actuating piston42has moved downward the distance, d, to shoulder44, driven by the expansion of main spring40and pressure above the piston. Shoulder44allows the axial force on collet48to be relieved of the force of main spring40. Actuating piston42has driven collet48downward by distance d and because die cylindrical protrusions and grooves on the outside of collet48remain in registration with trigger sleeve50, the trigger sleeve moves down distance d with the collet. Trigger sleeve50is affixed to or in contact with auxiliary spring52, which may be a coil spring, and auxiliary spring52applies an upward force to trigger sleeve50that is much less than the force of main spring40. Preferably, the force of auxiliary spring52after compression the distance d is in the range from about 50 pounds to about 200 pounds. Auxiliary spring52, in combination with shoulder44, performs the important function of allowing axial force on collet48to be reduced from the axial force that is applied by main spring40to the axial force applied by auxiliary spring52. Auxiliary spring52is supported by shoulder54of housing22. Pressure bulkhead56is disposed at the bottom of mandrel20. The working compression range of auxiliary spring52, where it exhibits elastic behavior, is selected to be greater than the total displacement, d, of main spring40from its maximum to minimum compression position. The magnitude of the advantage of reducing axial force on collet48while mandrel20is moving will be discussed in more detail below. In prior art jars employing the collet-mandrel-sleeve trigger mechanism disclosed herein, the working compression range of auxiliary spring52, which was usually a wave spring, was not sufficient to allow piston42to return to shoulder44to relieve the axial force on collet48prior to impact and during resetting of the trigger mechanism. This allowed the force of main spring40to be exerted on collet48during movement of mandrel20.

The operation of actuating piston42is explained in U.S. Pat. No. 6,290,004. The piston provides a mechanism for substantially sealing the portion of the fluid chamber disposed above the piston to permit a buildup of pressure in the housing. The upper movement reduces the volume between the mandrel20and housing22above piston42, which causes an increase in the internal pressure of that portion of the housing, thereby generating an axial force to resist the relative movement and allow a larger force to build up more potential energy than is possible by use of main spring40alone. Annular piston42contains two parallel flow passages, one of which permits the restrictive flow of fluid from the portion of the housing above piston42and the other permitting flow in the opposite direction when the jar is reset.

The triggering and resetting of the collet require that the cylindrical protrusions on the outside and the inside of the collet have surfaces on each side of the protrusions that are sloped.FIG. 3shows collet48that may be used for a jar or other purposes. Slots62in the collet allow a weak spring action to allow the collet to expand or contract as matching protrusions and grooves are moved axially to either move into registration or out of registration with the cylindrical protrusions and grooves of the collet. Cylindrical protrusions60on the outside of collet48may include primary protrusion60A and secondary protrusions60B. Similar protrusions inside collet48cannot be seen inFIG. 3but are illustrated inFIG. 2in cross-section. The movement of matching grooves in trigger sleeve50into registration with the external cylindrical protrusions and grooves of the collet triggers the jar.

This slope on the cylindrical protrusions also results in a radial force inward on collet48, as shown inFIG. 4A. The axial force Faopposes the spring force FS. As illustrated inFIG. 4B, the vector F represents the force of trigger sleeve50(FIG. 2) on collet48. That force is normal to the slope of the sides of the cylindrical protrusions. The radial force inward on the collet is the radial component of the force F as shown inFIGS. 4B and 4C, or Fntan A, where A is the slope of each shoulder. A usual range of slopes of the shoulders of cylindrical protrusions in such collets is around 14.5 degrees. Therefore, the radial force is about tan 14.5° or 0.26 times the spring force. The drag force on the mandrel moving through the collet is a function of the coefficient of friction, which ranges from 0.08 to 0.20 for steel sliding on steel. Assuming a drag coefficient of 0.2, the drag of the mandrel is about 0.2×0.26-0.05 or 5% of the spring force.

As explained above, in prior art jars, most or all of the force of the main spring is exerted on the collet while the mandrel is moving upward after the jar is tired and while the mandrel is moving downward for resetting. A common force from the main spring is in the range of 4000 pounds. The drag force is thus estimated to be in the range of 5% of 4000=200 pounds. This drag force significantly reduces the impulse generated by the jar and slows the fall of the mandrel for resetting. As disclosed herein, instead of the force of the main spring being exerted on the collet while the mandrel is moving, a shoulder (as shown at44ofFIG. 2) relieves the main spring force from the collet and transfers the force to an auxiliary spring (such as shown at52ofFIG. 2) that is exerting much less axial force. Since auxiliary spring52preferably exerts a force of not more than 200 pounds, for example, the drag force on the collet is reduced to less than 10 pounds.

Although the present invention has been described with reference to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except as and to the extent that they are included in the accompanying claims.