US3038548A - Hydraulically operable percussion jar - Google Patents

Description

`lune l2, 1962 R. WSBROWN 3,038,548

HYDRAULICALLY OPERABLE PERCUSSION JAR R. W. BROWN HYDRAULICALLY OPERABLE PERCUSSION JAR June 12, 1962 5 Sheets-Sheet 2 Filed Nov. 6, 1957 ATTORNEY June l2, 1962 R. w. BROWN HYDRAULICALLY OPERABLE PERCUSSION JAR 5 Sheets-Sheet 4 Filed Nov. 6, 1957 INVENTOR.

Hob/fawn W Brow/7 June 12, 1962 R. w. BROWN HYDRAULICALLY OPERABLE PERCUSSION JAR 5 Sheets-Sheet 5 Filed Nov. 6, 1957 Hob/fawn VV. grow/7.

ATTORNEY tatcs riexas Fiied Nov. 6, 1957, Ser. No. 694,856 2 Claims. (Cl. 175-296) This invention relates to well jars and more partcularly to hydraulically operable percussion jar mechanism -for use in a string of drill pipe, well tubing, drill collar string or the like.

In the drilling and production of wells, such as oil and gas wells, it is often desirable to provide jarring mechanism incorporated in the drilling string or tubing string which may be operated when necessary to deliver anV impact on the string in the event that the same should become stuck in the well bore, or for other reasons. Heretofore, such jarring mechanism, as usually constructed, has been made up of telescopingly arranged parts connected into the string for rotation therewith and which are movable longitudinally relative to each other to deliver an impact to the string.

Jarring mechanism of this type, as heretofore commonly employed, however, possesses the disadvantage that some means must *be provided for holding the parts against relative longitudinal movement during normal operation of the string; and which may be released by manipulation of the string to place the mechanism in condition for the carrying out of the jarring operation. Packing means must also be provided between the longitudinally movable parts to prevent the entrance of well lluid into' or escape of fluid from the string. Another disadvantage of jarring mechanism of the type heretofore com-monly employed is that usually only a single impact can be delivered at one operation of the mechanism, after which the mechanism must be reset before the next impact can be delivered. Moreover, in the operation of jarring mechanism of this type the interval ibetween impacts is relatively great yand after the delivering of one impact the stuck portion of the string or iish may move longitudinally independently of the portion of the string above the same during the resetting of the parts, so that there is danger that the effectiveness of the impact will be lost by downward movement of the stuck portion during such resetting.

The present invention has for an important object the overcoming of the above mentioned disadvantages by the provision of jarring mechanism in which the impact delivering means is enclosed within the string and jarring is accomplished without longitudinal movement of any part of the string relative to any other part thereof.

Another object of the invention is to provide jarring mechanism which does not reduce the strength of the string, whereby such mechanism may be safely employed in the string during normal drilling operations.

A further object of the invention is` the provision of jarring mechanism which does not interfere with the circulation of well Huid through the string during the drilling operation.

Another object of the invention is to provide jarring mechanism which is operated by the circulation of Huid under pressure through the string and which may be operated continuously and automatically as long as such circulation is maintained.

Another object of the invention is to provide a jarring mechanism operable by a unidirectional input of fluid at the surface and in which the magnitude, frequency of impacts, and power delivered to the string can be controlled by the openator by varying the volume of fluid pumped through the mechanism.

3,038,548 Patented June l2, 1962 A further ohject of the invention is the provision of jarring mechanism of the kind referred to which may be operated while the string is under tension, compression or torque or a combination of such stresses.

A still further and important object is to provide a mechanism which will impart to the drill string a series of mechanical impulses in one direction alternating with hydraulic impulses in the opposed direction to produce -a strong vibratory motion in the string which is very etective in freeing the bit or any part of the string which may become stuck.

The above and other important objects and advantages of the invention may best be understood from the following detailed description, constituting a specification of the same when considered in conjunction with the annexed drawings, wherein- FIGURES 1A and 1B are fragmentary vertical, central, cross-sectional views of `a preferred embodiment of the invention showing the same as applied to -a drilling string and with the parts of the mechanism in the relative positions which they occupy at one stage of the jarring operation, FIGURE 1B being a downward continuation of FIGURE 1A;

FIGURES 2A and 2B are views similar to those of lA and 1B, respectively, showing the parts of the mechanism in the relative positions which they occupy at another stage of the jarring operation;

FIGURE 2C is a cross-sectional View, on a somewhat enlarged scale taken along the line ZC-ZC of FIGURE 2B, looking in the direction indicated by the arrows;

FIGURES 3A and 3B lare views similar to those of FIGURES 1A and 1B, respectively, showing the parts of the mechanism in the relative positions ywhich they occupy at still another stage of the jarring operation; and

FIGURES 4A and 4B are views similar to those of FIGURES 1A and 1B, respectively, illustrating a somewhat ditferent form of the jarring mechanism of the invention and showing the parts in the relative positions which they occupy at a stage in the jarring operation corresponding substantially to the stage of operation shown in FIGURES lA and 1B.

Referring now to the drawings in greater detail, the jarring mechanism of the invention is illustrated in FIG- URES 1A, 1B, 2A, 2B, 3A and 3B in connection with its application to a drilling string of usual construction, the mechanism having an upper tubular section 10 provided with an externally threaded pin portion 12 at its lower end and a lower tubular section 14 provided with an externally threaded pin portion 16 at its upper end. The jarring mechanism of the invention comprises a tubular barrel or housing 18 whose opposite end portions are internally threaded as indicated at 20 and 22 for the connection thereto of an upper tubular connector element 24 and a lower sub 27.

The upper connector element 24 is provi-ded with an externally threaded pin portion at its lower end for connection to the internally threaded upper end of the barrel with its lower end surface positioned to form an internal annular downwardly facing impact face 28 within the upper end portion of the barrel.

A lower connector element 26 is provided which has an internally threaded pin portion at its upper end for connection to the lower internally threaded box portion 25 of the tubular sub 27 whose upper externally threaded pin portion 29 is threadably connected to the lower end of the barrel.

At its upper end the upper connector element 24 is provided with an internally threaded =box portion 32 for the connection thereto of the lower externally threaded end of the upper section 10, and the lower connector element 26 is provided at its lower end with an internally 3 threaded box portion 34 for the connection thereto of the externally threaded upper end of the lower section 14.

The upper connector element 24 has an enlarged, internal, upwardly opening counterbore 38 therein which is in communication near its lower end with the exterior of the element through one or more openings 40.

The tubular impact element or hammer 41 is movably positioned in the barrel for longitudinal movement therein, and has a tubular extension 42 at its upper end of reduced external diameter to provide an upwardly facing, annular, impact `face 43 on the impact element positioned to move into and out of contact with the face 38. The extension 42 extends upwardly into the upper connector element and into the counterbore 38 thereof, and is of smaller diameter than the internal diameter of the connector element 24 below the counterbore 38, to provide clearance between the extension and the upper connector element to form a passageway 44 externally of the extension. The barrel 18 also has one or more openings 46 in communication fwith the interior and exterior of the lbarrel near its upper end and through which iiuid may ow through the passageway 44 and through opening 40. Within the barrel 18 the impact element 41 has an external enlargement 45 which carries a seal forming element 47 in an external groove provided for the same, to form a uid tight seal between the impact element and the barrel below the openings 46.

Within the counterbore 38 the extension 42 carries a piston 48 forming a part of the impact element and means is provided thereon, such as the O- rings 50 and 52 for Iforming a fluid tight seal between the piston and the internal wall of the counterbore and between the piston and the extension.

The impact element or hammer 41 has a reduced externally threaded lower end portion 54 to which a tubular valve actuating element 56 is threadably connected at its upper end. At its lower end the valve actuating element 56 has an internally thickened portion 58 forming an upwardly facing, internal, annular shoulder 60.

A tubular valve 62 is movably positioned in the actuator 56 for longitudinal movement therein, and extends downwardly through the internally thickened portion 58 land into the sub 27. The portion of the valve which is movably extended through the portion S8 of the actuator and into the sub 27 is of smaller external diameter than the internal diameter of the portion 58 but fits closely within the reduced bore in the upper part of the sub 27. The valve has an upper end portion 64 which is externally thickened to form an annular, external, dov/nwardly `facing shoulder 66 positioned to be engaged by the shoulder 60 of the valve actuator 56 to move the valve upwardly with the impact element 41 when the impact element reaches a predetermined point in its upward travel, and at its upper end the valve is formed with an external annular ange 68.

An annular spring seat member 70 is movably positioned in the actuator 56 in position to bear against the -upper end of a coil spring 72 surrounding the valve 62 and whose lower end rests upon the shoulder 60. The spring seat member 70 has an internal flange 74 thereon positioned for engagement with the external flange 68 of the valve so that the spring will be compressed upon upward movement of the valve actuator 56 relative to the valve until the shoulder 60 of the actuator engages the shoulder 66 of the valve.

The sub 27 is formed with upper and lower counterbores 76 and 78, respectively, the counterbore 76 opening at its lower end into the bottom of the counterbore 78, and a tubular valve seat forming member 80 is positioned in the counterbore 78 and has an upper end extension 82 extending upwardly in the counterbore 76 and whose upper end is formed with a valve seat 84 positioned for engagement with the lower end of the valve 62 when the valve is in closed position. The valve seat member 80 is `formed with one or more passageways 86 in communication with the interior of the counterbore 76 exteriorly of the seat member and with the interior of the seat member. The valve seat member also has an internal tapered valve seat 88 located above the passageways 86 for a purpose to be explained hereinafter. A resilient washer shaped element 90, such as a rubber washer, or the like, is positioned in the counterbore 78 in contact with the lower end of the seat forming member 80, and is held therein by contact with the upper end of the connector element 26 to retain the resilient member 90 in position.

The clearance between the exterior of the valve 62 and the internal wall of the sub 27 above the counterbore 76 is very small to form a fluid seal between the space 63 above the sub and the space within the counterbore 76.

A go-devil 92 is provided for insertion into the drilling string for movement downwardly therein to a position extending through the valve 62. The go-devil has an external enlargement 94 near its lolwer end which is provided with a tapered lower end face 96 positioned for engagement with the internal seat `88 of the valve seat men"- ber 80 to close said member. At its upper end the godevil 92 has a fishing head 98 by which the go-devil `may be retrieved from the spring by any suitable means, such as a wire line and grapple device. The go-devil may also be provided with an externally enlarged portion 100, positioned to restrict the downow of iluid through the impact element 41 in all positions of the impact element.

In making use of the invention constructed as described above, -the jar mechanism, without the go-devil 92, is incorporated in the drilling string, or other string of pipe to be used in a well, and inserted with the string into the well. With the jar mechanism so incorporated in the string normal drilling or other operations may be conducted while circulating drilling fluid through the string and mechanism in the normal manner. During such normal drilling operations the impact element 41 will be in its uppermost position in the barrel 18, as shown in FIGURES 2A and 2B, and the valve 62 will be fully open and out of contact with the valve seat 84, as shown in FIGURES 3A and 3B.

When it is desired to carry out a jarring action with the mechanism, the go-devil 92 is inserted into the string at the surface and pumped downwardly under the inuence of the downwardly circulating drilling uid into contact with the seat 88 to close the central opening through the seat.

Before the go-devil 92 has reached its seated position on the sea-t 88, the hammer element 41 could have been in either its lower position, shown in FIGURES 1A and 1B, or in an uppermost position yas shown in FIGURES 2A and 2B. The position of the hammer element belfore the go-devil seats is dependent upon the difference in pressure existing Within the barrel 18 and that existing in the annular space between the outside of the barrel and bore of the drilled hole. This difference in pressure will vary with the volume of fluid Ibeing pumped, the length and size -of opening from the valve seat member 80 to the bit, and the size of the openings through the bit.

In most cases, the hammer element 41 will be in its uppermost position, FIGURES 2A and 2B, just prior to the go-devil landing on its seat 88.

Regardless of the position of hammer element just prior `to the landing of the go-devil on its seat, the jar will start to operate when the go-devil reaches its seat.

If the hammer element 41 is in its uppermost position, the beginning of the jarring cycle will be as follows:

The go-devil 92 lands on its seat 88 land plugs the central opening through the valve seat element 80. The externally enlarged portion 100 of the go-devil is now positioned within the central bore of the hammer element 41. The valve 62 is olf of its seat 84, and therefore fluid is free to flow through the central bore of the hammer element, past the restriction created by the enlarged section 100 of the go-devil 92, through the valve 62, counterbore 76, ports 86, the bore of the sub 27 and through the openings in the bit, not shown. The restriction in the bore of the hammer element caused by the enlarged section 100 of the go-devil 92 serves the specific purpose of creating a pressure drop past it under iiowing conditions. This pressure drop causes a -higher pressure to exist above the top piston 48 than that existing below the hammer element, in the space 63. The higher pressure above the top piston 48 acts on the area of this piston to create a force downward; at the same time the iower pressure in the space l63 below .the hammer element acts on an area dened by the outside diameter of the hammer element 41 at the seal 47. A1- though the effective area of the top piston 48 is less `than that defined by the seal 47, when the fluid velocity has reached a given value the pressure difference between the space above the top piston and the space 63 below the hammer element 41 will be suiiicient to cause the hammer element to move down.

If the hammer element is in the lower position as shown in FIGURES lA and 1B just prior to the godevil 92 landing on its seat 88, then the starting of the jarring cycle will be as follows:

As soon as the go-devil 92 reaches its seated position on the seat 88, downward flow of iluid through the mechanism will be suddenly checked causing a rapid increase in pressure above the seat 88. Since there is no iow of liuid at this time, there will be no pressure differential existing between the space above the topV piston 48 and the space 63` below the hammer element. rIlherefore the static pressure existing inside of the jar mechanism will be constant throughout the length of the mechanism. This high static pressure will act on the cross sectional area of the ham-mer element 41 at the seal point 47 to create an upward force on the hammer element. At the same time, a downward -force will be created on the top pis-ton 48 and will have a value equal to the cross sectional area of the top piston multiplied by the static pressure. However, since this latter area is less than the cross sec- -tional area of the hammer at Ithe seal point 47, the resulting force on the hammer element 41 will be upward.

Regardless of `the position of the hammer 41 when the go-devil 92 rst seats, the jarring mechanism will start to operate. The first few cycles will be relatively slow with intermittent hesitatons or a stuttering action. These rst few stuttering cycles represent the transition from a steady ow condition before the go-devil 92 became seated to a steady dynamic state of intermittent flow. The starting operation under the two possible conditions which could exist having -been explained, the operation of the mechanism after a steady dynamic state has been reached will now be explained in more detail.

Let it be considered that each cycle starts with thev parts of the mechanism in the position as shown in FIG- URES lA and 1B. At this point of the cycle, the valve 62 is on its seat 84 and the hammer element 41 is in one of its lower positions so that the impact face 43 is positioned away from the impact face 28. With the parts in this position, no flow can exist through the mechanism, and therefore, a high water hammer pressure exists within the interior of the jarring mechanism. This pressure will act on the cross sectional area of the hammer element 41 at the seal point 47 to force the hammer upward. As the hammer moves upward under very rapid acceleration, the valve :62 remains stationary on its seat 84 because the static pressure above the valve is much higher than that existing below the valve seat element 82. During the upward travel of the hammer, the upper end of the valve spring 72 is being held stationary by the shoulder 68 on the valve 62 and the spring seat 70, while the lower end of the valve spring is being forced upward by the enlarged section 5S at the lower end of the actuator 56. Therefore, it may be seen that the valve spring 72 is being compressed as the hammer element 41 moves upward. A short distance before the hammer impact face 43 strikes the anvil impact face 28, the upward facing shoulder 69 formed by the thickened section 58 at the lower end of the actuator 56 strikes the shoulder 66 formed on the valve 62. When these .two latter faces make contact, the valve is jerked off of its seat 84, thus establishing a passage for uid to flow between the lower end of the valve 62 and its seat 84. Immediately thereafter, the impact face ofthe hammer element 43 strikes the impact face 28 of the anvil. The position of the parts is now as shown in FIGURES 2A and 2B. Circulation through the impact 4mechanism has no-w been established so that the pressures existing above the valve seat 84 and those existing outside and below the valve seat will now become balanced. As these pressures balance, there no longer exists the force tending to hold the valve 62 on its seat. Therefore, the spring 712 which had formerly been compressed will lift the valve 62 upward with respect both to the hammer 41 and the valve seat 84, thus fully opening the space within the counterbore76 to carry fluid therethrough, through the ports 86, the bore of the sub 27, and hence on through the openings in the bit. The upward stroke of the hammer has now been completed and has resulted in transferring the kinetic energy existing in the hammer to the drill string. After the hammer strikes the anvil and the valve 62 is a considerable distance off of its seat 84, the fluid velocity through 4the impact mechanism will increase, and in so doing will cause a pressure differential lto exist between the area above the top piston 48 and the space 63 below the hammer eley ment 41. This pressure differential is caused principally by the enlarged section 10ft` near the upper end of the go-devil which enlarged section remains within the central bore of the hammer 41. As the iluid velocity through the bore of the hammer increases the pressure loss past this restriction increases approximately to the second power of the fluid velocity. Thus, when the pressure differential existing between the area above the top piston 48 and the area below the hammer element, for example in the space 63, reaches a given value, the forces acting on the hammer element 41 will serve to force it downward. This -may be understood by considering the balance of forces acting on the hammer element 4l. Since the `hydrostatic head existing within the impact mechanism is equal to that existing outside of it and within the bore of the drilled hole, these hydrostatic pressures will cancel out and need not be considered in determining the net forces acting on the hammer. Since the hydrostatic pressures will cancel and therefore any value may be as-v signed to them without affecting the results in calculating the direction of net forces, a value of zero will be assigned to the hydrostatic head in order to simplify the problem. A-t any instant during the cycle, the forces acting upwardly on the hammer element will be the product of the cross sectional area of the hammer at the seat point 47, multiplied by the pressure exis-ting below the hammer element which will be equal to that existing at any point below the seal 47 and above the valve seat 84. The force acting downward on the hammer will be equal to the product of the cross sectional area of the top piston 48, multiplied by the pressure existing just above this top piston. Since the cross sectional area of the top piston is` always less than that of the hammer, it is obvious that the pressure above the top piston rnust be considerably higher than that below 4the seal point 47 on the hammer for the resulting net force to be downward. As explained above, when the fluid velocity reaches a predetermined value,

the pressure above the top piston will be sufficiently greater than that below the hammer seal 47 so that the product of this higher pressure and the cross sectional area of 'the top piston will be greater than the product of the cross sectional area of the hammer and the pressure existing below the hammer. At this time, the hammer will start to move downward. l ust after the hammer starts on its downward return stroke, the parts will assume the positions shown in `FIGURES 3A and 3B. The spring 72 has now extended to it-s full length as limited by the distance between the upward facing shoulder 60 of the actuator 56 and the lower face of the spring seat 74 so that the valve 6.2 and the hammer element 41 are moving at the same velocity. The valve 62 approaches its seat 84, `and at a given distance from the seat, it will suddenly jump 4to closure, thus blocking circulation through the impact mechanism. This sudden checking of fluid ow will cause a pressure increase, or water hammer pressure, to exist throughout the inside of the impact mechanism. The high static pressure, now reformed, will be equal throughout the length of the mechanism and therefore equal at a point above the 'top piston 48 and below the seal 47 on the hammer so that the net forces acting on the hammer are again upward. This may be easily understood by considering that the pressures acting on the cross sectional area of the hammer and the cross sectional area of the top piston are identical, but the cross sectional area of the hammer 41 is larger than that of the top piston 4S, therefore, the net result is an upward force. After the valve 62 seats, the hammer will first be decelerated and come to a stop. `its direction will then be reversed as it is again accelerated upward to start a new cycle.

Throughout the operating cycle, the holes 40 in the connector 24, and the holes 46 in the barrel 18 serve to allow iluid to be freely displaced as the hammer 41 moves up and down. They also serve the purpose of allowing the difference of pressure between that existing within the mechanism and that existing outside of the mechanism to act on the top piston and the cross sectional area of the hammer to create the net unbalance of forces as discussed above.

Each time the valve 62 closes, the rapidly moving column of iluid within the drill string is suddenly stopped. This results in a strong reaction downward so that the net result of the mechanism is to create alternately a mechanical impulse upwardly and then a hydraulic reaction downwardly. This transmits to the drill string an intense and high frequency vibration which is very effective in freeing the bit or any other components of the drilling assembly which may become stuck in the drilled hole.

It may be seen in the illustrations that, by the proper spacing of the valve 62 with respect to the actuator 56 and the valve seat 88, the hammer element may be made to alternately strike the anvil face 28 and the upper face 30 of the connector 27. This would result in both upward and downward mechanical impulses being transmitted to the drill string. Also, by a slightly different spacing of the above elements, the mechanism can be adjusted to strike only the upper face 30 of the connector 27 at each cycle resulting in transmitting to the drill string alternate mechanical and hydraulic impulses each of which is directed downward.

A somewhat diierent -form of the invention is illustrated in FIGURES 4A and 4B, wherein the barrel 18' is connected at its upper end in the same manner as previously described to the upper tubular section of the drilling string by means of an upper connector element 24' similar to the connector element 24, and the lower end of the barrel is provided with an externally threaded pin portion 102 for the connection thereto of an upper end box portion 104 of a lower connector element or section of the string.

Near its lower end the barrel is formed with an internal counterbore 106 of reduced diameter within which a seat forming element 108 is located, which may be provided with an annular insert 110, forming a valve seat.

The connector element 24 has an internally enlarged counterbore 112, which opens upwardly at the upper end of the element.

A longitudinally movable, tubular impact or hammer element 41 is positioned in the barrel 18', and has an externally reduced upper end extension 42' to provide an external, annular, upwardly facing impact shoulder 111 positioned to engage the lower end face of the connector element 24' and which extends upwardly into the counterbore 112 and carries at its upper end a piston 48'. Suitable seal kforming means, such as the O-rings 54) and 52 are provided on the piston 48 in annular grooves provided for the same, in position to form fluid tight seals between the extension 42 and the piston and between the piston and the interior wall of the counterbore 112. Suitable seal forming means, such as that shown at 47 is also provided positioned in an external groove in the impact element 41 to form a fluid tight seal between the element and the interior wall of the barrel 18'. The impact element 41' also has an externally reduced downward extension 114 which is provided with one or more openings 116 therein in communication with the interior of the impact element and leading to the exterior thereof. Below the openings 116 the impact element has an internal, annular, upwardly facing shoulder 11S.

A tubular bushing 120 is positioned in the lower end of the impact element, which bushing has an external enlargement in its upper end forming an external, annular downwardly facing shoulder 122 positioned for engagement with the shoulder 118.

A longitudinally movable, tubular valve 124 extends through the bushing 12) and has at its upper end a tubular cap 126 forming a shing head, and at its lower end an external shoulder 130 upon which the lower end of the bushing 120 is seated. The valve 124 is closed at its upper end yby a tapered plug 132. The lower end of the valve has a bevelled end face which may be provided with an annular insert 134 positioned for contact with the insert 110 of the seat forming element 108 when the valve is in its closed position.

A coil spring 136 surrounds the valve 124 which spring is seated at its lower end upon the upper end of the bushing 120 and bears at its upper end against the lower end of the cap 126.

The barrel 18 has an opening 138 in communication with the interior of the barrel just below the lower end of the connector element 24' and with the exterior of the barrel, and the extension 42 is of somewhat smaller external diameter than the internal diameter of the connector element to provide a passageway 140 through which fluid may tlow between the interior of the counterbore 112 beneath the piston and the exterior of the barrel 18' through the opening 138.

In the use of the form of the invention illustrated in FIGURES 4A and 4B, the jarring mechanism, with the valve 124 and its bushing 120 and spring 136 removed, is connected into the drilling string in a manner similar to that explained in connection with the form of the invention previously described, and lowered into the well bore with the string. The drilling operation may then lbe conducted in the usual manner by rotating the string while circulating drilling luid therethrough.

In the event that it is desired to carry out a jarring operation with the mechanism, the valve mechanism may be inserted into the string and pumped downwardly therein with the drilling fluid until the valve is seated on the seat forming element 108.

As soon as the valve reaches closed position the downward ow of fluid in the string `will be suddenly cheeked, whereupon the pressure of the drilling iluid causes an upward movement of the impact element 41' to move the impact shoulder 111 into contact with the lower end face 113 of the connector element 24' to deliver an upward jar on the string. During the upward movement of the impact element the internal shoulder 122 thereof engages the external shoulder 118 of the bushing 120 to move the bushing upwardly to compress the spring 136, whereupon the valve 124 will be lifted to open position.

Upon opening of the valve the downward flow of Huid through the `string will be resumed to permit the impact element to return to its down position under the influence of gravity and the downward pressure of fluid on the piston 4S. During such downward movement of the impact element the bushing 120 moves downwardly under the inlluence of the spring 136 and the valve 124 is held open until the impact element reaches a lowered position. As soon as the valve again reaches closed position the downward ow of fluid is again suddenly checked to produce a water hammer pressure build up to move the impact element upwardly to strike the lower end face 113 to deliver another impact on the string.

By selecting the proper dimensions of the working parts of the mechanism it may be adapted to operate over a wide range of fluid volumes and pressures, thus enabling both the magnitude and the frequency of impact to be controlled by the operator by merely adjusting the speed of the pumps at the surface.

`It will -thus be seen that the invention provides jarring mechanism which is automatically operated by the pressure and rate of Iflow of the circulating fluid in the string and which operates entirely independently of the rotary or longitudinal movement of the string.

While the invention is disclosed herein in connection with certain specific embodiments of the same, these are intended by way of illustration only, and various changes can be made in the construction and arrangement of the parts within the spi-rit of the invention `and the scope of the appended claims.

Having thus clearly shown and described the invention, what is claimed as new and desired to secure by Letters Patent is l. Jarring mechanism comprising a tubular barrel adapted to be connected into a string of pipe for insertion therewith into a well bore, la tubular impact element movably positioned in the barrel for longitudinal movement therein and having an upwardly facing surface and a downwardly facing surface whose area exceeds that of the upwardly lfacing surface, means restricting the `flow of liuid downwardly .through the barrrel, means subjecting said upwardly and downwardly facing surfaces, respectively, to the iluid pressure in the barrel upstream and downstream, respectively, of said restricting means, means forming an impact face in the barrel positioned to be engaged by the element upon upward movement of the element, means forming a valve seat in the barrel below said restricting means and the element and through which Huid may flow downwardly through the barrel, a tubular valve movably positioned in the barrel for movement to one position to close the seat against downward flow of iluid therethrough to cause the fluid to exert an upward force on said element to move the element upwardly, and to another position to open the seat, means on the valve and element positioned for coaction upon upward movement of the e-lement to move the valve to open position, whereby the pressure acting on the downwardly facing surface is reduced and the element is lowered by the pressure acting on its upwardly facing surface, the valve moving to close the seat as the element is lowered.

2. larn'ng mechanism comprising a tubular barrel adapted to be connected into a string of pipe for insertion therewith into a well bore, a tubular impact element positioned in the barrel for longitudinal movement therein and having upwardy facing surface exposed to the pressure of fluid in the barrel and a downwardly facing surface of larger area than said upwardly facing surface exposed to such pressure, means for restrict-ing the flow of iluid through the barrel at a location to cause a difference in the pressure exerted by the fluid on said surfaces to cause the element to move downwardly, means forming an impact face in the barrel positioned to be engaged by the element upon upward movement of the element, and means for closing the barrel against the downward flow `of fluid therethrough upon downward movement of the element, at a location to cause equalization of the pressure exerted by the fluid on said surfaces to cause the element to move upwardly and for `opening the barrel to `such ow upon such upward movement of the element.

References Cited in the file of this patent UNITED STATES PATENTS 1,892,517 Pennington Dec. 27, 1932 2,756,723 Bassinger July 3l, 1956 2,786,451 Dulaney Mar. 26, 1957 2,813,516 Dulaney Nov. 19, 1957

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