CA1221960A - Latch-pin tripping mechanism for use in association with a mechanical drilling jar - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The specification describes an improved latching assembly for use in a mechanical drilling jar. The latching assemblies currently in use are subject to wear through friction when in the unlatched position as maximum pressure is on the latch at that point and also when in the latched position due to axial movement caused by the positioning of the latch assembly between sets of springs. The latching assembly described in the specifi-cation reduces wear in the unlatched position as maximum pressure is placed on the latch assembly when in the latched position.
This is accomplished by using a split collet with a profile on its face as a means of engaging an accommodating profile on a latching seat of the inner mandrel. Latch pins are used to move the split collet off the latching seat when a preset plateau of tension or compression is reached. Axial movement is eliminated by having the latch assembly held against a shoulder on the outer housing by a single set of springs.

Description

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This inven~ion relates to an improved tripping or latch mechanism for use in mechanical jarring tools of a type used in oilfield drill strings to remove drill bits, drill pipe or other objects which have become lodged within the borehole.
Mechanical jarring tools consist of four primary elements. The first is the combination of telescopically relating inner member (inner mandrel) and outer member (outer housing) having impact surfaces that can be engaged by telescoping motion.
The second is a latch mechanism to engage the inner mandrel with 10 the outer housing until a preset release plateau is reached where-upon the members can telescope freely up or down to bring the impact surfaces together in a violent manner. The third is a means for exerting pressure on the latch to keep it in a locked position until the preset release plateau is reached. The fourth is a means of pressure balancing the tool so its operation is not adversely afEected by external hydrostatic pressure.
The latch mechanisms most commonly in use are the threaded engagement, friction sleeve engagement and notch and roller engagement types.
The threaded engagement type latch has an expansible contractible sleeve member having internal threads that mesh with companion external threads formed on a reduced diameter section of the inner mandrel. The threads have a stub form providing in-clined wall surfaces. When the sleeve member and the mandrel are forced in opposite longitudinal directions, the inclined wall surfaces provide radial force components tending to expand the sleeve outwardly to a condition where the threads are disengaged.

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The friction sleeve engagement type latch has a plur-ality of outwarc]ly extending annular ridges provided on an inner mandrel adapted for relative longitudinal movement through an annular friction sleeve with inwardly extending annular ridges.
The annular ridges on the inner tubular element engage alternately with the annular ridges on the Eriction sleeve. The annular friction sleeve has flexible annular portions which permit the inwardly projecting ridges to bend upwardly, disengaging the annular ridges when suhjected to predetermined weight loads.
The notch and roller engagement has peripherally spaced, external longitudinal grooves in the inner part and longitudinal spaced sets of peripherally extending, longitudinal spaced notches opening into the groove into which longitudinally spaced rollers, rotatably mounted on the outer part are movable by relative rota-tion of the parts to hold the parts against relative longitudinal movement. Upon the exertion of a predetermined longitudinal force on the parts tending to move the parts longitudinally relative to each other, relative rotational movement will be imparted to the parts to cause the rollers to roll out oE the notches and into the grooves whereupon the members will become disengaged.
Each of the above described latch engagements has operating limitations arising from its design. One such problem is the susceptibility to torque. torque is the rotating power the drilling rig imparts to the drill stringO Torque can place addi-tional force on the drill string especially with directional drilling which can prevent the notch and roller engagement from disengaging when torque applied from drag caused by friction

- 3 -between the drill string and the bore hole walls in directional drilling can place an additional load on the notch and roller engagement preventing it from disengaging.
A second problem is wear caused by axial movement. The threaded latch engagements have springs on either side of the latch in order to exert pressure on the latch to keep it in the latched position until the preset triggering plateau is reached resulting in axial movement. The friction sleeve engagement has inherent in its design a degree of axial movement. Axial movement results in severe wear.
In order to avoid the severe wear caused by axial move-ment it has become the practice in the industry to run the mech-anical jar in the unlatched and open position. This creates a third problem; specifically, if the latch engayement is to be left open, care must be taken as to where the mechanical jar is placed in the drill string. If the mechanical jar is placed in a neutral position or under compression the latch will close. It has there-fore become the practice in the industry to place the mechanical jar near the top portion of the drill collar under tension. When run in this position the tool is unable to impart the optimum jarring effect as there is not enough drill collar weight ahove the jar to cause a yood impactO
A fourth problem with the threaded latch engagements is that the latch mechanism is subjected to maximum pressure when fully unlatched~ The considerable force trying to re-engage the latch mechanism results in wear throuyh friction.
A fifth problem with the above described latch engage-ments is that the configuration of the latch mechanism requires atool length of approximately 30 feet. Every joint over the length of the tool is subject to the risk of stress failure. There are also practical restraints with respect to the shipping and above ground handling of a tool oE that length.
The present invention is a latch mechanism which has two unique features. The first is that the tension on the latch decreases as it disengages. This is accomplished by use of a split collet and latch pins. The beneficial effect of this fea-ture is that wear on the tool when in the unlatched position isreduced. The second feature is that although the latch permits the tool to jar in either direction springs are only required on one side of the latch as the latch mechanism rests against a solid shoulder on the housing. The beneficial effect of this feature is that it eliminates axial movement so the tool can be run in the latched position and placed anywhere in the drill string. This also means that the length of the tool can be reduced eliminating the number of joints and making handling easier.
According to one aspect, the invention may be described as a well jarring tool comprising two telescopically arranged tubular members adapted for incorporation in a drill string, a first pair of impact surfaces one of which is on one of the members and the other of which is on the other member and a second pair of impact surfaces one of which is on one of the members and the other of which is on the other member and a latch mechanism for locking the two members together against mutual axial movement until a first preset tension force or a second preset compression force i5 applied with respect to the two members at which the latch mechanism unlocks permitting relative axial movement of the two members and subsequent sudden mutual engagement oE one of the pairs of impact surfaces, the latch mechanism comprising a first latch ring he~d against axial movement in one direction by engage-ment with a shoulder on the outer tubular member, a second latch ring held against axial movement in the other direction by engage-ment with spring means, a split collet positioned between the first and second latch rings and having a profile on its inner face removably engaging a corresponding profile on an outer sur-face of the inner tubular member and latch pins engaged between the latch rings and ends of the collet, the latch pins being pivotable to allow radial outward movement of the collet to disen-gage from the inner tubular member when the first or second preset force is reached.
The invention will now be described in more detail with reference to the accompanying drawings, in which:
Figure 1 is a longitudinal sectional view of a mechan-ical drilling ~ar containing a latch mechanism according to the present inventioni Figure 2 is a cross-sectional view ta~en on A-A of Figure 1 and showing the latch in the latched posi-tion;
Figure 3 is a cross-sectional view similar to Figure 2 but showing the latch in the unlatched position;
Figure 4 is a perspective view, partl~ broken away, of the latch mechanism;
Figure 5 is a longitudinal sectional view taken on B-B

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of Figure 2 and showing the latch mechanism in the latched posi-tion during the beginning of a jarring down cycle;
Figure ~ i5 a view similar to Figure 5 but showing the mechanism just as the latch is beginning to release in the jarring down cycle;
Figure 7 is a view similar to Figure 6 but showing the mechanism after the latch has fully released in the jarring down cycle, this view corresponding to a section taken on C-C of Figure 2; and Figures 8, 9 and lO are views corresponding respectively to figures 5, 6 and 7 but illustrating the progressive steps in a jarring up cycle.
The present invention is a latch mechanism which fits within a mechanical jar configuration having the four elements previously described.
The first element is the combination of a telescopically relating inner member and outer member~ The inner member (common-ly referred to as the inner mandrel) depicted in Figure l com-prises two segments, namely a splined mandrel 1 and a knocker mandrel 5. The :Lower portion (left hand and as seen in Figure 1) of knocker mandrel 5 is formed with a radially outwardly extending flange 20 which is internally threaded to mate with the externally threaded upper end portion 21 of splined mandrel 1, thereby forming, in eEfect, a unitary inner member insofar as axial motion is concerned. A sealing ring 22 in the upper lateral surface of upper end portion 21 engages a corresponding lateral surface in knocker mandrel 5 and effects a fluid tight seal between members 1 and 5. The lower end 23 of splined mandrel 1 is formed with a tapered external thread for mating with the next lower sub (not shown) in the drill string. The upper end 24 of knocker mandrel 5 is externally threaded and receives an oversize safety nut 25 the purpose of which will be described hereinafter.
The outer member (commonly referred to as the outer housing) as depicted in Figure 1 comprises three segments, namely a splined housing 2, a latch housing 3 and a top sub 4.
Splined housing 2 is formed at its upper end portion 27 with a tapered internal thread which mates with a complementary externally threaded portion 28 on the lower end of latch housing 3 which in turn has a tapered internally threaded upper end portion 29 mating with a complementary externally threaded portion 30 on the lower end oE sub 4. The upper end of sub 'l is formed with a tapered internally threaded portion 31 for mating with the next higher sub (not shown) in the drill string. From the above des-cription it can readily be understood that members 2, 3 and 4 are interconnected for unitary axial motion. Sealing rings 32 serve to keep the connections between these members fluid tight.
Splined mandrel 1 has an external splined portion 33 which extends upwardly from a lower full diameter portion 34 which defines an upwardly facing impact surface 35. The splined housing 2 has an internally splined lower end portion 36 which is comple-mentary with and rides on splined portion 33 of splined mandrel 1.
The lower transverse face 37 of splined housing 2 serves as an impact surface which is normally spaced from impact surface 35 as shown but during a jarrlng operation in a downward direction would - 8 ~

impact against surface 35 to jar downwardly splined mandrel 1 and the rest of the drill string below it.
The splined end portion 36 of housing 2 is formed with an upwardly facing impact surface 39 which is normally spaced from the transverse free end surface 40 of Elange portion 20 of knocker mandrel 5. During a jarring up cycle the surface 39 would impact against impact surEace 40 to jar upwardly splined mandrel 1 and the rest of the clrill string below it. The spacing between impact surfaces 39 and 40 is substantially the same as between impact surfaces 3S and 37.
The second main element oE the invention is a latch assembly which is located within the latch housing 3. It com-prises a lower latch ring 7 which rests against a solid upwardly facing annular internal shoulder 13 on the latch housing 13.
Lower latch pins 9A integrate the lower latch ring 7 with a split collet 6. The split collet 6 is in four equal, separate segments spaced around the knocker mandrel 5. On the inside face 14 of the split collet 6 is a configuration of pyramidal teeth and indenta-tions. The knocker mandrel 5 has an accommodating, complementary configuration of pyramidal teeth and indentations on its external surface at the point where the split collet latches to the knocker mandrel which is referred to as the latching seat 15. At the upper extremity oE the latch assembly is an upper latch ring 8.
Upper latch pins 9B integrate the upper latch ring 8 with the split collet 6.
A stack of preloaded Belville springs 1i is located in the cylindrical space between latch housing 3 and the knocker g ~ ?

mandrel 5, and is in engagement with upper latch ring 9 and the lower lateral face 42 of bottom portion 30 of top sub 4. The 3elville springs 11 serve as the third main element of the inven-tion, namely a means Eor e~erting pressure on the latch until a preset plateau is reached.
The fourth element of the invention is a means of pressure balancing the tool so its operation is not adversely affected by external hydrostatic pressure. Referring to Figure 1 the present invention uses a configuration of seals and rings 12.
The split collet 6 is in the latched position shown in Figures 1, 2, 5 and 8 with the configuration of pyramidal teeth and indentations on its face 14 interlocked with the accommodating configuration of pyramidal teeth and indentations on the latching seat 15 of the knocker mandrel 5 when the jarring tool is placed within the drill string. In order to activate the telescoping motion of the tool to dislodge objects stuck in the bore hole the tool is placed under tension or compression.
Reference will now be made particularly to Figures 8 to 10 which illustrate the operation of the latch mechanism when the jarring tool is operated in the jarring up mode. An upward force is applied to the drill string by pulling on the upper end of the drill string, this force being transmitted through sub 4, latch housing 3, lower latch ring 7, latch pins 9A and split collet 6 which engages latching seat 15 of knocker mandrel 5, thereby placing the telescopically relating inner and outer members of the jarring tool in tension.
When a preset triggering plateau is reached the external force tending to expand the split collet outward toward the outer housing exceeds the force exerted by the Belville springs 11 to keep the latch on the latching seat 15. The split collet begins to expand outward toward the outer housing 3 as seen in Figure 9, compressing the 3elville springs 11 and altering the angle of the latch pins 9A and 9B. Once the angle of the latch pins is altered the force holding the latch onto the latching seat is decreased resulting in rapid movement of the split collet 6 to the Figure 10 position in which the latch is disengaged~ This rapid disengage-ment of the latch causes sudden upward movement of the outer tele-scopic member relative to the lnner member and a sudden impact exerted by impact surface 39 on impact surface 40 thereby jarring the inner member upwardly. If, due to repeated impacts over time, cyclical movement should cause joint failure, safety nut 25 would engage a shoulder 43 in the bore of top sub 4, thereby preventing complete disengagement of the inner and outer members.
In order to ensure the successful operation of the latch the importance of the angle of the latch pins must be emphasized.
The inventor has determined through experimentation that in the embodiment described the latch works most effectively when the angle of the latch pins is approximately 35 degrees when in the latched position and approximately 10 degrees when in the un-latched position. If the angle of the latch pins when in the latched position exceeds approximately 35 degrees the latch may not unlatch. If the angle of the latch pins when in the latched position is less than approximately 35 degrees a heavier spring load is required to maintain the position of the latch on the 2~

latching seat. If the angle of the latch pins when in the un-latched position exceeds appro~imately 10 degrees some wear may be encountered through friction. If the angle of the latch pins when in the unlatched position is less than approximately 10 degrees there may be problems experienced in re-engaging the latch.
The above values for angles were determined using the profile of pyramidal teeth and indentations shown. It should be realized that the latch assembly could operate using a differing profile but in doing so the proper angles for most efficient oper-ation might be effected.
When the jarring tool is operated in the jarring downcycle, a downward, compression Eorce is applied to the drill string using the weight of the drill string and this force is applied through sub 4, Belville springs 11, upper latch ring 9, latch pins 9B and split collet 6. Figure 5 shows the relative position of the components of the latch mechanism. Again, the split collet 6 stays engaged with latch seat 15 until a predeter-mined triggering plateau is set at which point the force exerted by the Belville springs is overcome and the collet rapidly moves through the Figure 6 position to the Figure 7 position in which the outer telescopic member is seen to be moving downwardly over the inner telescopic member. This causes impact surface 37 to rapidly engage impact surface 35, thereby imparting a downward jar on the drill string.
The triggering plateau for a downward jar is different than for an upward jar and the inventor has determined that using the existing profile and angle of latch pins the force required for a downward jar i5 approximately 45 per cent of the force required for an upward jar. This difference is desirable because, as a practical matter, greater tensile forces than compression forces can be applied to a drill string without damaging it.
The triggering plateau is determined by the force exerted by the Belville springs. The up and down jarring ratio remains constant regardless of the springload. Should one wish to alter the up and down jarring ratio this can be accomplished by changing the length of the upper or lower latch pins. Specifi-cally, lengthening lower latch pins 9A would decrease the latchingangle and would result in unlatching at a lower force in the jarring up mode. Lengthening upper latch pins 9B would cause the triggering plateau for the jarring down cycle to decrease.
It can be seen that the latch pins 9A and 9B are not connected to either the latch rings 7 or 8 or the split collet 6 but, as seen in Figures 5-10, in particular, have their opposite axial ends located in recesses 44 of the latch rings and aligned recesses 45 in the top and bottom ends of split collet 6. As seen in Figure 4 the recesses are elongate, i.e., they extend tangen-tially along the ends of the collet and the latch rings and thelatch pins are similarly elongated Eor snug reception in the recesses. The axial ends of the latch pins are rounded as at 46 and the bottoms of the recesses are rounded in a complementary fashion so as to permit pivoting of the latch pins about their axial ends to move the split collet to the unlatched position.
For specific lengths of latch pins 9A and 9B the triggering plateau can be altered by changing the loading provided - 13 ~ 6~

by the Belville springs 11 ~hich, of course, is carried out by increasing or decreasing the number of individual Belville springs. Instead of a stack of Belville springs, some other biasing means such as a heavy coil spring could be used instead~

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A well jarring tool comprising two telescopically arranged tubular members adapted for incorporation in a drill string, a first pair of impact surfaces one of which is on one of the members and the other of which is on the other member and a second pair of impact surfaces one of which is on one of the members and the other of which is on the other member and a latch mechanism for locking the two members together against mutual axial movement until a first preset tension force or a second preset compression force is applied with respect to the two members at which the latch mechanism unlocks permitting relative axial movement of the two members and subsequent sudden mutual engagement of one of the pairs of impact surfaces, the latch mech-anism comprisinq a first latch ring held against axial movement in one direction by engagement with a shoulder on the outer tubular member, a second latch ring held against axial movement in the other direction by engagement with spring means, a split collet positioned between the first and second latch rings and having a profile on its inner face removably engaging a corresponding pro-file on an outer surface of the inner tubular member and latch pins engaged between the latch rings and ends of the collet, the latch pins being pivotable to allow radial outward movement of the collet to disengage from the inner tubular member when the first or second preset force is reached.

2. A well jarring tool is claimed in claim 1 in which the spring means is a stack of Belville springs.

3. A well jarring tool as claimed in claim 1 in which the profiles of the inner face of the collet and of the outer surface of the inner tubular member comprise a series of pyramidal teeth and indentations.

4. A well jarring tool as claimed in claim 1 in which the latch pins are configured to lie at an angle of approximately 35°
with respect to the axial orientation of the tubular members, when the latch mechanism is in the locked position.

5. A well jarring tool as claimed in claim 1 or claim 4 in which the latch pins are configured to be at an angle of approxi-mately 10° with respect to the axial orientation of the tubular members, when the latch mechanism is in the unlocked position.

6. A well jarring tool as claimed in claim 1 in which the ends of the latch pins are rounded and are received in aligned recesses in the latch rings and collet, the recesses having curved bottoms complementary in shape to the ends of the latch pins.

7. A well jarring tool as claimed in claim 1 in which all of the latch pins are substantially the same length.

8. A well jarring tool as claimed in claim 1 in which the latch pins engaging the first latch ring are longer than the latch pins engaging the second latch ring.