Jar for well strings
United States Patent [1 Anderson Apr. 29, 1975 i 1 JAR FOR WELL STRINGS [22] Filed: Mar. 12. 1974 [2]] Appl. No: 450,368  
 Related US. Application Data [63] Continuationinpart of Serv No. 320.200. Janv 2.  
 I973, abandoned.  
 Primary livumiuvr- David H. Brown Attorney. Agent. or Firm.lack W. Hayden I57] ABSTRACT A jar for a well string includes an outer housing having means whereby the housing may be connected with one portion of a well string with a mandrel telescopi cally fitting in the housing and having means for connection with another part of the well string. Means connect the mandrel and housing together for relative longitudinal movement therebctween while inhibiting relative rotation therebetween.  
 First and second one-way acting coupling means are mounted in spaced relation in the housing and coupling engaging means are mounted on the mandrel so that the coupling enaging means on the mandrel is movable into engagement with either of said one&#39;way acting coupling means upon longitudinal movement of the mandrel relative to the housing.  
 Shoulder means on the housing and mandrel are provided so that when the mandrel is moved longitudinally relative to said housing in one direction it engages the coupling engaging means thereon with one of the one-way acting coupling means. A predetermined force may then be exerted on the mandrel to move the coupling engaging means through the one-way acting coupling means. and when the coupling engaging means is thus disengaged from the one-way acting coupling means the shoulder means on the housing and mandrel strike to deliver a jar or impact to the well string. When the mandrel is moved in the opposite direction in the housing to engage the coupling engaging means thereon with a second one-way acting coupling means and a force exerted on the mandrel in a predetermined amount to move the coupling engaging means through the one-way coupling means. the shoulder means on the mandrel and housing again strike and deliver a jar or impact to the well string in the opposite direction. The coupling engaging means. after engagement with either of said one-way acting coupling means. is disengageable from either of said one-way acting coupling means upon longitudinal movement of the mandrel relative to the housing in a direction opposite to that which engages the coupling engaging means with either of said one-way acting eoupling means. The foregoing is accomplished without imparting a jar or impact to the well string and enable the mandrel and well string portion connected therewith to be moved freely longitudinally relative to the housing and well string portion connected therewith.  
 33 Claims. 10 Drawing Figures PMENTEUAFMQIQYS 3 0 249 suzu m 3 JAR FOR WELL STRINGS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my prior copending application Ser. No. 320,200 filed on Jan. 2, 1973, now abandoned, for Jar For Well Strings.  
 DISCUSSION OF THE PRIOR ART The prior art with which applicant is familiar is as follows: U.S. pat. Nos. 2.0l3,l27; 2.059.540; 189L772; 3.050.13l&#39;, 3,208.54l; 3,233,690; 3.685.598; and 3.685.599.  
  So far as known to applicant. there is no jar in the prior art which is adapted to be carried in the well string during drilling operations and which is constructed and arranged so that a jar or impact may be delivered to the well string in either an up or down direction as desired and which is also constructed and arranged so that part of the jar and well string may be freely movable longitudinally relative to another part of the jar and well string without delivering a jar or impact to the well string.  
  Also, so far as known to applicant, there is no jar in the prior art that is adapted to be carried in the well string during drilling operations and which includes a mandrel for connections to one part of the well string and a housing for connection to the other part of the well string with engageable means on the mandrel and housing whereby a jar or impact may be delivered in either an up or down direction to the well string, and which engageable means on the housing and mandrel, after engagement, may be disengaged without delivering a jar or impact to the well string.  
 SUMMARY OF THE INVENTION An object of the present invention is to provide a double acting jar for a well string during drilling operations wherein a jar or impact may be applied in either an up or down direction to the well string. and wherein the jar is constructed and arranged so that the arrange ment which effects the jar may be engaged and then disengaged without necessarily effecting a jar to the well string to enable a part of the well string to be moved freely longitudinally relative to another part of the well string.  
  Yet a further object of the present invention is to provide a double acting jar to be carried in a well string during drilling operations for delivering either an upward or downward jar or impact to the well string, which jar is constructed and arranged to enable the drill string to be freely moved up or down a desired amount independent of the outer conditions which may exist in the well string.  
  Yet a further object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which is constructed and arranged so as to provide for free travel to enable the well string in which the tool is mounted to be moved up or down without a jarring action.  
  Still a further object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which jar is constructed and arranged to accommodate relative longitudinal movement between the portions of the drill string in which it is connected without necessarily delivering a jar or impact to the well string and which jar has a large internal diameter to permit the passage of survey instruments and other wire line tools therethrough.  
  Still a further object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which jar is constructed and arranged to accommodate relative longitudinal movement between the portions of the drill string in which it is connected without necessarily delivering a jar or impact to the well string and which may be employed in deviated holes without affecting the direction of the hole.  
  Yet another object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which jar is constructed and arranged to accommodate relative longitudinal movement between the portions of the drill string in which it is connected without necessarily delivering a jar or impact to the well string and which may be employed in well strings in connection with directional drilling where downhole motors are employed without necessarily changing the course of the motor drill and the well bore being drilled.  
  Still another object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which jar is constructed and arranged to accommodate relative longitudinal movement between the portions of the drill string in which it is connected without necessarily delivering a jar or impact to the well string and which may be employed in well strings wherein the well bore is at least partially drilled by a jet deflection method of hole deviation.  
  Yet a further object of the invention is to provide a well string jar for delivering either an upward or downward impact to the well string and which can be adjusted to deliver a selective amount of impact in either an upward or downward direction to the well string.  
  Still another object of the invention is to provide a well string jar for delivering either an upward or downward impact to the well string and which can be adjusted to deliver a selective amount of impact in either an upward or downward direction to the well string and which impact amount in either direction is selectively independent of the impact amount in either an upward or downward direction.  
  Still a further object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which jar is constructed and arranged to accommodate relative longitudinal movement between the portions of the drill string in which it is connected without necessarily delivering a jar or impact to the well string and which jar is adjustable to deliver a different amount of impact in either an upward or downward direction and independently of the impact amount in either an upward or downward direction.  
  Yet another object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which jar is constructed and arranged to accommodate relative longitudinal movement between the portions of the drill string in which it is connected without necessarily delivering a jar or impact to the well string and including a mandrel movable longitudinally relative to a housing with spaced seal means therebetween of substantially the same diameter to provide a substantially constant volume between the mandrel and housing upon movement of the mandrel relative to the housing.  
  Still a further object of the present invention is to provide a jar to be carried in a well string during drilling operations for delivering either an upward or downward impact or jar to the well string and which jar is constructed and arranged to accommodate relative longitudinal movement between the portions of the drill string in which it is connected without necessarily delivering a jar or impact to the well string and which enables the present invention to be employed in floating vessels or other structures subject to movement without necessarily actuating the tool of the present invention.  
  Another object of the present invention is to provide an arrangement in a jar of the class described herein including means to equalize the pressure existing externally and internally of the jar.  
  Another object of the present invention is to provide an arrangement in a jar of the class described herein including means to equalize the pressure existing externally and internally of the jar and wherein such means include a piston means sealably fitting within the jar and port means in the jar for conducting fluid from externally of the jar to act on the piston whereby the pressure internally and externally of the jar is equalized when the external pressure is larger than the internal pressure.  
  Other objects and advantages of the present invention will become apparent from a consideration of the following description and drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic illustration of a form of the present invention showing the mandrel in partial dotted line position at the upper end of the figure and the coupling engaging means on the mandrel. to illustrate the position of the mandrel when the coupling engaging means therein is engaged with one of the one-way acting coupling means on the housing and ready for delivering a downward impact to the well string when a predetermined force is exerted on the mandrel. The full line position of the figure diagrammatically illustrates the relative position of the mandrel and housing immediately prior to impact of the shoulder means on the housing and mandrel after the coupling engaging means has been moved downwardly through one of the one-way acting coupling means;  
  FIG. 2 schematically illustrates the relationship of the mandrel and housing when the mandrel is freely movable relative to the housing between the spaced oneway coupling means on the housing;  
  FIG. 3 is a schematic illustration showing in dotted line the position ofthe mandrel when it is engaged with another of the one-way acting coupling means, and shows in full line view the position of the mandrel relative to the housing after the coupling engaging means has been upwardly moved through the other one-way acting coupling means to enable the shoulders on the housing and mandrel to strike and deliver a jar or impact to the well string in an upward direction;  
  FIG. 4 is a longitudinal sectional view of a preferred embodiment of the present invention;  
  FIG. 5 is a vertical sectional view on the line 5-5 of FIG. 4;  
  FIG. 6 is a partial horizontal view illustrating a form of the one-way acting coupling means carried by the housing and a means of adjustment thereof;  
  FIG. 7 is an elevational view ofa form ofa slip means which may be employed in the one-way acting coupling means;  
  FIG. 8 is an elevational view of a form of the adjustment means for the slip means and shows in exploded view the means of locking such adjustment means after the slip means have been adjusted;  
  FIG. 9 is a partial longitudinal sectional view of a modified form of the invention; and  
 FIG. 10 is a continuation of FIG. 9.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is first directed to FIG. 4 of the drawings wherein the invention is referred to generally by the numeral 10. The well tool of the present invention is adapted to be connected into a well string and carried therein during drilling operations and includes a mandrel referred to generally at 12 which is provided with means 13 for connection with the portion of the well string extending upwardly therefrom and to the earth&#39;s surface. The mandrel extends longitudinally within a housing referred to generally at 15, and the housing 15 includes suitable threaded means I6 so that it may be connected into the portion of the well string extending downwardly therefrom in the well bore.  
  Means referred to generally at 13 are provided for connecting the mandrel l2 and housing I5 together to accommodate relative longitudinal movement therebetween while inhibiting relative rotation therebetween.  
  First and second one-way acting coupling means are carried by the housing 15 and are referred to generally at 18 and 19. It will be noted that the one-way acting coupling means 18 and 19 are mounted in longitudinal spaced relationship in the housing 15 as diagrammatically illustrated in FIGS. 1 through 3 and shown in greater detail in FIG. 4.  
  Coupling engaging means referred to generally at 22 in FIGS. I through 4 are carried on the mandrel 12 for engagement and disengagement with the spaced oneway acting coupling means 18 and I9 as will be described in greater detail.  
  The mandrel I2 is provided with a bore I4 extending longitudinally therethrough for circulation of drilling fluids during drilling operations in a manner well known in the art. The lower end of the mandrel 12 is slidably received within the bore I7 at the lower end of the housing 15 and is sealed off by the seal means 24 to inhibit communication between the interior of the housing and the exterior thereof as the mandrel is moved longitudinally relative to the housing.  
  Similarly, the upper portion of the mandrel 12 extends through the bore designated at the upper end of the housing and the seal means 23 slidably engages the mandrel and inhibits communication between the interior of the housing and the exterior thereof as the mandrel is moved longitudinally relative to the housing 15. Seal means 23 slidably engages the mandrel 12 in housing bore 170 and is substantially the same diameter at seal means 24 and housing bore 17 which will provide a substantially constant interior volume as the mandrel 12 is moved longitudinally relative to the housing 15.  
  lf desired, a suitable liquid may be placed within the housing to lubricate the components of the tool and to further inhibit entry of contaminants from the exterior of the housing during drilling operation and during operation of the jar.  
  The connecting means designated generally at 13&#39; between the mandrel l2 and the housing to accom modate relative longitudinal movement therebetween while inhibiting relative rotational movement therebetween includes a plurality of circumferentially spaced recesses 25. better shown in FIG. 5, extending longitudinally of the housing 15 on the interior surface thereof as shown in FIGS 4 and 5. A plurality of projections 26 formed on the enlargement 27 on the mandrel 12 are circumferentially spaced on such enlargement to fit within the recesses as shown in FIGS. 4 and 5 of the drawings whereby the mandrel 12 may be moved longitudinally relative to the housing 15 while inhibiting relative rotational movement therebetween. it will be noted that the longitduinally extending recesses 25 in the housing 15 are of suitable extent to accommodate the desired longitudinal movement of the mandrel 12 relative to the housing 15 during operation of the tool as will be described.  
  The first and second one-way acting coupling means 18 and 19 may be of any suitable form to accomplish the desired functions of the tool. and as illustrated in FIG. 4 each includes an annular bowl 29, one of which faces upwardly, and the uppermost of which is shown as facing downwardly. Slip means referred to generally at are carried on the bowls 29 as illustrated in FIG. 4 of the drawings.  
  As shown more clearly in FIG. 7, each annular slip means 30 includes a plurality of longitudinally spaced, radially extending ridges 3! and recesses 31&#39; which face inwardly for engagement with the coupling engaging means 22 on the mandrel 12. Also. surface means are provided on the slip means 30 to provide predetermined yieldable passage of coupling engaging means 22. Such surface means includes a plurality of circumferentially extending projections 33 with recesses 34 therebetween on the outer surface of each slip means 30 to provide an irregular surface which will tend to allow coupling engaging means 22 to be forcibly operated through slip means 30 to provide an adjustable detent with the longitudinal travel of mandrel 12.  
  Additionally, each slip means 30 includes longitudinally extending. circumferentially spaced grooves 38 which define segments 40 on each slip means so that the slip means 30 may expand and contract radially during functioning of the jarring tool.  
  The coupling engaging means 22 may be of any suitable form and is shown as including an enlargement 42 carried by the mandrel 12 having a plurality of circumferentially extending recesses 43 and annular projections or ridges therebetween, which recesses and projections interfit and engage the circumferentially extending projections 3| and recesses 31&#39; on each slip means 30 when such coupling engaging means 22 is engaged with either of the one-way acting coupling means 18 or 19.  
  For reference purposes, the one-way acting coupling means 18 may be designated the first one-way acting coupling means. and the one-way acting coupling means 19 may be designated as the second one-way acting coupling means.  
  The housing 15 is formed of a plurality of sections that are adapted to be connected together in any suitable manner with seal means therebetween (not shown) to inhibit communication between the interior and exterior of the housing.  
  The slip means 30 is of somewhat smaller longitudinal extent than the annular tapered surface 35 of each bowl means 29 to provide a void or space 37 for longitudinal movement of the slip means 30 relative to their respective bowl means 29 before engaging the shoulder or end 60 of the adjustment means 50 or the shoulder 37a of the housing IS.  
  The amount of force necessary to be exerted on the mandrel l2 and the amount of impact orjar thus delivered by the tool of the present invention is determined before it is lowered in the well bore. To accomplish this. the adjustment means referred to at 50 are provided for each of the slip means 30. The adjustment means 50 determines the amount of grip exerted by each of the slip means 30 when engaged with the coupling engaging means 22, and this determines the amount of force necessary to be exerted on the mandrel 12 to move the coupling engaging means 22 through either the first or second one-way acting coupling means to deliver either an upward or downward jar or impact to the well string.  
  The adjustment means 50 each include an annular member 51 having threads 52 thereon for engaging with the threads 53 in the housing. A plurality of longitudinally extending serrations 55 are provided adjacent one end of the annular member 51 and such serrations may be engaged by suitable means such as a screwdriver 550 or the like extending through the housing for rotation of the annular member 51 either toward or away from its respective slip means 30. After. the desired amount of adjustment has been accomplished, suitable means such as the Allen screw 56 with the pointed end thereon may be engaged in the threaded opening in the housing and in turn engaged in the serrated portion 55 to lock the annular member 5] at the desired adjusted position.  
  The construction and arrangement of the adjusting means is well known in the prior art as is its function, and it is believed that a detailed description thereof is unnecessary.  
  The adjustment means 50 enables the annular slip means 30 to be positioned relative to the annular tapered surface 35 of its respective bowl means 29 and relative to the coupling engaging means on the mandrel 12 so that when the coupling engaging means 22 is engaged with either the first or second one-way acting coupling means 18 or 19, the amount of force necessary to be applied to the mandrel 12 to move the coupling engaging means 22 through either the first oneway acting coupling means 18 or the second one-way acting coupling means 19 is predetermined.  
  By way of illustration. when it is desired to deliver a downward impact by the tool of the present invention to the well string in which it is connected. the tool components will be in the relative positions schematically shown in FIG. 1 of the drawing. In such position the mandrel I2 is illustrated in dotted line position at its upper end when the coupling engaging means 22 thereon is engaged with the second one-way acting coupling means 19. The engagement of the coupling engaging means 22 with the second one-way acting coupling means 19 is illustrated in dotted line at 66.  
  The housing i is provided with shoulder means 39 and mandrel 12 is provided with shoulder means 38 that are adapted to strike when a downward force is exerted on the mandrel l2 to move the coupling engaging means 22 of the mandrel through the second one-way acting coupling means 19.  
  When this occurs. the mandrel l2 moves to the full line position shown in FIG. 1 and the coupling engaging means 22 thereon moves through the second oneway acting coupling means 19 as illustrated at 67. It can be appreciated that disengagement of the coupling means 22 with the second one-way acting coupling means 19 occurs quickly to enable the shoulders 38 and 39 to strike to deliver the downward impact to the portion of the well string connected to the housing 15.  
  The construction and arrangement of the slip means 30 and bowl means 29 is such that when the mandrel 12 is moved from the position shown in FIG. 1 to the position illustrated in full line view in FIG. 2, the coupling engaging means 22 on the mandrel 12 moves easily through the second one-way acting coupling means 19 without engaging or locking therewith. Since the first one-way acting coupling means 18 and second one-way acting coupling means l9 are spaced longitudinally relative to each other. it can be appreciated that the mandrel 12 may be moved freely relative to the housing 15 which enables the well string portion connected with the mandrel 12 to be moved relative to the well string portion connected with the housing 15.  
  Also. the construction and arrangement of the slip means and bowl means 29 as well as the relationship of the components of the present invention enable the mandrel 12 to be moved into engagement with either the first one-way acting coupling means 18 or the second one-way acting coupling means 19 and to then be disengaged therefrom by moving the mandrel in a direction opposite to that which engaged the coupling engaging means 22 in either the first or second one-way acting coupling means 18 or 19. For example, the coupling engaging means 22 on the mandrel 12 will engage with the second one-way acting coupling means 19 when the mandrel 12 is moved downwardly; however. by reversing the direction of the mandrel and moving it upwardly, the coupling engaging means 22 disengages from the slip means 30 in the second one-way acting coupling means 19 without imparting a jar or impact to the well string.  
  Similarly, the coupling engaging means 22 may be moved upwardly to engage in the first one-way acting coupling means 18 and if it is desired to then disengage the coupling engaging means 22 from the first one-way acting coupling means 18 without imparting a blow to the well string, the mandrel may be moved in an opposite direction. that is downwardly. whereupon the coupling engaging means 22 disengages from the first oneway acting coupling means 18 without imparting a blow to the well string in which the tool is connected. Thus. the tool of the present invention enables the mandrel and well string connected therewith to be moved freely a predetermined amount relative to the housing and well string connected therewith without imparting a jar or blow up or down and/or the mandrel and well string connected therewith may be moved freely longitudinally a predetermined amount to deliver a predetermined jar or blow. selectively up or down without regard to other conditions existing in the well bore. as illustrated in FIG. 2.  
  If the well string in which the present invention is stuck in a manner in which it is desired to impart an upward blow. to the well string. this may be accomplished as illustrated in FIG. 3 by engaging the coupling engaging means 22 on the mandrel 12 with the first oneway acting coupling means l8 and by then moving such coupling engaging means 22 through the one-way coupling means l8 to disengage therefrom. whereupon the shoulder means designated 38a on the mandrel 12 engages the shoulder means designated 39a on the housing 15 and imparts an upward jar or impact to the well string.  
  The free movement of the mandrel l2 relative to the housing l5 without imparting a jarring or blow to the well string may be quite useful in drilling operations where drill collars above or below the tool of the present invention are stuck. or are differentially stuck. or are trying to stick. Should the drill collars become stuck. either an upward or downward impact to the well string may be imparted after a predetermined force has been applied to the well string as previously described.  
  In those situations where the tool is employed in wells where the pressure in the well bore annulus may exceed the pressure internally of the jar by a substantial amount. it may be desirable to employ that form of the present invention illustrated in FIGS. 9 and 10. The mandrel is again illustrated generally at 12 with thread means 13, and the housing is referred to generally by the numeral 15. Means referred to generally at l3 connect the mandrel l2 and housing 15 together to accommodate relative longitudinal movement therebetween while inhibiting relative rotation therebetween. The components of the FIG. 9 and 10 modification are similar to the previously described with regard to FIGS. 1-8 and are given the same reference numerals in FIGS. 9 and 10 except as noted hereinafter.  
  As previously noted, the present invention may be employed in situations when the well bore pressure externally of the housing 15 such as represented by the numeral is substantially greater than the pressure existing internally of the tool between the mandrel l2 and housing 15, such pressure being represented gener&#39; ally by the numeral 8]. The pressure internally of the mandrel is represented by the numeral 82.  
  In some situations the exterior annulus hydraulic pressure such as represented at 80 may be substantially greater, or exceed the pressure 81 between the mandrel i2 and housing 15 so that such pressure differential may alter the ability of the tool to perform other hydraulic or mechanical functions as desired.  
  In order to substantially equalize the pressure 80 externally of the jar with the pressure 81 internally of the jar between the mandrel l2 and housing 15, an arrangement as illustrated generally by the numeral is provided. Such arrangement includes the piston means I06 with annular seal means 107 thereon for sealably engaging within the outer housing 15, such piston means l06 surrounding the mandrel 12 as shown.  
  Port means 108 are provided in the outer housing for conducting the pressure 80 externally of the housing to act on the piston means 106.  
  The arrangement 105 includes the first portion represented by the piston 106 and an annular skirt means 110 extending from the first portion and surrounding the mandrel, such skirt portion 110 being integrally formed with the piston 106. Seal means as represented at 111 are provided between the skirt portion 110 and the outer housing 15, and it will be noted that the port means 108 is positioned in the outer housing between the seal means 107 on the piston means 106 and the seal means ill on the skirt portion H0.  
  Thus, pressure externally of the tool represented by the numeral 80 is sealed off from communicating with the pressure internally of the tool, such pressure being represented by the numeral 81. but such external pressure represented by the numeral 80 may be communicated through the port 108 to act on the piston means 106, when such external pressure exceeds the internal pressure 81 to move the piston means and skirt to dotted line position represented at 115, and thus equalize the pressure externally and internally of the tool.  
  The skirt portion 110 is of suitable extent so that even though it may move longitudinally between the mandrel l2 and body 15, it will maintain sealing engagement with the outer housing.  
  From the foregoing, it can be seen that this arrangement enables the external pressure 80 to equalize with the internal pressure 81 between the mandrel l2 and housing when such external pressure 80 exceeds the internal pressure 81.  
  The present invention is very useful to be run in conjunction with any type of downhole motor used in directional drilling. Ordinarily. a motor should be oriented in a particular direction according to a drilling plan. The operation of the jar of the present invention does not cause it to torque or twist, which would change the desired course of the motor. Also, the position of the scribe line indicating the face of the tool (the direction that the downhole motor is facing) is always ascertainable when the present invention is employed.  
  Additionally, where a well bore is being drilled by jet reflection, that is, where the well is being jetted with a big eye bit for deflection run, the tool of the present invention may be slacked off so as to effect a positive downward spudding operation necessary in such method.  
  Also, the jar of the present invention will allow rotation of the drill pipe out of the hole which eliminates the possibility of causing the jar to trip prematurely to effect a jar in either an upward or downward direction, which occurs in some other types of jars, such as a torque jar.  
  Since the first and second one-way acting coupling means 18 and 19 each include adjustment means 50, it can be appreciated that gripping action of each first and second one-way acting coupling means 18 and 19 may be independent of each other. By way of illustration, it may be more desirable to adjust first one-way acting coupling means 18 so that a tighter gripping action is effected with coupling engaging means 22 on mandrel 12 in an amount greater than the gripping action set in second one-way acting coupling means 19. Thus, when the tool of the present invention is actuated to deliver an upward impact, the amount of such impact will be greater than that which is set in the second one-way acting coupling means 19. ln other words, the amount of upward impact, or the amount of downward impact to be delivered by the tool of the present invention may be selected independently of each other without affecting the operation of the tool.  
  The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.  
 What is claimed is:  
 l. A jar for a well string including:  
 a. an outer housing;  
 b. a mandrel extending longitudinally within said housing; c. means connecting said mandrel and housing for relative longitudinal movement therebetween while inhibiting relative rotation therebetween;  
 d. first and second one-way acting coupling means mounted in spaced relation in said housing;  
 e. coupling engaging means on said mandrel, said coupling engaging means movable into engagement with either of said one-way acting coupling means upon longitudinal movement of said mandrel relative to said housing and disengageable from either of said one-way acting coupling means upon longitudinal movement of said mandrel relative to said housing in a direction opposite to that which engaged said coupling engaging means with either of said one-way acting coupling means on said housing;  
 f. shoulder means on said housing and mandrel;  
 g. said coupling engaging means and said first oneway acting coupling means cooperating when said mandrel is moved longitudinally relative to said housing in one direction to engage and thereafter releasable when a predetermined force is exerted on said mandrel in said one direction to effect disconnection of said coupling engaging means and first one-way acting coupling means to cause said shoulder means on said housing and mandrel to strike and deliver a jar to the well string in said one direction; and  
 h. said coupling engaging means and said second oneway acting coupling means cooperating when said mandrel is moved longitudinally relative to said housing in another direction to engage and thereafter releasable when a predetermined force is exerted on said mandrel in said other direction to effect disconnection of said coupling engaging means and second one-way acting coupling means to cause said shoulder means on said housing and mandrel to strike and deliver a jar to the well string in said other direction.  
  2. The invention of claim 1 wherein said connecting means between said mandrel and housing includes a plurality of longitudinally extending recesses on said housing and projections on said mandrel fitting in said recesses.  
  3. The invention of claim 1 including spaced seal means between said mandrel and housing to seal off the interior of said housing from the exterior without changing the volume between said seal means as said mandrel is moved longitudinally relative to said housing.  
  4. The invention of claim 3 wherein said connecting means between said mandrel and housing includes a plurality of longitudinally extending recesses on said housing and projections on said mandrel fitting in said recesses.  
  5. The invention of claim 1 including means on said mandrel and housing for connecting the jar in a well string.  
  6. The invention of claim 5 including spaced seal means between said mandrel and housing to seal off the interior of said housing from the exterior without changing the volume between said seal means as said mandrel is moved longitudinally relative to said housing.  
  7. The invention of claim 5 wherein said connecting means between said mandrel and housing includes a plurality of longitudinally extending recesses on said housing and projections on said mandrel fitting in said recesses.  
  8. The invention of claim 1 including means to equalize the pressure existing on the outside of said outer housing with the pressure in the jar between said outer housing and mandrel.  
 9. The invention of claim 8 wherein said means to equalize includes piston means sealably engaging said outer housing and surrounding said mandrel. said outer housing having port means therein for communicating pressure exteriorly of said housing to act on said piston means.  
  10. The invention of claim 9 wherein said piston means includes one portion surrounding said mandrel. said one portion having seal means thereon to sealably engage within said outer housing, and skirt means extending from said first portion and surrounding said mandrel. said skirt portion and outer housing having seal means therebetween and wherein the port means in said outer housing is between said seal means on said one portion and the seal means between said skirt portion and outer housing.  
  ll. The invention of claim 1 wherein said first and second coupling means each include:  
 a. bowl means;  
 b. slip means carried by said bowl means; and  
 c. said slip means having surfaces thereon for engaging said coupling engaging means.  
  12. The invention of claim 11 including means on said mandrel and housing for connecting the jar in a well string.  
  [3. The invention of claim ll including spaced seal means between said mandrel and housing to seal off the interior of said housing from the exterior without changing the volume between said seal means as said mandrel is moved longitudinally relative to said housing.  
  14. The invention of claim 11 wherein said connecting means between said mandrel and housing includes a plurality of longitudinally extending recesses on said housing and projections on said mandrel fitting in said recesses.  
  15. The invention of claim ll including adjustable means carried by said housing to set the force necessary to be exerted on said mandrel to effect a jar in either of said directions.  
  16. The invention for claim 15 including means on said mandrel and housing for connecting the jar in a well string.  
  17. The invention of claim l5 including spaced seal means between said mandrel and housing to seal off the interior of said housing from the exterior without changing the volume between said seal means as said mandrel is moved longitudinally relative to said housing.  
  18. The invention of claim 15 wherein said connecting means between said mandrel and housing includes a plurality of longitudinally extending recesses on said housing and projections on said mandrel fitting in said recesses.  
  19. The invention of claim 11 including adjustment means engaging said slip means whereby the grip of said slip means on said coupling engaging means may be varied.  
  20. The invention of claim 19 including means on said mandrel and housing for connecting the jar in a well string.  
  21. The invention of claim 19 including spaced seal means between said mandrel and housing to seal off the interior of said housing from the exterior without changing the volume between said seal means as said mandrel is moved longitudinally relative to said housing.  
  22. The invention of claim 19 wherein said connecting means between said mandrel and housing includes a plurality of longitudinally extending recesses on said housing and projections on said mandrel fitting in said recesses.  
  23. The invention of claim ll including surface means on said slip means to enable said slip means to yield when said coupling engaging means moves therethrough.  
  24. The invention of claim 23 wherein said surface means includes a plurality of recesses on the surface of said slip means adjacent said bowl means.  
  25. The invention of claim 23 including adjustable means carried by said housing to set the force necessary to be exerted on said mandrel to effect a jar in either of said directions.  
  26. The invention of claim 23 including adjustment means engaging said slip means whereby the grip of said slip means on said coupling engaging means may be varied.  
  27. The invention of claim 23 including means on said mandrel and housing for connecting the jar in a well string.  
  28. The invention of claim 23 including spaced seal means between said mandrel and housing to seal off the interior of said housing from the exterior without changing the volume between said seal means as said mandrel is moved longitudinally relative to said housing.  
  29. The invention of claim 23 wherein said connecting means between said mandrel and housing includes a plurality of longitudinally extending recesses on said housing and projections on said mandrel fitting in said recesses.  
 30. A jar for a well string including:  
 a. a housing;  
 b. a mandrel movable longitudinally in said housing;  
 and  
 c. means on said mandrel and spaced cooperating means on said housing engageable upon nonrotational movement of said mandrel relative to said housing for selectively moving said mandrel relative to said housing and for selectively delivering an upward or a downward impact to the well string.  
  31. The invention of claim 30 including adjustable means adjacent each of said spaced cooperating means to preset the amount of upward and downward impact independently of each other.  
  14 arranged to accommodate relative longitudinal movement between said mandrel and housing without imparting either an upward or downward impact to the well string.