Patent Publication Number: US-8985227-B2

Title: Dampered drop plug

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a method and apparatus for hydraulic actuation of a downhole tool and, in particular, to an apparatus and method for actuating one or more functions of a downhole tool with a dampered drop plug. 
     2. Brief Description of Related Art 
     A variety of tools exist to perform downhole functions in a well. Some tools may be actuated in response to mechanical movement or manipulation of the drill pipe, including rotation. Others may be actuated by dropping a ball or dart into the drill string, then applying fluid pressure to the interior of the string after the ball or dart lands on a seat in the tool. The tool may be attached to the liner hanger or body of a running tool by threads, shear elements, or by a hydraulically actuated arrangement. 
     Oil and gas wells are conventionally drilled with drill pipe to a certain depth, then casing is run and cemented in the well. The operator may then drill the well to a greater depth with drill pipe and cement another string of casing. In this type of system, each string of casing extends to the surface wellhead assembly. 
     In some well completions, an operator may install a liner rather than an inner string of casing. The liner is made up of joints of pipe in the same manner as casing. Also, the liner is normally cemented into the well. However, the liner does not extend back to the wellhead assembly at the surface. Instead, it is secured by a liner hanger to the last string of casing just above the lower end of the casing. The operator may later install a tieback string of casing that extends from the wellhead downward into engagement with the liner hanger assembly. 
     When installing a liner, in most cases, the operator drills the well to the desired depth, retrieves the drill string, then assembles and lowers the liner into the well. A liner top packer may also be incorporated with the liner hanger. A cement shoe with a check valve will normally be secured to the lower end of the liner as the liner is assembled. When the desired length of liner is reached, the operator attaches a liner hanger to the upper end of the liner, and attaches a running tool to the liner hanger. The operator then runs the liner into the wellbore on a string of drill pipe attached to the running tool. The operator sets the liner hanger and pumps cement through the drill pipe, down the liner, and back up an annulus surrounding the liner. The cement shoe prevents backflow of cement back into the liner. The running tool may dispense a wiper plug following the cement to wipe cement from the interior of the liner at the conclusion of the cement pumping. The operator then sets the liner top packer, if used, releases the running tool from the liner, and retrieves the drill pipe. 
     For tools that are set by dropping a ball or dart into the drill string, such as the above described liner hanger, a seat in the running tool couples to the running tool by shear elements downhole from the hydraulically actuated tool. The shear elements are chosen to fail at a pressure greater than the pressure needed to operate the tool. The ball drops into the drill string to land on the seat in the running tool. Once landed, fluid pumps into the drill string, increasing the pressure within the drill string above the seated ball. Once the fluid pressure reaches a predetermined pressure, the tool actuates. Fluid pressure continues to increase until the shear pressure of the seat is reached. At this point, the shear elements of the seat fail, and the ball and seat fall, allowing the pressurized fluid to flow down the well. 
     In some instances, the drop ball will also be used to actuate a second hydraulically actuated tool. In these examples, a second seat in the running tool couples to the running tool axially below the first seat. Again, the second seat couples through the use of shear elements. Preferably, when the first shear elements fail, the ball drops to the second seat, again blocking the flow of fluid into downhole elements below the ball. Fluid continues to pump into the drill string, raising the pressure behind the ball until the second function actuates. Practically, when the first shear elements fail, the ball drops to the second seat, and the fluid pressure behind the ball acts as a water hammer on the second shear elements. The weight of the fluid column above the ball suddenly lands on the seat shear elements. The force exerted by the suddenly falling fluid often exceeds the shear strength of the second shear elements. This then causes the second shear elements to fail prior to activation of the second hydraulically activated tool. Therefore, there is a need for a drop ball system for actuating multiple hydraulically activated tools that overcomes the water hammer shear problems of current drop ball systems. 
     SUMMARY OF THE INVENTION 
     These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of the present invention that provide a dampered drop plug, and a method for using the same. 
     In accordance with an embodiment of the present invention, a dampered drop plug configured to be dropped down a bore of a drill string comprises a retainer configured to land on an upward facing shoulder of a tubular sleeve, and a plug releasably coupled to the retainer. The plug couples to the retainer while at a first pressure in the bore and decouples from the retainer at a second pressure in the bore. The retainer controls the flowrate of a fluid passing through the retainer after the plug decouples from the retainer. 
     In accordance with another embodiment of the present invention, a downhole tool for actuating a first and second function while dampening a water hammer effect comprises a tubular mandrel having an inner passage and an upper end that secures to a string of conduit to receive a flow of fluid, and an outer sleeve sealingly surrounding and axially movable relative to the mandrel. The outer sleeve defines an annulus between the outer sleeve and the mandrel. A piston is interposed between the mandrel and the outer sleeve, defining upper and lower chambers in the annulus. The tool further comprises an upper fluid port between the inner passage of the mandrel and the upper chamber, and a lower fluid port between the inner passage of the mandrel and the lower chamber. The chambers have piston areas configured such that pressurized fluid flow from the inner passage simultaneously into both of the ports causes a net axial force on the outer sleeve to move the outer sleeve and an engaging member in a first axial direction to actuate the first function. Pressurized fluid flowing through only the upper fluid port causes a net axial force on the outer sleeve to move the outer sleeve and the engaging member in a second axial direction to actuate the second function. The tool also comprises a dampered drop plug, and a seat in the inner passage between the upper and lower fluid ports. The dampered drop plug is configured to control the pressurized fluid flow through the inner passage following actuation of the second function. The seat is positioned such that positioning the dampered drop plug on the seat prevents communication of the pressurized fluid flow with the lower chamber, and allows communication of the pressurized fluid flow with the upper chamber. 
     In accordance with yet another embodiment, a method for actuating a plurality of functions with a dampered drop ball while dampening a water hammer effect comprises dropping a dampered drop plug into a drill string. The method further includes the step of actuating a first function with the dampered drop plug. The method then releases a plug of the dampered drop plug, and dampens a water hammer with a retainer of the dampered drop plug. The method then actuates a second function with the plug of the dampered drop plug. 
     An advantage of a preferred embodiment is that the dampered drop plug disclosed herein provides a means to actuate a plurality of hydraulically actuated functions in a downhole tool while dampening any water hammer effect associated with prior art drop ball methods and apparatuses. This dampening advantageously prevents premature shear of shear seat elements downhole from the actuation of the first function. In addition, the dampered drop plug disclosed herein can employ reusable parts and materials, extending the life of the dampered drop plug. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic sectional view of inner and outer concentric strings during drilling. 
         FIG. 2  is an enlarged partial sectional view of a liner hanger control tool of the system of  FIG. 1 , employing the dampered drop plug of  FIG. 10 , and shown in a position employed during drilling. 
         FIG. 3  is an enlarged partial sectional view of the liner hanger employed in the system of  FIG. 1  and shown in the retracted position. 
         FIG. 4  is an enlarged partial sectional view of a drill lock tool employed with the system of  FIG. 1 , with its cone mandrel shown in a run-in position. 
         FIG. 5  is a sectional view of a check valve employed with the inner string of the system of  FIG. 1  and shown in a closed position. 
         FIG. 6  is a sectional view of the drill lock tool of  FIG. 4  with its cone mandrel shown in a set position. 
         FIG. 7  is a sectional view of the liner hanger control tool of  FIG. 2 , with the liner hanger control tool in the process of moving from the set position to a released position. 
         FIG. 8  is a sectional view of the liner hanger control tool of  FIG. 2 , shown in the released position and with its ball seat sheared. 
         FIG. 9  is a sectional view of the drill lock tool of  FIG. 4 , with its cone mandrel in the released position. 
         FIG. 10  is a schematic sectional view of a dampered drop plug in accordance with an embodiment of the present invention. 
         FIG. 11  is a partial sectional view of a diverter valve shown in a closed position and optionally coupled to the inner string of  FIG. 1 . 
         FIG. 12  is a partial sectional view of the diverter valve of  FIG. 11  shown in an open position. 
         FIG. 13  is a partial sectional view of the diverter valve of  FIG. 11  shown in operation with an alternate dampered drop plug of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and the prime notation, if used, indicates similar elements in alternative embodiments. 
     In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. Additionally, for the most part, details concerning drilling rig operation, materials, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the skills of persons skilled in the relevant art. 
     Referring to  FIG. 1 , a well is shown having a casing  11  that is cemented in place. An outer string  13  is located within casing  11  and extends below to an open hole portion of the well. In this example, outer string  13  is made up of a drill shoe  15  on its lower end that may have cutting elements for reaming out the well bore. A tubular shoe joint  17  extends upward from drill shoe  15  and forms the lower end of a string of liner  19 . Liner  19  comprises pipe that is typically the same type of pipe as casing, but normally is intended to be cemented with its upper end just above the lower end of casing  11 , rather than extending all the way to the top of the well or landed in a wellhead and cemented. The terms “liner” and “casing” may be used interchangeably. Liner  19  may be several thousand feet in length. 
     Outer string  13  also includes a profile nipple or sub  21  mounted to the upper end of liner  19 . Profile nipple  21  is a tubular member having grooves and recesses formed in it for use during drilling operations, as will be explained subsequently. A tieback receptacle  23 , which is another tubular member, extends upward from profile nipple  21 . Tieback receptacle  23  is a section of pipe having a smooth bore for receiving a tieback sealing element used to land seals from a liner top packer assembly or seals from a tieback seal assembly. Outer string  13  also includes in this example a liner hanger  25  that is resettable from a disengaged position to an engaged position with casing  11 . For clarity, casing  11  is illustrated as being considerably larger in inner diameter than the outer diameter of outer string  13 , but the annular clearance between liner hanger  25  and casing  11  may be smaller in practice. 
     An inner string  27  is concentrically located within outer string  13  during drilling. Inner string  27  includes a pilot bit  29  on its lower end. Auxiliary equipment  31  may optionally be incorporated with inner string  27  above pilot bit  29 . Auxiliary equipment  31  may include directional control and steering equipment for inclined or horizontal drilling. It may include logging instruments as well to measure the earth formations. In addition, inner string  27  normally includes an underreamer  33  that enlarges the well bore being initially drilled by pilot bit  29 . Optionally, inner string  27  may include a mud motor  35  that rotates pilot bit  29  relative to inner string  27  in response to drilling fluid being pumped down inner string  27 . 
     A string of drill pipe  37  is attached to mud motor  35  and forms a part of inner string  27 . Drill pipe  37  may be conventional pipe used for drilling wells or it may be other tubular members. During drilling, a portion of drill pipe  37  will extend below drill shoe  15  so as to place drill bit  29 , auxiliary equipment  31  and reamer  33  below drill shoe  15 . An internal stabilizer  39  may be located between drill pipe  37  and the inner diameter of shoe joint  17  to stabilize and maintain inner string  27  concentric. 
     Optionally, a pack off  41  may be mounted in the string of drill pipe  37 . Pack off  41  comprises a sealing element, such as a cup seal, that sealingly engages the inner diameter of shoe joint  17 , which forms the lower end of liner  19 . If utilized, pack off  41  forms the lower end of an annular chamber  44  between drill pipe  37  and liner  19 . Optionally, a drill lock tool  45  at the upper end of liner  19  forms a seal with part of outer string  13  to seal an upper end of inner annulus  44 . In this example, a check valve  43  is located between pack off  41  and drill lock tool  45 . Check valve  43  admits drilling fluid being pumped down drill pipe  37  to inner annulus  44  to pressurize inner annulus  44  to the same pressure as the drilling fluid flowing through drill pipe  37 . This pressure pushes downward on pack off  41 , thereby tensioning drill pipe  37  during drilling. Applying tension to drill pipe  37  throughout much of the length of liner  19  during drilling allows one to utilize lighter weight pipe in the lower portion of the string of drill pipe  37  without fear of buckling. Preferably, check valve  43  prevents the fluid pressure in annular chamber  44  from escaping back into the inner passage in drill pipe  37  when pumping ceases, such as when an adding another joint of drill pipe  37 . 
     Drill pipe  37  connects to drill lock tool  45  and extends upward to a rotary drive and weight supporting mechanism on the drilling rig. Often the rotary drive and weight supporting mechanism will be the top drive of a drilling rig. The distance from drill lock tool  45  to the top drive could be thousands of feet during drilling. Drill lock tool  45  engages profile nipple  21  both axially and rotationally. Drill lock tool  45  thus transfers the weight of outer string  13  to the string of drill pipe  37 . Also, drill lock tool  45  transfers torque imposed on the upper end of drill pipe  37  to outer string  13 , causing it to rotate in unison. 
     A liner hanger control tool  47  is mounted above drill lock tool  45  and separated by portions of drill pipe  37 . Liner hanger control tool  47  is a hydraulic mechanism employed to release and set liner hanger  25  and also to release drill lock tool  45 . Drill lock tool  45  is located within profile nipple  21  while liner hanger control tool  47  is located above liner hanger  25  in this example. 
     In brief explanation of the operation of the equipment shown in  FIG. 1 , normally during drilling the operator rotates drill pipe  37  at least part of the time, although on some occasions only mud motor  35  is operated, if a mud motor is utilized. Rotating drill pipe  37  from the drilling rig, such as the top drive, causes inner string  27  to rotate, including drill bit  29 . Some of the torque applied to drill pipe  37  is transferred from drill lock tool  45  to profile nipple  21 . This transfer of torque causes outer string  13  to rotate in unison with inner string  27 . In this embodiment, the transfer of torque from inner string  27  to outer string  13  occurs only by means of the engagement of drill lock tool  45  with profile nipple  21 . The operator pumps drilling fluid down inner string  27  and out nozzles in pilot bit  29 . The drilling fluid flows back up an annulus surrounding outer string  13 . 
     If, prior to reaching the desired total depth for liner  19 , the operator wishes to retrieve inner string  27 , he may do so. In this example, the operator actuates liner hanger control tool  47  with a dampered drop plug  70 , as described in more detail with respect to  FIGS. 7-10 , to move the slips of liner hanger  25  from a retracted position to an engaged position in engagement with casing  11 . The operator then slacks off the weight on inner string  27 , which causes liner hanger  25  to support the weight of outer string  13 . Using liner hanger control tool  47 , the operator also releases the axial lock of drill lock tool  45  with profile nipple  21 . This allows the operator to pull inner string  27  while leaving outer string  13  in the well. The operator may then repair or replace components of the bottom hole assembly including drill bit  29 , auxiliary equipment  31 , underreamer  33  and mud motor  35 . The operator also resets liner hanger control tool  47  and drill lock tool  45  for a reentry engagement, then reruns inner string  27 . The operator actuates drill lock tool  45  to reengage profile nipple  21  and lifts inner string  27 , which causes drill lock tool  45  to support the weight of outer string  13  and release liner hanger  25 . The operator reengages liner hanger control tool  47  with liner hanger  25  to assure that its slips remain retracted. The operator then continues drilling. When at total depth, the operator repeats the process to remove inner string  27 , then may proceed to cement outer string  13  into the well bore. More details of the various components and their operation are shown in US published patent application 2009/0107675, published Apr. 30, 2009. 
       FIG. 2  illustrates one example of liner hanger control tool  47 , which may also be referred to as a running tool. In this embodiment, liner hanger control tool  47  has a tubular mandrel  49  with an axial flow passage  51  extending through it. The lower end of mandrel  49  connects to a length of drill pipe  37  that extends down to drill lock tool  45 . The upper end of mandrel  49  connects to additional strings of drill pipe  37  that lead to the drilling rig. An outer housing  53  surrounds mandrel  49  and is axially movable relative to mandrel  49 . In this embodiment, an annular upper piston  55  extends around the exterior of mandrel  49  outward into sealing and sliding engagement with outer housing  53 . An annular central piston  57 , located below upper piston  55 , extends outward from mandrel  49  into sliding engagement with another portion of outer housing  53 . Outer housing  53  is formed of multiple components in this example, and the portion engaged by central piston  57  has a greater inner diameter than the portion engaged by upper piston  55 . An annular lower piston  59  is formed on the exterior of mandrel  49  below central piston  57 . Lower piston  59  sealingly engages a lower inner diameter portion of outer housing  53 . The portion engaged by lower piston  59  has an inner diameter that is less than the inner diameter of the portion of outer housing  53  engaged by upper piston  55 . 
     Pistons  55 ,  57 ,  59  and outer housing  53  define an upper annular chamber  61  and a lower annular chamber  63 . An upper port  65  extends between mandrel axial flow passage  51  and upper annular chamber  61 . A lower port  67  extends from mandrel axial flow passage  51  to lower annular chamber  63 . Sleeve  69  is located in axial flow passage  51  between upper and lower ports  65 ,  67 . Sleeve  69  faces upward and preferably is an annular sleeve, as described below with respect to  FIG. 10 , retained by a pin or bolt  71 . Preferably, bolt  71  is not a shear element. 
     A collet  73  is attached to the lower end of outer sleeve  53 . Collet  73  has downward depending fingers  75 . An external sleeve  74  surrounds an upper portion of fingers  75 . Fingers  75  have upward and outward facing shoulders and are resilient so as to deflect radially inward. Fingers  75  are adapted to engage liner hanger  25 , shown in  FIG. 3 . Liner hanger  25  includes a sleeve  76  containing a plurality of gripping members or slips  77  carried within windows  79 . When pulled upward, slips  77  are cammed out by ramp surfaces so that they protrude from the exterior of sleeve  76  and engage casing  11  ( FIG. 1 ). Slips  77  are shown in the retracted position in  FIG. 3 . While slips  77  are extended, applying weight to sleeve  76  causes slips  77  to grip casing  11  more tightly. Fingers  75  ( FIG. 2 ) of collet  73  snap into a recess in slips  77  ( FIG. 3 ) to lift them when outer sleeve  53  moves up relative to liner hanger  25 . When outer sleeve  53  moves downward relative to liner hanger  25 , the sleeve  74  contacts slips  77  to prevent them from moving up. 
     In explanation of the components shown in  FIGS. 3 and 4 , liner hanger control tool  47  is shown in a released position. Applying drilling fluid pressure to passage  51  causes pressurized drilling fluid to enter both ports  65  and  66  and flow into chambers  61  and  63 . The same pressure acts on pistons  55 ,  57  and  57 ,  59 , resulting in a net downward force that causes outer sleeve  53  and fingers  75  to move downward to the lower position shown in  FIG. 2 . In the lower position, the shoulder at the lower end of chamber  61  approaches piston  57  while sleeve  74  transfers the downward force to slips  77  ( FIG. 3 ), maintaining slips  77  in their lower retracted position. 
     As will be explained in more detail subsequently, to retrieve inner string  27  ( FIG. 1 ), the operator drops dampered drop plug  70  ( FIG. 7 ) onto first sleeve  69 . The drilling fluid pressure is now applied only through upper port  65  to upper chamber  61  and not lower port  67 . The differential pressure areas of pistons  55  and  57  causes outer sleeve  53  to move upward relative to mandrel  49 , bringing with it fingers  75  and slips  77  ( FIG. 3 ). Then, slacking weight off inner string  27  will cause slips  77  to grip casing  11  ( FIG. 1 ). Liner hanger control tool  47  thus has porting within it that in one mode causes outer sleeve  53  to move downward to retract liner hanger slips  77  and in another mode to move upward to set slips  77 . Arrangements other than the three differential area pistons  55 ,  57  and  59  may be employed to move outer sleeve  53  upward and downward. 
     An example of drill lock tool  45  is illustrated in  FIG. 4 . Drill lock tool  45  has a multi-piece housing  81  containing a bore  83 . Annular seals  82  on the exterior of housing  81  are adapted to sealingly engage profile nipple  21  ( FIG. 6 ) to form the sealed upper end of annular chamber  44  ( FIG. 4 ). Torque keys  85  are mounted to and spaced around the exterior of housing  81 . Torque keys  85  are biased outward by springs  87  for engaging axial slots (not shown) located within profile nipple  21  ( FIG. 1 ). When engaged, rotation of housing  81  transmits torque to profile nipple  21  ( FIG. 1 ). Drill lock tool  45  also has an axial lock member, which in this embodiment comprises a plurality of dogs or axial locks  89 , each located within a window formed in housing  81 . Each axial lock  89  has an inner side exposed to bore  83  and an outer side capable of protruding from housing  81 . When in the extended position, axial locks  89  engage an annular groove  90  ( FIG. 6 ) in profile nipple  21 . This engagement axially locks drill lock tool  45  to profile nipple  21  and enables inner string  27  ( FIG. 1 ) to support the weight of outer string  13 . 
     Referring to  FIG. 4 , axial locks  89  are moved from the retracted to the extended position and retained in the extended position by a cone mandrel  91  that is carried within housing  81 . Cone mandrel  91  has a ramp  93  that faces downwardly and outwardly. When cone mandrel  91  is moved downward in housing  81 , ramp  93  pushes axial locks  89  from their retracted to the extended position. Cone mandrel  91  has three positions in this example. A run-in position is shown in  FIG. 1 , wherein ramp  93  is spaced above axial locks  89 . Downward movement of cone mandrel  91  from the run-in position moves it to the set position, which is shown in  FIG. 6 . In the set position, axial locks  89  are maintained in the extended position by the back-up engagement of a cylindrical portion of cone mandrel  91  just above ramp  93 . Downward movement from the set position in housing  81  places cone mandrel  91  in the released position, which is illustrated in  FIG. 9 . In the released position, annular recess  94  ( FIG. 4 ) on the exterior of cone mandrel  91  aligns with the inner ends of axial locks  89 . This allows axial locks  89  to move inward to the retracted position when drill lock tool  45  is lifted. 
     Referring again to  FIG. 4 , shear screws  95  are connected between cone mandrel  91  and a ring  96 . Ring  96  is free to slide downward with cone mandrel  91  as it moves from the run-in position ( FIG. 4 ) to the set position ( FIG. 7 ). In the set position, ring  96  lands on an upward-facing shoulder formed in bore  83  of housing  81 , retaining cone mandrel  91  in the set position. Shear screws  95  shear when cone mandrel  91  is moved from the set position to the released position ( FIG. 9 ). 
     Reentry shear screws  97  are shown connected between cone mandrel  91  and a shoulder member  102 , which is a part of housing  81 . Preferably reentry shear screws  97  are not installed during the initial run-in of the liner drilling system of  FIG. 1 . Rather, they are installed only for use during re-entry of drill lock tool  45  back into engagement with profile nipple  21 . 
     In this example, cone mandrel  91  is moved from its run-in position to its set position by a downward force applied from a threaded stem  99  extending axially upward from cone mandrel  91 . Stem  99  has external threads  101  that engage mating threads formed within bore  83 . Rotating threaded stem  99  will cause it to move downward from the upper position shown in  FIG. 3  to the lower position in  FIG. 5 , exerting a downward force on cone mandrel  91 . Cone mandrel  91  is a separate component from threaded stem  99  in this embodiment, and does not rotate with it. Threads  101  may be of a multi-start high pitch type. Threaded stem  99  is connected to drill pipe  37  ( FIG. 1 ) that extends upward to liner hanger control tool  47 . While threaded stem  99  is in the lower position, it will be in contact with shoulder member  102  located in bore  83  of housing  81 . 
     A seat  103  is formed within an axial flow passage  104  in cone mandrel  91 . Seat  103  faces upward and in this embodiment it is shown on the lower end of axial passage  104 . A port  105  extends from passage  104  to the exterior of cone mandrel  91 . An annular cavity  107  is located in bore  83  below the lower end of cone mandrel  91  while cone mandrel  91  is in its run-in ( FIG. 4 ) and set ( FIG. 6 ) positions. When cone mandrel  91  is in the lowest or released position, which is the position shown in  FIG. 9 , ports  105  will be aligned with cavity  107 . This alignment enables fluid being pumped down passage  104  to flow around plug  125  of dampered drop plug  70  when it is located on seat  103  as shown in  FIG. 9 . 
     Referring to  FIG. 5 , an example of check valve  43  is illustrated. Check valve  43  has a body  109  that is tubular and has upper and lower threaded ends for a connection into drill pipe  37 . One or more ports  111  extend from axial passage  113  to the exterior of body  109 . A sleeve  115  is carried moveably on the exterior of body  109 . Sleeve  115  has interior seals that seal to the exterior of body  109 . Sleeve  115  also has an upper end that engages a seal  117 . Sleeve  115  has an annular cavity  119  that aligns with ports  111  when sleeve  115  is in the closed or upper position. The pressure area formed by annular cavity  119  results in a downward force on sleeve  115  when drilling fluid pressure is supplied to passage  113 . Normal drilling fluid pressure creates a downward force that pushes sleeve  115  downward, compressing a coil spring  121  and allowing flow out ports  117 . When the drilling fluid pumping ceases, the pressure within passage  113  will be the same as on the exterior of body  109 . Spring  121  will then close ports  111 . As shown in  FIG. 1 , the closure of ports  111  will seal the higher drilling fluid pumping pressure within inner annulus  44 , maintaining the portion of drill string  37  between seals  82  ( FIG. 6 ) of drill lock tool  45  and pack off  41  in tension. 
     In the operation of the embodiment shown in  FIGS. 1-6 , the operator would normally first assemble and run liner string  19  and suspend it at the rig floor of the drilling rig. The operator would make up the bottom hole assembly comprising drill bit  29 , auxiliary equipment  31  (optional), reamer  33  and mud motor  35  (optional), check valve  43 , and pack off  41  and run it on drill pipe  37  into outer string  13 . When a lower portion of the bottom hole assembly has protruded out the lower end of outer string  13  sufficiently, the operator supports the upper end of drill pipe  37  at a false rotary on the rig floor. Thus, the upper end of liner string  19  will be located at the rig floor as well as the upper end of drill pipe  37 . Preferably, the operator preassembles an upper assembly to attach to liner string  19  and drill pipe  37 . The preassembled components include profile nipple  21 , tieback receptacle  23  and liner hanger  25 . Drill lock tool  45  and liner hanger control tool  47  as well as intermediate section of drill pipe  37  would be located inside. Drill lock tool  45  would be axially and rotationally locked to profile nipple  21 . The operator picks up this upper assembly and lowers it down over the upper end of liner  19  and the upper end of drill pipe  37 . The operator connects the upper end of drill pipe  37  to the lower end of housing  81  ( FIG. 3 ) of drill lock tool  45 . The operator connects the lower end of profile nipple  21  to the upper end of liner  19 . 
     The operator then lowers the entire assembly in the well by adding additional joints of drill pipe  37 . The weight of outer string  13  is supported by the axial engagement between profile nipple  21  and drill lock tool  45 . When on or near bottom, the operator pumps drilling fluid through drill pipe  37  and out drill bit  29 , which causes drill bit  29  to rotate if mud motor  35  ( FIG. 1 ) is employed. The operator may also rotate drill pipe  37 . As shown in  FIG. 2 , the drilling fluid pump pressure will exist in both upper and lower chamber  61 ,  63 , which results in a net downward force on sleeve  74 . Sleeve  74  will be in engagement with the upper ends of slips  77  ( FIG. 3 ) of liner hanger  25 , maintaining slips  77  in the retracted position. 
     Referring to  FIG. 10 , dampered drop plug  70  comprises a retainer  123  and a plug  125  coupled together by shear screws  127 . Shear screws  127  comprise shear elements selected to shear at a predetermined fluid pressure. In the illustrated embodiment, two shear screws  127  are used. A person skilled in the art will understand that more or fewer shear elements of any suitable material may be used as desired, provided that together the elements will fail at the predetermined fluid pressure. 
     Retainer  123  comprises an annular upset  129  extending from a top portion of retainer  123  radially outward. Upset  129  defines a downward facing shoulder  131 . Retainer  123  further defines a threaded bore  133  near a center of retainer  123 , and a non-threaded bore  135  coaxial with and below threaded bore  133 . Non-threaded bore  135  has a diameter that is less than a diameter of threaded bore  133 . A bit jet  136  threads into threaded bore  133  and directs the passage of fluid through a jet opening  139  from the area of a mandrel axial flow passage  51  ( FIG. 2 ) above dampered drop plug  70  to an area of mandrel axial flow passage  51  below retainer  123  following shear of shear screws  127 . Bit jet  136  may be formed of any suitable material such as plastics, brass, and the like. 
     Retainer  123  further comprises an axial annular extension  137  extending from a lower portion of retainer  123  toward plug  125 . An inner diameter surface of annular extension  137  defines an interior wall of non-threaded bore  135 . Annular extension  137  also defines threaded shear screw holes  143  in an outer diameter surface of annular extension  137 . Threaded shear screw holes  143  are configured to receive a portion of shear screws  127 . Retainer  123  also defines a lower downward facing shoulder  141  extending from the outer diameter surface of retainer  123  to a base of annular extension  137 . 
     Plug  125  comprises a convex shaped lower portion  145 , an upper extension  147 , and a center plug  149 . Convex shaped lower portion  145  is configured to land on a ball seat, such as seat  103  of  FIG. 4 , described in more detail below. Upper extension  147  comprises an annular ring extending from an upper portion of plug  125  parallel to annular extension  137  of retainer  123 . An exterior diameter of upper extension  147  defines the exterior surface of plug  125 . An interior surface of upper extension  147  abuts an exterior surface of annular extension  137 . Upper extension  147  terminates at lower downward facing shoulder  141 . Upper extension  147  defines exterior threaded shear screw holes  151 . Exterior threaded shear screw holes  151  pass through upper extension  147  and are proximate to threaded shear screw holes  143 . Exterior threaded shear screw holes  151  are configured to receive a portion of shear screws  127 . 
     Center plug  149  comprises an extension of plug  125  protruding from the upper portion of plug  125  and substantially filling non-threaded bore  135 . Center plug  149  defines a surface configured to receive a fluid and transmit the force of the fluid through plug  125  to shear screws  127 . In the illustrated embodiment, center plug  149  has a height approximately equal to the height of upper extension  147 , thereby defining a channel into which annular extension  137  of retainer  123  is inserted. 
     Sleeve  69  comprises an annular sleeve coupled to mandrel  49  ( FIG. 2 ) along a wall of mandrel axial flow passage  51  ( FIG. 2 ). Sleeve  69  defines upper narrowed axial flow passage  153  and lower narrowed axial flow passage  155 . A diameter of lower narrowed axial flow passage  155  is approximately equal to the exterior diameter of dampered drop plug  70 . Similarly, a diameter of upper narrowed axial flow passage  153  is approximately equal to the exterior diameter of upset  129 . Sleeve  69  forms an upward facing shoulder  157  at the transition between upper narrowed axial flow passage  153  and lower narrowed axial flow passage  155 . As illustrated, downward facing shoulder  131  lands and rests on upward facing shoulder  157 , holding dampered drop plug  125  axially in place in mandrel axial flow passage  51  ( FIG. 2 ). 
     In operation, an operator drops dampered drop plug  70  into a drill string at the surface of a drilling rig and then pumps dampered drop plug  70  down to land at sleeve  69  coming to rest as depicted in  FIG. 10 . As illustrated in  FIG. 7 , dampered drop plug  70  blocks the flow of fluid further down the drill string  37 . Continued pumping of fluid into the drill string builds the fluid pressure until a hydraulically actuated tool, such as liner hanger control tool  47  ( FIG. 7 ), actuates. Operators continue to pump fluid into the drill string until a predetermined pressure is reached that is high enough to shear screws  127 , releasing the plug  125  to travel further down the drill string. 
     When shear screws  127  shear and plug  125  releases from retainer  129 , bit jet  136  then controls flow of fluid past retainer  129 . Rather than allow the weight of the entire column of fluid above retainer  129  to suddenly slam down onto the column of fluid below retainer  129 , causing premature shear to subsequent shear elements, such as seat  103  ( FIG. 4 ), bit jet  136  allows fluid to pass in a controlled manner. This prevents the entire weight of the fluid column above bit jet  136  from slamming into the fluid column below bit jet  136 . By controlling the rate at which fluid flows past retainer  129 , the dampered drop plug  70  prevents premature shear of subsequent shear elements. This allows a hydraulically actuated tool to operate as originally designed by first landing plug  125  on a seat below sleeve  69 , and then repeating the fluid pressure buildup process to perform another function. 
     The flow rate through bit jet  136  is selected based on the particular application of dampered drop plug  70  and the downhole tools to be operated. Most downhole tools have much smaller operating volume than the volume of fluid pumped by a mud pump connected to a drill string. Therefore, bit jet  136  and the diameter of bit jet opening  139  will be selected to provide the flowrate needed for operation of the selected downhole tool. 
     As a further example, while drilling, if it is desired to repair or replace portions of the bottom hole assembly, the operator drops dampered drop plug  70  down drill pipe  37 . As illustrated in  FIG. 7 , dampered drop plug  70  lands on sleeve  69  in liner hanger control tool  47 . The drilling fluid pressure now communicates only with upper chamber  61  because dampered drop plug  70  is blocking the entrance to lower port  67 . This results in upward movement of outer sleeve  53  and fingers  75  relative to mandrel  49 , causing liner hanger slips  77  to move to the set or extended position in contact with casing  11  ( FIG. 1 ). The operator slacks off weight on drill pipe  37 , which causes slips  77  to grip casing  11  and support the weight of outer string  13 . 
     The operator then increases the pressure of the drilling fluid in drill pipe  37  above dampered drop plug  70  to a second pressure level. This increased pressure shears shear screws  127  ( FIG. 10 ), causing plug  125  to move downward out of liner hanger control tool  47  as shown in  FIG. 8 , leaving retainer  123  in place on sleeve  69 . Plug  125  drops down into engagement with seat  103  in cone mandrel  91  as shown in  FIG. 9 . Bit jet  136  ( FIG. 10 ) controls the flow of fluid through liner hanger control tool  47  preventing the weight of the drilling fluid column above bit jet  136  from causing a water hammer effect further down drill pipe  37 . In this manner, dampered drop plug  70  prevents premature shear of seat  103  in cone mandrel  91 . Once plug  125  lands on seat  103 , the drilling fluid pressure then acts on plug  125 , shears shear screws  95 , and pushes cone mandrel  91  from the set position to the released position shown in  FIG. 9 . When in the released position, the drilling fluid flow will be bypassed around plug  125  and flow downward and out pilot bit  29  ( FIG. 1 ). The operator then pulls inner string  27  from the well, leaving outer string  13  suspended by liner hanger  25 . If no reentry is desired, the operator would then proceed to cementing. 
     In an alternative embodiment of the present invention, a valve  48  ( FIGS. 11 and 12 ) is positioned upstream of liner hanger control tool  47 . Valve  48  is employed to meter flow from within inner string  27  to the outer annular space to thereby maintain sufficient flow rate in the annular space to prevent cuttings from the drilling operation to settle on liner hanger control tool  47 . 
       FIGS. 11 and 12  illustrate a partial sectional view of valve  48  connected to an upstream end of liner hanger control tool  47  is shown. The valve may have threaded ends to connect to the tool or a short distance above liner hanger control tool  47 , and may be either retrievable or non-retrievable. Valve  48  is symmetrical about axis  158 .  FIG. 11  shows valve  48  in a closed position while  FIG. 12  shows valve  48  in an open position. Valve  48  also has intermediate positions to allow metering of flow. The valve comprises a housing  159  having threaded connections at each end with a machined internal profile  163  to accept internal components. The valve maintains a minimum flow rate to the downstream side while exhausting excess flow to the outer annular area. In this embodiment, housing  159  has ports  165  that communicate an inner diameter with an outer diameter of housing  159 . Ports  165  are inclined radially outward in an upstream direction. 
     Still referring to  FIG. 11 , a sleeve  167  is shown within internal profile  163  of housing  159  such that an outer surface  169  of sleeve  167  is in close reception with internal profile  163 . Sleeve  167  can axially slide relative to the housing  159 . In this embodiment, sleeve  167  has ports  171  that communicate an inner diameter of sleeve  167  with an outer diameter of sleeve  167 . As with ports  165  on housing  159 , ports  171  on sleeve  167  are inclined radially outward in an upstream direction. When valve  48  is in the closed position shown in  FIG. 11 , ports  171  of sleeve  167  do not align with ports  165  of housing  159 . This closed position may be associated to a low flow rate, such as 100 GPM or less, depending on the application. When partially or fully open, as shown in  FIG. 12 , sleeve  167  will slide down relative to housing  159  such that ports  171  will at least partially align with ports  165  to thereby allow a portion of the fluid flowing in the inner string  27  ( FIG. 1 ) to flow through ports  171 ,  165  and into the outer annular space. As an example, the valve may be designed to be partially open when the flow rate is approximately 150 GPM and fully open at higher flow rates, such as 200 GPM. In one embodiment, housing  159  has a larger inner diameter than drill pipe  37 , defining a recess  161  for sleeve  101 . In that embodiment, the inner diameter of sleeve  101  is the same as drill pipe  37 . Recess  161  has an upper end and a lower end as shown in  FIG. 4 . 
     In this embodiment, sleeve  167  may have shear screws or pins  173  at a downstream end  175  that protrude inward to engage a groove  177  formed on an orifice ring  179  located within sleeve  167 . Orifice ring  179  has a centrally located orifice  181  through which fluid can pass when not obstructed. The diameter of orifice  181  is smaller than the inner diameter of drill pipe  37 . Orifice ring  179  may have a partially spherical profile  183  of a “drop ball” on its lower end and a tapered shoulder  185  at an upper end. Shear screws  173  have an appropriate shear value that when sheared release orifice ring  179  from sleeve  167  to allow drop ball profile  183  to manipulate downstream equipment. In this embodiment, a spring element  187  can be seated on an upward facing shoulder  189  of the housing  159  to support a lower end  175  of sleeve  167  and return sleeve  167  and to a closed position under less than minimum flow conditions, as shown in  FIG. 11 . When sufficient fluid flow exists within the drill string, the pressure acting on orifice ring  179  will compress spring element  187  to at least partially align ports  171  of sleeve  167  with ports  165  of housing  159 , thereby metering fluid flow outward from the inner string  27  to the annular space. After orifice ring  179  has sheared and moved below valve  48 , spring  187  will return sleeve  101  to the closed position. Because the inner diameter of sleeve  167  is the same as drill pipe  37 , it does not provide a reduced diameter orifice that would result in a downward force on sleeve  167 . Compression of spring element  187  and thus downward movement of sleeve  167  is limited by a stop shoulder  191  formed on inner profile  163  of housing  159 . Stop shoulder  191  may contact downstream end  175  of sleeve  167  at higher flow conditions. Valve  48  maintains a minimum flow rate down drill pipe  37  because it is flow dependent and thus restrictions downstream do not affect the metered flow. Further, a plurality of valves  48  may be located at different points along the drilling assembly to stage flow into the annular area. 
     Referring to  FIG. 13 , a dampered drop plug  70 ′ is shown that may be dropped into the inner string  27  and landed on orifice ring  179 . Dampered drop plug  70 ′ comprises a modified dampered drop plug  70  comprising the elements of dampered drop plug  70  as indicated by the prime notation. Retainer  123  has been modified as retainer  123 ′ wherein upset  129 ′ now comprises a curved upper annular portion of retainer  123 ′ configured to land on sleeve  167 . In addition, convex shaped lower portion  145 ′ of plug  125 ′ comprises only a partial ball shape. The profile of convex shaped lower portion  145 ′ is configured to complete the convex shaped profile of orifice ring  179 . A circlip  193  may be located in a groove of ball shaped lower portion  145 ′ of plug  125 ′ that prevents orifice ring  179  and plug  125 ′ from becoming separated when moving downstream. 
     Generally, dampered drop plug  70 ′ operates as described above with respect to dampered drop plug  70 . In the illustrated embodiment, dampered drop plug  70 ′ drops to the location shown on diverter valve  48  in the open position of  FIG. 12  closing ports  165 ,  171 . Shear screws  127 ′ and  173  are then loaded and sheared such that the combined orifice ring  179  and plug  125 ′ will drop as a unit to a ball seat, such as seat  103  ( FIG. 4 ) or sleeve  69  ( FIG. 3 ) which may now couple by means of shear pins, allowing for further operation of downhole tools. Alternatively, when dampered drop plug  70 ′ lands on sleeve  167 , a gap may exist between plug  125 ′ and orifice ring  179 . In the alternative embodiment, shear screws  127 ′ will load and shear as described above with respect to dampered drop plug  70 , allowing plug  125 ′ to drop to orifice ring  179 . Additional loading will then cause shear of shear screws  173 , dropping plug  125 ′ and orifice ring  179  as a single unit. As described above with respect to  FIG. 10 , following shear of shear screws  127 ′, bit jet  136 ′ will control the flow of fluid passing through retainer  123 ′, thereby preventing premature shear of downhole elements such as orifice ring  179 . 
     Accordingly, the disclosed embodiments provide numerous advantages over prior drop ball tool actuation systems. For example, the disclosed embodiments herein allow for use of a drop ball actuation system that can activate more than one function within a drill string. In addition, the disclosed embodiments provide a drop ball actuation system that dampens water hammer effects in the drill string, preventing premature shear of secondary shear seats. Furthermore, the drop ball actuation system of the disclosed embodiments provide primary components that are reusable. For example, plug  125  and retainer  123  may be removed from the running tool and reassembled for reuse using new shear screws  127 . 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.