Abstract:
In a fracking context the object that will ultimately block a passage in an isolation device is introduced into the zone with the bottom hole assembly. The object is not released until the guns fire to create a pressure spike in the borehole that triggers the object retaining device to release the object. The retaining device is placed in close proximity to the isolation device and its setting tool to allow a larger object and passage in the isolation device to be used. If the guns misfire, the object is not released and comes out with the guns. The replacement guns can be pumped in because the passage in the isolation device has stayed open during the misfire. Direct and indirect object release in response to pressure created from the firing of the guns is contemplated.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is plug and perforate methods of sequential zone fracturing and more particularly devices and methods that allow retrieval of a frack plug occluding object designed to selectively plug an isolation device in the event the guns misfire and new guns need to be run in after the original guns are removed. 
       BACKGROUND OF THE INVENTION 
       [0002]    In typical plug and perforate systems the bottom hole assembly (BHA) comprises an isolation device with a passage through it and a surrounding seat on the passage for an object to land on the seat and obstruct the passage. The object can be delivered with the isolation device or pumped to the isolation device after the perforating guns are shot and removed from the borehole with the setting tool for the isolation device. Delivering the object with the isolation device has the advantage of saving time to get the passage in the isolation device closed as compared to pumping down an object from the surface. However, this prior method has a drawback if the guns misfire. In essence, if the guns misfire they must be removed and new guns run in to the desired location which is frequently in a horizontal portion of the wellbore. Thus, gravity is not much help in running in the replacement guns. Furthermore, if the object was run in with the isolation device, then the object would be forced against the seat in the passage of the isolation device if any effort to use pressure or flow to deliver the replacement guns was employed. The closing off of the passage in the isolation device means the replacement guns cannot be delivered on wireline with a pressure or flow assist and that alternative means such as coiled tubing or tractors have to be used to get the guns into position. This adds enormous expense to the operation and creates issues of delay. Even if the object is dropped after the misfired gun is removed, it still takes time to pump the object from the surface to the seat on the isolation device that is thousands of meters away costing time and additional fluid displacement. 
         [0003]    In the past one way to cut the time to get an object seated on a seat in an isolation device was to include a ball release device above the guns. The idea in US 2013/0175053 was to release the object into the annulus from above the fired gun and have the object make its way around the fired gun and the isolation device setting tool to a seat on a passage in the isolation device. A physical pull on the wireline sheared an unnumbered pin and allowed a ball  24  to escape through a lateral opening  28  to make its way toward the isolation device  14 . There are many issues with this design. Frequently the guns  18  have very low clearance around them to the casing  12 , which means the ball  24  will not fit in the annular space or would have to be so small that the passage in the isolation device  14  would also have to be small. A smaller passage in the isolation device could mean delays if a replacement gun has to be delivered with flow after an original gun misfires. The spent perforating gun could also have burrs and sharp edges that could hang up or damage the object so badly that it might not seal at all when landing in the seat. Finally, in a horizontal run the object may not actually land on the seat if the seat surrounding the passage in the isolation device is considerably smaller than the casing inside diameter, a condition made necessary by the object being small enough to travel past the gun in the surrounding annulus around the gun. 
         [0004]    Generally related to operation of lateral passages that can be selectively opened in a fracking context are US2013/0024030 and US2013/0020065. 
         [0005]    What is needed is a device and method that allows retention of the object that is designed to go onto a seat for a passage in an isolation until such time as the gun actually fires. The reason is that if the guns misfire and need to be replaced, it will still be possible to deliver the replacement guns with pressure or flow because the passage in the isolation device will be open because the object has been retrieved with the misfired guns. What is also provided is a launcher for the object that is placed in close proximity of the isolation device which allows the use of a larger object than when the launcher is above the guns and has to deliver the object into an annulus between the gun and the casing after the gun fires. What is also provided is an object launching device that responds directly or indirectly to the concussive pressure shock created by the guns initially firing so that the object is only released if the guns actually fire. This allows for the object to be retrieved without release if the guns misfire so that the replacement guns can be delivered with flow through the still open passage in the isolation device. On the other hand, if the guns fire then the pressure that is built up from the firing will release the object allowing the start of fracturing after the guns and setting tool for the isolation device are pulled out. Those skilled in the art will further appreciate additional aspects of the invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims. 
       SUMMARY OF THE INVENTION 
       [0006]    In a fracking context the object that will ultimately block a passage in an isolation device is introduced into the zone with the bottom hole assembly. The object is not released until the guns fire to create a pressure spike in the borehole that triggers the object retaining device to release the object. The retaining device is placed in close proximity to the isolation device and its setting tool to allow a larger object and passage in the isolation device to be used. If the guns misfire, the object is not released and comes out with the guns. The replacement guns can be pumped in because the passage in the isolation device has stayed open during the misfire. Direct and indirect object release in response to pressure created from the firing of the guns is contemplated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a prior art section view of a cemented production tubing in a horizontal portion of a borehole; 
           [0008]      FIG. 2  is the view of  FIG. 1  showing the bottom hole assembly in position; 
           [0009]      FIG. 3  is the view of  FIG. 2  with the frack plug set and the guns separated from the set plug while the ball for the plug is also released and floating; 
           [0010]      FIG. 4  is the view of  FIG. 3  shows the guns being fired; 
           [0011]      FIG. 5  is the view of  FIG. 4  showing the BHA removed; 
           [0012]      FIG. 6  is the view of  FIG. 5  showing the ball seated in the frack plug as pressure is built up to fracture the perforations created by the guns; 
           [0013]      FIG. 7  is a prior art view of a horizontal portion of a borehole with cemented casing to illustrate the problem of gun misfire; 
           [0014]      FIG. 8  is the view of  FIG. 7  showing the BHA run into position; 
           [0015]      FIG. 9  is the view of  FIG. 8  showing the frack plug set and the frack ball released; 
           [0016]      FIG. 10  is the view of  FIG. 9  showing the guns having misfired; 
           [0017]      FIG. 11  is the view of  FIG. 10  with the BHA removed and the frack ball on the seat of the frack plug preventing a replacement gun from being delivered on wireline with a pressure assist; 
           [0018]      FIG. 12  shows the present invention with the BHA in position and the ball release tool between the setting tool and the frack plug; 
           [0019]      FIG. 13  is the view of  FIG. 12  with the frack plug set; 
           [0020]      FIG. 14  is the view of  FIG. 13  with the guns being pulled after a misfire with the frack ball still in the release tool; 
           [0021]      FIG. 15  is the view of  FIG. 14  with the substituted guns in the hole and where the shock wave from firing is starting to migrate from the guns; 
           [0022]      FIG. 15   a  is a detailed view of the ball releasing tool in a direct pressure actuated embodiment; 
           [0023]      FIG. 16  is the view of  FIG. 15  with the shock wave migrating to the release tool for a ball release; 
           [0024]      FIG. 16   a  shows the ball release tool just as the shock wave reaches it; 
           [0025]      FIG. 17  is the view of  FIG. 16  with the guns fired and the ball released from the ball release tool; 
           [0026]      FIG. 17   a  shows a detail of the ball release tool in the ball released position; 
           [0027]      FIG. 18  is the view of  FIG. 17  showing the BHA removed; 
           [0028]      FIG. 19  is the view of  FIG. 18  showing fracking with the plug ball on the seat of the frack plug; and 
           [0029]      FIGS. 20   a - 20   b  are an alternative embodiment to the ball release tool that responds to a pressure spike by moving other parts from a breakable barrier to drive the ball from the ball release tool. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]      FIGS. 1-6  illustrate a known way of doing a plug and perforate fracturing technique in a horizontal cemented production casing  10 .  FIG. 2  shows the BHA  12  in the desired location of the casing  10 . The BHA  12  comprises perforating guns  14  followed by a setting tool  16  and a frack plug  18 . The BHA  12  is run in on wireline  20 . In  FIG. 3  the setting tool  16  has set the frack plug  18  and released from the frack plug  18  so that the frack ball  22  is released. The wireline  20  provides power to the setting tool  16  which can be an E-4 setting tool sold by Baker Hughes Incorporated. The BHA  12  that is suspended by wireline  20  is aided in travelling into the horizontal portion of the well by pressure from the surface that creates flow to carry the BHA  12  into the horizontal portion of the borehole. At this time the frack plug is unset and flow can get past it and into an already perforated zone that is lower or into the formation if it is the initial zone to be perforated. The frack plug  18  has a through passage and surrounding ball seat  24  on which ball  22  lands to close the passage when there is flow urging the ball  22  toward the seat around passage  24 .  FIG. 4  shows the guns  14  being fired to create the perforations  26 .  FIG. 5  shows the BHA  12  removed from the casing  10 . Note that the ball  22  is still floating because there is no applied pressure from the surface that creates flow in the direction of arrow  28 . In  FIG. 6  the pressure represented by arrows  28  is applied that forces ball  22  against the ball seat on passage  24  so that pressure is built up onto the perforations  26  to frack them. 
         [0031]    The sequence of  FIGS. 7-11  represent an illustration of what can go wrong if the guns  14  misfire.  FIG. 7  is the same as  FIG. 1  showing the cemented casing  10  in a horizontal portion of the well  30 . The same BHA  12  is run in as in  FIG. 2  as is shown in  FIG. 8 . The frack plug  18  is set in  FIG. 9  and an attempt to fire the guns  14  after a release of the setting tool  16  from the plug  18  results in a misfire of the guns. However, the ball  22  is released in this separation process between the setting tool  16  and the frack plug  18 . The problem now created when the BHA  12  is pulled out is evident by looking at  FIG. 11 . There is a need to run in a replacement BHA  12 ′ into the position formerly occupied by the original BHA  12  that had the guns  14  that misfired. The problem is that the ball  22  is blocking the passage  24  by sitting on the associated seat if there is any pressure applied in the casing  10 . With the misfire there are no perforations  26  and the zone below is effectively isolated by the frack plug  18 . What this means is that it will not be possible to use pressure that creates a flow to carry the BHA  12 ′ into the lateral or horizontal portion  30 . This means that the alternative is to deliver the BHA  12 ′ with coiled tubing or a tractor (not shown). Delivering the BHA  12 ′ using either of these techniques is slow and therefore expensive. In the case of coiled tubing, there may also be issues of space for the coiled tubing unit at the wellsite particularly in offshore applications. Tractors are far slower than a delivery on wireline with a flow assist. A flow assist is not possible in an unperforated section of a casing that has a frack plug  18  in a set position with a ball  22  landed on the seat surrounding its passage  24 . 
         [0032]    With the above as a background, the present invention will be described in greater detail starting with  FIG. 12  where the BHA  40  that comprises perforating guns  42 , a plug setting tool  44  and a ball release tool  46  are disposed above the frack plug  48 . In  FIG. 13  the frack plug  48  is set as before. In  FIG. 14  the release tool separates from the frack plug  48  while still retaining the frack ball  50 . If the guns  42  misfire at this point then the frack plug  48  has a clear through passage  52  because the ball  50  has not obstructed it. The BHA  40  with the ball  50  can be pulled from the casing  54  with wireline  56 . 
         [0033]    On the other hand if the guns fire as shown in  FIG. 15  then the perforations  58  are made. The operation of the guns creates a pressure wave  60  that migrates in the direction of arrow  62  toward the ball release tool  46  that is disposed between the setting tool  44  and the frack plug  48 .  FIG. 16  shows the pressure wave  60  reaching the ball releasing tool  46  so that the ball  50  is released from the release tool  46 . Preferably the ball  50  is in alignment with the passage  52  in the frack plug  48  to facilitate seating the ball on a seat that surrounds the passage  52 . This is shown in  FIG. 17 . The BHA  40  is now removed as shown in  FIG. 18  and the perforations  58  are fracked as represented by pressure arrows  64 . 
         [0034]    Thus one aspect of the present invention is a method that allows retention of an object that can be a ball or plug or other shape that is designed to land in the passage of a frack plug, in the event the guns do not fire, and despite the fact that portions of the BHA have released from the frack plug  48  when that plug was set by the setting tool  44 . The release of the frack ball  50  is dependent on the guns firing to create a signal that allows the ball release tool  46  to release the ball  50 . Thus if the guns fire there is no problem in releasing the ball because there will be a flow path to allow a replacement gun to be wireline delivered with a flow assist. The gun can have multiple stages that sequentially fire so it possible to get one or more but not all stages to fire. In that event the gun has to be pulled and a new gun or the same gun redressed have to be run in later. In either case the method allows the completion process to continue. A misfire on the initial stage firing will not result in a ball release so that the next gun can be delivered on wireline with a flow assist with flow going through the frack plug that has an open passage. If at least one stage fires the ball is released but a subsequent gun can still be delivered on a wireline with a flow assist because the stage that did fire creates a fluid path for the flow assist to move the replacement gun into position. 
         [0035]    In another aspect of the invention the placement of the ball release tool  46  immediately adjacent the frack plug  48  allows the use of a larger passage  52  through the frack plug  48  as well as a larger associated ball, or plug or dart  50 . This is because unlike Madero US 2013/0175053 the ball does not need to travel in an annular space past the guns. The ball  50  is delivered below the guns  42  so it can be larger than a ball that has to travel in an annular gap which can be very small. The ability to use a larger passage in the frack plug  48  also speeds the delivery of a replacement gun if the original gun misfires because there is less pressure drop for the flow going through the passage of the frack plug  48  when the replacement gun is delivered. The release tool  46  can be up against the frack plug  48  or spaced from frack plug  48  with no intervening equipment in between. Alternatively, the ball can drop through another tool disposed between the release tool  46  and the frack plug  48 . 
         [0036]    Referring to  FIG. 15   a  a direct responding release tool  46  is shown. Direct means the pressure wave  60  has enough force to break a breakable member  70  such that well pressure in the surrounding annulus  72  can be brought to bear on the piston  74  that has a surrounding seal  76  so that an upper sealed variable volume chamber is defined and grows in volume as pressure from annulus  72  displaces the piston  74  and its associated push rod  78  to contact the ball  50  and push it past a retainer  80 . Piston  74  pushes against variable volume chamber  75  that is initially at atmospheric pressure. When barrier  70  breaks there is a pressure differential on the piston  74  that is enhanced by the low pressure in chamber  75 .  FIG. 16   a  shows the shock wave  60  arriving at the breakable member  70  and breaking through and  FIG. 17   a  shows the resulting movement of all the parts that will launch the ball  50  in the manner described above. Those skilled in the art will appreciate that  FIGS. 15   a - 17   a  are schematic and intend to portray both direct and indirect actuation using the developed pressure from the discharge of the guns. In an indirect system, the generated pressure from shooting off the guns is sensed with a sensor that is powered with a stored energy source such as a battery to then take action to get parts moving to eject the ball  50 . This can be accomplished by forcibly breaking the breakable member  70  or actuating a motor that moves piston  74  or in other ways getting part movement sufficient to expel the ball  50  so that it lands on the passage  52  of the frack plug  48  to allow subsequent pressure buildup for fracking represented by arrows  64 .  FIGS. 20   a - 20   b  generically illustrates an indirect system which processes the existence of the pressure wave to either harness it for part movement or to trigger part movement in other ways that release the ball. Thus an indirect system can still employ wellbore hydrostatic but the opening of access to the hydrostatic pressure is done with a sensed pressure signal that opens access to annulus pressure. In  FIG. 20   a  instead of barrier  70  there is a pressure sensing module  100  to sense the presence of the pressure wave  60  and use that signal to operate a valve  102  that opens passage  104  to drive the piston  74  in the manner previously described. Alternatively, such a sensed pressure can provide power to a motor from a stored power supply that moves a mechanical element that expels the ball  50 . 
         [0037]    The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: