Abstract:
A fracturing jet nozzle assembly has nested telescoping sections that each have nozzles in them. The outermost stage makes for a large perforation as it and the adjacent stages begin extension. As the stage adjacent the outermost stage continues to extend into the perforation and reaches maximum extension the nozzles in the outermost stage are cut off from fracturing fluid flow and that flow is in turn redirected to the remaining stages that have not yet fully extended. The innermost stage preferably does not get cut off from jet fluid flow even at its full extension.

Description:
FIELD OF THE INVENTION 
     The field of the invention is nozzles used in formation fracturing and more particularly nozzles used to enhance the initiation and propagation of formation fractures by adding a feature of continuing extension during fracturing and diverting fracture flow away from extended portions and into portions still capable of further extension. 
     BACKGROUND OF THE INVENTION 
     Fracturing in open hole is a complex subject and has been studied and written about by various authors. Whether using explosives or fluid jets one of the problems with the initiated fractures is in the way they propagate. If the propagation pattern is more tortuous as the fractures emanate from the borehole an undesirable condition called screenout can occur that can dramatically decrease the well productivity after it is put on production. 
     Hydraulically fracturing from any borehole in any well orientation is complex because of the earth&#39;s ambient stress field operating in the area. This is complicated further because of the extreme stress concentrations that can occur along the borehole at various positions around the well. For instance, there are positions around the borehole that may be easier to create a tensile crack than other positions where extreme compressive pressures are preventing tensile failure. One way that has been suggested to minimize this condition is to use jets that create a series of fan shaped slots in the formation with the thinking that a series of coplanar cavities in the formation will result in decreased tortuosity. This concept is discussed in SPE 28761 Surjatmaadja, Abass and Brumley Elimination of Near-wellbore Tortuosities by Means of Hydrojetting (1994). Other references discus creating slots in the formation such as U.S. Pat. Nos. 7,017,665; 5,335,724; 5,494,103; 5,484,016 and US Publication 2009/0107680. 
     Other approaches oriented the jet nozzles at oblique angles to the wellbore to try to affect the way the fractures propagated. Some examples of such approaches are U.S. Pat. Nos. 7,159,660; 5,111,881; 6,938,690; 5,533,571; 5,499,678 and US Publications 2008/0083531 and 2009/0283260. 
     Other approaches involved some form of annulus pumping in conjunction with jet fracturing. Some examples of this technique are U.S. Pat. Nos. 7,278,486; 7,681,635; 7,343,974; 7,337,844; 7,237,612; 7,225,869; 6,779,607; 6,725,933; 6,719,054 and 6,662,874. 
     Pulsing techniques have been used in jet drilling or in conventional drilling to pulse the bit nozzle flow as described in U.S. Pat. Nos. 4,819,745 and 6,626,253. Also related to these applications is SPE paper 130829-MS entitled  Hydraulic Pulsed Cavitating Jet Assisted Deep Drilling: An Approach to Improve Rate of Penetration.    
     Jets mounted to telescoping assemblies have been suggested with the idea being that if the jet is brought closer to the formation the fracturing performance will improve. This was discussed in U.S. application Ser. No. 12/618,032 filed Nov. 13, 2009 called Open Hole Stimulation with Jet Tool and is commonly assigned to Baker Hughes Inc. In another variation of telescoping members used for fracturing the idea was to extend the telescoping members to the borehole wall and to set spaced packers in the annulus so as to avoid the need to cement and to allow production from the telescoping members after using some of them to initially fracture the formation. This was discussed in U.S. application Ser. No. 12/463,944 filed May 11, 2009 and entitled Fracturing with Telescoping Members and Sealing the Annular Space and is also commonly assigned. 
     The present invention seeks to improve the extent of the fracturing that is accomplished beyond the initial formation perforation that is initiated explosively or with a direct impingement nozzle. This is accomplished with a telescoping assembly that directs jet streams from each stage. As the largest stage extends fully the flow of fracturing fluid to it is cut off and redirected to the smaller stages that it surrounds. In turn as the perforation grows from jet impingement some portion of the assembly can continue to extend to keep the gap distance from the nozzle face to the depth of the perforation to a minimum so as to improve the starting and propagating of fractures. 
     SUMMARY OF THE INVENTION 
     A fracturing jet nozzle assembly has nested telescoping sections that each has nozzles in them. The outermost stage makes for a large perforation as it and the adjacent stages begin extension. As the stage adjacent the outermost stage continues to extend into the perforation and reaches maximum extension the nozzles in the outermost stage are cut off from fracturing fluid flow and that flow is in turn redirected to the remaining stages that have not yet fully extended. The innermost stage preferably does not get cut off from jet fluid flow even at its full extension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of a current telescoping frac nozzle design; 
         FIG. 2  is a graph showing the relationship of nozzle to wellbore distance to stagnation pressure; 
         FIG. 3  is a perspective cutaway view of half the nozzle assembly before the onset of flow; 
         FIG. 4  the view of  FIG. 3  with flow initiated and all stages moving an identical initial distance to reach the formation; 
         FIG. 5  is the view of  FIG. 4  with the intermediate stage fully extended cutting off jet flow to the outer stage that is also fully extended; 
         FIG. 6  is a side view of  FIG. 4  showing all the stages initially extended to adjacent the borehole wall. 
         FIG. 7  is the view of  FIG. 6  with the outer stage fully extended and the perforation enlarged to allow the middle stage to further extend and cut the jet flow to the outer stage; 
         FIG. 8  is the view of  FIG. 7  with the middle and inner stages fully extended cutting off the jetting flow to the middle stage. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates the problem to be overcome by the present invention in a telescoping fracturing nozzle  10  that can be secured with threads  12  to an opening in a tubular string (not shown) so that a jet of fluid represented by arrow  14  can result in telescoping action to the borehole wall  16 . The force of the flowing fluid represented by arrow  14  causes the sliding stages  18  and  20  to slide out toward the borehole wall  16 . Stage  22  is fixed to the tubular that is not shown. The perforation  24  is not there initially when the stages  18  and  20  extend and it is the force of the jet fluid stream represented by arrow  26  that forms the perforation  24 . As the jetting continues and the perforation  24  gets bigger the distance from the nozzle face  28  and the deep end  30  of the perforation  24  increases. Looking at the graph of  FIG. 2  it is easy to see how the stagnation pressure in the perforation  24  will exponentially decline when the distance from the nozzle to the perforation bottom at  30  increases. 
     The present invention deals with this issue in a way that allows the nozzle to telescope as the perforation gets larger during the fracturing process. Using nozzles in the adjacent outer stages to enlarge the perforation to make further stage extension possible the apparatus also cuts off jet fluid to fully advanced stages as the next stage inboard goes to full extension. In this manner the outermost stage with jet flow makes the perforation larger to enable the adjacent stages that are inboard to advance as the perforation grows. As the next stages advance they also direct a larger flow to the now enlarged perforation to further aid the stages that have not yet fully advanced to further do so. The innermost stage that is generally coincident with the axis of the assembly sees a continuous flow to full extension without flow cutoff. The detailed explanation for how the above is accomplished is illustrated in detail below with regard to  FIGS. 3-8 . 
       FIG. 3  shows the run in position of a nozzle assembly  40 . There is an outer housing  42  with a mounting flange  44  that is sealingly secured to an opening in a tubular string that is not shown. An outermost stage  46  has openings  48  that are preferably equally spaced on a common radius. When travel stop  50  hits shoulder  52  of outer housing  42 , the outer travel limit of stage  46  is reached, as shown in  FIG. 4 . As shown in  FIG. 4  arrows  54  represent jet flow through stage  46  that continues despite the full extension of stage  46  as the stop  50  hits shoulder  52 . Nested within stage  46  is intermediate stage  56  that has an outer annular shape  58  with an array of nozzles  60  that are preferably equally spaced on a common radius with arrows  62  representing the jet flow through nozzles  60 . At the inner end of the intermediate stage  56  is a segmented flange ring  64  that is made of alternating tabs  66  and gaps  68 . The stages  56  and  46  can be optionally locked against relative rotation while still optionally be placed in the outer housing  42  in a way that the stages can all rotate in tandem. Axial advancing of the intermediate stage  56 , when the outer stage  46  is fully extended, brings the tabs  66  in contact with nozzles  48  as shown in  FIG. 5 . When that happens, flow to the nozzles  48  is cut off but is redirected to nozzles  70  on the leading face  58  of the intermediate stage  56 . At the same time there is also an increase in flow through the inner stage  72  through its central nozzle  74 . In  FIG. 5  the enhanced flow through the intermediate stage  56  and the inner stage  72  is represented respectively by the arrows  75  and  76 . 
       FIG. 7  is a side view of  FIG. 5  showing the flow through the intermediate stage  56  and the inner stage  72 . The perforation  80  has already been enlarged at its outer periphery  82  and the flow to nozzles  48  has been cut off by the tabs  66 . The intermediate stage  56  has been able to advance to full extension to near the perforation surface  84  as flow through the intermediate stage  56  continues as indicated by arrow  75  through nozzles  70 . That flow continues to enlarge the perforation  80  to create another and deeper shoulder  86  whose formation is assisted by the enhanced flow through nozzle  74  as indicated by arrow  76 . 
     The inner stage  72  has a front face  88  and a rear segmented flange  90  that has alternating tabs  92  and gaps  94  as seen in  FIG. 5 . As seen in  FIG. 8  when the tabs  92  contact the nozzles  70  in the intermediate stage  56  then the flow to nozzles  70  is cut off and the flow to the inner stage  72  through its nozzle  74  is enhanced. The stages  56  and  72  can be locked optionally against relative rotation but can still be allowed to rotate in tandem relative to the outer stage  46  or relative to the outer housing  42  such as when all the stages turn together.  FIG. 8  represents the full extension of all the stages with the shoulder  86  still not contacted by the front face  88  of the inner stage  72 . It is also possible that at the end of the fracturing process that all the stages have not fully extended notably the inner stage  72 . It is also possible that more inboard stages can extend before stages that surround them extend. As the perforation  80  enlarges it will allow innermost stages to extend even if the outer stages are held back from full extension. As the perforation  80  changes shape the outer stages may then extend. 
     Variations on the preferred embodiment are also envisioned. While three stages are described, two or more stages can be used. The nozzle pattern on any specific stage can have unequal spacing on a common radius or use of a single or multiple rows of nozzles or a random placement of the nozzles on any particular stage. The stages can be built out of a hardened material or the nozzles themselves can be hardened inserts in a stage built out of a softer material where the inserts are supported in the outer wall of the stage or with a flange internally to the stage to hold the insert in position with flow running through the insert. While the use of tabs that advance to cover the nozzles in the surrounding stage are preferred other devices that shut off flow to an exterior stage when the next adjacent stage gets to maximum extension are also contemplated. While the interior stage  72  is illustrated with a single nozzle  74  with a common axis to the axis of the other stages, it can also have multiple nozzles in an ordered or random spacing. While the nozzles in the various stages have been shown on exes that are parallel to the axis of the overall assembly, the orientation of the nozzle axes can be askew in more than a single plane or one plane to the axis of the assembly so that the nozzle axis may not even intersect with the axis of the assembly so as to cause one or more of the stages to rotate as the jet stream exits so as to deliver a pulsating impact to a particular location in the perforation to enhance the initiation and propagation of fractures from the perforation. Ratchet devices can be used to prevent any retraction of stages after extension. 
     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.