Abstract:
A lateral exit in a casing is formed by starting with a shaped charge to produce a semi-circular cut of about 180 degrees in the casing. A spreader tool pushes in opposed directions at opposed ends of the cut making some of the casing wall at the cut curl inwardly. A wedge shaped tool is advanced behind the curled metal to force it to collapse on itself to create a long tapered ramp that act as would a whipstock. A one trip operation is contemplated. The drill is then guided by the doubled and tapered casing wall right into the formation without having to mill a window in the casing wall.

Description:
FIELD OF THE INVENTION 
   The field of this invention is making lateral exits from tubulars downhole and more particularly directing a mill to make an exit with a diverter fashioned from the tubular itself as opposed to a traditional whipstock. 
   BACKGROUND OF THE INVENTION 
   Frequently in the life of a well there comes a need to create additional lateral from a main bore or other branch bores to increase production from a producing zone or to exploit new zones or for various other purposes such as fluid injection to stimulate production from other wells. When this need arises a procedure is undertaken that involves setting and anchor that can receive a whipstock and using MWD equipment as an aid to obtain proper orientation of the whipstock. The whipstock is initially connected to a series of mills that are rotated to break loose from the now anchored and oriented whipstock. The whipstock diverts the mills into the casing wall to start a window or opening in the casing for a lateral exit. Equipment has been developed to produce the window in a single trip. 
   Frequently, the whipstock is left in the well after the window is produced. This creates an expense for the operator as the operator must buy all service equipment left in the well. Another issue in traditional window milling operations is the cost of the service. The milling through the casing wall creates cuttings that need to be circulated out of the well. Problems with cuttings or with milling are also possible and sometimes the window is not properly formed or the lateral exit angle doesn&#39;t turn out as planned. 
   While eliminating all potential problems in window milling is an ideal, the present invention addresses a part of this process and seeks to find a reliable and low cost way to be able to have a suitable diverter downhole for the mills and avoid having to manufacture and run a whipstock into position. In essence, the invention addresses ways to actually use the casing itself as a diverter and position a portion thereof as such where the drilling of the lateral will not even require milling up a long window in the casing and the attendant issues of dealing with cuttings that such milling raises. As such the concept represents a dramatic departure from prior techniques of window milling and production of laterals through them. 
   As an example, explosives have been used to blow out a part of the casing with shaped charges such as shown in U.S. Pat. No. 5,636,692. In this case, the mill supported explosives right above a whipstock. One issue with trying to make a complete or nearly complete window with explosives has been the debris generated from the process and how to effectively remove it from the wellbore. Other attempts have simply blown through casing to create an opening in it but in so doing created a fair amount of debris that potentially undermined subsequent operations. 
   The present invention while using explosives reduces or eliminates such issues and finds a way to use the casing itself as a diverter while allowing the lateral to begin without having to mill up a window in the casing. The present invention also affords a way to produce a window through which a lateral can be drilled by a technique that allows a portion of the tubular to be cut and bent back on itself to from a window without the debris that characterized prior attempts to make windows with explosives, chemicals, abrasive jets or other cutting or milling tools. These and other advantages of the present invention will be more readily apparent to those skilled in the art from the description of the preferred embodiment, the drawings and claims that appear below. 
   SUMMARY OF THE INVENTION 
   A lateral exit in a casing is formed by starting with a shaped charge to produce a semi-circular cut of about 180 degrees in the casing. A spreader tool pushes in opposed directions at opposed ends of the cut making some of the casing wall at the cut curl inwardly. A wedge shaped tool is advanced behind the curled metal to force it to collapse on itself to create a long tapered ramp that act as would a whipstock. A one trip operation is contemplated. The drill is then guided by the doubled and tapered casing wall right into the formation without having to mill a window in the casing wall. Alternatively the wedge shaped tool bends the tubular on itself to create a window through which the lateral can be drilled using a bent motor sub and other known directional drilling tools. 

   
     BRIEF DESCRIPTION OF TH DRAWINGS 
       FIG. 1  is a section view of the tool showing the shaped charge cutting a semicircular slot in the casing; 
       FIG. 2  shows insertion of a wedge tool behind a partially collapsed wall of the casing adjacent the slot; 
       FIG. 3  is the view along lines  3 - 3  of  FIG. 2  showing how the slot in  FIG. 1  is pushed in opposed directions at it ends to create the collapsed wall shown in  FIG. 2 ; 
       FIG. 4  is a perspective view after the wedge tool of  FIG. 2  is sufficiently advanced to collapse the casing on itself to create a long sloping diversion ramp oriented into the formation; 
       FIG. 5  is a section view showing the tubular being cut on top and on bottom with associated cuts in between; 
       FIG. 6  is the view of  FIG. 5  showing the start of folding the tubular segment on itself to create a window; 
       FIG. 7  is a continuation of the process from  FIG. 6  showing the casing portion doubled on itself throughout its length; 
       FIG. 8  is a section drawn along lines  8 - 8  of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  schematically illustrates a wellbore  10  having a casing  12  with cement  14  outside the casing  12 . The tool T has a tapered lower end  16  for reasons which will be explained below. A shaped linear cutter  18  is provided on the tool T that when properly oriented and triggered will make a semi-circular cut  20  as shown in  FIG. 2 . Those skilled in the art will appreciate that the tool T can be delivered on electric line, coiled tubing or other equivalent known conveyances to the proper depth in the wellbore  10 . Similarly, the tool T can be combined with known MWD tools, not shown, or other known orientation devices to properly rotationally position the shaped charge  18  with respect to the desired exit orientation of a lateral to be drilled. Furthermore, upon having obtained the required orientation with an MWD tool or equivalent, an anchor feature in the tool T, not shown, can be deployed to hold the tool T in position as the shaped charge  18  is set off. The preferred embodiment of the shaped charge  18  is such that a semi-circular slot of about 180 degrees will be blown though the casing  12  when the charge  18  is set off. Greater or lesser included angles are contemplated as is some variation in the height of the slot made by the charge  18  in the casing  12 . One objective is to be able to more easily initiate an inward deflection  22  adjacent the slot  20 , as shown in  FIG. 2 . One way this is accomplished with tool T is schematically illustrated in  FIG. 3 . In essence the tool T puts opposed forces represented by arrow  24  at or near the opposed ends of the slot  20 . What this does is encourage an initial inward collapse of wall  26  as the cross-section of the casing  10  goes from a circular shape to a more oval shape, as shown in  FIG. 3 . Since  FIG. 3  is a section view looking down along lines  3 - 3  of  FIG. 2 , those skilled in the art will appreciate that gap  28  is now directly exposed to the cement  14  or the formation behind it if there is no cement or the cement has been cleared away by the firing of the charge  18 . The lower tapered end  16  of the tool T can now be advanced into gap  28  to force wall  26  further back on itself, as shown in  FIG. 4 . As the tool T is advanced, its cylindrical portion doubles the wall  26  on itself, while the tapered leading end  16  creates a sloping surface  30  that comes to a point  32  both of which still experiencing support along edges  34  and  36  that are inclined and additionally possibly along straight edges  38  and  40 . Sloping surface  30  acts as a whipstock for a drilling operation that produces a lateral through gap  28  in a known manner. One difference is that the drill that deflects off the sloping surface  30  does not have to go through the wall  26  of the casing  12  as in the past with a window milling system. In essence, the window is created by the combination of the explosive charge  18  and the tool T that together bend the wall  26  of the casing  12  back on itself while uniquely leaving a sloping surface  30  to deflect a drill or mill out of the casing  12  to drill the lateral. 
   In some instances particularly involving very hard formations, there may be a concern for the strength of the tapered segment  30  do its deflection duties rather than getting drilled or milled out. The rigidity of the sloping surface  30  and the loads that it sees can be varied by changing the angle of the leading end  16  of the tool T as well as the wall thickness and materials of the casing  12 . Clearly, less consolidated or softer formations will present less of a concern for the use of this technique. 
   Another benefit of this technique is that whipstocks that are expensive to manufacture and store in a variety of sizes and deliver to a remote job location need not be used at all. The operator is also not stuck with the cost of whipstocks left in the hole. Fishing operations to retrieve whipstocks no longer are required. If desired, the tapered segment  30  can be pushed flat against the remaining casing wall opposite the lateral produced to allow access to the main bore below. Alternatively, the tapered segment  30  can be cut and retrieved or allowed to fall to the bottom of the wellbore to allow access to the main bore below. Pushing the segment flat can be done with an inflatable tool or a known spreader tool while complete removal is contemplated using available milling tools while providing a deflector to temporarily isolate the new lateral while the mill is directed straight through to remove the tapered segment  30 . 
   Referring now to  FIG. 5 , an alternative embodiment is described. This time, the tool T has end cutters  52  and  54  at opposed ends. In the preferred embodiment these cutters are oriented at  90  degrees to the longitudinal axis but other orientations are possible. The extent of end cutters  52  and  54  is preferably about 180 degrees but other lengths are possible and the width or even shape of the cut they make can be varied. Preferably, they are a line charge that creates a circumferential slot but they can also be individual charges in a line that either perforate the wall of casing  56  or simply score it to weaken in for subsequent operations, as will be described. In addition, stitch cutters  58  are preferably oriented in longitudinal alignment with the ends of the slots produced by end cutters  52  and/or  54 . Again, they may perforate or rip through or simply score the casing  56  to simplify the next operation illustrated in  FIG. 6 . The stitch cutters may be a series of arc cuts that are about  30  degrees that are parallel to each other. Other configurations are envisioned that ultimately help to take a wall segment  60  and double it back on casing  56  as shown in  FIGS. 6-8 . Locations  62  and  64  in  FIG. 8  show where the stitch cutters  58  have weakened or penetrated the wall of casing  56 . 
   After making the cuts shown in.  FIG. 5 , which can be done with explosives or chemicals or jet cutting tools or equivalent known tools, the tool T is retracted and a spreading operation as previously described using tool T and shown in  FIG. 3  is undertaken to create an inwardly oriented lip  66  that can then be engaged by tapered end  68  of tool T, as shown in  FIG. 6 . Since the preferred shape of the body of tool T is cylindrical above taper  68 , advancing the tool T downhole from the position shown in  FIG. 6  will peel back section  60  against the opposing wall of casing  56  and create a window  70  having a half-cylindrical shape, as more clearly seen in  FIG. 8 . After window  70  is produced in the manner described a drill using a bent sub can be directed out through the window  70  without need for a whipstock to drill a lateral. Those skilled in the art will appreciate that the window  70  can be produced in a direction opposite that shown in the Figures. 
   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.