Abstract:
A fracturing operation is done in open hole. The annular space is spanned by telescoping members that are located behind isolation valves. A given bank of telescoping members can be uncovered and the telescoping members extended to span the annular space and engage the formation in a sealing manner. Pressurized fracturing fluid can be pumped through the telescoped passages and the portion of the desired formation fractured. In a proper formation, cementing is not needed to maintain wellbore integrity. In formations that need annular space isolation, the string in a preferred embodiment can have an external material that grows to seal the annular space in lieu of a traditional cementing operation.

Description:
PRIORITY INFORMATION  
     This application is a continuation of U.S. patent application Ser. No. 12/463,944 filed on May 11, 2009. 
    
    
     FIELD OF THE INVENTION 
     The field of the invention is fracturing and more particularly a method for fracturing in open hole without external zone isolators and more particularly with an ability to seal the annulus without a traditional cementing job. 
     BACKGROUND OF THE INVENTION 
     There are two commonly used techniques to fracture in a completion method.  FIG. 1  shows a borehole  10  that has a casing string  12  that is cemented  14  in the surrounding annulus  16 . This is normally done through a cementing shoe (not shown) at the lower end of the casing string  12 . In many cases if further drilling is contemplated, the shoe is milled out and further drilling progresses. After the string  12  is cemented and the cement  14  sets a perforating gun (not shown is run in and fired to make perforations  18  that are then fractured with fluid delivered from the surface followed by installation and setting of packer or bridge plug  20  to isolate perforations  18 . After that the process is repeated where the gun perforates followed by fracturing and followed by setting yet another packer or bridge plug above the recently made and fractured perforations. In sequence, perforation and packer/bridge plug pairs  22 ,  24 ;  26 ,  28 ;  30 ,  32 ; and  34  are put in place in the well  10  working from the bottom  36  toward the well surface  38 . 
     A variation of this scheme is to eliminate the perforation by putting into the casing wall telescoping members that can be selectively extended through the cement before the cement sets to create passages into the formation and to bridge the cemented annulus. The use of extendable members to replace the perforation process is illustrated in U.S. Pat. No. 4,475,729. Once the members are extended, the annulus is cemented and the filtered passages are opened through the extending members so that in this particular case the well can be used in injection service. While the perforating is eliminated with the extendable members the cost of a cementing job plus rig time can be very high and in some locations the logistical complications of the well site can add to the cost. 
     More recently, external packers that swell in well fluids or that otherwise can be set such as  40 ,  42 ,  44 ,  46 , and  48  in  FIG. 2  can be set on the exterior of the string  49  to isolate zones  50 ,  52 ,  54 , and  56  where there is a valve, typically a sliding sleeve  58 ,  60 ,  62  and  64  in the respective zones. The string  49  is hung off the casing  66  and is capped at its lower end  67 . Using a variety of known devices for shifting the sleeves, they can be opened in any desired order so that the annular spaces  68 ,  70 ,  72  and  74  can be isolated between two packers so that pressurized frac fluid can be delivered into the annular space and still direct pressure into the surrounding formation. This method of fracturing involves proper packer placement when making up the string and delays to allow the packers to swell to isolate the zones. There are also potential uncertainties as to whether all the packers have attained a seal so that the developed pressure in the string is reliably going to the intended zone with the pressure delivered into the string  49  at the surface. Some examples of swelling packer are U.S. Pat. Nos. 7,441,596; 7,392,841 and 7,387,158. 
     In some instances the telescoping members have been combined with surrounding sleeves of a swelling material to better seal the extended ends of the telescoping members to the formation while still leaving open the remainder of the annular space to the formation in a given zone. Some examples of this design are U.S. Pat. No. 7,387,165 and U.S. Pat. No. 7,422,058. US Publication 2008/0121390 shows a spiral projection that can swell and/or be expanded into wellbore contact and leave passageways in between the projections for delivery of cement. 
     What is needed and provided by the method of the present invention is a technique to pinpoint the applied frac pressure to the desired formation while dispensing with expensive procedures such as cementing and annulus packers where the formation characteristics are such as that the hole will retain its integrity. The pressure in the string is delivered through extendable conduits that go into the formation. Given banks of conduits are coupled with an isolation device so that only the bank or banks in interest that are to be fractured at any given time are selectively open. The delivered pressure through the extended conduits goes right to the formation and bypasses the annular space in between. Beyond that the string exterior can have a covering of a swelling material such as rubber or a shape memory polymer, either of which can fill the annular gap and replace the traditional and expensive cement job. Those and other features of the present invention will be more readily understood to those skilled in the art from a review of the description of the preferred embodiment and the associated  FIGS. 3-10  while understanding that the full scope of the invention is determined by the literal and equivalent scope of the appended claims. 
     SUMMARY OF THE INVENTION 
     A fracturing operation is done in open hole. The annular space is spanned by telescoping members that are located behind isolation valves. A given bank of telescoping members can be uncovered and the telescoping members extended to span the annular space and engage the formation in a sealing manner. Pressurized fracturing fluid can be pumped through the telescoped passages and the portion of the desired formation fractured. In a proper formation, cementing is not needed to maintain wellbore integrity. The telescoping members can optionally have screens. Normally, the nature of the formation is such that gravel packing is also not required. A production string can be inserted into the string with the telescoping devices and the formation portions of interest can be produced through the selectively exposed telescoping members. In formations that need annular space isolation, the string in a preferred embodiment can have an external material that grows to seal the annular space in lieu of a traditional cementing operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a prior art system of cementing a casing and sequentially perforating and setting internal packers or bridge plugs to isolate the zones as they are perforated and fractured; 
         FIG. 2  is another prior art system using external swelling packers in the annular space to isolate zones that are accessible with a sliding sleeve valve; 
         FIG. 3  shows the method of the present invention using extendable passages into the formation that are selectively accessed with a valve so that the formation can be fractured directly from the string while bypassing the annular open hole space; and 
         FIG. 4  is a detailed view of a telescoping passage in the extended position; 
         FIGS. 5   a  and  5   b  show a telescoping member extended with a sliding sleeve and opened for formation access at the same time; 
         FIGS. 6   a  and  6   b  show a running string with extendable devices for extending the telescoping passages to the formation; 
         FIG. 7  is an embodiment showing the run in position of an assembly with sealing between the telescoping members that can seal the annulus in lieu of cementing; 
         FIG. 8  is the view of  FIG. 7  with the annulus sealed; 
         FIG. 9  is the view of  FIG. 8  with a telescoping passage extended; and 
         FIG. 10  is the view of  FIG. 9  with all the telescoping passages extended. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 3  illustrates one embodiment of the invention where the formation has the characteristics that make annular space isolation between the assemblies  108  optional. The preferred embodiment with annular space isolation is shown in  FIGS. 7-10 . 
       FIG. 3  illustrates an open hole  100  below a casing  102 . A liner  104  is hung off casing  102  using a liner hanger  106 . A fracturing assembly  108  is typical of the others illustrated in the  FIG. 3  and those skilled in the art will appreciate that any number of assemblies  108  can be used which are for the most part similar but can be varied to accommodate actuation in a desired sequence as will be explained below. As shown in  FIG. 4  each assembly  108  has a closure device that is preferably a sliding sleeve  110  that can be optionally operable with a ball  114  landing on a seat  112 . In one embodiment, the seats and balls that land on them are all different sizes and the sleeves can be closed in a bottom up sequence by first landing smaller balls on smaller seats that are on the lower assemblies  108  and progressively dropping larger balls that will land on different seats to close the valve  110 . 
     The array of telescoping members  116  selectively covered by a valve  110  can be in any number or array or size as needed in the application for the expected flow rates for fracturing or subsequent production. The telescoping assembly  116  is shown in the retracted position in  FIG. 3  while telescoping members  116 ′ are shown in the same  FIG. 3  in the extended position against the borehole wall  100 . In the preferred embodiment all the telescoping assemblies  116  are initially obstructed with a plug  118  so that internal pressure in the liner  104  will result in telescoping extension between or among members in each assembly, such as  120  and  122  or however many relatively moving segments are needed depending on the width of the annular gap that has to be crossed to get the leading ends  124  into the formation so that directed pressure will penetrate the formation and not go into the open annulus  126 . The plugs  118  are there to allow all the assemblies  116  to extend in response to the valves  110  at each assembly  116  being open and pressure applied inside the liner  104 . Once all the telescoping assemblies are extended, the plugs  118  in each can be removed. This can be done in many ways but one way is to use plugs that can disappear such as aluminum alloy plugs that will dissolve in an introduced fluid. Each or some of the assemblies can have a screen material  128  in the through passage that forms after extension and after removal of the plug  118 . 
     The valve  110  associated with each telescoping assembly  116  can also be operated with a sleeve shifter tool in any desired order. Each valve can have a unique profile that can be engaged by a shifting tool on the same or in separate trips to expedite the fracturing with one valve  110  and its associated telescoping array  116  ready for fracturing or more than one valve  110  and telescoping array  116 . 
     As another alternative for closing the valve  110  articulated ball seats can be used that accept a ball of a given diameter and allow the valve  110  to be operated and the ball to pass after moving the seat where such seat movement configures a another seat in another valve  110  to form to accept another object that has the same diameter as the first dropped object and yet operate a different valve  110 . Other techniques can be used to allow more than one valve to be operated in a single trip in the well. For example an articulated shifting tool can be run in and actuated so that on the way out or into the well it can open or close one or more than one valve either based on unique engagement profiles at each valve, which is preferably a sliding sleeve or even with common shifting profiles using the known location of each valve and shifting tool actuation before reaching a specific valve that needs shifting. 
     Alternatively rupture discs set to break at different pressure ratings can be used to sequence which telescoping passages will open at a given pressure and in a particular sequence. However, once a rupture disc is broken to open flow through a bank of telescoping passages, those passages cannot be closed again when another set of discs are broken for access to another zone. With sliding sleeves all the available volume and pressure can be directed to a predetermined bank of passages but with rupture discs there is less versatility if particular zones are to be fractured in isolation. 
     The above method of the present invention allows fracturing in open hole with direction of the fracture fluid into the formation without the need for annular barriers and in a proper formation the fracturing can take place in open hole without cementing the liner. Such a technique in combination with valves at most or all of the telescoping assemblies allows the fracturing to pin done in the needed locations and in the desired order. After fracturing, some or all the valves can be closed to either shut in the whole well where fracturing took place or to selectively open one or more locations for production through the liner and into a production string (not shown). The resulting method described above saves the cost of cementing and the cost of annulus barriers and allows the entire process to the point of the fracturing job to be done in less time than the prior methods such as those described in  FIGS. 1 and 2 . 
     While telescoping assemblies are discussed as the preferred embodiment other designs are envisioned that can effectively span the gap of the surrounding annulus in a manner to engage the formation in a manner that facilitates pressure transmission and reduces pressure or fluid loss into the surrounding annulus. Those skilled in the art will appreciate that the above described method is focused on well consolidated formations where hole collapse is not a significant issue. In other applications, described below, the bottom hole assembly will also feature a swelling material or a shape memory polymer to fill the surrounding annular space  126  described above and left open in the above described embodiment. 
     One alternative to extending the assemblies  116  hydraulically is to do it mechanically. As shown as  130  in  FIG. 5 , the telescoping units are retracted into the casing so as not to extend beyond its outside diameter  132  when installed. When sliding sleeve  134  shifts in  FIG. 5   b , such as when ball  138  lands on seat  140  the sliding sleeve  134  has a taper  136  which applies mechanical force onto the telescoping units  130  and extends them to touch the formation as shown as  131 . Although a sliding sleeve is preferred, any mechanical devices can be used to mechanically extend the telescoping units. One example, shown in  FIGS. 6   a  and  6   b , is to use a running string  142  with collapsible pushers  144  to push out the telescoping units as shown in  FIGS. 6   a  and  6   b . The pushers can be extended with internal pressure or by another means. In this case, a closure device is optional. 
     Another alternative to pushing out the assemblies  116  with pressure using telescoping components is to incorporate expansion of the liner  104  to get the assemblies to the surrounding formation. This can be with a combination of a telescoping assembly coupled with tubular expansion. The expansion of the liner can be with a swage whose progress drives out the assemblies that can be internal to the liner  104  during run in. Alternatively, the expansion can be done with pressure that not only expands the liner but also extends the assemblies  116 . 
     Optionally, the leading ends of the outermost telescoping segment  122  can be made hard and sharp such as with carbide or diamond inserts to assist in penetration into the formation as well as sealing against it. The leading end can be castellated or contain other patterns of points to aid in penetration into the formation. 
       FIG. 7  is identical to  FIG. 3  but with one major difference. There are still a plurality of spaced apart fracturing assemblies  108  that have valves  110  telescoping assemblies  116 . In  FIGS. 7-10  there are sealing members  200  that have a small dimension for run in as shown in  FIG. 7  and that grow in the borehole  202  until they seal it off. The annular spaces  126  shown in  FIG. 7  are closed off in  FIG. 8  as the sealing members get larger preferably by swelling. The sealing members  200  can swell in the presence of well fluids such as hydrocarbons when they are made of rubber, for example. They can also incorporate a cover that delays the swelling to allow time to get the assembly into position in the wellbore. These covers can be dissolved by well fluids for example. The sealing members  200  can also be formed from a shape memory polymer that in the presence of well fluids or heat artificially added with a heater or by inducing a chemical reaction that is exothermic, for example and all schematically represented by arrow  204 , will swell to seal the annular spaces  126 . In this manner a very expensive cement job can be avoided. In formations where it is beneficial to seal the annular space apart from the access locations to the formation from assemblies  108 , the use of the members  200  is an economical way to seal without the cost and logistical issues involved in a cementing job. This is an even more significant factor in offshore wells where the logistics of conducting a cementing job grow far more complex and therefore expensive. 
       FIG. 9  shows one set of the telescoping members  116  extended as the fracturing starts in the manner described above, while  FIG. 10  illustrates all the telescoping assemblies  116  extended and the annular space  126  sealed by members  200  with breaks around the extended telescoping assemblies  116 . 
     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: