Abstract:
A method for completing a wellbore having a plurality of stimulation valves disposed therein at longitudinally spaced apart locations includes moving a spoolable rod into the wellbore. The rod includes a plurality of spaced apart sensors therein. At least one valve operating dart is applied to an exterior of the spoolable rod. The dart is configured to engage a selected one of the stimulation valves. A position of the at least one dart is estimated during pumping of fluid into the wellbore by measuring output of the sensors in the rod.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to the field of wellbore based reservoir stimulation operations. More specifically, the invention relates to methods for wellbore intervention during reservoir stimulation through the wellbore. 
       BACKGROUND ART 
       [0002]    To increase productivity of oil and/or gas wells, hydraulic stimulation (fracturing) is typically used. One method of fracturing in wells including a plurality of depth-separated producing formations includes installation of stimulation valves, so-called “frac sleeves”, adjacent to each of the formations to be stimulated by fracturing. The fracturing is performed by pumping fluid within a string of casing or tubing installed in the wellbore. A typical well completion configuration is shown in  FIG. 1A  for multiple formations  17  each having an associated frac sleeve.  FIG. 1B  shows a ball  13  which is used to open the frac sleeve  10  having been inserted into the sleeve  10  in a selected position in the casing or tubing  12 . 
         [0003]    Each of the valves or frac sleeves wherein a plurality of such frac sleeves is used, can be opened by dropping a matching or mating ball ( 13  in  FIG. 1B ) or “dart” into the casing from the Earth&#39;s surface, and then pumping the ball or dart down the well until the ball seats in a profile in the frac sleeve to be opened. Pressurizing the well from surface further after engagement of the ball or dart with the profile forces the ball or dart downward, which results in opening a valve in the frac sleeve. After the valve is opened, fluid is injected into the particular formation through the opened valve, as shown in  FIG. 1B . 
         [0004]      FIG. 1B  also illustrates zonal isolation devices  14  disposed between the frac sleeves. Such devices can be packers or similar annular sealing devices. Also the entire string of tubing or casing with frac sleeves disposed therein can be cemented in place in the wellbore, where the cement creates a fluid tight barrier between the various formations. 
         [0005]    Because it is desirable to monitor in real time the stimulation process in the wellbore, which can be performed for example, using longitudinally distributed sensors such as temperature sensors, pressure sensors, acoustic sensors, etc., it is desirable to be able to use a device having such sensors thereon that is compatible with pumping darts or balls into the wellbore. 
         [0006]    A method for completing a wellbore according to one aspect of the invention, where the wellbore has a plurality of stimulation valves disposed therein at longitudinally spaced apart locations, includes moving a spoolable rod into the wellbore. The rod includes a plurality of spaced apart sensors therein. At least one valve operating dart is applied to an exterior of the spoolable rod. The dart is configured to engage a selected one of the stimulation valves. A position of the at least one dart is estimated during pumping of fluid into the wellbore by measuring output of the sensors in the rod. 
         [0007]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIGS. 1A and 1B  shows a typical wellbore completion where a number of zonal isolation packers and ball-drop operated sleeves are utilized. 
           [0009]      FIG. 2  shows a first dart dropped and landed in stimulation valve (“frac sleeve”), where dart opens valve by pressurizing tubing from surface. 
           [0010]      FIG. 3  shows dropping second dart into the wellbore. 
           [0011]      FIG. 4  shows using a selective locating system on the darts that matches similar profiles in the stimulation valves (“frac sleeves”). 
           [0012]      FIGS. 5A and 5B  show example selective profiles. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    A semi stiff, spoolable rod system containing sensing fibers and/or electrical cable(s) for sensing has been developed and demonstrated by the assignee of the present invention. Such spoolable rod is used to provide services under the service mark ZIPLOG, which is a service mark of the assignee of the present invention. The system is based on pushing the spoolable rod into producing and/or fluid injection wellbores. The spoolable rod is typically disposed on a reel or winch and is pushed inside a tubing string (production tubing) inserted into the well coaxially with the wellbore casing by operating the winch. By having sensing elements, for example, optical fiber temperature and/or pressure sensing elements, at spaced apart positions incorporated into the spoolable rod, it is possible to provide real time data to the surface about well conditions during production, injection and shut-in. The foregoing spoolable rod to provide ZIPLOG services includes such sensing elements. See the Uniform Resource Locator http://www.ziebel.biz/ziplog.htm. 
         [0014]    Referring to  FIG. 2 , the spoolable rod  20  is deployed into a casing  12  cemented in a wellbore  18  and past one or more of the stimulation valve(s)  10  (which can be frac sleeves as described in the Background section herein). Prior to inserting the spoolable rod  20 , one or more darts or balls  16  of suitable dimension can be mounted externally on the rod  20  at the Earth&#39;s surface. The darts or balls  16  are mounted into a system at the surface where the operator is able to release them when and as required. Then, the darts or balls  16  are released, and fluid can be pumped into the casing  12  from the surface. The darts or balls  16  are then pushed into the casing  12  by the pumped fluid. The darts or balls  16  will move along the outer surface of the rod  20  into the casing  12  until they land in a matching one of the stimulation valves  10  (frac sleeves). As each dart or ball  16  reaches the matching stimulation valve  10  it stops at a shoulder or “no-go” (see  FIGS. 5A and 5B ) formed into the interior surface of the valve  10 . Further fluid pressurizing the casing  12  from the surface pushes the dart or ball  16  downward against the shoulder or no-go ( FIGS. 5A and 5B ), resulting in shifting a sleeve in the stimulation valve  10 , causing the stimulation valve  10  to open. Opening the stimulation valve  10  enables fluids to be pushed out into the rock formation ( 17  in  FIG. 1A ) adjacent to the stimulation valve  10  from within the casing  12 . 
         [0015]    The dart&#39;s or ball&#39;s  16  position along the exterior of the spoolable rod during pumping into the wellbore can be estimated during fluid pumping by measuring the amount of fluid pumped in, or by cooling of the spoolable rod  20 . Cooling of the rod  20  can be estimated or monitored by measurements from distributed temperature sensors  19  in the spoolable rod  20 , as well as by acoustic detection (using suitable pressure sensors incorporated into the rod  20 ) of the dart or ball  16  traveling into the casing  12 . The fluids pumped into the casing  12  typically have a different temperature than exists at many depths within the wellbore; therefore, temperature measuring along the spoolable rod  20  will generally suffice to indicate the position of the fluids moving down into the casing  12  from the surface. 
         [0016]      FIG. 3  shows an example of how more balls or darts  16  can be pumped into the wellbore to a valve placed shallower than a valve used earlier. One drawback of a fixed diameter shoulder or no-go as a landing place for the dart or ball as described above is that the balls or darts must become successively smaller in diameter (toward the bottom of the well) as more stimulation valves are included in a particular completion. Such diameter limitation is a result of the fact that in order for a dart or ball to reach a valve at greater depth than other valves in the wellbore, the dart or ball must be able to freely pass through all the shallower placed stimulation valves. The foregoing may result in very small internal diameter in the lowermost valves, and can cause the available internal diameter to be insufficient for deploying a well logging tool or similar device through the lowermost valve(s), or may limit the effective flow rate of the stimulation fluid. 
         [0017]      FIG. 4  illustrates an alternative to the above described no-go or shoulder in each stimulation valve  10 . In the example of  FIG. 4 , each stimulation valve  10  can have the same internal diameter. A locating profile (see  FIGS. 5A and 5B ) having a unique shape as compared to that in the other stimulation valves in the wellbore, a so called “selective profile”, can be implemented in each stimulation valve sleeve shifting device. The darts  16  each have a matching locating profile for only one of the stimulation valves  10 . Each dart  16  will land and position itself only in the one valve  10  having the matching landing profile. Using such a dart and stimulation valve configuration, a plurality of valves can be installed in the wellbore without having internal diameter changes. 
         [0018]      FIG. 5A  illustrates examples of selective profiles on the darts can be used with stimulation valves in the well having matching profiles. The profile shown at in  FIG. 5A  if applied to the exterior of a dart will not engage in a receiving profile on a valve having shape shown in  FIG. 5B , but only in a profile having the shape shown in  FIG. 5A . The same is the case for a profile having the shape in  FIG. 5B , which will only engage in a matching shaped profile. Each stimulation valve can have a unique landing profile so that a correspondingly shaped dart will only engage in such valve. 
         [0019]    During fluid pumping operations, as explained above, distributed temperature and/or pressure sensors included in the spoolable rod ( 20  in  FIG. 2 ) may be used to monitor progress of the fluid as it is pumped into the casing ( 12  in  FIG. 2 ). Upon completion of wellbore stimulation, the well can be opened for production whereupon the darts will be transported by fluid production to the surface. Alternatively, the spoolable rod ( 20  in  FIG. 2 ) can be pulled out of the casing ( 12  in  FIG. 2 ), bringing all the darts  16  to the surface. 
         [0020]    A completion system as explained above may have stimulation valves all having substantially the same interior diameter, and may include the capability of estimating progress of fluid pumped into the wellbore during pumping operations. 
         [0021]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.