Abstract:
A system and method for more efficiently stimulating and producing from a production string. The present invention comprises production tubing; at least one selectively-openable valve assembly located inline with the production tubing; and at least one flapper valve assembly located inline with the production tubing. One flapper valve assembly is associated with each selectively-openable valve assembly. The flapper valve assembly is orientated to impede fluid flow in the downwell direction when closed.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 61/305,325 filed Feb. 17, 2010 and entitled Multistage Production System and Method, which is incorporated by reference herein. 
     
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a system for producing hydrocarbons from multiple stages in a hydrocarbon production well. More specifically, the present invention relates to a multistage production system that associates a flapper valve assembly with each production valve assembly in the multistage system. 
         [0005]    2. Description of the Related Art 
         [0006]    During stimulation of a production zone (e.g., fracing) using a system incorporating multiple selectively-openable valve assemblies, the valve assembly furthest downwell is opened first with a shifting tool and a fracing material thereafter forced into the surrounding formation. The valve assembly is then closed and positive-pressure tested to insure system integrity before repeating the operation at the next upwell stage of the system. Positive pressure testing insures that the kinetic energy of the fracing material (i.e., fluid velocity) is concentrated at a single stage rather than egressing through another open (or partially open) stage. Focusing the kinetic energy of the fracing material at a single stage allows the fracing material to penetrate deeper into the formation, which results in greater effectiveness. 
         [0007]    This process is repeated at each stage (i.e., through each valve) until the regions of the formation adjacent each of the stages have been stimulated. After this zonal stimulation, a shifting tool is again run through the production tubing and the valve assemblies are opened for production. This process, however, is time-consuming, and therefore expensive. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is a system and method for more efficiently and quickly producing from a production string. The present invention comprises production tubing; at least one selectively-openable valve assembly located inline with the production tubing; and at least one flapper valve assembly located inline with the production tubing. One flapper valve assembly is associated with each selectively-openable valve assembly. The flapper valve assembly is orientated to impede fluid flow in the downwell direction when closed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a partial sectional view of a well with a cemented open hole fracing system located in a producing zone. 
           [0010]      FIG. 2  is a partial sectional view of the production string of  FIG. 1  showing a tooling string disposed through two sets of valve assemblies. 
           [0011]      FIG. 3  is a partial sectional view of the production string of  FIG. 1  showing a tooling string disposed through one valve assembly after having opened a another valve assembly. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  shows a multistage production system having the features of the present invention. A production well  10  is drilled in the earth  12  to a hydrocarbon production zone  14 . A casing  16  provides structural stability to the vertical portion of the borehole and is held in place in the production well  10  by cement  18 . A liner hanger  22  is located at the lower end of the casing  16 . A length of production tubing  24  is connected to the liner hanger  22  and orientated to extend into the production zone  14  through the lateral portion of the borehole. 
         [0013]    A number of selectively-openable sliding valve assemblies  28   a - 28   c  and flapper valve assemblies  30   a - 30   c  are positioned inline with the production tubing  24 . Each of the flapper valve assemblies  30   a - 30   c  is associated with and positioned upwell from one of the corresponding sliding valve assembly  28   a - 28   c —that is, the first flapper valve assembly  30   a  is associated with and positioned upwell from the first sliding valve assembly  28   a,  the second flapper valve assembly  30   b  is associated with and positioned upwell from the second sliding valve assembly  28   b,  and the third flapper valve assembly  30   c  is associated with and positioned upwell from the third sliding valve assembly  28   c.  Each of the flapper valve assemblies  30   a - 30   c  is orientated to block fluid flow in the downhole direction when closed. While the preferred embodiment discloses three sliding valve assemblies  28   a - 28   c,  more or fewer sliding valve assemblies may be used. The entire production tubing  24 , sliding valve assemblies  28   a - 28   c,  and flapper valve assemblies  30   a - 30   c  are surrounded with cement  32 . Each of the selectively-openable sliding valve assemblies  28   a - 28   c  is mechanically actuatable with a shifting tool. U.S. Pat. No. 7,267,172 (issued Sep. 10, 2007) to Hofman describes one such specific embodiment of a mechanically actuatable shifting tool. 
         [0014]      FIG. 2  and  FIG. 3  more clearly illustrate the portion of the production tubing  24  shown in  FIG. 1  that includes the second and third sliding valve assemblies  28   b,    28   c  and second and third flapper valve assemblies  30   b,    30   c.  The flapper valve assemblies  30   b,    30   c  each include a flapper plate  31   b,    31   c  moveable between an opened and closed position. In  FIG. 2 , each of the flapper plates  31   b,    31   c  is in an open position to allow flow through the production tubing  24 . In  FIG. 3 , the second flapper plate  31   b  is open to permit downwell fluid flow and the third flapper plate  31   c  is closed to inhibit fluid flow in the downwell direction. 
         [0015]    To initiate zonal stimulation, a shifting string  34  is run down the production tubing  24  with a first tool  36  adapted for actuating the flapper valve assemblies  30   a - 30   c  and a shifting tool  38  for opening the sliding valve assemblies  28   a - 28   c.  Prior to running the shifting string  34 , each of the flapper valve assemblies  30   a - 30   c  is closed. The first tool  36  actuates the first flapper valve assembly  30   a  (see  FIG. 1 ), after which the shifting string  34  may be run through the first sliding valve assembly  28   a  (see  FIG. 1 ) and to the second flapper valve assembly  30   b.  Thereafter, the first tool  36  actuates the second flapper valve assembly  30   b  and third flapper valve assembly  30   c  in order that the shifting tool  38  may be caused to actuate the third sliding valve assembly  28   c.  ( FIG. 2 ) The third sliding valve assembly  28   c  is then actuated to provide a flow path between the production tubing  24  and surrounding cement  32  and production zone  14 . ( FIG. 2 ) Fracing fluid  40  is then injected into the region  42  of the production zone  14  adjacent the third sliding valve assembly  28   c.    
         [0016]    After stimulation of the adjacent region  42  causing fracturing  44  of the production zone  14  proximal to the third valve assembly  28   c,  the shifting string  34  is positioned upwell to the second sliding valve assembly  28   b.  ( FIG. 3 ) After sliding the shifting string  34  upwell from the portion of production tubing located downwell from the third flapper valve assembly  30   c,  the third flapper plate  31   c  closes to prevent fluid flow in a downwell direction past its position within the production tubing  24 . The third sliding valve assembly  28   c  remains open to the surrounding production zone  14 . This same process is repeated with the second sliding valve assembly  28   b  and first sliding valve assembly  28   a  respectively, such that after all zonal stimulation the sliding valve assemblies  28   a - 28   c  remain open and all flapper plates  31   a - 31   c  remain closed. 
         [0017]    The present invention is described in terms of preferred embodiments in which a specific system and method are described. For example, while the present invention is described with respect to a cemented open lateral hole, the present invention can also be used in a cased vertical hole. Those skilled in the art will recognize that alternative embodiments of such system, and alternative applications of the method, can be used in carrying out the present invention. Other aspects and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims. Moreover, the recited order of the steps of the method described herein is not meant to limit the order in which those steps may be performed.