Abstract:
A valve for use in fracing through cement casing in a well allows for flow of cement down the well during the cementing process and in the open position allows for fracing fluid to be directed through the cement casing for fracturing the formation adjacent the valve. The valve is constructed so as to reduce the likelihood of the valve to jam as a result of cement or other foreign material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of co-pending U.S. patent application Ser. No. 13/223,909, entitled “Valve for Hydraulic Fracturing Through Cement Outside Casing”, filed Sep. 1, 2011, in the name of the inventors Michael Sommers and Stephen Jackson. The earlier effective filing date of that application is hereby claimed pursuant to 35 U.S.C. §120.That application is also hereby incorporated by reference for all purposes as if set forth herein verbatim. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention is directed to a valve utilized for hydraulically fracturing multiple zones in an oil and gas well without perforating the cement casing. A relatively new oil/gas well completion method involves the use of a valve that is installed as pan of the easing string of the well and provides for cement flow within the casing when the valve element is in a closed position and allows for axial flow of fracturing fluid through the cement casing to fracture the formation near the valve. The invention disclosed herein is an improved valve used in this process. 
     2. Description of Related Art 
     Current designs for valves used in the completion method disclosed above are prone to failure because cement or other debris interferes with the opening of the valve after the cementing process has been completed. Portions of the sliding sleeve or pistons commonly used are exposed to either the flow of cement or the cement flowing between the well bore and the casing string. 
     SUMMARY OF THE INVENTION 
     The valve according to the invention overcomes the difficulties described above by isolating a sliding sleeve between an outer housing and an inner mandrel. A rupture disk in the inner mandrel ruptures at a selected pressure. Pressure will then act against one end of the sliding sleeve and shift the sleeve to an open position so that fracturing fluid will be directed against the cement casing. The sliding sleeve includes a locking ring nut to prevent the sleeve from sliding back to a closing position. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of the valve according to one embodiment of the invention. 
         FIG. 2  is a cross sectional view of the valve in the closed position taken along line  2 - 2  of  FIG. 1   
         FIG. 3  is a cross sectional view of the valve taken along line  3 - 3  of  FIG. 2   
         FIG. 4  is a cross sectional view of the sliding sleeve 
         FIG. 5  is a cross sectional view of the locking ring holder 
         FIG. 6  is a cross sectional view of the locking ring 
         FIG. 7  is an end view of the locking ring 
         FIG. 8  is a cross sectional view of the valve in the open position 
         FIG. 9  is an enlarged view of the area circled in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , an embodiment of valve  10  of the invention includes a main housing  13  and two similar end connector portions  11 ,  12 . 
     Main housing  13  is a hollow cylindrical piece with threaded portions  61  at each end that receive threaded portions  18  of each end connector. End connectors  11  and  12  may be internally or externally threaded for connection to the casing string. As show in  FIG. 2 , main housing  13  includes one or more openings  19 , which are surrounded by a circular protective cover  40 . Cover  40  is made of a high impact strength material. 
     Valve  10  includes a mandrel  30  which is formed as a hollow cylindrical tube extending between end connectors  11 ,  12  as shown in  FIG. 2 . Mandrel  30  includes one or more apertures  23  that extend through the outer wall of the mandrel. Mandrel  30  also has an exterior intermediate threaded portion  51 . One or more rupture disks  41 ,  42  are located in the mandrel as shown in  FIG. 3 . Rupture disks  41 ,  42  are located within passageways that extend between the inner and outer surfaces of the mandrel  30 . Annular recesses  17  and  27  are provided in the outer surface of the mandrel for receiving suitable seals. 
     Mandrel  30  is confined between end connectors  11  and  12  by engaging a shoulder  15  in the interior surface of the end connectors. End connectors  11  and  12  include longitudinally extending portions  18  that space apart outer housing  13  and mandrel  30  thus forming a chamber  36 . Portions  18  have an annular recess  32  for relieving a suitable seal. A sliding sleeve member  20  is located within chamber  36  and is generally of a hollow cylindrical configuration as shown in  FIG. 4 . The sliding sleeve member  20  includes a smaller diameter portion  24  that is threaded at  66 . Also it is provided with indentations  43  that receive the end portions of shear pins  21 . Sliding sleeve member  20  also includes annular grooves  16  and  22  that accommodate suitable annular seals. 
     A locking ring holder  25  has ratchet teeth  61  and holds locking ring  50  which has ratchet teeth  51  on its outer surface and ratchet teeth  55  on its inner surface shown in  FIG. 9 . Locking ring  50  includes an opening at  91  as shown in  FIG. 7  which allows it to grow in diameter as the sliding sleeve moves from the closed to open position. 
     Locking ring holder  25  has sufficient diameter clearance so that the locking ring can ratchet on the mandrel ratcheting teeth  63  yet never loose threaded contact with the lock ring holder. Locking ring holder  25  is threaded at  26  for engagement with threads  24  on the mandrel. Locking ring holder  25  also has a plurality of bores  46  and  62  for set screws, not shown. 
     In use, valve  10  may be connected to the casing string by end connectors  11 ,  12 . One or more valves  10  may be incorporated into the easing string. After the casing string is deployed within the well, cement is pumped down through the casing and out the bottom into the annulus between the well bore and the casing as typical in the art. After the cement flow is terminated, a plug or other device is pumped down to wipe the casing and valve clean of residual cement. When the plug or other device has latched or sealed in the bottom hole assembly, pressure is increased to rupture the rupture disk at a predetermined pressure. The fluid pressure will act on sliding sleeve member  20  to cause the shear pins to break and then to move it downward or to the right as shown in  FIG. 7 . This movement will allow fracing fluid to exit via opening  23  in the mandrel and openings  19  in the outer housing. The fracing fluid under pressure will remove protective cover  40  and crack the cement casing and also fracture the foundation adjacent to the valve  10 . 
     Due to the fact that the sliding sleeve member  20  is mostly isolated from the cement flow, the sleeve will have a lessor tendency to jam or require more pressure for actuation. 
     In the open position, locking ring  50  engages threads  63  on the mandrel to prevent the sleeve from moving back to the closed position. 
     A vent  37  is located in the outer housing  13  to allow air to exit when the valve is being assembled. The vent  37  is closed by a suitable plug after assembly. 
     Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.