Patent Abstract:
A valve for use in a tool positioned in a well that includes a body having a bore and a port connected to permit fluid communication between the well and the bore. A piston is supported in the body for movement between an open position to open the port and a closed position to close the port. A rupture disc is responsive to fluid pressure in the well and ruptures when a predetermined pressure is applied so that fluid pressure is communicated to the piston to move it from the closed position to the open position. A lock member secures the piston in the closed position after the piston moves from the open position to the closed position.

Full Description:
This claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/074,493, entitled “Reclosable Circulating Valve for Well Completion Systems,” filed Feb. 12, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     In the completion of wells drilled into subterranean formations, a casing string is normally run into the well and cemented to the wall of the well. Then perforating guns are used to create perforation tunnels through the casing. The perforation tunnels are created adjacent the formation at pay zones to allow fluids, such as oil or gas, to flow from the formation into the well. 
     During the well completion phase, a fracture operation may be used to increase the permeability of the formation. A fracture operation typically involves lowering a work string to a point adjacent the formation to be fractured, i.e. near the perforation tunnels. Then fracturing fluid is pumped out of the lower end of the work string and into the perforation tunnels at a pressure sufficient to cause the bedding planes of the formation to separate. This separation of the bedding planes creates a network of permeable fractures through which formation fluid can flow into the well after completion of the fracture operation. 
     The fractures have a tendency to close once the fracture pressure is relaxed. Thus, proppants (e.g. sand, gravel, or other particulate material) are routinely mixed with the fracturing fluid to form a slurry which carries the proppants into the fractures where they remain to prop the fractures open when the pressure is reduced. A condition referred to as screen-out may occur when a portion of the proppants comes out of the perforation tunnels and fills up the annular space between the casing and the work string. Screen-out can occur more than once during a fracture operation. 
     Whenever screen-out occurs or after the fracture operation is completed, it is necessary to circulate the fracturing fluid out of the work string. Typically, a mechanical valve with multiple open/close capability is required to permit circulation of the fracturing fluid out of the work string. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect, the invention features a valve for use in a tool positioned in a well that includes a body having a bore and a port connected to permit fluid communication between the well and the bore. A piston is supported in the body for movement between an open position to open the port and a closed position to close the port. A rupture disc is responsive to fluid pressure in the well and ruptures when a predetermined pressure is applied so that fluid pressure is communicated to the piston to move it from the closed position to the open position. A lock member secures the piston in the closed position after the piston moves from the open position to the closed position. 
     Other features will become apparent from the following claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic of a well completion system in which an embodiment of the invention is used. 
     FIGS. 2A-2B are vertical cross-sectional views of a circulating valve in respective first and second positions according to an embodiment of the invention. 
     FIG.3 is a horizontal cross-section view of a portion of the circulation valve; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings wherein like characters are used for like parts throughout the several views, FIG. 1 depicts a well completion system  10  which includes a wellbore  12  extending from the surface (not shown) through a fracture zone  14 . Lining the wellbore  12  is casing  16  which is held in place by a cement sheath  18 . The casing  16  and the cement sheath  18  are provided with a plurality of perforations  20  which are aligned to define perforation channels  22  through which fluids may flow into or out of the formation adjacent to the wellbore  12 . While the wellbore  12  is shown as a cased, vertical wellbore, it should be clear that the invention is equally applicable in open, underreamed, horizontal, and inclined wellbores. 
     A downhole tool  26  positioned in the wellbore  12  includes a tubing string  28  which extends from the surface (not shown) to the fracture zone  14 . The tubing string  28  is concentrically received in the wellbore  12  such that an annular passage  30  is defined between the inner wall  32  of the casing  16  and the outer wall  34  of the tubing string  28 . Packers  36 ,  39  are set in the annular passage  30  to isolate the section of the wellbore  12  which lies adjacent the fracture zone  14 . Packer  36  divides the annular passage  30  into an upper annular passage  38  and a lower annular passage  40 . The downhole tool  26  includes a circulation valve  42  which may be actuated to permit fluid communication between the inside of the tubing string  28  and the upper annular passage  38 . 
     The tubing string  28  can be divided in two segments, with an upper segment  58  connected to the upper end of the circulating valve  42  and the bottom segment  62  connected to the lower end of the valve  42 . 
     In operation, fracturing fluid with proppants is pumped down the bore of the tubing string  28 . The circulation valve  42  is maintained in the closed position so that the fracturing fluid pumped down the bore of the tubing string  28  exits the lower end of the tubing string and rises up the lower annular passage  40 . As the lower annular passage  40  fills with the fracturing fluid, the fracturing fluid is forced into the perforation channels  22  to initiate fractures in the formation. As more fluid is pumped down the bore of the tubing string  28 , the fractures are enlarged. 
     Eventually a point of screen-out is reached at which a portion of the proppants come out of the perforation channels and fills the lower annular passage  40  surrounding the bottom segment  62  of the tubing string  28 . When screen-out occurs, pumping more fracturing fluid will only further exert pressure on the formation. Proppants will also build up in the tubing string  28 . 
     When screen-out occurs, the proppants can be removed by circulating the fracturing fluid out of the tubing string  28 . To accomplish this, fluid is pumped from the surface through the upper annular passage  38  between the casing  16  and tubing string  28 . When the flow reaches a predetermined pressure, the circulation valve  42  opens to allow the fluid in the upper annular passage to flow into the tubing string  28 . The fluid flowing into the tubing string  28  then pushes the fracturing fluid (along with the proppants) up the tubing string  28  to the surface. The same operation can also be performed in conditions other than screen-out, such as after completion of the well. 
     Referring to FIGS. 2A-2B, and  3  the circulating valve  42  includes a housing body  50  having a top portion  52  which is threadably connected to a bottom portion  54 . The upper end of the top portion  52  includes a threaded receptacle  56  for connecting to the upper segment  58  of the tubing string  28  (shown in FIG.  1 ). The lower end of the bottom portion  54  includes a threaded stub  60  for connecting to the lower segment  62  of the tubing string  28  (shown in FIG.  1 ). The housing body  50  is provided with a throughbore  64  which permits fluid communication between the upper segment  58  and the lower segment  62  of the tubing string  28 . 
     In the top portion  52  of the housing body  50  is a pocket  65  in which a rupture disc  66  is mounted. The rupture disc  66  is exposed to the casing pressure, i.e., the pressure in the upper annular passage  38 , through a port  68  at the outer edge of the pocket  65 . The inner edge  70  of the pocket  65  is connected to a port  72  which opens to the interior of the housing body  50 . The top portion  52  of the housing body  50  also includes circulating ports  74  which may communicate with the throughbore  64 . 
     A mandrel  80  disposed inside the housing body  50  is held in place in the housing body by a collet  82  which is mounted on a collar ring  84  in the bottom portion  54  of the housing body  50 . The mandrel  80  can be movable up and down by fluid pressure relative to the housing body  50 . The mandrel  80  includes a bore  86  which is coincident with the throughbore  64  of the housing body  50 . In its up position as shown, the mandrel  80  closes the circulating ports  74  such that fluid communication between the upper annular passage  38  and the throughbore  64  is prevented. Sealing rings  106  are seated in slots in the mandrel  80  to seal the circulating port  74 . 
     A mandrel lock  90  that includes radial segments  92  is engageable in a groove  94 , as shown in FIG. 2B in the bottom portion  54  of the housing body  50 . The radial segments  92  are held in place against the end wall  96  of the groove  94  by screws  98 . The mandrel lock  90  also includes garter springs  99  which are arranged to force the lock  90  radially inward to engage the mandrel  80  when the screws  98  are sheared. Once the screws are sheared, the lock  90  can snap into a locking groove  100  in the mandrel  80  to permanently maintain the mandrel  80  in a closed position, i.e. a position where the mandrel  80  covers the circulating ports  74 . 
     The rupture disc  66  prevents casing pressure from acting on the mandrel  80  until the disc  66  is burst by applying a predetermined pressure on the casing. When the rupture disc  66  bursts, casing pressure is communicated to the pressure surface  112  through the port  72 . The casing pressure acts on the pressure surface  112  to push the mandrel  80  downwardly until a shoulder  114  on the mandrel  80  lands on the mandrel lock  90  and shears the screws  98 . When the mandrel  80  moves downwardly, the circulating ports  74  are uncovered to permit fluid to flow into the throughbore  64  and up the tubing string  28 . 
     In operation, the circulating ports  74  are initially closed by the mandrel  80 , which is in its up position. Fluid pumped into the tubing string  28  from the surface passes through the bore  86  of the mandrel to the lower segment  62  of the tubing string where it exits into the lower annular passage  40 . When it is desired to move a fluid mixture out of the tubing string  28 , fluid is pumped down the upper annular passage  38 . The rupture disc  66  is exposed to the fluid pressure in the upper annular passage  38 . The rupture disc  66  bursts when the fluid pressure in the upper annular passage  38  reaches a predetermined rupture pressure. 
     When the rupture disc  66  bursts, fluid flows into the port  72  to the pressure surface  112  of the mandrel  80  to apply pressure on the mandrel  80 . The fluid pressure acts on the mandrel  80  and moves the mandrel  80  down to uncover the circulating ports  74 . At the end of the downward stroke of the mandrel  80 , the mandrel shoulder  114  hits the lock segments  92  and, if sufficient force is applied, the screws  98  holding the segments  92  in the groove  94  are sheared. Once the screws  98  are sheared, the garter springs  99  move the lock  90  radially inward until the lock segments  92  are resting on the outer wall of the mandrel  80 . 
     To close the circulating ports  74 , a pressure differential between the inside of the tubing string  28  and the casing  16  is required to move the mandrel  80  up. This is achieved by pumping fluid at high rate into the tubing string  28 . The fluid pumped into the tubing string  28  exits through the circulating ports  74  into the upper annular passage  38 . The pressure loss across the circulating ports  74  creates the pressure differential required to move the mandrel up to close the circulating ports  74 . At the end of the upward stroke of the mandrel  80 , the lock segments  92  snap into the locking groove  100  and lock the mandrel  80  permanently in the closed position. 
     The fluid rate of the circulating ports  74  can be controlled by varying the diameter of the ports. A lower flow rate results in a lower pressure applied on the mandrel. 
     The opening of the valve does not depend on pressure differential and the rupture disc is exposed to absolute casing pressure. Therefore, accurate knowledge of fluid density or pressure at the valve is not critical. The inner wall of the mandrel can be made smooth to minimize susceptibility to erosion during very high rate large volume fracturing operations. 
     In an operation where it is desired to fracture multiple zones or where a valve with multiple open/close capability is required, multiple circulating valves may be used to circulate fluid out of the tubing string. The valves may be arranged in the upper section of the tubing string above the packer. The rupture disc of the different valves can be pre-set to burst at different casing pressures. 
     Although the circulation valve has been described with respect to fracturing operation during well completion, it should be clear that the circulation valve may be used in any downhole application where it is desired to recirculate fluid out of a flow conduit concentrically received in a wellbore. For instance the circulation valve may be used during a well clean-up operation or with a fracture/gravel-packing operation. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. The appended claims are intended to cover all such modifications and variations which occur to one of ordinary skill in the art.

Technology Classification (CPC): 4