Patent Publication Number: US-2003221824-A1

Title: Downhole isolation device with retained valve member

Description:
FIELD OF THE INVENTION  
       [0001] The field of this invention is downhole isolation devices and more specifically those devices that permit flow to the surface and are removable by milling or drilling.  
       BACKGROUND OF THE INVENTION  
       [0002] In certain downhole operations, it is desirable to isolate a portion of the wellbore. This can occur when perforation a zone in a cased borehole. Another occasion is when fracturing a formation through a set of perforations in one zone and having to isolate the remainder of the wellbore from the applied pressures of that procedure. Usually, these barriers are temporary and need to be removed from the wellbore when a perforating or fracturing operation is concluded. For these reasons, these devices have been made with non-metallic materials to enhance drillability.  
       [0003] In the past, these devices have had a passage through them to permit flow toward the surface. When isolation between zones was needed, a ball was dropped from the surface to land on a seat in the isolation device and pressure was built up on the seated ball. There were two main disadvantages to this design. Even if the ball was run with the isolation device instead of being dropped in later the mill-out was problematic because the ball could rotate on the seat during the milling. So even though the isolation device was predominantly of non-metallic materials, the milling process was still prolonged. The other issue with the prior designs was that the ball was not retained to the isolation device so that flow towards the surface could bring the ball out with it and get it stuck in the blowout preventers, creating a safety concern. An example of this type of design is the FAS DRILL Bridge Plug offered by Halliburton. Other prior designs for zone isolation involved flapper type valves held open with a stinger or sliding sleeve designs operated with a stinger.  
       [0004] The present invention seeks to address the issue and solve the problems associated with the known devices. It comprises a non-spherical valve member that will not rotate during mill-out. The valve member is also retained so that it will not be carried uphole to wind up in the blowout preventers. Non-metallics are used to promote drillability. A plurality of the isolators of the present invention can be used and milled out after all the zones have been completed. These and other benefits of the present invention will be apparent to those skilled in the art from a review of the description of the preferred embodiment described below.  
       SUMMARY OF THE INVENTION  
       [0005] A downhole zone isolation device is disclosed that features a non-spherical valve member that will not rotate while being drilled out. The valve member is retained in the isolation device so that flow uphole will not allow the valve member to exit the body of the isolation device. Bypass passages around the valve member are provided so that flow uphole can lift the valve member off its seat and flow can go around its periphery. Pressure from above seats the valve member. Non-metallic materials speed drill-out. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0006]FIG. 1 is a section of the isolation device with the valve member in the seated position;  
     [0007]FIG. 2 is a section of a portion of the isolation device showing the valve member off the seat during flow uphole;  
     [0008]FIG. 3 is a section view along lines  3 - 3  of FIG. 2, showing the bypass flow passages and how the valve member is constrained against rotation.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0009] Referring to FIG. 1, the apparatus A can have the components of known bridge plugs or packers by way of a body  10 , slips  12  and a sealing element  14 . FIG. 1 illustrates the set position downhole against a casing  16 . A passage  18  extends through body  10 .  
     [0010] The present invention comprises a plug  20  movably mounted in passage  18 . A travel stop  22  which can be one or more pins, a shoulder or any other obstruction, prevents plug  20  from being driven out of body  10  when uphole flow occurs through passage  18 . Passage  18  has a plug seat  24  located within body  10 . The seat  24  location is to be contrasted with prior devices that used a dropped ball. These devices had the seat at the very top of the passage such as  18 , making mill-out difficult, as the ball would spin on the seat in response to the operation of the mill. In the present invention, the seat  24  is within the body  10 , which is preferably made of a non-metallic such as, laid up fiberglass. The plug  20  is preferably a molded phenolic compound although other soft materials for the body  10  and the plug  20  could be used. During mill-out, the plug  20  is so far into the body  10  that milling the body  10  will distort it dimensionally to a degree sufficient to prevent the plug from rotating by the time the bit or mill reaches it.  
     [0011] The passage  18  accommodates uphole flow by the use of lobes  26 , shown in FIG. 3. These lobes  26  form flow passages around plug  20  when uphole flow forces it off the seat  24  and against travel stop  22 . Although  3  lobes are shown a different quantity may be used or some other flow path can be used to permit uphole flow as long as that flow path is closed when the plug  20  is seated on seat  24 .  
     [0012] Optionally, the plug  20  may be biased away from seat  24 . Those skilled in the art will appreciate that plug  20  is delivered into the well inside body  10  as is movably retained therein by travel stop  22 . The present invention prevents the escape of plug  20  during uphole flow, keeping it out of the blowout preventers (not shown). The use of soft nonmetallic material for the body  10  and the placement of seat  24  within passage  18  provides a mechanism to rotationally lock the plug  20  when milling out. This happens because the body  10  collapses around passage  18  by the time the mill reaches plug  20 . Additional protection against relative rotation can be obtained by making surface  28  and seat  24  have an undulating or sinusoidal shape instead of a frusto-conical shape. The travel stop may be below the plug  20  as opposed to above it. The seat  24  can be near or at the top of the uphole end of passage  18 . The combination of a travel stop on the bottom of plug  20  and an undulating seating surface  24  allows the seat to be located near the uphole end of the body  10  without the mill-out problem associated with prior designs that used spheres on seats that were dropped from the surface. Additionally, the plug is retained to the body  10  even when the seat  24  is at or near the top. In this embodiment, the lobes  26  can be omitted as the plug  20  can rise out of body  10  while still held on the travel stop that is now below it. The travel stop can be a J-slot mechanism with the slot on the plug  20  and the pin extending into the passage  18 . The plug would then be free to go up or down but not rotate. The slot can be closed after admitting the pin so as to secure the plug  20  from escape from passage  18 . The pin can be on the plug and the slot on the passage to get the same result. Rotational locking of the plug  20  can be done with mating splines  30  that can be straight or helical in a direction opposite to the rotation of a mill or drill that would later be used to drill out.  
     [0013] 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: