Patent Publication Number: US-9422785-B2

Title: Internal blow out preventer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/521,564 filed Aug. 27, 2012, now U.S. Pat. No. 8,950,430, entitled “Internal Blow Out Preventer,” which is a 35 U.S.C. §371 national stage application of PCT/NO2011/000010 filed Jan. 10, 2011, which claims the benefit of Norwegian Application No. 20100037 filed Jan. 11, 2010, all of which are incorporated herein by reference in their entireties for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     1. Field of the Disclosure 
     There is presented an internal blow out preventer. More precisely there is presented an internal blow out preventer for use in a drill string, comprising a housing with a valve closure element and associated seals, wherein the valve closure element is configured to be moved between an open and a closed position. 
     2. Background of the Technology 
     The primary function of an Internal Blow Out Preventer (IBOP) is to shut off the mud (drilling fluid) passage on the inside of a drill string in the event well pressure exceeds limits during drilling operations on a drill rig. 
     However, the IBOP is also frequently used to prevent spillage of drilling fluids during each instance the top drive of the drill rig is disconnected from the drill string, e.g. each instance a new pipe or section of pipes is added to the drill string. This secondary function of the IBOP as a “mud saver” results in increased wear of the seals of the valve that has several un-desirable consequences. 
     One disadvantage is reduced service life of the IBOP valve, leakage when the valve is being used as mud saver after pressure testing, risk of rig downtime earlier than predicted, and more frequent need for seal replacements. 
     Although the use of two individual valves would solve the above problems, that solution would require additional space in the drill stem of the top drive (drilling machine), space which is not always available. The length of the drill stem located between the top drive and drill string, is limited by the travel of the top drive pipe handler, which needs to be able to grip around the box of the uppermost pipe of the drill string, just below the drill stem. 
     A normal set up of the drill stem between the top drive and drill string includes a cross-over sub, a remotely operated IBOP, and a second IBOP, the second IOBP being used as a closing valve at the upper end of the drill string remaining in the well and disconnected from the top drive, and a saver sub that takes the wear and damage of threads when the top drive and the drill string are connected or disconnected. 
     The IBOP is normally a ball valve, with the advantage that sealing has a radial symmetry, making it relatively easy to manufacture. 
     This disclosure relates to apparatuses intended to address at least some of the disadvantages of the prior art. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     There is presented an internal blow out preventer for use in a drill string, the internal blow out preventer comprising a housing with a valve closure element and associated seals and where the valve closure element is configured to be moved between an open and a closed position, wherein the valve closure element is provided with an inner valve closure element that is configured to be moved between an open and a closed position inside the outer valve closure element. 
     A valve body is provided with an additional inner valve closure element which is operated independently of the outer valve closure element enabling the mud saving operation without compromising the sealing performance of the IBOP and without the need for additional length of the drill stem, i.e. between the top drive and drill string. 
     The flow area of the inner valve closure element may be comparable to, substantially equal to or equal to the flow through area of the outer valve closure element. Thus the inner valve closure element will not restrict flow through the IBOP when fully open. 
     The outer valve closure element may be separable, and a junction between a first part and a second part may be positioned so as to be out of contact with the seals during movement between the open and the closed position. This feature is intended to decrease wear of the seals that might otherwise occur. 
     The inner valve closure element may have a spherical or cylindrical form. Shaped as a ball, the inner valve closure element maintains certain benefits of using flat, circular seas. However, it may be more challenging mechanically to fit a ball rather than a cylinder inside another ball. Shaped as a cylinder, the inner valve closure element requires more complex machining to accommodate seals but eases the machining of the inner valve closure element and improves the structural integrity of the outer valve closure element. It is worth mentioning that small leaks during mud saving operations are generally acceptable and may permit less stringent machining tolerances. 
     The outer and inner valve closure elements may be rotatable about a common axis of rotation. 
     Certain embodiments of the valve described herein are intended to address problems of reduced service life for the IBOP seals as the valve closure element remains stationary while the inner valve closure element is closed for the mud saving operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An example of an embodiment of an IBOP is explained with reference to the enclosed drawings, where: 
         FIG. 1  shows a cross section of an internal blow out preventer, IBOP, according to the disclosure herein; 
         FIG. 2  shows a larger scale cross section of IBOP parts when used as a mud saver; 
         FIG. 3  shows the IBOP in an exploded view; 
         FIG. 4  shows a cross section of the IBOP in an initial stage of closing as a blow out preventer; and 
         FIG. 5  shows the same as in  FIG. 4  in the completely closed position. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS 
     On the drawings the reference number  1  denotes an internal blow out preventer comprising a housing  2 , a spherical outer valve closure element  4  and a spherical inner valve closure element  6 . 
     The housing  2  in this embodiment is provided with internal threads  8  at its upper end portion  10  and external threads  12  at its lower end portion  14  in order to connect to a pin/box configuration of a not shown Top Drive drill stem. 
     ‘Upper’ and ‘lower’ here refers to the IBOP in its normal working position as shown on the drawings. 
     A central, longitudinal bore  16  extends between the two end portions  10 ,  14 . The bore  16  corresponds with a bore of the not shown drill string. 
     A shoulder  18  is formed in the bore  16  as an upper portion  20  of the bore  16  has a larger diameter than the rest of the bore  16 . 
     The outer valve closure element  4  is positioned in the upper portion  20  of the bore  16  and connected to two hollow shafts  22  that are protruding through shaft openings  24  in the housing  4 . The outer valve closure element  4  and the hollow shafts  22  are rotatable about axis  26 . One of the hollow shafts  22  is connected to a not shown first actuator. 
     A lower ring  28  that abuts the shoulder  18 , is provided with a first sealing surface  30  that is configured to seal against the outer valve closure element  4 . A lower ring seal  32  provided in the lower ring  28  prevents fluid flow between the lower ring  28  and the body  2 . 
     An upper ring  34 , placed above the outer valve closure element  4 , is provided with a second sealing surface  36  that is configured to seal against the outer valve closure element  4 . An outer ring seal  38  provided in the upper ring  34  prevents fluid flow between the upper ring  34  and the body  2 . 
     The first sealing surface  30  and the second sealing surface  36  constitute the outer valve sealing surfaces. 
     The outer valve closure element  4  has an opening  40 , with an area comparable, substantially equivalent to or equal to the cross section area of the lower portion of bore  16 . 
     The inner valve closure element  6  is positioned inside the outer valve closure element  4  and connected to two shafts  42 . Each of the shafts  42  extend through a concentric bore  44  in the respective hollow shafts  22 . The inner valve closure element  6  and the shafts  42  are rotatable about axis  26 . 
     A not shown second actuator is connected to one of the shafts  42 . 
     Seals  46  prevent fluid from flowing between the hollow shafts  22  and the housing  2  and between the hollow shafts  22  and the shafts  42 . 
     Inner valve seals  48  positioned in corresponding recesses  50  inside the outer valve closure element  4  prevent fluid from passing between the outer valve closure element  4  and the inner valve closure element  6 . 
     The inner valve closure element  6  has an opening  52  of comparable, substantially equal or equal cross section area to that of the opening  40  of the outer valve closure element  4 . 
     In an embodiment as shown in  FIG. 2 , the outer valve closure element  4  is made of a first valve segment  54  and a second valve segment  56 . 
     After the inner valve seals  48  and the inner valve closure element  6  are positioned inside the outer valve closure element  4 , the first and second valve segments  54 ,  56  are joined at an interface  58  using bolts  60 . 
     In  FIGS. 3 to 5  the housing  2  is removed in order to better show the operating functions of the IBOP  1 . 
     When used as a mud saver, the inner valve closure element  6  of the IBOP  1  is rotated about axis  26  to close the valve opening  40  thus preventing mud from flowing through the IBOP  1 , see  FIG. 2 . 
     The outer valve closure element  4  is not turned, and no wear is caused on the first and second sealing surfaces  30  and  36 . 
     When used as an IBOP, the inner valve closure element  6  is placed in the open position, see  FIGS. 4 and 5 . The inner valve body seals  48  are thus not utilised for IBOP mode of operation. 
     The outer valve closure element  4  is rotated about axis  26  to a closed position, see  FIG. 5 , preventing flow through the IBOP  1 . The first and second sealing surfaces  30  and  36 , not subject to wear from mud saver use, function as a reliable, leak-proof barrier against the well pressure. 
     The interface  58  does not pass over the sealing surfaces  30 ,  36  during closing or opening of the outer valve closure element  4 .