Patent Publication Number: US-5890541-A

Title: BOP isolation test tool

Description:
TECHNICAL FIELD 
     This invention relates in general to subsea well tools and in particular to a tool that will seal in the bore of a wellhead for testing a blowout preventer located above. 
     BACKGROUND ART 
     In one type of offshore drilling, a subsea wellhead will be installed at the sea floor. A riser will connect to the wellhead and extend upward to a drilling vessel floating at the surface. A blowout preventer stack, hereinafter referred to as a BOP, will be located within the riser. 
     It is a good practice to test a BOP by closing the BOP on drill pipe and applying pressure below the drill pipe. In addition, it is a good practice to test full closure of the BOP with the drill pipe pulled above the BOP. These operations also test the seal of the wellhead connector to the subsea wellhead housing. While test tools are available, improvements are desired. 
     DISCLOSURE OF INVENTION 
     A test tool having a lower body, an upper mandrel, a ball valve and a bore is lowered on a string of drill pipe and inserted sealingly into a casing hanger bowl in a wellhead housing. The ball valve seats within a passage in the body and has an actuating mechanism located on one side. The actuating mechanism moves the ball valve between open and closed positions. 
     The ball valve is installed in the body in an open position to facilitate running of the test tool through the riser. In the first part of the test, the BOP clamps around the drill pipe to form a seal. Fluid is then pumped down a choke and kill line to test the ability of the BOP to seal around the pipe. 
     In the second part of the test, the operator rotates the drill string and mandrel, which closes the ball valve automatically. The rotation also disengages the body from the mandrel so that the drill pipe and mandrel may be lifted above the BOP. The BOP is then sealed in a closed position and fluid is once again pumped down the choke and kill line to test the seal. 
     After the second part of the test, the BOP is opened and the drill pipe and mandrel are once again lowered below the BOP. The mandrel reengages the body and is rotated, thereby opening the ball valve. The drill pipe, mandrel and body are then pulled upward to the surface. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a sectional side view illustrating a well tool constructed in accordance with this invention, and showing the well tool in a sealed and locked position to the wellhead for testing. 
     FIG. 2 is an enlarged sectional side view of the well tool of FIG. 1 showing the ball valve in the open position. 
     FIG. 3 is a further enlargement of the sectional side view of the well tool of FIG. 1. 
     FIG. 4 is an exploded isometric view of the ball valve and the components of the actuating mechanism. 
     FIG. 5 is a front view of the ball valve in the open position and the rocker arm in a starting position. 
     FIG. 6 is an enlarged sectional side view of the well tool of FIG. 2, showing the ball valve in the closed position. 
     FIG. 7 is a front view of the ball valve in the closed position and the rocker arm fully rotated. 
     FIG. 8 is a front view of the ball valve in the closed position and the rocker arm in the starting position. 
     FIG. 9 is a front view of the ball valve in the open position and the rocker arm fully rotated. 
     FIG. 10 is a schematic drawing of the well tool during installation. 
     FIG. 11 is a schematic drawing of the well tool during testing of the BOP closing on the drill pipe. 
     FIG. 12 is a schematic drawing of the well tool during testing of the BOP in full closure. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring to FIG. 1, a wellhead housing 11 has a casing hanger 13 landed and sealed in it. Casing hanger 13 is part of the wellhead housing assembly. A test tool 15 is lowered on a string of drill pipe 17 and inserted sealingly into casing hanger 13. Test tool 15 has a lower tubular member or body 21, an upper tubular member or mandrel 23, a ball valve 25 and a bore 27. Body 21 has an enlarged lower portion 22 that will nest and seal in casing hanger 13 with seals 24. 
     As shown in FIG. 2, ball valve 25 seats and seals within bore 27 of body 21. Ball valve 25 has an actuating mechanism 31 located on one side. Actuating mechanism 31 extends through a lateral opening 33 in body 21. Mandrel 23 has a center portion 34 with a vertical slot 35, an internal flange 37 and a downward-facing shoulder 39 that lands on an upward-facing shoulder 41 on body 21 to limit the downward movement of mandrel 23. A C-ring or retainer ring 43 having internal threads 45 is carried by mandrel 23 on flange 37. Threads 45 engage outer threads 47 on body 21. Retainer ring 43 has a vertical slot 49 which engages a tab 51 that is carried within flange 37. Tab 51 is urged upward by a spring 53 located between flange 37 and tab 51. The upward movement of tab 51 is limited by a stop shoulder 55. When slot 49 engages tab 51, retainer ring 43 and mandrel 23 will rotate together. When mandrel 23 moves downward a short distance relative to retainer ring 43, tab 51 disengages slot 49 and mandrel 23 can rotate relative to retainer ring 43. 
     Referring to FIGS. 3 and 4, actuating mechanism 31 is provided to move ball valve 25 between open and closed positions. Ball valve 25 has a drive slot 61 which is used to couple with actuating mechanism 31. Drive slot 61 has two parallel drive walls 63 which closely receive a drive plate 65 so that there is no relative movement therebetween. Drive plate 65 has a cylindrical body 67 with a rectangular plate 69 on a rearward side and four raised wedges 71 on a forward side. The radially outer surface of body 67 is smooth. Wedges 71 are generally quarter-circular in shape and have a stop surface 75 on one edge and a ramp surface 77 on the other edge. The arcuate sides 79 of wedges 71 align with the circular portion of body 67. Drive plate 65 also has a central bore 66. 
     A cylindrical clutch 81 has a smooth inner surface for sliding engagement with the radially outer surface of o cylindrical body 67. Clutch 81 and drive plate 65 are engaged such that drive plate 65 may rotate relative to clutch 81, but there is no axial movement therebetween. Clutch 81 is a cylindrical ring with two wedges 85 on its inner surface that are similar to wedges 71. Each wedge 85 has a stop surface 87 and a ramp surface 89 that are located opposite of stop surface 75 and ramp surface 77, respectively, on wedges 71. As shown in FIG. 5, wedges 71 on drive plate 65 are located in the three, six, nine and twelve o&#39;clock positions. Wedges 85 on clutch 81 are located at the three and six o&#39;clock positions. The outer cylindrical surface of clutch 81 is press-fit into opening 33 or otherwise secured in body 21 to prevent clutch 81 from moving relative to body 21. 
     Referring back to FIG. 4, a hub 91 is slidingly received by and extends through bore 66 in drive plate 65. Hub 91 has a flange 93 on a rearward end and two arcuate arms 95 on a forward end. Flange 93 rotatingly seats between drive plate 65 and drive slot 61. Flange 93 prevents axial movement of hub 91 relative to ball valve 25. Hub 91 will rotate relative to drive plate 65 and clutch 81. 
     A generally rectangular rocker arm 101 is closely received between arms 95 on hub 91. Rocker arm 101 is pivotally secured to hub 91 by a pin (not shown) which extends through holes 99 in arms 95 and through a hole 103 in rocker arm 101. Rocker arm 101 has a cylindrical inner finger 105 facing inward which engages drive plate 65. Rocker arm 101 also has a cylindrical outer finger 107 facing outward which engages slot 35 in mandrel 23. Fingers 105 and 107 are tapered or slightly conical such that their distal diameters are smaller than their proximal diameters. 
     A torsional spring 111 urges rocker arm 101 and hub 91 to rotate in a clockwise direction. Spring 111 has a tab 113 that lands on one side of rocker arm 101 and another tab 115 which lands on a stop surface 87 on clutch 81. 
     A compression spring 121 is used to pivotally urge outer finger 107 in a forward direction and inner finger 107 in a rearward direction. Spring 121 seats in a hole 97 in hub 91 on one end and applies compression force against a rearward surface of rocker arm 101 on the other end. 
     In operation, ball valve 25 is installed in body 21 in an open position. As shown in FIG. 10, a riser 123 is secured to wellhead housing 11. Test tool 15 is lowered through riser 123 on a string of drill pipe 17 and sealed in casing hanger 13 below a blowout preventer or BOP 133. Referring to FIG. 11, BOP 133 clamps around drill pipe 17 to form a seal. Fluid is then pumped down a choke and kill line 135 to test the seal of BOP 133. 
     Full closure of BOP 133 may also be tested. First, mandrel 23 is picked up and rotated clockwise, as viewed from above. The rotation of mandrel 23 causes ball valve 25 to rotate to the closed position automatically. As mandrel 23 rotates, tab 55 engages slot 49 of retainer ring 43 (see FIG. 2) to force concurrent rotation of retainer ring 43. This causes retainer ring 43 to unscrew from and disengage body 21. 
     Before ball valve 25 is rotated to the closed position, rocker arm 101 is in a starting position wherein inner finger 105 rests against a stop surface 87 on clutch 81 (FIG. 5). As mandrel 23 (not shown in FIGS. 5-9) rotates and moves upward, slot 35 engages outer finger 107, thereby forcing rocker arm 101 to rotate with hub 91 in a counterclockwise direction. As rocker arm 101 rotates, inner finger 105 applies pressure to stop surface 75 to force drive plate 65 and ball valve 25 to rotate. Rocker arm 101, drive plate 65 and ball valve 25 continue to rotate for approximately 90 degrees until inner finger 105 strikes ramp surface 89 on clutch 81. Clutch 81 is rigidly secured to body 21 and is thus fixed from rotation. As shown in FIG. 7, ball valve 25 is now in the closed position. 
     Referring to FIGS. 6 and 7, the tapered surface of inner finger 105 coupled with the incline on ramp surface 89 causes inner finger 105 to pivot in an outward direction, out of contact with drive plate 65. Outer finger 107 simultaneously moves inward and disengages slot 35. When mandrel 23 is raised out of engagement with outer finger 107, torsional spring 111 (not shown in FIGS. 5-9) forces rocker arm 101 to rotate in a clockwise direction toward its starting position. As rocker arm 101 rotates, inner finger 105 rides up ramp surface 77 and over wedge 71 in the six o&#39;clock position on drive plate 65. Rocker arm 101 ceases rotation when inner finger 105 strikes stop surface 87 on clutch 81, thereby causing rocker arm 101 to stop in its starting position (FIG. 8). Compression spring 121 returns rocker arm 101 to an upright position, parallel to bore 27. As mandrel 23 continues to rotate, retainer ring 43 unthreads from body 21 so that mandrel 23 may be lifted above and separated from body 21 (FIG. 12). Mandrel 23 is lifted above BOP 133. BOP 133 is then moved to a closed position and fluid is once again pumped down choke and kill line 135 to test the seal. 
     After the full closure test, drill pipe 17 is lowered again. Mandrel 23 lands on body 21 with retainer ring 43 engaging body 21. Retainer ring 43 ratchets over and fully engages the threads on body 21 after stabbing mandrel 23 onto body 21. 
     As shown in FIG. 8, inner finger 105 rests against stop surface 87. Without picking up mandrel 23, the operator then rotates mandrel 23 which causes slot 35 to engage outer finger 107, thereby forcing inner finger 105 to rotate drive plate 65 and ball valve 25. Rocker arm 101, drive plate 65 and ball valve 25 continue to rotate for approximately 90 degrees until inner finger 105 strikes ramp surface 89 on clutch 81. Ball valve 25 is now again in the open position as shown in FIG. 9. The tapered surface of inner finger 105 coupled with the incline on ramp surface 89 causes inner finger 105 to pivot outward and out of contact with drive plate 65. Outer finger 107 simultaneously pivots inward and disengages slot 35. Because mandrel 23 was not lifted relative to body 21 during re-connection, tab 51 will be below retainer ring 43 and will not engage slot 49. Retainer ring 43, which has fully engaged the threads on body 21, does not rotate with mandrel 23 during the opening of ball valve 25. After ball valve 25 is opened, the entire test tool 15 is retrieved. 
     The invention has several advantages. The test tool allows a BOP to be tested both while closed on the drill pipe and also during full closure. The ball valve allows running-in of the test tool in an open position to fill the drill string. The ball valve automatically closes when the mandrel is picked up, leaving the body in the wellhead as a plug. By again opening the ball valve when re-engaging, the drill string is pulled upward when retrieving the test tool. 
     While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.