GB2164981A - Inside blowout preventer - Google Patents

Abstract

An inside blowout preventer 11 for use in an earth boring drill string has features to reduce erosion. The blowout preventer has a valve body 13 for connection into the drill string with a longitudinal passage 21 extending through the body. The ball seat 31 is located in the longitudinal passage. A ball storage location (39, Fig. 7) is located below the seat, and offset from the longitudinal passage. A ball 41 is carried in the storage location during downward flow, and moves into the longitudinal passage to seat against the seat if the upward flow is sufficient. The storage location is located in an area of the longitudinal passage which has a much larger flow area than through the seat. The downward flow impinges on a portion of the ball. A communication passage 59 extends from the storage location downward to a reduced diameter section of the longitudinal passage. <IMAGE>

Description

SPECIFICATION Drill pipe inside blowout preventer This invention relates in general to check valve assemblies, especiallythose for preventing uncon trolled or excessive upward flow offluid in drill strings used in earth boring.

Oil and gas wells are conventionally drilled by rotating a drill string of drill pipe and drill collars that support a bit. Drilling fluid, known as "mud", is pumped down the inner passage ofthe drill string, through the bit, and up the annular passage between the borehole wall and drill pipe. The mud circulates cuttings to the surface and cools the bit. Also, the weight of the mud is adjusted to provide a bottom hole hydrostatic pressure greater than the formation pressureto prevent a "blowout".

If the mud pressure gets too low when the surface pump is disconnected from the drill pipe (as when a joint of pipe is being added orthe pipe being removed or replaced during a "trip"), fluid will flow into the hole and can result in uncontrolled upward flow up the drill string as well as up the annulus. this is called a gas kick which can result in a blowout if not quickly controlled.

Also, heavier fluids with weighting materials cannot be quickly pumped through the system to prevent a blowout, because the surface pump is disconnected from the drill string.

"Outside" blowout preventers, which have been marketed and used for year, are presently used to close around the drill pipe at the surface and seal the annulus betweenthepipe andthewall of the hole.

These devices do not prevent the upward flow of mud inside the pipe during the blowout. "Inside" blowout preventers are also marketed. Atypical inside blowout preventer is kept on the rig floor. Once flow starts up the inside ofthe drill pipe, the inside blowout preventer is screwed into the top ofthe drill pipe, and a valve is closed. Then the mud hose is hooked back up to kill thewell. Sincetheflowstarts before connecting up the inside blowout preventer of this type, the usage can be messy and dangerous.

There have been several proposals in the patented artto use inside blowout preventers which remain with the drill string while drilling. Examples ofthese inside blowout preventers are shown in U.S. Patent Nos.3850 191,3850 194,4040441,4049015,4088 298, 4108 203 and 4263936. In these patents, the device comprises a subforconnection into the string.

The sub has a longitudinal passage, with a recess or side pocket on one side and a valve seat in the passage abovetheside pocket. A ball is carried in the side pocketduring normal drilling. Itmoves intothe- longitudinal passage and seats if substantial flow exists during a blowout. An equalizing passage, connecting the base of the side pocket with the longitudinal passage belowthe side pocket, determines the rate of upward flowwhich will move the ball into the longitudinal passage. The cross-sectional area ofthe equalizing passage prevents seating of the ball intheball seatfromthenormal upwardflow caused by running the drill string into the well.

Erosion is a continuing problem for inside blowout preventers of the type shown in the patented proposals. High flow rates and solids or sand contained in the mud cause erosion of the seat and passages inside the blowout preventer, preventing long-term effective operation. Experience indicates that the ball tends to move partially into the longitudinal passage even during downward fluidflow. In this position, the ball causes aflow restriction of varying area duetothe oscillation ofthe ball resulting in excessive fluid velocities around the ball and the longitudinal passage.Turbulentflowand erosion ofthe passage and ball inevitably results.

In this invention, an inside blowout preventer is provided of the type that connects into the drill string during drilling operations. The inside blowout preventer has a ball which remains in a ball storage location on one side during downward flow. The ball moves upward to contact a seat during upward flow of sufficient amount.

The ball storage location is located in a portion of the sub that has a considerably greaterflowarea than through the seat. This greaterflow area lowers the velocity ofthe fluid past the ball. The downward flow directly impinges on a portion ofthe ball. The portion ofthe longitudinal passage from the valve seat down to the ball can boa diffuserordiverging passage to uniformly decelerate the fluid.-To further assist in keeping the ball in the storage location, a communication passage leads from a point below the ball to a point of much higher velocity and lesser cross-section area than the point at where the ball is located.

Preferably, the main flow longitudinal passage leads from the ball storage location to a cylindrical section of smaller diameter. The communication passage terminates adjacent the cylindrical section to provide a pressure drop to retain the ball in the ball seat. The longitudinal passage will allowthe passageoftools through the sub.

Fig. lisa vertical cross-sectional view of an inside blowout preventer constructed in accordance with this invention.

Fig. 2 is an enlarged sectional view ofthe blowout preventer of Fig. 1, taken along the line ll-ll of Fig. 1.

Fig. 3 is an enlarged sectional view of the blowout preventer of Fig. 1 taken along the line Ill-Ill of Fig. 1.

Fig. 4 is an enlarged sectional view ofthe blowout preventer of Fig. 1, taken along the line IV-IV of Fig. 1.

Fig. 5 is an enlarged sectional view of the blowout preventer of Fig. 1, taken along the line V-V of Fig. 1.

Fig. 6 is an enlarged sectional viewofthe blowout preventer of Fig. 1 ,taken along the line VI-VI of Fig. 1.

Fig. 7 is a partial, enlarged vertical sectional view of a portion of the blowout preventer of Fig. land shown without the ball.

Fig. 8 is an enlarged side view of a portion ofthe lower insert, which is a part of the blowout preventer of Fig. 1.

Referring to Fig. 1, blowout preventer 11 includes a tubular housing 13. Housing 13 has internal threads 15 atthe top for connection to a drill string member (not shown). A pin adapter 17 is secured to the lower end of housing 13. Pin adapter 17 has external threads 19for connecting to another drill string member (not shown). A longtudinal passage 21 extends through the housing 13 and adapter 17 forthe passage of drilling fluid.

An supper insert 23 is located within the housing 13 nearthe upper end. Upper insert 23 is a tubular memberwith a tapered bore section 25, which forms a partofthe longitudinal passage 21 forthe passage of drilling fluid. Tapered section 25 is conical, with the lower end being smallerthan the upper end and offset from the axis 26 of the housing 13. The axis 24 of tapered section 25 intersects axis 26.

A ball orvalve seat 31 is located in a recess atthe bottom oftapered passage 25. A seat retaining insert 27 joins the lower end of the upper insert 23, and also is located in the hbusing 13. Insert 27 is atubular memberwith a cylindrical bore section 29 which aligns withthe lower end of the tapered bore section 25. Valve seat 31 is retained by recesses formed in the inserts23and27.

An intermediate insert33 joins the lower end ofthe insert 27. Insert 33 is atubularmemberwith a bore section 35, which at its upper end is the same diameter and joins with the cyclindrical bore section 29. The tapered section 35 is conical like the tapered section 25, also having an axis 34thatis inclined with respect to the axis 26, but it is inverted from the tapered section 25. Fig. 5 showsthetapered passage section 35 looking upwardly toward the seat 31.

Thetapered section 35 leads into an enlarged central section 37, as shown in Fig's. 2.and 7, which is generally cylindrical. The cross-sectional area, orflow area, at the central section 37 is greaterthan through the seat 31. The axis ofthe central section 37 is offset from axis 26, but in a direction opposite to the direction of offsetof seat31.

Referring still to Fig. 7,a ball storage location 39 is located within the central section 37. Ball storage location 39 supports a ball 41- (Fig. 1) during downward flow. Fig. 2 is a sectional view showing the ball 41 located on the ball storage location 39. The axis of the ball storage location 39 is offsetfrom the axis 26 in an opposite direction from the offset of the axis ofthe ball seat 31 (Fig. .1). The flow area atthe ball storage location 39 comprises the cross-sectional area ofthe central section 37, less the cross-sectional dimension ofthe ball storage location 39. This flow area is -considerablygreaterthantheflowarea ofthe seat31 (Fig. 1), which is less than the cross-sectional area of the ball 41.

As shown in Fig. 2, ball storage location 39 is circular in cross-section, with a smaller diameter than central section 37, and with its axis offset from the axis of central section 37. The outer side of ball storage location 39 is tangent to the outer side of central section 37. The flow area atcental section 37 may be described asa crescent, with one edge (the left in Fig.

2) being concave and the other edge convex.

The ball storage location 39 comprises the upper end 6f a ball storage member43. Ball storage member 43, as shown in Figs. 2,3 and 6, is a cylindrical member with a diameter slightly greaterthan the diameter of the ball.41. The ball storage member 43 fits within a cylindrical hole 44 (Fig.'s 3 and 6). formed in a lower insert45. Lower insert 45 is a tubular memberwith an upper end that contacts the lowerend ofthein- termediate insert33. Lower insert 45 fits within the housing 13, and has a tapered bore section 47 that extends from the top downwardly, forming a part-of longitudinal passage 21. Tapered section 47 is shown in Fig's2 and 3 as well as Fig. 7.Tapered section 47 is also conical, with an axis 46 (Fig. 7) that is inclined with respectto axis 26, and with a smaller diameter at the lower end than at the upper end.

The lower end of tapered section 47 leads to a cylindrical section 49 in lower insert45that is smaller in flow area than the flow area at central section 37.

The axis ofthe cylindrical section 49 coincides with the axis of the valve seat 31, both of which are offsetfrom the housing 13 axis 26. The cylindrical section 49 leads to a tapered bore section 51,which extends to the lower end ofthe lower insert 45. Tapered section 51 is conical, as shown in Fig. 4, with an axis 52 (Fig. that intersectsthe axis 26, similarto the other tapered sections 25,35 and 47. The lower end-of tapered - section 51 is larger than its upper end. Sections 47,49 and 51 togetherform a venturi.

Part ofthe lower insert 45 is shown removed from housing 13 inFig. 8. It has a cylindrical wall which fits closely within the housing 13. On one side, a slot 55 is cutthrough the wall. This slot also is shown in Fig. 3.

Slot 55 exposes a part ofthe outer side ofthe ball storage member 43. This allows the ball storage member 43 to be welded to the insert 45. Slot 55 does not extend thefull length ofthehole44,orthe ball storage member 43. The dotted line57, as shown in Fig. 7, indicates howthetapered section47 would appear, if the ball storage member43were notwelded in place, and if a hole 44 did not exist. The merger of the tapered section 47 intothecylidrical section 49 can be seen by comparing Fig's 2,3 and 6. In Fig,6, the taperedsection 47 is no longer seen, showing onlythe cylindrical section 49.

Referring to Fig. 7, a communication passage 59 extends through the ball storage member43 inclinded with respect to the axis 26. The communication passage 59 has an enlarged upperend6l,which is circular, butoflesser diameterthan the diameter of ball 41. The upper end 61 defines a circular sealing surface which is located in a plane, perpendicular to axis 26 (Fig. 1 ),forcausing the ball 41 to seal against the upperend of passage 59 during downward flow.

During downward flow, ball 41 will prevent any fluid from flowing downwardly in passage 59. The passage lower end 63 terminates in a beveled section 65. The beveled section 65 extends from the lower end 63 of passage 59 to the lower end 67 ofthe ball storage member 43. The beveled section 65 is a flattened section on the sidewall of ball storage member 43. The lower end 67 extends slightly intothe cylindrical section 49.

An open channel 69 extends upwardlyfrom a point nearthelowerend ofinsert45tothelowerendof storage member 43. Channel 69 isformed in the wall oftapered bore section 51 Channel 69 aligns with a channel 70 that extends upward from the lower end 67 ofthe ball storage member 43to the lower end 63 of the communication passage 59. As shown in Fig. 4, the channel 69 joins channel 70 to provide a flow path for upward flow into the lower end 63 of the passage 59. Channels 69 and 70 are inclined with respectto the axis 26 (Fig. 1).

Additional structureforthe blowoutpreventerl 1 includes a tooth shaped guide member 71 ,which is located on the inner side ofthe ball storage location 39. As shown in Fig. 8, guide member 71 forms a crest above the upper end 61 of passage 59. Guide member 71 serves as a guide means to assist the ball41 in locating within the ball storage location 39 during downward flow. Fig. 1 shows belleville springs 73, which are located between the adapter 17 and the lower end of the lower insert45for retaining the inserts 23,27,33 and 45 tightly within the housing 13.

in operation, the blowout preventer 11 is secured into the drill string while drilling. Drilling mud is pumped down the drill string, passing through the blowout preventer 11. The drilling fluid will pass through the longitudinal passage 21, tapered section 25, and seat 31. The drilling fluid passes through the cylindrical section 29, then enters the tapered section 35.

As shown in Fig. 1 and Fig. 5, the gradually increasing cross-sectional area or flow area ofthe tapered section 35 results in a diffuserunderdown- ward flow. The fluid velocity will decrease to a minimum in the vicinity ofthe central section 37. The fluid flows around the ball storage member43, entering the tapered section 47. Some ofthe downward fluid stream impinges directly on ball 41. In tapered section 47, the velocity ofthe fluid will increase, reaching a maximum velocity in cylindrical section 49. The pressure at the cylindrical section 49 will be less than the pressure in the central section 37.

The ball storage location 39 is in communication with the lower pressure adjacent cylindrical section 49 by means ofthe communication passage 59. This creates a pressure differential on ball 41. Normally, underdownwardflowthe ball 41 will not move out into the main flow area on the other side ofthe guide member 71. Even if ball 41 did move offofstorage location 39, the distance between the ball storage member43 and the opposite side ofthe tapered section 47 is smaller than the dimension ofthe ball 41, thus it could not move downwardly. Also, as can be seen in Fig. 2, even if the ball 41 happens to move from ball location 39 and contactthe opposite wall ofthe tapered section 47, it will not greatly restrict the flow, because of the large crescent shaped flow area surrounding the ball storage member43.The fluid flow, once leaving the cylindrical section 49 enters tapered section 51,andflowsthrough adapter 17.

If the formation pressure inthewell becomes greater than the hydrostatic pressure due to the column of mud, and if fluid starts flowing upwardly, then the drilling fluid may start flowing up the inside of the drill pipe. The flow upward will flow through the tapered section 47, which now acts as a diverging section. Some of the flow will flow upwardly through the communication passage 59. The fluid flowing through the communication passage 59, if sufficient, unseats ball 41, pushing it into the mainstream of flow up the tapered section 35. Ball 41 will flow upward to seat against the ball seat stopping further upward flow. The well can then be killed by pumping into the well with heavier mud.The ball 41 will remain against seat 31 until the pressure above the ball 41 is greater than below.Whenthe pressure abovethe ball 41 is greaterthan below, ball 41 will fall and return to the ball location 39. Guide member 71 will guide the ball back to the ball location 39.

The dimensions of the components in the blowout preventer 11 are selected so that a minimum upward flow must be achieved before ball 41 will move upward and seat against ball seat 31. For ball 41 to contactseat31, a minimum upward velocity is necessary, so that the ball 41 will not normally move into contact with seat 31 during normal "running-in" ofthe drill string. During running-in, mud in the boreholewill enterthe string to equalizethe pressure inside and outside the drill pipe. The ball 41 and the various bore sections are dimensioned so that the ball will contact seat 31 preferably during upward flow rates of about 5681 per minute for drilling fluid having a weight of 1.9 g/cm3 and 7571 per minute for clear water.The maximum upward flow rate expected during normal running-in, even with large nozzles and heavy mud, is about 5081 per minute.

The minimum clearances through valve seat 31 and cylindrical section 49areselectedso asto allow normal wirelinetoolsto be lowered intothedrill string during certain operations. The distance between the extreme inner side ofthe ball storage member43 and the opposite side of the tapered section 47 is calculated to allowthe sametoolsto pass.

The dimensions of the bore sections are selected to reduce erosion during normal downward flow. Aflow velocity of approximately 30.5 m per second is assumed herein as a value atwhich erosion would begin for most muds. The smallestflow area in the blowout preventer 11 is the ball seat 31, at which velocities of 30, 5m per second occur with 28401 per minute flow, assuming an inner diameter of cm for seat 31. A velocity of 30.5 m per second through seat 31 reduces to about 13.1 m per second when in the central section 37 around ball 41. This reduced velocity is well belowtheassumed erosional threshold.

The lower end 63 ofthe communication passage 59 is preferably in a portion ofthe tapered section 47 that has a flow area less than the flow area around the ball storage location 39. This results in a pressure differential on ball 41 during downward flow, the magnitude of which depends upon the fluid velocity and drilling fluid weight. For example, at 7571 per minute, the estimated pressure differential would range from 0.16 barforwaterto3.1 barfor 1.9 g/cm3 drilling mud.

In the preferred embodiment, the diameter of seat 31 is 44,5 cm, providing a flow area of 155 cm2. The nominal flow area of central section 37 is approximately 35.5 cm2. The distance along axis 26 from the lower edge of seat 31 to the top of ball 41 while on storage location 39 is approximately 28 cm. The ball is preferably steel and has a diameter of 5.4 cm. Theflow area ofthe cylindrical section 49 is approximately 19 cm2. The distance from the centerline of ball 41 while on storage location 39 to the upper edge of cylindrical section 49 is approximately 20.3 cm. The diameter of communication passage 59 is 0.8 cm.

The diameter ofsection 35 at itsiunction wiih central section 37 is about 6.6cm. The diameter of central section 37 is about9.8 cm. The main flow stream atthetop of central section 37 is conical.The edge ofthe conical flowstream will impinge on ball 41 apprnximately 3.8 cm from the inner side (right side in Fig. 1) of bail 41. Thus, approximately3/4 of the ball will be directly in the main downwardflowstream in the preferred embodiment.

The invention has significant advantages. The streamlined nature ofthe converging and diverging passages, and the placing ofthe ball storage location in a point of greatly reduced velocity, reduces erosion substantially. Utilizing the pressure differential caused bythe communication passage belowthe ball keeps the ball in the ball location to prevent oscillation and turbulence. The offset axes ofthe converging and diverging sections in the ball seatallowwireline tools to easily pass through the blowout preventer.

While the invention has been shown in only one of its forms, it should be apparentto those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope ofthe invention.

Claims (10)

1. An inside blowout prevented for use in a driii string, comprising in combination: a valve body having a longitudinal passageforthe passage oaf fluid and upper and lower ends for connection to the drill string; a ball seat located in the longitudinal passage; a ball storage location located belowtheseat; and a ball carried in the storage location during downward flow, and movable in caseofupwardlilowof sufficient velocity into the longtudinal passage and into contact with the seat to stop the upward flow; the storage location at least partially projecting into the longitudinal passage, exposing at least a portion oftheballtoatleasta portion of the direct impingement of downward flowing fluid.

2. The inside blowout preventer according to claim 1 comprising: a diffusersection within the longitudinal passage, beginning with a minimum flow area atthe valve seat and gradually increasing in flow area in a downward direction to provide a lower velocity of fluid at the lowered of the diffuser section than atthe upper end; said ball storage location being disposed at the lower end ofthe diffuser section; and said ball carried said the storage location during downward flow being movable from the storage location upwardly into contact with the seat if upward flow of a selected velocity occurs.

3. The inside blowout preventer according to claim 1, wherein said longitudinal passage has upper and lowersectionswith smallerflowarea portions than a central section; said ball seat is located in the upper section; said ball storage location is located in the central section of the longitudinal passage; and a communication passage leads from the storage location downwardly to a smaller flow area portion of the lower sectic.n to provide a pressure differential on the ball during downwardflowto retain the ball on the storage location, and to assist in moving the ball to the seat during upward flow of predetermined velocity.

4. The inside blowout preventer according to claim 3, wherein said ball storage location is generally circular in cross section, with an axis offset from the axis of the central section, which is also circular, defining a generally crescent-shaped flow area atthe ball storage location; the crescent shape oftheflow area at the ball storage location preventing the ball from blocking downward flow should the ball be off of the ball storage location during downward flow.

5. The inside blowout preventer according to anyone ofthe claims 1 to 4, comprising guide means extending upwardlyfrom the storage location for guiding the ball into the storage location.

6. The inside blowout preventer according to claim 1, wherein said longitudinal passage has an upper section, a central section and a lower section with a reduced diameter portion having a smallerflow area than in the central section; said ball seat has a smallerflow area than the central section and is located in the upper section, coaxial with the reduced diameter portion and offset from the axis ofthe body; said ball storage location is located in the central section and offsetfrom the axis of the body in a direction opposite to the ball seat; and communication passage means lead from the ball storage location toward the reduced diameter portion for communicating lower pressure to the ball than in the central section during downwardflowto retain the ball in the storage location, and for diverting a portion of upwardflowto belowthe ball to assist the bail in movement outward into the upward flow in the central section and up against the seat if a predetermined upward flow velocity is reached; the coaxial alignment ofthe seat and reduced diameter portion and the offset ofthe ball storage location allowing the passage oftools through the longitudinal passage.

7. The inside blowout preventer according to claim 1, wherein said longitudinal passage has an uppersection, a central section, and a lower section with a reduced diameter portion having a smaller flow area than in the central section; said ball seat is located in the upper section; said ball storage location is located in the central section; and communication passage means extend from the storage location toward the reduced diameter portion for communicating lowerpressureto the ball than in the central section during downward flow, and to assist in moving the ball to the seat during upward flow.

8. The inside blowout preventer according to claim 3,wherein the uppersection has a diffuser section beginningwitha minimumflowareaatthe ball seat and gradually increasing in flow area in a downward direction to provide a lower velocity of fluid atthe lower end ofthediffusersectionthan atthe upper end.

9. The inside blowout preventer according to claim 7, wherein said ball storage location is generally circular in cross section, with an axis offset from the axis ofthe central section, which is also circular in cross-section, defining a generally crescent-shaped flow area atthe ball storage location.

10. The inside blowout preventer according to claim 1 wherein said longitudinal passage extends through the body for the passage of fluid. having an upper section tapering gradually to a central section with a largerflow area and a lower section tapering gradually downwardly from the central section to a smallerflowarea portion.