Method Of Providing A Removable Packing Insert In A Subsea Stationary Blowout Preventer Apparatus

Abstract

A stationary blowout preventer having a balloon-type packing unit with a central opening therein, a retrievable packing insert positioned within said opening by the engagement of a lower ring with the preventer and releaseable secured therein by hydraulically releasable dogs latchingly engaging a latching notch in an upper ring, whereby a central rubber portion of the packing insert sealingly engages the pipe tool therethrough when the packing unit is pressurized by fluid. The blowout preventer has a fluid accumulator which absorbs the surge pressure and excess fluid to maintain a constant pressure on the packing insert as a pipe tool joint is stripped therethrough to maintain the sealing engagement between the insert and the pipe.

Parent Case Text

REFERENCE TO RELATED APPLICATION

This application is a division of my copending application Ser. No. 868,870 filed Oct. 23, 1969, entitled "Tool Joint Stripping Stationary Blowout Preventer With a Retrievable Packing Insert."

Description

BACKGROUND OF THE INVENTION

This invention relates to stationary blowout preventers and more particularly to a method of providing a stationary blowout preventer with a retrievable insert therein and a fluid accumulator attached thereto which permits the joints of a pipe tool to be stripped therethrough while a sealing engagement is maintained.

The oil well industry has had a continuing problem, associated with subsea drilling from a floating platform, of providing a suitable stationary blowout preventer that could strip tool joints i.e., pass the enlarged collars joining two pipe tools together, through the packing of the blowout preventer while the packing maintained a sealing engagement around the pipe tools and the tool joint. A subsea blowout preventer is mounted on the wellhead over the wellhole at the bottom of the sea and is used to hold the pressure within the well and to exclude the water therefrom. The stationary blowout preventer utilizes a radially compressible rubber packing unit which, in response to hydraulic fluid pressure from the surface, expands radially inwardly about a well tool inserted therethrough to sealingly engage the well tool. The well tool so engaged is commonly made up of a series of lengths of pipe tools joined together by collars or tool joints which usually have a larger diameter than the pipe tools themselves. When the subsea blowout preventer is closed about a drill pipe tool run therethrough, sooner or later a pipe tool joint must pass through the blowout preventer.

In the past, a string of stationary blowout preventers have been provided so that one blowout preventer may be open to admit the tool joint therethrough while others maintain the seal and so on until the tool joint is through the blowout preventer string. However, if the tool joint is in a position close to the blowout preventer, the vertical motion of the floating platform because of waves is transferred to the pipe tool and pulls the tool joint back through the blowout preventer. When this occurs, conventional blowout preventers are damaged, sometimes to the point of being inoperative, and must be replaced by dismantling the wellhead on the bottom of the sea.

Therefore, it is the primary object of this invention to provide a subsea stationary blowout preventer that will strip tool joints therethrough when closed.

It is another object of this invention to provide such a blowout preventer which will maintain a seal around the drill pipe as the tool joint is being stripped therethrough.

It is yet another object of this invention to provide such a subsea stationary blowout preventer that will strip a tool joint therethrough without damage to the preventer to make it inoperative.

It is a further object of this invention to provide such a subsea stationary blowout preventer with a retrievable packing insert which will strip tool joints therethrough.

It is yet a further object of this invention to provide such a blowout preventer with such a packing insert which is automatically properly positioned within the blowout preventer as it is lowered therethrough.

It is yet another object of this invention to provide such a blowout preventer with such a packing insert which is releasably latchingly maintained therein after positioning.

It is yet a further object of this invention to provide such a stationary blowout preventer with such a packing insert having an accumulator system which absorbs the incompressible fluid maintaining the packing in sealing engagement with the pipe therethrough as the tool joint thereof is stripped therethrough and returns the fluid so absorbed to maintain the pressure and the sealing engagement between the packing and the pipe tool after the joint has passed therethrough.

It is yet another object of this invention to provide such a stationary blowout preventer with such a packing insert which may, in an emergency, be used as a rotary blowout preventer, with the wear on the packing seal from the rotating pipe therethrough being on the retrievable packing insert which is replaceable from the surface.

SUMMARY OF THE INVENTION

The stationary blowout preventer of this invention has a radially compressible annular packing mounted therein and a central bore therethrough for receiving a retrievable packing insert to seal about a tool run thereto upon radial compression of the annular packing by hydraulic fluid pressure. The retrievable packing insert is automatically positioned by the engagement of a landing shoulder thereof with the bore of the blowout preventer and releaseably latchingly secured to the blowout preventer by hydraulically releasable dogs engaging a latching notch in the packing. The blowout preventer is also provided with an accumulator apparatus which absorbs the surge pressure and excess hydraulic fluid as a tool joint passes through the packing insert and the blowout preventer and returns the fluid afterward to maintain the sealing engagement therebetween.

These and other objects and advantages of the stationary blowout preventer of this invention will become apparent from the following detailed description and drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation, in elevation, of a floating vessel positioned above a subsea well having a wellhead with an improved stationary blowout preventer apparatus according to this invention;

FIG. 2 is an enlarged cross section elevational view of the stationary blowout preventer apparatus of FIG. 1 taken along the plane II-II;

FIG. 3 is a view of a portion of FIG. 2 showing a drill pipe and collar passing through the stationary blowout preventer apparatus of FIG. 1; and

FIG. 4 is a view similar to FIG. 3 showing a retrieving tool removing the packing insert from the stationary blowout preventer apparatus of FIG. 1.

Referring now to the aforedescribed FIGS. and especially to FIG. 1, a floating vessel or barge 10 is positioned by suitable anchor means (not shown) in a body of water or sea 11 over a well hole 12 in the sea bottom 13 and having mounted thereover a subsea wellhead 14. A conventional drilling rig 15 is provided on the barge or vessel 10 for running a conduit riser 16 from the barge 10 to the wellhead 14 to guide individual lengths of drill pipe tools 17 connected together by collars 18 into the wellhead 14. The conduit riser 16 also contains hydraulic pressure lines 19 and return lines 20 therein for connection to the subsea wellhead 14.

The subsea wellhead 14 includes an improved stationary blowout preventer apparatus with a stationary blowout preventer 25, a removable or retrievable packing insert 45, means positioning the insert 50, and latching means for releasably latching the insert 55 therein. The blowout preventer 25 also has connected thereto a fluid accumulator means 75 for absorbing the surge pressure caused by a pipe collar passing through the packing insert 45 of the blowout preventer 25 and then restoring the pressure to the blowout preventer 25 and the packing insert 45.

As best illustrated in FIG. 2, the stationary blowout preventer apparatus 25 includes a preventer body or housing 26 having a lower central bore 27 meeting a horizontal annular surface 28 at a chamfered landing shoulder 29, and an upper cylindrical internal surface 30 extending upwardly from the annular surface 28 to the open top of the preventer body 26.

An annular packing unit indicated generally at 31 is inserted into the open top of the preventer body 26. The packing unit is of the pure bag or balloon type and an outer annular or tubular element 32 having a central rubber portion 33 mounted between upper and lower reinforcing rings 34 and 35. An inner annular or tubular element 36 is positioned within the outer tubular element 32 and also contains a central rubber portion 37 with a radially inwardly opening V-notch 38, and upper and lower reinforcing rings 39 and 40.

A preventer cap 41 is conventionally mounted by bolts to the preventer body 26 to close the open upper end thereof. The preventer cap 41 has an upper central bore 42 axially aligned with the center bore 27 of the preventer body 26 but of a slightly larger diameter and a flat annular surface 43 which is parallel to the horizontal annular surface 28 of the preventer body 26 but spaced a distance therefrom to form a housing chamber. The two horizontal annular surfaces 28 and 43 engage the upper and lower, inner and outer rings 39 and 34 and 35 and 40, respectively, to locate and maintain the packing unit 31 in a housing chamber within the blowout preventer 25. A suitable number of seals 44 are provided to seal the cap 41, the rings 28, 34, 39 and 43 and the body 26.

The removable or retrievable packing insert 45 is annular or tubular in shape and includes a central rubber portion 46, mounted between a rigid upper ring 47 and a rigid lower ring 48. The insert 45 has an external diameter slightly less than the internal diameter of the upper central bore 42 but slightly greater than the internal diameter at the lower central bore 27, and an internal diameter greater than both the external diameter of the drill pipe tools 17 and the collars or tool joints 18.

The packing insert 45 is for insertion into the stationary blowout preventer 25 and includes means, indicated generally at 50, for properly positioning the insert within the stationary blowout preventer 25. In the preferred embodiment, the means for positioning the packing insert 50 includes a chamfered landing shoulder 51 on the lower metal ring 48 and the chamfered landing shoulder 29 of the preventer body 26 which engage, because the lower ring 48 has a greater diameter than the lower central bore 27, as the retrievable packing insert 45 is slid into the blowout preventer 25. This engagement halts downward movement of the packing insert 45 at the proper position within the blowout preventer 25.

The blowout preventer 25 and the packing insert 45 have latching means, indicated generally at 55, associated therewith for releasably latching the packing insert 45 to the stationary blowout preventer 25. In the preferred embodiment, the latching means 55 includes a circumferentially outwardly opening latching notch or groove 56 on the upper ring 47, and radial openings 57 through the preventer cap 41 containing movable dog means 58 for releasable engagement with the latching notch or groove 56.

The movable dog means 58 includes a dog 59 slidably inserted in each radial opening 57. The dog 59 has a downwardly sloping radially inwardly extending nose 60 for mating insertion into the latching notch 56. The dog 59 is connected to a piston rod 61 extending radially outwardly therefrom and through an opening 62 in a hollow cylinder 63 secured to the preventer cap 41 in each opening 57. The outward end of the piston rod 61 is conventionally attached to a piston 64 movably positioned with the cylinder 63.

The cylinder 63 has its outward end closed by a cylinder cap 65 having a spring 66 extending radially inward from the end thereof and engaging the radially outward end of the piston 64 to bias the piston 64 radially inwardly and thereby bias the dog 59 also radially inwardly. The cylinder 63 has a pair of openings 67 and 68 adjacent either end of the cylinder, operably connected to surface-controlled fluid supply lines (not shown) part of the pressure lines 19. The cylinder piston assembly is provided with a suitable number of seals 69 to prevent the escape of fluid or pressure therein.

The dog 59 is moved from the latching position shown in FIGS. 2 and 3, radially outwardly to the open position shown in FIG. 4 against the biasing action of the spring 5 by a differential fluid pressure via the openings 67 and 68, and upon release of the differential fluid pressure is returned to the latching position of FIGS. 2 and 3 by the biasing of spring 65.

The stationary blowout preventer 25 also has means indicated generally at 70 associated therewith for selectively applying hydraulic fluid pressure thereto. In the preferred embodiment, the means 70 includes a pressure line 71, one of the pressure lines 19, is attached to the preventer body 26 and supplies fluid under pressure through inlet opening 72 in the preventer body 26 to the space between outward surface of the rubber portion 33 of the outer element 32, and the upper cylindrical internal surface 30 of the preventer body 26, as is best seen in FIG. 1.

The fluid accumulator means 75 includes an outlet opening 76 through the preventer body 26. A line 77 from the opening 76 conducts the fluid into an opening 78 in the upper end of an accumulator cylinder 79. The accumulator cylinder 79 has a vertically slidable piston 80 therein suitably sealed by seals 81 to maintain the fluid in the cylinder 79 on the top thereof. A spring 82 is mounted within the cylinder 79 between the bottom of the piston 80 and the bottom of the cylinder 79 to bias the piston 80 upwardly. The cylinder 79 also has a lower opening 83 to line 84 containing pressurized gas which acts as a balance between the spring 82 and the fluid above the piston 80.

As the pressure on the fluid in the blowout preventer 25 increases, it drives the piston 80 lower against the biasing of the spring 82 and the pressurized gas to permit more of the fluid to escape out of the blowout preventer 25. Conversely, when the pressure on the fluid in the blowout preventer drops, the biasing of spring 82 and the pressurized gas raises the piston 80 to drive the fluid thereabove back into the blowout preventer.

The packing insert 45 is slid in the stationary blowout preventer 25 from the vessel 10 by sliding a drill pipe tool 17 therethrough and then mounting a pin sub (not shown) below the packing insert 45 and above the bit (not shown). The drill pipe tool 17 with the packing insert 45 is lowered down the conduit riser 16. As the lower ring 48 of the packing insert 45 reaches the blowout preventer 25, the landing shoulder 51 engages the sloping nose 60 of the dog 59 and slides it radially outwardly against the biasing of the spring 66 in the open position permitting the packing unit 45 to pass thereby.

As best seen in FIG. 4, the packing insert 45 slides through the upper central bore 42, and through the blowout preventer 25 until landing shoulder 51 engages the chamfered landing shoulder to halt the downward movement of and position the packing insert 45 properly in the blowout preventer 25.

When the packing insert 45 is being positioned within the stationary blowout preventer 25, the slope nose 60 of the dog 59 is slid radially inwardly by the spring 66 into latching notch 56 which is simultaneously aligned therewith. The nose 60 of the dog 59 engages the latching notch 56 on the upper ring 47 to hold the insert 45 within the blowout preventer 25.

The blowout preventer 25 is actuated from the surface vessel 10 by hydraulic fluid under pressure supplied through pressure line 71, through inlet opening 72 into the stationary blowout preventer 25 space between the upper cylindrical internal surface 30 and the outward surface of the central rubber portion 33 of the outer tubular element 32 to expand the outward surface of the rubber portion 33 in the outer tubular element 32 bulging the center thereof radially inwardly to bulge the rubber portion 37 of the inner tubular element 36 radially inwardly to press the central rubber portion 46 to the packing insert 45 radially inwardly until the inner surface thereof sealingly engages the drill pipe 17 run therethrough. The pressure on the exterior surface of the rubber 33 of the outer element 32 is also exerted on the piston 80 of the fluid accumulator 75 but is balanced by the spring 82 and the gas pressure from the well.

If, for some reason, such as the vessel 10 bobbing up and down on the surface of the sea 11, a collar or tool joint 18 is forced through the blowout preventer 25, as is shown in FIG. 3, the passage of the collar 18 locally expands the center rubber portion 46 of the retrievable packing insert 45 with the balance of the center rubber portion 46 surrounding the pipe 17 to sealingly engage the pipe tool 17 and the collar 18 as the collar 18 passes therethrough. The bulging of the rubber 46 in turn presses against the rubber portion 37 of the inner tubular element 36 to press against the rubber portion 33 of the outer tubular element 32 to raise the hydraulic pressure between the outward surface of the rubber portion 33 and the internal surface 30 of the preventer body 26. Because the fluid is essentially incompressible in order for any expansion of the rubber portions 46, 37 and 33 to occur, the surge pressure applied to the fluid must exhaust some of the fluid therein. The fluid should not be forced up the pressure line 71, and so it exhausts into the fluid accumulator 75 through the opening 76 and the line 77 and opening 78 into the cylinder 79 on the upper side of the piston as is shown in FIG. 3. The piston 80 is driven downwardly thereby against the biasing of spring 82 in the pressure of the wellhead 14 as has been previously explained.

Once the collar 18 is through the blowout preventer 25, the additional pressure is released and the biasing of the spring 82 and the gas pressure in the wellhead 14, acting against the bottom side of the piston 80, returns the fluid above the piston 80 via opening 78, line 77 opening line 76 to the space between the rubber portion 33 of the outer element 32 and the upper cylindrical internal surface 30 of the preventer body 26 to maintain the central rubber portion 46 of the packing unit 45 in sealing engagement with the pipe 17. This action occurs as many times as the collar 18 on the drill pipe 17 is forced through the blowout preventer 25.

If after repeated use, the rubber portion 46 of the packing insert 45 is thought to be worn, the packing insert 45 may be removed from the blowout preventer 25 for inspection at the surface. To remove the packing insert 45, the pressure in the pressure lines 19 is released, permitting the central rubber 46, the rubber 37, and the rubber 33 to return to the open position shown in FIG. 4.

A retrieving tool 85 is attached to the drill pipe 17. The retrieving tool 85, as shown in FIG. 4, includes radially movable flanges 86 extending through openings 87 in the retrieving tool 85. The flanges 86 are biased by spring 88 radially inwardly. The retrieving tool 85 also contains a wedge 89 which drives the flanges 86 radially outwardly against the spring biasing.

The retrieving tool 85 is lowered through the packing insert 45 with the flanges 86 retracted, and the wedge 89 is driven downwardly spreading the flanges 86 radially outwardly until they will engage the lower metal ring 48 of the packing insert 45. With the flanges 86 of the retrieving tool 85 extended radially outwardly, the tool 85 is raised until the flanges 86 thereof engage the lower metal ring 48.

The latching means 55 is then released by supplying fluid under pressure through opening 68 to the radially inward end of the piston 64 moving the piston 64, the piston rod 61 and the dog 59 radially outwardly against the biasing of spring 65, to move the sloped nose 60 out of the latching notch 56 in the upper metal ring 47. As seen in FIG. 4, this releases the packing insert 45, so that the retrieving tool 85 and the packing insert 45 can be raised by raising drill pipe 17 using derrick 15 to the barge or vessel 10 where the insert 45 can be inspected and replaced if need be by repeating the insertion operation.

Thus the improved stationary blowout preventer according to this invention adds a retrievable packing insert within the blowout preventer and latching means securing the packing insert within the blowout preventer, and adds a fluid accumulator to facilitate the action of the packing insert in allowing the collar of a drill pipe to pass therethrough without breaking the sealing engagement between the rubber of the packing insert and the drill pipe.

Claims

I claim:

1. A method of providing a removable packing insert in a subsea stationary blowout preventer apparatus having a housing mounted in a subsea wellhead and connected by a well riser conduit to a remote vessel floating on the sea above the associated subsea well comprising the steps of:

providing an annular rubberlike packing insert with an outside diameter of a size allowing its passage down said riser conduit and into the bore of an annular radially compressible packing of said preventer apparatus;

running said insert down said riser conduit from said floating vessel remote from said wellhead and preventer apparatus packing; and

compressing said preventer apparatus packing about said insert.

2. The method of providing a removable packing insert of claim 1 with the additional step of:

landing said insert upon a shoulder provided in said blowout preventer apparatus prior to said step of compressing said apparatus packing.

3. The method of providing a removable packing insert of claim 1 with the additional step of:

latching said insert in said preventer apparatus prior to said step of compressing said apparatus packing.

4. The method of providing a removable packing insert of claim 1 with the additional steps of:

running a retrieving tool down said riser conduit and engaging said insert thereon;

relieving the compression of said apparatus packing about said packing insert; and

removing said packing insert by said tool to place a substitute packing insert in said preventer apparatus.

5. The method of providing a removable packing insert of claim 1 wherein said step of compressing said preventer apparatus packing about said insert includes the substeps of:

applying hydraulic fluid under pressure about said preventer apparatus packing to compress said packing about said insert; and

providing a compressible fluid in association with and pressurized in an accumulator means by said hydraulic fluid to allow said insert and packing to expand against the compressive pressures of said hydraulic and associated compressible fluids upon the running of an enlarged portion of a tool through said insert.