U.S. patent application number 11/147887 was filed with the patent office on 2006-12-14 for rod lock for ram blowout preventers.
Invention is credited to Michael Wayne Berckenhoff, Robert Arnold Judge.
Application Number | 20060278406 11/147887 |
Document ID | / |
Family ID | 37523087 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060278406 |
Kind Code |
A1 |
Judge; Robert Arnold ; et
al. |
December 14, 2006 |
Rod lock for ram blowout preventers
Abstract
A blowout preventer to hydraulically seal a wellbore includes a
housing configured to be positioned above a wellhead and to
surround a drillstring, a plurality of rams positioned
perpendicular to an axis of the drillstring to engage the
drillstring and hydraulically isolate an annulus between the
wellbore and the drillstring when in a closed position, and a
roller lock positioned about a thrust rod of each ram configured to
maintain the rams in the closed position.
Inventors: |
Judge; Robert Arnold;
(Houston, TX) ; Berckenhoff; Michael Wayne;
(Spring, TX) |
Correspondence
Address: |
OSHA LIANG L.L.P.
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Family ID: |
37523087 |
Appl. No.: |
11/147887 |
Filed: |
June 8, 2005 |
Current U.S.
Class: |
166/386 ;
166/85.4; 251/1.1 |
Current CPC
Class: |
E21B 33/062
20130101 |
Class at
Publication: |
166/386 ;
166/085.4; 251/001.1 |
International
Class: |
E21B 33/06 20060101
E21B033/06 |
Claims
1. A blowout preventer to hydraulically seal a wellbore,
comprising: a housing configured to be positioned above a wellhead
and to surround a drillstring; a plurality of rams positioned
perpendicular to an axis of the drillstring, the rams configured to
engage the drillstring and hydraulically isolate an annulus between
the wellbore and the drillstring from components located above the
housing when the rams are a closed position; and a roller lock
positioned about a thrust rod of each ram, the roller locks
configured to maintain the rams in the closed position.
2. The blowout preventer of claim 1, wherein the roller lock
includes a plurality of spherical rollers in contact with inclined
surfaces, the inclined surfaces configured to thrust the spherical
rollers into compressive engagement with the thrust rods when the
rams are displaced away from the drillstring.
3. The blowout preventer of claim 2, wherein the spherical rollers
and the inclined surfaces allow movement of the rams into
engagement with the drillstring.
4. The blowout preventer of claim 2, wherein the roller lock
includes a release cage configured to retrieve the spherical
rollers out of compressive engagement with the thrust rods to allow
movement of the rams out of the closed position.
5. The blowout preventer of claim 4, wherein the release cage is
also configured to retain the spherical rollers within contoured
pockets containing the inclined surfaces.
6. The blowout preventer of claim 2, wherein the inclined surfaces
comprise planar surfaces.
7. The blowout preventer of claim 2, wherein the inclined surfaces
comprise contoured surfaces.
8. The blowout preventer of claim 1, wherein the roller lock
comprises a plurality of cylindrical rollers in contact with
inclined planes, the inclined planes configured to thrust the
cylindrical rollers into compressive engagement with the thrust
rods when the rams are displaced away from the drillstring.
9. The blowout preventer of claim 1, wherein the roller lock
includes a release mechanism to allow the rams to be displaced from
the closed position.
10. The blowout preventer of claim 1, wherein the roller lock
includes a release mechanism actuated when hydraulic pressure is
applied to retract the piston.
11. A locking apparatus to be used with a blowout preventer
comprising: a plurality of spherical locking elements to engage and
restrict movement of thrust rods connected to rams of the blowout
preventer; a plurality of receptacles for the spherical locking
elements, each receptacle including an inclined surface configured
to thrust the spherical locking elements into compressive contact
with the thrust rods when the operating rams are urged open; and a
release cage to retract and retain the spherical locking elements
into the receptacles and to direct them out of compressive contact
with the thrust rods when the operating rams are to be opened.
12. The locking apparatus of claim 11, wherein the spherical
locking elements permit movement of the operating rams in a
direction of closure when in contact with the thrust rods.
13. The locking apparatus of claim 11, wherein the inclined
surfaces of the receptacles are planar surfaces.
14. The locking apparatus of claim 11, wherein the inclined
surfaces of the receptacles are contoured surfaces.
15. The locking apparatus of claim 14, wherein the contoured
surfaces correspond to the spherical locking elements.
16. The locking apparatus of claim 11, wherein the receptacles
include pockets into which the spherical locking elements can be
fully retracted away from the thrust rods.
17. The locking apparatus of claim 11, wherein the release cage
prevents the loss of the spherical locking elements when no tubular
objects extend through the blowout preventer.
18. A method to lock rams of a blowout preventer, comprising:
positioning spherical locking elements inside receptacles located
adjacent to thrust rods of the rams, wherein the receptacles
include inclined surfaces configured to engage the spherical
locking elements into the thrust rods when the rams are urged open;
locking the thrust rods with compressive engagement of the
spherical locking elements therewith; and retracting the spherical
locking elements into their respective receptacles with a release
cage to unlock the rams.
19. The method of claim 18, further comprising: retaining the
spherical locking elements in the receptacles with the release
cage, wherein the release cage includes apertures to allow the
spherical locking elements to contact the thrust rods without
falling out of the receptacles.
20. The method of claim 18, wherein the release cage is a single
component configured to retract all the spherical locking elements
into their respective receptacles.
21. The method of claim 18, wherein the release cage is comprised
of a plurality of components, each configured to retract one or
more spherical locking elements into their respective receptacles.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to locking mechanisms for a
blowout preventer as deployed in the petroleum exploration and
recovery industry. More particularly, the invention relates to a
roller lock mechanism to prevent the undesirable reversal of a
thrust rod for a ram-type blowout preventer.
[0003] 2. Background Art
[0004] Wellbores are drilled deep into the earth's crust to recover
oil and gas deposits trapped in the formations below. Typically,
these wellbores are drilled by an apparatus that rotates a drill
bit at the end of a long collection, or string, of threaded pipes
known as a drillstring. Because of the energy and friction involved
in such an operation, a drilling fluid, commonly referred to as
drilling mud, is used to lubricate and cool the drill bit as it
cuts the rock formations below. Furthermore, the drilling mud is
capable of performing the secondary function of removing the drill
cuttings from the bottom of the wellbore to the surface. Typically,
drilling mud is delivered to the drill bit under high pressures
through a central bore of the drillstring. From there, nozzles on
the drill bit direct the pressurized mud to the cutters on the
drill bit where the pressurized mud cleans and cools the bit. As
the fluid is delivered downhole through the central bore of the
drillstring, the fluid returns to the surface in the annulus formed
between the outside of the drillstring components and the cut
wellbore. Therefore, a hydrostatic column of drilling mud typically
extends from the surface to the bottom of the hole being cut.
[0005] As wellbores are drilled several thousand feet below the
surface, the hydrostatic column of drilling mud serves to help
prevent blowout of the wellbore as well. Often, hydrocarbons and
other fluids trapped in subterranean formations exist under
significant pressures. Absent any flow control schemes, fluids from
such ruptured formations can blow out of the wellbore like a geyser
and spew hydrocarbons and other undesirable fluids into the
atmosphere. Several thousand feet of hydraulic head from the
drilling mud column helps to prevent the wellbore from blowing out
under normal conditions. However, under certain unforeseen
circumstances, the drill bit will encounter pockets of pressurized
formations and will cause the wellbore to "kick" or experience a
rapid increase in pressure. Because formation kicks are
unpredictable and would otherwise result in disaster, flow control
devices known as blowout preventers ("BOP's"), are mandatory on
most drilling rigs in use today.
[0006] Blowout preventers are devices configured to seal the
annular space that surrounds the drillstring. One of the most
common types of blowout preventer is known as a ram-type blowout
preventer. A ram-type blowout preventer includes a large housing
mounted atop the wellhead that includes a large passageway through
which the drillstring (and any components connected thereto) is
able to pass. The housing also includes two or more rams located in
a plane substantially normal to the axis of the drillstring and
wellhead that are configured to move between retracted and extended
positions. The ends of the rams are configured so that when
extended, they provide a complete annular hydraulic seal around the
drillstring disposed therethrough.
[0007] Referring initially to FIG. 1, a typical ram-type BOP 100 is
shown schematically. Ram-type BOP 100 shown includes a main housing
102, two or more piston ram housings 104, and top 106 and bottom
108 bolting flanges for connection to other wellhead components
(not shown). Ram-type blowout preventer 100 is preferably
constructed such that a generally cylindrical through bore 110
allows oilfield tubulars 112 to unobstructedly pass through along a
drillstring axis 114. Oilfield tubulars 112 are typically
components of a drillstring and may include, but are not limited
to, drill pipe, drill collars, measurement tools, coiled tubing, or
wirelines. Under normal conditions, through bore 110 is open and
not obstructed such that fluids pass through an annulus 116 formed
between the outer profile of tubulars 112 and the inner profile of
through bore 110. When the wellbore below is to be shut off such
that fluids below BOP 100 can no longer communicate with the
wellbore above BOP 100, ram assemblies 118 are activated to provide
a 360.degree. seal of annulus 116 between bore 110 and tubulars
112.
[0008] Each ram assembly 118 includes a sealing ram 120 having a
leading edge 122 connected to a hydraulic piston 124 through a
thrust rod 126. Leading edge 122 is preferably contoured such that
it corresponds with an outer profile of oilfield tubular 112 so
that a tight seal can be formed therebetween. Connected to sealing
rams 120 through thrust rods 126, hydraulic pistons are activated
by an external hydraulic source (not shown) to engage leading edges
122 against tubular 112 and seal off annulus 116. While it may be
typical for there to be two ram assemblies 118, each with a
corresponding semi-circular profile for leading edges 122, it
should be understood that a ram-type BOP 100 may employ three or
more ram assemblies 118 with corresponding circular portions for
leading edges 122 to shut off and seal annulus 116.
[0009] To seal off annulus 116, pressurized fluids are applied to
hydraulic port 128 in communication with a reservoir 130 of ram
housing 104. Increases in pressure in reservoir 130 urge back face
132 of piston 124, causing piston 124, rod, 126, and ram 120 to be
thrust toward tubular 112. The higher the pressure in communication
with reservoir 130, the higher the loads transmitted through rod
126 to ram 120. To retract rams 120 out of annulus 116, pressure to
port 128 is reduced and piston 124 is able to retract into
reservoir 130. Retraction of pistons 124 may be assisted through
the use of retraction springs (not shown), hydraulic retraction, or
through any other means known in the art. Particularly, a
retraction port 129 can be used to provide hydraulic access to a
retraction reservoir 131, such that an increase in hydraulic
pressure displaces piston 124 to retract ram 120.
[0010] With rams 120 extended and leading edges 122 engaging
oilfield tubular 112, a strong hydraulic seal prevents fluid from
escaping the wellbore through annulus 116. As long as hydraulic
pressure is maintained in reservoir 130, rams 120 will continue to
seal annulus 116. However, there are circumstances where it is
desired to maintain the annular seal regardless of the operational
abilities of ram-type BOP 100. For example, it is desirable to
maintain seal integrity in the event of a power failure at the
rigsite. Furthermore, if wellbore is to be shut-in for an extended
period of time, maintaining hydraulic pressure over that time
period is not always reliable or prudent. Therefore, systems and
mechanisms to "lock" hydraulic rams 120 in place once activated are
highly desirable in the oilfield.
[0011] One former method to lock hydraulic rams 120 in place
involves the tightening of mechanical screws to lock pistons 124 in
place once displaced in reservoir 130. Such screws were tightened
either manually or through power devices and would effectively lock
rams 120, thrust rods 126, and pistons 124 in place. However,
accessibility concerns make such a solution less than optimal.
Particularly, in deep-sea installations, these locking screws must
be activated by remotely operated vehicles or through electrical
actuators. As such, their reliability is suspect in depths of
several hundred feet or more. Furthermore, on land-based rigs, the
BOP 100 is typically located beneath the rig floor. As such,
engaging and disengaging the locking screws takes considerable
time, time that is not always available in the event of an
emergency.
[0012] Additional solutions to lock hydraulic rams are available to
lock thrust rods 126 in place. Formerly, ratchet profiles (e.g.
U.S. Pat. No. 3,941,141 to Robert, hereby incorporated by reference
herein) have been used upon the outer profiles of thrust rods 126
in conjunction with matching locking members to retain thrust rods
126 in place. Furthermore, various internal threaded mechanisms
(e.g U.S. Pat. No. 4,052,995 to Ellison and U.S. Pat. No. 4,076,208
to Olson, both hereby incorporated by reference herein) have been
employed to secure thrust rods 126 in place using whereby thrust
rods 126 are threaded and corresponding jam-nut devices lock thrust
rods 126 in place. Finally, various wedging solutions (e.g. U.S.
Pat. Nos. 4,305,565 to Abbe and U.S. Pat. No. 4,969,390 to
Williams, both hereby incorporated by reference herein) have been
proposed to lock thrust rods 126 in place. While promising, each of
these solutions are considered by many to be less than optimal in
that they exhibit a slight amount of slip or "play" in the reverse
direction known as backlash before they engage and lock the thrust
rods 126 in place. In the event of a high pressure "kick" to a
wellbore, even infinitesimal displacements in rams 120 connected to
thrust rods 126 can result in a catastrophic release of wellbore
fluids.
[0013] Therefore, there is a long-felt need in the industry for an
apparatus to quickly, positively, and solidly lock ram-type blowout
preventers in an engaged position with minimal operator interaction
and with minimal backlash of the rams before locking occurs.
SUMMARY OF INVENTION
[0014] In one embodiment, a blowout preventer includes a housing
configured to be positioned above a wellhead and to surround a
drillstring, a plurality of rams positioned perpendicular to an
axis of the drillstring, and a roller lock positioned about a
thrust rod of each ram. The rams may be configured to engage the
drillstring and hydraulically isolate an annulus between the
wellbore and the drillstring from components located above the
housing when the rams are in a closed position. The roller locks
may be configured to maintain the rams in the closed position.
[0015] In one aspect, the present invention related to a locking
apparatus to be used with a blowout preventer. In one embodiment,
the locking apparatus includes a plurality of spherical locking
elements to engage and restrict movement of thrust rods connected
to rams of the blowout preventer. The locking apparatus may also
include a plurality of receptacles for the spherical locking
elements, wherein each receptacle includes an inclined surface
configured to thrust the spherical locking elements into
compressive contact with the thrust rods when the operating rams
are urged open. Furthermore, the locking apparatus may also include
a release cage to retract and retain the spherical locking elements
into the receptacles and to direct them out of compressive contact
with the thrust rods when the operating rams are to be opened.
[0016] In one aspect, the present invention relates to a method to
lock rams of a blowout preventer. The method may include
positioning spherical locking elements inside receptacles located
adjacent to thrust rods of the rams, wherein the receptacles
include inclined surfaces configured to engage the spherical
locking elements into the thrust rods when the rams are urged open.
The method may further include locking the thrust rods with
compressive engagement of the spherical locking elements. The
method may further include retracting the spherical locking
elements into their respective receptacles with a release cage to
unlock the rams.
[0017] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a schematic section-view drawing of a ram-type
blowout preventer.
[0019] FIG. 2 is a schematic drawing of a thrust rod retainer in
accordance with an embodiment of the present invention.
[0020] FIG. 3 is a schematic drawing of a thrust rod retainer in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
[0021] Referring now to FIG. 2, a schematic representation of a
thrust rod lock 250 in accordance with an embodiment of the present
invention is shown. In this embodiment, thrust rod lock 250 is
preferably located within a piston ram housing (e.g. 104 of FIG. 1)
in a fixed position surrounding a thrust rod 226. Thrust rod lock
250 is desirably configured to allow displacement of thrust rod 226
in a locking direction 252, while disallowing displacement of
thrust rod 226 in an unlocking direction 254. Thrust rod lock 250
includes a main body 256, into which one or more roller receptacles
258 are formed. Roller receptacle 258 is shown including a deep
section 260 that extends to a shallow section 262 through an
inclined surface 264.
[0022] As such, each roller receptacle 258 is configured to retain
and deploy a roller 266 within and from receptacle 258 when locking
of thrust rod 226 is selectively desired. Particularly, when roller
266 is located within deep section 260, substantially no contact
occurs between roller and thrust rod 226, but as roller 266 travels
down inclined surface 264, thrust rod 226 is increasingly locked
into a bind by roller 266 and surface 264. Furthermore, once so
locked, further increases in load upon thrust rod 226 in unlocking
direction 254 tend to cause roller 266 in contact with inclined
surface 264 to compress against thrust rod 226 even tighter,
resulting in an even stronger locked position. Displacements of
thrust rod 226 in locking direction 252 tend to roll roller 266 up
inclined surface 264 toward deep section 260 of main body 256, such
that rod 226 is free to move in locking direction 252.
[0023] Furthermore, a retainer cage 268 of thrust rod lock 250
retains roller 266 within receptacle 258 and is configured to
retrieve roller 266 into deep section 260 when thrust rod 226 is to
be released. Retainer cage 268 preferably includes a slot (not
shown) adjacent to roller 266 to allow retainer cage 268 to
displace roller 266 without interfering with the roller's
engagement with thrust rod 226. In the case where roller 266 is a
spherical roller, slot can be a longitudinal slot or a spherical
section to match the outer profile of roller 266. Alternatively, in
the case where roller 266 is cylindrical, the slot can be a
transverse slot approximately the same width as roller 266.
Regardless of configuration, when thrust rod 226 is to be displaced
in unlocking direction 254, retainer cage 268 is displaced in
direction 270 to retrieve roller 266 up inclined surface 264 and
into deep section 260, away from the engagement with outer surface
of thrust rod 226. Retainer cage 268 may be biased so that roller
266 is biased in the direction opposite 270 and into thrust rod
226. Alternatively, cage 268 may be unbiased allowing movement of
thrust rod 226 to be the sole force in causing roller 266 to be
engaged therewith.
[0024] It should be understood that any means to displace or bias
retainer cage known in the art may be employed, including, but not
limited to, hydraulic lines, springs, and tension cables.
Particularly, retainer cage can be constructed to be displaced when
hydraulic pressure is applied to a hydraulic actuator attached
thereto. Furthermore, if a hydraulic device is employed to retract
thrust rod 226 into unlocking direction 254, a control system (not
shown) can be used to direct such hydraulic pressure to either the
retainer cage actuator, the thrust rod retractor, or both.
Alternatively, a hydraulic system to release thrust rod lock 250
can be distinct from a hydraulic system to displace thrust rod 226
in unlocking direction 254.
[0025] Furthermore, it should be understood that inclined surface
264 can be any of various types known in the art. Particularly,
surface 264 can be a mere planar surface or can be profiled to fit
the contours of spherical rollers 266. Furthermore, while rollers
266 are described generically, it should be understood that they
can be constructed as spherical or cylindrical devices and can be
constructed with various hardness and friction values to facilitate
contact and engagement between thrust rod 226 and inclined surface
264.
[0026] Referring now to FIG. 3, a schematic of a thrust rod lock
350 in accordance with an embodiment of the present invention is
shown. Like thrust rod lock 250 of FIG. 2, thrust rod lock 350 of
FIG. 3 is preferably located within a piston ram housing 304 in a
fixed position surrounding a thrust rod 326. While a single thrust
rod lock 350 is shown, it should be understood that a plurality of
rod locks 350 can surround thrust rod 326 radially and axially.
[0027] Thrust rod lock 350 is desirably configured to allow
displacement of a thrust rod 326 in a locking direction 352, while
resisting displacement of thrust rod 326 in an unlocking direction
354. Thrust rod lock 350 includes a main body 356, into which two
series of roller receptacles 358A, 358B are formed. Like
receptacles 258 of FIG. 2, inner roller receptacle 358A is profiled
to urge a roller 366A into engagement with thrust rod 326 when
thrust rod 326 is displaced in unlocking direction 354. At the same
time, outer roller receptacle 358B is profiled to urge a roller
366B into engagement with an outer wear plate 380 when main body
356 is displaced in unlocking direction 354. Therefore, for each
location about and along thrust rod 326, one roller 366A bites with
thrust rod 326 and another roller 366B bites with wear plate 380 to
resist displacement of thrust rod 326 in unlocking direction 354.
As such, for each incremental displacement in unlocking direction
354, thrust rod 326 of FIG. 3 will experience double the radial
compression as would be experienced by a thrust rod in a single
roller configuration (e.g. FIG. 2).
[0028] Furthermore, inner and outer retainer cages 368A, 368B
retain rollers 366A, 366B inside receptacles 358A, 358B and allow
for rod lock 350 to be released once retraction of thrust rod 326
is desired. As with retainer cage 268 of FIG. 2, retainer cages
368A, 368B allow rollers 366A, 366B to contact thrust rod 326 and
wear place 380 through slots or other forms of apertures (not
shown) therethrough. As before, such apertures in retainer cages
368A, 368B can take the form of longitudinal slots or spherical
sections in the case where rollers 366A, 366B are spherical or can
be transverse slots if rollers 366A, 366B are cylindrical. A pair
of bias springs 382, 384 is shown working in conjunction with main
body 356 and retainer cages 368A, 368B to thrust rollers 366A, 366B
into locking engagement with thrust rod 326 and wear plate 380 by
default. As inner retainer cage 368A is fixed relative to housing
304, spring 382 urges main body in the direction of arrow 352 such
that inclined surface 364A urges roller 366A into contact with
thrust rod 326. Likewise, spring 384 between main body 356 and
outer retainer cage 368B urges cage 368B and roller 366B in the
direction of arrow 352 such that inclined surface 364B urges roller
366B into contact with wear plate 380.
[0029] To release rollers 366A, 366B from their engagement with
thrust rod 326 and wear plate 380, an unlocking mechanism 386 is
employed. Unlocking mechanism 386 can be constructed any number of
ways, but is preferably configured to retract rollers 366A, 366B
into their respective receptacles 358A, 358B so that thrust rod 326
can be retracted in unlocking direction 354. Unlocking mechanism
386 of FIG. 3 is shown within a recess 388 of housing 304. A
hydraulic seal 390 surrounding mechanism 386 ensures that when
hydraulic pressure is increased to a hydraulic port 392, mechanism
386 is displaced in the direction of 354 such that a thrust face
394 engages a corresponding load shoulder 396 of outer retainer
cage 368B. When pressure to port 392 is sufficiently elevated,
springs 384 and 382 are compressed such that rollers 366A, 366B are
retained within recesses 358A, 358B to enable thrust rod 326 to be
retracted. Once thrust rod 326 is retracted, pressure to port 392
can be released so that thrust rod 326 can be quickly engaged and
held in place without any secondary locking step necessary. In its
ordinary, equilibrium state, rod lock assembly 350 resists
disengagement of thrust rod 326 without any supplemental steps,
even in the event of total loss of hydraulic power.
[0030] Rod lock assemblies 250 and 350 of the present invention
exhibit many advantages over locking mechanisms currently
available. In particular, rod lock assemblies 250, 350 are capable
of securing thrust rods 226, 326 almost instantaneously and with
little or no backlash or slippage. Furthermore, rod lock assemblies
250, 350 are disclosed as "fail safe" devices, in that they lock by
default. No affirmative steps are necessary to lock thrust rods
226, 326 in place once they are extended. Rod lock assemblies 250,
350 automatically engage and resist disengagement of thrust rods
226, 326. As no external power source is necessary to engage rod
locks 250, 350, their effectiveness is not compromised by power
failures. In contrast, hydraulic (or other) power is only necessary
to disengage rod locks 250, 350. Finally, as rod locks 250, 350 are
configured to engage smooth outer profiles of thrust rods 226, 326,
no obstructive features are necessary on thrust rods 226, 326.
Former solutions required special profiles that could obstruct
thrust rod 226, 326 operation and engagement.
[0031] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *