Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02259680 1999-O1-18
ROTATING BOP AND METHOD
1. Field of the Invention
S The present invention relates generally to rotating blow-out preventers and,
more
specifically, to a highly flexible rotating bladder and seal assembly remotely
latchable
within the BOP housing.
2. Background of the Invention
Underbalanced drilling is advantageous in many circumstances. Underbalanced
drilling generally involves the practice of drilling with anticipated downhole
pressure
greater than hydrostatic pressure of the mud column. Formation pressure is not
sufficiently contained or controlled by drilling fluids to prevent flow from
the formation.
Formation flow could potentially reach the surface to blow out the well if
downhole
pressure were great enough but for the surface pressure control systems that
are used to
control well pressure. The rotating blow-out preventer allows the operator to
seal around
the drill pipe and continue drilling even when the well pressure at the
surface is greater
than atmospheric pressure.
In horizontal well drilling as compared to vertical well drilling, it may be
more
difficult to establish well control by hydrostatic fluid head due at least in
part to the
slower build-up of hydrostatic pressure with well depth (which is not vertical
depth) as
compared with the build-up that normally occurs rapidly with well depth when
drilling
vertically oriented wells. The well control problems caused by lack of
hydrostatic
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pressure may be made worse by hole conditions such as abnormal pressures,
formation
seepage, and lost circulation. In some cases, operators have saved hundreds of
thousands
of dollars in drilling fluid costs alone by drilling horizontal wells
underbalanced. The
safety of the operation may also be improved by this method because of the
additional
pressure control capability of the rotating blow-out preventer used for
underbalanced
drilling pressure control purposes. While drilling with the rotating blow-out
preventer,
sudden changes in hole conditions do not result in a dangerous blowout
condition that
may sometimes not be detected in sufficient time to effectively close in the
well. For
instance, drilling into a lost circulation zone whereby hydrostatic pressure
may be reduced
due to fluid loss could result in a sudden loss of pressure control. However,
the seal in
the rotating blow-out preventer quickly and automatically increases around the
drill pipe
to account for such sudden changes. In drilling vertical wells, the rotating
blow-out
preventer may be useful as an additional safety control device because similar
fluid loss
conditions may also result in well pressure control problems that could be
easily handled
1 S by use of a rotating blow-out preventer.
Another significant advantage of underbalanced drilling, in either vertical or
horizontal wells, is the avoidance of formation damage caused by overbalanced
drilling
fluids. Repair of formation damage caused by overbalanced drilling may be
difficult,
time consuming, and limited. Thus, formation damage may significantly reduce a
well's
ability to produce, thereby significantly affecting profitability of the well.
Another advantage of underbalanced drilling is the result of greatly increased
accuracy of logging tools and other measurement devices. Formation invasion by
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drilling fluid is perhaps the greatest cause of inaccuracies in well logs. For
instance, to
obtain good measurements of uninvaded formation characteristics, logging tools
are
expected to compensate for mud cake build-up of the drilling fluid in the
borehole, a
flushed zone around the borehole wherein all moveable formation fluids have
been
flushed therefrom, and a partially flushed zone around the borehole wherein
moveable
formation fluids have been partially flushed therefrom by a not necessarily
evenly
decreasing percentage until non-invaded formation is reached. It will be
understood that
compensation techniques, while very useful, cannot always compensate for and
accurately
determine the characteristics of the non-invaded formation. Therefore,
significant zones
of oil or gas may remain undetected, or have distorted readings, that cause
valuable
production zones to be passed over when the operator reviews and selects what
may
incorrectly appear to be the best producing zones. In the absence of invasion
of drilling
fluid into the formation due to underbalanced or even near balanced drilling,
the accuracy
of logging tools is greatly increased because the formation is not invaded and
the
formation fluids present themselves somewhat more naturally the borehole. This
means
that the operator has more accurate information with which to make decisions.
Other
well measurement tools, such as coring tools, will also produce more accurate
readings.
Thus, there are many advantages to underbalanced drilling.
For underbalanced drilling, the rotating blowout preventer is mounted to the
top
of a stack of conventional BOP's and can control surface back pressure in a
range
depending on the rotating blow-out preventer pressure rating. The well is
drilled with an
underbalanced fluid, such as diesel, water mixed with nitrogen, air, gas, or
the like. The
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rotating blow-out preventer allows rotating and stripping of the drill string
during the
drilling operation, a significant advantage that normal BOP's do not provide.
Because the rotating blow-out preventer is typically mounted on top of a
conventional BOP stack, the length or height of the rotating blow-out
preventer is often
important depending on the rig set up. Space between the conventional BOP
stack and
the rotary table and/or drill floor may be strictly limited by the size of the
drilling rig and
the depth of the cellar to a length required to manipulate the largest drill
stands it can drill
with. Thus, for general purpose use with many drilling rigs, it is highly
desirable for the
rotating blow-out preventer to be limited in height. As a result of height
restraints, the
length of sealing area is limited and must still safely seal variable sized
drill pipe, drill
pipe connections, and the square or hexagonal kelly, if present for rotary
table drilling
operations. For purposes of the present application, it assumed that the word
tubular
defines drill pipes, kellys, and so forth.
The rotating blow-out preventer may use hydraulically activated packing
elements
mounted for rotation with the drill pipe. If the packing elements are large
and heavy, then
the bearings may wear more rapidly. Large packing elements and large bearings
are quite
time consuming to change out, if it becomes necessary to make a replacement.
In some
rotating blow-out preventer's, the entire top of the rotating blow-out
preventer housing
must be removed before the bearings can be changed. This may also require
removal of
the driller's rotary table, which may also be time consuming and may often
require a
competent rig mechanic to be present.
Large packing elements may not be flexible enough to seal with all drilling
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elements, such as square or hex-shaped kellys, thereby requiring an additional
kelly
packing device that adds additional complexity to operation and cost of the
Rotating
blow-out preventer. Most rotating blow-out preventer's have some provision for
changing out at least the most wearable parts of the drill pipe packing
elements without
the need to remove the rotating drill table. Generally, the packing element,
or the most
wearable portion thereof, is retrievable through the hole in the drill table.
In some
designs, this requires fishing to secure the most wearable portion of the
packing element.
The least wearable portion of a dual element packer may not be available for
replacement
without extensive time to disassemble the rotating blow-out preventer. Designs
for more
quickly releasing the packing elements may include removable clamps that have
to be
manually released, as by a threaded bolt latch, and then manually detached
from the
rotating blow-out preventer housing. In some designs, hydraulic controls may
release the
clamp, but the clamp holding the packing elements within the rotating blow-out
preventer
must then be manually detached from the rotating blow-out preventer housing
before the
packing elements are removed. Such work with heavy moveable equipment within
small
enclosures can well be hazardous.
Another problem with presently existing rotating blow-out preventer's is the
high
failure rate of the upper bearing seal and/or upper bearing. Failure may occur
due to the
fact that most of the pressure drop between wellbore pressure and ambient
pressure is
across the upper bearing and seal. The upper and lower bearing seals must seal
between a
stationary element, such as the rotating blow-out preventer housing, and the
rotating
elements of the packing assembly. Typically, the pressure drop across the
bottom seal
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and/or bottom bearing is a pressure drop of only about 250 psi or so, because
hydraulic
activating fluid is typically maintained in the range of from 0 to 500 psi
above the well
head pressure for activating the packing elements to seal against the drill
pipes.
However, the upper seal and/or upper bearing must then have the remainder of
the
pressure drop between the well head pressure and ambient pressure, which
pressure
depends on the rating of the rotating blow-out preventer and the well head
pressure upon
which it is used. The large pressure drop across the upper seal and/or bearing
places a
strain on the upper bearing elements and the upper seal that may cause earlier
failure of
such bearings. In rotating blow-out preventer systems where bearing change-out
is a
lengthy process, this is an especially significant problem due to excessive
lost rig time
caused by such an upper bearing and/or seal failure.
Consequently, an improved rotating blow-out preventer is desirable to provide
accurate sealing over a wide range of profile variations in pipe and kellys,
quick change-
out not only of seals but also of bearings through the rotary table, and
provisions to
improve the lifetime of especially the upper rotary seals and bearing. Those
skilled in the
art will appreciate the present invention that addresses these and other
problems.
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SUMMARY OF THE INVENTION
The present invention relates to a rotating BOP for reliably and conveniently
sealing tubulars such as drill pipe that include various profile variations.
For purposes
herein tubulars also include pipes with square or hexagonal cross-sections, or
non-
rounded cross-sections, such as the kelly drive often used in rotary drilling.
The present invention and method relate to a highly flexible bladder within an
insertable bladder assembly that includes bearings and the bladder, and which
is latched
into position by built-in hydraulic latch members, such as arc-shaped dogs,
and piston
actuators that may be remotely operated for releasing the bladder assembly.
The bladder
may be readily replaced from the removed bladder assembly as it is held in by
only two
end caps. Preferably a spare bladder assembly is kept available for immediate
change out
when it is necessary to replace the bladder and/or bearings. The assembly is
manufactured at a relatively low cost as compared to some bladder assemblies.
The time
to change out the bladder assembly may be about 30 minutes or even less once
the rig
crew becomes familiar with the relatively simple process. The removed and now
spare
bladder assembly can then be rebuilt at a convenient time without cessation of
drilling so
that it is ready for subsequent use, if further replacement is required.
Thus, the rotating blow-out preventer of the present invention includes a
latch for
removably securing a rotating seal assembly, the rotating seal assembly being
operable for
sealing between down hole pressure and ambient pressure across axially
moveable
tubulars having profile variations along the length of the tubulars. For
purposes of the
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present application, it is assumed that tubulars can also have different cross-
sections than
round such as square or hexagonal that correspond to the kelly in an oil rig.
A housing is
provided in surrounding relationship to the rotating seal assembly and the
housing defines
a cavity into which the rotating seal assembly is insertable. At least three
latch members,
and in the presently preferred embodiment six latch members or dogs, are
provided with
each latch member mounted for radially inwardly and outwardly movement with
respect
to the rotating seal assembly to latchingly engage and disengage the rotating
seal
assembly.
A non-rotating portion of the rotating seal assembly is positionable within
the
housing and the non-rotating portion has a non-rotating latch engagement
surface. Each
latch member is mounted for radially inwardly and outwardly movement with
respect to
the rotating seal assembly to latchingly engage and disengage the non-rotating
latch
engagement surface. In a presently preferred embodiment, the latch members, or
dogs,
are mounted wholly within the rotating blow-out preventer housing to provide a
streamlined profile for the housing.
In a presently preferred embodiment, the latch includes at least one latch
piston
for actuating the at least one latch. As described hereinafter one latch
piston drives six
latches but other arrangements are possible. To conserve radial space, the at
least one
latch piston is mounted for a movement such that a component of the movement
is
substantially parallel to the borehole axis. In this preferred embodiment, the
piston is
mounted within the wall of the housing and moves vertically up and down.
In other words, the preferred embodiment includes a plurality of latch members
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with each latch member having at least a portion thereof that is movable in a
straight line
toward the rotating seal assembly so as to be latchable therewith. Preferably
the straight
line movement is directly towards the centerline of the rotating blow-out
preventer
housing. In the presently preferred embodiment, the latch members move in a
straight
line rather than in a curved travel path.
Preferably, one or more pistons are available for actuating the one or more
latching
members or dogs. In the presently preferred embodiment, one piston is used to
drive six
arc-shaped latches. A wedgeable connection of power transmission between the
one or
more pistons and the one or more latching members is preferably used as the
one or more
pistons move vertically and the latch members move substantially radially. The
one or
more latching members are responsive to wedgeable contact of the wedgeable
connection
for urging the one or more latching members into latching engagement with the
rotating
seal assembly. In a preferred embodiment, the piston and latch member make
direct
wedgeable contact rather than using an intermediary member to form the
wedgeable
connection.
The rotating blow-out preventer housing is preferably in surrounding
relationship
to the rotating seal assembly and the rotating blow-out preventer housing
preferably
adapted to receive fasteners for fastening the housing to the pressure tree
assembly so that
the housing defines an uppermost portion of the borehole. A connector is
preferably
provided on the rotating seal assembly, such as a connector for a cat line or
the like. The
connector is operable for receiving a removal force applied by the cat line to
remove the
rotating seal assembly from the housing. In a preferred embodiment, remotely
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controllable latch members are mounted for movement with respect to the
housing for
latching and unlatching the rotating seal assembly. The rotating seal assembly
is
removable from the housing by applying the removal force to the connector, as
with a cat
line, without the need to remove the remotely controllable latch members from
the
housing, which members are preferably built into the rotating blow-out
preventer
housing.
In a presently preferred embodiment, a plurality of piston lock members, such
as
hand-operated levers, are provided for releaseably fastening the one or more,
and
preferably one, latch piston in the actuating position. Thus, the one or more
hydraulic
latch pistons may include a ratcheting assembly that allows movement for
latching but
prevents movement in the opposite direction so that the latch will be
maintained even if
hydraulic control pressure to the preferably hydraulic one or more latch
pistons is
momentarily lost. Preferably for simplicity, the plurality of piston latch
members are
non-remotely operable as with a lever action to engage and disengage a spring-
loaded
ratchet plate. However, these could also be remotely operable, if desired.
A rotating seal assembly is preferably disposed within the rotating blow-out
preventer housing for sealing between down hole pressure of a borehole and
ambient
pressure across one or more tubulars having profile variations along the
length of the one
or more tubulars. The tubulars are moveable into and out of the borehole in an
axial
direction through the rotating seal assembly. The rotating seal assembly
preferably
includes a tubular frame mounted for rotation with respect to the housing. A
substantially
hour glass-shaped tubular bladder secured to opposing ends of the tubular
frame when the
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tubular is small or absent. However, the resting shape of tubular bladder
depends on the
materials available for construction and could easily change if other stronger
materials
were available for a thinner, more flexible bladder. The present bladder is
sufficiently
flexible to provide sealing contact with profile variations of the one or more
tubulars
including round, square, or hex cross-sectional tubulars. A pressure chamber
is defined
radially outwardly of the tubular bladder. The pressure chamber is adapted for
receiving
a fluid under pressure for activating the tubular bladder to flexibly conform
to the one or
more tubulars. In a presently preferred embodiment the tubular frame includes
both
rotating and non-rotating components and the pressure chamber is defined
between the
bladder and preferably the non-rotating component of the tubular frame.
Conceivably
the pressure chamber could be defined at least in part by the housing of the
rotating blow-
out preventer, which is also non-rotating.
In a presently preferred embodiment, a one-piece tubular bladder is secured to
the
tubular frame. The one-piece tubular bladder is sufficiently flexible for
sealing contact
with profile variations of the one or more tubulars, including tubulars with
round, square,
hexagonal cross-sectional profiles, that may increase and decrease in diameter
along the
length of the tubular. The pressure chamber is responsive to a fluid
receivable into the
pressure chamber for activating the one-piece bladder to conform to the one or
more
tubulars.
First and second end caps are preferably removably securable to the tubular
frame
for securing the bladder in position. The preferably elastomeric tubular
bladder is
removably securable to the tubular frame at opposite ends thereof with the
first and
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second end caps. By elastomeric it is meant any pliable material such as
polymers,
urethane, plastics, and the like, useful for sealing purposes. The presently
preferred
embodiment uses a urethane material. The end caps are preferably metallic,
circular, and
have an inner diameter that defines the largest tubulars that may extend
through the
tubular frame presently positioned within the rotating blow-out preventer
housing.
A hydraulic fluid control system is preferably used to circulate hydraulic
fluid
through the pressure chamber and to maintain a desired seal pressure of the
fluid within
the pressure chamber which pressure typically is between 0 and 500 psi above
the well
bore pressure directly below the tubular frame. A wellbore seal is mounted to
seal the
tubular frame and seals between the seal pressure of the pressure chamber and
the well
bore pressure. A pressure drop element is provided to produce a significant
pressure
drop from the seal pressure to a lower pressure much closer to ambient
pressure. An
ambient seal is mounted to seal the tubular frame between the lower pressure
and the
ambient pressure.
The bladder preferably has a first portion and a second portion that are
axially
displaced from each other. The first portion and the second portion each have
an inner
surface for contacting the tubulars. The first portion being disposed axially
adjacent to
the down hole pressure and the second portion being axially disposed adj acent
to the
ambient pressure. The first portion has a smaller radial thickness than the
second portion
such that the first portion wears more rapidly than the second portion.
Therefore a hole in
the first portion due to wear would still permit a seal to be maintained by
the second
portion as the well bore pressure itself would activate the second portion to
seal around
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the tubular prior to closing the BOP to permit change out of the rotating seal
assembly.
In operation, the method of removing a bladder assembly from a rotating blow
out
preventer housing comprises remotely releasing latches that latch the bladder
assembly
within the rotating blow out preventer housing. A connection to the bladder
assembly
through a rotary table is made, such as with a cat-line. The bladder assembly
is pulled
through the rotary table without the need to remove the latches from the
rotating blow out
preventer housing.
An object of the present invention is to provide an improved rotating blow-out
preventer.
Another object of the present invention is to provide a unique bladder that is
thin
enough to be highly flexible and yet provides inherent backup ability in case
of
unmonitored wear.
Yet another object is to provide a remotely controllable latch system that
permits
removal of the rotating seal assembly without removal of the latch from the
rotating
blow-out preventer housing.
Yet another obj ect of the present invention is to provide a more durable seal
and
bearing for the rotating seal assembly.
A feature of the present invention is a one-piece bladder.
Another feature of the present invention is a bladder clamped within the seal
assembly by two end caps.
Yet another feature of the present invention is a bladder having variations in
radial
thickness along its axial length so as to provide a more rapidly wearing
portion so that the
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thicker portion can maintain a seal even if a leak should occur in the rapidly
wearing
portion of the bladder.
Another feature of the present invention is one or more hydraulic latch
pistons
built within the rotating blow-out preventer housing, although preferably one
hydraulic
latch piston is used.
Yet another feature of the present invention is that the one or more hydraulic
latch
pistons are mounted for vertical movement within the rotating blow-out
preventer
housing, although preferably one vertically moveable cylindrical hydraulic
latch piston is
used. The cylindrical latch piston preferably encircles the borehole within
the wall of the
rotating blow-out preventer housing.
An advantage of the present invention is a rotating seal assembly flexible
enough
to seal with tubulars including tubular joints as well as with square or hex-
shaped
tubulars such as the commonly used kelly tubular drive elements.
Another advantage of the present invention is a rapid change out time of both
the
bladder and bearings of the rotating blow-out preventer.
Yet another advantage of the present invention is the ability to remotely
release
the entire rotating seal assembly for change out.
These and other objects, features, and advantages will become apparent to
those
skilled in the art upon review of the drawings, claims, and disclosure of the
invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view, in section, of a rotating blowout preventer in
accord
with the present invention;
S FIG. 2 is an elevational view, in section, of a rotating blowout preventer
in accord
with the present invention;
FIG. 3 is an elevational view, in section, of a rotating seal assembly in
accord with
the present invention;
FIG. 4 is a top view of the rotating seal assembly of FIG. 3;
FIG. 5 is a top view of a rotating blowout preventer housing in accord with
the
present invention;
FIG. 6 is an elevational view, in section, of the blowout preventer housing of
FIG.
5 along the lines B-B;
FIG. 7 is an elevational view, in section, of the blowout preventer housing of
FIG.
5 along the lines A-A;
FIG. 8 is a bottom view of the blowout preventer housing of FIG. 5;
FIG. 9 is an elevational view, partially in section, of a blowout preventer in
accord
with the present invention;
FIG. 10 is a top view of the blowout preventer of FIG. 9;
FIG. 11 is an enlarged view of the blowout preventer of FIG. 9 along the lines
A'-
A'
FIG. 12 is an enlarged view of a section from FIG. 10; and
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FIG. 13 is a schematic view of a remote hydraulic control system for a
rotating
blowout preventer in accord with the present invention.
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BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and more specifically to FIG. 1 and 2, there
are
shown two different sectional views of a rotating blowout preventer 10 in
accord with the
present invention. Rotating blow-out preventer 10 is comprised of a rotating
seal
assembly 12 inserted within bore 14 of housing 16. Rotating seal assembly 12
is shown
separately from housing 16 in FIG. 3 and FIG. 4. Likewise housing 16 is shown
separately from rotating seal assembly 12 in FIG. 5 - FIG. 8.
Rotating seal assembly 12 preferably includes components that rotate with
respect
to housing 16 as well as components that do not rotate. Top cap assembly 18 is
non-
rotating with respect to rotating blow-out preventer housing 16. Bearing
housing 20 is
also non-rotating. The rotating components of rotating seal assembly are
mounted for
rotation on radial thrust bearings 22 and 23 and also on axial thrust bearing
24. Bladder
support housing 26 includes top mandrel 28 and bottom mandrel 30. Top mandrel
28 and
bottom mandrel 30 are preferably threadably secured together and may also
preferably
utilize a mandrel set screw 31 to prevent any rotating therebetween. Bladder
support
housing 26 is used to mount bladder 32. Under hydraulic pressure, discussed
hereinafter,
bladder 32 contracts inwardly to seal around a pipe such as a drilling pipe
having
relatively large pipe interconnections (not shown) as compared to the long
body of the
pipe. In fact, bladder 32 can expand to seal off the borehole 33 through
rotating seal
assembly 12, if desired.
Upper and lower end caps 34 and 36, respectively, fit over upper and lower
ends
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38 and 40 of bladder 32 to hold it within bladder support housing 26. In this
embodiment, lower end cap 36 is held in position with bladder set screw 42
that allows
some axial movement of lower end cap 34 and bladder 32. Upper end cap 36 is
secured
in position by socket head screw 44. Socket head screw 44 is positioned within
hole 46
of guide ledge 48 that guides the drill pipe into rotating seal assembly 12.
Upper and
lower seals 50 and 52 in the respective end caps seal pressure chamber 54 that
is presently
preferably defined radially outwardly of bladder 32 and radially inwardly of
bladder
support housing 26. The end caps are made of metal and the maximum size pipe
which
may extend through rotating seal assembly 12 is limited by the inner diameter
of the end
caps. The end caps are easily removable to allow easy and quick replacement of
bladder
32.
Bladder supply port 56 provides hydraulic fluid under a controlled pressure.
The
hydraulic fluid supply is indicated schematically as hydraulic control 58,
shown in FIG.
13, secured to rotating blow-out preventer 10 by various hydraulic and control
lines
indicated at 60. The construction details of hydraulic control 58 are not
required to
understand operation of rotating blow-out preventer 10 of the present
invention.
Essentially, hydraulic control 58 maintains and monitors hydraulic pressure
within
pressure chamber 54 and elsewhere. The hydraulic fluid is preferably filtered
and cooled
for warm weather operation , or heated for cold weather operation. The
hydraulic fluid
controls bearing temperature and provides bearing lubrication. Pressure
transducer 55,
shown in FIG. 2, may be used to measure well head pressure. Hydraulic control
also
preferably operates latching of rotating seal assembly 12 within rotating blow-
out
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preventer housing 16, as discussed hereinafter. Other pressure sensors may
also be used
to control the pressure chamber 54 and other functions, as discussed
hereinafter.
Hydraulic pressure P2 within pressure chamber 54 is preferably maintained by
hydraulic control 58 from about 0 to 500 pounds above the well bore pressure
at the
surface indicated as P 1. Thus, if P 1 is 1000 psi, then P2 may be about 1250
psi. Bladder
32 is sufficiently flexible that bladder surface 62 is pressed against the
pipe at
approximately the same pressure P2 to thereby seal off the pipe on which
pressure P 1
acts. Hydraulic control 58 responds quickly and accurately to maintain the
desired
pressure differential between pressure chamber 54 at pressure P2 and well bore
pressure
P1.
Hydraulic fluid flows into port 56, shown in FIG. l, through flowline or
flowlines
64 to recess ring 66 in rotating blow-out preventer housing 16 which may be
seen more
easily in FIG. 6 and FIG. 7. Seals 68 and 70 above and below recess ring 66
maintain
fluid pressure and flow into bearing housing hydraulic ports 72, recess 73,
and finally into
pressure chamber 54 through upper mandrel port 74. Lower dynamic seal 76 seals
the
hydraulic flow path with respect to well bore pressure P l and maintains the
seal as top
mandrel 28 rotates with respect to bearing housing 20. Therefore, the pressure
drop
across dynamic seal 76 is fairly small and equal to from about 0 to 500
pounds, the
desired pressure differential between P2 and P 1 required for sealing the
pipe. Hydraulic
fluid flows out of pressure chamber 54 through exit port 78 as indicated by
the arrows.
Fluid flow proceeds through radial thrust bearing 22 and then through axial
thrust bearing
24 to provide cooling and lubrication.
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At this point the pressure P2 is still approximately equal to about P 1 plus a
few
hundred pounds, which may be a sizeable pressure drop to ambient pressure if
the entire
drop occurs across bearing 23 and upper dynamic seal 80. A large pressure drop
would
be likely to cause upper seal 80 and bearing 23 to wear much more quickly than
lower
dynamic seal 76. Therefore, pressure drop device 82, or a collection of such
devices that
effectively provide a pressure drop, is used to drop the pressure
significantly in the
hydraulic flow path before reaching bearing 23 and upper seal 80. The device
used
herein is a labyrinth ring that limits flow there through and provides a
suitable pressure
drop by an amount which may be a factor in the range of about ten. However,
the actual
pressure drop is dependent on many factors such as temperatures, viscosity,
and the like.
Therefore, a 3000 psi pressure might be reduced to about 300. The pressure
drop factor
may vary, such as between about five and twenty, depending on the particular
pressure
drop device or labyrinth selected and the amount of hydraulic flow required.
Hydraulic
fluid exits through top cap port 84. Hydraulic connectors such as supply and
return
connectors 86 and 88 shown in FIG. 9 - FIG. 12 provide a hydraulic connection
to
hydraulic control 58.
Thus, hydraulic pressure within pressure chamber 54 acts to energize bladder
32
for sealing around the drill pipe by providing a force from pressure P2 that
is greater than
that of P1, as required for positive sealing. Due to the flexibility of
bladder 32, it also
conveniently seals around irregular shaped drill pipe such as a square or
hexagonal kelly.
No additional seal member is required for the kelly as in other rotating blow-
out
preventers'. In the present embodiment, bladder 32 may extend radially
inwardly at its
Page 20 of 43 Pages
CA 02259680 1999-O1-18
center portion to substantially form an hour-glass shape, when no pipe is
present. It will
move outwardly as larger pipes are placed therein. Actually, the inner bore
defined by
surface 62 is substantially straight but still is inwardly extending with
respect to the end
caps. Of course, this shape may vary considerably during drilling operations.
As well,
this shape may vary due to the material used to form bladder 62.. Ideally,
bladder 32
would be very strong and quite thin and flexible so that it could then have a
straight
without the hour-glass shape.
The movement of bottom end cap 36 due to the loose connection 42 allows some
additional flexibility for bladder 32 to conform to the pipe for sealing.
Support fingers
90 support bladder 32 at the most stressful area of the seal between well head
pressure P 1
and ambient pressure. Upper region 92 is also much thicker than lower region
94 of
bladder 32. An advantage of this is that the thinner lower region 94 will wear
through
faster than the thicker region. If a hole should form in bladder 32, then it
will occur in the
lower region. The upper region would then still be held outwardly at the well
head
pressure and provide a seal until the standard BOP could be closed and the
bladder
changed out. In reality, this is a very unlikely scenario because hydraulic
control 58
would sense any hydraulic leakage long before it wore a hole but this extra
safeguard is
nonetheless built in. Thinner region 94 also provides increased flexibility
for sealing so
that the bladder of the present invention can seal over a wide range of drill
pipe sizes and
at higher pressures. Bladder 32 may be comprised of numerous materials such as
elastomeric or polymer based materials. A urethane material is presently used
due to
limited friction, chemical resistance, and ease of molding. However, other
materials may
Page 21 of 43 Pages
CA 02259680 1999-O1-18
also be suitable.
The entire rotating seal assembly 12 is readily changed out as necessary.
Preferably, a spare rotating seal assembly 12 is kept so that the assembly can
be
immediately replaced for ongoing drilling without taking the time to dress
rotating seal
assembly. The unique hydraulic latch mechanism 100 provides a quick and remote
means for releasing rotating seal assembly 12 from rotating blow-out preventer
housing
16. Once manual safety lock levers 136 are released, there is no need for
personnel to
wrestle with heavy moving components within a small space thereby greatly
improving
rig safety.
Referring now to FIG. 2, there is shown hydraulic latch release port 102 and
latch
close port 104. To secure rotating seal assembly 12 within rotating blow-out
preventer
housing 16, hydraulic fluid is pumped under pressure into close port 104.
Hydraulic fluid
line 106 carries hydraulic fluid pressure through port 108 into chamber 110.
Latch piston
112 reacts to pressure in chamber 110 by moving upwardly. Chamber 110 is
sealed with
1 S upper and lower seal 114 such as O-rings. Latch piston 112 is tubular and
surrounds
rotating seal assembly 12. Chamber 110 preferably communicates with the entire
latch
piston simultaneously. In the presently preferred embodiment, the upper O-ring
114 also
encircles latch piston 112. It will be understood that while the present
invention uses
only one latch piston 112, it would be possible to have a plurality of latch
pistons rather
than a single latch piston 112, if desired..
Latching is produced as a result of pressure in chamber 110 that is developed
by
hydraulic control 58. Latch piston 112 moves upwardly in a direction
substantially
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CA 02259680 1999-O1-18
parallel to the center line of bore 33. Latch piston 112 has a wedge surface
116 that
engages a wedge surface 118 of dog 120. Dog 120 then moves radially inwardly,
so that
lock surface 122 of dog 120 engages radially extending sloping surface 124.
The sloping
surface of 124 and 122 is used, as explained hereinafter, to disengage the
dogs for release
of rotating seal assembly 12 after the latch piston is moved downwardly. As
illustrated
in FIG. 2, latch piston 112 is in the locked position so that rotating seal
assembly is
securely fixed within rotating blow-out preventer housing 16. Furthermore,
because the
piston moves in a direction parallel to that of the borehole, there are no
radially extending
pistons that might make the profile of the rotating blow-out preventer
irregular if the
pistons were oriented to move radially. While disadvantageous to do so with
respect to
maintaining an economical profile, a plurality of radially movable pistons
could also be
used to effect movement of the dogs. Dog 120 is similar to a plurality of
other dogs. The
dogs are each arc- shaped and combine to form a segmented ring with each dog
being an
arc of the ring. The arc-shaped dogs are driven radially inwardly
substantially in a
straight line toward the center line. Alternatively, a plurality of smaller
dogs for smaller
contact areas, driven by a plurality of pistons, could be used for operation
but the shown
arrangement is considered the preferred arrangement, and is much sturdier.
To ensure that the dogs maintain securely latched even should a hydraulic
pressure loss occur, mechanical backup latches 136 as best shown in FIG. 1 are
used that
operate in ratchet fashion to lock latch piston 112 in a locked position. When
engaged,
spring loaded ratchet block 126 has ratchet surfaces 128 that engage rod
ratchet surfaces
130. Connector rod 132, secured to lock piston 112 at slip connection 134, is
permitted
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CA 02259680 1999-O1-18
by ratchet action to move upwardly with lock piston 112, but is prevented by
the ratchet
surfaces 128 and 130 from moving downwardly. Moving lever 136 out of the shown
lock
position into an upward position moves ratchet block 126 radially outwardly to
disengage
ratchet surfaces 128 and 130 thereby permitting lock piston 112 to move
downwardly.
Latch piston 112 is moved downwardly by removing pressure in chamber 110 and
then applying a downward force to latch piston 112 by activating pressure in
latch release
chamber 13 8. Hydraulic pressure is produced in chamber 13 8 through latch
release port
102 and passage or passages 140 that lead to latch release chamber 138. Like
chamber
110, latch release chamber 13 8 encircles rotating blow-out preventer housing
16 to
activate the entire latch piston 112 simultaneously and upper and lower O-
rings 144 and
142 seal the chamber. Latch open and latch close hydraulic connectors 145 and
147
shown in FIG. 11 attach to suitable control lines. The lines and connectors
are preferably
labeled/color coded or otherwise distinguished to simplify connection.
Dog retainer cap 146 contains the latch mechanism components and dogs 120 and
is threadably securable to rotating blow-out preventer housing 16. Thus, the
chambers
and components are readily available for assembly and machining of the chamber
is
straight forward. The O-rings can be used to hold the latching assembly
components
together when dog retainer cap 146 is screwed on. It will be noted that lip
148 holds dogs
120 within dog retainer cap 146 by limiting the allowable radial inward
movement of
dogs 120.
In operation, rotating blow-out preventer housing 16 is normally attached to
the
top of the BOP stack by means of well head flanges 150. Rotating blow-out
preventer
Page 24 of 43 Pages
CA 02259680 1999-O1-18
housing may typically weigh in the range of about 2000 lbs depending on the
size.
Lifting eyelets 152 are used to provide a convenient lifting point for the
hoist, such as the
rig cat line. If not already present, rotating seal assembly 12 may be
inserted into rotating
blow-out preventer housing 16. The diameter of rotating seal assembly 12 is
small
enough to fit through the hole in the rotary table. The rotating seal assembly
may weigh
in the range of about 1800 lbs. Preferably, two rotating seal assemblies are
used in
operation so that one rotating seal assembly is kept in reserve and may be
quickly
changed out without the need to dress the assembly. The removed assembly can
then be
dressed and refurbished at a convenient time.
When installed, handles 136 may be placed in the locked position if they are
not
already in that position. To latch in rotating seal assembly 12, hydraulic
control 58
applies pressure at latch close port 104. Pressure is released from latch open
port. The
pressure moves latch piston 112 upward and dogs 120 radially inwardly to
solidly latch
rotating seal assembly 12 into rotating blow-out preventer housing 16.
Drilling
operations may proceed while hydraulic control 58 maintains the desired
pressure
differential between well head pressure P 1 and pressure chamber 54 pressure
P2. This
active seal mechanism that energizes bladder 32 provides a gas tight seal at
all times. If it
should become necessary to change out rotating seal assembly 12, then the
standard BOP
can be used to provide a static seal on the drill pipe. The well head pressure
P 1 can be
bled off and then pressure P2 in pressure chamber 54 may be bled off. To
remove
rotating seal assembly 12, release handles 152 are pointed upwardly to allow
latch piston
112 to move downwardly at the desired time. Latch pressure at latch close port
104 is
Page 25 of 43 Pages
CA 02259680 1999-O1-18
then reduced and latch open pressure at port 102 is applied to move latch
piston 112
downwardly so as to enable dogs 120 to move radially outwardly. There is no
need to
have personnel below the rig floor as rotating seal assembly 12 is removed as
required
with other blow-out rotating preventer's. Rig lines such as cat lines are
attached to hoist
rings 154, shown in FIG. 4, and lifting force is conveniently applied. Sloping
edge 122
on dogs 120 and sloping edge 124 on top cap 18 then wedge dogs radially
outwardly as
rotating seal assembly 12 is moved upwardly to be easily removed from rotating
blow-out
preventer housing 16. The spare rotating seal assembly then goes quickly back
into place
and drilling can continue with very little lost drill time. Thus, one of the
big advantages
of the present invention is a quick, safe, and easy change out of the rotating
seal
assembly.
It will now be recognized that a new and improved rotating blowout preventer
has
been disclosed. Since certain changes and modifications may be made in the
disclosed
embodiment without departing from the inventive concepts involved, it is the
aim of this
specification, drawings and appended claims to cover all such changes and
modifications
falling within the spirit and scope of the present invention.
Page 26 of 43 Pages
