Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
s The present invention relates generally to an apparatus and method for
allowing a drill string to rotate and reciprocate while drilling mud is being
displaced from a wellbore.
Exploration and production of hydrocarbons from subsea reservoirs
is an expensive and time-consuming process. The mechanics of drilling in a
marine environment differ significantly from land operations. Drilling
operations utilize a weighted drilling fluid, such as drilling mud, which is
pumped down the drill string and circulated back to the surface through an
annulus between the drill string and the borehole wall. The drilling fluid
serves
many purposes, such as to cool the drill bit as it rotates and cuts into the
earth
~s formation, provide a medium for returning the cuttings created by the drill
bit
to the earth's surface via the annulus, and control pressure in the borehole
to
help prevent blowouts. During land operations, the drilling fluid and cuttings
are returned to the surface via the borehole annulus. Such is not the case in
offshore operations.
zo Offshore operations, including inland water operations, generally
require location of a host drilling facility, such as a floating drilling
unit, in
waters located above the reservoir of interest. The depth of the water may
range from several feet to depths of several thousand feet. A drill string
must
travel from the surface of the drilling facility, down through the surface and
zs seabed equipment, and then into the wellbore of interest prior to
initiating
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cutting/drilling operations. Unlike land operations, there is no annulus
between the floor of the seabed and the drilling facility at the surface.
Accordingly, a drilling riser comprised of generally cylindrical elements is
provided for and extends generally from a wellhead located at the seabed up
s to the drilling facility located above the surface of the water. The riser
operates to protect the drill string during operations and acts as an
artificial
annulus.
Subsea drilling operations must provide a means for shutting down
the well in emergency situations during drilling completion operations.
o Generally, a series of blowout preventers (BOPs), referred to as a BOP
stack,
are used to control well flow in such instances. The BOP stack is connected to
the wellhead and generally consists of a combination of ram BOPs and
annular BOPs. In conventional subsea drilling systems, the BOP stack is
located on the seafloor and requires various umbilical and control lines in
~s order to monitor conditions and hydraulically operate the BOP stack.
A ram BOP is a device that can be used to quickly seal the top of
the well in the event of a well control event. A ram BOP consists of two
halves
of a cover for the well that are split down the middle. Large-diameter
hydraulic
cylinders, normally retracted, force the two halves of the cover together in
the
zo middle to seal the wellbore. These covers are constructed of steel for
strength
and fitted with elastomer components on the sealing surfaces. The halves of
the covers, formally called ram blocks, are available in a variety of
configurations. In some designs, they are flat at the mating surfaces to
enable
them to seal over an open wellbore. Other designs have a circular cutout in
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the middle that corresponds to the diameter of the rig's drill string (e.g.
drill
pipe) to seal the well when the drill string is in the hole. Still other ram
blocks
are fitted with a tool steel-cutting surface to enable the ram BOPs to
completely shear through drill pipe, hang the drill string off on the ram
blocks
s themselves and seal the wellbore. This last design, referred to a shear ram
BOP, is employed only as a last resort to regain pressure control of the
wellbore.
An annular BOP is a large valve in which the sealing element
resembles a large elastomeric doughnut that is mechanically squeezed
o inward to seal on either pipe (drill collars, drill pipe, casing, or tubing)
or the
openhole. The ability to seal on a variety of pipe sizes is one advantage the
annular BOP has over a ram-type BOP. Most BOP stacks contain at least
one annular BOP at the top of the BOP stack, and one or more ram BOPs
below.
~s The riser pipe is typically installed on top of the BOP stack.
Typically, three smaller lines are attached to the outside of the riser and
extend up to the surface drilling facility. Two of the lines, the choke and
kill
lines, run to connections within the BOP stack and provide a greater means
for drilling mud to enter and exit the well when the BOPs are closed. The
third
Zo line is called a boost line and connects above the BOP stack and provides
additional hydraulic support and circulating rates when needed.
After drilling is complete, it is necessary to displace the drilling fluid
from the wellbore. This is typically accomplished by closing at least one
section of the BOP stack to isolate the wellbore from the riser. Drilling
fluid is
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then displaced out of the riser by pumping fluid, such as seawater, through
either the choke or kill line through the BOP stack and up the riser to the
surface facility. Drilling fluid can then be displaced from the wellbore by
pumping fluid, such as completion brine, down the work string, through the
s drill bit, up the wellbore annulus, and up the choke or kill line to the
surface
facility.
The problem with this technique is that it is often desirable to be
able to rotate and reciprocate the work string while displacing drilling mud
from the wellbore in order to improve displacement efficiencies. However, it
is
to cost prohibitive to rotate and reciprocate the work string with the annular
BOPs closed around the work string because of the wear on the rubber
elements in the annular BOPs. What is needed is a device and method that
would allow for rotation and reciprocation of the work string while drilling
fluid
is being displaced from the wellbore.
IS
SUMMARY OF THE INVENTION
A novel displacement annular swivel tool and a method for using such
a tool is provided to solve the aforementioned problems.
A displacement annular swivel is disclosed consisting of a mandrel with
ao a sleeve assembly positioned around the outside diameter of the mandrel.
The sleeve assembly consists of at least one radial bushing such that the
mandrel can be rotated and reciprocated within the sleeve assembly when the
sleeve assembly is fixed in a stationary position. At least one sealing
element
is present on the sleeve assembly to radially seal against the outside
diameter
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of the mandrel.
A method for displacing drilling fluid from a completed subsea wellbore
is also disclosed consisting of closing a blowout preventer around the
aforementioned tool connected to the work string. The tool thereby allows the
s work string to be rotated and reciprocated when the blowout preventer is
closed. Drilling fluid can then be displaced from the wellbore by pumping
fluid, such as completion brine, through the work string and out the choke and
kill lines.
to BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be
obtained with reference to the accompanying drawing:
Figure 1 illustrates a displacement annular swivel tool in accordance
with certain teachings of the present invention.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
With reference to Figure 1, a preferred embodiment of displacement
annular swivel tool 10 is shown. The tool 10 has an upper sub 12, a lower
sub 14, a mandrel 16, and a sleeve 18. Sleeve 18 consists of a top body cap
zo 20, a bottom body cap 22, a top radial bushing 24, and a bottom radial
bushing 26. The mandrel may be constructed of any suitable material, such
as a P-110 equivalent material, preferably AISI 4145 HT with a yield of 125K.
The radial bushings 24 and 26 may be constructed of any suitable material,
preferably bronze.
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Both the upper sub 12 and the lower sub 14 contain sealing elements
28 at the connections that make up the mandrel 16. The bottom body cap 22
of sleeve 18 also contains at least one, and preferably two (as shown in
Figure 1), sealing elements 30, that seal radially on the outside diameter of
s the mandrel. In a preferred aspect of the present invention, Viton~ o-rings
are
used for sealing elements 28 and 30, although one of ordinary skill in the art
will appreciate that selection of a sufficient alternative sealing element
will
inherently depend upon, for example, chemical compatibility, application
temperature, and sealing pressure.
o Upper sub 12 and lower sub 14 are connected to sections of drill string
above and below said subs such that sleeve 18 is aligned with an annular
BOP in a BOP stack when the fully assembled string is run to the bottom of
the wellbore. When the annular BOP is closed around sleeve 18, a non-
rotating, sealing engagement is created between the elastomeric sealing
~s elements of the annular BOP and sleeve 18. Sealing elements 28 and 30
isolates all fluid circulation below the annular BOP, thereby preventing
fluids
from back-flowing through the tool and contaminating above the tool.
With annular BOP closed about sleeve 18, sleeve 18 will remain
stationary relative to the annular BOP. The drill string and specifically
zo mandrel 16 can then be rotated independent of sleeve 18 due to radial
bushings 24 and 26. Furthermore, the drill string and specifically mandrel 16
can also be reciprocated (i.e. raised and lowered) independent of sleeve 18
due to radial bushings 24 and 26, with the length of reciprocation being
limited
to length of exposed mandrel 16 between upper sub 12 and lower sub 14. In
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a preferred aspect of the present invention, mandrel 16 is approximately 25 to
35 feet long with sleeve 18 being approximately 10 feet long, thereby
providing approximately 15 to 25 feet of reciprocation in either direction
from
the center of the tool. However, additional mandrel sections (typically 25 to
35
s feet long) can be added to the tool in order to increase the range of
reciprocation.
With the annular BOP closed about sleeve 18, drilling mud in the
wellbore is then isolated from fluid in the riser. Drilling mud displacement
can
then proceed. Drilling mud is displaced out of the riser by pumping fluid,
such
o as seawater, through the choke or kill line, through the BOP stack, and up
the
riser to the surface facility. Drilling mud is then displaced from the
wellbore by
pumping fluid, such as completion brine, down the work string, through the
drill bit, up the wellbore annulus, and up the choke or kill lines to the
surface
facility. During this displacement step, the work string can be rotated and
~s reciprocated about sleeve 18, which remains stationary, without any damage
to the elastomeric elements of the annular BOP.
As described above, upper sub 12 and lower sub 14 are connected to
sections of drill string (or work string more generally) such that sleeve 18
is
aligned with an annular BOP in a BOP stack when the fully assembled string
Zo is run to the bottom of the wellbore. In a preferred aspect of the present
invention, displacement annular swivel tool 10 is approximately 31 to 40 feet
long, which can correspond to approximately the length of a typical section of
string. Accordingly, the fully assembled string including the tool can be
assembled in the same manner as a typical drill string. The displacement
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annular swivel tool 10 can either be fully assembled prior to connection with
the adjoining sections of string, or alternatively it can be assembled in a
"top-
down" or "bottom-up" manner. Top-down assembly would occur, for example,
by first connecting upper sub 12 to the adjoining top string section, then
s connecting mandrel 16 with sealing element 28. Next, the full sleeve
assembly 18, including top body cap 20, bottom body cap 22, top radial
bushing 24, bottom radial bushing 26, and sealing elements 30 are slid onto
mandrel 16. A stop, such as a casing clamp for example, is used to hold
sleeve assembly 18 on mandrel 16 until lower sub 14 with sealing element 28
o is connected to the bottom of mandrel 16. Once fully assembled, lower sub
14 is then connected to the adjoining bottom string section. The displacement
annular swivel tool may be stood back in the derrick until lowered downhole.
Although the preferred embodiment is described for use with an
annular BOP, it is envisioned that one of ordinary skill in the art can design
a
~s tool in accordance with the teachings of the present invention to be used
in
conjunction with a pipe ram-type BOP. In such an alternative embodiment the
outside diameter of sleeve 18 must be substantially equivalent to the outside
diameter of the drill string for which the ram BOP was designed in order to
properly seal the riser from the wellbore.
zo Similarly, although the preferred embodiment is described for use with
a single annular BOP, it is envisioned that one of ordinary skill in the art
can
design a tool in accordance with the teachings of the present invention to be
used in conjunction with more than one BOP. For example, sleeve 18 can be
designed with sufficient length so as to be able to receive the elastomeric
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sealing elements of two or more annular BOPs in a BOP stack. As another
example, sleeve 18 can be designed with sufficient length and with the
appropriate outside diameter as described above so as to be able to receive
the sealing elements for a combination of one or more annular BOPs and one
s or more ram-type BOPs.
It will be apparent to one of skill in the art that described herein is a
novel displacement annular swivel tool and a method for using such a tool to
provide for rotation and reciprocation of the work string during drilling mud
displacement. While the invention has been described with references to
o specific preferred and exemplary embodiments, it is not limited to these
embodiments. The invention may be modified or varied in many ways and
such modifications and variations as would be obvious to one of skill in the
art
are within the scope and spirit of the invention and are included within the
scope of the following claims.
