WELLBORE DRILLING USING DUAL DRILL STRING
PRIORITY
This application is an International Application of and claims priority to U.S. Provisional
Patent Application No. 61/820,059, entitled, "METHOD AND SYSTEM FOR SUBSEA
RISERLESS DRILLING," filed May 6, 2013, the disclosure of which is hereby
incorporated by reference in its entirety.
FIELD
The present disclosure relates generally to oilfield equipment, and in particular to drilling
systems, and drilling techniques for drilling wellbores in the earth. More particularly still,
the present disclosure relates in part to offshore drilling techniques and systems.
BACKGROUND
Various drilling methods and systems are known in the art. Most arrangements use a
rotating drill bit that is carried and conveyed in the wellbore by a drill string, which is in
turn carried by a drilling rig located above the wellbore. The drill bit may be rotated by the
drill string, and the drill string may also include as part of a bottom hole assembly
downhole rotary motor for rotating the drill bit.
The drill string is substantially made up of individual stands of drill pipe that are assembled
as the drill bit advances into the earth. Drilling fluid is pumped to the drill bit through the
drill string and is directed out of nozzles in the drill bit for cooling the bit and removing
formation cuttings. The drilling fluid may also serve the purpose of providing hydraulic
power to downhole tools, such as a mud motor located in a bottom hole assembly (BHA)
for rotating the drill bit. The spent drilling fluid and entrained formation cuttings are
forced from the bottom of the wellbore and carried upwards through the annulus that exists
between the drill string and the wellbore wall.
In cases of drilling offshore wells, the drilling rig is positioned above the surface of the
water, generally over the wellbore. A riser is commonly provided between the drilling rig
and the wellbore at the seafloor for allowing the drill string to be conveniently run into and
tripped out of the wellbore. The riser also provides an extension of the annular wellbore
flow path for returning the drilling fluid and cuttings to the rig for processing and reuse.
Recently developed drilling methods and systems may substitute a coaxial dual drill string
in place of the prolific single-pipe drill string. A coaxial dual drill string has an inner pipe
fixed within an outer pipe, thereby defining an inner flow channel within the inner pipe and
an outer flow channel within the annular region defined between the inner and outer pipes.
In such arrangements, drilling fluid may be supplied to the drill bit via the outer flow
channel, and the return drilling fluid, laden with formation cuttings, may be removed from
the wellbore via the inner flow channel. A single crossover port may be provided at a
distal end of the drill sting, commonly at a location just uphole of the BHA, if supplied,
which fluidly connects the inner flow path to the wellbore, thereby allowing spent drilling
fluid at the bottom of the wellbore to re-enter the drill string and return uphole via the inner
flow channel.
The use of a dual drill string as has been generally described includes a flow channel for
return drilling fluid flow and may provide several advantages over drilling with single-pipe
drill string. In certain offshore conditions, such a system may obviate the need to deploy a
drilling riser, provided an alternative barrier between the seawater and the wellbore
annulus is established. The return flow channel leaves the wellbore clear of formation
cuttings. Improved hole cleaning results in less downtime. Finally, because the entire
wellbore annulus no longer forms a flow path for drilling fluid circulation, the fluid within
the wellbore annulus is essentially static, which may be preferable for certain techniques
for managing wellbore pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments are described in detail hereinafter with reference to the accompanying
figures, in which:
Figure 1 is an elevation view in cross section of a riserless dual drill string drilling system
according to an embodiment, showing a dual drill string extending from an offshore
platform to a wellhead and subsea stack at the seafloor and associated support components;
Figure 2 is a flowchart that outlines the steps of a method according to an embodiment for
remotely replacing a seal assembly of a rotating control device of the drilling system of
Figure 1;
Figure 3 is an elevation view of a rotating control device of Figure 1 with a longitudinal
quarter cut away to reveal internal structure, showing details of a removable seal assembly
and lubrication flow path;
Figure 4 is a plan view of a clamp of the rotating control device of Figure 3 for removably
connecting the seal assembly to the housing of the rotating control device;
Figure 5 is an elevation view in partial cross section of a dual drill string drilling system 10
according to an embodiment;
Figure 6 is a transverse cross section of a dual drill string taken along line 6-6 of Figure 7,
looking down upon a crossover port according to an embodiment;
Figure 7 is an axial cross section of the crossover port of Figure 6, showing a valve
assembly and actuator arranged for remote, independent operation;
Figure 8 is an axial cross section of a portion of the dual drill string of Figure 5, showing a
check valve assembly positioned within the inner flow channel and in an open position;
and
Figure 9 is an axial cross section of the dual drill string and check valve assembly of Figure
8, showing the check valve assembly in a shut position.
DETAILED DESCRIPTION
The foregoing disclosure may repeat reference numerals and/or letters in the various
examples. This repetition is for the purpose of simplicity and clarity and does not in itself
dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as "beneath," "below," "lower," "above," "upper,"
"uphole," "downhole," "upstream," "downstream," and the like, may be used herein for
ease of description to describe relationships as illustrated in the figures. The spatially
relative terms are intended to encompass different orientations of the apparatus in use or
operation in addition to the orientation depicted in the figures.
Figure 1 is an elevation view in partial cross section of a riserless dual drill string drilling
system 10 according to an embodiment. Referring to Figure 1, drilling system 10 includes
a drilling rig 14, which may include a rotary table 15, a top drive unit 16, a hoist 17, and
other equipment necessary for drilling a wellbore in the earth.
In the embodiment of Figure 1, drilling system 10 includes an offshore platform 19 located
at the surface of a body of water 11. Offshore platform 19 may be a tension leg platform,
spar, semi-submersible, or drill ship, for example. In other embodiments, the drilling
system of the present disclosure may be located onshore.
Drilling rig 14 may be located generally above a wellhead 20, which in the case of the
offshore arrangement of Figure 1 is located at the seafloor of body of water 11. Drilling rig
14 suspends a concentric dual drill string 12, which extends downward through body of
water 11, through a passage 30 formed through wellhead 20, and into the wellbore 32 that
is being drilled. The annular region between the wall of wellbore 32 and the exterior wall
of dual drill string 12 defines a wellbore annulus 34.
Wellhead 20 ideally carries a blowout preventer (BOP) stack 21, which may include ram
BOPs 22, 24 and an annular BOP 26, for example. BOPs 22, 24, 26 include an axial
passage 23 to accommodate drill string 12 and are arranged with closure devices, such as
shear, blind or pipe rams in the case of ram BOPs 22, 24, or elastomeric packers, in the
case of annular BOP 26, to shut in wellbore 32 in the case of an emergency. A BOP
control pod 28 may be located in proximity to wellhead 20, for example on the seafloor, for
redundant actuation of BOP stack 21. Hydraulic choke and kill lines 27, 29 are also ideally
provided to BOP stack 2 1 for emergency well pressure control.
A rotating control device (RCD) 40, also referred to by routineers as a rotating control
head, rotating blowout preventer, or rotating diverter, is carried atop BOP stack 21. RCD
40 has a housing 4 1 with an axial passage 42 formed therethrough for accommodating drill
string 12. As discussed in greater detail below with respect to Figure 3, RCD 40 includes a
rotatable seal assembly 43, which may include one or more elastomeric sealing elements
and a bearing assembly, for example. Seal assembly 43 creates a dynamic seal between the
outer wall of drill string 12 and housing 4 1 thereby fluidly isolating wellbore annulus 34
from body of water 11 while allowing drill string 12 to axially translate and rotate. RCD
40 may be an active- or passive-style device, and it may also take the form of an annular
BOP.
A subsea hydraulic production unit (HPU) 50 is provided on the seafloor in proximity to
RCD 40. HPU 50 is fluidly coupled to RCD 40 via one or more lubrication conduits 52 to
selectively provide hydraulic lubrication to seal assembly 43 and/or the outer wall of drill
string 12 immediately above and/or below the sealing element of RCD 40. In particular,
suitable lubrication may be achieved by providing lubricant at or near the top of the sealing
element when drill string 1 is run into wellbore 32 (including drilling operations) and at or
near the bottom of the sealing element when drill string 12 is tripped out of wellbore 32.
HPU 50 may be a closed circulation system, or it may be dead head lubrication system, for
example.
In one or more embodiments, seawater supplied from body of water 11 may be used as a
lubricant for cooling and lubrication of RCD seal assembly 43. If additional lubricity is
required, it may be provided by using alternative lubricating fluid or by mixing the
seawater with a suitable additive, such as an environmentally sensitive detergent. Such an
additive or lubricant may be supplied to HPU 50 by a feed line 53 from the surface of body
of water 11 or a tank 54 located at the seafloor.
The sealing element of RCD 40 may be a consumable item that needs replacement during
drilling operations. Accordingly, seal assembly 43 is preferably designed to be removable
from housing 42 and carried to or from the surface of body of water 11 by drill string 12.
A removable clamp 44 holds seal assembly 43 in place within or against RCD housing 42
against the fluid pressure of wellbore annulus 34. Clamp 44 may include an actuator 45
that can be remotely operated. In one or more embodiments, HPU 50 may selectively
operate actuator 45 of RCD clamp 44. For example, actuator 45 may be a hydraulic pistoncylinder
assembly or a hydraulic motor, and HPU 50 may be fiuidly coupled to actuator 45
via hydraulic conduit 55.
Figure 2 is a flowchart that outlines the steps of a method 150 for replacing seal assembly
43. Referring to both Figures 1 and 2, at step 152, drill string 12 is raised by drilling rig 14
until drill bit 212 (figure 5) carried at the distal end of drill string 12 is located above the
closure devices, i.e., the rams and/or the annular packer, of BOP stack 21.
Drill string 12 may include a BHA 210 (Figure 5) at its distal end that has a larger outer
diameter than the inner diameter of seal assembly 43. Thus, seal assembly 43 can be
engaged and carried to drilling rig 14 (and back) by riding atop the BHA. However,
provided it has a sufficiently large outer diameter, any transport member carried by drill
string 12, including a drill collar, sub, or simply a drill bit 212 (Figure 5) may be used in
lieu of a BHA for engaging and transporting seal assembly 43.
A tubular spacer 60 may be provided between BOP stack 2 1 and RCD 40 as necessary to
accommodate, at step 154, the length of the BHA between the uppermost BOP wellbore
closure device (e.g., blind rams) and the lowermost portion of the sealing element of RCD
40. Additional structural supports 6 1 may be provided align with tubular spacer 60 to carry
and reinforce RCD 40.
At step 156, once the BHA is clear of the uppermost BOP closure device but before it
reaches the lowermost portion of seal assembly 43, accommodated within tubular spacer
60 as necessary, BOP stack 1 is actuated to shut one or more of its closure devices and
thereby fluidly isolate wellbore 32.
At step 158, any differential pressure across seal assembly 43 may be equalized. For
example, passage 42 of RCD 40 may be selectively vented by a conduit 72 to a surge tank
70, which may collect and hold the pressurized well annular fluid. A pump 74 may also be
provided at the seafloor to purge the fluid contents of passage 42 and tubular spacer 60
with seawater, collecting any well fluids in surge tank 70 to prevent contaminating body of
water 11. To facilitate pressure equalization, as well as to enhance operation of RCD 40
during drilling operations, it is advantageous to have pressure sensors 76, 77 above and
below seal assembly 43 to accurately determine the differential pressure.
At step 160, RCD clamp 44 is released via the actuator 45. HPU 50 may selectively operate
actuator 45 via hydraulic conduit 55, and HPU 50 may be remotely controlled from the
surface of body of water 11 by a communication link 80.
At step 162, drill string 12 is raised to the surface of body of water 11 by drilling rig 14.
Because the BHA has a greater outer diameter than the inner diameter of seal assembly 43,
seal assembly 43 is carried to offshore platform 19 by drill string 12 as it is tripped out.
Alternatively, should it be desired to completely remove RCD 40, clamp 44 is not released.
Instead, a remotely operated vehicle (ROV) may be deployed to disconnect RCD 40, or a
different remotely operated clamping device that connects RCD 40 to BOP stack 2 1 may
be released. Then, the entire RCD 40 may be carried to offshore platform by drill string 12
in the same manner.
A replacement seal assembly 43 (or RCD 40, as the case may be) can be lowered into place
at the seafloor by reversing the above steps, using a ROV as necessary to guide drill string
12 into position.
Referring back to Figure 1, drilling system 10 may also include a drill string guide 90
carried atop RCD 40. Offshore platform 19 may experience surge, sway and yaw motions
under the environmental conditions of tides, waves, wind, and currents. Additionally, drill
string 1 is unconstrained as is passes from offshore platform 19 through body of water 11
and likewise encounter currents. Accordingly, drill string 12 is subject to lateral movement
with respect to the location of wellhead 20 at the seafloor. Guide 90 functions as a fairlead
to align drill string 12 with the common axis of RCD 40, BOP stack 21, and wellhead 20,
thereby relieving stress and minimizing wear and tear on seal assembly 43. The upper end
of guide 90 may have a wide, tapered opening to enhance engagement between guide 90
and drill string 12.
In addition to or as an alternative to supporting seal assembly 43 replacement as described
above, pump 74 may be used to support well control operations and managed pressure
drilling (MPD) techniques. For example, pump 74 may apply a controlled backpressure to
the fluid in wellbore annulus 34, such as via passage 42 of RCD 40. However, other
pressure sources may also be used for annular pressure control, including choke line 27.
At least one communication link 80 is provided between one or more locations at the
surface of body of water 11 and one or more of BOP control pod 28, HPU 50, and pump
74, for control of one or more of BOP stack 21, RCD 40, and annulus 32 pressure,
respectively.
In one or more embodiments, communication link 80 may be implemented by an umbilical
82. Umbilical 82 may include a number hydraulic, electrical and/or fiber optic lines, for
example, including feed line 53 and choke and kill lines 27, 29. In one or more
embodiments (not expressly illustrated), umbilical 82 extends from the seafloor to offshore
platform 19. In another embodiment, to prevent entanglement of the umbilical 82 with the
drill string 12, a floating vessel or apparatus 84, such as a drilling support ship, may be
provided at the surface of body of water 11 at a distance separated from offshore platform
19.
In one or more embodiments (not expressly illustrated), communication link 80 may
employ other remote telemetry technology, such as is commonly used with pipe lines and
subsea production trees and wellheads. For example, communication link 80 may include
an acoustic link operable through said body of water 11.
Figure 3 is an elevation view in partial cross section of a RCD 40 according to an
embodiment. RCD 40 is used to seal off wellbore annulus 34 (Figure 1), which is in fluid
communication with passage 42 formed within housing 4 1 of RCD 40. Housing 4 1 is
sealed against the exterior wall of drill string 12 within passage 42, even while drill string
12 rotates and translates longitudinally therein. For this purpose, RCD 40 includes
removable seal assembly 43, which includes one or more resilient annular sealing elements
46. If multiple sealing elements 46 are used, seal assembly 43 may include a shroud 47.
To permit sealing elements 46 and shroud 47 to rotate as drill string 12 rotates, seal
assembly 43 includes a bearing assembly 48, which may in turn include an inner carrier
ring 110 that rotates within and outer carrier ring 112 using bearings 114 and seals 116.
Inner carrier ring carries sealing elements 46 and shroud 47. Clamp 44 releasably secures
outer carrier ring 112, and thereby the entire seal assembly 43 (with sealing elements 46,
shroud 47 and bearing assembly 48), to housing 4 1.
RCD 40 may include one or more lubrication flow paths 120 for supplying bearings 114
and the sealing element 46 / drill string 12 interface(s) with a supply of lubricant 57.
Lubrication flow paths 120 fluidly connect at housing 4 1 to HPU 50 (Figure 1) via
lubrication conduits 52. In one or more embodiments, within housing 41, a first lubrication
flow path 120a fluidly connects to a bearing region 123, demarcated between inner and
outer carrier rings 110, 112 and between upper and lower seals 116a, 116b, for supplying
bearings 114 with lubricant. Lubrication flow path 120a may include a manifold 122,
which rotates with inner carrier ring 110 and which fluidly connects to bearing region 123
through one or more ports formed through inner carrier ring 110 Lubricant 57 is supplied
to the outer wall of drill string 12 between upper and lower sealing elements 46a, 46b via
manifold 122. Manifold 122 may also extend to the top of upper sealing element 46a for
selectively supplying lubricant 57 to that location during downward travel of drill string 12.
Manifold 122 may include nozzles or the like to direct lubricant 57 at the sealing element
46 / drill string 12 interfaces. A second lubrication flow path 120b may be provided
through housing 4 1 to selectively direct lubricant 57 to the bottom of lower sealing element
46b during upward movement of drill string 12. Although particular lubrication flow paths
120 are disclosed herein, a routineer will understand that a wide variety of lubrication flow
paths may be suitable for a particular RCD, including lubrication flow paths with
selectively isolable branches for selective lubrication.
Figure 4 is a plan view of clamp 44 of RCD 40 according to an embodiment. Clamp 44
may include first and second movable clamping arms 130a, 130b. In the embodiment
illustrated, clamping arms 130a, 130b are arcuate and are translatable between a clamped
position (shown in broken line) in which they are in proximity or otherwise abut one
another and a released position (shown in solid line) in which they are separated by a
sufficient distance to allow outer carrier ring 112 to fit between them. However, in other
embodiments (not illustrated), clamping arms may have other shapes and/or may pivot or
tilt to provide clearance outer carrier ring 112 to be removed from RCD housing 4 1 (Figure
3). Additionally, any number (including one) of clamping arms may be provided as
appropriate.
In the embodiment illustrated, clamp 44 includes first and second actuators 45a, 45b
connected so as to selectively move clamping arms 130a, 130b. Each actuator 45 may
include a hydraulic motor 132 that rotates a lead screw 134. Each lead screw has oppositehand
thread sections 135a, 135b upon which clamping arms 130a, 130b are threaded. Each
actuator may include a bracket 136 to support motor 132 and lead screw 134. Actuator 45
may be fluidly connected to HPU 50 (Figure 1) by hydraulic conduits 55. In other
embodiments, any number (including one) of actuators 45 may be provided, and actuator(s)
45 may include piston-cylinder arrangements or other suitable mechanisms.
Figure 5 is an elevation view in partial cross section of a dual drill string drilling system
10' according to one or more embodiments. As with drilling system 10 of Figure 1, drilling
system 10' of Figure 5 includes drilling rig 14, which may be located on land or offshore.
Drilling rig 14 may be located above well head 20 and may include rotary table 15, top
drive 16, hoist 17, and other equipment necessary for drilling a wellbore in the earth. Blow
out preventers (not expressly shown) and associated equipment may also be provided at
well head 20. Drilling rig 14 suspends dual drill string 12 through RCD 40, wellhead 20,
and into wellbore 32.
Dual drill string 12 includes an inner pipe 202 that is disposed within an outer pipe 204.
Inner pipe 202 and outer pipe 204 may be eccentric or concentric. An annular outer flow
channel 208 is defined between inner pipe 202 and outer pipe 204, and an inner flow
channel 206 is defined within the interior of inner pipe 202. Wellbore annulus 34 is
defined between the exterior of drill string 12 and the inside wall of wellbore 23.
The distal end of drill string 12 may include BHA 210 and rotary drill bit 212. BHA 210
may include a downhole mud motor 214, centralizer 216, and various other tools 218, such
as those that provide logging or measurement data, orientation data, telemetry, etc.
Drilling fluid 220 may be pumped from reservoir 222 by one or more drilling fluid pumps
224, through conduit 226, to the upper end of drill string 12 extending out of well head 20.
The drilling fluid 220 then flows through outer flow channel 208 of drill string 12, through
BHA 210, and exits from nozzles formed in rotary drill bit 212.
A distal crossover port 250 located near the distal end of drill string 12 fluidly connects
annulus 34 with inner flow channel 206 during normal drilling operations. At bottom end
31 of wellbore 32, drilling fluid 220 may mix with formation cuttings and other downhole
fluids and debris. The drilling fluid / cuttings mixture then flows upwardly through
wellbore annulus 34, past BHA 210 and into inner flow channel 206 through the distal
crossover port 250. The mixture continues to flow upwards through the inner flow channel
206 of drill string 12. Conduit 228 may return the fluid to reservoir 222, and various types
of screens, filters and/or centrifuges (not expressly shown) may be provided to remove
formation cuttings and other downhole debris prior to returning drilling fluid 220 to
reservoir 222.
In a particular well pressure control operation, the upper end wellbore annulus 34 may be
filled via RCD 40 with a well control fluid, for example, a high-density fluid to alter the
density of fluid within annulus 34. The previous fluid displaced by the newly-introduced
high-density fluid may be forced out of wellbore annulus 34 via distal crossover port 250
and inner flow channel 206. In an alternate well pressure control operation, by reversing
fluid flow through inner flow channel 206, a high-density fluid may be pumped downward
through inner pipe 202 and into wellbore annulus 34 through crossover port 250 near the
distal end of drill string 12 to help fill the annulus. Displaced wellbore fluid may be
recovered via RCD 40. Accordingly, dual drill string 12 may be raised or lowered within
wellbore 32 while filling annulus 34 via distal crossover port 250 to facilitate filling the
entire length of wellbore annulus 34.
However, according to an embodiment, one or more medial crossover ports 252 are
provided at various intervals along dual drill string 12 in addition to distal crossover port
250. Crossover ports 250, 252 can be independently, remotely, and preferably repeatedly,
opened and shut by using one or more conventional techniques. Accordingly, each
crossover port 250, 252 includes a valve assembly with an actuator for operating the valve
that can be remotely and independently controlled. The valve assembly may include a
valve component such as a gate, flapper, ball, disc and sleeve, for example, that pivots,
translates, or rotates between open and shut positions. The actuator causes the valve
component to position between open and shut positions and may be controlled for example,
by mud pulse telemetry, radio-frequency identification (RFID) tags, drop balls, or utilizing
the inner and outer electrically conductive pipes, 202, 204 of dual string 12 as a
communication bus. The actuator may be powered hydraulically by a drilling fluid
differential pressure, or electrically from a battery, by generating electricity from a turbine
rotated by a drilling fluid flow, or by utilizing dual string 12 as a pair of electrical
conductors, for example. Additionally, other arrangements for remotely controlling and
powering crossover ports 250, 252 may be used as appropriate.
Therefore, in the embodiment of Figure 5, the entire volume of fluid within wellbore
annulus 34 can be easily replaced without the necessity of running-in or tripping drill string
12 or having to pump high-density fluid all the way up wellbore 32. For example,
crossover port 250 may be opened and crossover ports 252a, 252b may be shut. A highdensity
fluid can be pumped through inner flow channel 206 to fill the annulus from
crossover port 250 to crossover port 252a, with the previous lighter-density fluid exiting at
the top of wellbore 32 via RCD 40. Next, crossover port 250 is shut, and crossover port
252a is opened. Pumping is continued through inner flow channel 206 and crossover port
252a to fill annulus 34 with the high-density fluid until crossover port 252b is reached, and
so on, up wellbore 32.
According to one or more embodiments, dual drill string 12 may include one or more on e
way check valves 260 disposed within inner pipe 202 and intervaled along drill string 12.
Check valves 260 may be oriented so as to check downward flow and thereby prevent
heavy cuttings and earthen particular matter suspended within drilling fluid 220 in inner
flow channel 206 from settling all the way to the bottom of drill string 12 during prolonged
periods of non-circulation. In some embodiments, may be simple mechanical valves, and
in other embodiments, check valves 260 may be remotely actuated to an opened position to
allow downward flow through inner flow channel 206, such as for well pressure control
operations described above. In the latter embodiments, check valves 260 may be
controlled and powered in the same manner as described above with respect to crossover
ports 250, 252. Check valves 260 may be ported or otherwise provide small fluid channels
(not illustrated) to provide pressure communication and limited flow capability between
bottom 31 of wellbore 32 and the upper end of drill string 12.
Figure 6 is a transverse cross section of dual drill string 12 looking down upon a crossover
port 250, 252 according to an embodiment. Figure 7 is an axial cross section of the
crossover port 250, 252 of Figure 6. Referring to both Figures 6 and 7, crossover port 250,
252 may include a cylindrical body 300 positioned within outer flow channel 208 of dual
drill string 12 and sealing with seals 302, 304 against the outer wall of inner pipe 204 and
the inner wall of outer pipe 204, respectively.
One or more apertures 310 longitudinally formed through body 300 fluidly couples outer
flow channel 208 above and below body 300. One or more apertures 320 radially formed
through body 300, inner pipe 202, and outer pipe 204 selectively fluidly couples inner flow
channel 206 with wellbore annulus 34. Body 300 may be keyed to inner and outer pipes
202, 204 so as to maintain proper rotational alignment.
A valve assembly is provided, which in the embodiment illustrated in Figures 6 and 7
includes flappers 330 that pivot between open positions (shown in solid line) and shut
positions (shown in broken line) for selective isolation of aperture 320. However, the
valve assembly may include any suitable valve component such as a gate, flapper, ball,
disc and sleeve, for example, that pivots, translates, or rotates between open and shut
positions. Flappers 330 are positioned by electrical actuators 334, such as solenoids.
However, any suitable actuator, including electrical, mechanical, hydraulic, pneumatic, or
the like, may be used.
In certain embodiments, electrical power and device-addressable control may be
transmitted to actuators 300 by inner pipe 202 and outer pipe 204 along the length of drill
string 12. Actuators 300 may be electrically connected to inner and outer pipes 202, 204
with leads 336. Inner pipe 202 may be the "hot" conductor and outer pipe 204 may be
grounded, because outer pipe 204 is likely to be in conductive contact with the grounded
drilling rig 14 (Figure 5). The outer wall of inner pipe 202 and/or the inner wall of outer
pipe 204 may be coated with an electrical insulating material (not expressly shown) to
prevent short circuiting of the inner pipe 202 through the drilling fluid or other contact
points to the outer pipe 204. Examples of dielectric insulating materials include polyimide,
polytetrafluoroethylene or other fluoropolymers, nylon, and ceramic coatings. Body 300
may similarly be made of ceramic material or a metal alloy with a dielectric insulating
coating. Ceramics offer a high erosion resistance to flowing sand, cuttings, junk and other
particulate matter. However, other forms for providing of communication and power to
actuators 300 may be used as appropriate, including mud pulse telemetry, radio-frequency
identification (RFID) tags, drop balls, and the like.
Figures 8 and 9 are axial cross sections of a check valve 260 of Figure 5 according to an
embodiment. Check valve 260 may include a body 370 that is positioned and sealed within
inner pipe 202 using seals 372. A pivoting flapper 374 allows flow in an upward direction
as shown in Figure 8 and prevents flow in a downward direction as shown in Figure 9.
Flapper may be urged into the shut position of Figure 9 by a toroidal spring 376 wound
about a pivot pin 378. Fluid flow of a sufficient pressure will overcome the shutting force
of spring 376. In another embodiment, check valve 260 may include an actuator, such as
disclosed with respect to crossover ports 250, 255, for allowing controlled, selective,
remote operation of check valve 260.
In summary, drilling systems and methods for drilling a wellbore have been described.
Embodiments of a drilling system may have: A drilling rig; a concentric dual drill pipe
string carried by the drilling rig and extending into a wellbore, the concentric dual drill
pipe string including an inner pipe disposed within an outer pipe, a region within the
wellbore and external to an outer wall of the string defining an annulus; a first valve
disposed along the string selectively fluidly coupling an interior of the inner pipe with the
annulus; and a second valve disposed along the string selectively fluidly coupling an
interior of the inner pipe with the annulus; wherein the first and second valves can be
independently and remotely actuated. Embodiments of an offshore drilling system may
have: A wellhead on a seafloor of a body of water, the wellhead defining a passage; a
rotating control device having a housing carried atop the wellhead, the housing defining a
passage in fluid communication with the passage of the wellhead; an offshore platform
disposed above a surface of the body of water; a concentric dual drill pipe string carried by
the platform and extending through the passage of the rotating control device into the
passage of the wellhead, the wellhead and the string defining an annulus therebetween, the
rotating control device including a sealing element that dynamically seals against an outer
wall of the string so as to fluidly isolate the annulus from the body of water, the outer wall
of the string above the rotating control device being in contact with the body of water; a
hydraulic power unit near the seafloor and coupled to the rotating control device so as to
supply a lubricant to the sealing element; a source of pressurized fluid selectively fluidly
coupled to the annulus; and at least one communication link operable between a location at
the surface of the body of water and at least one of the hydraulic power unit and the source
of pressurized fluid. Embodiments of a method for drilling a wellbore may include:
Providing a blowout preventer at a seafloor of a body of water; providing a rotating control
device carried above the blowout preventer, the rotating control device including a housing
and a releasable seal assembly characterized by an inner diameter; providing a drill string
extending from a surface of the body of water through the rotating control device and
blowout preventer into the wellbore, the drill string carrying a drill bit at a distal end, the
drill string carrying a transport member characterized by an outer diameter that is greater
than the inner diameter of the seal assembly; raising the drill string to a position where the
drill bit is higher than the blowout preventer and the transport member is lower than the
seal assembly; then shutting a closure device of the blowout preventer to fluidly isolate the
wellbore; equalizing pressure across the seal assembly; remotely unclamping the seal
assembly from the housing; and then raising the drill string to the surface, the transport
member carrying the seal assembly.
Any of the foregoing embodiments may include any one of the following elements or
characteristics, alone or in combination with each other: A bottom hole assembly carried
at a distal end of the string; a blowout preventer carried atop the wellhead at a position
below the rotating control device, the blowout preventer having a passage formed
therethrough that is in fluid communication with the passages of the wellhead and the
rotating control device, the blowout preventer including a closure device arranged so as to
selectively isolate the passage of the wellhead from the passage of the rotating control
device; a clamp included with the rotating control device so as to selectively connect the
sealing element to the housing of the rotating control device; a tubular spacer carried atop
the blowout preventer at a position below the rotating control device, the spacer having an
axial length great enough so that the bottom hole assembly can be positioned between the
closure device of the blowout preventer and the sealing element of the rotating control
device; the hydraulic power unit is arranged so as to actuate the clamp; the clamp is
remotely controllable from the location at the surface of the body of water; a guide carried
atop the rotating control device; the guide has a tapered upper end; the source of
pressurized fluid includes a pump disposed at the seafloor and selectively fluidly coupled
to the annulus; the pump is remotely controllable from the location at the surface of the
body of water; the source of pressurized fluid includes a choke line extending between a
point at the surface of the body of water and the seafloor, the choke line being selectively
fluidly coupled to the annulus; the choke line is connected to a blowout preventer that is
carried atop the wellhead at a position below the rotating control device; a lubrication flow
path formed through the rotating control device in fluid communication with the outer wall
of the string at or near the sealing element, the lubrication flow path being selectively
fluidly coupled with the hydraulic power unit; the hydraulic power unit is arranged to
deliver a quantity of the body of water through the lubrication flow path to the outer wall
of the string; a tank disposed at the seafloor and containing a volume of lubricant, the tank
being selectively fluidly coupled to the hydraulic power unit, the hydraulic power unit
being arranged to deliver a quantity of the lubricant through the lubrication flow path to the
outer wall of the string; a lubricant line extending between a point at the surface of the
body of water and the seafloor, the lubricant line being selectively fluidly coupled to the
hydraulic power unit, the hydraulic power unit being arranged to deliver a quantity of a
lubricant from the lubricant line through the lubrication flow path to the outer wall of the
string; a tank disposed at the seafloor and selectively fluidly coupled to the passage of the
rotating control device for transferring a fluid between the passage of the rotating control
device and the tank; the location at the surface of the body of water is at the offshore
platform; a floating vessel disposed at the surface of the body of water, wherein the
location at the surface of the body of water is at the floating vessel; an umbilical extending
from the floating vessel to the at least one of the hydraulic power unit and the source of
pressurized fluid, the at least one communication link provided via the umbilical; a
blowout preventer carried atop the wellhead at a position below the rotating control device;
a choke line and a kill line each extending from the floating vessel to the blowout
preventer, the choke and kill lines being selectively fluidly coupled to the blowout
preventer; a first pressure sensor included with the rotating control device and positioned
for measuring a pressure at a first point above the sealing element; a second pressure
sensor included with the rotating control device and positioned for measuring a pressure at
a second point below the sealing element; the first and second pressure sensors are coupled
to the at least one communication link for communication with location at the surface of
the body of water; at least one communication link operable between the first and second
valves and the drilling rig for independently and remotely actuating the first and second
valves from the drilling rig; at least one communication link operable between the first and
second valves and the drilling rig for independently and remotely actuating the first and
second valves from the drilling rig; a plurality of check valves disposed at a plurality of
points along the string within the inner pipe so as to prevent downhole flow within the
inner pipe; providing a tubular spacer between the blowout preventer and the rotating
control device; accommodating the transport member within the tubular spacer; and said
transport member is a bottom hole assembly.
The Abstract of the disclosure is solely for providing the patent office and the public at
large with a way by which to determine quickly from a cursory reading the nature and gist
of technical disclosure, and it represents solely one or more embodiments.
While various embodiments have been illustrated in detail, the disclosure is not limited to
the embodiments shown. Modifications and adaptations of the above embodiments may
occur to those skilled in the art. Such modifications and adaptations are in the spirit and
scope of the disclosure.

WHAT IS CLAIMED
1. A drilling system comprising:
a wellhead on a seafloor of a body of water, the wellhead defining a passage;
a rotating control device having a housing carried atop the wellhead, the housing
defining a passage in fluid communication with the passage of the wellhead;
an offshore platform disposed above a surface of the body of water;
a concentric dual drill pipe string carried by the platform and extending through the
passage of the rotating control device into the passage of the wellhead, the wellhead and
the string defining an annulus therebetween, the rotating control device including a sealing
element that dynamically seals against an outer wall of the string so as to fluidly isolate the
annulus from the body of water, the outer wall of the string above the rotating control
device being in contact with the body of water;
a hydraulic power unit near the seafloor and coupled to the rotating control device
so as to supply a lubricant to the sealing element;
a source of pressurized fluid selectively fluidly coupled to the annulus; and
at least one communication link operable between a location at the surface of the
body of water and at least one of the hydraulic power unit and the source of pressurized
fluid.
2. The drilling system of claim 1 further comprising:
a bottom hole assembly carried at a distal end of the string;
a blowout preventer carried atop the wellhead at a position below the rotating
control device, the blowout preventer having a passage formed therethrough that is in fluid
communication with the passages of the wellhead and the rotating control device, the
blowout preventer including a closure device arranged so as to selectively isolate the
passage of the wellhead from the passage of the rotating control device;
a clamp included with the rotating control device so as to selectively connect the
sealing element to the housing of the rotating control device; and
a tubular spacer carried atop the blowout preventer at a position below the rotating
control device, the spacer having an axial length great enough so that the bottom hole
assembly can be positioned between the closure device of the blowout preventer and the
sealing element of the rotating control device.
3. The drilling system of claim 2 wherein:
the hydraulic power unit is arranged so as to actuate the clamp; and
the clamp is remotely controllable from the location at the surface of the body of
water.
4. The drilling system of claim 1 further comprising:
a guide carried atop the rotating control device.
5. The drilling system of claim 4 wherein:
the guide has a tapered upper end.
6. The drilling system of claim 1 wherein the source of pressurized fluid further
comprises:
a pump disposed at the seafloor and selectively fluidly coupled to the annulus;
wherein
the pump is remotely controllable from the location at the surface of the body of
water.
7. The drilling system of claim 1 wherein the source of pressurized fluid further
comprises:
a choke line extending between a point at the surface of the body of water and the
seafloor, the choke line being selectively fluidly coupled to the annulus.
8. The drilling system of claim 7 wherein:
the choke line is connected to a blowout preventer that is carried atop the wellhead
at a position below the rotating control device.
9. The drilling system of claim 1 wherein:
a lubrication flow path formed through the rotating control device in fluid
communication with the outer wall of the string at or near the sealing element, the
lubrication flow path being selectively fluidly coupled with the hydraulic power unit.
10. The drilling system of claim 9 wherein:
the hydraulic power unit is arranged to deliver a quantity of the body of water
through the lubrication flow path to the outer wall of the string.
11. The drilling system of claim 9 further comprising:
a tank disposed at the seafloor and containing a volume of lubricant, the tank being
selectively fluidly coupled to the hydraulic power unit, the hydraulic power unit being
arranged to deliver a quantity of the lubricant through the lubrication flow path to the outer
wall of the string.
12. The drilling system of claim 9 further comprising:
a lubricant line extending between a point at the surface of the body of water and
the seafloor, the lubricant line being selectively fluidly coupled to the hydraulic power unit,
the hydraulic power unit being arranged to deliver a quantity of a lubricant from the
lubricant line through the lubrication flow path to the outer wall of the string.
13. The drilling system of claim 2 further comprising:
a tank disposed at the seafloor and selectively fluidly coupled to the passage of the
rotating control device for transferring a fluid between the passage of the rotating control
device and the tank.
14. The drilling system of claim 1 wherein:
the location at the surface of the body of water is at the offshore platform.
15. The drilling system of claim 1 further comprising:
a floating vessel disposed at the surface of the body of water, wherein
the location at the surface of the body of water is at the floating vessel.
16. The drilling system of claim 1 further comprising:
an umbilical extending from the floating vessel to the at least one of the hydraulic
power unit and the source of pressurized fluid, the at least one communication link
provided via the umbilical.
17. The drilling system of claim 1 further comprising:
a blowout preventer carried atop the wellhead at a position below the rotating
control device; and
a choke line and a kill line each extending from the floating vessel to the blowout
preventer, the choke and kill lines being selectively fluidly coupled to the blowout
preventer.
18. The drilling system of claim 1 further comprising:
a first pressure sensor included with the rotating control device and positioned for
measuring a pressure at a first point above the sealing element; and
a second pressure sensor included with the rotating control device and positioned
for measuring a pressure at a second point below the sealing element; wherein
the first and second pressure sensors are coupled to the at least one communication
link for communication with location at the surface of the body of water.
19. A drilling system comprising:
a drilling rig;
a concentric dual drill pipe string carried by the drilling rig and extending into a
wellbore, the concentric dual drill pipe string including an inner pipe disposed within an
outer pipe, a region within the wellbore and external to an outer wall of the string defining
an annulus;
a first valve disposed along the string selectively fluidly coupling an interior of the
inner pipe with the annulus; and
a second valve disposed along the string selectively fluidly coupling an interior of
the inner pipe with the annulus; wherein
the first and second valves can be independently and remotely actuated.
20. The drilling system of claim 19 further comprising:
at least one communication link operable between the first and second valves and
the drilling rig for independently and remotely actuating the first and second valves from
the drilling rig.
2 1. The drilling system of claim 20 wherein:
the at least one communication link includes a first conductor defined by the inner
pipe and a second conductor defined by the outer pipe.
22. The drilling system of claim 19 further comprising:
a plurality of check valves disposed at a plurality of points along the string within
the inner pipe so as to prevent downhole flow within the inner pipe.
23. A method for drilling a subsea wellbore, comprising:
providing a blowout preventer at a seafloor of a body of water;
providing a rotating control device carried above the blowout preventer, the rotating
control device including a housing and a releasable seal assembly characterized by an inner
diameter;
providing a drill string extending from a surface of the body of water through the
rotating control device and blowout preventer into the wellbore, the drill string carrying a
drill bit at a distal end, the drill string carrying a transport member with an outer diameter
that is greater than the inner diameter of the seal assembly;
raising the drill string to a position where the drill bit is higher than the blowout
preventer and the transport member is lower than the seal assembly; then
shutting a closure device of the blowout preventer to fluidly isolate the wellbore;
equalizing pressure across the seal assembly;
remotely unclamping the seal assembly from the housing; and then
raising the drill string to the surface, the transport member carrying the seal
assembly.
24. The method of claim 23 further comprising:
providing a tubular spacer between the blowout preventer and the rotating control
device; and
accommodating the transport member within the tubular spacer.
25. The method of claim 24 wherein:
said transport member is a bottom hole assembly.