U.S. patent application number 09/788058 was filed with the patent office on 2001-12-13 for apparatus and method for returning drilling fluid from a subsea wellbore.
Invention is credited to Calder, Ian Douglas, Johnson, Ready J., Nelson, John.
Application Number | 20010050185 09/788058 |
Document ID | / |
Family ID | 26878869 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050185 |
Kind Code |
A1 |
Calder, Ian Douglas ; et
al. |
December 13, 2001 |
Apparatus and method for returning drilling fluid from a subsea
wellbore
Abstract
An apparatus and method are provided for controlling hydrostatic
pressure in drilling fluid in a subsea well. A main pump forces
drilling fluid down the drill pipe, out of the end of the drill
pipe, and upward in an annulus surrounding the pipe. A rotating
drilling head is attached to a wellhead assembly at the sea floor.
The drilling head has an inner body rotatably carried in an outer
body landed in a bore of a housing. An energizable gripper in a
bore of the inner body grips an outer surface of the drill pipe.
The drilling head diverts the drilling fluid into a lateral passage
in the sidewall of the housing. An auxiliary pump forces seawater
through a venturi into a conduit, creating a lower pressure to draw
drilling fluid into the conduit to be carried back to the surface
vessel. Pressure and flow rate measurements are sent to a control
system that modulates the speed of each pump to control hydrostatic
pressure.
Inventors: |
Calder, Ian Douglas;
(Houston, TX) ; Johnson, Ready J.; (Houston,
TX) ; Nelson, John; (Houston, TX) |
Correspondence
Address: |
James E. Bradley
BRACEWELL & PATTERSON, LLP
Sutie 2900
711 Louisiana Street
Houston
TX
77002-2781
US
|
Family ID: |
26878869 |
Appl. No.: |
09/788058 |
Filed: |
February 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60183201 |
Feb 17, 2000 |
|
|
|
Current U.S.
Class: |
175/5 ; 166/358;
166/53 |
Current CPC
Class: |
E21B 21/08 20130101;
E21B 21/001 20130101; E21B 33/085 20130101 |
Class at
Publication: |
175/5 ; 166/358;
166/53 |
International
Class: |
E21B 007/12 |
Claims
1. In an apparatus for drilling a subsea well, the apparatus having
a subsea wellhead assembly enclosing a drill pipe, the drill pipe
having a bore through which drilling fluid is delivered and a drill
pipe annulus between the drill pipe and a bore of the well, an
improved pump assembly for returning drilling fluid flowing up the
drill pipe annulus to a surface vessel, the pump assembly
comprising: a submersible pump having an inlet and an outlet, the
inlet being in fluid communication with seawater surrounding the
wellhead assembly; a conduit extending from the outlet of the pump
to the surface vessel for delivering seawater to the surface
vessel; a venturi in the conduit for creating a lower pressure area
due to the seawater flowing though the venturi; and a passage
extending from the drill pipe annulus to the venturi for drawing
drilling fluid from the drill pipe annulus into the conduit:
2. The apparatus of claim 1, wherein: the pump is a centrifugal
pump having at least one impeller and diffuser stage.
3. The apparatus of claim 1, further comprising: a drilling head
located in the annulus and above the passage, the drilling head
sealing around the drill pipe.
4. The apparatus of claim 1, further comprising: at least one
pressure sensor in communication with the fluid in the drill pipe
annulus; and a control system that receives a signal from the
pressure sensor and controls a rate of operation of the submersible
pump.
5. The apparatus of claim 1, further comprising: a bottom-hole
pressure sensor located near the bottom of the drill pipe for
sensing pressure of the drilling fluid on the drill pipe annulus; a
signal transmitter assembly for transmitting data from the
bottom-hole pressure sensor; and a control system that receives the
data and controls the submersible pump in response thereto.
6. The apparatus of claim 1, further comprising: a bottom-hole
pressure sensor located near the bottom of the drill pipe for
sensing pressure of the drilling fluid on the drill pipe annulus; a
signal transmitter assembly for transmitting data from the
bottom-hole pressure sensor; a detector located near the wellhead
assembly for detecting and relaying the data from the transmitter;
a pump pressure sensor located in the conduit near the outlet of
the submersible pump for sensing the pressure at the outlet of the
pump; and a control system that receives the data from the detector
and the sensor and controls the submersible pump in response
thereto.
7. The apparatus of claim 1, further comprising: a riser extending
from the wellhead to the surface vessel; and a rotational drilling
head that is run and retrieved through the riser, the drilling head
landing above the passage and sealing any fluid in the riser
surrounding the drill pipe from the drill pipe annulus and the bore
of the well.
8. A well drilling assembly, comprising in combination: a subsea
wellhead; a submersible, centrifugal pump having an inlet and an
outlet, the inlet being in fluid communication with seawater
surrounding the wellhead, the pump being adjacent the wellhead; a
conduit extending from the outlet of the pump to a surface vessel;
a venturi in the conduit for creating a lower pressure area due to
the seawater flowing though the venturi; a drilling head at the
subsea wellhead for sealing around a string of drill pipe and
blocking upward-flowing drilling fluid in the drill pipe annulus; a
passage extending from the wellhead to the venturi for drawing
drilling fluid from the drill pipe annulus to the venturi.
9. The apparatus of claim 8, further comprising: at least one
pressure sensor in communication with the fluid in the drill pipe
annulus; and a control system that receives a signal from the
pressure sensor and controls a rate of operation of the submersible
pump.
10. The apparatus of claim 8, further comprising: a bottom-hole
pressure sensor located near the bottom of the drill pipe for
sensing pressure of the drilling fluid on the drill pipe annulus; a
signal transmitter assembly for transmitting data from the
bottom-hole pressure sensor; and a control system that receives the
data and controls the submersible pump in response thereto.
11. The apparatus of claim 8, further comprising: a riser extending
from the subsea wellhead to the surface vessel; and wherein the
drilling head is retrievable through the riser.
12. A subsea well drilling apparatus, comprising: a subsea
wellhead; a string of drill pipe extending from a surface vessel
through the wellhead and into a well, defining a drill pipe annulus
in the well; a surface pump on the surface vessel for pumping
drilling fluid down the drill pipe, which returns back up the drill
pipe annulus; a drilling head at the wellhead that seals around the
drill pipe; a subsea pump adjacent the wellhead; a conduit leading
from the subsea pump to the surface vessel; a passage at the
wellhead that diverts the drilling find to the subsea pump for
returning through the conduit to the surface vessel; a control
system on the vessel that controls the flow rate of at least one of
the pumps; a bottom-hole pressure sensor that communicates
bottom-hole pressure to the control system; and a subsea pump
pressure sensor that communicates pressure at the subsea pump to
the control system.
13. The apparatus of claim 12, further comprising: a signal
transmitter assembly for transmitting data from the bottom-hole
pressure sensor; a detector for detecting the for receiving data
from the transmitter assembly, the detector being located near an
upper end of the wellhead; an electrical line for carrying the data
from the detector to the surface vessel; and wherein the
bottom-hole pressure sensor is located near the bottom of the drill
pipe for sensing pressure of the drilling fluid on the drill pipe
annulus.
14. The apparatus of claim 12, further comprising: a pressure
sensor located in the passage for measuring fluid pressure in the
passage.
15. The apparatus of claim 12, further comprising: a housing having
a bore and being adapted to be connected between a wellhead and a
riser, the riser extending to a surface vessel; a tubular outer
body adapted to land in the bore of the housing, the outer body
being releasably secured in the housing, the outer diameter of the
outer body adapted to be less than an inner diameter of the riser
to enable the outer body to be run and retrieved through the riser;
a tubular inner body rotatably carried in the outer body and having
a bore for receiving the drill pipe; a hydraulically-energized
gripping member in the bore of the inner body for gripping the
drill pipe; at least one port in the housing for connection to a
hydraulic fluid line; and at least one port in the outer body for
registering with the port in the housing to supply hydraulic fluid
to the gripping member.
16. A method of controlling pressure of a drilling fluid within a
bore of a subsea well being drilled by a string of drill pipe, the
fluid returning up an annulus defined by an outer surface of the
drill pipe and the bore of the well, the method comprising: (a)
using a surface pump on a surface vessel to pump the drilling fluid
down the drill pipe; (b) using a subsea pump at an upper end of the
well to pump the fluid to the surface vessel; (c) monitoring a
pressure of the drilling fluid in the wellbore; and (d) modulating
a rate of operation of at least one of the pumps for increasing or
decreasing pressure of the drilling fluid in the well.
17. The method of claim 16, wherein: step (c) comprises monitoring
a bottom-hole pressure of the drilling fluid.
18. The method of claim 16, wherein: step (c) comprises monitoring
a bottom-hole pressure of the drilling fluid with a pressure sensor
in the drill pipe, transmitting data from the pressure sensor to a
detector at the upper end of the well, and transmitting data from
the detector to the surface vessel via an electrical cable.
19. The method of claim 16 wherein step (b) comprises: providing a
submersible pump having an inlet and an outlet, the inlet being in
fluid communication with seawater surrounding the wellhead
assembly; connecting a conduit extending from the outlet of the
pump to the surface vessel for delivering seawater to the surface
vessel; providing a venturi in the conduit for creating a lower
pressure area due to the seawater flowing though the venturi;
connecting a passage extending from the drill pipe annulus to the
venturi for drawing drilling fluid from the drill pipe annulus into
the conduit; and wherein the pump is a centrifugal pump having at
least one impeller and diffuser stage.
20. A method of returning drilling fluid from a bore of a subsea
well, the well being drilled by a string of drill pipe, drilling
fluid being pumped down a bore of the pipe and returning up a drill
pipe annulus between the drill pipe and the bore, the method
comprising: providing a submersible pump having an inlet and an
outlet, the inlet being in fluid communication with seawater
surrounding the wellhead assembly; connecting a conduit to the
outlet of the pump, the conduit extending to a surface vessel for
delivering seawater to the surface vessel; providing a venturi in
the conduit for creating a lower pressure area due to the seawater
flowing though the venturi; and connecting a passage extending from
the drill pipe annulus to the venturi for drawing drilling fluid
from the drill pipe annulus into the conduit.
21. The method of claim 20, comprising: sealing the drill pipe
annulus at the wellhead.
22. A rotatable drilling head, comprising: a housing having a bore
and being adapted to be connected between a wellhead assembly and a
riser, the riser extending to a surface vessel; a profile located
in the bore of the housing; a tubular outer body adapted to land in
the bore of the housing, the outer body being releasably secured in
the housing, the outer diameter of the outer body adapted to be
less than an inner diameter of the riser to enable the outer body
to be run through the riser; a tubular inner body rotatably carried
in the outer body and having a bore for receiving drill pipe; a
hydraulically-energized gripping member in the bore of the inner
body for gripping the drill pipe; at least one port in the housing
for connection to a hydraulic fluid line; at least one port in the
outer body for registering with the port in the housing to supply
hydraulic fluid to the gripping member; and a latch carried on the
outer body for securing the outer body to the housing by engaging
the profile.
23. The drilling head of claim 22, wherein the latching system
comprises: a circumferential ring having a tapered outer surface
and a central axis parallel to the bore of the inner body; a
plurality of dogs movably carried in the outer body; and wherein
the ring is movable from an upper position to a lower position
along a path parallel to the axis, the upper position allowing the
dogs to remain in a disengaged position; and movement of the ring
to the lower position causing the dogs to move radially outward and
engage the profile.
24. The drilling head of claim 22, further comprising: a lateral
passage formed in a sidewall of the housing and extending from the
bore of the housing; and wherein the outer body engages the bore of
the outer housing above the lateral passage.
25. A method of sealing an annulus located between a drill pipe and
the bore of a wellhead, the method comprising: mounting a housing
having a bore to an upper end of the wellhead; landing a tubular
outer body in the bore of the housing; providing a tubular inner
body rotatably carried in the outer body and having a bore for
receiving the drill pipe; registering a port in the housing with a
port in the outer body for supplying hydraulic fluid to an annulus
in the outer body; energizing a gripping member in the bore of the
inner body by pressurizing the hydraulic fluid in the annulus of
the body, the gripping member engaging an outer surface of the
drill pipe and rotating with the drill pipe.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Benefit is herein claimed of the filing date under 35 USC
.sctn.119 and/or .sctn.120 and CFR 1.78 to U.S. Provisional Patent
Application Serial No. 60/183,201, filed on Feb. 17, 2000, and
entitled "Eduction Pump for Riserless Drilling."
FIELD OF THE INVENTION
[0002] This invention relates to a subsea well drilling system.
More particularly, this invention relates to a well assembly having
a rotating seal, a means for measuring and controlling the downhole
pressure of drilling mud, and a pump placed near the well for
pumping the drilling mud back to the surface.
DESCRIPTION OF THE PRIOR ART
[0003] To remove the load on the main drilling fluid pump while
drilling a well, it is known in the art to provide an auxiliary
pump for returning the drilling fluid to the surface. In fact,
using this type of system may obviate the need for a riser, as
shown in U.S. Pat. No. 4,149,603. However, reciprocating pumps are
difficult to use in subsea locations, and the abrasiveness of
cuttings entrained in the drilling fluid can destroy the internal
components of a centrifugal pump.
[0004] Excessive hydrostatic pressure in drilling fluids used while
drilling a well may damage surrounding formations. One method of
alleviating pressure in the column of fluid in the annulus is shown
in U.S. Pat. No. 4,091,881. Fluid is drawn out of the upper portion
of the annulus in the riser, and an inert gas is pumped into the
fluid to reduce the density of the fluid and lift the fluid through
a separate conduit to the surface. The rate of gas injection is
controlled to alter the hydrostatic pressure in the well.
SUMMARY OF THE INVENTION
[0005] An apparatus and method are provided for controlling
hydrostatic pressure in drilling fluid in a subsea well. A main
pump forces drilling fluid down the bore of a drill pipe running
through a wellhead assembly. The drilling fluid exits the drill
pipe at the drill bit at the bottom of the well and begins
traveling upward in an annulus surrounding the drill pipe.
[0006] A rotating drilling head assembly is attached to the upper
end of the wellhead assembly. The drilling head has an inner body
rotatably carried in an outer body, and the outer body is landed in
a bore of a housing, the bore of the housing aligning with the
annulus around the drill pipe. The drill pipe is located within a
bore of the inner body, and an energizable gripper located in the
bore of the inner body grips an outer surface of the drill pipe.
Drilling fluid travels upward in the annulus and into bore of the
housing. A lateral passage is formed through a sidewall of the
housing and communicates the bore of the housing. The drilling head
prevents the drilling fluid from moving further upward in the bore
of the housing, diverting the drilling fluid into the lateral
passage. The drilling head also isolates from the well hydrostatic
fluid pressure in the riser.
[0007] A submersible pump forces seawater into a conduit extending
from the outlet of the pump to the surface for delivering seawater
to a surface vessel. A venturi in the conduit creates a lower
pressure area due to the seawater flowing through the venturi. The
lateral passage of the housing is connected to the venturi, and
drilling fluid is drawn out of the annulus and into the conduit.
The drilling fluid mixes with the seawater to be carried back to
the surface vessel.
[0008] Drilling fluid pressure and flow rate measurements are sent
to a control system. The control system modulates the rate of
operation of each pump for increasing or decreasing hydrostatic
pressure in the fluid in the well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The novel features believed to be characteristic of the
invention are set forth in the appended claims. The invention
itself however, as well as a preferred mode of use, further objects
and advantages thereof, will best be understood by reference to the
following detailed description of an illustrative embodiment when
read in conjunction with the accompanying drawings, wherein:
[0010] FIG. 1 is a schematic of a subsea drilling operation
employing an eduction pump and pressure measurement system of the
present invention; and
[0011] FIG. 2 is a cross-sectional view of a rotating drilling head
installed in a manifold and constructed in accordance with the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Referring first to FIG. 1, in a subsea drilling operation
employing this invention, a blow out preventer stack (BOP) 10 is
landed on top of a wellhead housing assembly 12 on the sea floor. A
riser drilling head or manifold 14 is joined to BOP 10 and tubular
riser 16 extends from manifold 14 upwards to a floating drilling
platform or drilling vessel 18 at the surface. A tubular drill
string 20 extends from platform 18 concentrically through riser 16
and manifold 14 into wellhead 12, leaving an annular clearance 22
between string 20 and riser 16. Drill string 20 has a conventional
drill bit 24 at its lower end which cuts into the sea floor as
string 20 is rotated, thus drilling the well.
[0013] Manifold 14 has a lateral passage 26 leading off to the
side, and seals around string 20 with a drilling head 28 that
rotates with the drill string 20. Drilling mud is stored in a mud
sump 30 on platform 18 and is pumped down through the bore of drill
string 20 with a mud pump 31 on platform 18. The mud travels down
string 20, out drill bit 24, and back up annulus 22 toward rotating
drilling head 28. Drilling head 28 prevents the mud from continuing
upward as in conventional systems, and thus the mud must exit
through lateral passage 26.
[0014] A mud return line 32 is joined to lateral passage 26 and
leads upward to platform 18 and back to mud sump 30. Mud return
line 32 has an electric submersible pump 34 joined to is lower end
and beneath passage 26. Pump 34 is positioned to draw in the
surrounding sea water and pump the water up return line 30. Pump 34
is preferably a multistage centrifugal pump having a series of
impellers and diffusers, wherein the impellers impart motion to sea
water and the diffusers increase pressure.
[0015] Pump 34 does not contact the drilling mud itself, rather
pump 34 discharges seawater into the bottom of a venturi 36 near
passage 26, creating a lower pressure in passage 26 and drawing mud
into mud line 32. The mud then mixes with the seawater and is
carried up mud line 32 to platform 18 where the sea water is
separated out and mud is returned to sump 30. This reduces the load
on surface pump 31 because it does not have to pump the mud all the
way back to platform 18.
[0016] A control system may be employed to automatically control
pumps 31, 34. The control system may utilize a measurement while
drilling (MWD) system 38, which uses an pulse generator in drill
string 20 to transmit data through the annulus in the wellbore for
reporting the bottom hole pressure in the well from sensor 37 to a
control module 40 on platform 18. The pulses are detected by a
detector 39 in manifold 14 and transmitted through umbilical 44 to
the surface. A second pressure sensor 42 is positioned in passage
26 and sends a signal to control module 40 through umbilical 44
running alongside mud line 32. A third pressure sensor 46 is
positioned above venturi 36 and sends a signal to control module 40
through umbilical 44. A flow meter 48 is placed above venturi 36
and sends a signal to control module 40 through umbilical 44.
Control module 40 is linked to pumps 31 and 34 to control the rate
at which each operates. Using the outputs from MWD 38, pressure
sensors 42 and 46, and flow meter 48, control module 40 modulates
pump 34 and pump 31 to balance the pressure of the drilling mud
being channeled through string 20 and being drawn up through mud
line 32. Control module 40 can thus control the wellbore back
pressure and compensate for pressure variations in the well.
[0017] The details of a preferred rotating drilling head 28 are
shown in FIG. 2. Drilling head 28 prevents drilling mud from
traveling up annulus 22 to the surface, causing drilling mud
flowing from annulus 22 into manifold to flow into lateral passage
26 formed in the lower portion of manifold 14. Drilling head 28
comprises a tubular outer body 50 and a tubular inner body 52
rotatably carried within outer body 50 for rotating with string 20.
Drilling head 28 is lowered through riser 16 (FIG. 1) until outer
body 50 lands in manifold 14. Manifold 14 has a bore 54 that aligns
with annulus 22 (FIG. 1) and has an upward-facing shoulder 56
formed therein for receiving a corresponding downward-facing
shoulder 58 on the lower end of the outer surface of outer body 50.
Inner body 52 has a bore 60 through which string 20 is lowered
toward the wellbore. Drilling head 28 is releasably attached to
manifold 14 by dogs 62 that are moved outwardly using a
circumferential ring 64. Ring 64 has a tapered surface 66 which
engages the inner surface of dogs 62 as ring 64 is moved downward,
causing dogs 62 to engage recesses 68 in bore 54 of manifold 14.
The left side of FIG. 2 shows ring 64 in its upper position, and
dogs 62 are in their disengaged position. The right half of FIG. 2
shows ring 64 having moved downward, engaging dogs 62 and forcing
them outward to engage recesses 68. Passage 26 has an external
flange 70 for attaching a conduit (not shown) leading to venturi 36
(FIG. 1). An elastomer stripper 72 is attached to the lower end of
inner body 52 for sealingly engaging string 20.
[0018] Upper and lower tapered roller bearings 74 support inner
body 52 within outer body 50 and are located within an annulus 76
defined by the outer surface of inner body 52 and the inner surface
of outer body 50. An energizable, elastomer gripper 78 is located
in the central portion of inner body 52. An upper metal seal 80 and
three lower metal seals 82 dynamically seal outer body 50 to inner
body 52. Hydraulic-fluid ports 84 in manifold 14 and openings to
passages 86 in outer body 50 align when outer body 50 is landed in
manifold 14. Ports 84 carry hydraulic fluid from a source exterior
of manifold 14 through the sidewall of manifold 14 and into
passages 86, passages 86 leading to seals 80, 82 and communicating
with annulus 76. The fluid lubricates bearings 74 and seals 80, 82
and energizes gripper 78 for frictionally engaging drill string.
Seals 82 slidingly engage a sleeve 83 that rotates with gripper 73
and the drill pipe. Seal 80 slidingly engages a neck 85 that is a
rotating part of inner body 52.
[0019] The left side of FIG. 2 shows gripper 78 before being
energized, and the right side of the figure shows gripper 78
energized and engaging string 20. Fluid pressure in annulus 76 is
communicated through a hole 88 in the sidewall of inner body 52 to
apply an inward force to the outer surface 90 of gripper 78.
Gripper 78 expands radially inward until the inner surface 92 of
gripper 78 contacts string 20. Fluid pressure is maintained in
annulus 76 to ensure a sufficient frictional force between gripper
78 and string 20.
[0020] In operation, a BOP 10 is landed on wellhead housing
assembly 12, and manifold 14 is joined to BOP 10. Riser 16 is
connected to manifold 14 and extends upwards to vessel 18 at the
surface. Drilling head 28 is lowered through riser 16 and locked
into manifold 14 by actuating dogs 62 with ring 64. Drill string 20
is lowered from platform 18 through riser and manifold 14 into
wellhead 12.
[0021] Drilling mud is pumped down through the bore of drill string
20 by mud pump 31 on platform 18. The mud travels down string 20,
out drill bit 24, and back up annulus 22 toward drilling head 28.
Drilling head 28 prevents the mud from continuing upward in annulus
22, diverting the mud through lateral passage 26. Pump 34 pumps
surrounding seawater up return line 30, forcing the water through
venturi 36 and creating a lower pressure in venturi 36. Mud return
line 32 is connected to lateral passage 26, and mud is drawn from
annulus 22, through passage 26, and into mud line 32. The mud then
mixes with the seawater and is carried up mud line 32 to platform
18 where the sea water is separated out and mud is returned to sump
30.
[0022] MWD system 38 transmits acoustic signals in the drilling mud
to transmit bottom hole pressure data to control module 40.
Pressure sensors 42, 46 and flow meter 48 transmit data to control
module 40 through umbilical 44. Control module 40 modulates pump 34
and pump 31 to balance the pressure of the drilling mud being
channeled through string 20 and being drawn up through mud line 32
to control the wellbore back pressure and compensate for pressure
variations in the well.
[0023] The advantages of the present invention include reducing the
load on the main drilling mud pump by providing an auxiliary pump
for pumping mud to the surface through a separate conduit. The pump
forces seawater through a venturi to draw the drilling mud into the
conduit, thus the abrasive mud does not contact the components in
the pump. Another advantage is that the bottom hole pressure can be
automatically controlled by measuring pressure and flow volume and
transmitting the measurements to a control system that modulates
the rates of operation of the pumps. By increasing or decreasing
the volume of mud moved by each pump, the pressure in the wellbore
can be controlled. Also, the drilling head can be lowered and
retrieved through the riser.
[0024] While the invention is shown in only one of its forms, it
should be apparent to those skilled in the art that it is not so
limited, but is susceptible to various changes without departing
from the scope of the invention.
* * * * *