U.S. patent application number 09/779758 was filed with the patent office on 2002-02-21 for deepwater drill string shut-off.
Invention is credited to Gonzalez, Romulo, Smits, Frans Sippo Wiegand.
Application Number | 20020020558 09/779758 |
Document ID | / |
Family ID | 26877083 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020020558 |
Kind Code |
A1 |
Gonzalez, Romulo ; et
al. |
February 21, 2002 |
Deepwater drill string shut-off
Abstract
A drill string shut-off valve system for controlling the mud
circulation system for deepwater marine drilling operations is
disclosed, the drill string shut-off valve having a valve body
having a cylinder, a main flow path, and a drilling mud flow
channel, an upper and a lower connector on the valve body for
installing the drill string shut-off valve into a drill string, and
a valve positioned to selectively interrupt in the main flow path
through the valve body or to complete the main flow path through
the drilling mud flow channel. A piston in the cylinder is operably
connected to the valve to drive it from an open to closed position.
The piston has a first pressure face, a port presenting pressure
from the upstream side of the valve to the first pressure face,
anda second pressure face on the back of the piston. Exhaust ports
present pressure from the annulus to the second pressure face and a
spring biases the drill string shut-of valve to a closed position,
but balanced with the area of the first pressure face to ensure
valve opening at normal pump operation pressures. A spring
adjustment assembly whereby the tension of the spring can be
readily adjusted to allow for different drilling conditions is also
disclosed.
Inventors: |
Gonzalez, Romulo; (Slidell,
LA) ; Smits, Frans Sippo Wiegand; (New Orleans,
LA) |
Correspondence
Address: |
Eugene R. Montalvo
Shell Oil Company
Legal - Intellectual Property
P.O. Box 2463
Houston
TX
77252-2463
US
|
Family ID: |
26877083 |
Appl. No.: |
09/779758 |
Filed: |
February 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60181327 |
Feb 9, 2000 |
|
|
|
Current U.S.
Class: |
175/5 ;
175/243 |
Current CPC
Class: |
E21B 21/001 20130101;
E21B 21/106 20130101; E21B 21/10 20130101 |
Class at
Publication: |
175/5 ;
175/243 |
International
Class: |
E21B 007/12 |
Claims
What is claimed is:
1. A drill string shut-off valve for marine drilling, comprising; a
valve body having a cylinder, a main flow path, and a drilling mud
flow channel; an upper and a lower connector on the valve body for
installing the drill string shut-off valve into a drill string; a
valve positioned to selectively interrupt in the main flow path
through the valve body or to complete the main flow path through
the drilling mud flow channel; a piston in the cylinder operably
connected to the valve to drive it from an open to closed position
and further comprising: a first pressure face; a port presenting
pressure from the upstream side of the valve to the first pressure
face; and a second pressure face on the back of the piston; and
exhaust ports presenting pressure from the annulus to the second
pressure face; and a spring biasing the drill string shut-of valve
to a closed position, but balanced with the area of the first
pressure face to ensure valve opening at normal pump operation
pressures.
2. A drill string shut-off valve for marine drilling in accordance
with claim 1, further comprising a spring adjustment assembly
whereby the tension of the spring can be readily adjusted to allow
for different drilling conditions.
3. A drill string shut-off valve for marine drilling, comprising; a
valve body having a cylinder, a main flow path, and a drilling mud
flow channel; an upper and a lower connector on the valve body for
installing the drill string shut-off valve into a drill string; a
valve positioned to selectively interrupt in the main flow path
through the valve body or to complete the main flow path through
the drilling mud flow channel; a piston in the cylinder operably
connected to the valve to drive it from an open to closed position
and further comprising: a first pressure face; a port presenting
pressure from the upstream side of the valve to the first pressure
face; and a second pressure face on the back of the piston; and
exhaust ports presenting pressure from downstream of the valve to
the second pressure face; a spring biasing the drill string shut-of
valve to a closed position, but balanced with the area of the first
pressure face to ensure valve opening at normal pump operation
pressures; and a spring adjustment assembly whereby the tension of
the spring can be readily adjusted to accommodate different
drilling conditions.
4. A drill string shut-off valve for marine drilling in accordance
with claim 1, wherein the exhaust ports presenting pressure from
downstream of the valve are pressure equalizing ports opening to
the well annulus.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to drilling systems and
operations. More particularly, the present invention is a method
and system for handling the circulation of drilling mud in
deepwater offshore drilling operations.
[0002] Drilling fluids, also known as muds, are used to cool the
drill bit, flush the cuttings away from the bit's formation
interface and then out of the system, and to stabilize the borehole
with a "filter cake" until newly drilled sections are cased. The
drilling fluid also performs a crucial well control function and is
monitored and adjusted to maintain a pressure with a hydrostatic
head in uncased sections of the borehole that prevents the
uncontrolled flow of pressured well fluids into the borehole from
the formation.
[0003] Conventional offshore drilling circulates drilling fluids
down the drill string and returns the drilling fluids with
entrained cuttings through an annulus between the drill string and
the casing below the mudline. A riser surrounds the drill string
starting from the wellhead at the ocean floor to drilling
facilities at the surface and the return circuit for drilling mud
continues from the mudline to the surface through the riser/drill
string annulus.
[0004] In this conventional system, the relative weight of the
drilling fluid over that of seawater and the length of the riser in
deepwater applications combine to exert an excess hydrostatic
pressure in the riser/drill string annulus.
[0005] Systems have been conceived to bring the drilling fluid and
entrained cuttings out of the annulus at the base of the riser and
to deploy a subsea pump to facilitate the return flow through a
separate line. One such system is disclosed in U.S. Pat. No.
4,813,495 issued Mar. 21, 1989 to Leach. That system requires
complex provisions to ensure the closely synchronous operation of
the supply and return pumps critical to the approach disclosed.
However, the durability and dependability of such a mud circulation
system is suspect in the offshore environment and particularly so
in light of the nature of the fluid with entrained cuttings that is
handled in valves and pumps on the return segment of the
circuit.
[0006] A greatly improved system is illustrated in assignee's
related invention, a Subsea Drill fluid Pumping and Treatment
System for Deepwater Drilling, published Apr. 1, 1999 as WO
99/15758, the disclosure of which is hereby incorporated by
reference. That application includes a disclosure of a method and
apparatus for reducing the excess hydrostatic pressure exerted by
the mud column return in the riser/drill string annulus and which
isolates the excess pressure from formation during operations,
maintaining an ambient pressure when pump operations cease.
[0007] However, the practice of that illustrative embodiment which
is disclosed in that publication ordinarily employs a significant
pressure drop across the drill string shut-off valve, causing a
significant energy loss due to friction and challenging the
operational life expectancy of the valve. Further, those
illustrative embodiments do not provide for easily adjusting the
drill string shut-off valve characteristics to accommodate changing
downhole conditions during the course of drilling a well.
A SUMMARY OF THE INVENTION
[0008] One aspect of the present invention is a drill string
shut-off valve system for controlling the mud circulation system
for deepwater marine drilling operations, the drill string shut-off
valve having a valve body having a cylinder, a main flow path, and
a drilling mud flow channel, an upper and a lower connector on the
valve body for installing the drill string shut-off valve into a
drill string, and a valve positioned to selectively interrupt in
the main flow path through the valve body or to complete the main
flow path through the drilling mud flow channel. A piston in the
cylinder is operably connected to the valve to drive it from an
open to closed position. The piston has a first pressure face, a
port presenting pressure from the upstream side of the valve to the
first pressure face, and a second pressure face on the back of the
piston. Exhaust ports present pressure from the annulus to the
second pressure face and a spring biases the drill string shut-off
valve to a closed position, but balanced with the area of the first
pressure face to ensure valve opening at normal pump operation
pressures.
[0009] Another aspect of the invention is a spring adjustment
assembly whereby the tension of the spring can be readily adjusted
to allow for different drilling conditions.
A BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The brief description above, as well as further objects and
advantages of the present invention, will be more fully appreciated
by reference to the following detailed description of the preferred
embodiments which should be read in conjunction with the
accompanying drawings in which:
[0011] FIG. 1 is a schematic illustration of one embodiment of a
subsea pumping system for deepwater drilling;
[0012] FIG. 2 is a side elevational view of a one embodiment of a
subsea pumping system for deepwater drilling;
[0013] FIG. 3 is a side elevational view of the dedicated riser
section in the embodiment of FIG. 2;
[0014] FIG. 4 is a top elevational view of the dedicated riser
section of FIG. 3;
[0015] FIG. 5 is a longitudinally taken partial cross sectional
view of the drill string shut -off valve of FIG. 2 in a closed
position;
[0016] FIG. 5A is a transverse cross section of FIG. 5, taken at
line 5A-5A;
[0017] FIG. 6 is a longitudinally taken cross sectional view of the
drill string shut -off valve of FIG. 2 in an open position;
[0018] FIG. 6A is a longitudinal cross section of a spring
adjustment assembly; and
[0019] FIGS. 7 is a graph of pressure drop against flow rate for a
drill string shut-off valve ported to the annulus and to the bore,
respectively.
A DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0020] FIG. 1 illustrates schematically one embodiment of a
drilling fluid circulation system 10 in accordance with the present
invention. Drilling fluid is injected into the drill string at the
drilling rig facilities 12 above ocean surface 14. The drilling
fluid is transported down a drill string (see FIG. 2), through the
ocean and down borehole 16 below mudline 18. Near the lower end of
the drill string the drilling fluid passes through a drill string
shut-off valve ("DSSOV") 20 and is expelled from the drill string
through the drill bit (refer again to FIG. 2). The drilling fluid
scours the bottom of borehole 16, entraining cuttings, and returns
to mud line 18 in annulus 19. Here, near the ocean floor, the
drilling mud is carried to a subsea primary processing facility 22
where waste products, see line 24, are separated from the drilling
fluid. These waste products include at least the coarse cuttings
entrained in the drilling fluid. With these waste products 24
separated at facilities 22, the processed drilling fluid proceeds
to subsea return pump 26 where it is pumped to drilling facilities
above surface 14. A secondary processing facility 28 may be
employed to separate additional gas at lower pressure and to remove
fines from the drilling fluid. The reconditioned drilling fluid is
supplied to surface pump system 30 and is ready for recirculation
into the drill string at drilling rig 12. This system removes the
mud's hydrostatic head between the surface and the sea floor from
the formation and enhances pump life and reliability for subsea
return pump system 26.
[0021] The embodiment of FIG. 1 can be employed in both drilling
operations with or without a drilling riser. In either case, the
hydrostatic pressure of the mud return through the water column is
isolated from the hydrostatic head below the blowout preventor,
near the sea floor. Indeed, with sufficient isolation the return
path for the mud could proceed up the drilling riser/drill string
annulus. However, it may prove convenient to have a separate riser
for mud return whether or not a drilling riser is otherwise
employed. Further, even if not used as the mud return line through
the water column, it may be convenient to have a drilling riser to
run the blowout preventor and separation equipment discussed below.
See FIG. 2.
[0022] Returning to FIG. 1, another advantage of this subsea pump
drilling embodiment is that gas resulting from a well control event
is removed at gas separator 52 and is expelled near seafloor 18.
Pump operation in such well events is critical. In a well control
event in which large volumes of gas enter the well, the overall
system must handle gas volumes while creating an acceptable back
pressure on the wellbore 16 by pumping down heavier weight mud at
sufficient volume, rate and pressure. Dropping below this pressure
in a well control event will result in additional gas influx, while
raising pressure to excess may fracture the borehole. The ability
to cycle through muds at weights suited to the immediate need is
the primary control on this critical pressure. However, multiphase
flow is a challenge to conventional pumps otherwise suited to
subsea return pump system 26. Thus, only substantially gas free mud
is pumped to the surface through subsea return pump system 26,
facilitating pump operation during critical well control events.
Additional gas may be removed at the surface atmospheric pressure
with an additional gas separation system, not shown.
[0023] FIG. 2 illustrates the subsea components of one embodiment
of drilling fluid circulation system 10, here with a drilling riser
that is not used for returning the mud through the water column.
The drilling fluid or mud 32 is injected into drill string 34 which
runs within marine drilling riser 36, through a subsea blowout
preventor ("BOP stack") 38 near the mudline 18, through casing 40,
down the uncased borehole 16 to a bottom hole assembly 42 at the
lower end of the drill string. The bottom hole assembly includes
DSSOV 20 and drill bit 44.
[0024] The flow of drilling mud 32 through drill string 34 and out
drill bit 44 serves to cool the drill bit, flush the cuttings away
from the bit's formation interface and to stabilizes the uncased
borehole with a "filter cake" until additional casing strings 40
are set in newly drilled sections. Drilling mud 32 also performs a
crucial well control function in maintaining a pressure with a
hydrostatic head in uncased sections of the borehole 16 that
prevents the uncontrolled flow of pressured well fluids into the
borehole from the formation.
[0025] However, in this subsea pump drilling embodiment, the
drilling mud is not returned to the surface through the marine
riser/drill string annulus 46, but rather is withdrawn from the
annulus near mudline 18, e.g., immediately above BOP stack 38
through mud return line 19. In this illustration, with a drilling
riser, the remainder of annulus 46, to the ocean surface, is filled
with seawater 48 which is much less dense than the drilling mud.
Deepwater drilling applications may exert a thousand meters or more
of hydrostatic head at the base of marine drilling riser 36.
However, when this hydrostatic head is from seawater rather than
drilling mud in annulus 32, the inside of the marine drilling riser
remains substantially at ambient pressure in relation to the
conditions outside the riser at that depth. The same is true for
mud leaving the well bore in riserless embodiments. This allows the
drilling mud specification to focus more clearly on well control
substantially from the mudline down.
[0026] Drilling mud 32 is returned to the surface in drilling fluid
circulation system 10 through subsea primary processing 22, subsea
return pump 26 and a second riser 50 serving as the drilling mud
return line. In this embodiment, subsea primary processing 22 is
illustrated with a two component first stage 22A carried on the
lowermost section of drilling riser 36 and a subsequent stage 22B
on the ocean floor.
[0027] In normal operation, solids removal system 54 first draws
the return of drilling mud 32. Here solids removal system 54 is a
gumbo box arrangement 68 which operates in a gas-filled ambient
pressure dry chamber 72. The hydrostatic head of mud 32 within the
annulus 46 drives the mud through the intake line and over weir 74
to spill out over cuttings removal equipment such screens or gumbo
slide 78. Cuttings 76 too coarse to pass between bars or through a
mesh screen proceed down the gumbo slide, fall off its far edge
beyond mud tank 80, and exit directly into the ocean through the
open bottom of dry chamber 72. The mud, less the cuttings
separated, passes through the gumbo slide and is received in mud
tank 80 and exits near the tank base.
[0028] Remote maintenance within gumbo box arrangement 68 may be
facilitated with a wash spray system to wash the gumbo slide with
seawater and a closed circuit television monitor or other
electronic data system in the dry chamber.
[0029] Cuttings 76 can be prevented from accumulation at the well
by placing a cuttings discharge ditch 84 beneath dry chamber 72 to
receive cuttings exiting the dry chamber (and perhaps the dump
valve). A jet pump 86 injects seawater past a venturi with a
sufficient pressure drop to cause seawater and any entrained
cuttings to be drawn into cuttings discharge line 88 from cuttings
discharge ditch 84. The cuttings discharge line then transports the
cuttings to a location sufficiently removed such that piles of
accumulated cuttings will not interfere with well operations.
[0030] FIGS. 3 and 4 illustrate in detail an alternate embodiment
in which components of first and second stage processing 22A and
22B as well as gas separator 52 are mounted on a dedicated riser
section 36A. The dedicated riser needs to be sized to be run
through the moonpool of the surface drilling facilities, preferably
having a horizontal cross section no greater that the BOP stack
outline 104, illustrated in FIG. 4 in dotted outline 100.
[0031] Components, here a pair of gumbo boxes 68 and a pair of
horizontal gas/mud separators 58, are mounted on frame 102 secured
to dedicated riser joint 36A. Cuttings discharge ditches 84, jet
pumps 86, and cuttings discharge lines 88 are also mounted to this
riser section. This allows connections between these initial
components and the annulus within marine drilling riser 36 and BOP
stack 38 to be fully modularly assembled on the surface before the
drilling riser is made up to the subsea well.
[0032] Returning to FIG. 2, the illustrated embodiment also
provides subsequent stage processing 22B, here a further solids
removal system 54A, in the form of a second gumbo box arrangement
68A in gas-filled ambient pressure dry chamber 72A. The hydrostatic
head of mud 32 within tank 80 drives the mud and over weir 74A to
spill out mud and entrained cuttings over more closely spaced bars
or a finer mesh screen gumbo slide 78A. Mud separated in mud/gas
separator 52 may join that from tank 80 in this second stage
processing. A finer grade of cuttings is removed and carried away
with cuttings discharge ditch 84A and jet pump 86B, as before, with
the processed mud passing to mud tank 80A.
[0033] It may also be desirable to provide the position of normal
tank exit and a tank volume that allows settling of additional
cuttings able to pass through the gumbo slide. A surface activated
dump valve 82 at the very bottom of the mud tank may be used to
periodically remove the settled cuttings.
[0034] The suction line 94 of subsea return pump 26 is attached to
the base of mud tank 80A. A liquid level control 90 in the mud tank
or subsequent subsea mud reservoir activates return pump. The
removal of the cuttings from the mud greatly enhances pump
operation in this high pressure pumping operation to return the
cuttings from the sea floor to the facilities above the ocean
surface through a return riser 50. The return riser may be
conveniently secured at its base to a foundation such as an anchor
pile 98 and supported at its upper end by surface facilities (not
shown), perhaps aided by buoyancy modules (not shown) arranged at
intervals along its length. In this embodiment, the return pump is
housed in an ambient pressure dry chamber 92 which improves the
working environment and simplifies pump design and selection.
[0035] In well control events, BOP stack 38 is closed and the gas
separator 52 intakes from subsea choke lines 32 associated with BOP
stack 38. The intake leads to a vertically oriented tank or vessel
58 having an exit at the top which leads to a gas vent 60 through
an inverted u-tube arrangement 62 and a mud takeout 64 near its
base which is connected into return line 66 downstream from solids
removal system 54. In such a well control event, gas separator 52
permits removal of gas from mud 32 so that subsea pump system 26
may operate with only a single phase component, i.e., liquid mud.
The gas separator 52 may be conveniently mounted to the lowermost
riser section 36 or, as illustrated in FIGS. 3 and 4, a dedicated
riser section 36A.
[0036] FIG. 5 details an embodiment of a drill string shut-off
valve (DSSOV) 20 of the present invention deployed at the base of
drill string 34 as part of bottom hole assembly 42 in FIG. 2. The
DSSOV is an automatic valve which uses ported piston
pressures/spring balance to throw a valve 112 for containing the
hydrostatic head of drilling fluid 32 within the drill string when
the bottom hole assembly is in place and the normal circulation of
the drilling fluid is interrupted, e.g., to make up another section
of drill pipe into the drill string. In such instances the DSSOV
closes to prevent the drilling fluid from running down and out of
the drill string and up the annulus 46, displacing the much lighter
seawater until equilibrium is reached. See FIG. 2.
[0037] FIGS. 5 and 6 illustrate DSSOV 20 in the closed and open
positions, respectively. The DSSOV has a main body 120 and may be
conveniently provided with connectors such as a threaded box 122
and pin 124 on either end to make up into the drill string in the
region of the bottom hole assembly. The body 120 presents a
cylinder 128 which receives a piston 116 having a first pressure
face 114 and a second pressure face 130. First pressure face 114 is
presented on the face of the piston and is ported to the upstream
side of DSSOV 20 through channel 132 passing through the piston.
Channel 132 may be conveniently fitted with a trash cap 134.
[0038] Second pressure face 130 is on the back side of piston 116
and is ported to the well annulus through one or more ports 118,
here presented as a pair, offset at 180% for the purposes of an
illustrative example. Further, the first and second pressure faces
of piston 116 are isolated by o-rings 136 slidingly sealing between
the piston and the cylinder. Equalizing ports 118 may be radially
or orthogal to a pair of opposed flow channels 126, or these may be
arranged in other numbers, symmetrical or not.
[0039] Body 120 also has a main flow path 140 interrupted by valve
112, but interconnected by drilling mud flow channels 126 and a
plurality of o-rings 142 between valve 112 and body 120 isolate
flow from drilling mud flow channels 126 except through ports
118.
[0040] The DSSOV is used to maintain a positive surface drill pipe
pressure at all times. When the surface mud pump system 30 (see
FIG. 1) is shut off, e.g., to add a section of drill pipe 34 as
drilling progresses, valve shut-off spring 110 shuttles valve 112
to a closed position in which valve ports 118 are taken out of
alignment with drilling mud flow channels 126 in body 120. See FIG.
5. The spring 110, the surface area of first pressure face 114, and
the surface area of the second pressure face 130 of piston 116 are
balanced in design to close valve 112 to maintain the pressure
margin created by the differences in density between seawater 48
and mud 32 over the distance between surface 14 and ocean floor 18.
See FIG. 1. This holds the excess positive pressure in drill pipe
34, keeping it from dissipating by driving drilling mud down the
drill pipe and up annulus 46, while isolating the excess pressure
from borehole 16. See FIG. 2. After a the new drill pipe section
has been made up or drilling is otherwise ready to resume, surface
pump system 30 (FIG. 1) is used to build pressure on valve 112
until the pressure on face 114 of piston 116 overcome the bias of
spring 110, opening valve 112 and resuming circulation. See FIG.
6.
[0041] A spring adjustment assembly 111 is illustrated
schematically with bolt 113. The spring adjustment assembly adjusts
the tension in spring 110, e.g., changing the length of the spring,
thereby affording easy adjustment of DSSOV 110 to changing
conditions downhole. Calibrating adjustment, e.g., turning of bolt
113, to the direct affect on spring 110 will facilitate the
adjustments.
[0042] FIG. 6A illustrates a particular embodiment of spring
adjustment assembly 111.
[0043] DSSOV 20 also facilitates a method of determining the
necessary mud weight in a well control event. With the DSSOV
closed, pump pressure is slowly increased while monitoring
carefully for signs of leak-off which is observed as an
interruption of pressure building despite continued pump operation.
This signals that flow has been established and the pressure is
recorded as the pressure to open the DSSOV. Surface pump system 30
is then brought up to kill speed and the circulating pressures are
recorded. Kill speed is a reduced pump rate employed to cycle out
well fluids while carefully monitoring pressures to prevent
additional influx from the formation. The opening pressure, kill
speed and circulating pressure are each recorded periodically or
when a significant mud weight adjustment has been made.
[0044] With such current information, the bottom hole pressure can
be determined should a well control event occur. Shutting of
surface pump system 30 after a flow is detected will close off
DSSOV 20. The excess pressure causing the event, that is the
underbalanced pressure of the formation, will add to the pressure
needed to open valve 112. Pump pressure is then reapplied and
increased slowly, monitoring for a leak-off signaling the
resumption of flow. The pressure difference between the
pre-recorded opening pressure and the pressure after flow is the
underbalanced pressure that must be compensated for with
adjustments in the density of mud 32. The kill mud weight is then
calculated and drilling and adjustments are made accordingly in the
mud formulation.
[0045] Porting to the annulus pressure, rather than the pressure
immediately downstream of DSSOV 20 lowers the pressure drop across
DSSOV 20. This, in turn, reduces the amount of energy in the system
that is lost to friction and will increase the service life of
DSSOV 20.
[0046] FIG. 7 illustrates the result of a computer simulation
estimating the difference in pressure drop when port 118 connects
to the annulus pressure as opposed to that directly downstream of
the DSSOV as addressed in the illustrative embodiment of WO
99/15758.
[0047] In the illustrated embodiment, some of the components of the
subsea primary processing system 22 are provided on the marine
drilling riser 36 and others are set directly on ocean floor 18. As
to components which are set on the ocean floor, it may be useful to
deploy a minimal template or at least interlocking guideposts and
receiving funnels to key components placed as subsea packages into
secure, prearranged relative positions. This facilitates making
connections between components placed as separate subsea packages
with remotely operated vehicles ("ROV"). Such connections include
electric lines, gas supply lines, mud transport lines, and cuttings
transport lines. A system of gas supply lines (not shown) supply
each of the dry chambers 72, 72A, and 92 to compensate for the
volumetric compression of gas in the open-bottomed dry chambers
when air trapped at atmospheric pressure at the surface is
submerged to great depths. Other combinations of subsea primary
processing components and their placement are possible. Further,
some components may be deployed on the return riser 50 analogous to
the deployment on marine drilling riser 36.
[0048] Other modifications, changes, and substitutions are also
intended in the foregoing disclosure. Further, in some instances,
some features of the present invention will be employed without a
corresponding use of other features described in these illustrative
embodiments. Accordingly, it is appropriate that the appended
claims be construed broadly and in a manner consistent with the
spirit and scope of the invention herein.
* * * * *