U.S. patent number 3,621,911 [Application Number 04/858,209] was granted by the patent office on 1971-11-23 for subsea production system.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Charles Ovid Baker, Warren B. Brooks, Eugene L. Jones.
United States Patent |
3,621,911 |
Baker , et al. |
November 23, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
SUBSEA PRODUCTION SYSTEM
Abstract
This specification discloses a subsea system for the production
of fluid minerals. The system includes a plurality of underwater
wellheads, each having a remotely actuatable valve thereon which in
turn has a mechanical valve actuator. Flowlines connect each
wellhead with a production satellite which has means therein for
testing the production from the wells and for actuating the
remotely actuatable valves in response to the certain results of
the production testing. An anchoring means is provided at each
wellhead for anchoring a work chamber at the wellhead whereby the
mechanical valve actuator on the wellhead valves can be operated
from the work chamber.
Inventors: |
Baker; Charles Ovid (Garland,
TX), Jones; Eugene L. (Dallas, TX), Brooks; Warren B.
(New York, NY) |
Assignee: |
Mobil Oil Corporation
(N/A)
|
Family
ID: |
25327756 |
Appl.
No.: |
04/858,209 |
Filed: |
April 1, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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649960 |
Jun 29, 1971 |
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Current U.S.
Class: |
166/336; 166/357;
166/366; 166/356; 166/363 |
Current CPC
Class: |
B63G
8/001 (20130101); E21B 43/017 (20130101); B63C
11/42 (20130101) |
Current International
Class: |
B63C
11/00 (20060101); B63C 11/42 (20060101); B63G
8/00 (20060101); E21B 43/00 (20060101); E21B
43/017 (20060101); E21b 043/01 () |
Field of
Search: |
;166/.5,.6 ;175/8,7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Calvert; Ian A.
Assistant Examiner: Favreau; Richard E.
Parent Case Text
This application is a continuation of our prior application Ser.
No. 649,960 filed June 29, 1967, now abandoned.
Claims
We claim:
1. A system for the production of minerals from subaqueous deposits
through wells having wellheads located beneath the surface of a
body of water, comprising:
a. a plurality of underwater wellhead units for said wellheads,
each of said wellhead units being equipped with at least one
remotely actuatable valve for controlling the flow of produced
minerals from the respective well;
b. a mechanical valve actuator on each of said remotely actuatable
valves, each mechanical valve actuator being adapted to be actuated
by a manipulator arm of a submersible work chamber, whereby said
remotely actuatable wellhead valves may be controlled at the sites
of each of said wellhead units;
c. at least one production satellite station located beneath the
surface of said body of water;
d. flowlines connecting each of said plurality of wellheads,
through the respective remotely actuatable wellhead valve, with the
interior of said satellite station;
e. means within said satellite station for combining the produced
minerals from said wells flowing through said flowlines and
directing said produced fluid through a main outlet line;
f. means within said satellite station for selectively testing said
produced fluid flowing through each of said flowlines
individually;
g. means for actuating said remotely actuatable wellhead valves in
response to the results of the selective testing of the produced
fluid flowing through said flowlines to optimize production;
and
h. anchoring means for rigidly anchoring the submersible work
chamber adjacent a respective wellhead whereby said anchoring means
will absorb the reaction forces generated, as equipment including
said mechanical valve actuators is acted upon by the manipulator
arm of the submersible work chamber.
2. The system of claim 1 wherein said anchoring means comprises
means for cradling said submersible work chamber from below, said
cradling means being shaped so as to permit a diver to pass into
and out of the bottom of said submersible work chamber through
bottom airlocks therein.
3. The system of claim 1 wherein said means for anchoring said
submersible work chamber adjacent the respective wellhead unit
comprises at least a pair of spaced, magnetizable cradles fixed
with respect to the marine bottom; and
selectively actuatable electromagnets within the hull of said
submersible work chamber for causing said submersible work chamber,
when resting on said spaced cradles, to be firmly anchored when
said electromagnets are energized.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a subsea system for the recovery of
subaqueous deposits of fluid minerals. By the term "fluid" is meant
any slurry or other state of matter which will pass through a
conduit or pipe. More particularly, the invention relates to the
production of gas and/or oil from subaqueous formations utilizing a
system of submerged wellheads and a product-gathering network in
combination with submersible automated and/or semiautomated
equipment.
2. Description of the Prior Art
Present developments in the offshore oil and gas industry indicate
that production efforts will be extended, in the near future, to
undersea areas, such as the outer fringes of the continental
shelves and the continental slopes, where a submarine production
system is believed to be the most practical method of reaching the
subaqueous deposits. Although hydrocarbons are the main concern at
this time, it is contemplated that subaqueous deposits of sulfur
and other minerals will be produced from beneath the seas in a very
few years. While bottom-supported permanent surface installations
have proved to be economically and technologically feasible in
comparatively shallow waters, it is believed that in the deeper
waters of the continental shelves (over 300 feet) and the
continental slopes (depths over 600 feet), the utilization of such
surface installations must be limited to very special situations.
Installations extending above the water surface are also
disadvantageous even in shallower water where there are adverse
surface conditions, such as in the Arctic areas where the
bottom-supported structure of above-surface production platforms
are subject to ice loading. The tides, which may run up to 30 feet
in the northern latitudes, such as in Cook Inlet, Alaska, tend to
lift the ice formed on the legs of the platform and tear the
anchoring means therefor completely out of the sea bottom as well
as driving broken-up sheet ice laterally against the platforms at 6
to 8 knots or more. In some areas commercial shipping and pleasure
boats present a constant source of danger to above-surface
installations, while recreation and area beautification may provide
manmade obstacles to their erection, particularly near seaside
resort areas and seaport cities.
The sheltering of production equipment beneath the surface of the
sea, while believed to be economically feasible at depths of over
300 feet, even where adverse conditions are not present, still
presents many technical problems, particularly with respect to the
servicing and maintenance thereof. With a deep water subsea system,
the majority of the maintenance and servicing problems encountered
must be handled automatically, or at least by remote control, due
to the cost and limitations on deep diving at the present time;
however, there should be provisions for having divers at the scene
of installed subsea equipment in the event that the necessary
manipulations are too complicated for anything but direct human
control. The use of submersible vehicles, with articulated
manipulators, for performing a variety of subsea operations has
been generally proven and such vehicles can fill much of the gap
between completely automated equipment and operations that must be
performed by divers.
Robots, such as those shown in the Johnson U.S. Pat. No. 3,099,316,
issued July 30, 1963, the Shatto U.S. Pat. No. 3,165,899, issued
Jan. 19, 1965, and the Shatto, Jr., U.S. Pat. No. 3,163,221, issued
Dec. 29, 1964, have been developed for the most part for working on
subsea wellheads, in conjunction with guide rails or other engaging
and guiding devices built on the wellheads, as shown. The Haeber
U.S. Pat. No. 3,261,398, issued July 19, 1966, does show, in a
general way, the use of a track for guiding a robot through a
bottom-mounted array of production equipment. The use of a drill
string, extending from a surface vessel, also has been contemplated
for actuating the controls of subsea equipment ("Drill Pipe Becomes
Long-Handled Underwater Socket Wrench"--The Oil and Gas Journal,
Jan. 24, 1966, pages 90-93). The Popich U.S. Pat. No. 3,103,790,
issued Sept. 17, 1963, shows a pipe trenching robot while the Shell
British Pat. No. 1,021,264 disclosed a bottom traversing, general
purpose robot. The robots of both of these last two patents recited
are designed to be controlled from a surface mother ship. However,
no overall integrated design has been disclosed in the prior art
for handling the installation, repair, and maintenance of a deep
water subsea production system. For instance, there is no equipment
known for performing wire line operations completely under water.
The Ashe et al. U.S. Pat. No. 3,041,090 is illustrative of the
prior art, disclosing a foldable lubricator adapted to extend all
the way from a submerged wellhead to the surface of the body of
water where the wire line operations are conducted from a surface
ship.
The use of a pressurized traveling chamber for transporting divers
from the ocean bottom to a chamber aboard a surface ship is
disclosed in the article entitled "Diving-Chamber Complex Speeds
Subsea Salvage job," The Oil and Gas Journal, June 20, 1966, pages
82 and 83. However, the utilization of a submersible,
self-propelled, vehicle as a pressurized, onsite, rest station is
not shown in the prior art. The limiting of the use of surface
vessels to the transportation of subsea equipment from shore, the
lowering of subsea equipment to the marine bottom, and the
transporting of collected and stored products, increases the
independence of the production system from surface conditions.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided a subsea
production system including satellite-gathering stations for
testing the produced effluent from submerged wellheads of spaced
subaqueous wells whose products are directed therethrough, and in
response, controlling the wellhead valves of the respective
subaqueous wells. While the satellite stations are designed for
automatic and/or remote operation, there are provided means for the
safe entry of personnel for maintenance and repair. Furthermore,
the satellite stations are each constructed so as to prevent
pernicious vapor leaking from the production equipment from
contaminating the life support sections of a satellite station.
A power distribution network connects a power generating station
with the satellite stations and the wellheads. The power-generating
station if at the site can be a surface unit of the floating type
or it alternatively can be mounted on a bottom-supported platform,
depending, for the most part, on the water depth in which the
subaqueous deposits are being produced. Another possibility is that
of locating the power-generating station ashore and connecting it
with the offshore producing field through lines laid across the
marine bottom. Preferably the power-generating station is submerged
along with the rest of the production equipment. By encapsulating
the generating station within a shell, similar to those of the
satellite stations, only fresh air and communication lines need be
supported at the surface by small buoys.
The main subsea system discussed above also includes a backup or
fail-safe system adapted to manipulate the wellhead valves in case
of a failure in satellite station-to-wellhead communication and to
perform operations not adapted to be automatically controlled from
the satellite station. The fail-safe system is provided with
submersible vehicles, having articulated manipulators for the
remote manual control of the submerged wellhead and flowline valves
as well as for the installation of the subsea equipment. The
remotely controlled submersible vehicles, controlled from a surface
vessel, are complemented by manned submersible vehicles provided
with pressurized life support rest chamber sections for divers
working on the submerged equipment. A robot unit for welding pipe
sections, in conjunction with the submersible vehicles having
articulated manipulators, permits the units of the system to be
interconnected by flowlines without divers. In very deep water,
this becomes almost a necessity.
An integral part of the subsea system of the present invention is a
submersible wire line robot unit, lowered from the surface to a
submerged wellhead unit and powered either from the surface vessel
or at the site of the wellhead unit through the power distribution
network. The robot unit can be controlled remotely from the surface
or from an adjacent submersible vehicle with a connecting control
cable plugged into the robot wire line unit. Particularly where
workover operations, such as paraffin cutting, need not be
conducted frequently, the robot wire line unit provides a
significant saving over the TFL (through the flowline) tool
system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a pictorial representation of a portion of a subsea
producing system in accordance with this invention;
FIG. 2 is an elevational view, partially broken away, of a subsea
satellite station forming a portion of the subsea producing system
of the present invention;
FIG. 3 is an elevational view, partially in cross section, and
partially broken away, of a remotely controlled wire line robot
unit, lowered by a surface vessel and controlled from a nearby
submersible vehicle; and
FIG. 4 is a schematic representation of a submerged,
bottom-supported, power-generating station.
DESCRIPTION OF SPECIFIC EMBODIMENTS
The subsea production system of the present invention has been
designed specifically for offshore areas in which the water is too
deep for the economical utilization of bottom-supported surface
platforms, although it can be advantageously utilized in not so
deep water where there are adverse surface conditions. The subsea
system has the capability for automatic and/or remotely controlled
installation, servicing, and maintenance, and comprises submerged
wellheads spaced across a marine bottom and connected to an onsite
storage facility through satellite-gathering stations fixed on the
marine bottom. Each of the satellite-gathering stations is provided
with multiple chambers capable of being maintained at independently
controlled pressures: a central access chamber providing entry or
exit of personnel directly into the water or into a submersible
vehicle, a production chamber at one end including equipment, i.e.,
a test separator for providing the necessary information for
controlling the gas and/or oil production of the individual wells,
and a life support chamber at the other end having the air
purification system, pumping equipment, and the electrical and
electronic facilities for compiling and storing information and for
acting on the production test results to control the subaqueous
production equipment.
A remotely controlled unit, lowered from a surface vessel directly
over a submerged wellhead where wire line procedures are called
for, is controlled from a nearby submersible vehicle or from the
surface ship and obtains its power from the surface ship or through
power distribution lines from a central generating station through
the respective satellite-gathering station. The wire line operating
submersible vehicle is also capable of transporting divers to
attend to servicing and/or maintenance problems at the wellhead,
the submersible vehicle acting as a pressurized rest station in
which a number of divers are held. Due to the very short work time
permissible in deep water, perhaps only one-half hour, one diver
works for his allotted time, returns to the submersible vehicle,
and another diver goes out to continue the work.
The submersible vehicles, both manned and remotely controlled, with
their articulated manipulators, do more than just act to ferry
personnel between a surface vessel and the satellite station, and
control robot wire line units. Depending on the job to be
performed, a number of different tools connectable to the outer
ends of the individual manipulators can be utilized. With
submersible vehicles carrying their own supplies of tools, almost
any function that could be performed by a man with manual- or
power-operated handtools can be assigned to them. The submersible
vehicles can perform such operations as adjusting valves on the
wellheads and flowlines as well as aiding in the installation of
the subsea equipment.
Now referring to FIG. 1, there is shown a subsea production system
in operation in the background and a continuation of the flowlines
therefrom being installed on the ocean bottom in the foreground.
Submerged production oil and/or gas wellhead units, generally
designated 10, on the marine bottom 12 are connected into the
subsea system through satellite stations, generally designated 14
and 16, by means of flowlines 18. The satellite station 14
functions as a production-gathering point, information center, and
automatic control center for its associated wells, while the
satellite station 16 provides all of the functions of the station
14 while also having added pumping facilities for forcing the
produced hydrocarbons up to a floating storage tank 20. The stored
hydrocarbons are removed from the floating storage tank 20 by a
tanker 22, floating on the water surface 24, which visits the
storage tank 20 and is moored thereto at prescribed intervals. As
shown, the tanker 22 is located with respect to the storage tank by
mooring lines 21 while onloading through a floating hose 23
connected to an outlet of the storage tank 20. A floating central
control and power-generating station 26 is moored above the
subaqueous producing field by lines 27 and is connected to the
satellite 14 by a bundle of electrical lines 28 for information
input and retrieval, command signals, and the supplying of
electrical power to the subsea system. It is contemplated that
personnel would live on the station 26 to supervise continuously
the operation of the subsea production system. Electric power is
distributed, along the marine bottom 12, to the various wellhead
units 10 shown, the satellite station 16, and other satellite
stations 14 from the illustrated satellite station 14.
Although the central control and power-generating station 26 is
illustrated as floating on the surface of the body of water just
above the subsea production system, depending upon the distance
from shore, the floating station 26 could be dispensed with
entirely and the electrical power lines as well as the information
input and retrieval and command signal lines could be laid across
the ocean bottom to an onshore station. Another possibility is that
the floating station 26, while having the equipment for generating
power built thereon, would be merely a link between the submerged
satellite 14 and a station ashore for the transmission of
information to and from shore and command signals to the satellite
through the illustrated antenna 30. A microwave relay system, of
the type now utilized in conjunction with some platform-produced
fields in the Gulf of Mexico would be acceptable for this
purpose.
Various valves and controls situated at the wellhead units 10 would
normally be controlled by interconnecting hydraulic or electrical
lines from within the satellites 14 and 16. However, if there
should be a breakdown in communication between a wellhead unit 10
and its respective controlling satellite 14 or 16, articulated
armed robot submersible vehicles, generally designated 32, (the
nearer one shown handling pipe), remotely controlled from surface
vessels 34, would be utilized. Such vehicles, directed by the aid
of remote viewers such as television cameras 36 in clear water, or
sonic or laser viewers in murky water, mounted thereon, would be
much less expensive than a manned vehicle with its attendant life
support systems. However, in instances where direct observation is
necessary, submersible vehicles having articulated manipulators,
such as the illustrated submersible vehicles, generally designated
38, are useful; the vehicle 38 at the right is observing a
pipe-laying operation, while the vehicle 38 at the left is about to
operate a flowline valve 40 by the use of a rotary actuator tool 42
adapted to fit an upwardly extending nut 44 forming the valve
actuator. A tool, such as the rotary actuator tool 42, as well as a
number of other tools to be used in conjunction with the
articulated manipulators of submersible vehicles are pictured on
pages 653-661 of the book PROCEEDINGS OF DECON-- Offshore
Exploration Conference, 1966, published by M. J. Richardson Inc.
2,516 Via Tejon, Palos Verdes Estates, Cal. The other articulated
manipulator terminates in a platelike tool 46 used as a reaction
member to prevent the vehicle 38 from turning rather than the valve
actuator nut 44. The valve 40 would normally be controlled from a
satellite station 14, 16 through the control line 48 strapped
thereto. Along the outer shell of the submersible vehicles 38 are
pockets or hooks (not shown) for carrying as many different tools
as may be necessary. By using one of the many known quick release
couplings, an articulated manipulator can easily be released from a
first tool connected to the outer end thereof and to a second tool
fixed thereon. As will be explained later, a similar manned
submersible vehicle can also be utilized as a rest station for
divers working at a nearby wellhead unit 10 or other equipment.
Individual wellhead units 10, as well as the satellite stations 14
and 16, can be installed at the proposed location without the need
for divers. It is now well within the skill of the art to remotely
locate equipment on the marine bottom 12, in the proper
orientation, and secure it in place. One of the major problems
remaining, however, is that of connecting the individual production
units of the subsea system together. As shown in the foreground of
FIG. 1, sections of pipe 50 of a flowline 18', to be connected
between the illustrated satellite 14 and a wellhead unit 10 off to
the right of the drawing in the foreground, are being installed on
a shelf 51 of the marine bottom 12 by the use of one of the
unmanned remotely controlled articulated submersible vehicles 32
and a robot welder, generally designated 52.
The robot welder 52 comprises a tanklike body 54 supported above
the path of the flowline 18', being installed, on a pair of opposed
endless treads 56 driven by a motor and transmission means (not
shown) within the tank 54. The robot welder 52 would normally be
supported on the marine bottom 12 by the treads 56, but in areas
where bottom sediments would not support the weight of the robot
welder 52, buoyancy chambers would be built into the tanklike body
54.
Extending out ahead of the tank 54 is a welding ring 58 which
encircles the flowline 18' and is held in a vertical position by a
strut 60 extending out from the front of the tanklike body 54. A
welding head 62 is contained on a track (not shown) around the
inside face of the welding ring 58 so that a welding bead is formed
which completely encircles a joint 63 between abutting sections of
pipe 50. The welding ring 58 is formed of a pair of semicircular
members pivoted about the point of connection with the strut 60. A
hydraulic piston cylinder 61, connected between a point on each
semicircular member of the welding ring 58 and the pivot point to
control the opening and closing of the welding ring 58. The ability
of the welding ring to open permits the robot welder to mount a
flowline 18 intermediate the ends thereof. A pair of aligned pipe
clamps 64 and 66 hold the abutting ends of adjacent sections of
pipe 50 together and in alignment prior to and during the welding
operation. The pipe-gripping portion of clamp 64 and a pair of
semicircular jaws 68 are actuated by extensible struts having
hydraulic piston-cylinder arrangements 63 connected between each of
the jaws 68 and an outwardly extending anchoring arm 70 from which
the jaws 68 pivot. The jaws of the clamp 66 are pivoted from the
underside of the strut under the control of extensible struts 65.
With the jaws of the clamps 64 and 66 reopening, the robot welder
52 can move up the flowline 18' to the next point at which a weld
is needed. The closing of the clamp 66 aligns the end of the last
pipe section 50 of the flowline 18' and the welding ring 58. The
still opened jaws 68 of the clamp 64 permit the remotely controlled
submersible vehicle 32 (in the right foreground) to slide a new
pipe section 50' into the jaws 68 of the clamp 64 by means of the
hand- or vice-type extension tools 72 at the ends of its
articulated manipulators 74. A pile 86 of pipe sections is stacked
on the shelf 51 just behind the flowline 18' being fabricated. When
the remotely controlled submersible vehicle 32 delivers a pipe
section 50', that it is carrying, to the robot welder 52, it is
sent back to pick up another pipe section 50' from the pile 86. The
vessel 34 from which the remotely controlled submersible vehicle 32
and welder 52 are both controlled has a crane 88 capable of
lowering further stacks 90 of pipe sections 50 down to the flowline
18' being fabricated.
In connecting two of the subsea producing units with a flowline, it
is advantageous to use a collet connector (not shown) at each fixed
unit since the robot welder 52 is not suited to forming any but
abutting welds between pipe sections of substantially equal
diameters. To start the flowline, a first pipe section is
transported by the submersible vehicle 32 to the fixed producing
unit from which the flowline is to be started. The end of a pipe
section is inserted into a collet connector forming the outer
portion of a port in the unit. The collect connector is actuated to
lock the pipe section in place from a central facility, or a
surface vessel, or from the submersible vehicle. The robot welder
52 is then lowered onto the pipe section 50', forming the beginning
of a flowline with both sets of pipe clamps 64 and 66 as well as
the welding ring 58 held open. When the welder 52 has settled down
on the unfinished flowline, the welding ring 58 may be closed and
is not again opened until the flowline is completed. Sections of
pipe are added to the flowline and welded in place as discussed
above. As the flowline reaches a point at which it is only one pipe
section or less from the second producing unit, a measured pipe
section is brought up which will lock in a collect connector
terminating a port in the second unit while abutting the last pipe
section of the unfinished flowline. The last joint is then welded
between the measured pipe section and the unfinished flowline after
which the clamps 64 and 66 as well as the welding ring 58 are all
opened permitting the robot welder 52 to be lifted off of the
pipeline 18'. At this time the collet connector on the second
producing unit is actuated to complete the flowline.
Once the pipe section 50' has been inserted into the enlarged
opening through the clamp 64 and the new section of pipe 50' abuts
tightly against the last welded-on section 50, the jaws 68 of the
clamp 64 are closed, aligning the pipe sections 50 and 50' in
abutting relationship. The traveling welding head 62 is then driven
around the track within the ring 58 to form a circumferential bead
around the joint after which both of the clamps 64, 66 are opened.
The robot welder 52 then moves on up the flowline to the new outer
end of the flowline 18', one pipe section 50 away, and the sequence
of operations is repeated. Since the pipe sections 50 tend to sink
into the mud on the marine bottom 62, a means must be provided for
forming a temporary path under the flowline 18' so as not to hinder
the movement of the clamps 64, 66 and the ring 58 as the welder 52
moves forward. A shallow trench is formed ahead of the robot welder
52 by a jet pipe 76 extending out parallel to the flowline 18'. The
tip 78 of the jet pipe 76 is aimed to project fluid under pressure
transversely toward, and down slightly below, the flowline 18'. The
preferred method is to provide a pump (not shown) with the body 54
to pick up sea water through an intake port and drive the water out
through the jet pipe 76. A television camera 80 (or any other type
of remote viewer as previously discussed) is mounted on top and at
the front of the tanklike body 54 of the robot welder 52 so that
the welding operations can be observed from the ship 34 (at the
left-hand side of the drawing) at the surface. The ship 34 and the
robot welder 52 are connected by a hoisting line 82, and a control
cable 84 through which the television signals are sent to the ship
34 and commands are transmitted to the welder 52 from the ship.
Within the tanklike body 54 is the various equipment for directly
controlling the movement of the robot welder 52.
Now looking to FIG. 2, the satellite station 14 has a hollow shell
92 comprising a cylindrical center section closed by hemispherical
end sections and is divided interiorly into three airtight
chambers. A central access chamber, generally designated 94,
provides an entrance into the satellite station 14 from one of the
submersible vehicles 38 from above, or by a diver, through a lock
96 below. The access chamber 94 is cylindrical in shape and is
divided vertically, by an intermediate lock 98, into an upper
compartment 100 through which personnel move between the interior
of the satellite station 14 and the submersible vehicle 38 and a
lower compartment 102 through which a diver 103 enters and leaves
the satellite station 14. Since the satellite station 14 would
normally be maintained at atmospheric pressure, sealable hatches
104 and 107 are necessary at the lower and intermediate locks 96
and 98, respectively. An upper lock 105 is also sealed (by a
nonillustrated hatch) when no submersible vehicle 38 is engaged
thereto by a depending intermediate access tube 106. The
submersible vehicle 38 also operates at atmospheric pressure
normally, but an internal compartment therein, connected by the
access tube 106 to the upper lock 105 of the satellite station 14,
as well as the entire central access chamber 94, can be pressured
up to accommodate divers who have worked in the open sea and
require decompression. The divers in the pressurized compartment in
the submersible vehicle 38 are transported to a surface ship where
there are proper facilities for safe decompression.
All of the hydrocarbon products being produced through the
satellite station 14 are confined to a processing chamber 108, at
one end of the satellite shell 92, walled off by a bulkhead 110, to
prevent contamination of the atmosphere in the remainder satellite
station 14 if there should be a leak in the processing equipment.
The air purification equipment 112, pumping equipment 114, and
electrical power facilities 116 are in separate sealed compartments
118 to 122, respectively, of a control chamber 124 at the other end
of the satellite station 14 from the hydrocarbon-processing
equipment. An operator 126, shown sitting at a control console 128
in the control chamber 124, can monitor and direct the equipment in
the hydrocarbon chamber 108 as well as actuating valves at the
wellhead units 10 and flowlines 18.
Both the upper and lower compartments 100, 102 of the access
chamber 94 are normally closed to the sea and are held at
atmospheric pressure. After the access tube 106, depending from
under the submersible vehicle 38, makes contact with the lock 105
on the upper end of the satellite station 14, the two are sealably
connected and any water in the access tube 106 is pumped out by
equipment on the submersible vehicle 38. With an equalization of
pressure, the hatch in the lock 105 is opened. Personnel can then
enter the upper compartment 100 of the satellite station 14
directly from the submersible vehicle 38, through the access tube
106 at atmospheric conditions. Personnel from the submersible
vehicle 38 come down rungs 130, fastened to the interior wall of
the access chamber 94 to form a ladder, and enter the control
chamber 124 through a safety airlock 131 and a ladder 133.
If the service of a diver are necessary, scuba or "hard hat" diving
equipment, stored in the chamber 124, are utilized. Once the diving
equipment is donned, the diver 103 enters the lower compartment
102, through a safety airlock 132, reseals the safety airlock 132
and makes sure the intermediate lock 142 is sealed, and then floods
the lower compartment 102. As the lower compartment 102 fills with
water, the diver 103 opens the lower lock 96 and descends into the
water. If the job to be performed takes an extended time at depths
of more than several hundred feet, the diver 103 may be limited to
as short a working time as 1/2 hour before he must come back to the
satellite station 14 to rest. In such a case, more than one diver
103 could be used, the remaining members of the working team
resting in the atmospheric portions of the satellite station 14
while one of the team works in the water and each one exiting in
turn through the lower lock 96 when the last one returns to the
satellite station. In such a manner, work can continue over long
periods of time although any one diver 103 cannot stay very long in
the hostile environment.
When performing maintenance or inspection work in the processing
chamber 108, the possibility of a gas leak in the equipment is
checked by a workman donning life support gear such as scuba
apparatus entering the chamber 108 with a hand-carried device for
detecting toxic, pernicious gases that might be leaking from the
processing equipment. Alternatively, a leak detector is mounted in
the bulkhead 110 to sample the atmosphere within the compartment
108 while providing a visual indication to one either within the
access chamber 94 or the control chamber 124. If possible the leak
is stopped by shutting off the processing equipment from within the
control chamber 124. The processing chamber 108 is then flooded
while exhausting the contaminated atmosphere to the surrounding
water. After reestablishing atmospheric conditions in the
processing chamber 108, the atmosphere within the processing
chamber is again checked, and if it is safe a workman can enter to
make repairs. If the leak cannot be stopped in this manner, it will
be necessary for a workman, wearing life support gear, to enter the
contaminated processing chamber 108 to manually stop the leak. In
the event that gas is escaping into the processing chamber 108 at a
high pressure, too high a pressure for a man to exhaust through his
breathing equipment into the processing chamber 108, an exhaust
tube (not shown) would be connected from the life support gear back
into the control chamber 124.
It is important to contain the contaminated atmosphere in the
processing and access chambers 108, 94. By sealing the safety
airlock 132 and the intermediate lock 98 from within the access
chamber 94 before opening a safety lock 134, interconnecting the
access chamber 94 within the processing chamber 108, the noxious
fumes can be contained in the lower compartment 102 of the access
chamber 94 and the processing chamber 108. After the maintenance or
repair work is completed, the contaminated atmosphere within the
processing chamber 108 and the access chamber 94 can be purged, by
several alternate procedures. One way is to let in water under full
pressure to displace the contaminated air through a line 136 by a
hand-actuated control valve 138 in the lower compartment 102. The
contaminated air in the lower compartment 102 of the access chamber
94 and the processing chamber 108 would then be forced out through
a line 140 controlled by hand-actuated valve 142 also in the lower
compartment 102. After the compartment 102 and the processing
chamber 108 have been purged of the contaminated atmosphere therein
by sea water, the valve 142 is closed and the sea water is pumped
out through line 136 while air under atmospheric pressure is
introduced. The water can also be expelled, through the line 136
without directly pumping it out by fresh air that is pumped in
under pressure from the control chamber 124. Once all of the water
has been expelled and the air pressure in the lower compartment 102
is brought back to atmospheric, the safety airlock 132 is reopened
to allow the workmen to reenter the control chamber 124. There
would normally be no decompression problems associated with forcing
out the contaminated air with ambient pressure sea water as long as
the high pressure was not held for more than a few minutes.
Whenever a man is exposed to high pressures, even for a short time,
there is some risk. So, for maximum safety, it is preferred that
the contaminated air be evacuated into the surrounding water
through the line 140 with the help of a pump (not shown) in the
line. The water would be again brought in through the line 136. A
pressure regulator (not shown) should be included in the line 136
to prevent the water pressure inside the satellite shell 92 from
rising much above atmospheric. After all of the contaminated
atmosphere has been displaced, the water is pumped out as described
above while air under atmospheric pressure is reintroduced. At this
time the equipment is rechecked for leaks.
In the instance where there was a very high pressure leak into the
chamber 108, it would be dangerous for a man even to enter the
chamber 108 with any portion of his body uncovered since the
contaminated atmosphere therein could dissolve human skin. In fact,
a gas such as methane would pass right through flesh, into the body
fluids, altering the body chemistry and killing the man exposed to
these conditions. Workmen would either have to wear completely
protective clothing or the chamber 108 would have to be flooded
prior to being entered and the workman would then preferably work
in the chamber 108 under water. Very few materials possess the
ability to withstand the onslaught of the high-pressure gas and yet
have the flexibility necessary for a protective garment. If the
leak can be remotely stopped the diver would work under water at
atmospheric pressure. If it is not possible to stop the leak prior
to the workman entering the processing chamber 108 the
diver-workman must work at ambient water pressure.
If the diver-workman must work for a considerable time at ambient
pressure, he must be transported to a decompression chamber on an
attending surface vessel (not shown) after the repairs are
completed. After the repairs are completed in the flooded
processing chamber 108, the workman enters the compartment 102,
seals the safety lock 134, and has the water therein pumped out. A
breathable atmosphere is pumped into the compartment 102 at ambient
pressure. This can be done easily by opening the valve 138, or the
port 96, while pumping high pressure air into the lower compartment
102 to drive the water out. The upper compartment 100 is also
pressurized. When all the water is evacuated from the lower
compartment 102, the valve 138 or port 96, whichever was opened, is
closed and the intermediate lock 98 is opened. The workman can now
enter the pressurized compartment in the submersible vehicle 38 for
transportation to the decompression chamber on the surface vessel
without passing through an area of low pressure. Before a second
repairman can enter the processing chamber 108 to check on the
repair work, the pressure in the upper and lower compartments 100,
102 must be pumped down to atmospheric while the water in the
chamber 108 is pumped out and replaced with air at atmospheric
pressure so that leaks can be checked for at atmospheric
conditions.
The flowlines 18, extending into the satellite station 14 at the
end at which the processing chamber 108 is located, are each
operatively connected by two-position three-way valves 144 to
either a group manifold 146 or a test manifold 148. In turn, each
one of the flowlines 18 is separately connected to the test
manifold 148 while the remainder are connected to the group
manifold 146. From the group manifold 146 the effluent, flowing
through all but one of the lines 18, is conducted, through a main
conduit 150, to a main outlet line 152 which in turn depends
through the shell 92 of the satellite station 14 and extends across
the marine bottom 12 to the pumping station in the satellite
station 14 and therethrough to the floating storage tank 20. The
effluent, from a single flowline 18 at a time, is directed into the
test manifold 148 and therethrough into a test separator 154,
through an inlet line 156. The separated-out gas leaves the
separator 154 through an outlet line 158 and is injected back into
the main effluent stream at the main outlet line 152. A meter 160
in the gas outlet line 158 provides a means for indicating the
amount of gas flowing through the line 158. Also in the outlet line
158 is a manual shutoff valve 162 and an automatic valve 164 which
is controlled by equipment from within the control chamber 124 of
the satellite station 14 for increasing or decreasing the back
pressure on the separator 154. An oil outlet line 166 also extends
from the test separator 154 to the main outlet line 152. The oil
outlet line 166 also has a meter 168, a manual shutoff valve 170,
and an automatic valve 172. A dump line 174 is either connected
directly between the sump of the separator 154 and the water
outside the satellite station 14, for ridding the effluent of water
separated out in the separator 154, or if the pressure in the
separator is too low this waste liquid may have to be pumped out.
Line 174 also includes a meter 176, a manual shutoff valve 178, and
an automatic valve 180. An automatic satellite-gathering and test
system, of the type discussed above, has been explained in detail
in the A. E. Barroll et al. U.S. Pat. No. 3,095,889, issued July 2,
1963.
In FIG. 3 there is illustrated a semiautomatic robot wire line
unit, generally designated 182, acting in conjunction with a
surface vessel or support ship and specialized submersible vehicle
184, for providing a combination of remotely controlled and diver
repair-maintenance services at the wellhead units 10 including
completion and workover operations. The wire line unit 182 has
rollers 192 affixed to the lower end thereof for seating on a pair
of parallel tracks extending out to the side from each of the
submerged wellheads 188 of the wellhead units 10 (FIGS. 1 and 3).
The robot wire line unit 182, lowered from one of the surface
support ships, is set down on the pair of parallel tracks 186. The
robot wire line unit 182 rolls down the track 186 and over the
wellhead 188 at which time it comes to rest against a pair of stops
(not shown) at the lower ends of the pair of tracks 186, centered
over a wellhead 188. The flowlines 18 extending from the
illustrative wellhead are connected to a satellite station (not
shown in this view). The flowlines have been installed as
previously discussed by first attaching flowline sections to the
fixed unit with collet connectors 189 located outward of the
production valves 207.
The robot wire line unit 182 comprises an open lower frame 190
above which is centrally fixed a sealed compartment 194 containing
the wire line apparatus. The lower end of a hoisting cable 198 is
connected to the upper end of a buoyancy tank 196, secured to the
upper end of the compartment 194 for at least partially supporting
the weight of the unit 182 in the water while the robot unit 182 is
being lowered or raised between the surface ship and the wellhead
unit 10. The sealed compartment 194 contains wire line drums 200
(one shown) and electric motors 202 (also only one shown) for
operating them. Supported beneath the compartment 194, in a
withdrawn position just above upstanding lubricators 204 of the
wellhead 188 of a dually completed well, as shown in FIG. 3, is a
wire line tool storage and connector device, generally designated
206. The device 206 comprises a pair of relatively fixed parallel
storage tubes 208 slidably mounted over parallel sections of tubing
210 depending from through the bottom of the upper sealed
compartment 194. The parallel storage tubes 208 are slidably sealed
to the tubing sections 210 by O-rings 212 fitted therewithin and
coacting with the outer walls of the tubing sections 210. The tool
storage and connector device 206 is designed to telescope down over
the upstanding lubricators 204 being controlled by a pair of spaced
hydraulic piston-cylinders 214, extending down through the bottom
of the sealed compartment 194, the piston portions 215 being
attached at their lower ends to opposite sides of the device 206.
O-rings 216, fitted within the lower open ends of the parallel
storage tubes 208, are adapted to seal slidably the parallel
storage tubes 208 over the lubricators 204 to form unobstructed
throughbores. The depending tubing sections 210 are each a portion
of a rigid angled conduit, generally designated 218 (only one
completely shown), extending completely through the compartment
194. Horizontal tubing sections 220 of the conduits 218 intersect
the opposing sidewalls of the compartment 194 and connect up with
the respective depending sections 214 through 90.degree. bends. The
outer end of each of the horizontal tubing sections 220 is
connected to the lower end of a flexible line 222 extending upward
to the surface vessel and to the source of stored treating fluid;
thus, fluid paths are formed which extend from the surface vessel
into the lubricators 204 of the wellheads 188. A wire line 224
wound on each drum 200 is threaded into the respective depending
tubing section 210 through a vertical nipple 225, located at the
90.degree. bend, which provides a slidable pressure seal for the
wire line 224. The free ends of each of the wire lines 224, inside
of the respective storage tubes 208, terminate in a wire line tool
226 hanging therein, in the retracted position, and limited in its
upper movement by a perforated domed cap 228 fixed in each of the
storage tubes 208 above the respective tool 226. This arrangement
not only allows the wire line tools 226 to be guided down into the
upper ends of lubricators 204 but also allows treating fluids to be
simultaneously pumped down through the flexible lines 222 from the
surface vessel. Auxiliary fluids are necessary when performing
operations such as cutting paraffin, where a solvent is usually
injected in conjunction with the action of the scraping tool.
Furthermore, the fluid pressure in the storage tubes 208, when they
are telescoped over the lubricators 204, can be used for opening
lubricator valves 205 and shutting the production valves 207 as
taught in the G. D. Johnson U.S. Pat. No. 3,242,991, entitled
"Underwater Wellhead with Reentry lubricator," and issued on Mar.
29, 1966. The valves 205 and 207 are alternatively controlled from
the respective satellite station 14, 16 through interconnecting
control lines 209 and 211, respectively. Each of the valves on the
wellhead 188 has an auxiliary manual actuator (not shown) similar
to the actuator 44 illustrated in FIG. 1.
If the fluids to be injected into the subaqueous well are not too
corrosive, the angled conduits and the nipples 225 can be dispensed
with, only the vertical tubing sections being necessary. The fluid
would then be pumped directly into the interior of the sealed
compartment 194 filling the compartment, and exiting through the
vertical tubes 210. The wire line drums 200 would be immersed in
the fluid being injected into the subaqueous well.
The robot wire line unit 182 may be controlled from the surface
support ship, in which case a viewing system would be installed on
the robot unit 182 (not shown), or in an adjacent unmanned
submersible vehicle, or directions could be relayed from an
adjacent manned submersible vehicle. Where the operations are to be
controlled from the support ship, the power necessary for winding
the wire lines 224 on the respective drums 200, as well as for
actuating the hydraulic piston cylinders 214, may be supplied by
flexible electric lines extending to the accompanying ship.
However, it is considered preferable to have the robot unit 182
obtain its electrical power from a subsea power distribution
network having its point of origin at the satellite station 14,
rather than there being another line extending from the surface
vessel. A waterproof electrical junction box 230 is fixed on a
concrete base 232, which supports the various elements of the
wellhead unit 10, adjacent the wellhead 188, and has a
spring-loaded flexible extensible cable 234 that can be drawn out
of the junction box 230 far enough so that a plug 236 on the free
end thereof can be inserted into a mating connector 238, in one
face of the wire line compartment 194. A second connector 240, in
the same face of the compartment 194, is adopted to receive an
electrical plug 242 on the free end of a flexible control cable 244
for controlling the operations of the robot wire line unit 182.
Again the flexible control cable 244 could extend to the surface
vessel, but it is preferable as illustrated here, that the control
cable 244 originates at the adjacent submersible vessel 184 resting
on a docking platform, generally designated 246, anchored in the
concrete base 232 and forming part of the wellhead unit 10. When
not in use, the cable is stored in a retracted position in a
receptacle or pocket in the outer hull of the submersible vehicle.
The means for storing the cable 244 in the hull can be a
spring-biased reel (not shown) upon which the cable 244 is wound.
By pulling on the free end, the cable 244 is extended toward the
wellhead unit 182. The submersible vehicle 184 has a pair of
electromagnetic anchors (not shown) located within the lower hull
thereof which can be energized to lock the submersible vehicle 184
in a pair of spaced iron cradles 248 fixed on the tabletop 250 of
the docking platform 246. The tabletop 250 is supported above the
concrete base 232 on spaced legs 252 to permit a diver 258 to leave
the submersible vehicle 184 through lower locks 254 thereof which
register with holes 256 in the tabletop 250 when the submersible
vehicle is anchored in place.
The extensible cables 234 and 244 can be drawn out of their
receptacles and plugged into the stationary connectors 238 and 240,
respectively, by the use of articulated manipulators 260, 262
mounted in the front of the submersible vehicle 184 so that the
operation may be observed by a wire line operator 264 in the
submersible vehicle 184 through portholes 266 while the robot wire
line unit 182 completes a programmed operation directed from the
submersible vehicle 184 or the operator can personally control the
operation through panel 265. The specific circuitry for manually or
automatically operating the robot wire line unit 182 from a remote
point such as the submersible vehicle 184 is old in the art and
will not be discussed herein in detail. The lubricator valves 205
as well as the production valves 207 can be controlled from the
submersible vehicle 184. The control of the production valves 207
from the submersible vehicle 184 would override the normally
automatic control of these valves 207 from the respective satellite
station 14 or 16. This control function would require the control
signal to be transmitted through the control cable 244 to the robot
unit 182, from the robot unit 182 through the power cable 234 to
the respective satellite station, and from the satellite station
back out to the proper wellhead unit. A less complicated method of
controlling the lubricator valves 205 and the producing valves 207
would be mechanical actuation through articulated manipulators 260
or 262. Another situation is that in which the subaqueous well had
been shut in automatically in response to test results from the
satellite station 14 indicating that a workover was necessary. In
this case only the lubricator valve must be actuated. Both of the
articulated manipulators 260, 262 can be used to perform operations
at the wellhead unit 10, the reaction tool 46 (FIGS 1 and 2) not
being needed due to the positive anchoring of the submersible
vehicle 184.
It is desirable not to have to rely on surface vessels remaining
above the subsea system to transport the robot wire line unit 182
between each of the wellhead units 10. It would be better,
particularly in areas where rough seas are prevalent, to be able to
move the robot unit 182 between the various wellhead units 10 with
the help of a submersible vehicle, and use the support ship only
for lowering the robot unit 182 from the surface to the first
wellhead unit 10 to be worked over and raising the robot unit back
up to the ship from the last wellhead unit 10 worked over. The near
neutral buoyancy of the robot wire line unit 182, due to the
buoyancy tank 196, would allow the robot unit 182 to be moved
around beneath the surface with little effort. This movement can be
accomplished by a jetting system incorporated within the robot wire
line unit 182 and controlled from the submersible vehicle 184
through the interconnecting control line 244. The jetting system
can, for example, comprise a jetting pump 261, in the sealed
compartment 194, having an inlet port 263 extending through a wall
of the sealed compartment 194 to pick up sea water to be used as
the jetting agent. A valving arrangement in the pump 261 would
permit water under pressure to be ejected through jetting nozzles
affixed to the frame 190 of the robot wire line unit 182 under the
control of the submersible vehicle 184. Exemplary, horizontally
oriented jetting nozzles 265, and vertically downwardly oriented
jetting nozzles 267, connected with the pump 261, through internal
passages (not shown) in the frame 190 of the robot wire line unit
182, permit the robot wire line unit 182 to be lifted from one
wellhead unit 10, steered toward another wellhead unit 10, and
landed on the rails 186 of the second wellhead unit 10, under the
direction of the operator 264 in the submersible vehicle 184 which
is moved alongside. The jetting system, under the control of the
operator 264 in the submersible vehicle 184, can also be utilized
to perform the final locating of the robot wire line unit 182 over
the rails 186 of the first wellhead unit 10 when the robot wire
line unit 182 is first lowered from the support ship.
If the support ship is not to remain over the subsea system during
the operation of the robot wire line unit 182, provision must be
made for supplying treating fluids to the robot wire line unit 182
when such treating fluids are necessary in the operation being
performed. This can be accomplished by locating bottom storage
tanks (not shown) at each wellhead unit 10 or group of wellhead
units 10. The flexible upper ends of the flexible lines 222 can be
lowered from the support ship and connected to these tanks. A
submersible pump in each tank can pump out the treating fluid as
necessary The submersible pump would be powered through the subsea
power distribution network previously discussed. The free ends of
the flexible lines would be connected to the bottom storage tank,
and the pump therewithin would be actuated from one of the
submersible vehicles 32, 38, or 184, capable of performing such
functions.
If some difficulty is encountered that cannot be corrected by the
robot wire line unit 182 or by one of the multitooled articulated
manipulators 260, 262 of the submersible vehicle 184, the
workman-diver 258 emerges from the pressurized after-compartment
268 of the submersible vehicle 184 to make the necessary
adjustments. As discussed with respect to the submersible vehicle
38, illustrated as servicing the satellite 14 in FIG. 2, the
after-compartment is sealed after the diver 258 returns. The diver
258 is then taken to the attending surface vessel where he is
transferred to a decompression chamber. The after-compartment 268
is kept at atmospheric pressure unless the divers 258 are needed.
At that time the pressure is raised in the compartment 268 by the
addition of helium to balance the water pressure. Thus,
decompression would not be necessary unless the services of the
divers 258 had actually been needed.
The power-generating station 26, previously mentioned (shown in
FIG. 1). has large diesel engines, turbines, or any other
convenient type of prime mover for driving electrical generators to
provide the power necessary to operate the subsea equipment. The
power is transmitted to the producing system through a cable
forming a part of the bundle 28 extending between the surface
generating station 26 and the satellite station 14. From the
satellite station 14 the electrical power is distributed to the
satellite station 16 and the other satellite stations 14 (not
shown) which are necessarily spaced across the marine bottom 12.
From each satellite station 14 and 16 the distribution lines then
extend to each piece of subsea equipment at which electrical power
is needed, including each of the wellhead units 10 being
controlled, providing power for operating the valves of the
wellheads 188 as well as for operating auxiliary equipment such as
the robot wire line unit 182.
For the protection of the generating station, this too is
preferably located on the marine bottom 12. Such an arrangement is
shown in FIG. 4 where a prime power source, indicated at 270, is
enclosed in a pressure resistant shell 272. The fuel for the prime
power source 270 can be natural gas or a refined gasoline stored in
a bottom-mounted tank, particularly if the power source 270 is an
internal combustion engine or a gas turbine. When natural gas or
low gravity petroleum is being produced in the subsea system, this
is preferably taken directly from a subaqueous well and used as
fuel. When a steam engine is the prime power source, any petroleum
products produced, which will flow, can be burned to provide power.
As illustrated, the fuel is directed into the bottom-mounted shell
272 from one respective submerged wellhead 274 through an
interconnecting flowline 276 laying on the marine bottom 12 and
connected to the two fixed units by collet connectors 277. All of
the production of the well may be used as fuel or, if the
production capacity of the well is large, only a small portion of
the production fluid is directed to the generating station, the
remainder being fed directly into a flowline between the wellhead
274 and a satellite station 14, 16. The fresh air necessary for
combustion is supplied through a flexible conduit 278 connected
between the interior of the shell 272 and a small floating buoy
280. A compressor or blower 282 is mounted on the buoy 280 for
insuring a large enough volume of air. The products of combustion
from the power source 270 are directed through a line 284 into a
compressor or pump 286 from which they are driven, via line 288 to
discharge, either into the sea through conduit 290 or to the
atmosphere through a flexible conduit 292 extending from the line
288 to the floating buoy 280. The prime source, or engine, 270
drives an electrical generator 294 within the shell 272. The
resulting electrical power is transmitted directly to the pump 286
through the main electrical line 296 and to the blower 282 through
the lines 296 and 298. Electrical power is transmitted, by line
300, from the main line 296 to a transformer station 302 in the
shell 272 through a terminal board 304. A line 306 transmits
low-voltage power from the transformer station 302 to the valves
308 controlling the flow of combustion products. Power is
transmitted to a junction box 310 from the terminal board 304
through the interconnecting line 312. low-voltage power is obtained
at the junction box 310 by transformers therewithin. A watertight
electrical connector 314 on the junction box 310 provides power for
auxiliary equipment, as discussed with respect to the robot wire
line unit 182. A low-voltage line 316 transmits power from the
junction box 310 to the wellhead valves 318 for controlling the
rate of delivery of fuel from the well. Other power lines 320-324,
for example, transmit electrical power from the main terminal box
304 to the various wellhead units 10, satellite station 16, and
other satellite stations 14. Although electrical power can be
directly supplied to the individual wellhead units 10, it is
preferable to have the main power lines from the main terminal box
304 connect to terminal boxes (not shown) within each satellite
station 14, 16 and have the electrical power distributed therefrom
to the respective wellhead units 10.
The floating storage tank 20 has a rigid transportation pipe 326
depending to a point just above the marine bottom 12 and
terminating in a funnel 328, a flexible line 330 extending from the
funnel 328 to the pumping section in the satellite station 16. A
short section of the line 330, at the end of the line connected to
the rigid transportation pipe 326 within the funnel, is of a weaker
material or of the material as the rest of the line 330, but has a
thinner wall. By this arrangement, if the floating storage tank 20
should break its moorings and float away, the interconnecting
transportation path would tend to rupture, at its weakest point, in
the flexible line 330 within the funnel 328. This would permit most
of the fluid products to be saved and only the small amount in the
flexible line 328 to be lost. The fluid products in the rigid pipe
326 would be driven up into the storage tank 20 by the hydrostatic
pressure. A pressure-actuating switch (not shown) is included in
the flexible line 330 to shut off the pump in the satellite station
16 if the flexible line 328 were to rupture. Such a switch would be
actuated by abnormally high or low pressure, depending on the water
depth and the pump outlet pressure. It is also advisable to mount a
pressure controlled switch in the outer end of the flexible line
330, just below the designed rupture portion to retain the fluid
products in the flexible line 328. Furthermore, the storage tank 20
is moored as far to the side of the subsea field as possible so
that if it should break loose, its mooring lines 332, extending to
the marine bottom 12, would not snag in the subsea equipment.
Although the present invention has been described in connection
with details of the specific embodiments thereof, it is to be
understood that such details are not intended to limit the scope of
the invention. Each of the described units of the subsea system
previously discussed could conceivably be utilized without each and
every one of the other units. For example, the satellite station 14
could be used without the particular robot wire line unit 182 or
the robot welder 52. The terms and expressions employed are
intended to be used in a descriptive sense only and there is no
intention of excluding such equivalents in the invention described
as fall within the scope of the claims. Now having described the
subsea system herein disclosed, reference should be had to the
claims which follow.
* * * * *