U.S. patent number 3,653,349 [Application Number 05/038,218] was granted by the patent office on 1972-04-04 for self-propelled semi-submersible drilling rig.
This patent grant is currently assigned to Ocean Drilling & Exploration Company. Invention is credited to Elliot E. Brown.
United States Patent |
3,653,349 |
Brown |
April 4, 1972 |
SELF-PROPELLED SEMI-SUBMERSIBLE DRILLING RIG
Abstract
A self-propelled drilling rig of the semi-submersible type for
drilling wells at marine locations generally from an afloat
position and having hull members provided with self-contained
propulsion units for propelling the rig between marine
locations.
Inventors: |
Brown; Elliot E. (Metairie,
LA) |
Assignee: |
Ocean Drilling & Exploration
Company (N/A)
|
Family
ID: |
21898697 |
Appl.
No.: |
05/038,218 |
Filed: |
May 18, 1970 |
Current U.S.
Class: |
114/265;
114/166 |
Current CPC
Class: |
B63B
35/4413 (20130101); B63H 5/14 (20130101); B63H
25/42 (20130101); B63B 1/107 (20130101) |
Current International
Class: |
B63H
25/42 (20060101); B63H 25/00 (20060101); B63B
35/44 (20060101); B63b 035/00 () |
Field of
Search: |
;114/.5D,43.5,166
;61/46.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blix; Trygve M.
Claims
What I claim and desire to secure by Letters Patent is:
1. A self-propelled semi-submersible drilling rig, comprising:
a. a submersible base structure comprising a plurality of hollow,
cylindrical, elongate, spaced-apart parallel hull members; said
base structure comprising:
i. a pair of inboard members; and
ii. a pair of outboard members shorter in length than the inboard
members and substantially centered longitudinally with respect to
the latter;
b. a wave-transparent stabilizing superstructure mounted on the
base structure; said superstructure comprising;
i. a plurality of vertical hollow cylindrical stabilizing columns
disposed in angularly spaced-apart relation in a configuration
defined by a circle passing through the centers of said columns and
whose center coincides with the intersection of the longitudinal
and transverse center lines of the rig;
ii. hollow cylindrical cross members extending transversely of said
rig and connecting opposed ones of said columns at elevations above
said hull members; and
iii. cylindrical risers connecting said inboard members to at least
some of said cross members;
c. a working platform supported on said superstructure; and
d. steerable propulsion means mounted on at least two of said hull
members for propelling said rig through a water body.
2. A drilling rig according to claim 1 wherein said superstructure
comprises:
a. two of said stabilizing columns mounted on each of said hull
members disposed adjacent the opposite ends of said hull members;
and
b. additional vertical columns smaller in diameter than said
stabilizing columns supporting said platform from said hull members
at points intermediate said stabilizing columns.
3. A drilling rig according to claim 1 wherein each of said
propulsion means comprises:
a. a propeller rotatably mounted on the aft end of the hull
member;
b. a power unit enclosed within said aft end of the hull member
drivingly connected to said propeller;
c. a steerable accelerating nozzle enclosing said propeller and
mounted to the hull member for pivotal movement about said
propeller to steer said rig; and
d. means on the hull member for steering said nozzle.
4. A drilling rig according to claim 3 wherein said means for
steering said nozzle comprises:
a. a rudder post connected to said nozzle;
b. a tiller arm secured to said post; and
c. fluid pressure-operated means operably connected to said tiller
arm for turning the same.
5. A drilling rig according to claim 1 having a well drilling unit
centered on the intersection of the longitudinal and transverse
center lines of the rig.
6. In a drilling rig according to claim 1:
a. rearwardly tapering conical extensions on the aft ends of said
inboard members for housing and supporting said propulsion
means.
7. A drilling rig according to claim 3 wherein said nozzle is a
Kort nozzle.
Description
As offshore drilling has progressed into ever deepening waters,
bottom-supported drilling units reached their economic depth limit,
and the industry has had to develop floating structures for such
service. Two general types of drilling structures have been
developed and have enjoyed considerable success and acceptance by
the oil industry. One type was an adaptation of a conventional
ship, usually self-propelled, by adding moorings to hold it in a
drilling position and special machinery for the drilling operation,
the drilling operation usually being conducted through a hole cut
through the center of the vessel.
The second successful type is the semi-submersible barge, usually
of large dimensions, consisting of a lower base assembly or hull,
tubular supporting columns, and an upper working deck or platform.
The hull in some cases was a substantially continuous hollow,
box-like, structure, and in others consisted of a plurality of
hollow tubular members connected to form a base. The hull was
provided with tubular supporting columns on which was mounted an
upper working deck or platform. Such a semi-submersible barge is
designed to float on its lower hull and normally is moved by tugs
or other draft vessels from location to location in this afloat
position. When arriving at the drilling location, a number of
anchors and chains are streamed, usually with the aid of attending
vessels, and the hulls are then flooded in order to partially
submerge the unit, hence the designation "semi-submersible." In
this partially submerged operating position the lower hull is well
below the water line, and the upper deck remains substantially
above the water line, leaving sufficient clearance under the deck
for maximum expected wave height. The columns joining the upper
deck and lower hulls provide nautical stability and structural
support, and are arranged in such fashion as to achieve these
properties and still retain minimum obstruction or maximum
"transparency" to wave action.
It has been well established that the semi-submersible type of
platform offers many advantages in operation over the so-called
ship-type, the principal one being that of greater stability,
meaning that the semi-submersible responds in a much lesser degree
to the forces of wind and waves, and its roll, pitch, heave and
other movements are considerably less. This minimal movement is of
course very desirable for the efficient drilling of wells, as
excessive motion makes satisfactory drilling virtually impossible,
thus making the semi-submersible particularly advantageous in heavy
weather areas. Also, the forces on the moorings are substantially
reduced.
These advantages of the semi-submersible are achieved by virtue of
its usually large overall dimensions, together with the dispersed
and highly transparent configuration of the vertical members and
the constant inertia and drag of the large hull-like members at a
depth well below the water line, where in addition, they are less
affected by waves than they would be at the surface.
The principal disadvantage of the existing large semi-submersible
units when compared to the ship-type units lies in its greater
difficulty in being moved from place to place, and particularly so
on moves of great distances. Heretofore, such semi-submersibles
have not been self-propelled and have relied upon outside tugs to
tow them. To make such moves safe and efficient, two or more tugs
of large horsepower were usually required, and speed of advance has
been on the order of 4 knots. On the other hand, a typical
self-propelled drilling ship would advance at 10 to 12 knots under
its own power and not require outside tugs. The greater speed and
saving of tug costs thus give the ships significant competitive
advantage on long moves.
This invention, while preserving the available operating
characteristics of a semi-submersible, adds the capability of
cruising under its own power for extended periods and will thus
greatly reduce and even overcome the present advantages of mobility
available to ship-type structures. In order, however, to assure
maximum capability as a self-propelled unit, it is important in
accordance with this invention, to incorporate certain features of
design in the semi-submersible which together with the
self-propulsion units result in a unit capable of optimum mobility
and operating efficiency.
In accordance with this invention a semi-submersible unit is
provided in which the principal supporting hull or base comprises a
plurality of elongate, parallel, spaced-apart, tubular elements in
the aft ends of at least some of which are mounted propulsion units
driven by power sources aboard the vessel. The propulsion units are
capable of propelling the rig at speeds comparable to those
attained by ship-type units over long distances and add to the
operating efficiency of the rig as a whole.
The hull elements have mounted thereon a superstructure comprising
a plurality of large diameter vertical columns which are arranged
in a generally circular configuration adapted to provide uniform
stability in all directions and which are arranged to afford a
maximum degree of nautical stability under all conditions. The
superstructure includes a working deck, and the drilling location
is disposed in the center of the structure, again affording maximum
stability under all operating conditions.
The propulsion system comprises propulsion units mounted in at
least two of the parallel hull members, preferably the inboard
members. Each unit basically consists of a five bladed propeller
enclosed within a Kort nozzle, a known type of accelerating nozzle,
which is attached to the aft end of the hull member and made
steerable for purposes to be described hereinafter. The propeller
is driven by a straight shaft coupled directly to the D.C. electric
motor. The nozzle is pivoted in a support structure and turned by
an electro-hydraulic steering system.
Electric power for the propulsion motors is provided by the main
diesel-electric power plant required for the drilling operation.
The propulsion system is economically adaptable to a mobile
drilling unit since the main power plant is not needed during moves
of the rig and thus becomes available for driving the propulsion
motors. As the horsepower requirements are about the same for
drilling and for propulsion, power supplied by a diesel-electric
system can be readily transferred by a simple switching system from
drilling to propulsion, thereby rendering the system relatively
simple and economically attractive.
Other and more specific objects and advantages of the invention
will become more readily apparent from the following description
when read in conjunction with the accompanying drawing which
illustrates a useful embodiment in accordance with this
invention.
In the drawing:
FIG. 1 is a perspective view of the complete drilling rig;
FIG. 2 is a transverse sectional view taken generally along lines 2
-- 2 of FIG. 1;
FIG. 3 is a longitudinal sectional view taken generally in line 3
-- 3 of FIG. 2 showing one of the propulsion units;
FIG. 4 is a detail of one of the steerable propeller units;
FIG. 5 is a side profile of the rig structure; and
FIG. 6 is an aft end elevational view taken on line 6 -- 6 of FIG.
5.
Referring to the drawing, the drilling rig comprises the base or
main hull member designated generally by the numeral 10, a
superstructure, designated generally by the numeral 12, mounted on
the base member and in turn supporting a working platform,
designated generally by the numeral 14.
In the illustrative embodiment the base member comprises a
plurality of parallel spaced-apart hull elements of hollow
cylindrical form and includes a pair of inboard members 16 -- 16
and a pair of outboard members 18 -- 18 of lesser length than the
inboard members and centrally disposed longitudinally with respect
to the inboard members.
These hull members are of quite large diameter, for example 25 feet
6 inches, and together provide substantially all the required
buoyancy for floating the structure. Although not illustrated, it
will be understood that these hull members will be divided by means
of suitable bulkheads into a plurality of compartments which will
be connected to a suitable system for ballasting and de-ballasting
the compartments, all in accordance with known practices, to effect
submergence and raising of the rig as required in connection with
drilling and towing operations to be conducted therewith. Some of
the compartments in the hull members may be employed for storage of
fresh water, fuel oil and the like.
The superstructure comprises a plurality of large diameter hollow
cylindrical columns 19 totaling eight in number, two of which are
mounted on each of the hull members spaced near the opposite ends
thereof. These columns 19 which provide nautical stability,
particularly in raising and submerging of the rig, also provide
support for the working platform and its loads, and are arranged in
an annular configuration defined by a circle C (shown in broken
lines in FIG. 2) which passes through the centers of all of the
columns 19 and has its own center coincident with the center of the
drilling location indicated at 20 in FIG. 2, which is located on
the intersection of the longitudinal and transverse center lines of
the rig. The angular spacing of columns 19 on the circle, while not
necessarily equal in all cases, generally provides a symmetrical
arrangement about center 20. Opposed columns 19 mounted on outboard
members 18 are connected by hollow cylindrical cross members 21 --
21 disposed at a substantial elevation above the several hull
members and are secured inboard members 16 by risers 22. The
columns 19 mounted on inboard hull members 16 are likewise
interconnected by hollow cylindrical cross members 25, likewise
located at a substantial height above the hull elements. The height
of the several cross members above the hull members will preferably
be selected such that they will be well above the water surface
when the hull members are submerged to normal towing draft to
reduce the drag during towing of the rig. A number of additional
columns 24 substantially smaller in diameter than stabilizing
columns 19 are mounted to extend between the hull members and the
platform to provide additional support therefor and to generally
strengthen the structure. A few additional horizontally disposed
cylindrical members 25 are employed to connect the stabilizing
columns as bracing members; however, it will be evident that with
the geometric configuration illustrated, the superstructure
involves the use of a minimum number of structural elements thereby
providing maximum wave transparency for the structure while
assuring adequate strength under all conditions.
By providing the generally circular configuration of the main
stabilizing column a number of advantages result. This
configuration eliminates any directional weakness when considering
the energy required to overcome wind heeling force for stability
considerations. Also, the amount of topside weight allowables are
increased by this configuration.
By locating the rotary table of the drilling rig in the center of
the vessel, both longitudinally and transversely, lesser pitch and
roll motions at the rotary table during drilling operations will
result.
By making the various cross members circular in shape, drag effects
due to current are minimized as well as inertia and drag forces due
to waves while at drilling draft.
Mounted to the aft end of the inboard hull members are rearwardly
tapering conical extensions 26 -- 26 which house and support the
propulsion units. The latter, as best seen in FIGS. 3 and 4,
comprise five bladed propellers 30 mounted for rotation on straight
shafts 31 extending through the centers of extensions 26 for
connection to power units 32 which are preferably D.C. electric
motors. The current will be supplied to the motors from
conventional diesel-electric generating units (not shown) of
generally conventional form, mounted on the working platform. Each
propeller is enclosed within an accelerating type flow nozzle 33
which may be of the well known Kort form. The nozzle is mounted on
upper and lower shafts 34 and 35 respectively journaled in a
bracket 36 mounted on the aft end of extension 26 to render the
nozzle steerable. Upper shaft 34 extends into a housing 37 and is
secured therein to the center of a tiller arm 38, the opposite ends
of which are connected to fluid pressure-operated steering
cylinders 39 -- 39 which are powered by a conventional steering
motor and pump 40 mounted in extension 26 (FIG. 3.).
By making the Kort nozzle 33 steerable it becomes an effective
steering device, being referred to as a Kort rudder, which directs
the nozzle thrust as required to create a turning moment in the
vessel. This directed thrust is not dependent on the vessel speed
as with a conventional rudder. By the use of these rudders the
vessel may be steered by varying and reversing the speeds of the
propellers in the opposite hulls. Thus, these steerable nozzles
provide a safety measure in case one propeller is damaged in which
case one of the rudders could be used to hold the vessel on a
straight course. Moreover, these rudders are also highly useful in
maneuvering on location. For example, the propulsion motors will be
used while the vessel is moored on drilling location to reduce the
loads on the moorings during extreme weather thus reducing the
likelihood of anchor or chain failure. Another advantage of these
propulsion devices is that the installation of the anchor system at
the drilling site is facilitated by the unit's capability of moving
itself about or maintaining its position without assistance from
tugs while auxiliary vessels stream the anchors. Moreover, the
propulsion devices will also prove useful for assisting with
dynamically positioning the unit when drilling in deep water where
conventional moorings are not feasable.
Working platform 14 will be provided with the various housings for
men and equipment as shown in FIG. 1. Drilling derrick D is shown
mounted over the center of the vessel through which drilling will
be conducted as required.
In operation, the rig has variable draft capability. Vessel motions
(depending on the height and period of the seas) in any particular
location will dictate what operating draft results in the least
vessel motion. The propulsion units are sufficiently powered to
self-propel the rig for any required distance at a satisfactory
rate of speed, say 8 knots per hour. The system described is usable
for propulsion at drafts varying from that at which the vessel is
normally towed (about 19 feet) down to and including the normal
drilling draft (about 70 feet). While in transit the vessel can
submerge to drafts deeper than the normal towing draft to minimize
adverse motions resulting from heavy seas, and still maintain
headway. Such drafts could be expected to vary from about 45 to
about 60 feet depending on sea conditions.
By adding additional propellers or thrusters oriented transverse to
the fore and aft axis of the vessel, additional chain tension
relief in that direction can be gained. Further, addition of a
central control system would then result in a self-positioning
vessel, capable of operating in deep water without mooring
chains.
* * * * *