U.S. patent number 3,793,840 [Application Number 05/189,972] was granted by the patent office on 1974-02-26 for mobile, arctic drilling and production platform.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to George E. Mott, James P. Wilbourn.
United States Patent |
3,793,840 |
Mott , et al. |
February 26, 1974 |
MOBILE, ARCTIC DRILLING AND PRODUCTION PLATFORM
Abstract
The invention relates to a marine platform adapted to be
removably positioned at an offshore body of water, the surface of
which is periodically subjected to sheet ice and floating ice
masses. The platform includes a controllably buoyant
foundation-like base at its lower end, which normally rests on the
ocean floor. A shell-like body extends upwardly from said base and
is defined on its external surface by a progressively decreasing
cross sectional area from the body lower end, to a point adjacent
the upper end. A work deck disposed at, and operably carried at the
body upper end includes equipment necessary to function at said
off-shore site. A caisson extending uprightly through the platform
is partially embedded into the substratum beneath the platform,
firmly anchoring the latter and protecting wells during and after a
drilling operation.
Inventors: |
Mott; George E. (Metairie,
LA), Wilbourn; James P. (New Orleans, LA) |
Assignee: |
Texaco Inc. (New York,
NY)
|
Family
ID: |
22699532 |
Appl.
No.: |
05/189,972 |
Filed: |
October 18, 1971 |
Current U.S.
Class: |
405/211 |
Current CPC
Class: |
E02D
27/425 (20130101); E02B 17/02 (20130101); E02D
27/42 (20130101) |
Current International
Class: |
E02B
17/02 (20060101); E02B 17/00 (20060101); E02b
017/00 () |
Field of
Search: |
;61/46.5,46
;114/.5T |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shapiro; Jacob
Attorney, Agent or Firm: Whaley; Thomas H. Ries; Carl G.
Claims
I claim:
1. A marine platform adapted to be removably positioned at an
offshore body of water, the latter being in an environment subject
to floating ice, which platform includes;
a submergible base including buoyancy means incorporated therein
for controllably regulating the disposition of said base between
the floating position at the water's surface, and a resting
position at the floor of said body of water, said base having means
forming a vertical transverse opening therethrough, a guide column
having upper and lower ends, the latter being fixed to and
extending upwardly from said base in alignment with said vertical
transverse opening, the column upper end being of sufficient length
to extend beyond the water's surface when said base is positioned
at said floor,
a caisson disposed internally of and contiguous with said guide
column, extending longitudinally thereof and having the lower end
embedded into the substrate beneath said platform whereby to anchor
the latter during a drilling operation, and to subsequently permit
upward guided movement of said platform along the caisson when the
platform is raised from a submerged position,
an elongated shell characterized by a generally conical external
surface, having the broad end connected to said base and having the
upper constricted end in engagement with said guide column adjacent
the upper end thereof, and
a deck operably carried on said guide column upper end being
longitudinally movable therealong for positioning a desired
distance beyond the water's surface.
2. A marine platform as defined in claim 1, including a caisson
operably received in said guide column and longitudinally movable
through the latter whereby to permit lowering of said caisson
downwardly through said base to permit embedment thereof into the
floor of said body of water.
3. In an apparatus as defined in claim 2, wherein said guide column
is of substantially uniform diameter and slidable along said
caisson outer surface to guide the latter during lowering thereof
into the substrate.
4. In an apparatus as defined in claim 1, wherein said conical
shell is of sufficient height to position at least a portion
thereof beyond the water's surface when said base is resting at
said floor.
5. In a marine platform as defined in claim 1, wherein said caisson
extends upwardly along said guide column to position with the upper
end thereof adjacent to and beneath the water's surface.
Description
BACKGROUND OF THE INVENTION
A marine platform of the type presently disclosed can serve many
purposes and be utilized by a number of industries. In the specific
instance of the petroleum industry, the platform is generally
positioned in an offshore body of water to drill into and explore
the substratum for the possibility of producing crude oil and gas.
Normally, in water depths up to several hundred feet such marine
platforms are fixed to the drilling site by piles of similar
retaining means.
In the instance of such marine platforms built for use in Arctic
tideland waters, the problem of rigid positioning of the unit is
compounded by the presence of floating ice during certain periods
of, and smetimes for the entire year. More specifically, it is
known that for most of the year, the presence of large ice floes as
well as moving sheet ice, virtually prohibit the use of any sort of
conventional fixed platform.
On the other hand in more protected areas such as Alaska's Cook
Inlet, the problem of sheet ice which moves with the tide can be
met to a degree by incorporating into the platform specific
features to overcome the conditions prompted by the presence of the
moving ice.
One method found to be suitable for opposing the lateral thrust of
a moving ice mass, whether in the form of floes or an entire ice
field, is by fabricating a platform with sufficient mass and with
an adequate degree of stability to physically resist the displacing
forces exerted on the structure. Such platforms however as a rule
are of a relatively permanent nature in that once they are
installed at a particular site they are not amenable to be
subsequently readily removed or to be re-used in different water
depths. Thus, if the site proves to be nonproductive, the use of an
expensive nonsalvageable platform would result in excessive
operating expense.
In addition to the stated problems of initially drilling wells in
ice infested waters, the subsequently drilled wells and well head
equipment are further jeopardized by heavy ice floes. Ice floes are
known to reach to the ocean floor and be of such a magnitude as to
scour and dig out the latter. This results in the subjecting to
bending, breaking off or otherwise damaging, any sea floor
equipment installed in such an environment. Even though the said
equipment be buried to a desired depth beneath the ocean floor, it
may still be susceptible to physical damage when extraordinary size
icebergs or the like are in the area.
It is therefore economical and desirable to utilize a fixed type
platform for offshore drilling under ice conditions, and yet
provide such a platform that is mobile and can be reused in
different water depths if it is determined that a particular area
is nonproductive. This problem is suitably countered and overcome
by the present marine apparatus. Said structure comprises in effect
a platform adapted for drilling, producing or exploratory work in
an offshore body of water in which moving ice is prevalent.
The platform is provided with a relatively widespread
foundation-like base to afford a firm footing. Further, it is made
salvageable such that the platform can be removed from a particular
spot and subsequently reset at an alternate drilling or producing
location. The platform embodies a downwardly extending heavy walled
caisson through which the respective wells are drilled. Said
caisson is of sufficient strength and rigidity to resist
installation forces and to protect the wells during the drilling
operation. When the platform is removed, the caisson may be left in
place and thus serves as a well protector. The platform is
physically contoured along its exterior particularly along the
level at which ice would be concentrated, such as to expose a
minimum area thereof to contact with moving ice.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical elevation in partial cross section of the
instant marine structure shown submerged and anchored at an
underwater site.
FIG. 2 is similar to FIG. 1 illustrating the platform when buoyed
to a floating position.
FIG. 3 is a segmentary view in cross section showing a portion of
the structure shown in FIG. 1.
FIG. 4 is an enlarged segmentary view showing a well head
installation subsequent to removal of the anchoring caisson.
Referring to FIG. 1, a platform 10 of the type contemplated is
shown installed at the floor of an offshore body of water. Base 11
comprises in general a circular, octagonal or other multisided
barge-like unit disposed at the lower end of the platform, which
member ordinarily assumes a horizontal disposition. Base 11
supports an upstanding, conically shaped shell or body 12 having a
contoured external surface which connects a relatively broad lower
section to a relatively constricted narrow portion at the upper
end. Body 12 is further provided with an upwardly extending column
13 along which an equipment deck 14 is operably received. Thus,
when the platform is submerged at a working site, deck 14 can be
raised or lowered to a desired height beyond the water's surface.
Further, when the platform is installed at a drilling site, either
the upper end of said shell 12 or column 13 is disposed adjacent to
the water's surface whereby to meet, break up and deflect moving
ice at the water's surface.
Base member 11 comprises in effect a barge-like vessel formed of a
plurality of closed, individually controlled tanks. By regulation
of the buoyancy of the respective tanks, the attitude and
disposition of the base can be readily regulated between the ocean
floor and the water's surface. Base 11 is preferably formed with
welded steel or reinforced concrete sections of sufficient strength
and so reinforced, as to resist external forces and pressures
expected in the depths of water where the platform would normally
be positioned. The respective compartments such as 16 and 17 within
base 11 are individually separated by discretely placed bulkheads
and panels. Thus, selective adjustment of the buoyancy of said
compartments results in the platform being raised or lowered to a
desired depth or positioned at a desired attitude.
While not presently shown, each compartment 16 and 17 is connected
with a buoyancy system regulated from the water's surface and
adapted to urge a fluid medium such as water or drilling mud
through the respective compartments as required. Said system of
course includes means for regulating the flow of said fluids to
achieve the purpose of raising or adjusting the level of the
barge.
An opening 18 extends transversely and centrally of barge 11,
communicating the upper and lower surfaces thereof in a generally
vertical disposition.
Elongated, conically shaped shell 12 is disposed with its center
axis normal to base 11, extending into and being rigidly connected
to the latter. Column 13 also connects to and extends axially
through conical shell 12 and base 11. The respective members are
thus secured one to the other in a manner to form a rigid, upright
structure. The relationship between said members not only assembles
the respective parts into a unitary component, but transfers or
applies sheer stress and overturning loads applied to column shell
exterior, to the widespread base 11. A suitable fastening means
between base 11 and shell 12 may be provided by fabricating the
shell 12 of reinforced concrete whereby to achieve a satisfactory
bonded engagement between the body peripheral lower edge, and the
base.
Base 11 is further provided with means to assure its fixed
positioning at a desired offshore working site. Thus, said base
includes not only center transverse opening 18, but optionally may
include openings adapted to receive a plurality of relatively short
spud piles 27 which can be driven through the base to engage or be
embedded into the substratum after the platform comes to rest on
the latter.
The lower edge of conical shell 12 is secured to base 11 and
maintains the shell in a substantially upright disposition. One
embodiment of said shell comprises a hollow, heavy walled unit
formed of reinforced concrete, steel, or a combination of said
materials. Preferably, the shell is made in the form of a
geometrically conical member characterized by an outer wall surface
having a horizontal cross section which decreases as the distance
from base 11 increases.
The primary function of conical shell or body 12 is to provide a
relatively widespread footing for the platform in conjunction with
base 11. Further, said body is provided with a sloping outer
contour or surface to best encounter moving sheet ice whereby to
deflect the latter upwardly, causing it to break into smaller
pieces due to induced bending stresses. While not presently shown
in detail, compartments built into the interior of shell 12 are
vented to the atmosphere to better control the internal and
external pressures while the platform is being submerged.
Elongated, cylindrical column 13 extends coaxially of shell 12 from
the point adjacent to base 11 to which it is fastened, to a point
beyond the shell 12 upper end. Thus column 13 projects upwardly for
a substantial distance beyond the shell upper end when platform 10
is resting on the floor of an offshore drilling site. The primary
function of said column is to operably support work deck 14 during
the transportation of the platform as well as to provide a means of
elevating the work deck 14 a desired distance beyond the water's
surface during actual drilling operations.
Column 13 thus comprises an elongated cylindical member formed of
relatively heavy walled steel or reinforced concrete. The column
lower end is received in receptacle means forming opening 18 in
base 11 and is fastened to the latter by cementing, welding, or
other appropriate means. The upper end of shell 12 is further
fastened to the outer wall of column 13 to fixedly join the entire
assembly into a unitary structure. Intermediate support means such
as struts, braces 22 and 23 or bulkheads are further disposed
within body 12 and radiate outwardly from the column wall to
reinforce both the shell and the column, and to permit ballasting
of the conical shell 12 as needed.
Toward facilitating movement of deck 14 longitudinally along the
column 13 exterior, either to the upper or lower position, the
column can be provided with the necessary slots, indentations,
protrusions or the like. Said means facilitate gripping of the
column wall by a plurality of climbing jacks and claps carried
within deck 14. Such jacks are clamps known in the art and are
frequently utilized on mobile offshore structures for regulating
the disposition of retractable legs carried on the marine platform
or structure.
Subsequent to platform 10 being submerged at a desired offshore
location, a caisson 26, which has previously been secured inside
column 13 and extends longitudinally thereof, is released and
jetted into the sea bottom. Base 11 is thus firmly embedded in the
substratum beneath the platform quickly and easily without the use
of either piles or anchor. A sufficient embedment of said caisson
26 will assist platform 10 in absorbing and transmitting to the
ocean bottom, lateral forces imposed on the structure, thus further
insuring against the possibility of lateral displacement of the
platform.
As shown in FIG. 3, caisson 26 extends preferably in a downward
direction through the center of the platform to achieve the desired
anchoring function. Further, in connection with a drilling or
producing operation, and as shown in FIG. 4, when it is deemed
feasible to move the platform, column 13 is free to slide along the
embedded portion of caisson 26 as the platform is raised by
ballasting.
In such position, the lower remaining end of the caisson serves as
a protector or enclosure for both wells and well head equipment at
the floor of the drilling site.
In the event that icebergs of other relatively deep ice masses tend
to scour the floor of the ocean in the vicinity of submerged wells
28, the protruding portion of caisson 26 will form a barrier about
said wells. Should caisson 26 nonetheless be contacted by a
floating iceberg in a manner to bend or deform the caisson walls,
the internal wells 28 would still be protected due to their
position within the caisson which will tend to bend rather than
fracture as they are displaced by the ice mass.
Caisson 26 is initially assembled with platform 10 during
fabrication of the latter. Thus, it can be floated to the drill
site by the buoyant platform. It is appreciated that since caisson
26 will be lowered or driven into the substratum, it will be
necessary to add additional caisson sections if the platform is
moved to other locations. A number of caisson sections would thus
be carried, ancillary to the platform placing operation.
As shown in FIG. 3, when in the installed position, the lower end
of caisson 26 is disposed contiguous with walls of the column 13
extending through the shell lower surface. If it is desired to
permanently place a platform at a desired location, means may also
be provided for cementing or otherwise rigidly fastening the shell
12 upper and lower ends to the casing to rigidize the disposition
thereof and to avoid movement in response to pressure exerted
against the platform.
As shown in FIG. 1, subsequent to the platform being anchored into
position, deck 14 is elevated along column 13 outer surface, beyond
the water's surface a predetermined height to facilitate drilling
operation and to maintain deck carried equipment beyond the reach
of the anticipated waves and ice.
As shown in FIG. 4, wells 28 may be completed with subsea well
heads 31 or extended to the deck elevation for conventional surface
cntrols, or may be capped for future use. In the latter event, such
equipment may be embedded below the surface of the substratum as a
form of protection. In such instance, the remaining, protruding
portion of caisson 26 will serve to enclose said well head and
equipment until such time as the wells are connected to the surface
for producing petroleum fluids.
Subsequent to said drilling operation as noted, platform 10 is
separated from caisson 26 by ballasting the latter to raise it a
predetermined distance beyond the ocean floor. The platform will
then slide upwardly along caisson 26 in an orderly, controlled
manner. Thereafter, by controlled flotation of the base 11 and
venting of body 12, the platform can be entirely raised from its
position and refloated to an alternate working site.
* * * * *