Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Back~round of Invention
Field of Invention
This invention relates to arrangements for the collec-
tion and separation of uncontrolled blow out material from
bore holes in the ocean floor.
Boring for oil at sea involves the risk of the
catastrophic contamination of the marine environment and
of fire due to the uncontrolled blow out of petrochemical
raw materials from the bore holes.
Description of the Prior Art
One of the most relevant proposals for preventing the
damaging effects of such blow outs is based on placing a
bell or a hood on the ocean floor above the blow out loca-
tion so that the edge of the bell forms an abutment with
the floor and, if desired, bores down into the uppermost
loose layers thereof. ~s a resu]t, the blow out material
can be caught and sent up to the surface through a lift
conduit.
However, such a bell has to be provided with ballast
tanks and operating and control equipment therefor or be
able to be lowered down to the sea bottom from a relatively
powerful mother vessel. Besides, it must be operated
in a horizontal plane so as to be able to be positioned
accurately over the blow out location and it must
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be provided with separators in order to isolate oil, water
and gas. Despite this expensive additional equipment, it
is probable that the positioning of such a floor bell in a
blow out situation will create significant problems. At those
water depths which are encountered the gas content of the
blow out material will, in fact, cause buoyancy and ex-
pansion problems the extent of which is not yet known. The
large pressure difference between the bell and the surface
also creates special problems in a possible gas conduit in
the form of supersonic currents, pressure thrusts and the
like.
United States Patent Specification No. 3,389,559
(Logan) discloses mooring a flexible, air-impervious
sheet over an underwater discharge location, especially in
connection with leakages in pipe conduits, and anchoring
the sheet so that it is blown up with the edges submerged in
the water. The purpose of this is to permit the collection
of the discharge internally in the '-'bubble" which is formed.
However, it will be difficult to maintain such a sheet con-
struction sufficiently stable for it to be applicable forcollecting discharge from an uncontrolled blow out in
stormy seas as can be expected in certain ocean regions.
United States Patent Specification No. 3,611,728
(Van't Hof) discloses enclosing the blow out location
with an annular wall or boom in a manner corresponding
to that used fo~ collecting oil slicks. The flexible
annular wall described will, however, also be difficult to
keep stable in stormy seas and, moreover, provides no
opportunity for collecting gas discharge.
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Summary of the Invention
A main object of the invention is to provide
an arrangement for the collection and separation of uncon-
trolled blow out material from bore holes in the ocean bed
which is not encumbered or is encumbered to the least
possible degree with the disadvantages described above.
It is a particular aim-to create an arrangement which has
as simple a construction as possible and which, in addition,
is so small that it can be readily brought into position at
the blow out location.
Another purpose is to create an arrangement
which is so reasonable that it can be maintained in readiness
in the numbers which are necessary to ensure sufficient
security during boring operations at sea. Finally, there is
a need to provide an arrangement which gives rise, as far
as possible, to a complete collection of the discharge even ~
under unfavorable weather conditions.
According to the present invention an arrange-
ment for the collection and separation of uncontrolled
blow out material from bore holes in the ocean floor comprises
collecting means for positioning on the surface of the sea
above the discharge location so as to form an annular wall
surrounding a contaminated zone and preventing the spread
of said discharge, said collecting means comprising a bell-
shaped shell defining a hollow space and adapted to be
coupled to a source of reduced pressure for maintaining
said space at a reduced pressure.
Such an arrangement can, first of all, be
made very simple in construction. It will be able to be
manipulated in a ready manner, for example, with tug boats
or other sea vessels. Alternatively, it will be able to be
built into a sea vessel, for example as a portion of a
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tan~er.
Brief Description of the Drawin~s
In order that the invention can be more clear-
ly understood, convenient embodiments thereof will now be
described, by way of example, with reference to the accompany-
ing drawings in which:
Fig. 1 is a perspective view of an arrange-
ment according to a first embodiment,
Fig. 2 is a vertical section axially through
the arrangement of Fig. 1 and shows that arrangement
schematically at a location above a blow out, and
Fig. 3 is a schematic representation of an
arrangement according to another embodiment.
Referring to Figs 1 and 2, there is shown a
bell-shaped shell or ~ell 11 having a sklrt 12 which is
designed for positioning with its opening submerged in the
water. The bell 11 has an outer shell 13 of cylindrical
shape and an inner shell 14 having a shape which is approx-
imately the same as a paraboloid,the two shells preferably
being formed from steel or reinforced concrete for example,
based on ferro-cement, and being arranged coaxially so that
they form a common skirt and opening edge 15 having a
diameter D. They are further connected to an end wall 16
which forms the upper limit of the arrangement.
Between the shells 13 and 14, there is
formed thereby a chamber or hollow space 17~ while in the
inner shell 14 there is formed an inner space 18 which is
defined downwards by the surface of the liquid and upwards
communicates with the surroundings through a centrally locat-
30 ed lift conduit 19. The shells 13 and 14 can have any
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~ppropriate fGrm, both in a~ial section and cross-section.
They can, for example, both be cylindrical or hemispherical
or can have a polygonal cross-section. In a manner known
for floating systems, the bell 11 can be provided with
ballast tanks (not shown) which can be filled more or less
with liquid in order to regulate the submersion d of the
arrangement (see Fig. 2).
The skirt 12 of the bell 11 is provided in the
region of its edge with two parallel rows of openings 20
along the periphery in the form of ducts which extend down-
wardly and outwardly in oblique fashion from the inside.
The purpose of these openings which can alternatively have
the shape of slots or the like, will be described below.
The inner space 18 communicates with the chamber
17 through a row of ducts 21 which lie roughly centrally of
the height of the inner shell 14 or at the level of the sea.
Each of these ducts 21 is provided with a pump (not shown)
or connected to a pump installation for controlled transfer
of medium, especially liquid, such as oil, from the space
18 to the chamber 17. This will be described further below.
This arrangement can be utilised in the following
manner: -
It can be held in readiness on a so-called "oil field", that
is to say a sea region where boring after or extraction of
crude oil and/or gas is performed. By virtue of the simple
construction and the limited need for equipment, installation
and maintenance expenses will be low for such an arrangement.
Investigations have shown that a blow out column
of hydrocarbons in water from a certain, small height
(probably from 5 - 8 m) above the sea bottom, will extend
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-in a cross-sectional direction according to the formula:
D = 1.2 xax ~ where X is the distance up from the bottom.
The formula D = 1.2 x~x (h-d) indicates then the diameter
at the collection level, ~ being a universal constant (also
called "entrainment constant")which indicates the behaviour
of a blow out of gas or liquid in another heavier gas or
liquid under turbulent conditions, having regard to the
penetration of the surrounding heavier medium in the up-
wardly rising medium column. Furthermore, the depth of the
ocean = h at the blow out location and d = the submerged
depth. The constant ~ has in practice been close to 0.1.
In determining the opening diameter of the bell
an addition must be made so as to give place for the reverse
flow of water which is separated from the blow out column
under the bell, in addition, to permit a certain sideways
movement of the bell, for example during a storm.
The opening diameter D of the bell can, therefore,
be expressed by the following formula:
D = 0.12 (h-d) +aD, where aD is a necessary add-
ition to the diameter.
In order to simplify this formula, it can beassumed that the bell is disposed with a submerged depth
which is equal to 1/3 of the opening diameter. Furthermore,
the additional area which the openings 20 provide for the
reverse flow of water can be disregarded and besides the
need for overdimensioning so as to permit a certain wrong
positioning. The relationship between the diameter and the
blow out column at the collection level and the opening
diameter of the bell will thus be determined by the equation:
2,D = (D-~aD) .
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The formula for determining the opening diameter of
the bell can thus be simplified to D = 0.19 h, that is to
say about 1/5 h.
For an ocean depth h- 50m it will thus be sufficient
with an opening diameter of about lOm, while with an ocean
depth of lOOm it will be sufficient with a diameter of 20-25m.
The arrangement, in addition to collecting up the
discharge, also constitutes a separator into oil fraction
22 and gas fraction 23 so that special separators are re-
dundant. The water fraction which is forced into the dis-
charge column can by appropriate positioning of the openings
20 and with openings somewhat larger than the diameter of
the colu~l, flow out through these or back through the skirt
opening. The gas fraction 23 will collect in the space 18
and from there can be led up through the lift conduit 19 to
a torch tower or to an appropriate form of use. The oil
fraction 22 will be isolated on the surface of the water
and from there can be pumped into the chamber 17 through
the ducts 21, for example for replacement of ballast.
In order to obtain the pressure conditions in the
space 18 which at any given time are the most ~avorable for
effecting optimum oil-gas-water separation, there is insert-
ed in the lift conduit 19 a pressure regulating valve 24
which can be controlled with suitable equipment. In add-
ition or instead there can be utilised a pump for controll-
ing the pressure of the gas under the bell~ It is approp-
riate to create a reduced pressure so that the water l~vel
lies above the openings 20.
Furthermore, it can be desirable to provide the
under edge 15 of the skirt 12 with a downwardly depending
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curtain 25 as indicated in the Fig. 1 and 2 and which serves
to close in the oil and let out the water. Such a curtain
25 can be perforated or consist of filter-forming, slotted
louvers.
In order to be able to position the arrangement
above the blow out location so that at any given tlme it is
present centrally above the blow out column, there is arrang-
ed on the outer side of the bell 12 a series of gas feelers
26 in a row along the periphery. On deviating from the
correct positioning one or more of these feelers 26 will
record gas and give a signal to the positioning equipment
of the arrangement.
The arrangement in the example is shown in its
simplest constructional form as a bell-shaped unit which
is assumed to be operated and maintained in position by
one or another type of floating system, for example a ship.
This basic construction can be completed in various ways.
The arrangement can, for example, be made self-driven in
that it is e~uipped with pontoons or a suitable form of
body ("Skrag") with ballast tanks and possible collection
tanks. Furthermore it can be built on or into a vessel
which can be exclusively designed for driving the arrange-
ment or which can have another function in addition.
In FigO3 there is shown an embodiment where the
arrangement is built into a tanker as an integral portion
of the latter~ Tankers of average size will have sufficient
cross-dimension to be able to receive a bell-shaped unit
which is sufficiently large to cover the current ocean
depths. In the embodiment, a bell-shaped unit 27 of
rectangular cross-section in a horizontal plane is built
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into the central portion of a ship 28. Under normal
speeds the bottom of the ship is covered by two flaps 29
which are pivotable about lonyitudinal axes at the side of
the ship so that on the occurrence of a blow out they can
be swung as shown in dotted lines. Such a ship can be em-
ployed as a tanker without a substantial restriction of its
capacity. The arrangement of such a collecting bell will
certainly not create any constructional problems, since the
bell space 30 can include the necessary support elements
so long as there is free passage for gas and oil.
