US3667240A - Installations for submarine work - Google Patents

Abstract

An off-shore drilling platform for hydrocarbons has an oscillating column pivoted at its base and kept stable by upward hydrostatic pressure, with hydrocarbon storage in the column. The difference in the densities of water and hydrocarbons in the column is compensated whereby the forces acting on the base of the column and on the pivot remain substantially constant. The column has two compartments, a lower one filled with water, and an upper one forming a float. Compensating means are pumps and valves arranged so that when the hydrocarbon is introduced into the lower compartment it drives out water and corresponding mass of liquid is pumped into the upper compartment. The pumps and valves are servo-controlled to the levels of the two liquids. A gas pocket over the hydrocarbon is kept at constant pressure by a pumping system linked to the servo-control.

Description

United States Patent Vilain INSTALLATIONS FOR SUBMARINE WORK v inventor: Robert H. Vilain, Maisons-Alfort, France Assignee: Compagnie Francaise D'Entreprises Metalliques, Paris, France; a part interest Filed: Nov. 20, 1969 Appl No; 878,458

{30] Foreign Application Priority Data Nov. 21, 1968 France ..1748l2 [52] US. Cl ..6l/46.5, 61/0.5, 11410.5, 175/9 [51] Int. Cl. ...E02b 17/00, E2lb 15/02 [58] Field of Search ..6l/46.5, 46, 0.5; ll4/0.5 T; 9/8; 175/9 [56] References Cited UNlTED STATES PATENTS 2,772,539 12/1956 Sandberg 61/46.5 3,360,810 1/1968 Busking 3,470,838 10/1969 Daniell ..1 14/05 FOREIGN PATENTS OR APPLICATIONS 163,978 7/1958 Sweden ..61/46.5

OTHER PUBLICATIONS World Oil (pub) ofFeb. 1, 1968 pp. 38- 39 Primary llraminer-Jacob Shapiro Atwrney--Fleit, Gipple and Jacobson [57] ABSTRACT An off-shore drilling platform for hydrocarbons has an oscillating column pivoted at its base and kept stable by upward hydrostatic pressure, with hydrocarbon storage in the column. The difference in the densities of water and hydrocarbons in the column is compensated whereby the forces acting on the base of the column and on the pivot remain substantially constant. The column has two compartments, a lower one filled with water, and an upper one forming a float. Compensating means are pumps and valves arranged so that when the hydrocarbon is introduced into the lower compartment it drives out water and corresponding mass of liquid is pumped into the upper compartment. The pumps and valves are servocontrolled to the levels of the two liquids. A gas pocket over the hydrocarbon is kept at constant pressure by a pumping system linked to the servo-control.

9 Claims, 9 Drawing Figures June 6, 1972 PATENTEnJun 6 I972 3, 687. 240 sum 1 or 5 INVENTOR ROBERT H. VILA l N ATT EYS PATENTEDJun 6 I972 3. 667. 240

sum 2 0r 3 WI H IF III INSTALLATIONS FOR SUBMARINE WORK This invention relates to installations for submarine work, more particularly for the extraction of hydrocarbons, of the kind essentially including a column designed to have its base fixed to the seabed, notably in articulated fashion.

In the case of installations of this kind, it has already been proposed to store hydrocarbons in the column. However, more specifically in the case where a column is articulated at its base and stabilized by a hydrostatic thrust exerted upwardly, it is important to ensure that such storage does not result in substantial changes in the magnitude of the loads exerted on the articulation, i.e., in the magnitude of this thrust.

It is the object of the present invention to provide, in the case of installations of the kind referred to and more particularly those having articulated columns, means capable of compensating for the difference in density between the water and the hydrocarbons in order that the hydrostatic thrust should remain substantially constant. I

It is a further object of the invention to provide, in such installations, inside or outside the column and over at least most of the height thereof, at least one large-diameter tubular conduit through which can extend at least one petroleum pipe or through which appropriate tools or equipment can be lowered with ease.

The description which follows with reference to the accompanying non-limitative exemplary drawings will give a clear understanding of how the invention can be carried into practice.

IN TI-IE DRAWINGS F IGS. land 2 diagrammatically illustrate, in partial vertical section and in longitudinal section on an enlarged scale taken through IlII in FIG. 1, respectively, an offshore drilling platform according to the present invention having the base of its column articulated on the seabed;

FIGS. 3 and 4 are schematic horizontal sectional views of two further dispositions of the invention;

FIGS. 5 and 6 show fragmentally, in horizontal and vertical section respectively, certain elements of the column in FIG. 4;

FIG. 7 is a chematic sectional illustration of an alternative embodiment of the teachings of this invention already described in FIG. 1; and

FIGS. 8 and 9 portray, in vertical section and in greater detail, said alternative embodiment.

Referring to the accompanying drawings which illustrate an offshore drilling platform intended for the extraction of hydrocarbons from the seabed and their storage in the oscillating platform of column, such a platform includes a column 1 oscillatably connected to a base 2 anchored to the seabed 3, with an articulation or universal joint 4 therebetween, said column being weighted at its base at 5 and being furthermore equipped with a buoyancy system at its top consisting for instance of an empty compartment or float 6.

The internal capacity of the above-described system may be considerable (for example if the seabed is at a depth of 50 to 100 meters) and is used to store the hydrocarbons extracted from the drilling well (the head of which is shown at 7).

The ability to use this important storage volume in situ is of the greatest interest, since it then becomes very easy to supply the hydrocarbons to surface vessels that can be moored in front of the platform provided on the superstructure.

However, allowance must be made for the difference in the specific gravities of the water and the hydrocarbons (the latter being lighter by 10 to l5 percent), so that compensating means must be provided in order that the loads on the bottom support and on the pins of universal joint 4 may be kept substantially constant. For when the column is in its operative position after having been set down, its major part, or the height H of the compartment 8 located beneath the floatforming portion 6 (i.e., which is filled with air), is normally filled with water and the design is such that, under such conditions, a moderate hydrostatic thrust is exerted upwardly and consequently produces corresponding reactions on the pins of universal joint 4.

But if in accordance with the invention the compartment 8 is filled with hydrocarbon, which drives the water contained therein before it, the structure will be lightened and will in turn produce an increase in the reactions on the support and notably on said universal joint. In the case of a structure designed for depths of meters, this increase may reach several hundreds or thousands of tons.

In accordance with this invention, therefore, means are provided for compensating for this lightening effect, and these means are so devised that, as the said storage compartment 8 is filled (only a small portion of the total compartment height H being shown in FIG. 1), the float compartment 6 is filled at the same time over a suitable height either with sea-water or with the hydrocarbon itself.

Assuming that compensation is effected with hydrocarbon, then in order to achieve approximate equilibrium in the case under consideration it would suffice for the float compartment to be filled with hydrocarbon of 0.85 specific gravity over a height h equal to l5h/ 100, where h is the depth to which the storage compartment 8 is filled with hydrocarbon at the time.

Obviously, however, steps must be taken so that when the hydrocarbon is reclaimed from storage for delivery to a ship (or into a pipeline linked to the shore) hydrocarbon is at the same time reclaimed from the float compartment (for delivery into the storage compartment, for instance) so that the ratio h,/h can be maintained.

This can be accomplished in various ways, such as by resorting to the embodiment shown in the drawings and which will be described hereinbelow.

In accordance with this embodiment, the said means are so devised that the hydrocarbon is delivered into or expelled from the float compartment automatically through the agency of level measuring means which, through electrical channels for example, activate valving or pumping means capable of producing the desired displacements of liquid.

For the purpose of illustrating such means in highly diagrammatic fashion, it has first been assumed, in the case of FIG. 1, that the hydrocarbon extracted from well-head 7 is delivered to storage compartment 8 by apump 9 connected into a circuit 10, l1 and powerful enough to drive out the water contained in said compartment, which water drains out from the base through openings 12.

Concurrently, float compartment 6 is caused to be filled (with possible compression of the air contained therein) through a communicating conduit 13, 14 into which a valve 15 is connected.

There are additionally provided:

a conduit 16 for reclaiming the hydrocarbon from the storage compartment for delivery via 17 to any convenient receiving means (ship, pipeline, etc.

pumping means 18 for returning the hydrocarbon contained in float compartment 6 to storage compartment 8 via conduits 19, 20,

and the said level measuring means, consisting for instance of two sets of electrical resistors or contacts (schematically illustrated at 21, 22) which are connected to electric circuits 23, 24 for controlling the pump 18 and the valve 15 respectively.

The active elements of the devices 21 22 are represented schematically on the drawing by lines 27, 28 and cause a control signal to be emitted whenever the hydrocarbon level (shown at 29 in the storage compartment and at 30 in the float compartment) appears before them. In other words, assuming the pump 9 to be operating to fill the storage compartment through 11, then as soon as the level 29 appears before an element 28 it will activate the servo device 26 to open valve 15, which valve will remain open until the level 30 reaches the next element 27 of the device 21.

The same operations will also occur in reverse order, i.e., for activating the pump 18 through the servo device 25 and causing hydrocarbon to be expelled from compartment 6 into compartment 8 when hydrocarbon is drawn off at 16, 17.

Manifestly, any other convenient means well known to the specialist in the art may be used for automatically controlling the valve 26 and the pump 25 as. a function of changes in the levels 29 and 30.

' Clearly, also, the valve 15 and the pump 18 could be operated manually so as to maintain the required liquid height 1511/ 100 at all times in the compartment 6, in accordance with indications supplied by gauges displaying the heights of the levels 29 and 30.

In either event, the hydrostatic pressure on the column will be kept constant notwithstanding differences in the specific gravities of the two liquids considered, namely the hydrocarbon and the water.

Represented at 31 is a hydrocarbon purification device interposed downstream of pump 9.

The foregoing applies equally in cases where, instead of effecting compensatory filling of float 6 with hydrocarbon, this were to be done with sea-water. It would sufiice to modify the diagram in FIG. 1 accordingly to alloy sea-water to enter through the conduit 13, and to pump the sea-water instead of the hydrocarbon with the pump 18. In this instance also the air could be compressed in float 6, above the liquid phase. The compensatory filling-height would naturally be calculated according to some appropriate law that takes the density of the sea-water into account.

It is likewise to be clearly understood that the compensating means for maintaining constant the resultant of the hydrostatic pressures on the autostable oscillating column of this invention could take any other convenient form.

Thus, as FIG. 7 shows in highly schematic fashion, it could suffice to store the hydrocarbon in compartment 8 while leaving a gas or air pocket 36 above the level 37 of the hydrocarbon (the latter being shown at 38 and the water at 39), and so to regulate the gas pressure as to maintain the resultant hydrostatic pressure on the system constant. These requirements can be met by resorting to suitable means for maintaining such gas pressure constant that operate on appropriate exhausting and pumping devices. Such means are shown in greater detail in FIG. 8, which will be considered hereinafter.

The gas maintained at constant pressure in said pocket could be hydrocarbon gas issuing from a well.

The present invention includes in its scope certain other particularities such as the following, which however may be used singly if need be.

In accordance with one such particularity, a column of the kind referred to contains therein at least one large-diameter conduit extending substantially over the full height of the column structure and capable in particular of enabling oil pipes to be assembled or of allowing any desired tools or equipment to be lowered without difficulty into a drilling well or wells.

FIG. I shows a tubular conduit 32 of this kind, through which at least one oil pipe such as the oil pipe can be assembled.

FIG. 2 is a sectional view of the pipe 10, together with guide means 33 for lowering the same.

Where necessary a plurality of conduits of this kind can be provided, as schematically depicted at 32 in FIG. 3.

Alternatively, an arrangement of this kind may be provided externally of the column, as shown in FIGS. 4 through 6.

Reference to FIG. 4 shows a plurality of conduits 32 provided externally, which may be lowered for example with the aid of skids 34 (FIGS. 5 and 6) co-operating with guide rails 35.

It is to be noted furthermore that the arrangements hereinbefore described for the storage of hydrocarbons are equally applicable to submarine columns devoid of a work platform and submerged underwater, such columns serving solely for storage and being usable for instance in proximity to an offshore drilling column arrangement of the kind described precedingly, notably in order to increase the total storage capacity.

Such columns could be fixed to the seabed without an articulation if they can be expected to remain unaffected by the sea swell; otherwise, the articulation must be retained.

FIG. 8 portrays an arrangement of this kind that includes a fully submerged column 40 comprising at its top a buoyancy compartment 46 capable in addition of containing all the gear (notably the pumping and regulating gear), said compartment being located at a level low enough in relation to the water surface 48 to permit unhindered ship movements.

Such an arrangement is well suited to cases where the compensation is eflected by means of a constant-pressure gas or air pocket 36, in accordance with the principle illustrated in FIG. 7.

In FIG. 8, reference numeral 41 designates a feed and storage pump drawing from any convenient hydrocarbon source (such as from a remotely located well-head), a purifl-' cation system being provided at 42. The inlet is through a conduit 43 and delivery through a conduit 44. Offtakes are effected by means of a further pump 49 connected into a circuit 50, 51 linked to any suitable reception facility through flexible hoses or other piping means.

The gas pressure in the pocket 36 is regulated by means of a delivery and discharge system 45, activation of which may possibly be combined with operation of pump 41. The gas may be drawn off from the purification unit 42, as shown at 45,.

The air in machinery compartment 46 is compressed to the outside pressure, i.e., to the pressure corresponding to the depth of the column, and access means 47 are provided for the divers and for passage of the equipment. The machinery is controlled via an underwater cable.

Additional floats may be provided at the top of the structure if necessary.

Such a storage column, or a plurality thereof, could thus be combined with a drilling platform structure of the-kind shown in FIG. 1, in cases where the output from the well requires it.

FIG. 9 shows another alternative embodiment of the same kind, notably for use at very great depths, in which a smaller and lighter secondary column 52 is provided at the top and is articulated to column 40 at 53 and may include a work platform 54, such secondary column providing access for inspection and ventilation of the machinery compartment 46 through a conduit 55.

Clearly, the hydrostatic pressure could likewise be compensated for, in the case of such submerged columns, with the means described for the protruding column in FIG. 1.

Offshore drilling platforms as hereinbefore disclosed offer numerous advantages over prior art platforms of this kind, and the following in particular:

The hydrocarbon can be stored in situ, thus saving time.

Notwithstanding such storage, no substantial variation occuts in the magnitude of the reactions on the bottom support for the column.

Flnally, the oil pipe as well as all gear and equipment can be lowered more easily.

The advantage of being able to maintain constant the forces exerted on the articulation or universal joint 4 is a most important one. Like the case of a column rigidly anchored at its base, the upwardly directed forces (hydrostatic thrust) which the universal joint was normally designed to withstand cannot be allowed to vary, the more so since if no compensation were provided the resulting lightening in the stored oil replacing the sea-water over a considerable height of the column would produce a marked increase in those forces, and no universal joint could withstand them. The present invention consequently resolves this problem.

It goes without saying that many changes and substitution could be made in the forms of embodiment specifically described hereinabove, without departing from the scope of the invention.

What is claimed is:

1. An offshore drilling platform for hydrocarbons, having an oscillating column with an articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment'and in so doing drives out the water contained therein, a proportional mass of liquid is introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed wherein the pumps and valves associated with the compensating means comprise servo-control means adapted to compensate for variations in the levels of the two liquids in the two compartments 2. An offshore drilling platform for hydrocarbons, having an oscillating column with an articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment and in so doing drives out the water contained therein, a proportional mass of liquid is introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed wherein said compensating means is a gas pocket in constant contact with the hydrocarbon level in the relevant compartment, said pocket being maintained at constant pressure by means of an exhausting and pumping system which operates automatically in response to variations in the hydrocarbon level.

3. An offshore drilling platform for hydrocarbons, having an oscillating column with an articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment and in so doing drives out the water contained therein, a proportional mass of liquid is introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed wherein at least one large-diameter conduit extends through the entire height of the column, for lowering oil pipes, gear or other equipment therethrough.

4. A drilling platform according to claim 3, wherein said large-diameter conduit is disposed inside the column, along the axis thereof.

5. A drilling platform according to claim 3, wherein a plurality of said large-diameter conduits are disposed inside the column.

6. A drilling platform according to claim 3, wherein said large-diameter conduits are disposed externally of the column and are suitably guided along guide rails.

7. An offshore drilling platform for hydrocarbons, having an oscillating column with an articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment and in so doing drives out the water contained therein, a proportional mass of liquidis introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed adapted to be completely submerged with its top at a suitable depth below the surface of the sea, said column being fixed to or articulated on the seabed and including means for receiving the liquid to be stored and means for extracting the stored liquid.

8. A drilling platform according to claim 7, wherein the submerged column includes an upper compartment which is set under an air pressure corresponding to the immersion depth and a lock for ingress of the divers and equipment.

9. A drilling platform according to claim 7, wherein the submerged column includes an upper compartment which is linked to the surface of means of a smaller and lighter column articulated to said submerged column and comprising access means to said compartment.

Claims (9)

1. An offshore drilling platform for hydrocarbons, having an oscillating column with an articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment and in so doing drives out the water contained therein, a proportional mass of liquid is introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed wherein the pumps and valves associated with the compensating means comprise servocontrol means adapted to compensate for variations in the levels of the two liquids in the two compartments.

2. An offshore drilling platform for hydrocarbons, having an oscillating column with an articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment and in so doing drives out the water contained therein, a proportional mass of liquid is introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed wherein said compensating means is a gas pocket in constant contact with the hydrocarbon level in the relevant compartment, said pocket being maintained at constant pressure by means of an exhausting and pumping system which operates automatically in response to variations in the hydrocarbon level.

3. An offshore drilling platform for hydrocarbons, having an oscillating column with an Articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment and in so doing drives out the water contained therein, a proportional mass of liquid is introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed wherein at least one large-diameter conduit extends through the entire height of the column, for lowering oil pipes, gear or other equipment therethrough.

4. A drilling platform according to claim 3, wherein said large-diameter conduit is disposed inside the column, along the axis thereof.

5. A drilling platform according to claim 3, wherein a plurality of said large-diameter conduits are disposed inside the column.

6. A drilling platform according to claim 3, wherein said large-diameter conduits are disposed externally of the column and are suitably guided along guide rails.

7. An offshore drilling platform for hydrocarbons, having an oscillating column with an articulation at its base and kept stable by an upwardly directed hydrostatic pressure, with hydrocarbon storage in said column, characterized by the fact that compensating means are provided in the column for compensating for the difference in the specific gravities of the water and the hydrocarbons so that the forces acting at the base of the column and upon the articulation remain substantially constant, said column having at least two compartments, one at the base, normally filled with water, and the other at the top to form a float, said compensating means including pumping and valving means, and conduits connecting said two compartments whereby, when the hydrocarbon is introduced for storage into the base compartment and in so doing drives out the water contained therein, a proportional mass of liquid is introduced into the upper compartment, the same operations taking place in reverse order when the hydrocarbon is reclaimed adapted to be completely submerged with its top at a suitable depth below the surface of the sea, said column being fixed to or articulated on the seabed and including means for receiving the liquid to be stored and means for extracting the stored liquid.

8. A drilling platform according to claim 7, wherein the submerged column includes an upper compartment which is set under an air pressure corresponding to the immersion depth and a lock for ingress of the divers and equipment.

9. A drilling platform according to claim 7, wherein the submerged column includes an upper compartment which is linked to the surface of means of a smaller and lighter column articulated to said submerged column and comprising access means to said compartment.

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