FR2572049A1 - SEMI-SUBMERSIBLE INSTALLATION, IN PARTICULAR FOR DRILLING PLATFORM - Google Patents

Abstract

THE INVENTION CONCERNS SEMI-SUBMERSIBLE INSTALLATIONS. IT RELATES TO AN INSTALLATION WHICH INCLUDES A BRIDGE 12 AND SEVERAL 14 COLUMNS EXTENDING IT. 16 PONTOONS ARE MOUNTED AT THE LOWER ENDS OF THE COLUMNS. ACCORDING TO THE INVENTION, SLEEVE-SHAPED ELEMENTS 22, INTENDED TO MODIFY THE FLOATING CONFIGURATION OF THE INSTALLATION, ARE MOUNTED AROUND THE COLUMNS 14. THESE ELEMENTS CAN BE PLACED IN A TRANSPORT FLOATING PLAN OR IN A FLOATING PLAN SURVIVAL, DEPENDING ON CONDITIONS OF USE AND WEATHER CONDITIONS. APPLICATION TO SEMI-SUBMERSIBLE DRILLING PLATFORMS.

Description

The present invention relates to semi-submersible installations such

  drilling rigs of the type that remain afloat and anchor during operations

drilling.

  Recent situations, catastrophic or

  who approached the disaster, questioned the security of

  certain designs accepted so far for

  the realization of semi-drilling rigs

  submersible. However, as drilling rigs have a very functional shape, with pairs of thin columns that have only a small section

  in the flotation plan, the naval architects

  countered many difficulties in realizing

  they could improve the survival possibilities of the drill assemblies without reducing their function.

drilling.

  Two essential factors of profitability are to be taken into consideration for the design of semi-submersible drill assemblies, the variable load at the bridge (CVP which is the mass that can be supported, for example at about 1.5 m above the racks and the Weather Window (FM, which is the average number of days per year that the ensemble can drill, since wave-induced motion is sufficiently small). There is a contradiction between obtaining high values for the CVP load and the FM window since the CVP load is limited by the stability criteria, and a large section in the flotation plane, although it leads to stability.

  satisfactory, is markedly detrimental to the characteristics

displacement characteristics.

  As a result, the drill assemblies are made so that they drill with a tie

  drilling water under moderate weather conditions.

  and allow a reduction of draft and load on the overhead deck in a significant manner and in a reasonably short period of time so that they can withstand severe storm conditions. The operations of this procedure require the evacuation of a sufficient quantity of ballast and consumables

overboard.

  Accordingly, a significant refinement of semisubmersible realizations could be achieved if: (a) the CVP load could be increased without damaging the FM window, (b) the need for ballast and consumables disposal to change the FM window, mode of operation between the drilling draft and the

  draft, was reduced or eliminated.

  One or more of the following modifications are normally used to increase the CVP load of the semi-submersible drill assemblies: the use of additional columns, the use of caissons mounted on the connections between the columns and the pontoons so that the transport stability is improved, the arrangement of caissons on the columns at the draft

  work, and the increased displacement of the pontoons.

  The addition of columns and / or caissons to draft draft columns has a deleterious effect on the forces applied to the installation by the waves and currents during operation, and it can

  significantly increase construction costs.

  Increasing the displacement of the pontoons does not affect overall stability when it does not cause a corresponding increase in the amount of ballast and therefore it does not constitute an effective device for improving the stability; in addition, this solution can be expensive. Boxes mounted on the connections between the columns and the pontoons, although important for the transport condition, have no influence on the stability for the tie rods

drilling water and survival.

  The present invention relates to an increase in the survivability of semi-submersible installations such as drilling assemblies, by using a variable geometrical configuration of the buoyancy volume, and therefore relates to a semi-submersible installation which comprises a bridge structure, several overflowing columns, pontoons mounted on at least one of the columns, a buoyancy modifier, mounted on at least one of the columns, and a device for moving the modifying element along the associated column and positioning the element near the plant transport flotation plane or at the position of the survival flotation plane, on the associated column. In a preferred embodiment of the invention,

  a semi-submersible drill assembly has a structure

  bridging or drilling rig, several columns which project downwards from the pontoons at the ends of at least some of the columns, elements

  like sleeves, intended to modify the configuration

  flotation members and mounted around at least some of the columns, the sleeve-shaped members having a substantially annular section and a generally cylindrical shape and terminating, at their lower ends, with sleeves having a reduced outer diameter which gives the sleeves a curved or narrowing end

  inside, and a device intended to move in trans-

  the sleeves, along the associated columns, and position them close to the transport waterline of the assembly and also to

  a position of the survival flotation plane.

  The thickness of the sleeve-shaped members, having an annular section, and their height above the cuffs are advantageously uniform and chosen so that they give an optimal increase in buoyancy volume in the position of the survival flotation plane and that they give a sufficient range of displacement relative to the surface of the water as a result

  the movement of the installation and / or waves.

  The condition of transport of the drilling assembly is improved by arranging the sleeve-shaped members just above the pontoons, where they cooperate with the pontoons to increase the buoyancy volume at the level of the plane. transport flotation. The curvature or inward narrowing of the sleeves at the ends of the sleeves reduces the effects of shocks to the inlet of the sleeve-shaped member in the water, in the transport flotation plane or in the flotation plane survival. The headlines can also be used in such a way that they

  hydrostatic rigidity of the whole.

  The assembly also relates to - an installation, such as a single cylindrical buoy, having a column device which can be immersed in water, an element for modifying the flotation configuration, mounted on the column device, and a device for moving the modifying element along the column device and positioning it at a first position of the flotation plane of the installation near the upper end of the column device and in a second position on the column device, remote

  from the first position and below it.

  Other features and advantages of the invention

  tion will emerge more clearly from the following description

  of exemplary embodiments and with reference to the accompanying drawings in which: Figure 1 is a schematic elevation of a semi-submersible drilling rig, showing how the geometric configuration of this floatation volume can be changed; Figure 1A is a detail of a portion of the right end of Figure 1 column in hard sea; Figure 2 is a detail of a sleeve-shaped member mounted on a column;

  FIG. 3 is a detailed plan view

  schematically sensing a translational movement device of the sleeve-shaped member on the column; Figure 4 is a detail similar to Figure 3 but showing another embodiment of buoyancy configuration modifying elements; and FIG. 5 is a diagram of a cylindrical buoy

  unique having a sleeve-shaped element.

  In the drawings, reference numeral 10 generally denotes a semi-submersible drilling assembly having a structure 12 forming a bridge or a drilling platform, with several columns 14 protruding thereunder. The columns may advantageously have a circular section, although they may have

  other configurations, for example a rectangular section

  gular. Pontoons 16 of conventional shape are fixed to the lower parts of the columns 14 of conventional type and

  the assembly described until now has a known structure.

  Reference 18 designates the waterline during transport, that is the plane of the water surface when the drill assembly is towed or propelled to the desired location and when it is at a draft transport water, the upper parts of the hulls of pontoons being just outside the water, the reference 20 designating the buoyancy plan, which in practice can also be considered as the survival flotation plan although this latter plan may be different. The distance between deck 12 and the surface of the water, in the state of survival, must not be reduced, given the relative movements of the installation and the waves, below certain limits when the installation must withstand a storm

or must not be damaged.

  Elements 22 for modifying the flotation configuration, in the form of sleeves, are mounted around the end columns 14 on slides 24 (see FIG. 3). The elements 22 in the form of sleeves have a substantially annular section and a general shape

  cylindrical. The thickness Ar of the annular section of the elements

  22 and the height H of the cylindrical portion of the elements are selected to provide the desired increase in volume or buoyancy at the drill assembly, at the survival flotation plane 20, when the elements 22 are blocked at the level of the survival flotation plane 20 as shown in FIG. 1. The height H is

  chosen so that it gives a sufficient range of

  relative to the surface of the water, as a result of movements of the installation and / or waves, as indicated by reference 30. The elements 22 terminate, at their lower ends, with cuffs 32 which have a outer diameter which decreases and forms a surface which tapers inward, i.e., as shown, which have a frusto-conical configuration or an inwardly curved configuration. This end curved or narrowed to the inside of the sleeves reduces the effects of shocks when entering the element

in the form of a sleeve in water.

  As best shown in FIG. 3, the longitudinal slides 24 placed on the columns 14 cooperate with complementary devices in the form of rollers 38 placed in slots 40 formed between segments 42 of the annular wall of the element 22. A device translation movement, shown schematically in the form of a system 44 cable and pulleys, is also mounted in the slot 40 and is controlled by winches (not shown) mounted on the bridge 12 so that the element 22 can be moved along the column 14 between the lower transport position shown in Figure 1 and the upper position of the survival flotation plane. It should be noted that the element 22 can be blocked on the column in any one

  both positions and, in fact, in certain circumstances

  a device can lock the element on the column in positions other than those shown in Figure 1 so that the conditions

  may vary.

  Initially, when the drilling assembly is towed or propelled to the drilling site, the element 22 is locked on the column at the pontoons and, when a strong sea is encountered during towing, the element 22 increases the floatation volume of the structure by increasing the flotation at the pontoons. The configuration of the sleeve 32 ensures the absorption of the shock waves and / o2 other movements tending to immerse the pontoon, and H height of the element 22 improves the range of

stability during towing.

  When the installation has reached the location of fcrage, the pontoons are drowned in the amount necessary so that the drilling assembly is immersed to the drilling plane, the installation being then

  anchored. During this operation, element 22 remains

  roui: lé on the column, in its lower position,

and he is thus under water.

  During drilling, the relatively thin columns 14 of radius r (FIG. 2) give the minimum surface in the flotation plane at the drilling rig

  and wave-induced movements under conditions of

  acceptable weather conditions of drilling, are therefore minirals. However, after receiving a storm warning, the element 22 is unlocked from its lower position on the column and is moved to the survival flotation plane in which it is again locked. Under these conditions, it increases the section of the column in the plane. of flotation and modifies the vertical distribution of the flotation volume. As the thickness

  of the ring Lr and the height H of the elements 22 have been chosen.

  so that they give the necessary increase in Volume and the height necessary for the collection of significant relative movements, and as the movements of the installation are no longer to be considered, the drilling set can spread the sea , presenting

  roll and pitch with the waves so that the structure

  Drill rig 12 remains at a safe distance above the ridge 28 of the waves. After the calming of the storm, the elements 44 to cable and pulleys can be manipulated so that the elements 22 are lowered along the slides 24 and brought back

  in the submerged position, the lower position represents

  felt in Figure 1 for example. Element 22 is

  then stuck in this position and drilling may

  take, column 24 again having its weak section

  in the flotation plane, reducing

  evoked by the waves, this reduction being necessary

drilling.

  Although the elements 22 mounted on each of the columns carrying pontoons have been shown, it should be noted that, under certain conditions, the elements 22 may not be placed on all the columns or that special columns may be provided so that they carry elements 22. It should also be noted that, although the elements 22 have been represented with a shape

  generally cylindrical, they may have other configura-

  such as toroidal, or they can be segmented so that they are placed only on a part of the

  circumference of the column as represented by the reference

  22a in FIG. 4. These segments 22a can be advantageously mounted on a circular carriage 46 which cooperates with the slides 24 (in the same manner as for the configuration described with reference to FIG. 3), so that the segment 22a is maintained. positively in position. However, it must be made to provide good security against perforation and in fact, it is preferable that the elements 22 can be filled with concrete or other suitable substance, avoiding perforation and flooding, so that in case of breakage of the casing of the element 22, the water does not enter the empty interior and can not penetrate freely

  inside nor come out freely.

  It is also possible for several elements 22 to be replaced by a single element placed on a central column in which the wellbore passes.

  and obviously any displacement device in transla-

  of the element, any guide device or any suitably shaped locking device may be used. Figure 5 shows a different application

  of the invention. In this case, a cylindrical buoy 47

  carries a device 14 comprising only one column.

  No pontoon is attached to the column. An element intended to modify the flotation configuration, for example a sleeve-shaped element 22, is mounted so that it can move in translation on the column 14 and is movable so that it can occupy a first position in the flotation plane of the installation, as shown on the right in FIG. 5, and a second position in the lower part of column 14, as shown on the left in FIG. 5. The element 22 is still blocked at the lower end of the buoy, when the movements caused by the waves must be minimal. When the distance between the upper end of the buoy and the surface of the water must be maximum, the element 22 is locked in the flotation plane.

Claims (13)

  1. Semi-submersible installation, characterized in that it comprises a structure forming a bridge (12), several columns (14) protruding under the structure, a pontoon (16) at least, mounted on at least one of the columns , an element (22) modifying the flotation configuration, mounted on at least one of the columns, and a device   (44) for translational movement of the modifying element   float configuration along the associated column and position the element close to the facility   survival flotation plan, on the associated column.   2. Installation according to claim 1, characterized   in that the elements (22) which modify the configuration   Flotation ration are mounted on several columns (14).   3. Installation according to claim 2, characterized   in at least one of the modifying elements (22)   the flotation configuration has a generally cylindrical shape   of substantially annular section and is mounted so that it at least partially surrounds the associated column.   4. Installation according to claim 2, characterized   in that the elements (22) intended to modify the   flotation configuration have a generally cylindrical shape   ring section and are mounted so that they at least partially surround the columns associated (14).   5. Semi-submersible drill assembly, characterized   characterized in that it comprises a structure (12) having a drilling bridge, a plurality of columns (14) projecting under   this structure, a pontoon (16) at least mounted at the ends   at least some of the columns, elements (22)   like sleeves and intended to modify the configuration   flotation ration, these elements being mounted around at least some of the columns, and having a substantially annular section and a generally cylindrical shape, the elements terminating, at their lower ends, with cuffs (32) having a reduced outer diameter   so that they form a curved end or shrink   inwardly, on the sleeve, and a device (44) for translational movement of the sleeve-like members along the associated columns, for positioning them near the transport plane of flotation.   of the whole as well as the position of a flow plan- survival season.   6. The assembly of claim 5, characterized in that the thickness of the members (22) in the form of sleeves having an annular section and their height above cuffs (32) are uniform.   7. The assembly of claim 5, characterized in that the cuffs (32) have a general shape inverted frustoconical.   8. Assembly according to claim 5, characterized in that all the columns (14) terminate at pontoons (16), and members (22) similar to sleeves   are mounted on all the columns (14).   9. An assembly according to claim 8, characterized in that, in the position close to the transport flotation plane, the members (22) similar to sleeves.   are placed just above the pontoon (16).   10. An assembly according to claim 8, characterized in that each of the columns (14) has several longitudinal slides (24), and the members similar to sleeves (22) have complementary devices (38) intended to cooperate with the scenes.   11. An assembly according to claim 9, characterized   in that each column (14) has several longitudinal slots   (24) and the sleeve-like elements (22) have complementary devices (38) for co-operating with the scenes.   12. Installation according to claim 2, characterized   characterized in that at least one of the flotation configuration modifying elements (22) has a partially cylindrical shape of segmented annular section, and is mounted so that it partially surrounds the associated column (14). 13. Installation, characterized in that it comprises a device (14) to column which can be immersed in water, an element (22) for modifying the configuration of flotation, mounted on the column device , and a device (44) for translational movement of the modifying element along the column device and for positioning said element at a first position of the installation flotation plane near the upper end of the column device and in a second position on the column device, remotely   from the first position and below it.