WO2014057507A1

WO2014057507A1 - Drilling vessel

Info

Publication number: WO2014057507A1
Application number: PCT/IT2012/000311
Authority: WO
Inventors: Giuseppe CORONELLA
Original assignee: Fincantieri Cantieri Navali Italiani S.P.A.
Priority date: 2012-10-09
Filing date: 2012-10-09
Publication date: 2014-04-17

Abstract

The present invention relates to a drilling vessel, comprising: - at least one floating structure 10, provided with at least one operating deck 11; - at least one guiding tube 20 which in operating conditions extends from the vessel to the sea floor and inside which a drilling bit and a plurality of drilling strings are lowered interconnected to each other and to the bit; and- a drilling plant (30,40,50,60) which is installed on board ship on the operating deck 11 and is used to control the drilling bit and drill strings A. The drilling plant installed on board ship (30, 40, 50, 60) extends substantially parallel to the operating deck 11. The present invention also relates to an off-shore drilling method.

Description

DESCRIPTION

DRILLING VESSEL

FIELD OF APPLICATION

[0001] The present invention relates to a vessel for drilling, in particular for localising, exploring and exploiting fields of hydrocarbons or other energy and mineral resources. The drilling vessel which the present invention relates to is intended, in particular for operating in deep waters (over 450m) and ultra deep waters (over 1, 500m)

STATE OF THE ART

[0002] Over the last decade the activities of localising and exploiting hydrocarbon fields in deep waters and ultra deep waters have received a strong impulse and a new generation of vessels has appeared on the market suitable for satisfying the most stringent and specific requisites required.

[0003] Drilling plants have also adapted to the new needs, while continuing however to follow traditional configurations and conceptions.

[0004] The current configurations of drilling plants and systems, in the offshore field installed on floating means, such as drill ships and semi-submersible drilling rigs (SSDR) , follow those of land systems.

[0005] All the plants are devised for operations which take place "vertically" where the drilling tower (Derrick) is the main and characterising element of these units.

[0006] A drilling vessel of the single-hull type is schematised in Figure 1. A central well A (in the jargon "moon pool") is made in the hull, which well extends from the main deck as far as the bottom and through which there is direct access to the water. On the deck of the ship, above the "moon pool", a scaffolding B, in the jargon "substructure", is installed, which supports the so-called drill floor C and on which the Derrick D rests. The drilling tower D supports the drilling point (in jargon drilling bit, and the drill strings by means of the hoisting devices which comprise a draw works E, a crown block F, positioned on the top of the tower, and a travelling block G. The travelling block G supports a top drive H by means of a hook which gives the strings and the bit the rotation needed for drilling. A guiding tube I (known in jargon as riser) is connected to the drill floor C inside which the drilling bit and strings are made to pass. The guiding tube I extends from the drill floor as far as the sea floor, where a blow out preventer (BOP) has been installed.

[0007] Operatively, the hoisting devices accompany the descent of the drilling bit and strings connected to it. Once a "length" of strings N (i.e. a plurality of preassembled strings, known as "drill pipe stand" in the jargon) has been completely lowered, as far as the level of the drill floor, or inserted in the riser, it is disconnected from the top drive and momentarily supported by the rotary table L by means of slips. The top drive is then raised as far as the top of the derrick so as to permit the positioning of a new^' drill pipe stand M.

[0008] A drilling vessel of the traditional type having the general characteristics described above has a series of limits or drawbacks related to the characteristics of the drilling plant used on board.

[0009] The presence of the moon pool penalises the ship in terms of maximum speed, of transit. In fact, the moon pool significantly influences the hydrodynamic behaviour of the ship. Especially in the case of resonance arising, growing pendulations of the level of the water inside the moon pool, the resistance to motion proves considerably increased and the speed of the ship will therefore be inferior .

[0010] The presence of the Derrick and therefore of significant ^' weight placed high up in relation to the deck influences the stability of the vessel, imposing suitable dimensioning with an increase in costs during the const uction phase . - -

[0011] From an operative point of view, on account of the vertical extension of the plant the drilling activities are significantly influenced by the rolling and heaving movements of the vessel. This reduces the operativity of the ship depending on sea conditions.

[0012] The storage and movement of the drill pipe stands is strictly connected to the dimensions of the Derrick. The height of the Derrick defines, in fact, the maximum extension in length of the "lengths" of strings and poses a limit to the operative yield of the vessel.

PRESENTATION OF THE INVENTION

[0013] Consequently, the purpose of the present invention is to eliminate or at least attenuate the drawbacks of the prior art mentioned above, by making available a drilling vessel, which offers greater operativity during the drilling phase.

[0014] A further purpose of the present invention is to make available a drilling vessel, which can travel at higher speeds .

[0015] A further purpose of the present invention is to make available a drilling vessel, which makes the drilling operations less subject to rolling and heaving movements .

[0016] A further purpose of the present invention is to make available a drilling vessel, which is not more expensive than current drilling vessels. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The technical characteristics of the invention, according to the aforesaid purposes, can be seen clearly from the contents of the following claims and the advantages of the same will be more clearly comprehensible from the detailed description below, made with reference to the attached drawings, showing one or more embodiments by way of non-limiting examples, wherei :

[0018] - Figure 1 shows a schematised view of a side of a drilling vessel of the traditional type;

[0019] - Figure 2 shows a schematised view of a side of a drilling vessel according to the invention;

[0020] - Figure 3 shows a view from above of the drilling vessel illustrated in figure 2; and

[0021] - Figure 4 shows a schematised view of the vessel illustrated in figures 2 and 3 in operating conditions, with the riser connected to the BOP installed on the sea floor.

DETAILED DESCRIPTION

[0022] With reference to the appended drawings, reference numeral

globally denotes a drilling vessel according to the invention.

[0023] Here and henceforth in the description and the claims, the term "vessel" is understood to include in general any . marine vessel provided with propulsion systems and its own steering devices. Both single-hull vessels having a main direction of longitudinal extension with stern and bow (that is ships understood in the general sense of the word) , and semisubmersible platforms are therefore included in particular.

[0024] Here and henceforth in the description and the claims, reference will be made in addition to the drilling vessel 1 in conditions of use. References to an upper or lower position or horizontal or vertical direction should therefore be understood in this sense.

[0025] According to a general embodiment of the invention, the drilling vessel 1 comprises:

[0026] - at least one floating structure 10, provided with at least one operating deck 11;

[0027] - at least one guiding tube 20 which in operating^' conditions extends from the vessel to the sea floor, and inside which a drilling bit and a plurality of drilling strings are lowered, connected to each other and to the bit; and

[0028] - a drilling plant 30,40,50,60 which is installed on board ship on the operating deck 11 and is used to control the drilling bit and the. drill strings A.

[0029] As shown in Figure 4, in operating conditions the guiding tube T extends from the vessel as far as the sea floor, where .it is connected to a Blow Out Preventer (BOP) safety appliance. In general the structure and characteristics of the guiding tube, the BOP, the drilling bit and the drill strings are known to a person skilled in the art. A detailed description of such components will not therefore be provided.

[0030] According to the invention, the drilling plant 30,40,50,60 installed on board ship extends substantially parallel to the aforesaid at least one operating deck 11 of the vessel 1.

[0031] The expression "drilling plant installed on board ship" refers to the parts of the plant which are situated on board and responsible for the operative control of the bit and of the drill strings. The guiding tube is in any case excluded from the definition · of "drilling plant installed on board ship", including the upper part situated on board ship. The aforesaid definition therefore excludes the parts of the plant which in operating conditions (both in the preparatory phases and the fully operative drilling phases) are instead outside the vessel such as for example the guiding tube, the BOP, the drilling bit and the drill strings interconnected to each other and to the bit, already lowered toward the sea floor.

[0032] According to the invention, unlike traditional type drilling vessels the control operations of the drill strings on board ship no longer take place "vertically", that is to say in a direction substantially orthogonal to the operating deck of the vessel, but " horizontally", that is to say in a direction substantially parallel to the operating deck of the vessel.

[0033] In traditional type drilling vessels the drilling plant on board ship extends substantially in a vertical direction. Such traditional type vessels are in fact characterised by the fact of being provided with a drilling tower- (Derrick) which extends in height for at least 60 metres from the main deck of the vessel and which supports the devices needed to support the drill strings vertically.

[0034] Conversely, ,in the drilling vessel according to the invention, as described further below, the drill strings A are controlled substantially parallel to the operating deck 11 of the vessel, at least as regards the insertion steps into the guiding tube 20. The drilling plant on board ship, by extending substantially parallel to the operating surface 11, i.e. substantially horizontally, no longer needs to be provided with either the substructure or the drilling tower (Derrick) .

[0035] The expression "extension substantially parallel to the operating deck" referred to the drilling plant installed on . board ship is taken to mean that the drilling plant installed on board ship extends mainly in a direction parallel to the deck, as opposed to the prior art wherein the drilling plant extends mainly in an orthogonal direction. This does not however exclude that in the drilling vessel 1 according to the invention some parts of the drilling plant installed on board may extend at least partially, and in any case not mainly, in a vertical direction.

[0036] The fact that the drilling plant installed on board ship extends parallel to the operating deck brings several advantages.

[0037] In the first place, as said, the arrangement parallel to the operating deck leads to the complete elimination both of the substructure and the drilling tower (Derrick) . The consequent reduction of weight situated "high up" leads to a significant increase in the stability of the vessel.

[0038] In the second place, the horizontal extension of the plant makes for a significant increase in the operativity of the vessel. In . fact, thanks to the horizontal arrangement the plant as a whole is brought closer to the barycentre of the vessel. This makes the plant and the drilling activities much less influenced by th rolling and heaving movements of the vessel, to the advantage of the operativity of the vessel.

[0039] In addition, the arrangement of the drilling plant parallel to the operating deck makes the storage and movement of the drill pipe stands much simpler and faster. These operations are in fact no longer bound by the dimensional limits imposed by vertical extension constraints of the drilling tower (Derrick) . .The extension parallel to the deck makes it possible to exploit, for example, the dimensions of the floating structure, in particular the longitudinal dimension in the case of single-hull vessels. It is therefore possible to increase the maximum extension in length of the "lengths" of strings movable as a unit with relevant benefits in terms of increased operativity. In any case, the advantages related to the passage from a vertical movement to a horizontal movement of the strings are evident .

[0040] Lastly, the arrangement of the drilling plant parallel to the operating deck makes the dimensioning of the supporting means -of the drilling bit and drill strings for the operating phases of drilling less stringent, with benefits in terms of cost reductions of the plant .

[0041] According to the embodiment illustrated in Figures 2 and 3, the drilling plant ^'30, 40, 50, 60 installed on board ship extends substantially at the level of the operating deck 11. In other words, the plant has a reduced extension in height from the deck. The expression "substantially at the height of the deck" does not necessarily mean that the plant is adherent to the deck. Configurations are in fact included in which the drilling plant is partially raised from the deck by means of scaffolds or support structures.

[0042] An extension "substantially at the level of the operating deck" is the arrangement which permits the plant to be brought closer to the rotation axis of the vessel, thereby mostly reducing the influence of the rolling and heaving movements of the vessel, with advantage for operativity of the vessel.

[0043] According to the preferred embodiment illustrated in Figures 2 and .3, the vessel 1 comprises means 21 for the exit of the guiding tube 20 from the vessel substantially parallel to the operating deck 11. In other words, the guiding tube comes out of the vessel without crossing the bottom of the vessel, that is, without requiring the presence of a suitable crossing vertical well (moon pool) .

[0044] In particular, as illustrated in figures 2 and 3, the aforesaid means 21 for the exit of the guiding tube 20 from the vessel comprise a accompanying structure 22 (in the jargon "stinger") of the guiding tube in water. Such accompanying structure 22 supports the guiding tube 20 in abutment and extends at least partially outboard. Preferably, the accompanying structure 22 extends mainly outboard.

[0045] Advantageously the accompanying structure 22 may be provided with rolling means (such as rollers) to facilitate the movement of the guiding tube in the positioning and immersion steps in water.

[0046] Even more in particular, the aforesaid accompanying structure 22 may comprise a chute 23.

[0047] Operatively, once the guiding tube has been accompanied outboard with a position substantially parallel to the operating deck (i.e. substantially horizontal), thanks to its elasticity the guiding tube curves under its own weight to position itself substantially vertically as far as vertically joining at the "BOP" (Blow Out Preventer) , as shown in figures 2 and 4.

[0048] Advantageously, once positioned the guiding tube 20 (riser) therefore assumes a substantially upside down "J" shape, which comprises an upper end portion positioned on board substantially parallel to the operating deck 11 of the vessel. The guiding tube therefore presents- a curved^' part which then continues in the remaining (main in length) part . of the guiding tube which is arranged substantially vertically (disregarding the undulations induced by marine currents or by the movements of the drill strings) .

[0049] Thanks to this upside-down "J" conformation the guiding tube 20 will favourably succeed in absorbing the heaving movements, benefitting from the elasticity of shape of this configuration, with advantage for the operativity of the vess.el.

[0050] From an operating point of view, the deeper the sea floor the more the effects of the passage of the guiding tube from a horizontal position to a vertical position are attenuated. For such reasons the drilling vessel according to the present invention is intended, in particular, for operating in deep (over 450m) and ultra- deep (over 1,500m ) waters.

[0051] The expression "substantially parallel to the operating deck" is understood to also include configurations of non-perfect parallelism to the deck. Such substantially parallel position is to be seen in contraposition to the traditional configuration in which the guiding tube crosses the vessel instead in a substantially orthogonal direction.

[0052] Preferably, the means 21 for the exit of the guiding tube 20 from the vessel permit the guiding tube to exit substantially .at the level of the operating deck 11.

[0053] The expression "substantially at the level of the operating ^■ deck" is understood to also include configurations in which the guiding tube does not exit at the perfectly same height as the operating deck. Situations may in fact arise in which the guiding tube is placed higher than the level of the deck or lower than such level.

[0054] Thanks to the fact that the guiding tube is made to come out parallel to the deck, the drilling vessel 1 according to the invention does not need to be provided with a crossing well (moon pool) . The absence of the vertical well (moon pool) eliminates all the drawbacks related to disturbance of the hydrodynamic behaviour of the vessel. This enables the vessel 1 to have considerably higher maximum transit speeds than those of traditional vessels provided with crossing well (moon pool) .

[0055] Embodiments may however be envisaged (not shown in the appended drawings) in which the drilling vessel 1 has a drilling plant installed on board ship which extends substantially parallel to the operating deck and which is provided with a crossing well (moon pool) for the transit of the guiding tube. In particular the moon pool may be positioned at bow or stern. In this case the drilling vessel 1 has all the advantages described above, related to the horizontal position of the drilling plant, except for the increase in maximum transit speed.

[0056] According to a preferred embodiment solution, the drilling plant installed on board comprises means 30 of guiding one or more drill strings A parallel to the operating deck 11 between a loading position, in which the aforesaid one or more strings A are positioned outside the guiding tube, and an . insertion position, wherein the aforesaid one or more strings A are inserted into the guiding tube 20. Preferably the drill strings are loaded for insertion in the guiding tube as lengths of single strings interconnected to each other.

[0057] In particular the drilling plant installed on board comprises means 40 of supporting the bit and the drill strings A in their downward movement inside the guiding tube 20. The function of such supporting means is similar to those of the hoisting means in traditional vessels: 1) to prevent all the weight of the drill strings from weighing on the drilling bit below; 2) to permit a controlled descent of the bit and of the strings.

[0058] Such supporting means 40 are connected in a separable manner to the last drill string made to progressively enter into the guiding tube 20 in order of time, dragged towards the sea floor by the bit and by the strings already inserted and connected to it. Such supporting means 40 are at least partially mobile in relation to the operating deck 11 to accompany the drill strings in the aforesaid movement parallel to the operating deck 11 between the aforesaid loading position and the aforesaid insertion position, in particular on the guide means 30.

[0059] Advantageously, the drilling plant comprises means 50 for activating in rotation the last drill string connected to the supporting means 40. Such last string transmits the movement of rotation to the string and to the bit connected to it. The aforesaid activating means 50 are connected to the supporting means and are kinematically connectable to the last string in a separable manner.

[0060] Advantageously, the drilling plant installed on board comprises means 60 for keeping suspended (i.e. retaining without a downward movement) - and if necessary in slow rotation - the bit and the battery of drill strings, when the last string has arrived at the insertion position and is disconnected from the supporting means and from the activating means to permit the loading of one or more new strings .

[0061] In the appended schematic drawings 2 and 3,^' the supporting means comprise a draw works 41, a crown block 42 and a travelling block 43 positioned horizontally. The activating means of the rotation (top drive) 50 are kinematically connected to the travelling block. The supporting means may however be of any type suitable for the purpose. In particular the supporting means may comprise, as well as a draw works mechanism (for example as described above) , alternatively or in conjunction with, a rack mechanism and/or or piston mechanism.

[0062] Operatively, the supporting means 40 accompany the descent of the drilling bit and of the strings connected to it. Once a drill pipe stand has been completely inserted in the guiding tube, it is disconnected from the top drive means 50. The supporting means 40 and the top drive means 50 (connected thereto) are distanced so as to permit the positioning of a new drill pipe stand. During this step, the battery of strings just inserted in the guiding tube is temporarily connected to the means 60 responsible for keeping it supported by means of slips and if necessary in slow rotation.

[0063] According to the preferred embodiment illustrated in the appended Figures, the floating structure 10 of the vessel 1 is a single-hull which extends mainly in a longitudinal direction X.

[0064] Advantageously, the drilling plant 30,40, 50, 60 installed on board ship extends mainly in the aforesaid longitudinal direction X. This way the maximum extension ϊη· length of the drill pipe stands moveable as a unit is determined by the longitudinal dimension of the vessel i.e. generally the dimension of maximum extension. This is to the benefit of the operativity of the drilling vessel 1.

[0065] Preferably, the accompanying structure 22 of the guiding tube 20 is positioned at one longitudinal end of such single-hull vessel, preferably at the stern, even though its positioning at bow may also be envisaged.

[0066] Preferably, the operating deck 11 is positioned above the- water line of the vessel 1. With this configuration, the construction complications related to hydraulic sealing expedients for the exit of the guiding tube under the water line are avoided.

[0067] As already said embodiments may be envisaged (not shown in the appended drawings) in which the drilling vessel is not of the single-hull type but is a semi- submersible platform with propulsion systems and steering devices of its own.

[0068] Advantageously, due to the fact that the drilling plant installed on board ship extends parallel to the operating deck, the drilling vessel 1 may be provided with a partial or total roofing structure of the drilling plant installed on board. Such roofing structure (not shown in the appended drawings) may be made to offer the operators shelter from bad weather, for example creating a protected environment around the drilling plant or at least in the areas where the operators are mainly stationed. This is particularly useful and advantageous in the case of use of the drilling vessel in particularly cold climes or during the winter period. The use of a roofing structure of this type is not possible in drilling vessels of the traditional type due to the vertical extension . of the drilling plant installed on board.

[0069] The present invention also relates to an off-shore drilling method.

[0070] Such drilling method comprises the following operating steps:

[0071] - predisposing (a) a drilling vessel 1 according to the invention as described above;

[0072] - unrolling (b) a guiding tube 20 from the vessel 1 as far as the sea floor;

[0073] - inserting (c) a drilling bit into the guiding tube 20 ; and

[0074] - progressively inserting (d) inside the guiding tube 20 a plurality of drill strings A interconnected to each other and to the bit to accompany the- descent of such bit and transmit to such bit a rotation movement needed for drilling.

[0075] In the aforesaid progressive insertion step (d) the drill strings are progressively inserted into the guiding tube 20 moving them substantially parallel to the operating deck 11 of the vessel 1 by means of the aforesaid means of support 40.

[0076] Advantageously, in the aforesaid step (d) of progressively inserting the drill strings the · supporting means 40 move with reciprocated motion to accompany the drill strings under insertion in their movement parallel to the operating deck 11 between the aforesaid loading position and the aforesaid insertion position.

[0077] In particular, the reciprocated motion of the supporting means 40 is parallel to the operating deck 11 of the vessel 1.

[0078] Advantageously, as recalled above, at the end of step (b) of unrolling the guiding tube 20 from the vessel to the sea floor, the guiding tube 20 assumes a substantially upside down "J" shape which comprise an upper end portion positioned on board substantially parallel to the operating deck 11 of the vessel. The guiding tube therefore presents a curved part which then continues in the remaining (main in length) part of the guiding tube which is positioned substantially vertically (disregarding the undulations induced by marine currents or by the movements of the drill strings) .

[0079] Preferably, in the step (b) of unrolling the guiding tube 20 from the vessel to the sea floor, the guiding tube 20 is made to come out of the vessel substantially parallel to the operating deck 11, without crossing the bottom of the vessel vertically, i.e. without the need to use a crossing vertical well (moon pool) .

[0080] The invention permits many advantages to be obtained, some of which already pointed out above.

[0081] The position of the drilling plant parallel to the operating deck leads to the complete elimination both of the substructure and the drilling tower (Derrick) . The consequent reduction of weight situated "high up" leads to a significant increase in the stability of the vessel.

[0082] The horizontal extension of the plant makes for a significant increase in the operativity of the vessel. In fact, thanks to the aforesaid horizontal arrangement the plant as a whole is brought closer to the rotation axis of the vessel and this makes the plant and the drilling activities much less subject to influence by the rolling movements. In addition, the upside-down "J" conformation of the guiding tube 20 (riser) will favourably succeed in absorbing the heaving movements, benefitting from the elasticity of shape of this configuration, with advantage^" for the operativity of the vessel. [0083] The horizontal position of the drilling plant also enormously simplifies the storage and movement of the drill pipe stands. These operations are in fact no longer conditioned by the dimensional limits imposed by vertical extension constraints of the drilling tower. The extension parallel to the deck makes it possible to exploit, instead, the dimensions of the floating structure, and in particular the longitudinal dimension which in the case of a single-hull vessel is the maximum dimension available. It is therefore possible to increase the maximum extension in length of the drill pipe stands movable as a unit, with relevant benefits in terms of increased operativity of the drilling vessel.

[0084] The horizontal position of the drilling plant also makes the dimensioning of the supporting means of the bit and drill strings less stringent.

[0085] Thanks to the fact that the guiding tube is made to exit parallel to the deck, the drilling vessel 1 according to the invention may not be provided with a moon pool. This enables the vessel 1 to have considerably higher maximum transit speeds than those of traditional vessels provided, instead, with crossing well (moon pool ) .

[0086] The drilling vessel 1 according to the invention does not require the realisation of particular structures compared to . those of traditional vessels. On the contrary, the vessel 1 makes it possible to considerably simplify the support structures. Not only therefore is it expected that the vessel 1 according to the invention should be no more expensive than current drilling vessels, but it may even be more economical.

[0087] The invention thus conceived thereby achieves the intended objectives.

[0088] Obviously, its practical embodiments may assume forms and configurations different from those described while remaining within the sphere of protection of the invention.

[0089] Furthermore, all the parts may be replaced with technically equivalent parts and the dimensions, shapes and materials used may be varied as required.

Claims

1. Drilling vessel, comprising:

- at least one floating structure (10), provided with at least one operating deck (11);

- at least one guiding tube (20) which in operating conditions extends from the vessel to the sea floor and inside which a drilling bit and a plurality of drilling strings are lowered interconnected, to each other and to the bit; and

- a drilling plant (30,40,50,60) which is installed on board ship on said operating deck (11) and is used to control said drilling bit and said drill strings (A) , characterised by the fact that the drilling plant installed on board ship (30,40,50,60) extends substantially parallel to said operating deck (11).

2. Vessel according to claim 1, wherein the drilling plant (30, 40, 50, 60) installed on board extends substantially at the level of said operating deck (11).

3. Vessel according to claim 1 or 2, comprising means (21) for the exit of the guiding tube (20) from the vessel substantially parallel to said operating deck (11) -

4. Vessel according to one or more of the previous claims, comprising means (21) for the exit of the guiding tube (20) from the vessel, substantially at the level of said operating deck (11) .

5. Vessel according ^'to claim 3 or 4, wherein the means (21) for the exit of the guiding tube (20) from the vessel comprise an accompanying structure (22) of the guiding tube in water, said structure (22) supporting in abutment the guiding tube (20) and extending at least partially outboard.

6. Vessel according to claim 5, wherein said accompanying structure (22) comprises a chute (23) .

7. Vessel according to one or more of the previous claims, wherein the drilling plant installed on board comprises means (30) of guiding one or more drill strings (A) parallel to the operating deck (11) between a loading position, in which one or more strings (A) are positioned outside the guiding tube, and an insertion position, wherein said one or more strings (A) are inserted inside the guiding tube (20) .

8. Vessel according to claim 7, wherein the drilling plant installed on board comprises means (40) of supporting the bit and the drill strings (A) in their downward movement inside the guiding tube (20), said means being connected in a separable manner to the last drill string made to progressively enter inside the guiding tube (20) in order of time, dragged towards the sea floor by the bit and by the strings already inserted and connected to .it, said supporting means (40) being at least partially mobile in relation to the operating deck (11) to accompany the drill strings in said movement parallel to the operating deck (11) between said loading position and said insertion position on said guide means (30) .

9. Vessel according to claim 8, wherein the drilling plant comprises means (50) for activating in rotation the last drill string connected to the supporting means (40) , said last string transmitting the rotation movement to the strings and to the bit connected to it, said activating means (50) being connected to said supporting means and being kinematically connectable to the last string in a separable manner.

10. Vessel according to claim, 9, wherein the drilling plant installed on board comprises means (60) for keeping the battery of strings and bit suspended, when the last string has arrived at the insertion position and is disconnected from the supporting means and from the activating means to permit the loading of one or more new strings .

11. Vessel according to claim 8, wherein the supporting means (40) comprise a draw, works mechanism, a rack mechanism and/or piston mechanism

12. Vessel according to one or more of the previous claims, wherein the floating structure (10) is a single- hull which extends mainly in a longitudinal direction (X) .

13. Vessel according to claim 12, wherein the drilling plant installed on board ship (30, 40, 50, 60) extends mainly in said longitudinal direction (X) .

14. Vessel according to claim 5 or 6, and claim 12 or 13, wherein the accompanying structure (22) of the guiding tube is positioned at a longitudinal end of such single-hull vessel.

15. Vessel according to one or more of the previous claims, wherein the operating deck (11) is positioned above the water line of the vessel (1) .

16. .Vessel according to one or more of the previous claims, provided with a roofing structure of the drilling plant installed on board.

17. Off-shore drilling method comprising the following steps:

- predisposing (a) a drilling vessel (1) according to one or more of the previous claims ;

- unrolling (b) a guiding tube (20) from the vessel (1) as far as the sea floor;

- inserting (c) a drilling bit inside the guiding tube (20) ;

- progressively inserting (d) inside the guiding tube (20) a plurality of drill strings (A) interconnected to each other and to the bit to accompany the descent movement of such bit and transmit to such bit a rotation movement needed for drilling;

in said progressive insertion step (d) the drill strings being progressively inserted inside the guiding tube (20) with a movement substantially parallel to the operating deck (11) of the vessel (1) by means of supporting means

(40).

18. Method according to claim 17, wherein in said step (d) of progressive insertion of the drill strings, the supporting means (40) move with reciprocated motion to accompany the drill strings under insertion in their movement parallel to the operating deck (11) between a loading position and an insertion position.

19. Method according to claim 18, wherein the reciprocated motion of the supporting means (40) is parallel to the operating deck (11) of the vessel (1).

20. Method according to one or more of the claims from 17 to 19, wherein, at the end of step (b) of unrolling the guiding tube (20) from the vessel to the sea floor, the guiding tube (20) assumes a substantially upside down "J" shape which comprises an upper end portion positioned on board substantially parallel to the operating deck (11) of the vessel.

21. Method according to one or more of the claims from 17 to 20, wherein in the step (b) of unrolling the guiding tube (20) from the vessel to the sea floor, the guiding tube (20) is made to come out of the vessel substantially parallel to the operating deck (11).