The present invention relates to a system for executing an underwater well drilling program in the bed of a body of water.

The system comprises a jack-up of the type comprising a plurality of legs; a plurality of feet, each designed to rest on the bed of the body of water; a floating structure connected to move selectively with respect to each leg to vary the configuration of the floating structure, with respect to the body of water, between a plurality of positions comprising a floating position, in which the legs substantially extend above the floating structure; at least one deck over the floating structure; and at least one drilling installation.

BACKGROUND ART

A jack-up is a mobile well-drilling marine unit, which can float and be towed to a given drilling station, where the legs are lowered to rest the feet on the bed of the body of water, or drive the feet in, when working on soft beds. The floating structure is then raised above the surface of the water, to above maximum wave and/or tide level; and, once the jack-up is supported firmly on the bed of the body of water, drilling of the bed is commenced.

A drilling program comprises drilling a plurality of wells in given locations spread over a given area. The operating range of the jack-up depends on its structural characteristics. More specifically, the maximum length of its legs depends on how the jack-up is constructed, and the maximum water depth jack-ups can operate in rarely exceeds a hundred metres, whereas the minimum drilling depth is normally about six metres, and depends on the jack-up' s tonnage and draught.

Drilling programs sometimes call for drilling with a jack-up in very shallow water, i.e. shallower than the minimum allowed by the jack-up' s tonnage and draught; in which case, other types of jack-ups must be used, thus greatly increasing overhead of the drilling program as a whole .

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a system for executing an underwater well drilling program, designed to reduce the drawbacks of the known art .

According to the present invention, there is provided a system for executing an underwater well drilling program in the bed of a body of water; the drilling system comprising a jack-up having a floating structure, and a drilling installation supported on the floating structure; and an auxiliary floating unit connectable selectively to the jack-up.

By means of the present invention, the buoyancy of the jack-up can be altered, when necessary, to allow the jack-up to be set up and drill in relatively shallow, otherwise unreachable, water.

In a preferred embodiment of the invention, the jack-up comprises a plurality of legs; and a plurality of feet, each located at the bottom end of a leg and designed to rest on the bed of a body of water; the floating structure being connected to move selectively with respect to each of the legs to vary the configuration of the jack-up between a first configuration, in which the legs only extend above the floating structure, and a plurality of second configurations, in which the legs support the floating structure on the bed of the body of water and above the surface of the body of water; the auxiliary floating unit being connectable selectively to the floating structure .

By means of the present invention, the floating structure and the auxiliary floating unit are connected to increase buoyancy.

In a preferred embodiment of the invention, the jack-up and the auxiliary floating unit are complementary in shape .

The complementary design of the auxiliary floating unit and the floating structure safeguards against improper connection resulting in unstable buoyancy.

In a preferred embodiment of the invention, the auxiliary floating unit comprises two tanks designed for location on opposite sides of the jack-up; and at least one connecting member for connecting the tanks to each other, and designed for location beneath the floating structure .

The connecting member provides for transmitting buoyancy to an extensive area of the floating structure, and so preventing concentrated local stress.

In a preferred embodiment of the invention, the floating structure comprises a seat for at least partly housing the auxiliary floating unit.

The auxiliary floating unit can thus be set in a given position with respect to the jack-up, to improve stability of the floating assembly formed by the jack-up and the auxiliary floating unit.

Preferably, the jack-up has a first barycentre substantially aligned vertically with the buoyancy application point of the floating structure; the auxiliary floating unit has a second barycentre substantially aligned vertically with its own buoyancy application point; and the jack-up and auxiliary- floating unit are connected, to form a stable buoyancy system, as a function of the positions of the first and second barycentre and the buoyancy application points.

Determining a given position of the auxiliary floating unit with respect to the jack-up, in fact, enables a stable overall assembly to be achieved.

In a preferred embodiment of the invention, the auxiliary floating unit comprises at least one controlled- flooding hydraulic system for adjusting buoyancy .

Overall buoyancy can thus be adjusted as required. It is a further object of the present invention to provide a method of drilling underwater wells in the bed of a body of water.

According to the present invention, there is provided a method of drilling underwater wells in the bed of a body of water; the method comprising the steps of connecting, on the body of water, an auxiliary floating unit to a jack-up having a floating structure, and a drilling installation supported by the floating structure; and transferring, on the body of water, the jack-up and the auxiliary floating unit from a first drilling station to a second drilling station.

By means of the auxiliary floating unit, the jack- up can be set up at otherwise unreachable shallow-water drilling stations.

In a preferred embodiment, the method comprises the step of disconnecting the auxiliary floating unit from the jack-up.

This prevents the auxiliary floating unit from impeding operation of the jack-up when drilling.

In a preferred embodiment of the method, the jack- up comprises a plurality of legs; and a plurality of feet, each located at the bottom end of a leg and designed to rest on the bed of the body of water; the floating structure being connected to move selectively with respect to each of the legs to vary the configuration of the jack-up between a first configuration, in which the legs only extend above the floating structure, and a plurality of second configurations, in which the legs support the floating structure on the bed of the body of water and above the surface of the body of water; and the step of connecting the jack-up to the auxiliary floating unit comprises positioning the auxiliary floating unit underneath the floating structure, and lowering the floating structure onto the auxiliary floating unit to connect the floating structure to the auxiliary floating unit.

This provides for connecting the jack-up and the auxiliary floating unit relatively easily.

In a preferred embodiment of the method, the floating structure comprises at least one seat; and the step of connecting the jack-up to the auxiliary floating unit comprises positioning part of the auxiliary floating unit inside the seat.

By means of the present invention, the seat can be predefined according to the overall buoyancy guaranteed by the jack-up and auxiliary floating unit as a whole.

In a preferred embodiment of the method according to the present invention, the step of disconnecting the auxiliary floating unit from the jack-up comprises raising the floating structure along the legs.

The structure of the jack-up thus also provides for simplifying disconnection.

It is a further object of the present invention to increase the buoyancy of the jack-up.

According to the present invention, there is provided an auxiliary floating unit for a jack-up for underwater well drilling in the bed of a body of wate ; the jack-up having a floating structure, and a drilling installation supported on the floating structure; and the auxiliary floating unit being connectable selectively to the floating structure.

BRIEF DESCRIPTION OF THE DRAWINGS

A non- limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which : Figure 1 shows a side view, with parts removed for clarity, of a system comprising a jack-up in a first operating position, and an auxiliary floating unit;

Figure 2 shows a larger-scale plan view, with parts removed for clarity, of an auxiliary floating unit of the Figure 1 jack-up;

Figure 3 shows a side view, with parts removed for clarity, of the Figure 2 auxiliary floating unit;

Figure 4 shows a larger-scale side view, with parts removed for clarity, of the Figure 1 system in a second operating position;

Figure 5 shows a plan view, with parts removed for clarity, of the Figure 4 system;

Figure 6 shows a side view, with parts removed for clarity, of the Figure 1 system in a further operating position.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows as a whole a system for drilling wells (not shown) in the bed 2 of a bed of water 3, and comprising a jack-up 1 resting on bed 2 of body of water 3.

Jack-up 1 comprises a plurality of - in the example shown, three - legs 4; a plurality of feet 5, each at the bottom end of a leg 4; a floating structure 6 connected in selectively adjustable manner to each leg 4; at least one deck 7 over floating structure 6; a drilling installation 8 located on one side of and, in the example shown, projecting with respect to deck 7; a deck 9 located on the opposite side of deck 7 to drilling installation 8, and which serves as a helipad; a plurality of cranes 10 on deck 7; miscellaneous equipment, engine rooms and living quarters (not shown) ; and actuating devices 11, each associated with a respective leg 4 to adjust the position of leg 4 with respect to floating structure 6, and which may be hydraulic jack systems, rack-and-pinion systems, etc.

In the attached drawings, legs 4 are defined by lattice structures, but may be defined by tubular or other structures. Each leg 4 extends along an axis A, and the floating structure extends along a plane perpendicular to axis A.

The system comprises an auxiliary floating unit 12 connectable selectively to jack-up 1 - more specifically, to floating structure 6 - to increase the buoyancy of jack-up 1. Auxiliary floating unit 12 is actually only connected to floating structure 6 when necessary to station jack-up 1 in particularly shallow water, shallower than the minimum allowed by floating structure 6.

As shown in Figure 2, auxiliary floating unit 12 comprises two tanks 13 connected by three connecting members 14 - in the example shown, straight beams - extending beneath tanks 13 (Figure 3) . Each tank 13 is substantially defined by a hermetically sealed metal box, and is preferably equipped with a hydraulic system 15 by which to feed and drain water in and out of tank 13 to adjust the buoyancy of tank 13 and auxiliary floating unit 12 as a whole. Hydraulic system 15 is preferably also controllable from jack-up 1. Tanks 13 are spaced apart by connecting members 14 to form a sort of cradle to house floating structure 6 (Figure 1) .

In the Figure 2 example, each tank 13, in horizontal section, is rhombus-shaped, and the opposite faces of tanks 13 converge.

Figure 5 shows auxiliary floating unit 12 connected to floating structure 6, which, in horizontal section, is substantially in the form of an irregular hexagon. The total mass of jack-up 1 without

auxiliary floating unit 12 has a barycentre Bl aligned vertically with the buoyancy application point of floating structure 6; and auxiliary floating unit 12 has a barycentre B2 aligned vertically with its own buoyancy application point. Floating structure 6 and auxiliary floating unit 12 are connected to ensure the stability of the system as a whole by taking into account the relative positions of the two barycentres Bl, B2 and respective buoyancy application points. In the attached drawings, barycentres Bl and B2 are shown aligned vertically. Floating structure 6 and auxiliary floating unit 12 are connected by positioning auxiliary floating unit 12 beneath floating structure 6, and lowering floating structure 6 onto connecting members 14, with tanks 13 on opposite sides of floating structure 6. For which purpose (Figure 1) , floating structure 6 has seats 16 underneath for housing connecting members 14.

In an alternative embodiment not shown, seats are formed along the sides of the floating structure, to at least partly house the auxiliary floating unit tanks.

Precise connection is thus ensured, with barycentre Bl substantially aligned with barycentre B2.

In Figure 1, floating structure 6 is not connected to auxiliary floating unit 12, and jack-up 1 is positioned resting on bed 2 of body of water 3. When it becomes necessary to operate in particularly shallow water, auxiliary floating unit 12 is towed, by a tugboat not shown, into position beneath floating structure 6, and is maintained in a given position with respect to jack-up 1. Next, floating structure 6 is lowered by actuating devices 11 to connect with auxiliary floating unit 12; and, once the two are connected, actuating devices 11 raise legs 4 into a position (Figure 4) clearing, i.e. not projecting from, the underside of floating structure 6.

In the Figure 4 configuration, the buoyancy application points of floating structure 6 and auxiliary floating unit 12 are substantially aligned vertically. And jack-up 1 and auxiliary floating unit 12 as a whole are towed, by tugboats not shown, over body of water 3 into shallow water, as shown in Figure 6.

With reference to Figure 6, on reaching the new drilling station of jack-up 1, floating structure 6 is raised into a safe position, and feet 5 of legs 4 are positioned resting on bed 2 of body of water 3. As floating structure 6 is raised, it disconnects automatically from auxiliary floating unit 12.

At this point, auxiliary floating unit 12 is removed by a tugboat not shown, and jack-up 1 is ready to commence drilling.

The system described provides for extending the operating range of the jack-up in a reasonably simple manner .

Clearly, changes may be made to the embodiment described of the present invention without, however, departing from the protective scope of the accompanying Claims .