Abstract:
A system configured to execute an underwater well drilling program in the bed of a body of water has 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 to enable transfer of the jack-up over the body of water, even in very shallow water.

Description:
PRIORITY CLAIM 
     This application is a national stage application of PCT/IB2012/056692, filed on Nov. 23, 2012, which claims the benefit of and priority to Italian Patent Application No. MI2011A 002130, filed on Nov. 23, 2011, the entire contents of which are each incorporated by reference herein. 
     BACKGROUND 
     A jack-up is a mobile well-drilling marine unit, which can float and be towed to a designated 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 designated locations spread over a designated 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 meters, whereas the minimum drilling depth is normally about six meters, and depends on the jack-up&#39;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&#39;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. 
     SUMMARY 
     The present disclosure relates to a system configured to execute an underwater well drilling program in the bed of a body of water. 
     The system of various embodiments of the present disclosure comprises a jack-up of the type comprising a plurality of legs; a plurality of feet, each configured 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. 
     It is an advantage of the present disclosure to provide a system configured to execute an underwater well drilling program, configured to reduce certain of the drawbacks of certain of the known art. 
     According to the present disclosure, there is provided a system configured to execute 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. 
     In various embodiments of the present disclosure, the buoyancy of the jack-up can be altered, when necessary, to enable the jack-up to be set up and drill in relatively shallow, otherwise unreachable, water. 
     In one embodiment of the disclosure, the jack-up comprises a plurality of legs; and a plurality of feet, each located at the bottom end of a leg and configured 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. 
     In various embodiments of the present disclosure, the floating structure and the auxiliary floating unit are connected to increase buoyancy. 
     In one embodiment of the disclosure, the jack-up and the auxiliary floating unit are complementary in shape. 
     The complementary configuration of the auxiliary floating unit and the floating structure safeguards against improper connection resulting in unstable buoyancy. 
     In one embodiment of the disclosure, the auxiliary floating unit comprises two tanks configured to be located on opposite sides of the jack-up; and at least one connecting member configured to connect the tanks to each other, and configured to be located 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 one embodiment of the disclosure, the floating structure comprises a seat configured to at least partly house the auxiliary floating unit. 
     The auxiliary floating unit can thus be set in a designated position with respect to the jack-up, to improve stability of the floating assembly formed by the jack-up and the auxiliary floating unit. 
     In various embodiments, 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 designated position of the auxiliary floating unit with respect to the jack-up, in fact, enables a stable overall assembly to be achieved. 
     In one embodiment of the disclosure, the auxiliary floating unit comprises at least one controlled-flooding hydraulic system configured to adjust buoyancy. 
     Overall buoyancy can thus be adjusted as required. 
     It is a further advantage of the present disclosure to provide a method of drilling underwater wells in the bed of a body of water. 
     According to the present disclosure, 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. 
     Utilizing the auxiliary floating unit, the jack-up can be set up at otherwise unreachable shallow-water drilling stations. 
     In one 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 one 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 configured 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 one 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. 
     In various embodiments of the present disclosure, the seat can be predefined according to the overall buoyancy guaranteed by the jack-up and auxiliary floating unit as a whole. 
     In one embodiment of the method according to the present disclosure, 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 advantage of the present disclosure to increase the buoyancy of the jack-up. 
     According to the present disclosure, there is provided an auxiliary floating unit for a jack-up for underwater well drilling in the bed of a body of water; 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. 
     Additional features and advantages are described in, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A non-limiting embodiment of the present disclosure will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 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; 
         FIG. 2  shows a larger-scale plan view, with parts removed for clarity, of an auxiliary floating unit of the  FIG. 1  jack-up; 
         FIG. 3  shows a side view, with parts removed for clarity, of the  FIG. 2  auxiliary floating unit; 
         FIG. 4  shows a larger-scale side view, with parts removed for clarity, of the  FIG. 1  system in a second operating position; 
         FIG. 5  shows a plan view, with parts removed for clarity, of the  FIG. 4  system; and 
         FIG. 6  shows a side view, with parts removed for clarity, of the  FIG. 1  system in a further operating position. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the example embodiments of the present disclosure illustrated in  FIGS. 1 to 6 ,  FIG. 1  shows as a whole a system configured to drill 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  FIG. 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  ( FIG. 3 ). Each tank  13  is substantially defined by a hermetically sealed metal box, and is, in one embodiment, 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. In one embodiment, hydraulic system  15  is 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  ( FIG. 1 ). 
     In the  FIG. 2  example, each tank  13 , in horizontal section, is rhombus-shaped, and the opposite faces of tanks  13  converge. 
       FIG. 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 B 1  aligned vertically with the buoyancy application point of floating structure  6 ; and auxiliary floating unit  12  has a barycentre. B 2  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 B 1 , B 2  and respective buoyancy application points. In the attached drawings, barycentres B 1  and B 2  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 ( FIG. 1 ), floating structure  6  has seats  16  underneath configured to house 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 B 1  substantially aligned with barycentre B 2 . 
     In  FIG. 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 operating in particularly shallow water is necessary, auxiliary floating unit  12  is towed, by a tugboat (not shown), into position beneath floating structure  6 , and is maintained in a designated 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 ( FIG. 4 ) clearing, (i.e., not projecting from), the underside of floating structure  6 . 
     In the  FIG. 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  FIG. 6 . 
     With reference to  FIG. 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, floating structure  6  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 is configured to extend the operating range of the jack-up in a reasonably simple manner. 
     Clearly, changes may be made to the embodiment described of the present disclosure without, however, departing from the protective scope of the accompanying Claims. That is, various changes and modifications to the presently disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.