Patent Abstract:
The invention relates to an ice worthy jack-up rig that may extend the drilling season in shallow water off shore Arctic or ice prone locations. The inventive rig would work like a conventional jack-up rig while in open water with the hull jacked up out of the water. However, in the event of ice conditions, the legs are held in place by cans embedded in the sea floor to resist lateral movement of the rig and the hull is lowered into the water into an ice defensive configuration. The hull is specifically shaped with an ice-bending surface to bend and break up ice that comes in contact with the hull while in the ice defensive configuration.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/405,497 filed Oct. 21, 2010, entitled “Ice Worthy Jack-Up Drilling Unit,” and is a continuation-in-part application which claims benefit under 35 USC §120 to U.S. application Ser. No. 13/277,791 filed Oct. 20, 2011, entitled “Ice Worthy Jack-Up Drilling Unit” both of which are incorporated herein in their entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to mobile offshore drilling units, often called “jack-up” drilling units or rigs that are used in shallow water, typically less than 400 feet, for drilling for hydrocarbons. 
       BACKGROUND OF THE INVENTION 
       [0004]    In the never-ending search for hydrocarbons, many oil and gas reservoirs have been discovered over the last one hundred and fifty years. Many technologies have been developed to find new reservoirs and resources and most areas of the world have been scoured looking for new discoveries. Few expect that any large, undiscovered resources remain to be found near populated areas and in places that would be easily accessed. Instead, new large reserves are being found in more challenging and difficult to reach areas. 
         [0005]    One promising area is in the offshore Arctic. However, the Arctic is remote and cold where ice on the water creates considerable challenges for prospecting for and producing hydrocarbons. Over the years, it has generally been regarded that six unprofitable wells must be drilled for every profitable well. If this is actually true, one must hope that the unprofitable wells will not be expensive to drill. However, in the Arctic, little, if anything, is inexpensive. 
         [0006]    Currently, in the shallow waters of cold weather places like the Arctic, a jack-up or mobile offshore drilling unit (MODU) can be used for about 45-90 days in the short, open-water summer season. Predicting when the drilling season starts and ends is a game of chance and many efforts are undertaken to determine when the jack-up may be safely towed to the drilling location and drilling may be started. Once started, there is considerable urgency to complete the well to avoid having to disconnect and retreat in the event of ice incursion before the well is complete. Even during the few weeks of open water, ice floes present a significant hazard to jack-up drilling rigs where the drilling rig is on location and legs of the jack-up drilling rig are exposed and quite vulnerable to damage. 
         [0007]    Jack-up rigs are mobile, self-elevating, offshore drilling and workover platforms equipped with legs that are arranged to be lowered to the sea floor and then to lift the hull out of the water. Jack-up rigs typically include the drilling and/or workover equipment, leg jacking system, crew quarters, loading and unloading facilities, storage areas for bulk and liquid materials, helicopter landing deck and other related facilities and equipment. 
         [0008]    A jack-up rig is designed to be towed to the drilling site and jacked-up out of the water so that the wave action of the sea only impacts the legs which have a fairly small cross section and thus allows the wave action to pass by without imparting significant movement to the jack-up rig. However, the legs of a jack-up provide little defense against ice floe collisions and an ice floe of any notable size is capable of causing structural damage to one or more legs and/or pushing the rig off location. If this type of event were to happen before the drilling operations were suspended and suitable secure and abandon had been completed, a hydrocarbon leak would possibly occur. Even a small risk of such a leak is completely unacceptable in the oil and gas industry, to the regulators and to the public. 
         [0009]    Thus, once it is determined that a potentially profitable well has been drilled during this short season, a very large, gravity based production system, or similar structure may be brought in and set on the sea floor for the long process of drilling and producing the hydrocarbons. These gravity based structures are very large and very expensive, but are built to withstand the ice forces year around. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0010]    The invention more particularly relates to an ice worthy jack up rig for drilling for hydrocarbons in potential ice conditions in offshore areas including a flotation hull having a relatively flat deck at the upper portion thereof. The flotation hull further includes an ice bending shape along the lower portion thereof and extending around the periphery of the hull where the ice bending shape extends from an area of the hull near the level of the deck and extends downwardly near the bottom of the hull along with an ice deflecting portion extending around the perimeter of the bottom of the hull to direct ice around the hull and not under the hull. The rig includes at least three legs that are positioned within the perimeter of the bottom of the hull wherein the legs are arranged to be lifted up off the seafloor so that the rig may be towed through shallow water and also extend to the sea floor and extend further to lift the hull partially or fully out of the water. A jack up device is associated with each leg to both lift the leg from the sea bottom so that the ice worthy jack up rig may float by the buoyancy of the hull and push the legs down to the seafloor and push the hull partially up and out of the water when ice floes threaten the rig and fully out of the water when ice is not present. The rig further includes a moon pool in the deck and positioned within the perimeter of the bottom of the hull and inside the ice deflecting portion. 
         [0011]    The invention further relates to a method for drilling wells in ice prone waters. The method includes providing a flotation hull having a relatively flat deck at the upper portion thereof and an ice bending shape along the lower portion thereof where the ice bending shape extends from an area of the hull near the level of the deck and extends downwardly near the bottom of the hull and an ice deflecting portion extending around the perimeter of the bottom of the hull to direct ice around the hull and not under the hull. At least three legs are positioned within the perimeter of the bottom of the hull. Each leg is jacked down in a manner that feet on the bottom of the legs engages the sea floor and lifts the hull up and fully out of the water when ice is not threatening the rig while the rig is drilling a well on a drill site. The hull is further lowered into the water into an ice defensive configuration so that the ice bending shape extends above and below the sea surface to bend ice that comes against the rig to cause the ice to submerge under the water and endure bending forces that break the ice where the ice flows past the rig. The method includes drilling through a moon pool in the deck that is positioned within the perimeter of the bottom of the hull and inside the ice deflecting portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which: 
           [0013]      FIG. 1  is an elevation view of the present invention where the drilling rig is floating in the water and available to be towed to a well drilling site; 
           [0014]      FIG. 2  is an elevation view of the present invention where the drilling rig is jacked up out of the water; 
           [0015]      FIG. 3  is an elevation view of the first embodiment of the present invention where the drilling rig is partially lowered into the ice/water interface, but still supported by its legs, in a defensive configuration for drilling during potential ice conditions; 
           [0016]      FIG. 4  is an enlarged fragmentary elevation view showing one end of the first embodiment of the present invention in the  FIG. 3  configuration with ice moving against the rig; 
           [0017]      FIG. 5A  is an elevation view showing the derrick is in a cantilevered position drilling over the side of the deck in the conventional manner of a conventional jack-up drilling rig; 
           [0018]      FIG. 5B  is a partially fragmentary elevation view where a moon pool is shown included in the hull so that the drill string benefits from the ice protection of the ice worthy hull configuration; 
           [0019]      FIG. 6A  is a top view of the first embodiment of the present invention where a cantilever derrick is positioned to drill through the moon pool; and 
           [0020]      FIG. 6B  is a top view of the first embodiment of the present invention where a cantilever derrick is positioned to drill over the edge of the deck. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow. 
         [0022]    As shown in  FIG. 1 , an ice worthy jack-up rig is generally indicated by the arrow  10 . In  FIG. 1 , jack-up rig  10  is shown with its hull  20  floating in the sea and legs  25  in a lifted arrangement where much of the length of the legs  25  extend above the deck  21  of the hull  20 . On the deck  21  is derrick  30  which is used to drill wells. In the configuration shown in  FIG. 1 , the jack-up rig  10  may be towed from one prospect field to another and to and from shore bases for maintenance and other shore service. 
         [0023]    When the jack-up rig  10  is towed to a drilling site in generally shallow water, the legs  25  are lowered through the openings  27  in hull  20  until the feet  26  at the bottom ends of the legs  25  engage the seafloor  15  as shown in  FIG. 2 . In a preferred embodiment, the feet  26  are connected to spud cans  28  to secure the rig  10  to the seafloor. Once the feet  26  engage the seafloor  15 , jacking rigs within openings  27  push the legs  25  down and therefore, the hull  20  is lifted out of the water. With the hull  20  fully jacked-up and out of the water, any wave action and heavy seas more easily break past the legs  25  as compared to the effect of waves against a large buoyant object like the hull  20 . 
         [0024]    When ice begins to form on the sea surface  12 , the risk of an ice floe contacting and damaging the legs  25  or simply bulldozing the jack-up rig  10  off the drilling site becomes a significant concern for conventional jack-up rigs and such rigs are typically removed from drill sites by the end of the open water season. The ice-worthy jack-up drilling rig  10  of the present invention is designed to resist ice floes by assuming an ice defensive, hull-in-water configuration as shown in  FIG. 3 . In  FIG. 3 , ice tends to dampen waves and rough seas, so the sea surface  12  appears less threatening, however, the hazards of the marine environment have only altered, and not lessened. 
         [0025]    When the ice-worthy jack-up rig  10  assumes its ice defensive, hull-in-water configuration, the hull  20  is lowered into the water to contact same, but not to the extent that the hull  20  would begin to float. A significant portion of the weight of the rig  10  preferably remains on the legs  25  to hold the position of the rig  10  on the drill site against any pressure an ice flow might bring. The rig  10  is lowered so that inwardly sloped, ice-bending surface  41  bridges the sea surface  12  or ice/water interface to engage any floating ice that may come upon the rig  10 . 
         [0026]    The sloped ice-bending surface  41  runs from shoulder  42 , which is at the edge of the deck  26 , down to neckline  44 . Ice deflector  45  extends downward from neckline  44 . Thus, when an ice floe, such as shown at  51  comes to the rig  10 , the ice-bending surface  41  causes the leading edge of the ice floe  51  to submerge under the sea surface  12  and apply a significant bending force that breaks large ice floes into smaller, less damaging, less hazardous bits of ice. For example, it is conceivable that an ice floe being hundreds of feet and maybe miles across could come toward the rig  10 . If the ice floe is broken into bits that are less than twenty feet in the longest dimension, such bits are able to pass around the rig  10  with much less concern. 
         [0027]    In  FIG. 4A , the cantilevered derrick  30  is positioned to drill over the side of the deck  20  in accordance with conventional jack-up drilling rigs. Rig  10 , of course includes the ice worthy hull  20 , so the system illustrated in  FIG. 4A  is not entirely conventional. 
         [0028]    It should be noted that conventional jack-up drilling rigs do not have moon pools. As shown in  FIG. 4B , the cantilevered derrick is provided with a moon pool  32  so the riser  35  and the drill string  36  may be positioned within the perimeter of the ice deflector  45  and enjoy the ice protection that the ice-engaging surface  41  and ice deflector  45  provide. 
         [0029]    Ice has substantial compressive strength being in the range of 4 to 12 MPa, but is much weaker against bending with typical flexure strength in the range of 0.3 to 0.5 MPa. As shown, the force of the ice floe  51  moving along the sea surface  12  causes the leading edge to slide under the sea surface  12  and caused section  52  to break off. With the ice floe  51  broken into smaller floes, such as section  52  and bit  53 , the smaller sections tend to float past and around the rig  10  without applying the impacts or forces of a large floe. It is preferred that ice not be forced under the flat of bottom of the hull  20  and the ice deflector  45  turns ice to flow around the side of the hull  20 . If the ice is really thick, the ice deflector  45  is arranged to extend downwardly at a steeper angle than ice-bending surface  41  and will increase the bending forces on the ice floe. At the ice deflector  45 , an ice deflector is positioned to extend down from the flat of bottom of the hull  20 . In an optional arrangement, the turn of the bilge is the flat of bottom at the bottom end of the ice deflector  45 . 
         [0030]    To additionally resist the forces that an ice floe may impose on the rig  10 , the feet  26  of the legs may be arranged to connect to cans  28  set in the sea floor so that when an ice floe comes against the ice-bending surface  41 , the legs  25  actually hold the hull  20  down and force the bending of the ice floe and resist the lifting force of the ice floe which, in an extreme case, may lift the near side of the rig  10  and push the rig over on its side by using the feet  26  on the opposite side of the rig  10  as the fulcrum or pivot. The cans in the sea floor are known for other applications and the feet  26  would include appropriate connections to attach and release from the cans, as desired. 
         [0031]    It should probably be noted that shifting from a conventional open water drilling configuration as shown in  FIG. 2  to a hull-in-water, ice defensive configuration shown in  FIG. 3  may require considerable planning and accommodation depending on what aspect of drilling is ongoing at the time. While some equipment can accommodate shifting of the height of the deck  21 , other equipment may require disconnections or reconfiguration to adapt to a new height off the sea floor  15 . 
         [0032]    The ice-worthy jack-up drill rig  10  is designed to operate like a conventional jack-up rig in open water, but is also designed to settle to the water in an ice defensive position and then re-acquire the conventional stance or configuration when wave action becomes a concern. It is the shape of the hull  20  (as well as its strength) that provides ice bending and breaking capabilities. 
         [0033]    Referring to  FIGS. 5A and 5B , the hull (as viewed from above) may have a circular or oval configuration so as to present a shape that is conducive to steering the broken bits and sections of ice around the periphery of the rig  10  regardless of the direction of origin or path of travel. The ice tends to flow with the wind and sea currents, which tend not to be co-linear, or some path reflecting influences of both sea and air. 
         [0034]    The hull  20  preferably has a faceted or multisided shape that provides the advantages of a circular or oval shape, and may be less expensive to construct. The plates that make up the hull would likely be formed of flat sheets and so that the entire structure comprises segments of flat material such as steel would likely require less complication. The ice-breaking surface would preferably extend at least about five meters above the water level, recognizing that water levels shift up and down with tides and storms and perhaps other influences. The height above the water level accommodates ice floes that are quite thick or having ridges that extend well above the sea surface  12 , but since the height of the shoulder  42  is well above the sea surface  12 , the tall ice floes will be forced down as they come into contact with the rig  10 . At the same time, the deck  21  at the top of the hull  20  should be far enough above the water line so that waves are not able to wash across the deck. As such, the deck  25  is preferred to be at least 7 to 8 meters above the sea surface  12 . Conversely, the neckline  42  is preferred to be at least 4 to 8 meters below the sea surface  12  to adequately bend the ice floes to break them up into more harmless bits. Thus, the hull  20  is preferably in the range of 5-16 meters in height from the flat of bottom to the deck  20 , more preferably 8-16 meters or 11-16 meters. 
         [0035]    It should also be noted that the legs  25  and the openings  27  through which they are connected to the hull  20  are within the perimeter of the ice deflector  45  so that the ice floes are less likely to contact the legs while the rig  10  is in its defensive ice condition configuration as shown in  FIG. 3  and sometimes called hull-in-water configuration. Moreover, the rig  10  does not have to handle every ice floe threat to significantly add value to oil and gas companies. If rig  10  can extend the drilling season by as little as a month, that would be a fifty percent improvement in some ice prone areas and therefore provide a very real cost saving benefit to the industry. 
         [0036]    Referring to  FIGS. 5   a  and  5   b , the derrick  30  may be positioned to drill through a moon pool that is within the perimeter of the ice deflector  45  as shown in  FIG. 5   a  or may be arranged to drill over the side of the deck  21  in a cantilevered fashion as shown in  FIG. 5   b.    
         [0037]    In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiment of the present invention. 
         [0038]    Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims, while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.

Technology Classification (CPC): 4