US20150129234A1 - Offshore drilling unit and method of maintaining stability of the drilling unit in potential ice conditions - Google Patents
Offshore drilling unit and method of maintaining stability of the drilling unit in potential ice conditions Download PDFInfo
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- US20150129234A1 US20150129234A1 US14/537,405 US201414537405A US2015129234A1 US 20150129234 A1 US20150129234 A1 US 20150129234A1 US 201414537405 A US201414537405 A US 201414537405A US 2015129234 A1 US2015129234 A1 US 2015129234A1
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- drilling unit
- offshore drilling
- main body
- water
- sea floor
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Classifications
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02B—HYDRAULIC ENGINEERING
- E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
- E02B17/0017—Means for protecting offshore constructions
- E02B17/0021—Means for protecting offshore constructions against ice-loads
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
- B63B21/50—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers
- B63B21/502—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers by means of tension legs
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
- B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
- B63B35/4413—Floating drilling platforms, e.g. carrying water-oil separating devices
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02B—HYDRAULIC ENGINEERING
- E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
- E02B17/02—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02B—HYDRAULIC ENGINEERING
- E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
- E02B17/04—Equipment specially adapted for raising, lowering, or immobilising the working platform relative to the supporting construction
- E02B17/08—Equipment specially adapted for raising, lowering, or immobilising the working platform relative to the supporting construction for raising or lowering
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
- E21B41/0007—Equipment or details not covered by groups E21B15/00 - E21B40/00 for underwater installations
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/008—Drilling ice or a formation covered by ice
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/02—Drilling rigs characterized by means for land transport with their own drive, e.g. skid mounting or wheel mounting
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B2211/00—Applications
- B63B2211/06—Operation in ice-infested waters
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02B—HYDRAULIC ENGINEERING
- E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
- E02B2017/0056—Platforms with supporting legs
Definitions
- This invention relates to offshore drilling units, such as mobile gravity based structures, mobile offshore drilling units and submersibles, used in shallow water for drilling for hydrocarbons, as well as methods associated with drilling wells and maintaining stability of such offshore drilling units.
- Drilling these wells can be done in the exploration phase with different drilling units. Drilling has been done with gravity based structures, drillships, and in the future possibly jack-up and submersible units. The bottom support units all need some downward force to hold them in place. The required force is dependent on environmental loads which can be very high in ice.
- an offshore drilling unit in the form of a very large, gravity based drilling or 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.
- a submersible, jack-up or small gravity based structure could be brought in.
- the offshore drilling units are typically referred to as gravity based structures, submersibles or possibly a jack-up unit and all are bottom supported.
- the gravity based structures or submersibles must be ballasted to create a downward force on the offshore drilling unit.
- this ballasting can be done with water.
- sand, rocks or other solid materials have been used for ballast.
- This type of ballasting cannot be done on submersibles, and using solid ballast for gravity based structures is expensive, time consuming, creates environmental issues and limits movement to open water season only.
- an offshore drilling unit includes a main body and a ballast fillable with water to at least partially submerge the unit in a body of water with the unit resting on a sea floor.
- An anchoring assembly includes a pile secured to the sea floor.
- a tensioning system operatively couples to the pile and to the main body at a location above the water and is configured to apply a downward force on the main body to resist ice loads imposed on the offshore drilling unit.
- a method of maintaining stability of an offshore drilling unit in potential ice conditions includes positioning the offshore drilling unit in a desired location in a body of water and filling ballast with water to at least partially submerge the unit until resting on a sea floor of the body of water.
- the method further includes securing an anchoring assembly having a pile to the sea floor. Imposing a downward force on a main body of the offshore drilling unit at a location above the water occurs utilizing a tensioning system operatively coupled to the main body and the pile.
- a method of extracting hydrocarbons from a well in ice prone waters includes positioning an offshore drilling unit having a platform in a desired location in a body of water and filling ballast with water to at least partially submerge the unit until resting on a sea floor.
- the method includes securing to the sea floor an anchoring assembly having a plurality of piles at least partially embedded in the sea floor. Imposing a downward force on the platform of the offshore drilling unit with a tension member of a tensioning system occurs using the tension member operatively coupled to the platform and the piles.
- the unit also enables extracting hydrocarbons from the well.
- FIG. 1 is a schematic illustration of an offshore drilling unit having a tensioning system, where the offshore drilling unit is in an unanchored condition;
- FIG. 2 is a schematic illustration of the offshore drilling unit in an anchored condition and resisting ice loads
- FIG. 3 is a flow diagram illustrating a method of maintaining stability of an offshore drilling unit in potential ice conditions.
- FIG. 1 illustrates an offshore drilling unit 10 .
- the offshore drilling unit 10 is a structure located or suitable for location over a relatively fixed position on a sea floor 12 of a body of water 14 , which may be 20-25 meters deep.
- the offshore drilling unit 10 is suitable for use in ice prone waters that often include bodies of ice.
- the offshore drilling unit 10 includes a main body 16 and is configured to be at least partially submerged in the body of water 14 .
- the offshore drilling unit 10 may be a permanently installed offshore structure or a mobile offshore drilling unit.
- the main body 16 is a platform suitable as a buoyant or floating type of platform submersible until supported on the sea floor 12 of the body of water 14 .
- the platform of the offshore drilling unit 10 may be employed for various uses, including, but not limited to, offshore well drilling operations, hydrocarbon production, radar stations, heliports, and the like.
- Each of the aforementioned applications requires that the main body 16 of the offshore drilling unit 10 is relatively unaffected by tides, wave motion and by changes in the amount or distribution of the load. In ice prone waters, this is of particular concern due to potential contact with bodies of ice that may distribute a load on the offshore drilling unit 10 .
- An anchoring assembly 18 operatively couples to, and extends downwardly from, the main body 16 and secures the offshore drilling unit 10 to the sea floor 12 .
- the offshore drilling unit 10 may include at least one, but typically a plurality of legs 22 extending downwardly from the main body 16 .
- the legs 22 connect the main body 16 with a base portion 24 of the offshore drilling unit 10 .
- the offshore drilling unit 10 floats with the legs 22 and the base portion 24 submerged yet spaced from the sea floor 12 below.
- FIG. 2 shows the offshore drilling unit 10 after filling ballasts, such as the legs 22 and/or the base portion 24 , with water to lower the base portion 24 into resting contact with the sea bed 12 and maintain a fixed position of the offshore drilling unit 10 .
- ballasts such as the legs 22 and/or the base portion 24
- numerous contemplated anchoring assemblies may be employed to interact with the sea floor 12 to facilitate anchoring of the offshore drilling unit 10 .
- the legs 22 may not couple to the base portion 24 but rather engage piled sockets pre-positioned on the sea floor 12 .
- the anchoring assembly 18 further includes a plurality of piles 20 , with each of the plurality of piles 20 extending into the sea floor 12 .
- the plurality of piles 20 are at least partially embedded within the sea floor 12 to fix the offshore structure's location.
- the plurality of piles 20 may be formed in any conventional manner, with an exemplary embodiment comprising suction piles.
- the offshore drilling unit 10 couples to the piles 20 .
- the anchoring assembly 18 includes the base portion 24 of the offshore drilling unit 10 in an operatively coupled relationship with the plurality of piles 20 that maintain the overall position of the offshore drilling unit 10 .
- the illustrated base portion 24 is configured to rest on the sea floor 12 to provide partial anchoring strength for the offshore drilling unit 10 .
- the offshore drilling unit 10 when ballasted and resting on the sea floor may have more than 25 percent of its weight under the water and spaced (e.g., at least 10 meters) from the sea surface toward the sea floor 14 .
- Such bottom weight tends to prevent tipping of the offshore drilling unit 10 as may occur with the jack-up rig. Sliding of the offshore drilling unit 10 along the sea floor 12 due to the ice loads may still present a problem.
- the anchoring assembly 18 also includes a tensioning system 26 .
- the tensioning system 26 is employed to avoid the need for ballasting of the offshore drilling unit 10 with solid material denser than water. Avoidance of the need for solid ballasting advantageously allows quicker mobility of the offshore drilling unit 10 relative to gravity based structures with such solid ballast including sand, rocks or other expensive materials.
- the tensioning system 26 includes a tension member 28 extending between, and operatively coupled to, the main body 16 above the water 14 and the piles 20 .
- the tension member 28 is a line that may be formed of various suitable materials. The tensile strength of the material must be sufficient to sustain a tension force configured to impart a downward force on the main body 16 .
- An exemplary embodiment of the tension member 28 comprises steel wire. Typically, multiple intertwined steel wires forming a cable are employed as the tension member 28 . Steel is merely one example of a material that may be used as the tension member 28 and it is to be understood that numerous other materials may be suitable for operation of the tensioning system 26 .
- the tensioning system 26 also includes a tension member manipulation assembly 30 .
- the tension member 28 is controlled by the tension member manipulation assembly 30 .
- the tension member manipulation assembly 30 includes a winch 30 used to adjust the tension of the tension member 28 during operation of the tensioning system 26 .
- more than one tension member may be included in the tensioning system 26 .
- the tensioning system 26 may include a plurality of tension members and a plurality of tension member manipulation assemblies.
- the tension member 28 operatively couples to the tension member manipulation assembly 30 proximate one end of the tension member 28 and operatively couples to at least one of the piles 20 proximate the other end of the tension member 28 .
- Direct connection of the tension member 28 to the piles 20 without the piles 20 being otherwise secured to the offshore drilling unit 10 may facilitate relocation of the offshore drilling unit 10 since the tension member 28 may be released or severed from the offshore drilling unit 10 without requiring removal of the piles 20 .
- the ballast may be refilled with air to float the offshore drilling unit 10 for movement if desired.
- the precise attachment location of the tension member 28 may vary.
- the tension member 28 extends through the base portion 24 of the anchoring assembly 18 and is fixed to the plurality of piles 20 .
- the tension member 28 is attached to the base portion 24 .
- the tension member 28 is attached to a lower end of the plurality of legs 22 .
- the tensioning system 26 is configured to impose a downward force on the main body 16 of the offshore drilling unit 10 by manipulating the tension member 28 into tension.
- the desired downward force imposed on the main body 16 depends on the particular application, including factors such as weight and geometry of the main body 16 , for example.
- the tension member manipulation assembly 30 provides relatively fast and efficient adjustment of the tension of the tension member 28 and therefore the downward force applied to the main body 16 .
- the downward force applied with the tensioning system 26 avoids the need for solid ballasting, as discussed above.
- the downward force applied with the tensioning system 26 may provide an equivalent force as that of solid ballasting to resist ice loads, such as those imposed by one or more ice bodies 32 .
- the tensioning system 26 does not require external materials, as is the case with solid ballasting, and can be implemented in conditions when ice is already present. Additionally, the tensioning system 26 may be employed with submersibles in shallow water utilizing water ballasting without relying on solid ballasting.
- a method 100 of maintaining stability of an offshore structure in potential ice conditions is also provided with reference to FIGS. 1 and 2 .
- the offshore drilling unit 10 and, more particularly, the tensioning system 26 have been previously described and specific structural components need not be described in further detail.
- the method includes positioning the offshore structure in a desired location in a body of water and then submerging the structure by ballasting with water until resting on a sea floor, in an initial step 102 .
- a piling step 104 includes securing an anchoring assembly to the sea floor of the body of water.
- downward force is imposed on a main body of the offshore structure with a tensioning system operatively coupled to the main body.
- the offshore drilling unit 10 is configured to extract hydrocarbons from a well once the offshore drilling unit 10 is properly positioned, secured to the sea floor and stabilized with the downward force provided by the tensioning system 26 .
Abstract
An offshore drilling unit includes a main body configured to be bottom supported in shallow water. Also included is an anchoring assembly secured to a sea floor. Further included is a tensioning system operatively coupled to the main body and the anchoring assembly, wherein the tensioning system is configured to apply a downward force on the main body to resist ice loads imposed on the offshore drilling unit.
Description
- This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/903,084 filed Nov. 12, 2013, entitled “OFFSHORE DRILLING UNIT AND METHOD OF MAINTAINING STABILITY OF THE DRILLING UNIT IN POTENTIAL ICE CONDITIONS,” which is incorporated herein in its entirety.
- This invention relates to offshore drilling units, such as mobile gravity based structures, mobile offshore drilling units and submersibles, used in shallow water for drilling for hydrocarbons, as well as methods associated with drilling wells and maintaining stability of such offshore drilling units.
- In the 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.
- One promising area is the offshore Arctic. However, the Arctic is remote and cold where ice on the water creates considerable challenges for prospecting for and extracting 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.
- Drilling these wells can be done in the exploration phase with different drilling units. Drilling has been done with gravity based structures, drillships, and in the future possibly jack-up and submersible units. The bottom support units all need some downward force to hold them in place. The required force is dependent on environmental loads which can be very high in ice.
- Once it is determined that a potentially profitable well could be drilled, explored or developed, an offshore drilling unit in the form of a very large, gravity based drilling or 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. For just drilling wells, a submersible, jack-up or small gravity based structure could be brought in. The offshore drilling units are typically referred to as gravity based structures, submersibles or possibly a jack-up unit and all are bottom supported.
- Conventionally, the gravity based structures or submersibles must be ballasted to create a downward force on the offshore drilling unit. In benign environments without ice, this ballasting can be done with water. However, in areas where ice forces must be resisted, sand, rocks or other solid materials have been used for ballast. This type of ballasting cannot be done on submersibles, and using solid ballast for gravity based structures is expensive, time consuming, creates environmental issues and limits movement to open water season only.
- Therefore, a need exists for offshore structures that are cost efficient and can withstand ice conditions.
- In one embodiment of the invention, an offshore drilling unit includes a main body and a ballast fillable with water to at least partially submerge the unit in a body of water with the unit resting on a sea floor. An anchoring assembly includes a pile secured to the sea floor. Further, a tensioning system operatively couples to the pile and to the main body at a location above the water and is configured to apply a downward force on the main body to resist ice loads imposed on the offshore drilling unit.
- In another embodiment of the invention, a method of maintaining stability of an offshore drilling unit in potential ice conditions is provided. The method includes positioning the offshore drilling unit in a desired location in a body of water and filling ballast with water to at least partially submerge the unit until resting on a sea floor of the body of water. The method further includes securing an anchoring assembly having a pile to the sea floor. Imposing a downward force on a main body of the offshore drilling unit at a location above the water occurs utilizing a tensioning system operatively coupled to the main body and the pile.
- In yet another embodiment of the invention, a method of extracting hydrocarbons from a well in ice prone waters is provided. The method includes positioning an offshore drilling unit having a platform in a desired location in a body of water and filling ballast with water to at least partially submerge the unit until resting on a sea floor. In addition, the method includes securing to the sea floor an anchoring assembly having a plurality of piles at least partially embedded in the sea floor. Imposing a downward force on the platform of the offshore drilling unit with a tension member of a tensioning system occurs using the tension member operatively coupled to the platform and the piles. The unit also enables extracting hydrocarbons from the well.
- The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying figures by way of example and not by way of limitation, in which:
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FIG. 1 is a schematic illustration of an offshore drilling unit having a tensioning system, where the offshore drilling unit is in an unanchored condition; -
FIG. 2 is a schematic illustration of the offshore drilling unit in an anchored condition and resisting ice loads; and -
FIG. 3 is a flow diagram illustrating a method of maintaining stability of an offshore drilling unit in potential ice conditions. - Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not as a limitation of the invention. It will be apparent to those skilled in the art that various modifications and variation can be made without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the invention cover such modifications and variations that come within the scope of the appended claims and their equivalents.
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FIG. 1 illustrates anoffshore drilling unit 10. Theoffshore drilling unit 10 is a structure located or suitable for location over a relatively fixed position on asea floor 12 of a body ofwater 14, which may be 20-25 meters deep. In one embodiment, theoffshore drilling unit 10 is suitable for use in ice prone waters that often include bodies of ice. - The
offshore drilling unit 10 includes amain body 16 and is configured to be at least partially submerged in the body ofwater 14. As described below, theoffshore drilling unit 10 may be a permanently installed offshore structure or a mobile offshore drilling unit. In one embodiment, themain body 16 is a platform suitable as a buoyant or floating type of platform submersible until supported on thesea floor 12 of the body ofwater 14. The platform of theoffshore drilling unit 10 may be employed for various uses, including, but not limited to, offshore well drilling operations, hydrocarbon production, radar stations, heliports, and the like. Each of the aforementioned applications requires that themain body 16 of theoffshore drilling unit 10 is relatively unaffected by tides, wave motion and by changes in the amount or distribution of the load. In ice prone waters, this is of particular concern due to potential contact with bodies of ice that may distribute a load on theoffshore drilling unit 10. - An
anchoring assembly 18 operatively couples to, and extends downwardly from, themain body 16 and secures theoffshore drilling unit 10 to thesea floor 12. Theoffshore drilling unit 10 may include at least one, but typically a plurality oflegs 22 extending downwardly from themain body 16. In some embodiments, thelegs 22 connect themain body 16 with abase portion 24 of theoffshore drilling unit 10. Prior to being ballasted, theoffshore drilling unit 10 floats with thelegs 22 and thebase portion 24 submerged yet spaced from thesea floor 12 below. -
FIG. 2 shows theoffshore drilling unit 10 after filling ballasts, such as thelegs 22 and/or thebase portion 24, with water to lower thebase portion 24 into resting contact with thesea bed 12 and maintain a fixed position of theoffshore drilling unit 10. In addition to thebase portion 24 thereby forming part of the anchoringassembly 18, numerous contemplated anchoring assemblies may be employed to interact with thesea floor 12 to facilitate anchoring of theoffshore drilling unit 10. For some embodiments, thelegs 22 may not couple to thebase portion 24 but rather engage piled sockets pre-positioned on thesea floor 12. - The anchoring
assembly 18 further includes a plurality ofpiles 20, with each of the plurality ofpiles 20 extending into thesea floor 12. The plurality ofpiles 20 are at least partially embedded within thesea floor 12 to fix the offshore structure's location. The plurality ofpiles 20 may be formed in any conventional manner, with an exemplary embodiment comprising suction piles. - The
offshore drilling unit 10 couples to thepiles 20. For one embodiment, the anchoringassembly 18 includes thebase portion 24 of theoffshore drilling unit 10 in an operatively coupled relationship with the plurality ofpiles 20 that maintain the overall position of theoffshore drilling unit 10. As noted above, the illustratedbase portion 24 is configured to rest on thesea floor 12 to provide partial anchoring strength for theoffshore drilling unit 10. - In contrast to a jack-up rig when raised having almost all weight above the water, the
offshore drilling unit 10 when ballasted and resting on the sea floor may have more than 25 percent of its weight under the water and spaced (e.g., at least 10 meters) from the sea surface toward thesea floor 14. Such bottom weight tends to prevent tipping of theoffshore drilling unit 10 as may occur with the jack-up rig. Sliding of theoffshore drilling unit 10 along thesea floor 12 due to the ice loads may still present a problem. - In order to enhance the stability of the
offshore drilling unit 10, and to balance a buoyancy force imposed on themain body 16, the anchoringassembly 18 also includes atensioning system 26. As will be appreciated from the description below, thetensioning system 26 is employed to avoid the need for ballasting of theoffshore drilling unit 10 with solid material denser than water. Avoidance of the need for solid ballasting advantageously allows quicker mobility of theoffshore drilling unit 10 relative to gravity based structures with such solid ballast including sand, rocks or other expensive materials. - The
tensioning system 26 includes atension member 28 extending between, and operatively coupled to, themain body 16 above thewater 14 and thepiles 20. Thetension member 28 is a line that may be formed of various suitable materials. The tensile strength of the material must be sufficient to sustain a tension force configured to impart a downward force on themain body 16. An exemplary embodiment of thetension member 28 comprises steel wire. Typically, multiple intertwined steel wires forming a cable are employed as thetension member 28. Steel is merely one example of a material that may be used as thetension member 28 and it is to be understood that numerous other materials may be suitable for operation of thetensioning system 26. - The
tensioning system 26 also includes a tensionmember manipulation assembly 30. Thetension member 28 is controlled by the tensionmember manipulation assembly 30. In one embodiment, the tensionmember manipulation assembly 30 includes awinch 30 used to adjust the tension of thetension member 28 during operation of thetensioning system 26. As shown, more than one tension member may be included in thetensioning system 26. For example, thetensioning system 26 may include a plurality of tension members and a plurality of tension member manipulation assemblies. - The
tension member 28 operatively couples to the tensionmember manipulation assembly 30 proximate one end of thetension member 28 and operatively couples to at least one of thepiles 20 proximate the other end of thetension member 28. Direct connection of thetension member 28 to thepiles 20 without thepiles 20 being otherwise secured to theoffshore drilling unit 10 may facilitate relocation of theoffshore drilling unit 10 since thetension member 28 may be released or severed from theoffshore drilling unit 10 without requiring removal of thepiles 20. After release of thetension member 28, the ballast may be refilled with air to float theoffshore drilling unit 10 for movement if desired. - The precise attachment location of the
tension member 28 may vary. In the illustrated embodiment, thetension member 28 extends through thebase portion 24 of the anchoringassembly 18 and is fixed to the plurality ofpiles 20. In another embodiment, thetension member 28 is attached to thebase portion 24. Alternatively, thetension member 28 is attached to a lower end of the plurality oflegs 22. - In operation, irrespective of the precise attachment location of the
tension member 28, thetensioning system 26 is configured to impose a downward force on themain body 16 of theoffshore drilling unit 10 by manipulating thetension member 28 into tension. The desired downward force imposed on themain body 16 depends on the particular application, including factors such as weight and geometry of themain body 16, for example. The tensionmember manipulation assembly 30 provides relatively fast and efficient adjustment of the tension of thetension member 28 and therefore the downward force applied to themain body 16. - Application of the downward force with the
tensioning system 26 avoids the need for solid ballasting, as discussed above. The downward force applied with thetensioning system 26 may provide an equivalent force as that of solid ballasting to resist ice loads, such as those imposed by one ormore ice bodies 32. Thetensioning system 26 does not require external materials, as is the case with solid ballasting, and can be implemented in conditions when ice is already present. Additionally, thetensioning system 26 may be employed with submersibles in shallow water utilizing water ballasting without relying on solid ballasting. - Referring to
FIG. 3 , amethod 100 of maintaining stability of an offshore structure in potential ice conditions is also provided with reference toFIGS. 1 and 2 . Theoffshore drilling unit 10 and, more particularly, thetensioning system 26, have been previously described and specific structural components need not be described in further detail. The method includes positioning the offshore structure in a desired location in a body of water and then submerging the structure by ballasting with water until resting on a sea floor, in aninitial step 102. A pilingstep 104 includes securing an anchoring assembly to the sea floor of the body of water. During aloading step 106, downward force is imposed on a main body of the offshore structure with a tensioning system operatively coupled to the main body. Furthermore, theoffshore drilling unit 10 is configured to extract hydrocarbons from a well once theoffshore drilling unit 10 is properly positioned, secured to the sea floor and stabilized with the downward force provided by thetensioning system 26. - While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
Claims (17)
1. An offshore drilling unit comprising:
a main body;
a ballast finable with water to at least partially submerge the unit in a body of water with the unit resting on a sea floor;
an anchoring assembly having a pile secured to the sea floor; and
a tensioning system operatively coupled to the pile and to the main body at a location above the water, wherein the tensioning system is configured to apply a downward force on the main body to resist ice loads imposed on the offshore drilling unit.
2. The offshore drilling unit of claim 1 , wherein the tensioning system comprises at least one tension member and a winch configured to adjust tension of the at least one tension member.
3. The offshore drilling unit of claim 2 , wherein the at least one tension member comprises a wire cable.
4. The offshore drilling unit of claim 2 , wherein the anchoring assembly comprises a plurality of suction piles at least partially embedded in the sea floor.
5. The offshore drilling unit of claim 4 , wherein the at least one tension member is directly coupled to the plurality of suction piles.
6. The offshore drilling unit of claim 1 , wherein the main body comprises an offshore structure permanently installed at a drilling location.
7. The offshore drilling unit of claim 1 , wherein the main body comprises a mobile offshore drilling unit.
8. The offshore drilling unit of claim 1 , wherein more than 25 percent of weight for the unit is under the water and spaced from a sea surface toward the sea floor.
9. A method of maintaining stability of an offshore drilling unit in potential ice conditions, the method comprising:
positioning the offshore drilling unit in a desired location in a body of water;
filling ballast with water to at least partially submerge the unit until resting on a sea floor of the body of water;
securing an anchoring assembly having a pile to the sea floor; and
imposing a downward force on a main body of the offshore drilling unit at a location above the water with a tensioning system operatively coupled to the main body and the pile.
10. The method of claim 9 , further comprising adjusting the downward force with the tensioning system to provide a desired force configured to withstand loads imparted on the offshore drilling unit by contact between ice and the offshore drilling unit.
11. The method of claim 9 , wherein the main body is a platform and imposing the downward force on the main body increases the downward force on the platform.
12. The method of claim 9 , wherein imposing the downward force on the main body with the tensioning system comprises manipulating a winch configured to adjust a tension of a tension member.
13. The method of claim 9 , wherein securing the anchoring assembly to the sea floor comprises partially embedding a plurality of piles within the sea floor.
14. The method of claim 13 , wherein securing the anchoring assembly further comprises operatively coupling respective lower ends of a plurality of legs with a plurality of piled sockets operatively coupled to the plurality of piles, wherein the plurality of legs extend downwardly from the main body of the offshore drilling unit.
15. The method of claim 9 , wherein the method is performed in bodies of water where ice is present.
16. A method of extracting hydrocarbons from a well in ice prone waters, the method comprising:
positioning an offshore drilling unit having a platform in a desired location in a body of water;
filling ballast with water to at least partially submerge the unit until resting on a sea floor;
securing to the sea floor an anchoring assembly having a plurality of piles at least partially embedded in the sea floor;
imposing a downward force on the platform of the offshore drilling unit with a tension member of a tensioning system, the tension member operatively coupled to the platform and the piles; and
extracting hydrocarbons from the well.
17. The method of claim 16 , further comprising adjusting the downward force imposed on the platform by manipulating the tension member with a winch.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US14/537,405 US20150129234A1 (en) | 2013-11-12 | 2014-11-10 | Offshore drilling unit and method of maintaining stability of the drilling unit in potential ice conditions |
PCT/US2014/064831 WO2015073371A1 (en) | 2013-11-12 | 2014-11-10 | Offshore drilling unit and method of maintaining stability of the drilling unit in potential ice conditions |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US201361903084P | 2013-11-12 | 2013-11-12 | |
US14/537,405 US20150129234A1 (en) | 2013-11-12 | 2014-11-10 | Offshore drilling unit and method of maintaining stability of the drilling unit in potential ice conditions |
Publications (1)
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US20150129234A1 true US20150129234A1 (en) | 2015-05-14 |
Family
ID=53042712
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US14/537,405 Abandoned US20150129234A1 (en) | 2013-11-12 | 2014-11-10 | Offshore drilling unit and method of maintaining stability of the drilling unit in potential ice conditions |
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US (1) | US20150129234A1 (en) |
WO (1) | WO2015073371A1 (en) |
Cited By (3)
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CN107642078A (en) * | 2017-10-24 | 2018-01-30 | 佛山科学技术学院 | A kind of new cuff ice resistant structure |
CN107905769A (en) * | 2017-11-21 | 2018-04-13 | 中国石油天然气股份有限公司 | Side, the more well production water enchroachment (invasion) physical simulation experiment system and method for bottomwater gas field |
RU2667252C1 (en) * | 2017-11-09 | 2018-09-18 | Общество с ограниченной ответственностью "ЛУКОЙЛ-Инжиниринг" (ООО "ЛУКОЙЛ-Инжиниринг") | Self-elevating drilling rig for shallow water area operation with season ice cover |
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US4433941A (en) * | 1980-05-12 | 1984-02-28 | Mobil Oil Corporation | Structure for offshore exploitation |
US7934462B2 (en) * | 2008-03-06 | 2011-05-03 | Alaa Mansour | Offshore floating structure with motion dampers |
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NO145686L (en) * | 1974-06-03 | |||
FR2408509A1 (en) * | 1977-11-14 | 1979-06-08 | United Kingdom Government | DEPRESSION MARINE ANCHOR |
NZ507939A (en) * | 1998-04-02 | 2002-08-28 | Suction Pile Technology B | Marine structure with suction piles for embedment into the sub-sea bottom |
GB2364728B (en) * | 1998-05-16 | 2002-12-04 | Duncan Cuthill | Method of and apparatus for installing a pile underwater to create a mooring anchorage |
US20120125688A1 (en) * | 2010-10-21 | 2012-05-24 | Conocophillips Company | Ice worthy jack-up drilling unit secured to the seafloor |
SG191764A1 (en) * | 2011-01-28 | 2013-08-30 | Exxonmobil Upstream Res Co | Subsea production system having arctic production tower |
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- 2014-11-10 WO PCT/US2014/064831 patent/WO2015073371A1/en active Application Filing
- 2014-11-10 US US14/537,405 patent/US20150129234A1/en not_active Abandoned
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US4433941A (en) * | 1980-05-12 | 1984-02-28 | Mobil Oil Corporation | Structure for offshore exploitation |
US7934462B2 (en) * | 2008-03-06 | 2011-05-03 | Alaa Mansour | Offshore floating structure with motion dampers |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
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CN107642078A (en) * | 2017-10-24 | 2018-01-30 | 佛山科学技术学院 | A kind of new cuff ice resistant structure |
RU2667252C1 (en) * | 2017-11-09 | 2018-09-18 | Общество с ограниченной ответственностью "ЛУКОЙЛ-Инжиниринг" (ООО "ЛУКОЙЛ-Инжиниринг") | Self-elevating drilling rig for shallow water area operation with season ice cover |
CN107905769A (en) * | 2017-11-21 | 2018-04-13 | 中国石油天然气股份有限公司 | Side, the more well production water enchroachment (invasion) physical simulation experiment system and method for bottomwater gas field |
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WO2015073371A1 (en) | 2015-05-21 |
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