Method for preventing thaw settlement along offshore artic pipelines
First Claim
1. A method for installing a warm fluid-bearing pipeline across an arctic seafloor, said method comprising:
- (1) drilling a series of boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder;
(2) circulating a warm circulation fluid through the boreholes so as to create a slump trough on the surface of the seafloor by creating a prethawing zone in the permafrost zone; and
(3) installing a pipeline bearing a warm fluid along the bottom of the slump trough without causing further substantial slumping along the seafloor.
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Accused Products
Abstract
A method for installing a pipeline for transporting a warm fluid, such as newly-produced oil, across arctic seafloor underlain by a permafrost zone without danger of rupture of the pipeline caused by thawing in the supporting permafrost zone comprises (1) drilling a series of boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder, (2) circulating a warm fluid through each borehole so as to cause a zone of prethawing in the permafrost zone and thereby create a slump trough on the surface of the seafloor along a path marked by the series of boreholes; and (3) installing a warm fluid bearing pipeline along the bottom of the slump trough. Usually a temperature differential between the warm fluid and the bottom of the borehole of at least 2 degrees Fahrenheit is required to assure economical prethawing of the permafrost zone.
37 Citations
53 Claims
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1. A method for installing a warm fluid-bearing pipeline across an arctic seafloor, said method comprising:
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(1) drilling a series of boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder; (2) circulating a warm circulation fluid through the boreholes so as to create a slump trough on the surface of the seafloor by creating a prethawing zone in the permafrost zone; and (3) installing a pipeline bearing a warm fluid along the bottom of the slump trough without causing further substantial slumping along the seafloor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for installing a warm fluid-bearing pipeline across an arctic seafloor, said method comprising:
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(1) drilling at least one series of equally spaced boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder; (2) circulating a warm fluid through each borehole so as to thaw the region of permafrost surrounding the borehole; (3) prethawing the permafrost zone by the circulation of fluids in step (2) so as to create a substantially continuous slump trough upon the seafloor along a path marked by the boreholes extending across a portion of the seafloor wherein the zone of thermal influence of a warm fluid-bearing pipeline installed along the seafloor would penetrate the top of an unprethawed permafrost zone; (4) installing a warm fluid-bearing pipeline along the bottom of the slump trough created in step (3); and (5) passing warm fluid through said pipeline without causing further substantial slumping along the seafloor so as to protect the pipeline from ice gouging. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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34. A method for installing a pipeline across arctic subsea terrain carrying warm petroleum products from an offshore production platform to an onshore petroleum processing station without danger of rupture in the pipeline caused by thawing in a supporting zone of permafrost, said method comprising:
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(1) drilling a series of boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder; (2) installing within each borehole a conduit having a smaller diameter than the diameter of the borehole; (3) circulating a warm fluid through each conduit, said fluid passing downwardly through the conduit and upwardly through the annular space between the conduit and the side of the borehole so as to partially prethaw the surrounding zone of permafrost and thereby create a substantially continuous slump trough on the seafloor along a path marked by the series of boreholes; (4) excavating the slump trough so as to increase its depth sufficiently that the top of a pipeline installed therein lies below the level of ice gouging in the surrounding subsea terrain; (5) installing a pipeline along the bottom of the slump trough so as to connect the offshore production platform with the onshore petroleum gathering station; and (6) flowing warm oil through the pipeline without substantial further thawing of the underlying zone of permafrost. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41, 42, 43, 44)
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45. A method for installing a warm fluid-bearing pipeline across an arctic seafloor, said method comprising:
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(1) drilling a first series of equally spaced boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder; (2) drilling a second series of equally spaced boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder, the boreholes of the second series being positioned so as to form the apex of an equilateral triangle having a base defined by two boreholes in the first series of boreholes; (3) drilling a third series of equally spaced boreholes positioned so that each borehole lies substantially at the center of one of the equilateral triangles formed by the boreholes drilled in steps (1) and (2) above, a temperature-sensing device being positioned along each borehole in the third series; (4) circulating a warm fluid through each borehole in the first and second series of boreholes so as to thaw the region of permafrost surrounding the borehole and so as to form a substantially continuous slump trough upon the seafloor along a path marked by the boreholes and extending across a portion of the seafloor wherein the zone of thermal influence of a warm fluid-bearing pipeline installed along the seafloor would penetrate the top of the permafrost zone, the slump trough being substantially equivalent to the slump trough that would result if the warm fluid-bearing pipeline were installed along the seafloor at a depth sufficient to protect the pipeline from ice gouging; (5) ceasing circulation of the warm fluid when the temperature along the boreholes of the third series of boreholes undergoes a relatively rapid elevation; and (6) installing the warm fluid-bearing pipeline along the bottom of the slump trough so as to protect the pipeline from ice gouging. - View Dependent Claims (46, 47, 48, 49, 50, 51, 52)
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53. A method for installing a warm fluid-bearing pipeline across an arctic seafloor, said method comprising:
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(1) drilling a plurality of boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder; (2) circulating a warm fluid through at least some of said boreholes so as to create a slump trough on the surface of the seafloor by creating a prethawing zone in the permafrost zone; and (3) installing a pipeline bearing a warm fluid along the bottom of the slump trough without causing further substantial slumping along the seafloor.
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Specification