Rigid jacket of an offshore platform having a quadrapod structure

An offshore jacket for installation in a sea environment having a sea surface and a sea floor, said jacket having a base, a top and a height extending from said base to said top, and said jacket comprising:

• exterior framing including four outside legs each extending at least a majority of said height of said jacket upwardly from beneath the sea surface to at least the sea surface, wherein a first pair of said four outside legs is more closely spaced apart and a second pair of said four outside legs is more widely spaced apart to define four corners of a trapezoidal cross section of said exterior framing;
• a plurality of cross-sectional frame sections horizontally positioned at periodic intervals along said height of said jacket between said base and said top, wherein each said cross-sectional frame section encloses a cross-sectional conductor opening having at least one substantially perpendicularly oriented conductor passing therethrough from said base to said top and has a front member, a rear member, a first lateral member and a second lateral member interconnecting said four outside legs and included in said exterior framing of said jacket, and wherein said exterior framing defines an integral launch box having sufficient structural integrity to withstand a skid launch of said jacket from a launch barge;
• and
• a cross-sectional conductor guide positioned in each said conductor opening and connected to said cross-sectional frame section, wherein said cross-sectional conductor guide slidably engages said at least one conductor to laterally support said at least one conductor, thereby permitting independent vertical movement of said at least one conductor relative to said cross-sectional frame section while substantially preventing independent horizontal movement of said at least one conductor relative to said cross-sectional frame section, and further thereby enabling said at least one conductor to supplement lateral support of said jacket while isolating said jacket from vertical loads in said at least one conductor;
• wherein said jacket is rigid, said rigid jacket characterized as having a sway period shorter than a wave period of peak spectral energy of a surrounding wave environment in comparison to a compliant jacket characterized as having a sway period longer than a wave period of peak spectral energy of a surrounding wave environment.

A method for placing an offshore jacket at an offshore site in a sea environment having a sea floor and a sea surface, said method comprising:

• providing said jacket having a height extending from a base to a top, wherein said jacket comprises exterior framing including four outside legs each extending at least a majority of said height of said jacket, wherein a first pair of said four outside legs is more closely spaced apart and a second pair of said four outside legs is more widely spaced apart to define four corners of a trapezoidal cross section of said exterior framing and a plurality of cross-sectional frame sections horizontally positioned at periodic intervals along said height of said jacket between said base and said top, wherein each said cross-sectional frame section has a front member, a rear member, a first lateral member and a second lateral member interconnecting said four outside legs and included in said exterior framing of said jacket, and wherein said exterior framing defines an integral launch box;
• extending at least one conductor from said base to said top, wherein said at least one conductor passes through each said cross-sectional frame section;
• slidably engaging said at least one conductor with each said cross-sectional frame section to laterally support said at least one conductor, thereby permitting independent vertical movement of said at least one conductor relative to said cross-sectional frame section while substantially preventing independent horizontal movement of said at least one conductor relative to said cross-sectional frame section when said jacket is in a vertical orientation, and further thereby enabling said at least one conductor to supplement lateral support of said jacket while isolating said jacket from vertical loads in said at least one conductor;
• mounting a first launch runner on one of said first pair of outside legs more closely spaced apart and mounting a second launch runner on the other of said first pair of outside legs;
• positioning said jacket on a barge deck of a transport barge in a horizontal orientation with said first and second launch runners engaging said barge deck;
• transporting said jacket on said transport barge to said offshore site;
• launching said jacket from said transport barge at said offshore site by sliding said first and second launch runners along said barge deck, wherein said integral launch box bears launch loads on said jacket to prevent structural failure of said jacket;
• and
• fixing said jacket to said sea floor, wherein said base is proximal to said sea floor and said top is proximal to said sea surface with said outside legs extending upwardly from beneath the sea surface to at least the sea surface and wherein said jacket is rigid, said rigid jacket characterized as having a sway period shorter than a wave period of peak spectral energy of a surrounding wave environment at said offshore site in comparison to a compliant jacket characterized as having a sway period longer than a wave period of peak spectral energy of a surrounding wave environment.