Type of suction leg, an offshore caisson and a sit-on-bottom offshore platform

An offshore caisson, comprising:

• a watertight tank made of steel or reinforced concrete structure, wherein the watertight tank has at least one ballast compartment used for injecting or ejecting ballast seawater and a solid ballast to change a weight of the offshore caisson wherein the watertight tank is a cylindrical tank group, wherein the cylindrical tank group comprises a body formed by multi closely connected tank units in a honeycomb form or a single tank unit, and a top connection structure and a bottom connection structure surrounding the top and bottom of the body respectively;
• at least two pile sleeves arranged symmetrically around a bottom of the watertight tank, wherein the watertight tank and the pile sleeves are connected together via a bottom connection that surrounds the bottom of the watertight tank and is tangent to the watertight tank and a top connection, wherein the pile sleeves are part of the bottom connection wherein each pile sleeve as part of the bottom connection structure is tangent to the single tank unit or two adjacent tank units in the honeycomb form, wherein at an intersection of the top connection structure with each vertical central axis of the pile sleeve, there is a hole for traverse and fixation of a long pole, or a hole with a diameter equal to a diameter of a sealing long pile for traverse and temporary fixation of the sealing long pile if a suction leg has no long pole, or there is a mooring rope which raises and lowers the sealing long pile;
• and
• suction legs in the pile sleeves, wherein the suction leg with or without a long pole comprises a sealing long pile having a tubular pipe and a top head connected tightly to the tubular pipe to form a cylindrical integral structure with a sealing top and an opening bottom, wherein the sealing long pile of the suction leg slides up and down along or is fixed with the pile sleeve, wherein the sealing long pile serves as a foundation of the offshore caisson.

A sit-on-bottom offshore platform, comprising:

• a storage tank sitting on a seabed for storing platform-produced liquid or receiving input liquid and with or without a transparent moon pool, wherein at least two pile sleeves are arranged symmetrically around the bottom of the storage tank, the pile sleeves being connected to the storage tank to form an integral structure;
• suction legs comprising sealing long piles with or without long poles, the sealing long pile having a tubular pipe and a top head connected tightly to the tubular pipe to form a cylindrical integral structure with a sealing top and an opening bottom, the top head having an opening, wherein a number of the suction legs is equal to a number of the pile sleeves, wherein the sealing long piles of the suction legs are inserted into the pile sleeves, and slide up and down or are fixed to the pile sleeves;
• and
• a topsides located in a top of the storage tank, wherein the topsides is connected to the storage tank by deck legs or the long poles of the suction legs,
• wherein each suction leg is raised up at its upper position, bottoms of each sealing long pile and the storage tank are at a same horizontal plane, wherein the opening on the top head of the sealing long pile is closed during construction and towing, wherein the opening bottom of each sealing long pile is submerged underwater to form an enclosure for air inside the sealing long pile to increase buoyancy and metacentric height of the sit-on-bottom offshore platform during wet towing;
• wherein the sealing long piles of the suction legs are pressed down into the seabed and become a foundation of the sit-on-bottom offshore platform, wherein when the opening of the top head is open, the sit-on-bottom offshore platform sits on the seabed through a gravity penetration method or a suction pile penetration method and is re-floated or removed through a buoyancy uplift method or a suction pile uplift method, wherein when the opening of the top head is closed, the sit-on-bottom offshore platform sits on the seabed through the suction pile penetration method and is re-floated or removed through the suction pile uplift method,
• wherein the storage tank is a cylindrical tank group, wherein the cylindrical tank group comprises a body formed by multi closely connected tank units in a honeycomb form or a single tank unit, and a top connection structure and a bottom connection structure surrounding the top and bottom of the body respectively, wherein each pile sleeve as part of the bottom connection structure is tangent to the single tank unit or two adjacent tank units in the honeycomb form, wherein at an intersection of the top connection structure with each vertical central axis of the pile sleeve, there is a hole for traverse and fixation of the long pole, or a hole with a diameter equal to a diameter of the sealing long pile for traverse and temporary fixation of the sealing long pile if the suction leg has no long pole, or there is a mooring rope which raises and lowers the sealing long pile.