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

A suction leg, comprising:

• a sealing long pile with or without a long pole,
• wherein the sealing long pile comprises 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 top head has at least one opening to be opened or closed, wherein the long pole is a cylindrical or a triangle truss structure being fixed on a center of the top head of the sealing long pile and has a common axis with the sealing long pile, wherein a diameter of the long pile is smaller than a diameter of the tubular pipe, wherein the sealing long pile is penetrated into a seabed by one or more of:
• a gravity penetration method or a suction pile penetration method, or pulled out from the seabed by one or more of:
• a buoyancy uplift method or a suction pile uplift method.

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 a closed air inside the sealing long pile to increase buoyancy and GM 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 the sit-on-bottom offshore platform sits on the seabed through a gravity penetration method or a suction pile penetration method, or is re-floated or removed through a buoyancy uplift method or a suction pile uplift method.