Floating/tensioned production system with caisson

A drilling and production system for use at a drill site beneath a body of water having a floor and a surface, said drilling and production system comprising:

• a semisubmersible platform having production facilities thereon and comprising a working deck having an outer perimeter, at least one flotation means supporting said working deck and being configured and arranged about said outer perimeter leaving a substantially unobstructed area beneath said working deck and within said perimeter, said flotation means being adapted to be ballasted and de-ballasted, and mooring lines for anchoring said working deck at said drill site;
• a tension leg platform comprising a production deck, at least one buoyancy member for supporting said production deck, said buoyancy member being adapted to be ballasted and de-ballasted, a foundation anchored on said floor of said body of water above said drill site, at least one riser extending upwardly from said drill site to at least one wellhead located on said production deck, and at least one tether adjusted to hold said production deck above said foundation and below said surface of said body of water;
• a caisson being configured and arranged to provide a substantially water-free working area on said production deck;
• means to compensate for relative movement between said semisubmersible platform and said tension leg platform;
• and
• at least one flexible flowline for directing fluid from said wellhead on said production deck to said production facilities.

A drilling and production system for use at a drill site beneath of a body of water having a floor and a surface, said drilling and production system comprising:

• a plurality of mooring lines;
• a working deck having a bottom and being anchored by said mooring lines at a location generally centered over said drill site;
• at least one flotation means for supporting said working deck above the surface of said body of water by a buoyant force, said flotation means being configured and arranged so that an unobstructed area exists substantially centered beneath said working deck, said flotation means being adapted to be ballasted and de-ballasted, whereby said flotation means may be sufficiently de-ballasted to support said working deck above said surface of said body of water so that an air gap exists between said bottom of said working deck and said surface of said body of water;
• a production deck having at least one wellhead thereon;
• at least one buoyancy member for supporting said production deck, said buoyancy member being adapted to be ballasted and de-ballasted;
• a foundation anchored on said floor of said body of water at said drill site;
• at least one riser extending upwardly from said drill site to said wellhead on said production deck;
• at least one tether configured and adjusted to maintain said production deck above said foundation and below said surface of said body of water;
• at least one flexible flowline for directing produced fluid from said wellhead on said production deck to said production facilities;
• a caisson being configured and arranged to provide a substantially water-free working surface on said production deck;
• and
• means to compensate for relative movement between said production deck and said working deck.