Methods and apparatus for converting an offshore structure

A method of connecting a mat structure to an offshore structure, comprising:

• positioning a bottom of a hull of the offshore structure and a top of the mat at substantially the same elevation;
• disposing the mat structure beneath the offshore structure via horizontal movement between the mat structure and the offshore structure;
• positioning at least one leg of the offshore structure into alignment with a clamp of the mat structure by floating the offshore structure over the mat structure as the horizontal movement or by floating the mat under the offshore structure as the horizontal movement to position the at least one leg into alignment with the clamp;
• moving the clamp into engagement with the at least one leg to connect the mat structure to the offshore structure while offshore;
• and
• lowering the mat structure onto the seafloor subsequent to connecting the mat structure to the at least one leg.

A device, comprising:

• a mat;
• a clamp coupled to the mat and configured to engage a first leg of an offshore structure, wherein the clamp is configured to move into and out of engagement with the first leg to connect and release the mat to and from the offshore structure;
• and
• a stability caisson coupled to the mat, wherein the stability caisson comprises a floating type structure that provides buoyancy to the mat to allow the mat to float in a position wherein a top of the mat is at substantially the same elevation as a bottom of a hull of the offshore structure and to stabilize the mat when disposing the mat beneath the offshore structure via horizontal movement between the mat in the position and the offshore structure for connection of the mat to the offshore structure.