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I would be interested in learning from any direct previous experience anyone has of operating a semi-submersible rig in very shallow water depth, 20 to 40 metres. I am planning an offshore drilling campaign in the Gulf of Papua that includes a variety of wells in a water depth range of 20 to 100 metres. The lower limit rules out a semi-submersible on paper ; the upper limit rules out many jack-ups. I have read of the concept of sitting a semi-submersible rig on the seabed - is this a myth or is/was it actually done anywhere in our industry ?

One of the offset wells was drilled by Phillips in 1970 with a drillship, the "Glomar Conception", in 9 metres of water. The end of well report states that "...it was necessary to set the BOP equipment below the seabed to provide sufficient clearance for the drilling ship. This was done by jetting a caisson into the seabed and setting the wellhead approximately 30 feet below the mud line."