A freestanding offshore well structure includes a generally cylindrical caisson having a relatively small diameter drivepipe section connected to a larger diameter caisson section which is of sufficient strength to withstand wind and wave action. An upper portion of the drivepipe section is provided with a landing ring for a hanger for a conductor casing string or a wellhead body for a surface pipe string. A casing connector or nipple supports a diverter above the landing ring. The caisson is driven to refusal, the diverter attached to the upper end of the caisson and drilling operations and installation of the casing string, surface pipe and wellhead body are carried out through the diverter. The diverter is then removed and connection of wellhead valve bodies, handles and associated conduits to the wellhead is then carried out to complete the well assembly.
