Abstract: This invention relates to the installation of a Vertically Moored Platform over a selected well site. The platform or structure is supported on a buoyant gravity base and floated to a position over the subsea well site. The gravity base is then ballasted to effect tilting in a controlled manner. Ballasting is continued to bring the gravity base and platform back to a vertical position. Then the gravity base is lowered from engagement with the floating structure with cables to the sea floor while maintaining the floating structure in a positive buoyancy state. In the preferred embodiment a large-diameter drive pipe is inserted through each receiving passage in the gravity base and into the soil or rock beneath the gravity base where it is anchored. A conductor is then inserted through the drive pipe and anchored or cemented to the soil or rock beneath the drive pipe. A riser pipe is then inserted into the drive pipe and secured to the conductor.

Abstract: This invention relates to the installation of a vertically moored platform over a selected well site. The platform or structure is supported on a buoyant gravity base and floated to a position over the subsea wall site. The gravity base is attached or held to the platform by a plurality of short sections of riser pipes. The gravity base is then ballasted to give it a negative buoyancy. A joint of riser pipe is then added to each of the short riser pipe sections. The gravity base is then lowered by lowering all the riser pipes simultaneously until the top of the newly added joints is reached. Then a second group of riser joints is added and the process repeated until the gravity base has been lowered to the ocean floor. When the gravity base has reached bottom, heavy ballasting material, such as cement slurry, can be added if needed. The riser pipes which were used to lower the gravity base are the riser pipes which anchor the floating platform to the gravity base which serves as an anchor.