Riser pipe:

The pipe and special fittings used on floating offshore drilling rigs to establish a seal between the top of the wellbore, which is on the ocean floor, and the drilling equipment, located above the surface of the water.

A riser pipe serves as a guide for the drill stem from the drilling vessel to the wellhead and as a conductor of drilling fluid from the well to the vessel.

The riser consists of several sections of pipe and includes special devices to compensate for any movement of the drilling rig caused by waves.

It is also called a marine riser.