OFFSHORE UNIVERSAL RISER SYSTEM

摘要

An offshore universal riser system. A riser system includes a valve modul e which selectively permits and prevents fluid flow through a flow passage e xtending longitudinally through a riser string. An anchoring device releasab ly secures the valve module in the flow passage. A method of constructing a riser system includes the steps of installing the valve module in the flow p assage, and installing at least one annular seal module in the flow passage. The annular seal module is operative to prevent fluid flow through an annul ar space between the riser string and a tubular string positioned in the flo w passage. Drilling methods include injecting relatively low density fluid c ompositions into the annular space, and selectively varying a restriction to flow through a subsea choke in a drilling fluid return line. The riser stri ng, including housings for the various modules and external control systems, is dimensioned for installation through a rotary table.