Double walled riser

Abstract

A double walled riser extends from a platform to a subsea well and is connected, through a suitable connector, to the top of the wellhead housing. The wellhead housing has annulus access passageways therein. The connector has passageways therethrough which communicate at one end with the annulus access passageways in the wellhead housing and at the other end with small diameter annulus access tubes carried between the two walls of the double walled riser. The inner wall of the double walled riser comprises a pressure containing member, and the outer wall comprises a structural support member. The small diameter annulus access tubes disposed in the annulus between the inner and outer walls of the riser communicate at one end with one of the respective passageways through the connector, and extend at the other end to the platform. The riser comprises a plurality of joints having a male connecting end and a female connecting end, and adapted to be connected together end to end in locked, sealed relation to form a single riser string from the wellhead to the platform. The small diameter annulus access tubes disposed in the annulus of each riser joint have at one end a male stab nipple carrying a seal ring, and at their other end of female sealing receptacle. When the riser joints are made up on the rig, the small diameter tubes are stabbed together in sealed relation to form continuous, pressure-conveying tubes communicating selected wellhead annuli to the platform.