New Developments In Subsea Christmas Tree Workover Pressure Control Components

Subsea "horizontal" trees are now becoming commonplace, and in many areas of the world they are replacing conventional trees. Although their safety record has been excellent, concerns have been expressed regarding the reliability of their safety barriers particularly during intervention. The establishment of reliable (and verifiable) metal sealing pressure barriers is important in subsea christmas tree operational security. The recently developed valve, plug, and seal mechanisms described in this paper provide an improved second safety barrier for the vertical bore of the "horizontal" style tree, yielding a reliable and verifiable all-metal sealing pressure control package. These improved valve, plug, and metal seals have been designed, built, and tested for controlling potentially high pressure in the vertical bore of a "horizontal" style subsea christmas tree. This paper will describe these new developments, the testing performed, and the operational advantages they provide. These developments have application to the expanding base of "horizontal" style subsea christmas trees being manufactured and installed globally. The insert plug and metal sealing technologies also have application in conventional tree completions as well. Significant effort has been expended to develop a robust, metal sealing insert plug that has intrinsically verifiable setting features when deployed from the surface and locked in position subsea. The same "weight-set" metal seal design employed in this insert plug has also been developed for the primary tubing hanger annulus seals. The testing and field use for both applications will be described. Additionally, test results will be summarized for a retrievable 7" - 10,000 psi w/p horizontal tree "swab" valve and its' metal seals. These data include extreme pressure and temperature cycling results as well as conclusions regarding metal seal reliability and valve shearing capabilities. This 7" bore intervention ball valve that has been developed represents a unique concept in which the assembly is a full-time integral tree component, rather than this pressure barrier being just available for use only during actual intervention.