Deep water and ultra deep water intervention of wet trees has been a huge challenge for oil and gas producers. Currently, the only realistic way to do intervention is to use a conventional Mobile Offshore Drilling Unit (MODU) or intervention vessel (which is usually a smaller MODU) whether for a simple clean out or re-completing another producing interval. This is an extremely costly venture and the intervention is only scheduled when the economics of the operation are clearly justified. And even when the intervention is approved there is the problem of scheduling a MODU or intervention vessel. Sometimes the intervention can take months before a MODU or intervention vessel is available.
There is a new enabling technology, using a Self Standing Riser, (SSR), where a coiled tubing intervention and drilling system could be deployed by a cost effective vessel (not a conventional MODU) with all the coiled tubing and related equipment on the vessel. The SSR design is such that it would attach to the subsea tree and provide the support and a circulation conduit for the coiled tubing to have full circulation capabilities back to the intervention vessel. The vessel, itself, would have station keeping capabilities for a significant period of weather conditions for the Gulf of Mexico.
This paper presents the reasons why conventional and subsea coiled tubing approaches have been unable to provide a economically workable solution for coiled tubing intervention and drilling from wet trees in deep water. The paper describes a new system based on a SSR and a cost effective vessel (non MODU) design that could accommodate the coiled tubing equipment, and provide station keeping and support for the operations. The paper will discuss safety issues such as: the reliability and safety of the SSR, well control issues, emergency disconnects, and the event of a drive off by the vessel.
Unless, this type of technology is developed and deployed millions of barrels of barrels of oil and gas will remain behind pipe. In other cases, some fields will not be developed because the need for on-going intervention coupled with high capital costs that will not meet the economic threshold to commission the development.