The concept of riser-less coiled tubing (CT) interventions in offshore wells promises significant reductions in both cost and non-productive time associated with many offshore well interventions. However, conveying CT from a vessel through the open ocean into a high pressure subsea wellhead without a marine riser package poses several significant technical issues that must be identified and mitigated in system design and pre-job planning. Some of these issues include:
High stress to yield ratios in heavy seas.
Catastrophic buckling in the water column.
Synchronization of tubing payout and wellhead entry rates.
Subsea wellhead snubbing at high differential pressures.
This paper will present the overall system design of a riser-less offshore coiled tubing intervention system (slated for full scale testing in late 2016), engineering principles utilized for analysis, and will present an example riser-less CT operational envelope based on CT forces and stress limits. Also discussed is a set of tests performed to validate the forces model.
Number of Pages
Newman, K.R. Dynamic Well Intervention Modeling. Paper SPE 153180 presented at the SPE/ICoTA Coiled Tubing and Well Intervention Conference & Exhibition, The Woodlands, Texas, March 2012.
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