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.

You can access this article if you purchase or spend a download.