Diving deep into the world of risers

Risers are a key component of offshore drilling systems, linking the floating platform to the subsea wellhead. A riser is composed of a bundle of tubes with a main pipe extending the well and 5 safety and service lines, integrated into 23 m joints and assembled to one another. This system has demonstrated its efficacy to depths of up to 3,000 m of water.

Emmanuel Persent Applied Mechanics Division emmanuel.persent@ifpen.fr	Jean Guesnon Expert Director Mechanical Engineering of Offshore Applications jean.guesnon@ifpen.fr

Risers are either connected to the wellhead, during drilling operation, or disconnected during running and retrieval. However, these two situations are antagonistic and dimensioning of the riser needs to take them into account. It has been shown, in fact, that the weight required by the riser to guarantee its dynamic stability when it is disconnected becomes a major handicap when it is connected. This difficulty can be overcome by integrating the peripheral lines hyperstatically, i.e. by rigidly connecting their ends to the main pipe. The resulting sharing of loads between the tubes makes it possible to significantly reduce the weight of the overall system and gives the riser a high level of axial stiffness, which is beneficial to its dynamic behavior.

A parametric study has quantified these effects and enabled extension of the riser's operational range, in terms of water and drilling depths, to be evaluated. In particular, it is estimated that the new concept may allow water depths of 4,200 m to be reached.
Load sharing riser technology, which is patented by IFPEN, is currently being developed.

Detailed conceptual and design studies were performed according to a particular specification and a qualification testing program is planned, including static and fatigue testing of prototypes.

Increase in the operational scope of risers using load sharing technology. The range of conventional risers is indicated in green and that of hyperstatic ones in red.

Publications

• E. Persent, J. Guesnon, S. Heitz and D. Averbuch, New Riser Design and Technologies for Greater Water Depth and Deeper Drilling Operations, Paper SPE/IADC 119519 (2009)

• J. Guesnon, C. Gaillard, Method of dimensionning a drilling riser, US Patent 7,630,866 (2009)

>> See also IFPEN Publications database