Riser Deployment and Hang-Off Analysis for a Harsh Environment, Deepwater Site

Abstract

In planning for a deepwater well, running/retrieval of a drilling riser in advance of rapidly developing seas was identified as a critical operation. The harsh seastates required careful attention to the well-specific operating criteria, (WSOC), or the metocean conditions that limit specific operations. Certain conditions would warrant the operation being shut down so that the riser could be pulled or run before conditions became excessive. In deep water, a running/retrieval operation can take several days and the consequences of being shut down part way can be severe. Moderately high current profiles can cause the riser to bind in the diverter housing, preventing further running or retrieval. If binding occurs, a dynamically-positioned vessel can carry out “drift running” operations to increase its operability. However, if conditions prohibit further running/retrieval, the riser may need to be hung off “hard” (with no compensation) at the drill floor or “soft” on the tensioners and/or drill string compensator. In such a case, in addition to large top riser angles, vessel heave motion can cause tension variation, depending on the hang-off conditions and the length of the deployed riser. This paper discusses how riser analysis was used to support the operational understanding of the riser running/retrieval process for this deepwater well. The results were used to assist in the planning and decision-making involved in drilling this well.

Mechanical analysis of deepwater drilling riser system based on multibody system dynamics

“…A coupling model including the riser system and tensioners is then introduced to simulate the axial dynamic behavior of the riser system. Sullivan et al (2004) used spring elements to simulate tensioners to conduct suspension dynamic analysis of a riser system. Lang et al (2009) developed a dynamic analysis unit of tensioners and coupled it with the dynamic analysis model of a riser system to conduct riser recoil analysis.…”