HPHT Hands Free Drilling Riser System with Superior Fatigue Performance
Authors: Sandman Colton , Plichta Drew , Mills Darren , Kaculi Jim 
Published: April 2018

As the oil and gas industry continues its rapid research and development of unexplored or underdeveloped offshore resources, it is increasingly targeting areas with higher pressures and temperatures at deeper water depths. Operating in these harsh environments, combined with the need to reduce cost, requires the development of equipment with higher capacities, improved fatigue performance, reduced risk, and increased operating efficiencies. Functioning as the critical conduit between the drilling vessel and the blowout preventer (BOP), the marine drilling riser presents many design challenges due to the high pressure/high temperature (HPHT) environment. Conventional designs may not be able to withstand the higher combination of loads expected for offshore HPHT wells. This paper describes the development of a new generation marine drilling riser system with advanced automation capable of meeting these challenges.

When considering the various load combinations and fatigue performance requirements for drilling riser systems that endure severe loading, a boltless riser connection can provide an optimized load path while also eliminating risks associated with the use of bolts. Traditional bolted flanged connections create stress concentrations at each bolt with non-uniform loading, whereas a boltless riser system utilizing a split lock ring distributes the load evenly around the circumference of the connection. This optimized load path decreases stress concentrations, which allows for higher load capacities and superior fatigue performance resulting in extended field life.

The choke and kill lines, a crucial part of the well control system, also present design challenges for HPHT environments. Due to the HPHT requirements, the choke and kill line sizing increases significantly, which drives up the overall joint weight. This additional weight is offset by utilizing the choke and kill lines to share part of the overall joint loading, therefore reducing the main tube thickness.

This new generation drilling riser offers a safe and efficient method of connecting riser joints, ensures a consistent make-up and break-out of the connector, and provides operational feedback to actively track each riser for maintenance management. The boltless connection is made-up using an automated spider, which provides a quick, safe, and hands free alternative to conventional methods. The modular connector design also offers a simple method for inspection, repair, or replacement of the connector assembly with minimal downtime.

API 16F currently only requires tensile load testing to the rated load [1]. However, additional testing was performed to accurately validate the system to normal/extreme/survival envelopes in support of deep-water and HPHT applications consistent with recent revisions of API 16A/17TR7/17TR8 [2, 3, 4]. This includes combined loading of pressure, tension, bending, and auxiliary line load sharing.

This improved validation process for marine drilling risers accurately simulates load scenarios encountered in field use and validates the analysis methodology confirming the design margins of the riser. The design details, analysis, and test results will be presented.