Hydrodynamic Study of Free Standing Drilling Riser Under Hurricane Conditions

Abstract

Offshore structures are susceptible to damages due to hurricane. The main subject of this research, free standing drilling riser (FSDR), is an innovation to the drilling riser that enables rapid disconnection prior to hurricane conditions. This allows the offshore drilling rig and operator to move away from hurricane path prior to hurricane landing. Yet, currently, the emergency disconnection decision of FSDR is decided by a rig manager. Past incidents have shown that human error can cause catastrophic damage. Studies on FSDR operations under hurricane condition are scarcely available. The most relevant studies, free standing riser (FSR) behaves differently. With the increase in hurricane intensity over the past 50 years, this increases the risk in FSDR operations. In this work, the hydrodynamic response of FSDR under hurricane conditions was investigated. Four simulation studies were conducted in Orcaflex finite element modeling (FEM) software. These studies were conducted to determine the effect of emergency disconnection location, the optimum emergency disconnection location, the effect of various Saffir Simpson maximum significant wave height and hurricane generated swell on the hydrodynamic response of FSDR. Hurricane generated wave spectrum was used to replicate hurricane conditions. The simulation study shows that the lateral displacement of FSDR decreases in a 3rd order polynomial function with the emergency disconnection location, LD = −6e−6d3 + 0.0024d2 − 0.3348d + 19.179. In addition, the optimum emergency disconnection location along drilling riser line is at 87.50% of the original water depth. The lateral displacement of FSDR increases exponentially with Saffir Simpson scale storm intensity, y = 1.7537e0.0386x. Lastly, the stronger the swell component of hurricane generated swell, the higher the hydrodynamic responses. Wind wave component of hurricane generated swell did not influence FSDR as the riser was in the free standing mode. The limitation of this research is the findings are applicable for this simulation setup only. Further validations are required with experimental setup and various types of offshore structure.