STRUCTURAL RELIABILITY ANALYSIS FOR OFFSHORE DRILLING RISER DEPLOYMENT OPERABILITY

Drilling riser system provides a short-term connection between subsea oil well and drilling vessel or platform. The analysis of different operability envelopes are required for drilling riser analysis, for example, connected drilling, connected non-drilling and hang-off analysis. The operability envelope analysis could provide operators statistical information for riser operational management. The current practice to calculate the drilling operability envelope is to use deterministic approach. However, deterministic approach could not take the randomness from environmental loadings and structures into consideration. Structural reliability method is an analysis tool to quantify probability of failure of components or systems accounting for uncertainties in environmental conditions and system parameters. It is particularly useful in cases where limited experience exists or a risk-based evaluation of design is required. It is gaining increasing popularity in the offshore and marine industry to predict failure probability. In this paper, structural reliability analysis is adopted to analyze the offshore drilling riser deployment. The uncertainties are mainly from wave and current loadings. The significant wave height Hs is modeled by a Weibull probability density function, the zero-crossing wave period Tz conditional on Hs is modeled by a lognormal distribution, and the surface current speed is modeled as Weibull distribution. Multiple simulations are performed by software Flexcom [1] and efficient structural reliability methods are adopted to get the failure probabilities. The deployment operability will be calculated based on structural reliability methods and the results will be compared with those calculated based on deterministic approach.