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The Thunder Hawk field was developed through a Steel Catenary Riser (SCR) system connected to a DeepDraft Semi® Floating Production Unit (FPU) installed in approximately 6,060-ft. water depth in the central Gulf of Mexico (GoM). This paper presents an integrated riser design experience, focusing on the significant design challenges and solutions. The Thunder Hawk FPU was one of the first deepwater projects to address the enhanced GoM environment criteria. These criteria required the integrated design team to configure a feasible and robust hull, mooring and riser system. Model tests were performed to validate the design and calibrate the analysis model. Other challenges included the SCR fatigue and fracture design, titanium stress joint and receptacle design for the high pressure production risers, flex joint over-rotation design, and porch fatigue design. A significant amount of sensitivity analyses were performed to cover the uncertainty of the various hull, mooring, and riser design parameters that affected the SCR performance. The SBM Atlantia (SBMA) riser team worked closely with the Murphy Integrated Project Team (IPT) to achieve a robust and comprehensive riser design 16 months before the first SCR was installed. The highly integrated engineering approach enabled prompt and full considerations of the system interactions, and provided instant design evaluation throughout the project. The sensitivity analyses established the system design envelopes, and resulted in significant flexibility in offshore installation and operation.

Hydrate formation is a known flow assurance risk in deepwater flowlines, and remediation via single-sided depressurization presents unique challenges to ensure the mechanical integrity of the subsea infrastructure. This paper describes the gas lift depressurization technique that was developed for hydrate remediation and the engineering study that was conducted to assess the risks.

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Certain subsea jumper design features coupled with operating conditions can lead to Flow Induced Vibration (FIV) of subsea jumpers. Excessive FIV can result in accumulation of allowable fatigue damage prior to the end of jumper service life. For this reason, an extensive FIV management program was instated for a large development in the Gulf of Mexico (GOM) where FIV had been observed. The program consisted of in-situ measurement, modeling and analysis. Selected well and flowline jumpers were outfitted with subsea instrumentation for dedicated vibration testing. Finite Element (FE) models were developed for each jumper and refined to match the dynamic properties extracted from the measured data. Fatigue analysis was then carried out using the refined FE model and measured response data. If warranted by the analysis results, action was taken to mitigate the deleterious effects of FIV. Details on modeling and data analysis were published in [5]. Herein, we focus on the overall findings and lessons learned over the duration of the program. The following topics from the program are discussed in detail: 1. In-situ vibration measurement 2. Overall vibration trends with flow rate and lack of correlation of FIV to flow intensity (rho-v-squared); 3. Vibration and fatigue performance of flowline jumpers vs. well jumpers 4. Fatigue analysis conservatism Reliance on screening calculations or predictive FE analysis could lead to overly conservative operational limits or a high degree of fatigue life uncertainty in conditions vulnerable to FIV. It is proposed that in-situ vibration measurements followed by analysis of the measured data in alignment with operating conditions is the best practice to obtain a realistic understanding of subsea jumper integrity to ensure safe and reliable operation of the subsea system. The findings from the FIV management program provide valuable insight for the subsea industry, particularly in the areas of integrity management of in-service subsea jumpers; in-situ instrumentation and vibration measurements and limitations associated with predictive analysis of jumper FIV. If learnings, such as those discussed here, are fed back into design, analysis and monitoring guidelines for subsea equipment, the understanding and management of FIV could be dramatically enhanced compared to the current industry practice.