Cross-section of Marlim Sul umbilical containing two ½-in. HCR elements.Petrobras and Oceaneering Multiflex have developed steel-core chemical injection lines for thermoplastic subsea umbilical applications in water depths of 1,700 meters and greater. Oceaneering Multiflex is an Oceaneering International subsidiary. Petrobras is Brazil's national oil company. The two designed, tested, and delivered the industry's first high collapse-resistant (HCR) flexible steel piping for use in thermoplastic subsea control umbilicals.
HCR technology enables the injection of fluids of low specific gravity into subsea-completed wells under the high external pressure conditions of deepwater production. As such, the HCR pipes improve the efficiency and potential profitability of production from deepwater oil and gas fields.
Petrobras recently made significant advances in deepwater field development, most notably at the Marlim Sul and Roncador fields. As the depths of their ventures increased, Brazil's oil company realized the higher hydrostatic pressures would soon exceed the collapse ratings of certain conventional umbilical components.
The feasibility of Petrobras' planned deepwater projects depended on umbilicals capable of functioning under the extremely high external compression forces present at depths exceeding 2000 meters, while providing the flexibility in dynamic modes associated with thermoplastic designs.
In the past, collapse of umbilical component hoses from external pressure was of little concern as they were typically always filled with hydraulic fluid and generally had applied internal pressure. However, recent deepwater umbilical designs call for chemical injection lines carrying fluids with specific gravities less than one that are operated periodically and in some cases evacuated.
Traditional chemical injection lines may collapse in these situations due to insufficient collapse resistance strength. To produce from planned deepwater fields, Petrobras needed umbilicals with internal components capable of resisting the stresses of operating a mile or more below the ocean's surface, under hydrostatic pressures which could crush current umbilicals.
Petrobras' production schedules allowed only eight months for development, manufacture and delivery of thermoplastic control umbilicals containing deepwater-rated chemical injection lines. Petrobras signed an agreement to cooperatively develop a 1/2-in ID HCR pipe rated for water depths to 2,000 meters. Both the HCR pipes and the umbilicals incorporating them were of thermoplastic design to meet the dynamic requirements of Petrobras' floating production applications.
After evaluating several alternatives, the project team decided to utilize known flexible pipe technology in the form of a spirally wound, interlocked stainless steel carcass encased in extruded thermoplastic and aramid braiding. With metallic instead of conventional thermoplastic cores, the HCR flexible pipes would withstand high external pressures without the need for internal pressure and could be installed while evacuated.
Multiflex also developed the end fittings and seals to accommodate the steel interiors of the new injection lines. Swaged seal rings similar to those used with flexible pipes provide positive sealing members. Other mechanisms were introduced to the fitting design to limit relative movement between braid package and the core tube, slowing fatigue and defect growth.
In December 1996, Petrobras ordered the first umbilical containing HCR hose, a 4,800-meter length, intended for the Marlim Sul 3 well. The umbilical contained two 1/2-in. HCRs, nine 3/8-in. thermoplastic hoses and three twisted pair electricals. The product was delivered in April 1997 and installed in 1,710 meters of water, breaking the world depth record. To date, Petrobras has provided 10 HCR umbilicals.
Along with serving as sturdy, flexible chemical injection lines, HCR pipe can be used in other deepwater applications in dynamic mode, as umbilical flying leads, for annulus monitoring and circulation, and to perform water injection.
The HCR pipe provides the offshore industry with a cost-effective solution for deepwater production needs. Umbilicals with HCR pipe can now accommodate the strength and flexibility specifications of ultra-deepwater applications.
Copyright 1999 Oil & Gas Journal. All Rights Reserved.
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