Universal Subsea logs Gulf of Mexico well abandonment success
HOUSTON - Universal Subsea Inc. (USI) announced that its patent-pending Defender subsea isolation cap was successfully installed to the Bulleit subsea well, operated by Talos in the Gulf of Mexico at a water depth of 1,300 feet. The lightweight, thermoplastic cap was landed, locked and securely sealed to the wellhead in Green Canyon Block 21 using an ROV after deployment via wireline from the Noble Don Taylor drillship. The isolation cap and subsea wellhead were injected with USI’s proprietary, nontoxic, biodegradable Defender Stasis LT subsea equipment preservation fluid. The low-pressure isolation cap design ensured that seawater was completely purged from the wellhead bore and external chambers and replaced with the long-lasting preservation fluid.
The drilling program for the Talos-operated Bulleit well called for an estimated 12-month temporary abandonment period before the subsea tree installation, and protection against corrosion and marine growth during the abandonment was considered crucial. The technical team at Talos recognized the intrinsic value of maintaining the wellhead mandrel in the “as-installed” condition during the abandonment, and eliminating the costs and schedule impacts for remedial cleaning activities prior to subsea tree installation.
The Defender subsea isolation cap used on the Bulleit well fits all subsea wellheads with a 27-inch H-4 profile. Similar models are available for other subsea wellhead profiles and subsea tree applications. Defender’s one-piece, thick wall, nonmetallic body is manufactured from a marine- grade thermoplastic that is immune to corrosion and deterioration in the subsea environment while providing a 25-plus year operating life. Metal hardware is typically 316 stainless steel.
“Universal Subsea overcame numerous engineering barriers to develop a corrosion-proof, low pressure, plastic protector cap that would lock and seal reliably in water depths from 50 feet to 11,000 feet, with multiple patents pending,” noted Sean Thomas, PE, president and founder. “The new designs include a high capacity, damage resistant, ROV operated locking system and special body seals that we developed to allow ROV installation while providing reliable sealing performance. Defender’s dual containment zones and tertiary annular zone provide two elastomer seal barriers and two non-conductive fluid barriers between the wellhead ring gasket profile and the subsea environment. The non-electrolytic preservation fluid is a key part of the technology.”
Formulated from natural and modified bio-based oils with environmentally friendly additives, Defender Stasis LT preservation fluid is in a class by itself. This proprietary fluid provides superior corrosion protection for metallic components while being very friendly to elastomers and other non-metallic materials. The fluid is oil based, so it provides excellent water separation and high dielectric properties while being naturally long lasting to protect subsea equipment components. Since the fluid is derived from natural oils, it is nontoxic to aquatic life, biodegradable, and extremely safe for personnel.
Defender Stasis LT is the first non-aqueous subsea equipment preservation fluid that meets regulatory requirements for direct discharge to sea from subsea oil and gas facilities in U.S. offshore waters. The fluid is rated as an Environmentally Acceptable Lubricant (EAL) and a Total Loss Lubricant, and easily complies with the regulations of tightly-regulated markets such as Norway, the U.K. and Australia.
“For subsea trees, corrosion and calcareous deposits over the 10 to 25-year operating life of the tree will affect reliability of crown plugs, swab valves and internal tree caps, in addition to BOP connector locking and sealing performance,” remarked Thomas. “For the tree application, USI’s subsea isolation cap and preservation fluid will provide significant cost savings and risk reduction for each intervention, with real potential to extend tree operating life and well production life by several years for some wells.”
“We are grateful to Talos for partnering with us to set a global best practices milestone for protection of subsea wellheads during well abandonments,” stated John Fitzgerald, director of sales and marketing, Universal Subsea Inc. “Defender is the only ROV-installable protector cap that provides positive locking and reliable sealing to the wellhead mandrel. It is also the only cap of any size or rating that allows all seawater to be completely removed from the internal and external protection zones. The wellhead bore, ring gasket profile and external connector profile are completely isolated from the subsea environment and immersed in non-electrolytic preservation fluid to protect against deterioration.”