Universal Subsea Inc. (USI) has developed and deployed what is said to be the industry’s first high-density subsea equipment preservation and hydrate prevention fluid.
Defender Stasis HD was formulated specifically to protect subsea tree mandrels, tree access bores, tubing head spools and similar subsea equipment.
According to USI, the fluid has properties that protect subsea equipment from corrosion, calcareous deposits and marine fouling, while preventing costly methane hydrate formations in the access bore of trees where gas may accumulate.
The environmentally friendly fluid has been injected into the access bore of four subsea wells in the Gulf of Mexico to date.
It is classified as a subsea equipment preservation fluid in compliance with U.S. EPA NPDES GMG290000 and is approved for direct release to sea from subsea oil and gas facilities, the company said.
“Many subsea trees will slowly bubble natural gas past the crown plugs or swab valves. The methane gas mixes with seawater and freezes to form gas hydrate plugs in the well access bore,” said John Fitzgerald , director of Sales and Marketing at USI.
“The resulting hydrate blockage impedes well intervention, requiring methanol injection rigs to depressurize and melt the hydrates. This process can require 24 hours or more of vessel time, costing $200,000 to $1,000,000 depending on the vessel type.”
Unlike water-based fluids and glycols typically used for subsea tree caps, Defender Stasis HD is formulated with a high-density, biodegradable synthetic ester which is engineered to be similar to natural vegetable oils. When injected into the tree access bore it creates a non-aqueous environment, so that methane gas will bubble through the preservation fluid without forming hydrates.
“Whether injected into equipment subsea or tested in the lab, Defender Stasis HD immediately sinks to the bottom of equipment bores and immersed cavities filled with seawater or other fluids, displacing those fluids from the bottom upwards, completing a full sweep and replacement of the fluids with the high-density fluid,” added Sean Thomas , PE, USI president and founder.
Defender Stasis HD can be injected into a closed chamber such as a subsea tree cap, with venting at the top of the chamber, in open water with a dispensing hose or by holding an ROV hot stab over the bore of the subsea tree mandrel.
In all cases, it is said to immediately fall to the bottom of the access bore, equipment bore or container, displacing any fluids in the bore (SG < 1.14) and completing a uniform sweep with the Stasis HD.