(WO) — Endurance Energy has drilled and completed a subsea geothermal well and demonstrated net-positive electricity generation during a deep-sea test at Axial Seamount, an active underwater volcano about 300 mi off the Oregon coast. The Seattle-based startup said its three-week deployment marked the first end-to-end demonstration of its subsea geothermal power system.
During the deployment, the company drilled a 52-ft geothermal well at a depth of approximately 5,000 ft beneath the Pacific Ocean, installed its Adélie test plant on the seafloor and operated the system remotely from Seattle through a subsea fiber-optic network. The well was cased and cemented, and hot fluid flowed at 260°C (500°F) after completion.
Because the newly drilled well did not provide sufficient flow to operate the plant, the team connected Adélie to a nearby natural hydrothermal vent flowing at approximately 281°C (538°F). The turbine reached about 26,000 rpm, and the system generated more electricity than it consumed for 8.7 seconds. Endurance reported median net output of approximately 2 kW and a peak of 16.5 kW during the run.
The test also exposed technical challenges. Battery overcurrent protection ended the initial power-generation run, and a cable supplying the refrigerant pump failed during a subsequent restart attempt. Endurance said the deployment provided data on seafloor drilling, well flow, heat transfer, mineral buildup, high-temperature power generation and remote control of subsea equipment.
The company plans to deploy Gentoo, an upgraded version of Adélie, this winter to target higher output and longer operating periods. Its current drilling system can reach depths of up to 80 m, compared with the 16-m well completed during the test. Endurance is also developing Leopard, a planned 2-MW commercial generator, and a first commercial project in Tonga targeting initial power in 2027.
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