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4,100 Feet Underground, Scientists Test Unique Geothermal Energy System

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The team collaborates to assemble and test the “rock star” system 4,100 feet underground

A team of scientists have assembled a one-of-a-kind system to help them figure out how to harness energy from deep underground.

The Boost and Flow System is the newest “rock star” from Pacific Northwest National Laboratory (PNNL) and its partners, designed to study how water moves underground through extremely hot rocks and then transmits the surface heat.

The new system is part of Enhanced Geothermal Systems—or EGS—Collab, a project involving multiple national laboratories, universities, and industry partners working to improve geothermal technologies.

PNNL Pacing and Flow System

A team led by Pacific Northwest National Laboratory has assembled a one-of-a-kind system to help them figure out how to harness energy from deep underground. Credit: Chris Strickland | Pacific Northwest National Laboratory

Multiple components, one system

The mine, which was once considered the largest and deepest gold mine in North America, is currently used for a variety of scientific purposes. A project examines how geothermal energy could one day power 10 million homes.

The EGS Collab uses the underground facility as a test bed where water and other fluid mixtures will be pumped under high pressure into one of five boreholes – four-inch-wide “tunnels” drilled in the rock – then pumped out of the other boreholes. The team is studying how the fluids not only break up the rock between boreholes, but also how they obtain heat from the energy stored in the rock, energy that can eventually be pumped above ground to produce electricity.

To support the efforts of EGS Collab, the team developed the system, consisting of several instruments essential to their study.

“The uniqueness of this system is that it brings together several components necessary to glean important data for geothermal study in a single system,” said Chris Strickland, the PNNL scientist who co-leads the simulation and design team. EGS Collab stream. “It doesn’t exist anywhere else.”

PNNL Flow System Stimulation and Measurements

The unique stimulation and flow system measures 7 feet wide, 7 feet high and 30 feet long. Credit: Chris Strickland | Pacific Northwest National Laboratory

These components include two injection pumps that can each inject fluids into the rock at high pressure. One pump can be used for very precise flow and pressure control, while the other can be used when high flow rates are required.

A fluid cooler creates cold water so the team can study how water temperatures affect the thermal properties of rock. A reverse osmosis system allows the team to glean data on the water’s flow path by altering the salinity – or salinity – of the injected fluid.

The system also includes a set of five “packers” which are inserted into the boreholes. The conditioners are equipped with sensors that provide temperature and pressure measurements. Pressure bladders on the packers, along with control pumps, seal the boreholes and prevent leakage out of the intended borehole section.

“The uniqueness of this system is that it brings together several components necessary to glean important data for geothermal study in a single system. This does not exist anywhere else.” — Chris Strickland

The level of precise control and integration is a unique aspect of the system, providing quality data needed to advance scientific understanding.

“The best part is that the system is self-contained, which means we can operate it and collect data above ground using a laptop or home phone,” said Strickland. “That way we don’t spend as much time underground.”

Go deep, in pieces

“We first assembled and tested the system in an above-ground lab to make sure everything worked,” Strickland said. “Then we took it apart, ran the 4ft by 4ft parts underground a mile, took them to our underground site in a wagon, reassembled the system and tested it again.”

The complete system, which measures 7 feet high by 7 feet wide and 30 feet long, took three weeks to build underground. The system was built and tested by PNNL and EGS Collab partners at Sandia National Laboratories, Idaho National Laboratory, and Lawrence Berkeley National Laboratory.

Strickland added: “You would think working in a 7ft tunnel a mile underground would be uncomfortable. However, air is continuously pumped in from the surface to keep the tunnels at a constant 70 degrees and provide fresh air to breathe. Workdays are long, starting at 6:30 a.m. and ending at 6:30 p.m., with limited opportunities to get to the surface.

EGS Collab’s infrastructure and research is supported by the Department of Energy’s Office of Geothermal Technologies. The system will provide data for many months or even years. The results of this project will contribute to the development of new geothermal energy technologies for industry.

“Individually, the components provide good useful data,” Strickland said. “Together in one system, the EGS Collab will receive the most comprehensive data to help drive the future of geothermal energy.”