The team is collaborating to assemble and test the 4,100-foot-underground rock star system

A team of scientists has assembled a first-of-its-kind system to help them understand how to use energy deep underground.

The stimulus and flow system is the latest “rock star” from the Pacific Northwest National Laboratory (PNNL) and its partners, designed to study how water moves underground through extremely hot rock and subsequently transfers heat to the surface.

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

PNNL stimulation and flow system

A team led by the Pacific Northwest National Laboratory has put together a first-of-its-kind system to help them understand how to use energy deep underground. Credit: Chris Strickland Pacific Northwest National Laboratory

Several components, one unique system

The mine, once considered the largest and deepest gold mine in North America, is now used for a variety of scientific purposes. One project looks at how geothermal energy can power 10 million homes a day.

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 – 4-inch “tunnels” drilled in the rock – and then pumped by the other boreholes. The team is studying how fluids not only break the rock between boreholes, but also how they receive heat from the energy stored in the rock – energy that can eventually be pumped above the ground to generate electricity.

To support EGS Collab’s efforts, the team developed a system of several tools that are crucial for their research.

“The uniqueness of this system is that it combines several components needed to gather important geothermal research data into one system,” said Chris Strickland, a PNNL scientist who leads the EGS Collab simulation and flow team. “It doesn’t exist anywhere else.”

Measurements of the PNNL stimulation and flow system

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

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

A liquid cooler creates cold water so the team can study how water temperatures affect the thermal properties of the rock. The reverse osmosis system allows the team to collect data on the path of water flow by changing the salinity – or salinity – of the injected liquid.

The system also includes a set of five “packers” that are inserted into the boreholes. The packers are equipped with sensors that provide measurement of temperature and pressure. The packed pressure bubbles of the packers, together with the control pumps, seal the boreholes and prevent leakage outside the intended borehole section.

“The uniqueness of this system is that it combines several components needed to collect important data for geothermal research in one system. That doesn’t exist anywhere else. ” – Chris Strickland

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

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

Going deep, in pieces

“We first assembled and tested the system in an overhead lab to make sure everything was working,” Strickland said. “Then we disassembled it, traveled a mile underground with pieces 4 feet by 4 feet, took them to our underground site in a railroad car, reassembled the system, and tested it again.

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

Strickland added: “One might think that working in a 7-foot tunnel a mile underground would be inconvenient. However, air is constantly pumped from the surface to keep the tunnels constant at 70 degrees and to provide fresh air for breathing. The working days are long, starting at 6:30 in the morning and ending at 18:30, with limited opportunities to travel back to the surface. “

EGS Collab’s infrastructure and research are maintained by the Geothermal Technology Service of the Ministry of Energy. The system will provide data for many months, if not years. The findings of this project will help develop new geothermal energy technologies for industry.

“Individual components carry good, useful data,” Strickland said. “Together as one system, EGS Collab will receive the most comprehensive data to help elevate the future of geothermal energy.

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

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