The new system is part of the Enhanced Geothermal Systems or EGS Collaborative Project, which involves several national laboratories, universities and industrial partners working to improve geothermal technology.
Several components, a unique system
This once thought to be the largest and deepest gold mine in North America is currently used for a variety of scientific purposes. One such project is looking at how geothermal energy could one day power 10 million homes.
The EGS collaboration 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 into the rock, and then pumped from other Extracted from the drilled hole. The team is studying how these liquids not only break down the rock between boreholes, but also gain heat from the energy stored in the rock — which can eventually be pumped to the surface to generate electricity.
To support the efforts of the EGS collaborative project, the team developed the system, which consists of several instruments that are critical to their research.
“What’s unique about this system is that it combines multiple components needed to collect important data for geothermal research into one system,” said PNNL scientist Chris Strickland, co-leader of the EGS Collaborative Project’s Simulation and Flow teams. “That doesn’t exist anywhere else.”
These components include two syringe pumps, each of which injects liquids into the rock under high pressure. One pump can be used for very precise flow and pressure control, while the other pump can be operated when high flow is required.
A fluid cooler produces cold water so the team can study how water temperature affects the thermal properties of the rock. A reverse osmosis system allowed the team to gather data about the water’s flow path by changing the salinity, or salinity, of the injected liquid.
The system also includes a set of five “packers” that are inserted into the borehole. These packers are equipped with sensors that provide temperature and pressure measurements. The pressurized bladder on the packer, together with the control pump, seals the borehole against leakage out of the intended portion of the borehole.
The level of precise control and integration is a unique aspect of the system, providing the high-quality data needed to advance scientific understanding.
“The best part is that the system is autonomous, which means we can use a laptop or phone at home to operate it and collect data on the ground,” Strickland said. “That way, we don’t spend as much time underground.”
Go deep into the ground, sharding
“We first assembled and tested the system in the lab above ground to make sure everything was working,” Strickland said. “Then we took it apart, traveled a mile underground with the 4-by-4-foot pieces, railcared them to our underground site, reassembled the system, and tested it again.”
The complete system, 7 feet high, 7 feet wide and 30 feet long, took three weeks to build underground. The system was built and tested by PNNL and EGS collaborative project partners from Sandia National Laboratories, Idaho National Laboratories, and Lawrence Berkeley National Laboratories.
Strickland added: “One might think that working in a seven-foot tunnel a mile underground would be uncomfortable. However, air is constantly pumped in from the surface, keeping the tunnel at a constant 70 degrees Fahrenheit and providing fresh breathing air. “The workday is long, starting at 6.30am and ending at 6.30pm, with limited opportunities to get back on the ground.”
EGS Collab’s infrastructure and research are supported by the U.S. Department of Energy’s Office of Geothermal Technologies. The system will provide many months or even years of data. Findings from this project will help develop new geothermal energy technologies for industry.
“Individually, these components bring good, useful data,” Strickland said. “As a system, the EGS partnership will have the most comprehensive data available to help advance the future of geothermal energy.”
