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A RIVER RUNS UNDER IT

Geologist John Holbrook’s knowledge of Earth’s interior is part of the puzzle of a clean-energy future.

Rivers are the lifeblood of human civilization. They connect two essentials: land and water. Researchers examine rivers’ sedimentary record to understand how water transformed land and to get a good idea of how Earth used to look.

The remnants of long-dry and now-buried rivers have implications for the planet’s energy future, said John Holbrook, professor of geology in the College of Science & Engineering.

Few people know how to piece together the geologic past through the legacy of rivers. When someone wants to better comprehend “plumbing” below the surface, Holbrook said, “They’re liable to come a-callin.’ ”

TCU geology professor Dr. John Holbrook looking into a river

TCU geology professor Dr. John Holbrook. (photo by Jeffrey McWhorter)

 

Holbrook has traveled to the Palo Duro Canyon in the Texas Panhandle, the Parana Delta in Argentina and northwest Australia to research old and new rivers. Some of the professor’s projects involve getting wet while studying the flow of active rivers, but he isn’t as interested in the water as he is in the sediment the water carries. Those particles, mud to the untrained eye, are keys to the puzzle of Earth’s past.

Holbrook starts with what he knows from studying sediment flux in existing rivers and applies that knowledge to theorize about yesterday. Those old particles have modern implications because organic material settled onto the floors of sedimentary basins. That material eventually became the petrochemicals powering much of the 21st-century economy.

Holbrook is in high demand by oil and gas companies that want to find large amounts of petroleum and extract it at the lowest cost. “Anything you can do to give you some better predictions on what that plumbing looks like is extremely valuable,” he said.

To provide advice, Holbrook uses modern tools, including huge, hollow drill bits that extract samples, pictures from drones that are stitched together with software, and seismic images that give hints about underground topography suggestive of old rivers and valleys.

“You’re literally taking what you know about how rivers work and piecing together the most probable layout in terms of what to expect down there,” Holbrook said. Why? “People are trying to figure out how fluids move through that.”

Subterranean fluid motion has applications beyond oil and gas. When the National Science Foundation called for research proposals on sustainable energy, Holbrook’s application focused on assessing the potential of geothermal energy. He was awarded a $500,000 grant to assemble an interprofessional team to gauge the possibilities.

The idea behind geothermal energy is to drill holes deep into the Earth. Some are for pumping water down, and others are for harvesting the injected liquid, heated naturally by the scorching interior, to power clean-energy turbines.

Some geothermal energy already is in use, but widespread adoption has been slow, mainly because the cost of drilling a geothermal field can be 17 times higher than the price of an oil or gas well.

Holbrook said the potential is there for geothermal to become a competitive player in the energy market. The ideal scenario is related to his research into sedimentary basins because old fluid channels are easier to funnel new fluid through, compared with the hard granite making up most of the ground beneath our feet.

“Sedimentary basins have some plumbing,” Holbrook said. “They have pathways. They have flow. We know that because we’ve been drilling [into] and sucking oil out of them for ages.”

Holbrook’s specific knowledge is invaluable when determining how a large-scale geothermal operation might work, said Cathy Chickering Pace, a project specialist at the Southern Methodist University Geothermal Laboratory in Dallas and a research collaborator of Holbrook’s. “It requires a fair amount of homework to make sure you’ve got the right geological conditions for [geothermal energy] to operate effectively.”

But Holbrook said sedimentary basins do not reach the 200-degree centigrade mark that could make deep Earth water hot enough to theoretically power the world. “We’d be competitive with all the other energy sources if it was just about 50 degrees hotter down there.”

The NSF-funded consortium reached a possible solution called an earth battery. It would use the massive amounts of solar energy battering the Earth during daylight hours to superheat water before storing it in underground geothermal systems. During the night, plant operators would pump out the scalding liquid, which could then be transformed into clean, sustainable geothermal energy.

The earth battery concept is untested, but, “we could ideally couple those two energy sources together and make a steady power flow,” Holbrook said — the holy grail of green energy.

BY CAROLINE COLLIER