New method for tapping geothermal power

Pennsylvania State University (Penn State) scientists have proposed a new technique which might help prevent “short-circuits” that can cause geothermal power plants to halt production. According to the researchers, the technique has the potential to improve the efficiency of geothermal power.

“The public perception of geothermal is that since it’s renewable we should be able to produce from these resources infinitely,” says researcher and co-author Arash Dahi Taleghani, professor of petroleum engineering at Penn State. “In practice, it doesn’t work like that. [But we have] proposed a solution that could help overcome a major challenge in the field.”

Enhanced geothermal systems involve injecting cold water into hot dry rock deep underground. The water travels through fractures in the rock and heats up, and production wells then pump the heated liquid to the surface where a power plant turns it into electricity.

However, wide fractures may allow large volumes of water to move too quickly to sufficiently heat up before reaching the production wells. Cooler production liquid impacts the efficiency of the power plant and can compromise the economics of the project, the scientists say.

“With these projects, you can get cold-water breakthroughs,” Dahi Taleghani says. “Basically, the water takes a shortcut passing through the reservoir. And because the water doesn’t have a chance to heat up it can basically short-circuit the system.”

Producers try to prevent these shortcuts before they form by adjusting how much water circulates through the system or potentially shutting down production periodically, the scientists say. This means the plant cannot produce continuously.

The researchers instead have proposed adding materials or chemicals to the liquid pumped into the reservoir that would autonomously control flow from inside the rock itself. The process, called the fracture conductivity tuning technique, involves adding materials that could change properties with the temperature, hindering cold water and allowing hot water to flow through the fractures.

“All these things are happening inside rock – we don’t have any access, and it’s so hot and the pressure is so high that you can’t have a valve or sensor there,” Dahi Taleghani says. “[But this method] basically acts like an autonomous regulator, reducing the fluid passing through each fracture when some parts of the reservoir get cold and letting it go if it’s hot.”

Read more at the Penn State University website.

Image courtesy of Penn State University.