EGS without the Shakes or Clogs: GTherm’s single well GT system to be tested by EPRI

In California, the Electric Power Research Institute (EPRI) is about to kick off a series of tests on single well engineered geothermal systems, or SWEGS, developed by GTherm. If it works as advertised, SWEGS will be able to capture deep hole heat without fracturing – and the associated seismicity, without using local water supplies, without the need of an injection well and without having to move pipe-clogging brine. Indeed, the technology could be employed in the majority of thousands of abandoned oil and gas wells anywhere in the world.

On about the first of the year, EPRI and GTherm completed their contract and put internal EPRI funding in place for the work. SWEGS – for which GTherm has five patents pending – is closed loop system that uses heat exchange technology to ultimately convert heat to electricity in a closed, binary cycle system. But what makes the technology unique is creation of a “heat nest” at the bottom of a hole.

The key to the nest is the use of a cement-like grout licensed from the Department of Energy. The thermally conductive grout is injected into the hole to surround the heat exchanger and make contact with the hot rock, transferring the heat to the exchanger. A binary fluid is passed through the exchanger and brought to the surface for the generation of electricity.

According to Stan Rosinski, program manager for renewable generation at EPRI, the models that say the technique will work will be tested first in the research. If the models prove accurate, a small-scale demonstration application will then be tested. Rosinski noted that a deep well is not needed in this stage. EPRI only needs to know whether the heat of the earth will be transferred to the fluid, irrespective of what the starting temperature is. The research will move to a pilot scale demonstration, if the first tests pan out.

Rosinski says the technology is bested suited to dry holes and that a single well could produce from ½ to 1 MW of electricity. While that number seems small, he notes that abandoned oil fields routinely contain 50 to 100 holes that could be mined for electrical generation. In addition, horizontal drilling would produce more surface area for the grout to contact and thus make more heat available. The company says it can generate electricity effectively from rocks as cool as 195 degrees F.

EPRI is an independent, nonprofit organization that conducts research and development relating to the generation, delivery and use of electricity for the benefit of the public. Its members represent more than 90% of the electricity generated and delivered in the U.S., and international participation extends to 40 countries.