Young geothermal energy wells are like budding geniuses, each with the potential to surpass the others. However, just like humans, most people decline with age. In California, for example, the production of geothermal power plants decreased by 15% between 2001 and 2018, due in part to the deterioration of existing wells.
“The history of geothermal has been the idea of degradation,” says Josh Prueher, CEO of geothermal startup XGS Energy. “This is happening all over the world.”
Many geothermal power plants inject water underground, passing through cracks in the rock and absorbing the heat generated deep underground. Once brought to the surface, it is used to generate steam to drive turbines and generate electricity. However, as geothermal wells age, the cracks can absorb too much water or begin to close, separating the wellbore from the portion of the hot rock it was previously in contact with.
Pruehar's company believes there are many old geothermal wells around the world that can be repaired, and other previously neglected sites that could potentially provide heat if harnessed with the right technology. He said the technology is essentially a special mud that fills cracks around the well with minerals that conduct heat well.
The result is not only more productive wells, but more predictable: “We know within 30 days what it's going to be 30 years from now” in terms of power generation, Pluher said.
XGS Energy's technology can be used in existing or new wells. The new borehole itself is a simple vertical hole that does not require expensive drilling equipment. The startup covers each borehole, whether old or new, with a metal casing. Between the casing and the rock, we add a slurry of water and proprietary additives that sinks into the cracks around the borehole, up to several feet away from the casing.
Pluhar said the slurry is a mixture of water and minerals suspended by surfactants. (Surfactants are also known as emulsifiers and cause insoluble things to suspend in water, much like mustard reacts with oil in salad dressing or soap reacts with dirt.) Once depth (and therefore temperature) is reached, the surfactant “breaks down”. Minerals are then released and settle in the cracks. Pluhar didn't go into details, but his patent application says the conductive component could be a mixture of graphite-like materials and minerals such as silica.
XGS Energy requires only one borehole to generate heat, saving drilling costs. Other companies may inject water into one hole, let it flow through cracks in the rock, and then pump the water into another hole drilled some distance away. Along the way, those rocks may absorb some of the water and the company will have to add more water. The water that reaches the surface likely carries minerals and bacteria that can settle on the equipment that transfers heat from the water to the steam turbines. All of this increases the cost of operating a well. XGS Energy, on the other hand, never lets water out of metal-lined boreholes, saving you money.
Because the water is isolated, XGS Energy can use inexpensive equipment to extract the heat. You don't have to worry about minerals or bacteria present in the surrounding rocks. “If you turn the page, you'll have access to a number of very low-cost, high-efficiency heat exchangers that geothermal power hasn't been able to access before,” Pluhar said.
XGS Energy will begin construction of a commercial-scale prototype at an existing geothermal field in California in July. To help finance the project, the company recently raised $20 million in additional Series A funding led by Val Ventures and VoLo Earth Ventures, with participation from B Current Impact Investment, MIH Capital, and Thin Line Capital. told TechCrunch exclusively.
In the near future, XGS Energy plans to develop a version of the technology that will work in older oil and gas wells. Although not all are suitable as most drillers try to avoid excessive heat, there are many areas in the United States where oil and gas wells are hot enough to support geothermal power generation.
“This is a huge opportunity because you can very effectively avoid clogging and waste costs,” Pruer says. “This is a very well-suited technology for repowering these wells.”