Microwave Drilling Sounds Like Science Fiction, but So Does Drilling Down to the Hottest Rock

Abstract

_ When asked to describe Quaise Energy, Chief Financial Officer Kevin Bonebrake said, “At its simplest, we will manufacture steam.” Their goal is to produce steam that is hot enough to power an electric generator built to run on fossil fuel. They plan to do that by injecting water down 10–20 km to where the rock temperature is 400 to 500°C. The motivation for drilling wells into extremely hard basement rock is to make geothermal electric power affordable by producing steam that could be used to repower older plants connected to power grids serving major markets. In the past, geothermal power has been little used because there are few places in the world with the right combination of the hot rock, water, and permeability required to deliver high‑quality steam. Hot, dry rock is commonly available, but producing the supercritical steam needed requires drilling to depths of 10 to 20 km, depending on the temperature gradient in that part of the US. At that depth, the driller will be faced with rocks such as granite and basalt. The rock is capable of both producing superheated steam and destroying the microchips and seals required for directional drilling. Quaise plans to drill ultradeep holes by generating high‑powered microwaves at the drilling site. The microwaves will be transmitted downhole to make hole by melting and vaporizing the basement rock. The only downhole equipment is a long tube to guide the waves to their target. It is one of those ideas where the first reaction most people have is “that sounds like science fiction,” which speaks to both the problem and the proposed solution. “You have to think differently to deal with that type of temperature,” said Henry Phan, vice president of engineering at Quaise, whose job is to turn this invention into engineering reality. Where It’s Hot The high barriers to drilling wells 10 to 20 km deep (33,000 to 66,000 ft) beg the question, isn’t there an alternative? A simpler, faster, and cheaper option would be to use proven drilling methods to reach not‑so‑deep levels where the steam produced is not as hot. Phan described it as “colder, lower‑pressure, wetter steam.” That sort of geothermal energy can be useful for purposes such as providing heat for desalination or energy for central cooling systems, according to an analysis of Oman’s efforts to tap the energy of hot‑water zones beneath oil fields. These zones were not hot enough to generate electric power. There is talk of using steam from zones that are not as deep, but Quaise’s analysis concluded that the large investment required to build power plants capable of using that steam for electric generation would make the output uneconomically costly. Quaise argues that finding a way to drill extreme wells is worth the cost and technical risks that come with new technology and drilling into little‑known formations because it would save the cost of building a power plant. Its goal is to supply older fossil‑fueled plants whose owners would be eager to convert to geothermal steam because of the staggering cost of complying with environmental regulations.