• Dig Energy completes first project with novel geothermal drilling tech
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Dig Energy completes first project with novel geothermal drilling tech

The firm just wrapped work on a heating and cooling system for a Boston office. It says its rig makes drilling cheaper, quieter, and less water-intensive.
By Sarah Shemkus

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Overhead shot of a blue-sided and -roofed building with a compact drilling rig along side it and a few workers
Dig Energy’s innovative drilling rig outside Suffolk Construction’s Boston headquarters (Dig Energy)

Dig Energy, a startup on a quest to vastly improve geothermal drilling, has completed its first commercial project, digging seven boreholes for a geothermal heating and cooling system at the headquarters of Boston general contracting firm Suffolk Construction.

Dig first stepped into the public eye almost exactly a year ago, when it announced a $5 million funding round after some five years of developing its technology behind the closed doors of a barn in New Hampshire. At the same time, Dig was selected to participate in Boost, an accelerator program run by Suffolk Technologies, the venture capital affiliate of Suffolk Construction.

Dig’s innovation: a rig purpose-built to drill geothermal boreholes with less noise, less water usage, and far lower cost than conventional drilling equipment.

Geothermal systems, which use all-electric heat pumps to tap into thermal energy stored underground, are widely hailed as the most efficient way to warm and cool buildings. However, the upfront price of accessing this clean source of energy can be a major barrier. The expense of installing a geothermal system can be up to five times that of an equivalent air-source heat pump. Only about 1% of buildings in the United States use geothermal systems for heating and cooling, estimated Dig Energy co-founder and CEO Dulcie Madden.

Dig says its technology could upend this math, cutting the cost of drilling by up to 80% as compared to conventional geothermal drilling. The companies declined to share specific numbers, but Dig ​“put some early proof points out there that, from a cost and schedule perspective, they’re going to be very competitive in the market,” said Parker Mundt, a partner at Suffolk Technologies.

In the standard process, the borehole is drilled first, typically with a metal bit or compressor, and shored up along the way with a casing to prevent collapse before a heat exchange pipe is inserted.

Dig’s system, by contrast, uses a high-pressure nozzle that sprays water at 10,000 pounds per square inch to bore through soil and rock. The approach was explored by the oil and gas industry decades ago, but never gained traction because it didn’t increase productivity in those sectors, Madden said. She and her partners saw an opportunity to adapt the idea for geothermal and spent years honing the technology.

“It’s a known industry practice that’s being adopted in a novel way for the first time,” Madden said. 

Dig Energy’s innovative drill rig at a Boston jobsite (Dig Energy)

The team engineered a drill string — the long vertical pieces that connect the surface equipment to the drill tip — that stays in the ground once the hole is complete, becoming the heat exchanger that transfers thermal energy to and from the surrounding earth. The nozzle stays behind as well; it was designed to be cheap enough that it is still economical to use a new one each time.

That innovation means the hole can have a smaller diameter than in conventional geothermal systems, because no extra room is needed for casing and the insertion of the heat exchanger. This process reduces debris and, perhaps counterintuitively, even water usage, because standard drilling uses large amounts of water to lubricate and cool the drill bits, as well as to turn displaced earth into mud that can be more easily removed from the hole.

Drilling at the Boston jobsite last month used one-tenth the water that the conventional drilling would’ve used and created 75% less material to be carted away, Madden said.

The process was also much quieter than standard drilling operations, which Madden likened to a demolition site. Dig’s equipment operated at such a low volume that workers could hold a conversation right near the rig and people in nearby buildings couldn’t hear a thing, she said. Also, the rig’s small size — about the same footprint as a parking spot, Mundt said — made it easy to maneuver in a dense urban environment.

“You can have people working around the rig without any disruption,” Mundt said.

Dig has several more jobs lined up after its inaugural success; the company is booked until mid-summer 2027, Madden said. And work is underway on a new version of the rig that aims to cut down on drilling time, she said.

Already, though, Dig’s performance on its first outing bodes very well for its future, Mundt said. 

“The results from this initial commercial project at our headquarters were incredibly exciting for us,” he said.

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Sarah Shemkus is a reporter at Canary Media who is based in Gloucester, Massachusetts, and covers New England.

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