An idea that could spread

Colorado ‘Hot Rocks’ Enticing

There’s been much ado about oil and gas drilling and production in the Rocky Mountain region.

Today, there’s also another energy source in the region that’s receiving some close scrutiny: geothermal energy for electricity generation.

The research effort on the potential for geothermal in this area has focused on the Raton Basin, which is the southernmost classical Laramide Basin in the Rocky Mountain region and straddles the New Mexico-Colorado state line.

The central part of this sedimentary basin, just west of the town of Trinidad in southern Colorado, has been determined to be a region of high heat flow and an area of interest as a potential geothermal resource.

This discovery was made by piggybacking on existing old information without any need to acquire new data, according to AAPG member Paul Morgan, geothermal geophysicist at the Colorado Geological Survey, which sponsored the effort.

“There’s been extensive drilling for coalbed methane since 1998,” Morgan said, “and I went through 2,000 well logs, read the header and collected the (subsurface) temperature data.

“These data have been compiled, reduced and interpreted,” Morgan said, “and the results confirm there is a significant potential geothermal resource in the basin, concentrated on the eastern side of the basin.”

Hot Stuff

He noted that temperatures exceeding 150 degrees C, or 300 degrees F, are conservatively estimated at depths less than 8,200 feet, and they are sufficient to generate electricity using binary power plant technology. Temperatures close to these predicted temperatures have actually been measured at depths as shallow as 500 feet.

“No one has developed anything like that in the United States yet,” Morgan said, “mainly because they’ve been looking in crystalline rocks versus sedimentary rocks, so far.”

The sedimentary rock units at the depths where the temperatures are hot enough to generate electricity likely are not permeable enough to allow geothermal fluids to circulate at a rate necessary to generate electricity economically, according to Morgan.

However, the permeability in the rocks can be increased via hydrofracing to create artificial fractures. This would result in an enhanced geothermal system that would be new in practice, even though the technology to produce this kind of system in sedimentary rocks is mature.

Dependability?

Morgan said the Survey intends to seek project funding from the U.S. Department of Energy, probably in collaboration with Colorado School of Mines and Pioneer Natural Resources. Pioneer holds all the coalbed methane resource in the Basin where it has drilled extensively, generating the information about subsurface temperatures used in the research.

“If we can get the funding to go ahead, we would try to drill a deep hole to confirm the temperatures and test the fracturing and could be on line with a test facility in as little as three years,” Morgan said. “That will be just a couple of megawatts.”

Ultimately, the plant could top out at 10-20 megawatts. This would be adequate to power Trinidad, which is within 10 miles of the resource.

Morgan emphasized there’s no intention to solve the nation’s energy crisis with such a system, but to make a contribution.

He noted also that it’s a shallow resource, so if it can be proved this would provide incentive to go down to the 10,000 to 12,000-foot range. This means there would be many more basins throughout the Midwest that will be open to geothermal expectation.

The proposed binary power plant likely would be cost effective after seven to 10 years, depending on the price of oil. Once the plant is built, the fuel is cost-free – and always available.

“Geothermal is a base load system that runs 24 hours a day, seven days a week, 365 days a year,” Morgan said, “so it’s there when you need it, all the time.

“You don’t have to wait for the wind to blow or the sun to come out,” he emphasized. “Wind and solar make great contributions, but aren’t necessarily there at peak demand time whereas something meeting the base load is always there when it’s needed.

“Also, geothermal facilities have fewer working parts than most other plants,” Morgan noted. “You have a working load up around 97 percent, so it’s online longer than just about any other type of power plant – you have less downtime.”

A Few Concerns

Lest it sound too good to be true, there is a downside of sorts.

One must go to the resource rather than where it’s wanted. In other words, it has to be used where it’s generated.

“There’s no point in generating electricity and transporting it hundreds of miles, as you lose power,” Morgan said. “If a town uses electricity, let them use it there – it’s still a contribution and less demand on the national grid, especially if it’s a very reliable source.”

If you’re pondering the environmental blight of the binary power plant, not to worry.

“Most of them don’t use water cooling towers anymore,” Morgan said. “It will use air-cooled cooling, so it’s not much of a visual impact – probably no more than 40 feet high.

“It will be much smaller than a normal power plant with no effluents coming out,” he said. “It will look pretty benign, and Trinidad may build a wall to cut down on noise.”

Next on Morgan’s agenda is a similar project for Southern Methodist University to update some AAPG studies from a couple of decades ago.

“I’m going through material from the Midwest and the eastern states to do the same kind of thing,” he said, “harvesting data already there – it’s kind of picking the low hanging fruit.”


Graphics courtesy of Paul Morgan, Colorado Geological Survey

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