Oh, and some gas, too

Brine, High Pressure, High Temps: Perfect

American Association of Petroleum Geologists (AAPG)
Steve Munson
Steve Munson

High pressure. High temperature. Lots of brine.

Costly challenges in the eyes of oil and gas producers.

Music to the ears of Steve Munson.

Munson, an AAPG member, plans to start drilling wells along the Texas Gulf Coast next year, and he fully expects to produce gas.

As an afterthought.

The heat, pressure and brine are what he’s been looking for.

Munson’s company, GeoPower Texas Co. of Austin, wants to develop geothermal-driven electrical power plants using the energy from the hot-brine wells.

And the over-pressured Texas Gulf Coast geothermal area is just about perfect for that purpose, he said.

“Some people,” he noted, “have called Texas geopressure ‘geothermal on steroids.’”

Right now GeoPower Texas is eyeing two main operating locales, including a primary location in the Brazoria-Galveston counties area, according to Munson.

“We have a 60-square-mile lease there,” Munson said. “Down the coast, we have 90 square miles leased in the Matagorda area – we’ve leased them because they sit over the Frio formation’s proved, hot-brine reservoirs at depths of 10,000 to 11,000 feet down to the top of the formation.”

A Big Difference

The project can be seen as part of a resurgence of interest in geothermal power in Texas.

In 1989, a project funded by the U.S. Department of Energy began successful operation of a geothermal energy demonstration power plant at Pleasant Bayou in Brazoria County. It used a high-pressure brine and methane flow from the Frio Formation, coming from a depth of about 14,700 feet.

After the demonstration plant closed, interest in Texas geothermal waned. But it came back as interest in green power increased and more people became aware of the state’s geothermal resources, said Maria Richards, coordinator of the Southern Methodist University Geothermal Lab in Dallas.

“In a way, geothermal can be compared to the way wind energy developed. Geothermal can go into an existing field, where wells have been drilled, and go in with smaller units and a smaller footprint,” Richards said.

“The wind (power development) was hugely successful,” she noted. “I think people have seen that, and they’re entrepreneurs, and they see that the next big renewable resource will be geothermal.”

According to Richards, much of the shallow Texas co-produced fluids have a relatively small differential with the surface temperature. A difference of about 100 degrees Fahrenheit is needed as a minimum for geothermal power production.

“If you want to get started and be strong, you really need to have at least a 250-degree differential,” she said.

Because of the lower heat differential, Texas geothermal power typically involves a binary system using a heated working fluid to drive electrical-power turbines, instead of a direct-drive system.

The bigger the differential and the higher the pressure the better, and Munson projected that his wells will produce 300-350-degree brine at a wellhead pressure of 3,000 psi. He said the fluid also is likely to have entrained noncommercial gas.

“It can be burned and it raises the temperature of the working fluid, which makes the system more efficient,” he said.

Room to Grow

Geothermal power isn’t a new concept in Texas. Richards said the SMU Geothermal Lab has been in existence for more than 40 years, under the leadership of David Blackwell.

But the development of commercial-scale, geothermal-driven power in Texas is still in the early stages. GeoPower Texas hopes to be online with a commercial-scale power plant within 24 months, Munson said.

Another Texas geothermal company, GeoTek Energy LLC of Midland, recently received a DOE award to research and develop an innovative geothermal power technology.

Still unknown at this point is what amount of geothermal-driven power might be possible and might develop in Texas.

For a high-pressure and high-temperature well along the Texas Gulf Coast, Munson sees a 10-megawatt production facility as a real possibility.

“The average well output will likely range from five to 10 megawatts per production well, subject to final engineering results,” he said.

To put that number in perspective, one megawatt of power production is usually considered enough electricity for 1,000 homes.

Richards said the state’s geothermal resource allows Texas to have power projects scaled to many different usage levels, from a 50-kilowatt power production unit that might power an individual ranch or small neighborhood, up to 20-megawatt power plants.

“These geopressured areas are where you can get into the five megawatt to 20 megawatt plants,” she said.

GeoPower Texas wants to develop clusters of five-10 megawatt plants along the geopressured Gulf Coast province, Munson said.

“There’s a preliminary estimate that the Brazoria leases may produce 500 megawatts, subject to final drilling results,” he added.

As early as 1999, Texas required utilities to begin utilizing some renewable energy sources. The state now has a target of 10,000 megawatts of renewable energy capacity by 2025.

Munson doesn’t doubt demand will be high for geothermal-driven power production.

“Our estimate is that there is a tremendous market in Texas for green, renewable power that probably exceeds 4,500 megawatts,” he said. “There appears to be a 2,000 megawatt mandate for renewable power at just two municipal utilities.”

He referred to electricity produced from geothermal as “baseload renewable power.”

“We call it that because it’s very low emissions, low surface impact, reliable, 24-7 power.” Munson said “Geothermal power plants get 97 percent capacity, which is as good as a new gas plant, or better.”

A ‘Perfect Fit’

Texas has a couple of key advantages for geothermal-driven power. Richards noted the most promising geothermal resources are along the Gulf Coast and in east Texas, so many of the state’s largest cities and much of its population are near potential geothermal power development.

Also, the long history of oil and gas drilling in the state provides a wealth of information for the geothermal industry.

“We have massive amounts of well data and seismic data, and there’s a lot more seismic data available,” Munson said.

That information has helped GeoPower Texas find the best locations for leasing and drilling as it plans geothermal power operations, he observed.

“Along the Gulf Coast the sweet spots are the high-porosity, deltaic systems. You’re looking for the most continuous, stacked sandstone reservoirs,” he said.

In the United States, the leading developed geothermal resources are in the far west, mainly in California, Nevada and Oregon.

Munson thinks the geopressured, hot-brine Gulf Coast resource, with its abundance of existing well information, is a better bet.

“In our opinion, this is much lower risk drilling than the fracture systems in the Basin and Range province,” he said.

Ironically, Munson grew up in Oregon and Nevada, in the heart of the Western geothermal area. His home is still in Oregon.

“About 20 to 25 years ago I was interested in these alleged ‘renewable energy’ sources in California and I decided geothermal was most interesting,” he said.

Then, after becoming a self-described “geothermal pioneer” in Nevada, he began exploring opportunities in other parts of the country.

Munson said drilling for geothermal resources is similar to petroleum industry drilling, often using the same rigs and crews, something else that attracted him to the GeoPower Texas project.

“This is kind of a perfect fit with the oil and gas culture of the Texas Gulf Coast,” he said.

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