Geothermal Electricity Generation, Not Just for Iceland
Geothermal energy is a largely untapped resource that has the potential to provide limitless, carbon free clean energy with almost zero negative environmental impacts. Previously geothermal power generation was limited to areas such as Iceland, where hot molten magma lies closer to the earth's surface. A new technology of "low temperature" geothermal power generation has been developed which can utilize hot zones under much of North America to generate electricity.
Low-Temperature & Co-produced Resources represent a small but growing sector of hydrothermal development in geothermal resources below 150°C (300°F). Considered non-conventional hydrothermal resources, these technologies are bringing valuable returns on investment in the near-term, using unique power production methods." US Department of Energy Efficiency and Renewable Energy
What this technology needs to be implemented is typically two separate well bores that reach deep enough in the earth in an area where the temperature underground reaches at least 135 degrees Fahrenheit. There just happens to be more than 3.5 million abandoned oil wells in the US, which may be able to offer at least one of the required wells for almost free. Some of those old wells are environmental hazards which need to be plugged and abandoned, yet many, which no longer produce economically viable quantities of oil, may be able to be converted to low temperature geothermal wells since they are in areas where underground temperatures are great enough for the technology to work.
This is a win-win situation, in that it could possibly help solve the problem of abandoned oil and gas wells, and provide a nearly limitless supply zero carbon source of energy.
Here's how that technology got started in an unlikely place, a Texas oilfield.
How it Works
When electricity is produced from conventional geothermal wells, it'd done so using high pressure steam which drives conventional turbines. This process requires very hot temperatures and a constant source of steam, such as from a predictable flow groundwater that percolates down into geothermal hot spots deep underground where it's heated before returning to the surface as steam.
With low temperature geothermal, water may still be used, except that it's not used to drive turbines. Instead, water is circulated down one of the two wells and up through another. The wells can be directly or indirectly connected to each other but the end result is the same. Hot water returning to the surface then goes through a heat exchanger system, which in turn heats a more reactive fluid with a lower boiling point such as carbon dioxide, which then is used to drive a turbine generator. This binary system is highly efficient and has been used with water temperatures as low as 135 degrees Fahrenheit, as was demonstrated at Chena Hot Springs in Alaska.
Pilot Project in Texas
As you drive through Brazoria County Texas, located south of Houston, you would never know that among the cotton fields and cattle ranches once stood Texas' first working geothermal power plant. In the mid-1970s a group of researchers working for the US Department of Energy, including geologists and engineers, got the idea that abandoned natural gas wells in Texas could generate power from geothermal heat deep underground. Geologists have long known that deep rock formations such as the Frio sandstone in Texas, contained an almost limitless source of geothermal energy. Bottom hole temperatures of more than 300 degrees Fahrenheit have long caused problems for Texas oil and gas companies when drilling deep natural gas wells. Such high temperatures deep underground can damage drill bits, harm directional sensors and even interfere with drilling mud properties.
Knowing that such high bottom hole temperatures in abandoned Texas natural gas wells might be used to generate electrical power, a proposal for a pilot geothermal power plant was drawn up by a group of scientists working for the US Department of Energy. Several abandoned natural gas wells in the Gulf Coast region were chosen for the study, including the Pleasant Bayou #2 in Brazoria County, Texas and the Gladys McCall #1 in Cameron Parish, Louisiana. These “wells of opportunity” were purchased for little or nothing from oil and gas companies, who were glad to be rid of them since they were no longer economical to operate.
Since the abandoned natural gas well in Brazoria County could still produce small quantities of natural gas, it was decided that a hybrid geothermal power plant, (which used both heat energy and natural gas,) would be utilized. The plant would harness chemical energy (natural gas,) and thermal energy (geothermal.) In addition, scientists proposed harnessing mechanical energy from the high pressure fluid coming out of the well by using it to spin a turbine. Because the well produced thousands of gallons of highly corrosive brine water, anti-corrosion agents were added to the fluid before it entered the power generation equipment. The brine water was then re-injected into the same deep rock formation from which it had came, so the cycle could be completed once again.
The Texas geothermal energy project was actually a huge success in terms of economics. In its first 121 days of operation, from late 1989 to 1990, approximately 3,445 MWh (megawatt hours) of electricity were sold to Houston Power and Light. The economics of the Texas geothermal power plant experiment were in line with similar geothermal plants already in operation in other areas of the United States. So you may be wondering " if the geothermal project was so successful, why isn't it still in operation?" The project was probably doomed from the start because at the time there was no federal or state mandate for clean energy, and because of the extremely low cost of natural gas in that area. Without some government incentives to help get the technology up and running, it was simply cheaper for electric companies to expand their conventional power generation facilities rather than try and branch out to geothermal. Hopefully with new US government incentives, low temperature geothermal will begin to become more widely adopted as a reliable addition to our power grid. Recent widespread power outages in Texas due to ice storms have shown that both wind energy and natural gas can be affected by extreme weather events. Because the temperature several thousand feet below the earth's surface remains relatively constant, low temperature geothermal could help provide a much more reliable power source should it ever gain widespread adoption.
Renewed Interest In Using Abandoned Natural Gas Wells For Geothermal Energy
The success of the Brazoria County geothermal power plant project has not been forgotten by some in the oil and gas industry, who believe that it could be used to increase revenue from declining fields. In recent years studies have been conducted concerning the viability of large-scale geothermal electric power generation in Texas utilizing abandoned natural gas wells. There are five areas in Texas with potential to generate geothermal energy using the hybrid geothermal model. These areas are the Texas Anadarko Basin in the Panhandle region, the Delaware and Val Verde Basins and the Trans-Pecos Region in West Texas, and geo-pressured areas of East Texas and the coastal plains.
In 2000, a study of the feasibility of geothermal power generation in West Texas was conducted for client by the engineering firm of GeothermEx, Inc. The study examined a rock formation in West Texas at a depth of 19,000'. The formation contains small amounts of natural gas and oil, as well as highly pressured brine water (at 9000 psi,) with a bottom hole temperature of 280F or 137.8C
It was determined that for a capital cost of only $1,260,000, income of $235,000 could be generated each year, recouping all well and plant costs in five years. Income from the wells included sales of recovered oil and natural gas, as well as the sale of electric power generated by the hybrid plant. As the technology has advanced since that study, newer systems may be profitable without having to rely on the sale of co-produced oil and gas.
Drilling for geothermal energy using conventional drilling methods could potentially provide a needed source of jobs for unemployed oilfield workers as well as provide a much needed carbon neutral power source for millions of homes.
© 2021 Nolen Hart
Peggy Woods from Houston, Texas on March 07, 2021:
I think that is exciting news! It would be wonderful to use abandoned wells and put them to purposeful use such as this. Having lived through the deep freeze in Texas without power was not fun.