?The air-cooled geothermal binary power plant uses hot oilfield brine to generate renewable energy.

?The U.S. Department of Energy’s Rocky Mountain Oilfield Testing Center (RMOTC), based in Casper, Wyoming, recently announced its first successful generation of electricity using geothermal hot water from a producing oil field. The project is a cooperative research and development agreement with Reno, Nevada-based Ormat Technologies Inc.


The RMOTC is a 10,000-acre DOE-operated facility within the Naval Petroleum Reserve No. 3 (NPR-3), also known as the Teapot Dome oil field, about 35 miles north of Casper.


Renewable electricity for the field is generated by an organic Rankine cycle unit by harnessing hot water produced during oil production. Using geothermal to power oil fields can increase economical access to reserves, especially in older and semi-depleted fields, while potentially increasing the well’s productivity and longevity.


“We started testing the equipment in the field in the beginning of September,” says Lyle Johnson, project manager. “We have been testing it under different loads to see how it performs. This unit will produce a gross 250 kilowatts of electricity, net 225, and we have produced that maximum rate and 25% more than that. We normally run it at about 95% of load factor.”


Geologically heated water is produced from the Tensleep formation through a conventional production battery. Tensleep sandstone is widespread sandstone in the region that contains minor limestone and dolomite beds and varies between 1,000 and 400 feet in thickness.


“We are using about eight wells that produce oil and hot water for this system,” says Johnson. They are each about 5,500 to 5,600 feet deep. “Conventional geothermal wells can be as much as 13,000 to 16,000 feet deep and still be economical. The quantity and temperature of the water are the two main factors used to determine if this technology is suitable for any specific oil or gas play.”


The RMOTC wells currently produce 50 barrels per day of oil and as much as 42,000 barrels of 195-degree-Fahrenheit water.


At the beginning of the process, a conventional separator decouples hot oil and untreated oilfield brine water. The water goes into an insulated tank and then into the power-generation system. Due to the mild quality of the brine, the operators have not experienced deposition of solids during cooling­­­ in the power unit.


The brine is then funneled through a heat exchanger to vaporize isopentane, which is then fed through an expansion valve into a turbine. As the gas expands, it spins the high-speed turbine coupled to a generator that produces electricity. The produced energy is continually metered and monitored for reliability and quality.


After cycling through the turbine, the vaporized isopentane is passed through a heat exchanger, which cools and condenses the gas, and the cycle is repeated.


As a final step, the brine water is then piped into four treatment ponds for settling and removal of the few hundred parts per million of oil suspended in the water.


“The cool water is then discharged nearby into a drainage stream. The discharge water makes up approximately 99% of the stream,” says Johnson. “The farmers downstream appreciate the flow because their cattle have good water.”


At press time, the RMOTC was conducting tests to log how variations in ambient temperatures affect the power load.


“Our electricity goes into the oilfield production-system grid, and produces about 11% of the required power. To date, we produced a little more than 280 megawatt hours of power, and that is a significant amount.”
The unit at NPR-3 is similar to a 250-kilowatt unit that has been producing electricity from 210-degrees-Fahrenheit geothermal water at an Austrian resort for more than six years. Similar units are also in commercial operation in Nevada and Thailand.


In Texas, the DOE’s Geothermal Research Project Office identified some 8,000 similar oil and gas wells that produce hot water as well as hydrocarbon products. These wells, which generally produce fluids at temperatures below 220 degrees Fahrenheit, have been estimated to be capable of generating upwards of 5,000 megawatts of power.


“We haven’t tested this on a gas well, but there is a lot of deep, hot gas in the U.S.,” says Johnson.


The RMOTC partners with service companies and equipment manufacturers to test theories, technologies and environmental systems. Universities use the facilities to demonstrate real-life application in the field and conduct leading-edge research.

Comments