Electricity has been generated successfully from a producing oil well’s geothermal hot water for the first time, reported the US Department of Energy’s Fossil Fuel Office on Oct. 18.
DOE’s Rocky Mountain Oilfield Testing Center (RMOTC) and Ormat Technologies Inc., Reno, Nev., began a 12-month test in September at RMOTC’s Naval Petroleum Reserve No. 3 (NPR-3) site north of Casper, Wyo., DOE said. A standard commercial Ormat Organic Rankine Cycle power plant is being used, using hot water from a producing oil well to exchange heat in an Ormat Energy Converter, it indicated.
“This project is unique in its production of onsite renewable power and has the potential to increase the productivity and longevity of existing US oil fields. Harnessing hot water produced during production to power the oil field could lead to more economical access, especially in older, depleted fields,” said James A. Slutz, DOE’s acting assistant secretary for fossil energy.
A large number of US oil and gas fields produce hot water as well as hydrocarbons, he noted. Such wells, which typically produce fluids at temperatures below 220° F., could be capable of generating more than 5,000 Mw of electricity, he said.
In the current test, a binary power unit moves hot water from a producing well to a heat exchanger, where it vaporizes a secondary fluid with a lower boiling point, according to DOE. The secondary fluid’s vapor is used to turn a turbine coupled to a power generator. Electricity is then supplied to the field’s electrical system, where it runs production equipment, it said.
150-200 gross kw
DOE said the generated electricity is metered and monitored for both reliability and quality. The test has been producing 150-200 gross kw of power since it started in early September, it said.
It said the cooled geothermal fluid from power production can be reinjected into the reservoir or discharged, depending on the location. Currently, the 190° F. water produced from NPR-3’s Tensleep sandstone formation is treated before being safely discharged into a nearby stream. The unit’s energy converter captures the water’s heat and uses it before the water is discharged.
DOE said that while the unit at NPR-3 is the first to use geothermal water from a producing oil field, it is similar to a 250 kw Ormat unit, which has generated electricity at an Austrian resort from 210° F. geothermal water for more than 6 years. Similar units also have been in continuous operation in Nevada and Thailand since the 1980s and have been field-proved in 1,000 installations worldwide, it said.
About 8,000 wells that produce both hot water and hydrocarbons have been identified in Texas alone, DOE said. Ormat is assessing the feasibility of using such wells to support onsite power generation by employing its sub-Mw geothermal power units, it added.
