Emissions-free power at wellheads
During the summer of 2008, Southern Methodist University hosted a demonstration aimed at generating electricity from waste heat. Popular Science was so impressed with the compact unit connected to a boiler in the University’s Central Plant that editors named ElectraTherm’s “Green Machine” one of the top technology innovations of 2008.
Fast-forward to summer 2011, and the Green Machine is producing fuel-free, emission-free power at a Mississippi oil field, generating geothermal energy from the hot wastewater that oil and gas producers consider a nuisance. The Mississippi project, one of 13 Green Machine installations currently operating internationally, was under a spotlight as SMU’s Geothermal Lab mounted its fifth international symposium, June 14-15, aimed at spurring interest in geothermal energy from oil and gas producers.
“We are offsetting electric consumption on the site with power generated from hot water,” said Loy Sneary, CEO of Gulf Coast Energy, a Texas-based company that distributes the Green Machine for ElectraTherm, Inc. “It has been talked about for a long time, people have been researching it and there have been a lot of concepts tested – this is the first time it’s really been done with a modular solution, installed in 50 hours and with the entire system mounted to a tractor-trailer skid.”
Scientists in SMU’s Geothermal Lab see a natural partnership in co-production of geothermal energy from oil and gas wells. Large quantities of water are produced with the extraction of oil and gas, either because it was present in the reservoir before drilling, or because water was injected into the formation to force oil and gas to the surface.
Historically, geothermal production in the United States has been limited to tectonically active regions with extremely hot, naturally pressurized waters – like The Geysers Field in California. But newly developed technology like the Green Machine allows for the generation of electricity from moderately hot water. Sneary sought advice from SMU’s Geothermal Laboratory in finding oil and gas production sites likely to have sufficient heat flows to support the Green Machine’s production and, as a result, contacted Denbury Resources. The Plano-based company is in the business of revitalizing old wells by injecting carbon dioxide into the reservoir, which increases reservoir pressure while reducing the oil’s viscosity. This process allows the recovery of oil that otherwise would not be produced.
The data that SMU provided Sneary made it clear that the water being produced at approximately 204 degrees Fahrenheit by Denbury wells near Laurel, Miss., likely had sufficient heat flow for the Green Machine. “We try and support valid research projects where possible,” said Gordon Moore, regional facility engineering manager at Denbury. “At that point, the unit at SMU was operational, and they invited us to come down to SMU and take a look at it.”
The Green Machine is designed for 30-65 kilowatts of power output, but the lower temperature and flow at the Laurel demonstration site generates a lower output, producing 19 kilowatts of power. According to Moore, this is enough to offset about 20 percent of the energy required to run the down-hole pump on the oil well it is paired with. The machine was installed in May, and SMU geothermal experts say this kind of co-generation can be particularly effective to reduce the energy costs for pumping hard to reach oil.
The Green Machine is a relatively small unit – about the size of a small garden shed. This allows for easy transport, with the entire system mounted on one trailer skid. The hot water is separated from the oil and gas that it is pumped out with, and the produced water then heats refrigerant in the Green Machine that expands into high-pressure vapor and, in turn, drives a generator. Proponents of this type of unit say its portability is one of its biggest benefits.
“ElectraTherm deployed the Green Machine at Denbury to connect and generate electricity seamlessly, and we are excited with the results – 50 hours installation time is a great accomplishment for the first time,” said John Fox, CEO of ElectraTherm. “The ongoing operational lessons we learn from this demonstration will benefit future installations with higher performance capabilities.”