Tackling Climate Change | Geothermal
continued from page 26
Massachusetts Institute of Technology (MIT)
report, “The Future of Geothermal Energy,”
was very bullish on EGS and helped stir up a
lot of interest.
But while the EGS resource is extremely
large, exploiting it in a cost-effective way is no
trivial matter. For one thing, drilling costs go
up exponentially with depth. And then there
is the challenge of properly fracturing the
rock without inducing seismicity. The basic idea
is to have one injection well where high-pressure
water is pumped down into the hot rock, creating
permeability. The water then picks up heat as it
flows to one or more nearby production wells. But
fracturing the rock in a way that allows the flowing
water to communicate with a large volume of hot
rock without significant loss needs to be demonstrated. Water loss is not only an obvious problem
for arid regions typical of EGS resources, but it
also represents wasted pumping power.
The Obama administration
announced that $80 million
to support EGS R&D will
be provided from the
American Reinvestment
and Recovery Act.
The MIT study concluded that to be economical, an EGS project must obtain a continuous production well water flow rate of 80
kilograms per second at 200ºC (about 390ºF).
Limited water availability and high drilling costs
may result in shallower wells and lower temperatures, supporting binary-cycle plants. Thus far,
the highest achieved flow rate at an experimental
EGS site has been 25 kg per second.
A 2008 Department of Energy (DOE) study,
“An Evaluation of Enhanced Geothermal Systems Technology,” evaluated the MIT report
and described the significant amount of R&D
needed to create and sustain a viable EGS reservoir. The DOE has had limited funding to tackle
this. That changed recently when the Obama
administration announced that $80 million to
support EGS R&D will be provided from the
American Reinvestment and Recovery Act. Even
this is a small amount compared to what will be
needed. But the potential for EGS to produce
huge quantities of baseload power justifies the
expenditure and the risk. ST
