Enhanced Geothermal Systems

Enhanced Geothermal Systems (EGS, also called Engineered Geothermal Systems) work along the same premise as natural geothermal energy. Geothermal power originates when cracked hot rock heats water into steam. With natural geothermal energy, the earth provides the cracked rock and steam to power a generator. With artificial or enhanced geothermal energy, we have to coax the rock to crack by injecting water down a well, passing it through the resulting crevices in hot rock, and then extracting steam through another well. See our animation below.

 

How an Enhanced Geothermal System Works

There are four main types of geothermal power plants:
1. Drill Injection Well
An Injection well is drilled into hot bedrock that has limited permeablility and fluid content, This is considerably deeper than water tables, at depths greater than 5,000 feet.

2. Inject Water
Water is injected at sufficient pressure to ensure fracturing, or open existing fractures within the devolping reservoir and hot bedrock.

3. Hydro-fracture
Pumping of water is continued to extend fractures and reopen old fractures some distance from the injection wellbore.

4. Drill Production Well
A production well is drilled, intersecting the stimulated fracture system. The water is circulated to produce steam. The water, depleted of its heat, is re-injected to be heated again in the fractures.

5. Drill Additional Production Wells
More production wells are drilled to extract heat form large volumes of hot bedrock to meet power generation requirements.

Enhanced Geothermal System Potential

The EGS concept provides the potential to remove the "dry hole" risk associated with conventional hydrothermal geothermal, which requires finding existing fractures that contain high flows of hot water. EGS would also allow the placement of geothermal development in sites without conventional geothermal resources.

According to the recent MIT report "The Future of Geothermal Energy", such a manmade geothermal system could harvest as much as 40 percent of the heat in the bedrock and convert 15 percent of it into electricity via simple low-temperature steam turbines at the surface. Once in place, geothermal power plants can produce electricity nearly round the clock.

According to government estimates, 5 percent of U.S. power could come from geothermal by 2050. But some analysts say that deep geothermal power, accessed through Enhanced Geothermal Systems, could contribute far more to the world's energy grid. The potential is certainly enormous: The MIT report estimated that by tapping into geothermal energy, more than 200,000 exajoules of energy could be captured in the U.S. alone, or 2,000 times the total annual consumption of energy in the United States in 2005. "This is a very large resource that perhaps has been undervalued in terms of the impact it might have on supplying energy to the U.S." says chemical engineer Jefferson TesterT, lead author of the report.

Enhanced Geothermal System Challenges

Although EGS has many advantages — it produces no emissions of carbon dioxide, is available day and night (unlike sunshine or fickle winds), and can potentially be developed nearly anywhere in the world — much remains to be done before it can be put to use on a large scale. The main barriers are cost and developing sophisticated pumps that can move large volumes of water through fractures in the deep, hot rock.

Enhanced geothermal systems also face the barrier of drilling costs: For the oil and gas industry, those costs amount to more than $500 a foot for wells deeper than 18,500 feet. Tapping the geothermal heat in regions like the northeastern U.S. would require drilling nearly twice that deep, and geothermal wells need to be wider and more permanent (ie: more expensive) than their oil and gas wells.

 

Enhanced Geothermal Systems copyright 2011 Digtheheat.com