Geothermal Energy vs Hydrofracturing (Fracking)

At The Geysers the magma is believed to exist at least four miles below the earth's surface. The heat from the magma radiates to the layers of rock above heating water in the pores and fractures of the hot rock. A small portion of the heated water may rise to the surface causing hot springs, geysers, and fumaroles. At The Geysers, the reservoir water boils to steam and is trapped by an overlying layer of tight, unfractured rock, called cap rock.

Wells, some more than two miles deep, drill through the cap rock and tap the natural steam, which is piped to our 15 operating power plants at The Geysers complex. In the process steam is cleansed of tiny particles of rock that could damage turbine blades. Steam is then put to work spinning turbine generators in the power plants to create electricity.

Turbines are designed to operate with steam at 350 degrees Fahrenheit and 100 ponds of pressure per square inch. About two million pounds of steam per hour are necessary to operate a 110- megawatt-generating unit. After passing through the turbine, spent steam goes through a condenser where it is cooled and turns back into water. With existing technology, Calpine recycles approximately 25 percent of the water back into the steam reservoir with the remainder lost to evaporation.

As described in the video, a natural gas well is drilled like any other well (a process we now know much more about thanks to the BP oil spill in the Gulf of Mexico). A drill string drills a hole deep into the earth (see How Oil Drilling Works for details). Then, as seen in the video, horizontal drilling techniques can be used to drill horizontally as well.

Once drilling is complete, the drill string is extracted and the well bore is lined with steel pipe. Cement is pumped around the outside of the pipe to lock it in place. Once the cement hardens, shaped charges are pushed down the pipe to perforate it and start fracturing the rock around the steel pipe. Then gallons of “fracturing fluid” at high pressure are pumped in. This is where the name “hydraulic fracturing” comes from – water is one of the fluids commonly used. In the best case the water is mixed with sand, and the grains of sand act as a “proppant”. The grains of sand get into the fractures and will hold them open once the water pressure is released.

A sand/water mix is the best case. Apparently there are many toxic chemicals used in some fracturing fluids, and in many wells it takes millions of gallons of fluid to fracture the rock. So if the fractures stretch into the aquifer (as apparently they often do), those chemicals plus oily residue and chemicals from the shale formation get into the drinking water.