How does hydrofracturing work in natural gas wells? --- Denny, Syracuse, Utah
Marshall Brain Answers:
The following video provides an excellent explanation of the hydrofracturing (also known as fracking) process:
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.