This is a spin off from another thread, where people asked about the safety of fracking.
Horizontal slickwater fracturing (more commonly known as "fracking") involves shoving a fracturing fluid (mostly sand and water - 1 part sand to 9 parts water) down the well at high pressure, causing small fractures in the rock. The water then comes back out, leaving the sand behind to hold open the fractures so gas previously trapped can now escape.
Here's an animation of the process:
Sometimes instead of sand they use a different substance to prop the fractures open, such as small granules of glass or ceramic.
Sometimes they add a very small amount of radioactive isotopes to the fluid, to help track where the fluid is going (in the USA that's limited to 20 millicuries per injection).
The issues people are concerned about can be split into:
- Geological - eg will it cause earthquakes?
- Worker safety - eg will the people working on the well suffer from breathing in dust created by the process?
- Air contamination - eg if not all the natural gas released gets captured, will the escaping gas like methane cause local problems?
- Water contamination - eg will the additives in the fracking fluid escape into local groundwater and surface water?
- Resource consumption - fracking uses up a lot of water. some places are already short on water
- Global climate change - fracking will cause more carbon to end up in the atmosphere