hydraulic fracturing

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The process of extracting oil or natural gas by injecting a mixture of water, sand or gravel, and certain chemicals under high pressure into well holes in dense rock to create fractures that the sand or gravel holds open, allowing the oil or gas to escape.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun oil industry A technique in which a mixture of water and sand is forced down an oil well (or similar) in order to create fractures in the oil-bearing rock and thus release more oil.