 There are a good number of naturally fractured reservoirs in the United States, and over the past century, they have provided a substantial boost to the nation's net hydrocarbon production.The key concept is while low porosity, brittle rocks may have very little natural storage or flow capability, the rock is subjected to stresses that generate fractures, and these fractures can actually store a very large volume of hydrocarbons, capable of being recovered at very high rates.One of the most famous examples of a prolific naturally fractured reservoir was the Austin Chalk formation in South Texas.