Places where fluids collect are called reservoirs. The most common fluids found in reservoirs are water, hydrocarbons, and gas. Reservoirs can be natural or artificial (human-made). Examples of natural reservoirs include hydrocarbon reservoirs in rock formations (Figure 1) and water reservoirs that occur behind naturally occurring dams. Artificial dams mostly involve water, such as the reservoirs behind hydroelectric dams (Figure 2).
Within energy science the word reservoir usually refers to either:
Figure 1. Gas reservoirs are located deep underground.
Figure 2. The reservoir behind the Hoover Dam is called Lake Mead.