What is Oil?

Crude or “unprocessed” oil is a fossil fuel, meaning that it was made naturally from decaying plants and animals living in ancient seas millions of years ago. Wyoming was once an ancient sea.

Crude oil contains hydrocarbons, which are molecules that contain hydrogen and carbon. Hydrocarbons contain a lot of energy, which is why oil is so useful as an energy resource. These hydrocarbons formed from billions of tiny plants and animals that once inhabited the Earth’s ancient seas. When they die and sink, their bodies add carbon to the sea floor sediments. When underground carbon-rich sediments are heated for about 10 million years, the carbon compounds change into hydrocarbons, or oil. Because oil is lighter than water it can float up through cracks and pores in the rocks. When rocks without pores or cracks stop the oil from rising any higher, a pocket of oil is formed, which can be accessed using high-tech machinery for horizontal and vertical drilling.

Salt Creek Oil Field, Natrona County, Wyoming.

Finding Oil

Geologists gather information to predict where oil is located underground. Data from nearby wells, regional geology, geophysical tools, satellite imagery, and surface oil seeps help them predict where a successful drill site might be located. While some test wells lead to the successful discovery of oil others find what are called “dry holes.” On occasion, drilling a test well will find no oil in the predicted zone, but finds it in other layers of rocks.