Petroleum, one of the main objects of geological exploration, is a viscous, dark brown liquid, known as "the blood of industry". There are oil reserves in parts of the upper crust. The main components are mixtures of various alkanes, cycloalkanes and aromatics. There are two theories of oil formation mechanism of oil: biological deposition to oil and petrochemical oil. The former is widely accepted. It is believed that oil is formed by organisms in ancient oceans or lakes after a long evolution, belonging to biological deposition to oil, and is not renewable; The latter believes that oil is generated from carbon in the crust itself, has nothing to do with biology, and is renewable. Petroleum is mainly used as fuel oil and gasoline, and is also the raw material of many chemical industrial products, such as solutions, fertilizers, pesticides and plastics.