The so-called oil is a kind of mineral fuels which formed in the underground rock. It mean composition is liquid hydrocarbon. The oil and gas exist in the crust. Oil formed in underground, stored thousands of meters below the ground. It appears millions of years or even hundreds of millions of years evolution process. The oil formed in different geological environment have different physical properties in different times. The oil formed in different oil field has different density, viscosity, melting point and initial boiling point.
Oil is a kind of complex natural organic compounds. The basis of it is C and H. The carbon content is 80%-88% in general and hydrogen is 10%-14% in the oil. Also contains a small amount of oxygen (O) sulphur (S) nitrogen (N). The compound constituted by these elements called hydrocarbon. The natural gas’ main ingredient is also the hydrocarbon, it is gaseous state. Natural gas mainly contain alkenes (saturated alkenes) as oil. General the alkenes with 1-4 carbon is gas which we call it natural gas. The alkenes with 5-10 carbon is liquid which we call it oil. The alkenes contain 17 or more than 17 carbons is solid state such as paraffin and asphalt. The most intuitive physical property of crude oil is the rich color. It vary from bright to dark which contain gray, brown, dark green and dark. The common oil is dark. The oil’s color is determined by the mount of hydrocarbons, the mount of which is more, the color is lighter and the oil quality is better.
There are two view points on the oil and natural gas generation source. One is organic generation doctrine which thinks the oil and gas come from the dead creatures. Scientists think as early as 1billion years ago, creatures appear on the earth. The number and variety of creatures become more and more with the development of history. One of algae can multiply to 1036 generations; weight can reach 1.4 1017 tons in 8 days under suitable condition. Large mount of geology which mainly is plankton in the oceans and lakes after they died partly become carbon dioxide and the left is deposited with sediment. The deposited part becomes the source of oil and gas. The dead plants and animals buried up by the sediment on earth layer by layer. After a long time pressure and temperature effect, the organic matter changed into the oil and natural gas we find today. (For example, the rubbish dump can emit methane gas.)
The basis of organic generation point is that almost all the oil field is found in the sedimentary rock. And abundant lebensspur can be founded in the sedimentary rock (such as fossil). By experiment, we known protein, carbohydrate and fat the three major parts of biology can form the petroleum hydrocarbons similar matters. Hemoglobin and chlorophyll are found in the oil. The hemoglobin come from the blood of animal and the chlorophyll come from the plants. The reason of oil generated by dead creatures is so much and enough that make most people agree with it. Now, the research method and content are built on the basis of this view.
But it is still in dispute that is the marine species or the creatures in river and lake generated the oil. In reality, in the Middle East the oil fields in Saudi Arabia and Kuwait are all Marine strata while in china they ate all terrestrial strata. The other one is inorganic generation point which thick the oil and gas come from the inorganic matter. Refining the oil can get many products such as kerosene, paraffin, asphalt, power energy, gasoline used in car, diesel used in track, high purity aviation fuel used in plane and fuel oil used in heating.
Many other materials are also product with oil such as plastic, clothing materials(polyester fiber), daily-use chemical products and dyestuff etc. Natural gas dissolved in the oil just like the carbon dioxide dissolved in water. Due to the different types of oil wells, a barrel of oil may contain a cubic feet to more than 10000 cubic feet natural gas. This gas is much enough to fill the whole room.