[1] Research shows that it takes at least 2 million years to generate oil, and the oldest discovered oil reservoir is 500 million years. In the long historical process of the earth's continuous evolution, there are some "special" periods, such as Paleozoic and Mesozoic. After the death of a large number of animals and plants, the organic substances that make up their bodies are constantly decomposed and mixed with sediments or carbonate sediments to form sediments. Due to the continuous accumulation and thickening of sediments, the temperature and pressure rise. With the continuous advancement of this process, sediments become sedimentary rocks and then form sedimentary basins, providing a basic geological environment for the generation of oil. Most geologists believe that oil, like coal and natural gas, is gradually formed by long-term compression and heating of ancient organic matter. According to this theory, oil is formed by the changes of prehistoric marine animals and algae corpses. Plants on land generally form coal. After a long geological period, these organic substances are mixed with silt and buried under thick sedimentary rocks. Under the high temperature and pressure in the underground, they gradually transform, first forming waxy oil shale, and then degenerating into liquid and gaseous hydrocarbons. Because these hydrocarbons are lighter than the nearby rocks, they penetrate upward into the nearby rocks until they penetrate into the tightly impermeable rocks above, and the rocks themselves are empty. The oil accumulated in this way forms an oil field. People can get oil from oil fields by drilling and pumping water. Geologists call the temperature range of oil formation "oil window". If the temperature is too low, oil cannot be formed; if the temperature is too high, natural gas will be formed. Although the depth of oil formation varies around the world, the "typical" depth is 4 to 6 kilometers. Because oil will penetrate into other rock formations after formation, the actual oil field may be much shallower. Therefore, the formation of an oil field requires three conditions: rich source rocks, permeable channels and rock structures capable of accumulating oil.