The formation of oil: oil consists mainly of hydrocarbons. In the rock pores, often with liquid or gas (natural gas) are sometimes partially condense into solid. Petroleum is the ancient biological remains, accumulation in the lake, the sea, or on land, after high temperature, high-pressure role, by biological and chemical conversion of complex. Every little bit of oil generation in formation, and floating in the earth. Due to the buoyancy of the relationship, in the annual oil slowly down the formation or fault moves upward, closed reservoir until oil proof barrier and stay. When the closed point of the oil accumulating, they formed a oilfield. Closed structure of oil and gas reservoir structure a good storage of oil and gas, in addition to reservoir with good porosity and permeability of tight, impermeable to oil, gas, water beds must be above the reservoir, such as shale, mudstone caprock, this is the so-called, oil and gas and its role as the capping in the hotel, do not let oil and gas to escape. General petroleum common closed constructed according to their types can be divided into structural traps such as anticline, fault, and stratigraphic trap, combined with closed.