The drilling fluid is sent to drilling bit by a high pressure drilling string. The drilling mud is returned to the ground by the high pressure through the drilling hole. The drilling fluid must have high intensity and high viscosity. Some drilling bits are driven by drilling fluid. The advantage is that it has only drilling bit without having to rotate the whole drilling string. Usually a drill rig is built over a drilling hole in order to operate a very long drill string. In necessary conditions, engineers also can use directional drilling techniques to drill around the hole. This allows an oil field to to be mined from the side by bypassing the inhabited, geologically complex, protected or militarily used ground. The oil in the depth’s of the earth’s crust is crushed by the upper layer and possibly accompanying natural gas, which is lighter than the surrounding water and rock, so it tends to be squeezed out by pressure when the bit touches the oil layer. In order to prevent this jet, modern rigs have a special device at the upper end of a drilling string to prevent the well. Generally speaking, the oil pressure of oil field that newly mined is high enough to spray to the ground by itself. As the oil is being mined, the oil pressure decrease continuously. Then it needs a pump, which driven by a drilling string on the ground, to pump oil. The amount of oil will increase by pressing water or natural gas into the oil well. By injecting acid to dissolve some rocks(like carbonate) can increase the penetrability of oil-bearing rocks. As the mining time goes, the composition of water in the liquid is getting larger and larger. Later the composition of water is larger than the oil. Today some of the water components in the mine accounts for more than 90%. By above methods, according to the local conditions, today 20% to 50% of oil in an oil field can be mined. The remaining oil can’t be decomposed from the oil-bearing rocks. The amount of mined oil can be increased by following means.
- By pressing boiling water or high-temperature steam, even by burning part of the underground oil.
- By pressing nitrogen.
- By pressing carbon oxygen to decrease the viscosity of oil.
- By pressing light gasoline to decrease the viscosity of oil.
- By pressing an aqueous solution of an organic substance capable of decomposing oil from rocks.
- By pressing an aqueous solution of a substance (cleaner) that can improve the surface tension between oil and water, to decompose the oil from rocks.
- These means can be combined together. Even so, there is quite amount of oil that can’t be mined.
It’s most difficult to mine the oil field under water. Mining oil field under water requires a floating oil platform. It adopts most technology of directional drilling wells here. Adopting the technology can expand the mining area of the platform