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The harsh situation of the underground drilling operation promotes the research and the development of the polyacrylamide and the drilling fluid. It is required to meet the following critical requirements in the drilling process: the suspension, the pressure control, the rock stability, the buoyancy, the lubrication and the cooling.
The drilling fluids which flow along down the drill pipe or flow up from the borehole sometimes would stop flowing. There are only two reasons for such situation: one is the emergence of the fault, the other is that the drill bit is put out of the drill pipe when replacing the drill bit. When the drilling operation is stopped, the drilling cuttings which are suspending in the drilling fluid will sink into the bottom of the borehole, and then the borehole is blocked. The drilling fluid is designed to have a very interesting characteristic which can solve this problem. The consistency or the viscosity of the drilling fluid will increase when the flow rate of the drilling fluid gets down. When the drilling fluid stops moving, it will form a kind of thick gel. This kind of gel can make the rocket cuttings suspending inside and then prevent them from sinking to the bottom of the borehole. When the drilling fluid starts moving again, it will resume to its previous thin liquid formation.
The Pressure Control
Many people have seen the oil spraying into the air from the drilling well, and the people cheer for the great scene. As a matter of fact, such kind of blowout situation rarely happens, and it is not worthy celebrating, because the target of the oil drilling is to exploit the oil by means of controlling the oil flow rate. The drilling mud is designed to offset the natural pressure of the fluid in the formation, in order to prevent the occurrence of such accidents. There must have an appropriate balance between the pressures, that is to say, the pressure of the drilling fluid to the drill hole wall should be sufficient to offset the pressure of the strata and the oil or the gas, but the pressure can not be too large, otherwise it will cause damage to the oil well. If the weight of the drilling fluid is too big, it also can cause the rock burst and then the drilling fluid would be lost into the ground.
The pressure of the drilling fluid changes with the change of the concentration of the drilling fluid. By adding the weighting agent in the drilling fluid can help to improve its concentration and then increase the pressure to the drill hole. The concentration of the drilling fluid can be adjusted to meet the environment requirements of the oil well.
The Stability of The Bare Rock
The drilling process is divided into two stages: the first stage is the drilling of the petroleum free layers, the goal is to drill through the non petroliferous strata as soon as possible and reach the petroliferous strata, which is called the reservoir. At this stage, the focus is to keep the stability of the exposed rock formation in the borehole while avoiding the loss of the drilling fluid. If maintaining the high pressure of the drilling fluid to the pressure of the fluid pressure in the rock formation pore, the drilling fluid will appear the natural tendency to penetrate to the rock strata pore. By adding some special additives in the drilling fluid, it can prevent such phenomena from happening.
The drilling fluid may interact with the surrounding rocks by other means. For example, if the salt content of the salt is high, some salt will be dissolved in the water and then the wall of the borehole becomes unstable. Under this situation, the use of the oil base drilling fluid may achieve a better effect. The rock formation with higher clay content is tending to be washed away by water. In this kind of formation, the suppressed drilling fluid is required in order to maintain a stable wellbore, and to prevent the expansion of the drill bore or to prevent the erosion of the drill bore. With the continuous depending of the drilling, the borehole is protected by the steel casing while the steel casing is reinforced by the cement, by this way, it can not only maintain the stability of the wellbore but also provide the access to the oil from the reservoir to the ground surface after the oil exploitation reaches the reservoir. When reaching the reservoir, the composition of the drilling fluid must be changed, in order to avoid clogging the pores of the rock. Keep the rock pore not be blocked, can make the oil flow more smoothly into the drill hole, and then flow up to the ground surface.
An oil well may be drilled thousands of feet or several kilometers deep, but such a long steel drill pipe will be several tons in weight. If immersing the heavy drill rod into the drilling fluid, the drilling fluid can generate the buoyancy effect and then reduce the weight of the drill pipe, and furthermore, can reduce the load of the drilling mechanism.
An oil well may be thousands of feet or several kilometers deep. But a such a long steel drill pipe will be weighed several tons. If the drill rod immersed in drilling fluid, produces a buoyancy effect, reduce the drill pipe weight, andless stress on the drilling mechanism.
The Lubrication and the Cooling
When the metal is drilling into the rock, the friction will generate the heat. The drilling fluid can lubricate and cool the drill bit, make the smooth drilling, and at the same time to prolong the service life of the drill bit. On the extension of the regional or the horizontal wells, the lubrication effect may be particularly important, because in these places, the friction between the drill pipe, the drill bit and the rock surface must be kept to the minimum level.