The development of drilling technology mainly depends on solid control equipment. Mechanical solid control is an important link to maintain and ensure the good performance of drilling mud, and is also one of the components of conventional drilling technology.
In drilling mud, the size of solid particles that have a great impact on mud performance and mechanical penetration rate is more than 15 microns, accounting for about 70% of the total solids. People try to remove it at any time through more effective mechanical equipment. With the development of drilling technology, the requirements for mud performance are higher and higher. Practice has proved that the technology of improving mud performance by controlling mud solids has developed into an important auxiliary technology of drilling mud, which is closely related to stabilizing well conditions and improving drilling speed. In order to provide high-quality mud for drilling, it is necessary to have a set of complete and applicable mud purification equipment, which is the guarantee to maintain the excellent performance of drilling mud.
The solid phase in drilling fluid and mud can be divided into two categories according to their functions: one is useful solid phase, such as bentonite, chemical treatment agent, barite powder, etc. The other is useless solid, such as drilling cuttings, poor bentonite, sand, etc.
The so-called solid phase control of drilling fluid is to eliminate harmful solid phase and preserve useful solid phase to meet the requirements of drilling technology on the performance of drilling fluid. Generally, solid control of drilling fluid is referred to as solid control.
The importance of solid control is being paid attention to. It has become an important factor that directly affects the safe, high-quality and efficient drilling and the protection of oil and gas reservoirs. Solid control is one of the important means to achieve optimal drilling. Good solid control can provide necessary conditions for scientific drilling. Proper solid phase control can protect the oil and gas reservoir, reduce the drilling torque and friction, reduce the pressure fluctuation of the annulus suction, reduce the possibility of differential pressure sticking, improve the drilling speed, extend the life of the drill bit, reduce the wear of equipment and pipes, improve the life of vulnerable parts of the drilling fluid circulation system, increase the stability of the wellbore, improve the casing conditions, reduce environmental pollution, and reduce the cost of drilling fluid. The field statistical data shows that in the low density range, the mechanical penetration rate can be increased by about 8% for each 1% reduction in the solid content of drilling fluid (equivalent to 0.01 decrease in the density of drilling fluid). It can be seen that the benefits of solid control are very significant.
The existence of excessive useless solid in mud is the biggest hidden danger of damaging the performance of drilling fluid, reducing the rate of penetration and leading to various downhole complications. In long-term practice and continuous research, people have concluded that excessive useless solid phase in mud will bring the following adverse effects on drilling work.
The high solid content of mud, the larger specific gravity, and the increase of bottom hole pressure difference increase the pressure holding effect of the liquid column on the rock, which is not conducive to rock fragmentation at the bottom of the hole. The solid content of mud is high, the ability to carry drilling cuttings is weakened, and a large number of large particles of drilling cuttings cannot be discharged out of the hole in time, resulting in repeated breaking of rock cuttings by the drill bit, and thus increasing the wear of drilling tools, thus affecting the drilling speed.
During drilling, the water loss and solid particle content of mud will directly affect the quality of mud cake formed on the hole wall. The water loss of drilling fluid is small, the mud cake is thin and tough, and the wall protection is good, which is our goal. The high solid content will increase the water loss of the mud, which will lead to water absorption, hydration expansion and hole wall instability of the shale formation, resulting in poor lifting and tripping, leading to accidents in the hole. In addition, if the mud cake is too thick and loose, it will also increase the contact surface between the drilling tool and the well wall, which will easily lead to sticking accidents.
The greater the solid content, the greater the mechanical wear of the circulating system. Too much mud will accelerate the wear of the cylinder liner and piston of the mud pump, thus increasing the maintenance time and reducing the drilling efficiency. If the solid content is too high, it will also cause scaling on the inner wall of the drill pipe, affect the fishing of the inner pipe, and be forced to lift the drill pipe to handle scaling, thus interrupting the normal working procedure. The drilling efficiency will also be significantly reduced due to the large increase of the auxiliary operation time.
During the drilling process, the mud performance will change if the drilling cuttings are not removed in time because they are constantly entering the mud. When the sand content of the mud is more than 4%, it is considered as waste slurry. It needs to be discharged and replaced with new slurry. Most of the mud is alkaline solution, and random discharge will not only destroy vegetation, but also cause soil alkalization and affect vegetation regeneration. In addition, there are some additives in the mud that make the mud black, and a large amount of discharge will cause visual pollution to the environment.