How do the drillers replace the bit?

During drilling, the power of the drilling rig drives the rotary table, Kelly, drill pipe and drill bit to rotate. Observe the working condition of the down hole drill bit through the instruments on the ground of the drilling rig. After comprehensive judgment, if the drill bit is considered to have been worn, stop drilling immediately and replace the drill bit. After the drilling is stopped, the drilling fluid circulation shall be maintained for a period of time. The purpose is to adjust the performance of the drilling fluid, bring the rock cuttings suspended in the drilling fluid out of the ground, circulate to keep the new borewell wall stable, and conduct routine inspection of the drilling equipment. The driller uses the crown block, traveling block and hook on the derrick to pull out all drilling tools from the well according to the height of the derrick and the column (usually composed of two or three drill pipes). After pulling out, the drill pipe column is discharged into the derrick in sequence. While lifting the down hole drill string, the drilling fluid shall be continuously injected into the annular space with the drilling pump to keep the liquid level in the borewell from falling, so that the pressure in the borewell can balance the formation pressure, so as to prevent the borewell from collapsing or the fluid in the down hole formation from entering the borewell. At the same time, pay special attention to the possible sticking of the drill pipe due to the wall shrinkage, and the operator shall strictly control the lifting speed. After all the drill pipes and drill collars in the borewell are pulled out, the drill bits to be replaced will be pulled out at the same time. The workers can resume drilling after unloading the old drill bits, installing new drill bits and lowering them into the well according to the original column sequence.