1. Drill pressure
Theoretically, the drilling pressure depends on factors such as formation rock hardness, diameter, drilling speed, drilling rig, drilling tool capacity and drill bit structural strength.
The harder the formation, the larger the diameter, and the greater the WOB required. The higher the weight on bit, the faster the drilling speed. However, if the drilling pressure is too large and the hob is pressed into the rock too deeply, the drill bit will be broken and cannot be rotated, causing damage to the drill tool and the drill bit and causing an accident under the hole. At the same time, the bearing life of the cutting tool is directly related to the weight on bit. Therefore, the drilling pressure should be limited.
During the specific operation, the drilling pressure shall be matched with 1/2-3/4 of the normal torque value of the drill rod, and the value shall not exceed the recommended value of the under-reamers-hole openers manufacturer.
The rotation speed of the drill changes with the diameter of the drill bit. Generally, the linear speed of the outermost cutting tool of the drill bit is not more than 3m/s. Under normal circumstances, the rotation speed of the drill pipe is controlled within 40RPM.
3. Mud displacement
The role of mud is to carry cuttings and cool the bit. In theory, the larger the mud displacement, the better. In order to reduce drill bit wear in sandstone formations, pump capacity should be increased as much as possible.