1. Drill selection
In soft strata, steel-toothed or insert-toothed drill bits with both axis-shifting, over-top, compound cone, large tooth shape, and a small number of teeth should be selected to give full play to the shearing and rock breaking effect of the drill bit. As the hardness of the rock increases, the drill bit of the DTH drill pipe should shift the axis, exceed the top, and the complex taper value should be reduced accordingly, and the teeth should be shortened or densified accordingly; abrasive formations are particularly easy to wear the gauge teeth of the cone, the back cone The diameter of the drill bit is reduced, the diameter of the wellbore is reduced and the seal is ineffective, so a special diameter-gauge structure with the back of the palm should be selected; for anti-deviation drilling in easy-inclined formations, the drill bit that does not shift the axis or has a small amount of axis shift should be selected. Reduce the slippage of the drill bit at the bottom of the hole and prevent good deviation; in the alternating hard and soft formation, the type of drill bit with harder rock in this formation should be selected.
2. Drilling situation analysis
The operation of DTH drill pipe surface equipment, cuttings and WOB, torque, ROP, pressure, and other surface instruments can directly reflect the downhole conditions and should be closely watched, especially torque, pump pressure, ROP, and cuttings.
The torque variation depends on the bottom hole condition and the speed variation. The normal torque value is relatively stable, the torque value is lower in the soft or plastic homogeneous formation, the torque value in the medium-soft to medium-hard homogeneous formation is medium, and the torque value in the hard formation is larger and exists in certain range fluctuations. Torque changes may exist: centralizer reaming, drill bit gauge wear, interlayers, falling objects at the bottom of the well, keyways or doglegs in the wellbore, excessive weight on bit, changes in rotational speed, DTH bit or mud bag in the bottom hole assembly, Drilling hole or dry drilling, etc.