1. The footage is obviously slower when drilling, or it is obviously higher when drilling;
2. Increasing or reducing WOB has no obvious effect on drilling speed;
3. It has little effect on the drilling rate when the formation changes;
4. Drilling tool puncture occurs during drilling, and the circulation short circuit occurs, and the drilling speed obviously slows down after treatment.
5. The teeth of the drill bit cannot effectively penetrate into the formation, showing that the torque is reduced or the torque fluctuation range is reduced;
6. The phenomenon of "piston pulling" occurs during tripping and drilling.
1. Geological factors: the drilled stratum is soft mud with non-diagenetic upper part, which is very easy to stick to the surface of the drill bit, which will cause balling of the drill bit after compaction; although the shale in the stratum is diagenetic, it is easy to hydrate and disperse, making the mud or solid phase in the wellbore greatly increases, which is adsorbed on the surface of the drill bit and causes the bit balling; or the formation contains dispersed gypsum, which causes mud pollution, and the harmful solid phase in the mud is difficult to remove, which greatly increases the probability of formation of bit balling. Under the action of the pressure difference, the harmful solid phase in the wellbore and the cuttings that are not carried out in time are absorbed to form a thick mud cake, which accumulates under the PDC bit when starting the drill, causing the bit balling.
2. Mud performance factors: poor mud inhibition, unable to control the hydration and dispersion of shale; too high solid content and sticky cut, the drilled cuttings are difficult to remove and are easily adsorbed on the surface of the drill bit. If a solid-free phase drilling fluid is used, the drill bits will never have mud packs; the proportion of mud is too high, the water loss is large, and thick mud cakes are easily formed; the lubrication performance is poor, the surface of the drill bit cannot form an effective protective film, and the inferior solids in the drilling fluid are easily adsorbed on the drill bit.
3. Engineering technical factors: the drilling displacement is small, the bottom hole and the drill bit cannot be cleaned effectively, and the upward and backward speed is insufficient. The cuttings stay in the well for a long time and adhere to the well wall to form a thick mud cake, especially in the upper part of the drill. It is more serious when the speed is high; in the soft mudstone formation, the drilling pressure is too high, the formation or the drill cuttings and the surface of the drill bit form direct contact, causing the bit balling; the long open hole drilling does not carry out halfway circulation, and the mud cake scraped from the well wall or drill cuttings will cause the drill bit balling.
4. Drill bit selection factors: The water eye design cannot meet the chip removal requirements; the channel chip removal angle prevents the drilling cuttings from smoothly leaving the bottom of the well.