Judging from the used PDC drill bits, the main characteristics of most PDC bit damage are the fracture of the tooth column, the fragmentation of the composite sheet, the chipping, erosion, and the erosion of the drill bit matrix. Judging from the damage characteristics of the PDC bit, when the PDC bit is working downhole, in addition to the reaction force and the formation rock wear damage caused by the normal cutting of the formation, it is also subjected to additional force and influence. This additional force causes the PDC bit to be abnormal The main cause of damage. After statistics and analysis of the use of PDC bits, combined with the areas and strata where PDC bits are used, it is believed that the PDC bits are damaged due to the following reasons:
Gravel in the formation
The lower part of the stratum contains gravel layers of varying thickness. When PDC bits drill into this section of the well, chipping and chipping often occur when PDC teeth cut gravel, which is the main reason for the early damage of PDC bit cutting teeth in the upper stratum.
Many hard interlayers in the stratum
More hard interlayers in the formation are the main reason for the fragmentation, chipping or stub cutting fracture of the PDC drill bit. Because the PDC bit is drilling from the soft formation to the hard interlayer during the drilling process, due to the PDC bit crown profile The switch makes the cutting teeth on the surface of the drill bit have different hardness in contact with the formation, resulting in uneven force when the cutting teeth cut the formation, causing the drill bit to appear lame and jumping, and most of the load on the bit is concentrated in cutting hard interlayers. On the cutting teeth, the instantaneous load generated by the lame drill jump drill causes the cutting teeth to chip or break due to the greater force (especially when cutting some hard points in the hard formation, the instantaneous load is sufficient to cause Chipping of the cutting teeth or broken cutting teeth). For example, the PDC composite sheet and the base of the drill are not firmly welded. When subjected to a large instantaneous load, the composite sheet will fall off. If the stratum has an inclination angle and the inclination angle is large, the phenomenon of broken drill jumping when the drill bit encounters a hard interlayer is more serious, causing more serious damage to the cutting teeth. The reaction force of the drill bit into the hard formation is concentrated on the edge of the composite sheet, and the reaction force of the drill into the soft formation is all distributed on the cutting tooth surface. Therefore, even with the same drilling parameters, drilling into hard formations is easier to damage the cutting teeth than drilling into soft formations.
PDC bit hydraulic parameters are not suitable
When using a PDC drill bit, if the specific water power is selected too large, it will cause severe ice erosion on the drill bit matrix, causing the cutting tooth column or nozzle to fall off. If the nozzles are arranged in an improper position, the jetted fluid will reflect and directly erode the cutting teeth after hitting the bottom of the well. If the specific water power is too small, it will be unfavorable for the cleaning and cooling of the composite sheet, especially in the soft formation, it is easy to cause the bit mud bag, and it is easy to cause the thermal acceleration of the composite sheet in the hard formation.
Unsuitable drilling engineering parameters
The biggest difference between the PDC bit and the roller cone bit is that its drilling parameters are higher than the bit pressure and higher speed of the roller bit. Of course, we will formulate corresponding engineering parameters for different bit types and different formations. Ensure the service life of the drill bit and the mechanical drilling speed. Strive to improve the wellbore quality and drilling efficiency of the well team.