The oil and gas industry has been no stranger to technological advancements over the years. As drilling operations continue to push the boundaries of what is possible, one innovation stands out prominently: Polycrystalline Diamond Compact (PDC) drilling bits. PDC bits have revolutionized the drilling process, offering higher efficiency and longer lifespan compared to traditional roller cone bits. However, their effectiveness relies on proper handling and maintenance. In this article, we shed light on the essential considerations that drilling professionals must keep in mind when using PDC drilling bits.
Preparations before going down the well
- Check whether the previously used drill bit is damaged or has missing teeth, make sure there are no hard objects at the bottom of the well, and clean the bottom of the well if necessary.
- Check the drill bit, measure the inner and outer diameter of the drill bit, see if the cutting teeth are damaged, and install the nozzle as needed.
Put on the bits
- Clean the drill threads and apply thread oil.
- Put the drill bit and breaker together into the turntable core filler, and then tighten the drill bit according to the recommended torque for the corresponding thread.
Drill down
- Remove the breaker and carefully lower the drill bit.
- Pay attention to the blocked well section that occurred when tripping out last time. When encountering the reduced diameter well section and deflection during drilling, the drill bit should be passed slowly and the drill bit should be rotated.
About reaming
- We do not recommend diamond drill bits for reaming, but if it is really necessary, use maximum displacement and low rotation speed as much as possible, control it below 60 rpm, and have a low drilling pressure of 10~20KN.
Clean the bottom of the well
- When the drill bit is close to the bottom of the well, the last three individuals should be circulated at a large displacement and lowered slowly with a rotation speed of 40-60rpm.
- Observe the turntable torque and weight indicator to determine whether the drill bit has reached the bottom of the well. Once the drill bit touches the bottom of the well, the drill bit should be raised by 0.5 meters, cycle at a large displacement, and start the turntable at low speed for 5-10 minutes.
Establish bottom hole model
- Keep the rated displacement and lower the drill bit to the bottom of the well.
- Use a drilling weight of 10-20KN and a rotation speed of 60rpm to drill slowly for at least 1 meter to establish a bottom hole model.
Drilling rate test
- After the bottom hole modeling is completed, different combinations of drilling pressure and rotational speed can be selected within the recommended drilling parameter range to conduct drilling rate tests until an optimal drilling rate is found. If formation changes occur during normal drilling, the drilling rate test can be performed again.
During the drilling process
- After the drilling rate test is completed, normal drilling can be performed according to the optimal parameters. During drilling, it is necessary to ensure that the displacement meets the requirements and the drill is fed evenly.
- If drilling encounters a harder homogeneous formation, the penetration rate will drop significantly. At this time, a parameter combination of upper limit weight on bit and lower limit rotation speed can be used, or the penetration rate test can be re-carried out in order to obtain a more satisfactory penetration rate.
- If the drilling encounters a hard interlayer and slipping occurs, the drilling pressure can be appropriately reduced, and the rotation speed can be reduced at the same time. After the hard interlayer is drilled through, the normal parameters can be used.
- If slipping occurs while drilling in a suitable homogeneous formation, the method of increasing the rotational speed can generally restore stable drilling conditions.
- In the later stages of the drill bit's use, the PDC cutters will form a larger wear plane, making it difficult for the cutters to cut into the formation. Therefore, the weight on bit can be appropriately increased to maintain a higher drilling rate.
Pull out of the hole
- When encountering one of the following situations, pulling the bits should be considered:
- When the formation lithology changes little but the ROP and turntable torque decrease significantly, the standpipe pressure increases;
- When the standpipe pressure increases or decreases significantly;
- When there is continuous slipping or lagging, and the mechanical drilling speed is very low;
- In the later stages of the use of the drill bit, if the lithology has not changed significantly and the weight on bit used is relatively large, but the ROP has dropped significantly;
- When drilling costs per meter are too high.
Other things to note
- Prevent slippage and sudden drilling;
- It is prohibited to pressurize first and then rotate;
- Always pay attention to the riser pressure to prevent the nozzle from clogging, so as not to reduce the cooling effect and chip removal effect of the PDC cutters;
- When drilling in a section with high drillability, the drilling speed must be consciously controlled not to be too fast to avoid sudden encounter with hard interlayer and damage to the cutters.
In conclusion, the use of PDC drilling bits represents a significant leap forward in drilling technology, offering enhanced efficiency and durability. However, success with these advanced tools hinges on meticulous attention to detail. From selecting the right bit for the geological conditions to monitoring drilling parameters, maintaining cutters, and ensuring proper hydraulic performance, every aspect plays a crucial role in achieving optimal results. By consistently applying these considerations and staying vigilant in their maintenance, drilling professionals can harness the full potential of PDC drilling bits, making drilling operations safer, more efficient, and more cost-effective.