Usage and Fault Diagnosis of Tricone Bits

1. Bit Selection

When drilling to different depths and encountering varying formation abrasiveness, it is important to choose the right triCone Bit based on the drilling purpose (e.g., wellbore cleaning, plug drilling, or directional drilling). In the upper shallow well sections, select atricone rotary drill bit with high mechanical drilling speed and widely spaced teeth. For deeper sections, where formation drillability decreases, wellbore temperature rises, and the time for bit replacement increases, choose a bit with a longer lifespan, high-temperature resistance, and strong wear resistance, such as a tungsten carbide Tricone Drill bitor a TCI tricone bit. Adding wedge-shaped or conical teeth to the bit can improve its economic performance, especially when working with borewell drilling bits or in mining applications, where durability is crucial.

2. Tricone Bit Usage  

While selecting the appropriate bit is crucial, proper usage is equally important. Even with the right bit model, improper use can lead to unsatisfactory results.  

(1) Bit Inspection and Acceptance:  

This includes checking the appearance of the bit, ensuring compatibility with bit handling tools, nozzles, and nozzle wrenches. Before running the bit into the hole, manually check the rotation of the tricone and record the relevant details, including bit model, manufacturer, steel grade, water hole number and size, and connection thread type, ensuring it matches the adapter. If you're using a metal seal drilling bit, double-check the sealing system to avoid fluid loss issues.  

(2) Bit Handling:  

Use the correct bit handling tool, protect the bit, apply thread lubricant, and tighten it according to the recommended torque, confirming the bit is securely attached (ensure the wear sleeve is installed in the correct sequence or position).  

(3) Running in and Reaming:  

Control the lowering speed through blowout preventers, casing heads, reduced diameter sections, directional drilling sections, or dogleg sections. Lower the bit smoothly to avoid stuck pipe or bit jamming. For long sections, circulate in stages to prevent sticking, leaking, or loss of circulation. Ensure the pump is operating normally before reaming. A tricone rock bit is often suitable for these situations due to its ability to handle a range of formations.  

(4) Exploring the Bottom:  

When approaching the bottom, monitor the weight on bit (WOB) and torque. If WOB and torque increase, it indicates contact with the bottom or accumulated cuttings. Avoid blindly lowering the bit or probing the bottom, as it could clog the water holes. If there are cuttings or any obstruction, raise the drill string, slowly start the pump, ensure proper pump operation, and then clean the bottom while making connections. Always start the pump early and stop it late. If you're drilling through tough formations, insert tooth drill bits may be more effective.  

(5) Drilling or Plugging:  

After reaching the bottom, wash the wellbore to clean the hole before drilling. Use low WOB, low rotational speed, high flow rate, and low torque to maintain hole conditions. While circulating and rotating the drill string, moving it up and down helps clean the bit. Control WOB to avoid damaging the bit. Monitor pump pressure changes to prevent nozzle clogging. When encountering stick-slip or significant torque variations, adjust speed, reduce WOB, use low speed, and stabilize the torque. If using a powered drill string, reduce the flow rate; if using a non-powered drill string, increase the flow rate. There are differences in matching WOB and speed. High speed and low WOB are suitable for soft formations, while high WOB and low speed are better for hard formations. When working with abrasive formations, milled tooth tricone bits may provide better performance.

3. Tricone Bit Fault Diagnosis

(1) Bit Shrinking:  

When drilling through formations with high abrasiveness, the bit may experience shrinking. The performance of the bit and stabilizer cutting the wellbore shows increased torque on the rotary table or top drive, stuck drilling, unstable rotary speed (fluctuating over time), and no increase in drilling torque. The application of low WOB and low speed does not alleviate stuck drilling. If there is no blockage after raising the bit and stopping the pump, and no large rock cuttings are seen on the shaker, it can be concluded that the bit is shrinking. This issue is common when using three cones drill bits in harsh conditions.  

(2) Bit Seizure:  

If there is an increase in torque (e.g., increased load on the rotary table or top drive, periodic stuck drilling, large variations in power system output, or unusual engine noise), combined with the bit’s usage time and formation conditions, it suggests the bit may be seized. Immediate circulation and bit retrieval should be performed. A tricone rock bit can sometimes face this issue, especially in hard rock formations.  

(3) Tooth Loss:  

If there is an increase in torque on the rotary table or top drive, and when the rotary table or top drive is stopped, the bit starts to reverse, with severe stuck drilling, needle-like fluctuations in the weight indicator, significantly reduced or no rate of penetration, or direction change when raising the drill string, tooth loss may have occurred. This is more noticeable in deep wells, and should be checked and replaced in time to avoid further damage. In such cases, milled tooth bits for mining or TCI drill bits with enhanced durability can help reduce wear.  

Note: In case of any stuck or sudden drilling conditions, the bit should be pulled out and inspected or replaced immediately. Avoid probing the bottom in such situations to prevent further tooth loss.

In practice, different manufacturers, sizes, and models of tricone bits, even when used under recommended parameters, have a safe operating time. As long as no improper operation occurs within this time, the bit is generally safe. Otherwise, it should be handled cautiously. It is essential to choose between insert tooth drill bits or milled tooth tricone bits depending on the specific formation to ensure optimal performance.