Advantages and disadvantages of using PDC bits in hard rock drilling

1). Advantages of PDC bits

One of the main advantages of PDC bits is that they can drill faster and longer than other types of bits, such as roller cone bits or impregnated diamond bits. PDC bits have a higher rate of penetration (ROP) and a lower torque requirement, which means they can save time and energy. PDC bits also have a better steerability and directional control, which is important for horizontal and directional drilling. PDC bits can also withstand higher temperatures and pressures than other bits, making them suitable for deep and hot wells.

2). Disadvantages of PDC bits

However, PDC bits also have some disadvantages that limit their applicability in hard rock drilling. One of the main drawbacks of PDC bits is that they are more expensive than other bits, and they require more careful maintenance and handling. PDC bits are also more prone to wear and damage from abrasive and hard rocks, especially if the rock strength and drillability are not well matched. PDC bits can also suffer from vibration, impact, and thermal shock, which can cause cracks, fractures, and loss of cutters. PDC bits also have a lower cleaning efficiency and a higher risk of bit balling, which can reduce the ROP and increase the chances of stuck pipe.

3). How to choose the best PDC bit

To choose the best PDC bit for hard rock drilling, drilling engineers need to consider several factors, such as the rock properties, the drilling parameters, the wellbore geometry, and the operational constraints. Some of the key rock properties that affect the performance of PDC bits are the compressive strength, the abrasiveness, the hardness, the brittleness, and the heterogeneity. Generally, PDC bits perform better in soft to medium-hard rocks, with low to moderate abrasiveness and hardness, and high brittleness and homogeneity. Some of the key drilling parameters that affect the performance of PDC bits are the weight on bit (WOB), the rotational speed (RPM), the hydraulic flow rate, and the bit design. Generally, PDC bits require a lower WOB and a higher RPM than other bits, and a sufficient hydraulic flow rate to cool and clean the bit. The bit design should also match the rock properties and the drilling objectives, such as the number, size, shape, and orientation of the cutters, the gauge length, and the profile.

4). How to optimize the performance of PDC bits

To optimize the performance of PDC bits in hard rock drilling, drilling engineers need to monitor and adjust the drilling parameters, the bit wear, and the bit hydraulics. To do this, it is best practice to use a drill bit optimizer software to select the optimal bit for the formation and drilling objectives. Additionally, a drill string stabilizer should be used above and below the bit to reduce vibration and improve stability. Furthermore, a shock absorber or shock sub should be used to protect the bit from impact and thermal shock, while a bit breaker should be used to prevent bit balling and improve cleaning efficiency. A mud motor or rotary steerable system should also be used to enhance steerability and directional control. Moreover, a real-time data acquisition and analysis system should be implemented to track ROP, torque, WOB, RPM, bit temperature, and bit wear. Finally, a bit dull grading system should be used to evaluate the condition and performance of the bit after each run.

5). How to overcome the challenges of PDC bits

Despite the advantages and optimization techniques of PDC bits, drilling engineers may still encounter some challenges and difficulties in hard rock drilling. Common challenges include bit bounce, cutter wear, cutter loss, and stuck pipe. To prevent bit bounce, use a lower WOB, a higher RPM, and a smoother bit profile. For cutter wear, use a higher hydraulic flow rate, a lower WOB, and a more aggressive bit design. To avoid cutter loss, use a shock absorber, a lower WOB, and a more durable bit design. To prevent stuck pipe, use a bit breaker, a mud motor, and a proper wellbore cleaning program.