PDC Drill Bit Technology & Practical Guide for Deep Hole Drilling

PDC drill bits, short for Polycrystalline Diamond Compact drill bits, are also referred to as polycrystalline diamond cutter bits. Since the first PDC drill bit was developed in 1973, this product has been widely adopted in oil drilling. Featuring fast penetration rate, long service life and large drilling footage, PDC bits have become mainstream products, and most manufacturers have launched their own PDC bit series.

A PDC drill bit mainly consists of bit body, PDC cutters and nozzles. It is classified into steel body type and matrix body type according to structure and manufacturing technology.

• Steel Body PDC Drill Bit: It is made of medium carbon steel and formed by mechanical processing. PDC cutters are press-fitted into holes on the bit crown, which is further hardened by tungsten carbide spraying or carburizing to improve erosion resistance. This type has a simple manufacturing process, but suffers from poor erosion resistance and unstable cutter fixation, so it is rarely used nowadays.
• Matrix Body PDC Drill Bit: The upper part is steel structure, while the lower part is tungsten carbide alloy matrix manufactured by powder metallurgy sintering. PDC cutters are brazed into pre-machined grooves on the matrix with low-temperature solder. With high hardness and excellent anti-erosion performance, matrix body bits deliver longer service life and larger drilling footage, and are the most widely used type in the industry.

PDC drill bits break rock through cutting action. Under drilling pressure, self-sharpening cutters easily penetrate into rock formations and shear rock under torque. Multiple cutters work simultaneously to create numerous free surfaces on downhole rock, greatly improving rock breaking efficiency and drilling speed.

PDC drill bits perform best in homogeneous soft to medium-hard formations, and are not suitable for gravel layers or formations with alternating soft and hard rock.

The recommended working parameters are low drilling pressure, high rotational speed and large flow rate.

Clean the borehole thoroughly before running the bit down to remove all metal debris.

Start drilling with low pressure and low rotational speed for running-in. Resume normal drilling parameters after the borehole is fully stabilized.

PDC oil drill bits are essential tools for oil drilling. Equipped with multi-layer polycrystalline diamond structures, they possess superior cutting performance and wear resistance. However, the diamond layers are prone to damage under heavy load and severe abrasion. To extend service life and improve drilling efficiency, surfacing welding has been widely applied to repair and reinforce PDC oil drill bits.

Surfacing welding uses high-energy heat sources to melt and fuse metal materials. It is commonly used for workpiece repair and surface performance enhancement. For PDC drill bits, this technology can restore worn or damaged diamond layers, as well as improve the bit’s wear resistance and corrosion resistance. The complete surfacing welding process includes four key steps:

1. Surface Preparation
   Thoroughly clean the bit surface before welding to remove oil stains, oxide layers and impurities, ensuring a firm bond between surfacing materials and the base metal.

2. Material Selection
   Material selection plays a decisive role in welding quality. The selected materials must have high hardness, excellent wear resistance and corrosion resistance. Cobalt-based alloys are the ideal choice for polycrystalline diamond layers due to cobalt’s outstanding thermal conductivity and anti-corrosion ability.

3. Welding Process
   Heat the surfacing material until it melts and fully fuses with the drill bit base body. Common welding methods include manual arc welding, TIG welding and laser surfacing welding. Select the proper method based on the bit’s requirements and material properties.

4. Post-treatment
   Carry out follow-up processing after welding. Heat treatment is adopted to enhance the hardness and strength of the surfacing layer, while mechanical processing is used to calibrate the shape and dimension of the welded area.

Surfacing welding effectively prolongs the service life of PDC drill bits and reduces maintenance costs. The final repair effect depends heavily on process control and operator skills. Before construction, operators shall select materials and welding methods properly, standardize post-treatment procedures, and be equipped with professional knowledge and rich practical experience.

At present, surfacing welding technology has achieved remarkable results in the oil drilling industry. With continuous technological innovation, the surfacing process will be further optimized to provide better solutions for PDC drill bit application.

In the drilling industry, boreholes deeper than 1500 meters are defined as deep holes. Deep hole drilling is complicated and high-risk. Any operational mistake will lead to substantial loss of time and cost. Below are seven practical tips to help you complete deep hole drilling safely and efficiently.

1. Drill Slowly and Steadily
   Do not rush during deep hole drilling. A slow and stable pace can reduce equipment load and minimize tripping times. Minor faults in shallow holes may turn into serious accidents in deep holes over 1500 meters. Always stay patient and operate carefully.

2. Inspect and Maintain Equipment Completely
   Check all components of the inner tube, including core catchers, catcher seats, joints, bearings, latches, fishing heads, locks, balls and pins. Make sure all parts work normally, keep them clean and well-lubricated, and use degreaser when necessary. Well-maintained equipment operates more reliably downhole.

3. Prevent Borehole Deviation
   The deeper the borehole, the higher the risk of deviation. Take effective anti-deviation measures in advance. Prevention is always more time-saving, cost-effective and efficient than deviation correction.

4. Properly Use High Matrix Drill Bits
   Drill bits with 20mm or 26mm high matrix can extend service life and reduce tripping frequency. Field tests show that 26mm matrix bits can cut tripping times by more than 50% compared with 13mm standard bits. Note: This method is only recommended if you have a full understanding of local formation conditions, as formation characteristics vary from well to well.

5. Apply Drilling Fluid Additives
   Drilling mud is critical for deep hole drilling. Add polymers and targeted fluid additives according to actual formation conditions.

6. Select Qualified Drill Pipes
   Use straight drill pipes with qualified threads. Apply high-quality thread grease containing no less than 50% zinc, and deep-hole dedicated threads are highly recommended.

7. Choose Suitable Drill Bits
   Besides matching bits with formation hardness, full-face matrix bits are preferred for deep hole drilling to extend service life. When selecting core bits, prioritize service life over penetration rate.

If you are unfamiliar with equipment or rig functions, please operate cautiously and consult professionals in time to avoid unnecessary losses. Suzhou Energy Tool Co.,LTD has an experienced technical team with rich expertise in deep hole drilling, providing professional technical support for all clients.