Characteristics and Proper Use of PDC Drill Bits

PDC drill bit is the abbreviation for Polycrystalline Diamond Compact bit, also known as Polycrystalline Diamond cutters bit or composite tooth bit. Since General Electric introduced the PDC cutters in 1973 and developed the first PDC drill bit, PDC drill bits have been widely used in petroleum drilling due to their advantages such as fast drilling speed, long life, and high footage.

Structural Features of PDC Drill Bits

PDC drill bit consists of the drill bit body, PDC cutting teeth and nozzles among other parts, and is divided into two main series: steel body and matrix body, based on their structure and manufacturing process.

Steel body PDC drill bit uses medium carbon steel material for the entire drill bit body and is shaped using mechanical manufacturing processes. Holes are drilled on the working face of the drill bit, and the PDC cutting teeth are fixed to the drill bit crown using a press-fit method. The drill bit crown is treated with surface hardening processes (e.g., tungsten carbide coating, carburizing) to enhance its erosion resistance. The main advantages of this type of drill bit are simple manufacturing processes; however, its disadvantages include the drill bit body's poor erosion resistance and difficulty in securely fixing the cutting teeth, resulting in less current usage.

Matrix body PDC drill bit has a drill bit body with a steel upper part and a tungsten carbide-wear resistant alloy matrix lower part, manufactured using a powder metallurgy sintering process. The PDC cutting teeth are welded onto the pre-reserved slots of the matrix body using low-temperature solder. Due to the high hardness and erosion resistance of the tungsten carbide matrix, matrix body PDC drill bit has a long life and high footage and is currently widely used.

Working Principle of PDC Drill Bits

PDC drill bit breaks rocks by cutting. The self-sharpening cutting teeth easily penetrate the formation under drilling pressure and move forward to shear the rocks under rotational torque. With multiple PDC cutting teeth working simultaneously and many free surfaces on the formation, rocks are easily fractured under shearing, resulting in high rock-breaking efficiency and fast drilling speed.

Proper Use of PDC Drill Bits

• PDC drill bit is suitable for homogeneous formations ranging from soft to moderately hard and is not suitable for drilling alternating soft and hard formations or gravel layers.

  
  

• Use high drilling pressure, high speed, and large flow rate during drilling for optimal performance of the drill bit.

  
  

• Before lowering the drill bit into the well, ensure the well bottom is clean and free of metal debris. During initial drilling, use low drilling pressure and speed to smooth the well bottom and shape it.

  
  

• When first lowering the drill bit into the well, use low drilling pressure and speed; resume normal drilling after the well bottom is formed.

  
  

• PDC drill bit is a monolithic drill bit with no movable parts, making it suitable for high-speed turbine drilling.

Rock-breaking mechanism of PDC drill bits

• Cutting: (Shearing) breaks rock.

  
  

• Fragmentation process in soft plastic formations: continuous cutting, similar to a cutting tool processing metal.

  
  

• Fragmentation process in hard brittle formations: collision→crushing and minor shearing→major shearing.