In the realm of oil and gas exploration, the PDC drill bit stands as a vital tool for drilling. It’s not just efficient and long-lasting. It’s also highly regarded within the industry due to its distinctive structure and manufacturing methods. This article aims to provide an in-depth look into the definition, classification, characteristics, and more of PDC drill bits, aiding in a deeper understanding of this remarkable drilling instrument.
PDC drill bit definition
Polycrystalline Diamond Compact drill bit, referred to as PDC drill bit. It is formed by using a polycrystalline diamond (thin disc shape) to make a small cutting block and inserting or sintering it into the drill bit body.
Structure of PDC drill bit
PDC drill bit is mainly composed of the drill body, cutting teeth, gauge belt, nozzle, and other parts:
Drill body
The drill body is the main structure of the PDC drill bit, usually made of high-strength steel, which can withstand high-pressure and high-temperature working environments. It connects to the drill pipe and provides a platform for carrying cutting teeth and guide devices. The appropriate material is selected based on the different formations to be drilled, ensuring the stability and durability of the drill bit.
Cutting teeth
The cutting teeth are the primary working part of the PDC drill bit, which consists of multiple carbide teeth and breaks rocks by high-speed rotation and pressure. Cutting teeth have two structures: composite cutting teeth and tooth column type. Composite cutting teeth embed PDC composite pieces on steel or matrix brackets, while tooth column type directly sinter PDC composite pieces on steel or matrix tooth columns. This design gives the cutting teeth high hardness, high wear resistance, and impact resistance, which can cut the ground rock efficiently.
Gauge belt
The gauge belt is located between the cutting teeth and the drill body to maintain the stability and cleanliness of the wellbore.
Guide device
The guide device is an auxiliary part of the drill bit, primarily used to control its trajectory and direction and ensure the quality of the wellbore. The guide device includes a guiding disk, guiding teeth, a guiding knife, and other forms. The cutters are typically positioned either in the periphery or at the center of the drill bit.
Nozzle
The nozzle part controls the flow state at the bottom of the well, reducing friction and resistance to improve drilling efficiency and quality. In addition to these main structures, the PDC drill bit is equipped with auxiliary structures such as a cooling system and a positioning system to meet different drilling needs.
Working principle of PDC drill bit
The cutting teeth are utilized to generate shear stress on the formation, causing the rock to undergo plastic deformation and fracture and bringing the cuttings out of the wellbore. PDC drill bits generally use lower drilling pressure and higher speed to improve cutting efficiency and footage.
Classification of PDC drill bits
According to the material of the drill bit body, there are steel body PDC drill bits and matrix PDC drill bits.
Steel body PDC drill bit: material: steel. It is processed and formed from nickel, chromium, and molybdenum alloy steel. Following heat treatment, the drill bit body undergoes drilling, with pillar-type cutting teeth being installed into the holes and button-shaped carbide being positioned in the gauge area. Primarily, it’s well-suited for relatively straightforward and soft formations.
Matrix PDC drill bit: material: cast tungsten carbide (sintered body). Precision cast in an alloy mold, the cylindrical cutting teeth are welded onto the drill bit body, while diamonds are welded onto the gauge position. This type is primarily ideal for relatively uncomplicated and hard formations.
Features of PDC drill bits
- Efficient cutting: thanks to its exceptional hardness and resistance to wear, it can swiftly cut through large quantities of rock, significantly enhancing drilling efficiency.
- Strong impact resistance: it has high toughness, can maintain stable cutting performance in complex formations and harsh working conditions, and reduces drill bit damage caused by impact.
- Good cleaning effect: the cutting teeth are reasonably designed to effectively remove rock chips during the cutting process, keeping the wellbore clean and reducing drilling difficulties caused by the accumulation of rock chips.
- Good wear resistance: it has high wear resistance and can maintain cutting performance during long-term use and extend the service life of the drill bit.
- Good diameter protection effect: the diameter protection design of the PDC drill bit is reasonable, which can ensure that the drill bit maintains a stable diameter during the drilling process and improves the wellbore quality.
- Good guidance: it can maintain better guidance during the drilling process, reduce drilling deviations caused by formation changes, and improve drilling accuracy.
Under the same formation conditions, compared with roller cone bits, PDC drill bits can increase the mechanical penetration rate by 33%-200%, reduce costs by 30%-50%, and a single drill bit can achieve a footage increase of 3-4 times.
Advantages of PDC drill bits
- No moving parts, no parts lost in the hole.
- Drilling efficiency is relatively higher.
- The unit price is relatively high, but the total cost per meter is lower.
- It can work well in soft rock and medium-hard rock formations.
- Relatively long service life.
Disadvantages of PDC drill bits
- The alloy sheet may be damaged.
- Not suitable for high hardness formations.
- The unit price is relatively high.
Development of PDC drill bits
In the second half of the 20th century, the development of the drilling industry was closely related to the development of diamond drill bits. During the early 1960s, the adoption of synthetic diamonds significantly advanced diamond drilling technology, leading to a substantial reduction in drilling expenses. By the 1970s, the emergence of PDC drill bits markedly enhanced drilling efficiency and found widespread application in formations ranging from soft to medium-hard.
During the 1990s, Western nations recognized the utilization of PDC drill bits as a promising drilling technology with considerable potential. In the 21st century, PDC drill bits have experienced rapid development. Presently, PDC drill bits find extensive usage in oil and gas drilling operations across the globe. It has been expanded to solid mineral deposit exploration and other drilling projects and has achieved good application results.
Application of PDC drill bits in drilling operations
In addition to conventional vertical wells, PDC drill bits are particularly suitable for the following uses:
- Used for vertical wells in areas prone to deviation. Since PDC bits can achieve high drilling speeds at low bit pressure, PDC bits and suitable bottom hole tools can often achieve fast and high-quality results when drilling at low bit pressure in easily inclined areas.
- Used for directional drilling and horizontal drilling. PDC drill bits have no bearings, can withstand high rotational speeds, and are suitable for use with downhole power drilling tools. Through the reasonable design of PDC bit profile shape and retaining length, it can be successfully used in directional wells and horizontal wells to create (lower) slope and stabilize the slope drilling, especially when paired with guided drilling systems, PDC drill bits demonstrate superior performance compared to roller cone bits.
- Used for drilling into easily shrinkable formations. The wellbore diameter drilled using a bicentric or eccentric PDC bit is larger than the drill bit diameter, thus overcoming the complex problems caused by wellbore diameter reduction.
- For drilling small boreholes. Drilling small boreholes is a weakness of roller cone bits, while PDC bits can achieve higher economic benefits when drilling small boreholes. According to statistics, the PDC drill bits’ service life and drilling speed in small boreholes are twice as high as those of roller cone bits.
Conclusion
With the continuous development of drilling technology, the importance of PDC drill bits in drilling engineering has become increasingly prominent. The emergence of PDC drill bits not only improves drilling efficiency and reduces drilling costs, but also brings higher safety and reliability to drilling projects. In complex formations and harsh working conditions, PDC drill bits can maintain stable cutting performance and reduce downtime and economic losses caused by drill bit damage. In addition, the PDC drill bit has the characteristics of good guidance and a good diameter protection effect, which also provides higher accuracy and stability for drilling projects. In the future, spurred by trends like material innovation, technological advancements, and intelligent development, PDC drill bits are poised for even broader development prospects.
