PDC drill bits and tricone drill bits are two major types of rotary drilling tools. However, they remove rock in very different ways.

Choosing between them requires more than comparing price or diameter. In fact, the right choice depends on the formation, the rig and the total drilling cost.

PDC Bits Cut by Shearing

A PDC bit uses fixed cutting elements. As the bit rotates, these cutters shear material from the bottom of the borehole.

In suitable soft to medium-hard formations, this shearing action can produce a high rate of penetration. In addition, because there are no rotating cones, the bit does not rely on cone bearings.

As a result, the overall structure is simpler than that of a roller cone bit.

Tricone Bits Crush and Fracture Rock

A tricone bit normally contains three rotating cones. As the bit rotates, the cones roll across the formation and the teeth repeatedly contact the rock.

Depending on the design, the teeth may be:

• Milled steel teeth
• Tungsten carbide inserts

Different tooth structures are used for different formations. For example, steel teeth are common in softer rock, while tungsten carbide inserts are often used in harder or more abrasive rock.

Formation Selection: A Simplified Comparison

However, these are general guidelines rather than strict rules. Rock abrasiveness, fractures, mixed layers, rig performance and operating parameters can all change the final selection.

Drilling Stability: Why Vibration Matters

Stable drilling conditions are important for fixed-cutter PDC bits. For example, strong vibration or impact can damage the cutting elements.

On the other hand, tricone bits work differently with the rock. Because of their rolling and crushing action, they may be chosen for certain changing formations.

Wear Characteristics: Where Each Bit Wears

PDC bit wear often appears on the cutters, the gauge area and the blade edges.

Meanwhile, tricone wear may involve the teeth or inserts, the gauge structure, the cone parts and the bearings.

Therefore, examining a used bit can provide useful information about drilling conditions.

Cost Per Meter Matters More Than Bit Price

The cheapest bit is not always the least expensive drilling solution. Because of this, a contractor should consider several factors together:

• Purchase price
• Penetration rate
• Service life
• Number of bit changes
• Rig operating time
• Labor
• Fuel or energy consumption

For example, a more expensive bit may lower the total drilling cost if it drills more footage or drills faster.

What Information Should Be Provided to the Supplier?

For PDC bits:

• Diameter
• Connection
• Formation
• Application
• Rig information

For tricone bits, it also helps to provide:

• Required IADC code, if known
• Air or mud circulation conditions
• Previous bit performance

Frequently Asked Questions

Conclusion: Base the Decision on Formation and Economics

Neither PDC nor tricone bits are always better. PDC bits offer efficient shearing action in the right formations, while tricone bits provide a broad range of crushing structures for changing conditions.

In short, the correct decision should be based on the formation and the total drilling cost, not on the bit type alone.