Polycrystalline diamond compact (PDC) drill bits are high-performance fixed tools that use synthetic diamond tools to shear rather than break rock. Significantly increase the rate of penetration (ROP) and extend the life of the drill bit for water well, oil, gas and mining applications. They are especially suitable for medium hard to soft formations and have superior durability compared to conventional drill bits.

Core Mechanism Of PDC Bit: Cutting Action And Structure

To really understand the value of PDC bits in water well applications, we have to look back at the most basic engineering principles.

The biggest difference between PDC bits and traditional bits is the “Shearing Action”. The traditional roller cone bit relies on great pressure to crush the rock, while the PDC works more like a lathe in metal processing. Synthetic diamond cutting teeth are “scraping” down layers of rock. From the point of view of energy conversion, this shearing mechanism is much more efficient than crushing, which is why I mentioned earlier that it can lead to higher ROP.

Let’s look at the structure again. How long the drill can last depends on whether the “foundation” is played well. Usually we use tough steel body or carcass.

• Steel body: good toughness, strong impact resistance. In the case of complex borehole geometry, I generally tend to recommend steel bodies.
• Carcass: usually with tungsten carbide powder with metal binder sintering, it has the advantage of erosion resistance.

As for the cutting teeth themselves-the tungsten carbide substrate plus the synthetic diamond layer-provides extremely high hardness to keep the edge sharp. In some conventional applications, I ‘ve seen them last 100 times longer than conventional drills.

Flat PDC Cutter

Flat PDC Cutter features a flat structure for uniform force distribution, exceptional wear resistance for long service life, and a versatile, cost-effective design.

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Flat PDC Cutter

Dome PDC Cutter

Dome PDC cutter uses spherical geometry for superior impact resistance, ensures uniform heat dissipation to prevent thermal damage, and adapts to varied formations.

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Dome PDC Cutter

Ridge shaped

Ridge shaped PDC cutter features ridge-like projections to boost drilling efficiency, optimized chip removal channels, and an anti-rotary vibration design for stability.

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Ridge shaped

Step PDC Cutter

Step PDC cutter features a step structure for staged rock breaking, reduced contact area to minimize frictional heat, and enhanced stability for reliable performance.

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Step PDC Cutter

Special Design For Water Well Drilling

When talking about PDC bits for water wells, it is not enough to simply look at the material and must be classified according to hydraulic design. Different strata challenges need to match different hydraulic structures:

• Standard design: this belongs to the “golden oil”, can cope with a variety of mixed conditions. If you’re drilling into a mixed layer of moderate hardness, you’re right to choose it.
• Jetted Design: This design focuses on enhanced cleaning. It scrubs the surface of the cutting teeth directly through high-flow nozzles, taking away the debris before it accumulates.
• Large displacement design: Note that this is the key point. If you are drilling soft formations or extremely viscous formations (such as clay, mudstone), you must use this. It has an open large flow channel that allows large displacement drilling fluid to pass through. Without this large displacement to bring out the cuttings, the drill bit will burn to death in minutes.

Best Practices For Field Operations

Even if you have the best PDC bit on hand, if the operating parameters are wrong, you will not be able to play the theoretical efficiency. As mentioned earlier, PDC performs well in shale, sandstone and limestone, but performance is highly dependent on two mechanical inputs:

• WEIGHT ON BIT: This is where many drillers who turn from roller cone bits are prone to make mistakes. The cone needs a huge bit pressure to “crush” the stone, but the PDC needs a “proper” bit pressure-just enough to eat the cutting teeth into the formation, and if it is pressed too hard, it will collapse the teeth.
• High speed: Since it is the “shear” mechanism, the higher the speed, the faster the cutting. Stable bit pressure combined with high rotation speed can make the drill smoothly cut through the formation.

In addition, hydraulic cleaning is non-negotiable.

I am most afraid to see the situation is the “mud bag”-formation material (such as mud-like shale) in the cutting teeth around the compaction, the drill paste into a smooth ball, completely lost cutting force. Maintaining high water horsepower on the drill surface, ensuring that the cutting teeth are always clean and exposing new attack surfaces, is the key to the success of the job.

Selection Factors: Matching The Bit To The Formation

Choosing the right PDC bit configuration is essentially the science of balancing cutter density and size.

• Formation hardness and tooth density: the two are inversely related.
• Soft formation: we need to use large size cutting teeth, and the tooth density is low (less teeth), so as to maximize the depth of eating, drilling fast.
• Hard formation/abrasive formation: high density (many teeth), small size cutting teeth must be used. This distributes the load and prevents premature wear of the cutting teeth.
• Size requirements: The flexibility of the PDC is reflected in its wide range of sizes. Whether it is a small borehole (such as 3 7/8 inches) for exploration wells or a large diameter (such as 12 1/4 inches) for production wells, there are standard or custom sizes to match different drilling rig capabilities and casing procedures.

In conclusion, only by carefully evaluating these factors-hardness, cloth tooth density and size-can field personnel really squeeze the performance limits of PDC technology and achieve the durability and high drilling speed we want.

Author: Robert Stone

Hi, I’m Robert Stone, a drilling efficiency specialist. My work focuses on optimizing downhole performance using Polycrystalline Diamond Compact (PDC) technology. I help drillers understand how features like shearing action and hydraulic ‘big flush’ designs can significantly increase Rates of Penetration (ROP). I am passionate about guiding you to select the right cutter density and bit size to master any formation, from soft clay to abrasive limestone.”