In order to select the PDC bit for specific geological conditions, the core lies in how to find a balance between the uniaxial compressive strength (UCS) of the rock and the density of the teeth and the hydraulic design.

In short, for soft to medium hard formations (such as shale and sandstone), I usually recommend steel drill bits with 3 to 5 blades and large teeth with 16-19mm. This open profile design can maximize the rate of penetration (ROP) and prevent the bit from mud packing. Conversely, if it is a hard and abrasive formation (limestone, granite), you must replace the matrix drill bit, 6 to 9 blades, with 13mm small teeth, so as to disperse the impact load and extend the life of the drill bit.

Analyzing Geology And UCS

The foundation of any successful drilling operation is a thorough understanding of the relationship between the PDC bit and the uniaxial compressive strength (UCS) of the formation. The UCS does provide a baseline of the force required for rock failure, but a one-size-fits-all approach will not work.

High UCS rocks require a mechanism that focuses on extrusion and grinding, while low UCS rocks respond better to shear. Therefore, the first step in the selection is not to stare at the drill catalog, but to analyze the geological data first. From this we need to determine the specific balance between the tooth density (the number of compacts contacting the bottom of the well) and the hydraulic layout.

Optimization For Soft To Medium Hard Formations

When drilling soft to medium hard formations such as shale or sandstone, our primary goal is to achieve a full rate of penetration (ROP). In this type of geology, the rock is easily broken under shear, which allows us to adopt more aggressive bit designs.

• Steel body structure: I prefer to use steel PDC drill bit, because steel can realize the complex and high blade protruding design that is difficult to make with carcass powder. Moreover, the steel body is tough enough to withstand the high torque during aggressive drilling.
• Less blade wings (3-5 blade wings): less blade wings, chip slot is large. Soft strata will produce a large amount of debris in an instant. If hydraulic design cannot discharge these things efficiently, the drill bit will encounter “mud bag”-the debris will paste the blade and the composite sheet will be discarded.
• Large composite sheet (16mm-19mm): large teeth can provide deeper depth of cut (DOC). Since the rock is not very abrasive and does not have to worry too much about wear, the key point is naturally to “eat” as many rocks as possible in the circle.

Conquer Hard And Abrasive Formations

Once you enter a hard and abrasive environment like limestone or granite, the strategy has to turn around completely. At this time, don’t just think about ROP, durability and stability are the father, and the longer the PDC bit stays downhole, the better.

• Matrix Body structure: This drill is sintered with tungsten carbide powder and metal binder. This material has excellent erosion resistance. When drilling abrasive formations, the steel body may be “washed” away, but the carcass can withstand it.
• Multiple blades (6-9 blades): Increasing the number of blades can increase the contact area with the bottom of the well. Such a high density blade distribution is necessary for suppressing vibration, ensuring smooth operation, and protecting the composite sheet from impact damage.
• Small composite sheet (13mm): In hard rock, large teeth are easily chipped or broken because the point load is too high. By switching to 13mm small teeth, the PDC bit can spread the impact load to more contact points. This “heavy-set” design sacrifices a little ROP, but in exchange for a longer life-a bargain.

PDC CUTTERS

Meet the Demands of High lmpact, High-Wear Oil-Drilling Operations. Delivering Longer Lifespan and Less Downtime De signed for. Efficient and Durable Oil Drilling Applications with PDC Cutters.

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Compliance With The Economic Account Behind The IADC Code

The IADC code is not just a classification system, it is a blueprint for cost efficiency.

The last step in selection is to take your selection plan and cross-compare it with the abrasive IADC code of the formation. In hard rock with a soft formation bit, immediately will lead to composite wear and “ring-out “; and in soft rock with a hard formation bit, the drilling speed will be slow like a snail, but also mud bag.

Both of these conditions can lead to premature bit scrap. The end result is extremely high tripping costs. You have to know that because the failure of the drill bit brings up the drilling tool to change the drill bit, the production is not only stagnant, but the drilling time is burning at thousands of dollars per hour. Strictly following the design principles of body material, blade number and tooth size based on geological conditions, operators can avoid these wronged money.

Author: Michael Reed

With over 18 years of experience in downhole drilling operations, I specialize in PDC rock drill bit design and application. My passion lies in helping drilling teams analyze geological UCS data to select the precise blade configuration and cutter type needed to maximize ROP and extend bit life in challenging formations.