At the end of each drill column is the most important part - the drill bit. The drill bit consists of a synthetic diamond tool, insert, nozzle and drill body. Drill bit selection is critical and can have a huge impact on the total cost of a well construction operation. Today, we would like to focus on the most prominent drill bit in the oil and gas industry - the polycrystalline diamond compact drill (PDC)bit.
The PDC bit is named after the polycrystalline diamond composite cutting element that shears rock to drill an exploratory well. When it comes to drill bits, there are four main components to be familiar with: the tool, the cutting structure, the insert, and the bit body.
Polycrystalline diamond compact tools are usually cylindrical in shape, with a thin layer of synthetic diamond on a tungsten carbide substrate. These tools must remain intact to drive the performance of the drill and ensure its reliable operation, and are arranged in a 3D geometric structure called the cutting structure.
The cutting structure may seem simple, but it is often the most complex part of the PDC drill design.
Typically, the tools are aligned in rows to allow for better chip cleaning. Each row sits on top of the inserts protruding from the bit body, supporting the cutting structure and holding it in place while effectively attaching the cutting structure to the end of the drill column.
Between the inserts are trash slots that act as channels for the drilling fluid to flush chips away from the bit surface during drilling. The bit body consists of a combination of tungsten carbide base material and steel, depending on how much tungsten carbide is used and how they are manufactured.
The PDC bit body is made of steel at the pin connection and transitions to a tungsten carbide composite on the outer surface. Steel PDC bit bodies are made from raw steel and then coated with a hardfacing material to improve erosion resistance. Polycrystalline diamond composite bits can be designed in virtually unlimited combinations of variables and modified to suit the drilling application.
Many factors must be considered when designing a drill bit. The most important external factor in the design is the size of the borehole to be drilled, which can be 2 ½" to 36" (6 cm to 90 cm) in diameter. Other factors are more appropriate to its intended use, and we must consider factors such as rock and formation type, operating environment, capabilities of other drilling equipment, and borehole angle.
The design of the PDC varies from situation to situation, and using the data on external factor conditions, the design and engineering team can build the bit accordingly to suit the external environment and the needs of the drilling operation. There are many different rock types: for example, limestone, sandstone, shale, etc. These rocks are composed of different minerals and structures, which respond differently to torque, velocity, force and pressure. For example, if the rock is very hard and abrasive, a larger number of tools will be required, which will result in an increased number of blades. If drilling through hard rock, these tools will be slightly smaller, compared to drilling through relatively soft rock.
PDC bit technology has changed dramatically in recent years as awareness of drilling vibration and its impact on productivity has increased. Engineers and designers have had to change and adapt drill bit designs to account for and resist shock forces. The drill should also be modeled and balanced so that it does not cause its own vibrations and damage when drilling.
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