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Introduction Rotary drilling uses two types of drill bits: roller-cone bits and fixed-cutter bits. Roller-cone bits are generally used to drill a wide variety of formations, from very soft to very hard. Milled-tooth (or steel-tooth) bits are typically used for drilling relatively soft formations. Tungsten carbide inserts bits (TCI or button bits) are used in a wider range of formations, including the hardest and most abrasive drilling applications (see Figure 1.1). Fixed-cutter bits, including polycrystalline diamond compact (PDC), impregnated, and diamond bits, can drill an extensive array of formations at various depths.
Roller-cone bits are generally used to drill a wide variety of formations, from very soft to very hard. Tungsten carbide inserts bits (TCI or button bits) are used in a wider range of formations, including the hardest and most abrasive drilling applications (see Figure 1). Figure 1--Different bit types (from left to right: PDC, TCI, and milled-tooth bits).
Wide varieties of roller cone bits are available. They provide optimum performance in specific formations and/or particular drilling environments. Modern drill bits incorporate significantly different cutting structures and use vastly improved materials, resulting in improved bit efficiency. Manufacturers work closely with drilling companies to collect information about their bits to identify opportunities for design improvements. To achieve these goals, bit designers consider several factors. Replace this text with a brief (3-4 lines) introduction to what is covered on this page. Replace header name above, then begin creating your text in place of this text. To make subheads to this heading, use the Heading level 3 style from the drop down.
Hole deviation is the unintentional departure of the drill bit from a preselected borehole trajectory. Whether it involves drilling a straight or curved-hole section, the tendency of the bit to walk away from the desired path can lead to drilling problems such as higher drilling costs and also lease-boundary legal problems Figure 1 provides examples of hole deviations. It is not exactly known what causes a drill bit to deviate from its intended path. It is known that some resultant force acting on a drill bit causes hole deviation to occur. The mechanics of this resultant force is complex and is governed mainly by the mechanics of the BHA, rock/bit interaction, bit operating conditions, and, to some lesser extent, by the drilling-fluid hydraulics.
Polycrystalline diamond materials, for use in polycrystalline diamond compact (PDC) bits, are one of the most important material advances for oil drilling tools in recent years. Fixed-head bits rotate as one piece and contain no separately moving parts. When fixed-head bits use PDC cutters, they are commonly called PDC bits. Since their first production in 1976, the popularity of bits using PDC cutters has grown steadily, and they are nearly as common as roller-cone bits in many drilling applications. The two provide significantly different capabilities, and, because both types have certain advantages, a choice between them would be decided by the needs of the application.