Drilling bits are one of the key tools to achieve good performance drilling and there are several types of bits. Therefore, personnel need to understand in order to use the right bits for the task. Today, we would like to share this excellent VDO teaching you about drilling bits. This VDO is excellent for everybody because it has a lot of illustrations and animations along with full explanations. As usual, we have full VDO transcript for anyone who cannot catch the wording from this footage.
As we discussed in the last section, crew members install the bit on the on the bottom drill collar. Two kinds of bits are roller cone bits and fixed cutter bits. Fixed cutter bits are also called fixed head bits. Roller cone bits usually have three cone shaped devices with teeth or cutters. As the bit rotates the cone and cutters rotate to drill a head. Fixed head bits also have cutters but manufacturers embed them in the bit’s head. The bit’s head moves only when the bit rotates. It has no moving parts like the cones on a roller cone bit. Both roller cone bits and fixed head bits come in sizes ranging from 2 or 3 inches or about 50 – 75 millimeters in diameter to more than 36 inches about 1 m in diameter.
Two basic kinds of roller cone bits are available. One has steel teeth and the other has Tungsten Carbide inserts. On a still tool bit also called a middle tool bit, the manufacturer mills or forges the teeth out of the steel that makes up the cone. Steel tooth bits are the least expensive bits. When used properly they can make hole for many hours.
Manufacturers design steel tooth bits to drill soft, medium or hard formations. With Tungsten Carbide inserts the manufacturer presses very hard Tungsten buttons or insert into holes drilled into the bit’s cones. Tungsten Carbide is a very hard metal. Tungsten Carbide inserts insert bits cost more that steel tooth bits. However, they usually last longer because Tungsten Carbide is more resistant to wear than steel. In general Tungsten Carbide inserts bits drill medium to extremely hard formations but can also drill soft formations. Soft formation bits usually drill best with a moderate amount of weight and high road way speeds. Hard formation bits on the other hand usually drills best with high weight and moderate rotary speeds.
Three types of fixed cutter bits are available: Polycrystal and diamond compact or PDC bits, diamond bits and core bits. This PDC bit has cutters made from man-made diamond crystals and Tungsten Carbide inserts. Each diamond and Tungsten Carbide inserts cutter is called a compact. Manufacturers place the compacts in the head of the bits. As the bits rotate over the rock the compact shears it. PDC bits are very expensive. However, when used properly they can drilled soft, medium or hard formations for several hours without failing. A compact PDC layer is very strong and wear resistant. Manufacturers bond the diamond crystals to the Tungsten Carbide inserts backing under high pressure and temperature. The Tungsten Carbide backing, gives the compact high impact strength. It also reinforces the wear resistant properties of the cutters.
Manufacturers make diamond bits from industrial diamonds. But diamonds are the bits cutters. Diamonds are one of the hardest substances. A diamond bit breaks down the rock during drilling by either compressing it shearing it or grinding it as shown in this animation. Here, the diamond is acting like sand paper wearing the rock away. They embed the diamonds into the metal matrix that makes up the head of the bit. Diamond bits are expensive. When properly used however, diamond bits can drill for many many hours without failing.
Crew member run a core bit and barrel when a geologist wants a core sample of the formation being drilled. A core bit is normally a fixed head PDC or diamond bit. It has a hole in the middle. This opening allows the bit to cut the core. Diamonds or PDCs line the opening and sides of the bit. The ring crew fits the core to a core barrel. The core barrel is a special tube usually about thirty to ninety feet or nine to twenty-seven meters long. They run the core barrel at the bottom of the drill string, it collects the core, cut by the core bit. Cores allow geologists to take a look at a actual sample of the formations rock. From the sample, they can also tell whether the well will be productive