DRILL STRING
A drill string consists of the following:
- DRILL PIPE
The drill pipe is the pipe or rod to which the drill bit is connected. The drill pipe is made in differing sizes and lengths with various types of joints or couplings. One end, called the pin, has a modified tapered V-thread; the other end, called the box has a matching internal thread. As lengths of drill pipe are added, the pin end of one joint is connected to the box end of the other.
As the drill rods are subjected to great torsional strains the threads should be thoroughly cleaned and lubricated before making up each joint. The lubricant is available from various manufacturers and aids in preventing the joints from becoming galled or too tight.
- DRILL COLLAR
The drill collar is a heavy walled joint of pipe frequently used just above the bit in the drilling string. It provides extra weight just above the bit. This additional weight at the lower end of the string helps keep the hole uniform and straight. The drill collar outside diameter is larger than that of the drill pipe but small enough to clear the wall of the hole. The annular space remaining must allow enough room for an overshot die fishing tool in the event the drill collar twists off.
