Rotary system is responsible for rotating drill string. Drilling rig may have either TDS (Top drive system) or Kelly-swivel to transmit rotation to drill string. Rotary system components are TDS or kelly and drill string. The parts of drill string are drill pipe, heavy weight drill pipe, stabilizer,drill collar, x/o, bit sub and bit.
TDS Vs Kelly Swivel
Top drive rotate drill string from top where as kelly system rotation is provided at rig floor with help of rotary table.Top drive capable to drill with one stand of drill pipe and kelly can drill with one drill pipe. Therefore kelly system is time consuming as compared to TDS. Most of new rig coming with Top drive but still kelly system exist in drilling industry.
Drill string components
Drill Pipe
Drill pipe are hollow steel pipe that make major part of drill string . It have pipe body,threaded pin and box tool joint to make up drill pipes together. A drill pipe length is normally 30 ft.
Heavy weight drill pipe
As the name indicates heavy weight drill pipe are heavier than same size of drill pipe. Heavy weight drill pipes are part of BHA and are located between drill collar and drill pipe to work as transition zone.
Drill collar
Drill collars are most heaviest part of drill string and are also part of bottom hole assembly. Drill collar have thick steel wall and less inside diameter as compared to heavy weight drill pipe and drill pipe. Drill collar provide weight to bit for drilling action.
Stabilizer
stabilizer provide weight and mainly control hole deviation. There are two main types of stabilizers.
Near Bit Stabilizer
It is used just above bit, it have float valve inside it and have box x box connection on both ends.
String stabilizer
It is used between two drill collar and is located 30 or 60 ft away from bit. it have pin x box connection.
Cross over
are drill string components used to connect two tubular of different threads. Cross over can be of pin x box, pin x pin or box x box connection.
Bit
Drill bit is bottom most part of drill string, it drill formation or rock when apply rotation and weight on bit with circulation.
Bits are classified as
Dr
