Rotary drilling involves the use of a rotating drill that is forced down into the earth. The drill rotation facilitates penetration into hard rocks. The major drilling equipment is mentioned below.
The prime movers are equipment that supplies power for the rig. The major source of power on rotary rigs is diesel engines. However, gasoline and natural gas engines are also used for the generation of electricity. Electric power is required for the rig, hoisting equipment, and machinery required for the circulation. In addition, electricity is consumed by the water and lighting systems.
The hoisting mechanism includes the tools for lifting and lowering the drilling equipment. The most prominent component of this mechanism is called the derrick and has the shape of a tower. The derrick supports the cables and the pulleys used for the lowering and raising of equipment. The hoisting equipment may be required to be used for numerous purposes. For example, a drill bit may require to be changed due to extensive wear, or the rock subsurface may be too hard for an existing bit. In such cases, the complete drill pipe and the drill collars should be lifted to the top surface for changing the bit.
The rotating equipment consists of parts that rotate the drill bit. Thus, holes are dug deep into the soil. The rotating system transfers energy from the prime mover to the drill bit. The main components of the rotating system are a swivel that holds the drill string, a rotary table that provides the rotary motion, and the drill string. In addition, the casing ensures prevention of hole collapse, and permits circulation of the drilling mud.
The purpose of the circulating system includes lubrication and cooling of the drill bit, control of well pressure, and removal of fragments and cuttings. The circulation system mainly comprises the drilling fluid that is circulated in the well hole during the drilling, pumps, mud pit, reserve pit, and mud mixing hopper. Normally the drilling fluids are in a liquid state. The generally used liquid drilling fluids are called "mud" and may include chemicals, clay, oil, water, or gases. The circulating system starts at the mud pit for the storage of the drilling fluid. After mixing in the hopper, the drilling fluid passes through pumps to the swivel and reaches the drill pipe. The bit picks the drill cuttings and debris and reaches the surface.