There are a number of different types of oil rigs, each having their own unique function. Each one is specially designed to perform in a specific way for a designated job. Once an oil well has been dug there is usually adequate pressure to push the oil to the surface. However, after the initial force of the freed gas and oil decreases in pressure from below ground, a drilling rig is needed to continue to draw the oil to the surface. According to FutureOn Today, the three main types of drilling rigs are grasshoppers, horseheads, and air balances.
The main function of a drilling rig is to extract oil from the ground once the initial pressure is no longer sufficient to force it to the surface.
Each of these drilling rigs is designed with a drill rod that lowers and ascends from underground and a walking beam along the top. Oil is drawn from the ground each time the drill rod rises.
GRASSHOPPER OIL DRILLING RIG
Grasshopper oil drilling rigs are a combination of the air balance rig and the horsehead rig. Instead of the weights being located at the end of the walking beam, on the Grasshopper they are located in the middle of the beam. The walking beam is pulled down, pushing the drill rod into the earth. As the walking beam is raised, oil is drawn up from underground by the drill rod.
HORSEHEAD OIL DRILLING RIG
This is the standard design for a drilling rig. On this model, the pivot is located in the middle of the walking beam. One side of the beam features large steel beams. These are called counterweights. The other side of the beam holds the drill rods. The counterweights are rotated by a crank. This lowers the walking beam at consistent intervals. The rod is then raised at equally-timed intervals, extracting the oil from underground.
AIR BALANCE OIL DRILLING RIG
These drilling rigs feature pivots on one end of the rig’s walking beam. A compressed air cylinder is used in place of counterweights. With each descent of the drill rod, air is compressed in the cylinder. The walking beam is forced up by the compressed air, pulling the oil from underground.
For larger oil drilling projects, larger rigs are used. These rigs feature large diesel engines which are powered by diesel-fuel oil. This is their primary source of power. The diesel engines are used to power electrical generators to produce electrical power. The mechanical system is powered by electric motors. A hoisting system, consisting of a mechanical winch, a giant steel cable spool, a storage reel to receive the cable, and a block-and-tackle pulley system.
For rotary drilling, the oil rig is comprised of a swivel, which is basically a giant handle that bears the weight of the drill string and enables the rotation of the string in order to create a pressure-tight seal over the hole the oil is being accessed through. The kelly is a four or six-sided pipe used to create the rotary motion which operates the drill string and turntable.
The drill bit is located at the tip of the drill. This is the instrument that cuts through the layers of underground rock. Drill bits are generally made of diamond or tungsten carbide steel. The casing is a thick concrete pipe, very large in diameter, that is fit down into the drill hole and serves as a safety lining to allow the mud created by the drilling to circulate, and to prevent the sides of the hole from collapsing. A derrick is a sturdy steel structure that supports the drilling apparatus.
Once the entire rig is in place, the drilling is ready to begin. The crew will follow these steps to perform the drilling operations:
- The drill pipe and drill bit are placed into the hole.
- The kelly is attached and the drilling begins.
- The mud is circulated up the pipe, then through the drill bit to carry the cut rock pieces out and away from the hole as drilling progresses.
- New sections, called joints, are added to the drill pipe as the hole gets consistently deeper.
- The drill pipe is removed along with the drill bit when the predetermined depth is reached, This depth can range anywhere between a few hundred and a few thousand feet.