This article explains rotary drilling technology, which uses a similar principle to piercing paper with an awl to drill thousands of meters underground. It details the process of drilling through strata using compressive and rotational forces through equipment such as drill strings, mud circulation systems, and mud motors to overcome various underground obstacles.
If you’ve ever tried to pierce a board of wood or a stack of paper with an awl, you’ve probably realized that thin paper can be pierced with little force. But when it gets a little thicker, it’s harder to pierce it with just a little force. We instinctively turn the awl while applying pressure, which gradually pierces the paper and eventually creates a hole. This process of punching through paper is very intuitive in our daily lives, but not many people realize that a similar principle applies when we need to drill through geological formations. So what about drilling a hole in the ground – not just any hole, but one that needs to be drilled straight down for thousands of meters in the desired direction? Surprisingly, the ground can be drilled as cleanly as a hole in a piece of paper with compressive and rotational forces. This is the principle of rotary drilling.
First, you need a special awl to drill into the ground. This is called a drill string by drillers. The drill string consists of a BHA and a drill pipe. The BHA is a thick pipe structure that acts as the leading edge of the bit to drill through the ground, and the drill pipe is a thin, circular pipe that connects the BHA to the ground. Just as an auger can only drill so far, a drill string must be connected for the length of the hole to be drilled, which can be many kilometers.
It is this enormous length that gives this particular auger its strength. Imagine the weight of thousands of meters of steel pipe. That’s a lot of weight, and it gives them the power to drill through the rock underground. In the actual drilling site, the drill string is held up to prevent the pipe from pushing down on the ground with too much force. This process requires precise control of the drilling rig, as its force and rotation speed must be fine-tuned according to the depth and geological structure. Otherwise, there is a high risk of damaging the formation or damaging the rig.
So, how do you reduce the rotational force? As we explained earlier, the drill string is made up of circular pipes. If the actual awl was just a pointed shim, we wouldn’t be able to hold it and rotate it properly to drill the hole. That’s why awls have handles. Likewise, a round pipe isn’t very good at providing rotational force, so we attach a pipe with a hexagonal or square cross-section at the top to the top of the drill string. This pipe will act as a handle of sorts and is called a Kelly. A groove shaped like a Kelly is dug in the center of a rotating plate, and the drill string is inserted into the groove and rotates the plate to turn the giant drill. This plate is called a rotary table, and this method is known as the rotary table method. On the other hand, instead of a handle, the drill string is directly driven by a motor to rotate the drill string, which is called a top drive.
Rotational force is the key driver of drilling, so it is very important to control it properly. Excessive rotational force can damage the drill bit, and insufficient rotational force will result in poor drilling progress. This is why it is essential to constantly adjust the rotational speed and check the condition of the rig during the drilling process. Especially as the density and strength of the formation varies as you go deeper, the slightest adjustment in rotational force can make or break the operation.
We now know that we can apply compressive and rotational forces to a giant awl drilling into the ground. But that’s not all. When you punch through a real stack of paper with an awl, you’re dealing with as many pieces of paper as the hole you drill. In the real world, this is a simple matter of blowing into your mouth. But dealing with residue from thousands of meters underground is no easy task. To do this, mud is circulated in the hole, and the mud is brought up with the drilling residue. This is called the mud circulation system in drilling.
Mud does more than just dispose of residue. It prevents the rig from overheating by cooling the heat generated by the friction of the drilling bit underground. It also plays an important role in preventing explosions caused by collisions with gas in the formation. Furthermore, the mud helps stabilize the hole so that it doesn’t collapse under the lateral pressure of the formation. It’s like punching a hole in a piece of paper to keep it from crushing and deforming.
The flow of Mud plays another important role. It drives a device called the Mud Motor. The Mud Motor is a third way to provide rotational force, and unlike the previous two methods, it is installed directly above the bit and only rotates the bit. The mud motor is a key element of Directional Drilling technology, which allows drilling at different angles in addition to the vertical direction. When horizontal and non-linear drilling is required, this technology allows you to reach your target point with precision.
As you can see, the principles of augers and drilling overlap in many ways. From a small awl piercing a piece of paper to a huge drilling rig drilling thousands of meters deep, the principles remain consistent. It’s always amazing how simple principles we experience in our daily lives are the basis for complex and sophisticated industrial technologies.
