Directional Drilling: Everything You Ever Wanted to Know

Directional Drilling is a boring where the drilling can be done on a predetermined path underneath the ground level. Horizontal Directional Drilling (HDD) is the more common name for this technique and is called “Trenchless Drilling.”

The conventional way of constructing a pipeline, underground cables, or conduit, for whatever use it may be, is digging a trench. But the construction workers may come across a situation where it may be difficult or even impossible to dig a trench for this purpose at a particular construction site.

HDD technique comes into use in such situations, especially when we must avoid disturbing the ground area. That’s why it is also known as minimum impact technology.

Horizontal Directional Drilling has been used for over a hundred years but has improved significantly recently with the help of computer technologies.

Directional Boring VS Horizontal Directional Drilling

These two terms look similar, but there is a difference between them regarding the scale of work. Directional Boring is a small diameter bore that crosses a small horizontal distance. The term HDD is used when we need a more extensive diameter boring and have to travel a long distance.

How is it done?

It starts with the digging of an entrance pit, followed by the drilling of a pilot hole. Drilling is done in the shape of an arc, slowly going down the obstacle to be crossed and coming out of the ground on the other side.

Drilling is done with specialized machines and tools with the help of a drilling fluid. It comprises mainly water and a small quantity (usually 5%) of bentonite. This viscous fluid is pumped into the bore to reach the cutting tool.

This is a multipurpose fluid. It not only cools down the cutting head but also removes cuttings from the drilling bit. It gives firmness to the bore while lubricating the drilled hole. This fluid is re-useable. It is collected back through a machine that makes it usable again by removing cuttings and maintaining the desired level of viscosity.

The second step is widening the drilled hole. This is necessary to make pulling back the required pipes or cables easier. Usually, they widen the gap up to 25% of the initial diameter. This process is done with the help of a reamer. Finally, the pipeline or cable is pulled through the widened hole. This way, the entire pipeline/line crosses the obstacle completely underground.

Equipment

The main machine used for HDD is called a rig. The bore's estimated length determines this rig's size and capacity. The type of pipeline to be used must also be considered while selecting the rig. Another critical factor is the study/survey of the underground conditions of the proposed site.

Usually, there are two types of rigs: one for smaller distances and the other for considerable distances. The difference between both is their capacity, measured in thrust and rotary force units. For example, a large rig may have a thrust force of around 1,320,000 lbs with a rotary strength of 150,000 lbs, usually mounted on a trailer, and a small rig may have a thrust or pullback force of up to 100,000 lbs.

While a tremendous amount of drilling fluid is required for large rigs, very low or even only water may be needed in the case of small rigs, obviously, depending on the length of the bore.

The cutting head, also called the drilling head, is the following essential tool required for HDD. It contains drilling bits of various sizes and shapes, depending on the diameter of the hole. These tools are a very crucial part of the whole drilling process. So, selecting the right type and size of the cutter head is very important.

Where’s the Drilling Head?

The critical point for the construction engineers is to locate where the drilling head is at a specific time. The problem is that it is not visible as it is underground throughout the drilling process.

Locating the drilling head is essential to keep the drilling strictly on the pre-determined path. For example, construction engineers may use any or all of the following three methods to locate and guide the drilling head.

Walkover System

It works with a transmitter that is installed with the drilling head. It sends information to the monitoring staff about the direction and angle of the cutting head, thus enabling them to control the movement.

Wire-line System of monitoring

It is also known as MGS – Magnetic Guidance System; the construction supervisor can quickly locate the cutter head and direction with this magnetic system.

Gyro-Based Location System

This is the most helpful tool in the hands of a person supervising and monitoring the drilling process. It gives the best results with maximum accuracy.

Impact on Environment

Though this type of drilling is primarily required in areas away from the cities and towns, we still have to consider the impact of this whole process on the environment. Secondly, there may be instances where HDD has to be done near populated areas.

The first and perhaps most important is the noise created by the rig. This can be reduced by using buffer zones created around the construction site. Another possible hazard may be the leakage of drilling fluid. Usually, it doesn’t happen, as this fluid must remain within the bore.

However, there is a possibility that this fluid can spill out of the cracks in the ground or due to the porous nature of the earth at a particular point of the bore line. The drilling fluid is so viscous that it automatically fills cracks and prevents massive leakage.

Despite these minor risks, the HDD process is safe and environmentally friendly.

Legal Coverage

In the USA, the Pipeline Safety department governs the construction and designs related to Horizontal Directional Drilling.

Conclusion – Horizontal Directional Drilling

The HDD is a reliable and helpful technique for constructing tunnels, pipelines, and underground cabling systems. It is an environment-friendly technique, having the minimum possible impact. However, it can be carried out without any noticeable effect on the ground surface under which this drilling process is being made.

Guest Contributor: Syrah Abrar