How Are Underground Pipes Created? The Entire Construction Process Explained

Deep beneath the ground, pipes carry fuels and fluids over large distances. But how did they get in there without any seeming point of entry? 

Well, underground pipes came to fruition in a variety of ways. Each of the methods requiring a certain set of skills and tools to accomplish. It's no random task. 

In this article, we will cover the process of horizontal directional drilling for installing pipelines underground. 

Whenever you're ready to learn more about the most involved pipeline laying method for long distances, keep reading.

Horizontal Directional Drilling

The installation of underground pipes is usually achieved within three phases when done via horizontal directional drilling (HDD).

The first involves the process of directional drilling of a pilot diameter hole along the designed path. The second involves making the pilot hole larger to a certain size that is suitable for the pipeline installation. The third involves the process of pulling the pipes into the enlarged diameter hole.

The methods and tools used in the process of HDD have risen from the technological advances in the oil well industry. The parts of an HDD setup are quite similar to those used in an oil well setup with one exception. The HDD setup has an incline ramp instead of a vertical mast.

HDD pilot hole tasks are not much different from those in directional oil drilling. Downhole tools and drill pipes are mutually interchangeable, and drilling fluid helps move particles, stabilize the hole, and decrease friction.

Because of the similarities between the two, HDD is primarily referred to as drilling, and not boring. Some would argue both apply.

Pilot Hole Directional Drilling

The step of drilling a pilot directional hole occurs via a non-rotating drill string that has an asymmetrical edge. This asymmetry develops a steering bias, whereas, the non-rotating drill functionality allows the steering biased to remain in a certain position while drilling.

If a directional change is necessary, the drill string will be subject to rolling so that the directional bias accommodates that change. The direction of the steering bias is the tool face. Progress is only expected after drilling with off-setting tool face positions.

The drill string can then be subject to rotation continually when directional control is not necessary. Asymmetry in the leading edge can develop in multiple ways. First, the leading edge will have an angled offset from a bent motor housing or a bent sub. 

In soft soils, it's common to drill via hydraulic cutting and a jet nozzle. The direction of the nozzle flow will offset from the CenterPoint of the drill string, creating a steering bias. By closing off specific nozzles on the roller cone bit or via custom fabrication of a deflection bit, contractors achieve the steering bias.

If difficult spots are found in the soil, the drill string can be subject to rotation without biased control until the difficult spot is subject to complete drilling.

Downhole Motors

Downhole mechanical cutting that is necessary for difficult soils occurs with downhole hydraulic motors. Also referred to as mud motors, they convert hydraulic energy from the soil pumped from the surface to the mechanical bit energy. This allows the bit to rotate without the drill string rotates.

There are two primary types of downhole motors, a turbine, and positive displacement. Positive displacement motors are used in HDD scenarios. In essence, the motor has a spiral-shaped stator with a sinusoidal rotor.

Soil and mudflow through the stator, providing rotation to the rotor which is connected directly to the bit. In some cases, a bigger wash pipe diameter is rotated over the non-rotating drill string.

This helps prevent sticking of the string and allows the tool face to be easily manipulated. It also ensures the pilot hole is stable and the steerable string can exit if necessary.

Downhole Survey

The actual pilot hole path is subject to analysis closely during the drilling process. By taking regular readings of the leading edge azimuth and the inclination, success is imminent. The readings are taken with a probe instrument, it's inserted into a drill collar closer to the drill bit.

The downhole probe survey readings are transmitted through a wire in the drill string. The readings alongside drilled distance measurements help assess the vertical and horizontal coordinates in the pilot hole relative to the entry point.

Azimut readings are taken from the magnetic field of the earth, but they are subject to the tool, adjacent structure, and drill pipe magnetic interferences. Thus, the probe has to be subject to installation in a non-magnetic collar and placed in the string so it is isolated from the drill pipe and downhole tools.

The combo of subs, survey probe, bit, mud motor, and non-magnetic collar is a Bottom Hole Assembly.

Surface Monitoring

The pilot hole path is subject to monitoring via a tracking system. Surface monitoring software determines the probe downhole location by taking measurements from the grid.

For instance, a system can use a surface coil of a known point to produce a magnetic field and then communicate the data to the surface.

Pullback & Reaming

Making the pilot hole larger is necessary. To do this, pre-reaming passes before pipe installation work. As well as at the same time as the pipe is subject to installation.

Reaming tools usually have drilling fluid jets and a critical cutter. These tools are often made by contractors for a specific type of soil or hole size.

Most individuals will choose to pre-ream a hole before installing the pipe. For pre-reaming, reamers are linked to the drill string at the point of exit. They are then rotated and drawn into the drilling setup, resulting in a pilot hole widening. 

Drill pipe is subject to placement behind the reamers as they continue to move towards the drill setup. This ensures that the line of pipe is always assured in the hole. It's also possible to ream in the opposite direction of the drill setup. 

In that case, reamers are placed into the drill string in the rig and then rotated away from it. 

Pullback pipe installation occurs by linking a prefabricated pipe pull compartment behind the reamers at the point of exit, they are then pulling the reamers and the pull compartment moves towards the drilling setup.

This is usually done after pre-reaming is subject to completion. For smaller holes in soft soils, right after the pilot hole has been made is the best time to do it.

A swivel connects the pull compartment to the leading reamers. This helps to decrease pipe torsion transmission. The pull compartment is then supported by a combination of handling equipment, floatation ditches, and roller stands. 

Buoyancy Control Of Underground Pipes

The uplifting forces from the buoyancy of a large hole can be quite noticeable on the installation of underground pipes. The high pulling force is often necessary to overcome the drag from the uplift in buoyancy. 

Contractors will try to integrate measures that control the buoyance of pipelines over 30 inches in diameter. The easiest method for buoyance control is to fill the pipe with water. To do this, an internal fill line release water at the pull section leading edge. 

An airline is also necessary to stop the vacuum which can form at the edge as the pull section is moved towards the drill setup. The amount of water in the pipe is controlled to ensure that the most optimal distribution of forces is subject to the environment.

Some contractors will choose a constant buoyance for their drilling purposes. By inserting a small diameter line into the pull compartment, then filling it with water, buoyancy managed. The smaller line is chosen at a specific size to hold the water volume necessary per each linear foot to offset the forces in buoyance uplift.

Sonde Transmitters for You

Now that you know how underground pipes came to fruition over long distances, you have a little more understanding of how our civilized world works. In any case, whatever you do with knowledge is up to you.

If you work in the industry and you're interested in purchasing high-quality sonde transmitters, get in touch with us and we will happily set you up.