The Complete Industrial Guide to Horizontal Directional Drilling
Do you need to install a pipeline under a roadway, railroad, or river? In an urban or residential area? In an area with many other utilities already underground?
Horizontal directional drilling could be the answer.
Horizontal directional drilling (HDD) is a steerable trenchless drilling method. Operators use a surface-launched drilling rig to drill a horizontal hole beneath obstacles on the surface.
Find out how HDD works and its advantages over other forms of horizontal drilling. You'll be ready to tackle your next drilling project. If you are unfamiliar with some drilling terms or expressions, be sure to check out our Directional Drilling Glossary and Terminology.
How Does Horizontal Directional Drilling Work?
The horizontal directional drilling process has three basic stages: pilot drilling, expanding the drilling hole, and pulling the production pipe. First, the directional driller drills a pilot hole. They use a drill bit and pipe assembly to drill a small-diameter hole.
Drilling fluid helps the drill bit cut through the soil and rock. It lubricates and cools the drill bit. It also carries cuttings from the hole back to the surface.
An HDD locator system lets the contractors track the progress of the drill bit. This helps keep the drill on the right path and avoid obstacles.
After the pilot hole is finished, the drill team enlarges it in a process called reaming. A reaming tool expands the hole to a diameter that the pipeline will fit through. The contractor may ream the hole several times depending on the final diameter that the project needs.
Finally, the drill team pulls the pipeline into the reamed hole using the drill rig. When the pipe is in place, it undergoes testing. The drill team can then weld it to the pipe segments on either side.
Uses for Horizontal Directional Drilling
The most common form of traditional pipeline installation involves digging a trench and laying a pipe into it. A surface trench isn't always possible, however. If the pipeline needs to cross under an obstacle like a river or a road, horizontal directional drilling can be a better option.
HDD is suitable for laying several types of underground infrastructure. Common applications include:
- Water and sewer pipelines
- Oil and natural gas pipelines
- Electrical cables
- Fiber optic and telecommunication cables
Telecommunications installations make up the largest percentage of the global HDD market.
Advantages of Trenchless Drilling
Horizontal directional drilling gives you several advantages over other methods.
HDD lets you install utilities underground with minimal disruption to the surface. It's a good choice for urban or residential areas. It's also a good option if the underground is congested with other utilities.
The cost of the project is lower with HDD. HDD needs less equipment, fewer employees, and less fuel than traditional trench installation. You have lower surface restoration costs and over all environmental impact after installation, making directional drilling more cost effective.
Trenchless installation is faster. Drilling horizontally instead of down and across is more efficient. You don't spend time on extensive surface restoration after laying the drill pipe.
HDD pipeline installation is deeper than with the trench method. This means you have less chance of damaging other underground utilities.
Finally, getting permits approved for HDD can be easier than with traditional drilling. HDD creates less of a disturbance, less debris, and requires less equipment. This makes the permitting process go more quickly.
To learn more about the origins and history of directional drilling, check out our post - The History Of Horizontal Directional Drilling.
Ensuring the Best Conditions for HDD
Like all forms of drilling, horizontal directional drilling has some risks involved. Common risks include:
- Drilling fluid loss
- Hydraulic fracture
- Hole instability
- Pipeline damage during installation
Porous soil is often the cause of drilling fluid loss. A hydraulic fracture can also cause a loss of drilling fluid. A hydraulic fracture happens when the pressure of the drilling fluid is too great for the surrounding soil.
The soil type can contribute to hole instability. The diameter of the hole and the geometry of the drilling path are other factors.
A good design helps ensure the success of your project. Site investigations and planning begin months or years before drilling starts.
HDD design engineers study the proposed installation site to evaluate its topography and subsurface composition. They will also identify any environmentally-sensitive areas. The planning includes locating existing structures above and below the ground, like roadways, buildings, and utilities.
Important elements of the design include:
- Entry and exit sites
- Underground path of the drilled hole and pipeline
- Diameter and type of pipeline
Engineers design each HDD project to reduce risks as much as possible.
The type of soil the drilling path goes through has a large effect on the success of the HDD project. Clay, soft soil, and sandy soil are some of the best environments.
Rock is also good. However, rock requires more time and heavier equipment to complete the project.
Problems can occur if the soil is too soft because steering becomes difficult. The risk of hydraulic fracturing is higher.
Soils that contain a high percentage of gravel or cobbled rock also pose problems. Dense gravel makes it difficult to steer. The hole can become unstable, and inadvertent drilling fluid return is a higher risk.
In general, HDD isn't suitable for soil types that have 85% or more gravel by weight.
For HDD pipeline installations, the pipe can be made from one of several different materials. The pipe needs to withstand the drilling machine pulling it through the hole. Steel, ductile iron, PVC, polyethylene, and polypropylene are some of the options.
Most oil and gas HDD installations use high-strength steel pipe.
Polyethylene pipe is commonly used by oil companies for HDD because of its flexibility. It handles scratches well, but it can deform or collapse in unstable soil. It's suitable for applications including water, wastewater, chemicals, gas mains, and telecommunications conduits.
Using the Right HDD Equipment
The right equipment makes your horizontal directional drilling project safer and go more smoothly. One of the most important pieces of equipment is your HDD locator system. You need to accurately and efficiently track your drill head with real time data throughout the planned path.
PilotTrack has the parts or complete systems you need. We offer refurbished sonde transmitters backed by a 180-day warranty.
Contact us today for more information. We'll help get your project started and keep it on track.