What Does Horizontal Directional Drilling (HDD) Mean?
Horizontal directional drilling (HDD) is a trenchless construction method used to install pipes underground without disturbing the ground surface. The drill is launched from one end of the designed bore path and retrieved at the other end, and except for the launch and retrieving spaces above ground, the entire process takes place underground, out of sight.
HDD has become a choice alternative to conventional pipe-laying methods that require opening up the earth’s surface up to the depth of installation for the entire pipeline route.
Trenchlesspedia Explains Horizontal Directional Drilling (HDD)
Horizontal directional drilling is ideal for use where trenching needs to be avoided such as under a railroad, an embankment, highway, and beneath lakes and rivers. With advanced HDD steering technology, it is also now possible to install pipelines under busy city streets without disrupting the flow of traffic and affecting businesses.
History of HDD
HDD can be traced back to the early 1900s when it was discovered that the seemingly vertical wellbores were deviating at their own will with inclinations up to 50 degrees to the vertical. In 1926 gyroscopes by Sperry Corporation helped measure borehole inclination and azimuth.
In 1929, H. John Eastman developed the magnetic single-shot and multi-shot instruments that could measure both inclination and direction. This began the era of controlled directional drilling, which was accurate and could be intentionally deviated.
In the early 1960s, Martin Cherrington designed his own drill rig that was basic and lightweight.
In the 1980s, Tensor developed a steering technology that opened a wide avenue for the application of HDD from medium-sized to very large projects, including crossings.
Benefits of HDD
- HDD is a minimum impact method and especially useful in environmentally sensitive areas such as wetlands, estuaries, rivers, and lakes.
- It is a quick and accurate method that enables the operators to accomplish creditable accuracy even when crossings are complicated.
- Continuous monitoring and control during the operation allow operators to navigate in constrained spaces between existing utility lines.
- Drilling can be carried out at greater depths to bypass existing utilities altogether and requires only one launching shaft at the entry point and one reception shaft at the exit point.
The HDD Process
The HDD method consists of two main stages, i.e. drilling a pilot hole and back reaming. After reaming is completed, the pipe is pulled in through the hole.
The first stage involves drilling a pilot hole using a steerable guided drill along a planned path. The pilot hole is approximately 1 to 5 inches in diameter along the proposed centerline of pipe alignment. When the drill string reaches the exit point, the second stage is initiated.
The second stage involves attaching a reamer of approximately the same size as the product pipe to the end of the drill string after removing the drill bit and pulling it back to the entry point. Sometimes several passes may be required before the desired bore diameter is achieved.
The bore diameter is approx. 50% larger than pipe diameter to enable easy pull-through of the pipe string.
Once the reamer has done its job, it’s time for the pipe pullback, where the product pipe is attached to the reamer and pulled through the borehole.
All along the process, electronic monitoring of the drill path is carried out to obtain a maximum degree of accuracy. A slurry system helps circulate the drilling fluid and helps transport the drill cuttings back to the surface.