Directional Drilling, also known as Horizontal Directional Drilling (HDD), is a technology that has been evolving since the 1970's. The directional drilling process occurs in two distinct stages. First, a pilot hole is drilled between the desired start and stop points. The pilot hole determines the placement of the product line. Occasionally the product line can be installed using just the pilot hole, but often, back reaming is necessary in order to enlarge the bores diameter. Back reaming, the second stage of directional drilling, may need to be done several times before the required diameter is obtained and the product line can be pulled back through the earth. Both of these stages require a drilling fluid (also known as a mud mixture). Drilling fluid usually consists of bentonite; polymer or both in combination with water, lots of water!
The directional drilling process has many benefits when compared to other conventional methods. Environmental impact is minimized because directional drilling can take place without the excavation of a launching pit. Directional drilling is also useful when faced with restrained working conditions where a bore pit would be unfavorable. Another benefit of this technology is the fact that the operator has more control over the location of the product line. This added control spawns from the ability to maneuver the cutting head via the sonde locating device.
Directional drilling can be used effectively in many situations where conventional trenchless methods will not work. There are situations were additional precautions should be exercised before attempting this method:
• Operating around multiple electric lines can cause some interference in the sonde reading. This interference may create a false location of the cutting head making it dangerous when operating in critical situations.
• Soil conditions play a major role when it comes to choosing a directional drill. This technique is ideal in sand, silt, clay or dirt. Harder geological formations are drillable with the implementation of greater mud pressure, the use of mud motors or hammers. Generally, a harder material yields less control when operating a directional drill.
• The possibility of ground movement is also a concern when directional drilling. Depending on ground conditions and fluid pressure, the earth could shift causing the cutting fluid to seep into surrounding areas. These commonly referred to "frac-outs" (meaning literally to fracture out) hinder drilling fluid returns and disrupt the environmental surroundings.