Horizontal Directional Drilling (HDD)

The Pacific Connector Gas Pipeline project crosses a number of fish bearing streams and areas which may be problematic for conventional pipeline construction. To potentially avoid impacts to these sensitive areas, the HDD construction methodology is being reviewed for feasibility.

The use of the HDD methodology at these locations will be determined in consultation with a number of federal and state agencies including the U.S. Army Corps of Engineers, National Marine Fisheries Service, U.S. Fish and Wildlife Service, Oregon Department of Ecology, Oregon Department of Fish and Wildlife, and Oregon Department of Natural Resources.

What is a Horizontal Directional Drill?
The HDD construction method can be used to install pipelines beneath areas where conventional open trench or other construction techniques may cause undesirable surface disturbance.

The HDD method tunnels beneath surface obstacles and then pulls the pipeline back through the underground tunnel, leaving the surface undisturbed.

The tunnels are typically drilled to depths ranging from 25 to 100 feet below surface obstacles, depending upon the location, pipe characteristics, and subsurface conditions.

The HDD installation involves four main steps:

• Pre-Site Planning
  Extensive pre-site planning is required to determine if the HDD method is technically and geologically feasible. A topographic survey is performed along the proposed drill site to ensure adequate surface area is available to conduct the drilling process. In addition, a geotechnical investigation is conducted at each drill site to determine the subsurface conditions. Using the data from the geotechnical investigation and topographic survey, a specific drill path is determined.
  
  
• Drilling the Pilot Hole
  Once the entry location, exit location and trajectory have been determined, the next step is the drilling of a pilot hole. The drill rig is set up at the entry location.

  When the drill rig is in place, drilling of a pilot hole begins. At all stages along the drilling path, the operator receives information regarding the position, depth, and orientation of the drilling tool, allowing navigation of the drill head along the designed drill path to the exit point.

• Hole Opening Process
  Upon completion of the pilot hole, the hole opening or reaming process begins. This process consists of progressively enlarging the pilot hole to a diameter that will allow successful pullback of the prefabricated pipe string.
  
  
• Pipe String Pullback
  A pipe string consists of short sections (approximately 40 feet) of steel pipe which are welded together to form a continuous string of pipe for insertion into the drilled hole. The pipe string is slightly longer than the length of the drilled hole. The pipe string is coated with a layer of corrosion and abrasion resistant protective coatings and hydrostatically pressure tested to insure its integrity. The pipe string is then placed on rollers and cradles to assist with movement during pullback. Next, the pipe string is pulled over the rollers and down into the drilled hole. The pullback continues until the entire length of the pipe string has been pulled into the drilled hole.
  
  
• Environmental and Safety Measures
  Pacific Connector will employ specialists at each HDD installation with a proven record of successful completion for projects of similar length and complexity. One inspector is assigned full-time to each of the HDD sites and will assist in monitoring the progress of the drill. Excess drilling fluids (non toxic bentonite clay and water) and cuttings produced by the HDDs will be disposed of at an approved disposal site. Water, to mix the drilling fluids and complete the pipe string hydrotests, will be brought in from off site and stored in tanks at the entry and exit locations.