The use of horizontal direction drilling to install crossings under a vast range of surface obstacles was developed in the 1970s combining techniques used in conventional road boring and those used in oil and gas directional drilling. This method is currently used to install pipelines for oil, water, natural gas and wastewater, as well as conduits for power and fiber optic cables. The main objective is to install such services without using traditional trenching methods thus avoiding any unnecessary environmental impact and providing added security.
There are several benefits to horizontal directional drilling, including:
- Less invasive than the traditional open cut.
- Requires a relatively short set up time.
- Surface disruption is minimized.
- More secure than above ground or trenched installations.
- Can make deep installations and avoid surface obstacles such as rivers, railways, or highways.
The conventional horizontal directional drilling process generally includes four stages:
- Site investigation and designProject designs start with the gathering of necessary information. This information includes the site survey, including locations of existing pipelines and services, and a geotechnical site investigation. This will determine the tools necessary to successfully drill the crossing and determine the design.
- Pilot hole drillingThe pilot hole is drilled from the entry point to the exit point following a previously designed profile and alignment. The drilling tools and rig equipment selected for each job is largely determined based on the results of the geotechnical investigation and the size of the crossing (length and diameter). During the pilot hole drilling, a directional guidance system is used to navigate the pilot hole along its pre-designed profile.
- Hole enlargementIn small diameter crossings the pipeline may be directly installed in the pilot hole. However in most cases pilot hole enlarging, known as “pre-reaming,” will be necessary. Pre-reaming is required to provide a bore diameter large enough so that the pipeline can be installed in the drilled crossing. Based on the final desired diameter and soil conditions this process may include one or more stages.
- Pull backOnce the drilled hole has been enlarged to the required diameter and cleaned adequately, the pipeline is installed. When applicable, the pipeline is pre-assembled in a single string and placed on rollers prior to pullback. For pullback, a reamer is connected to the drill pipe. Behind the reamer a swivel is connected allowing the drill pipe to rotate the reamer without allowing the transfer of torque to the product pipe. The drill pipe is then pulled back towards the entry point until the pipeline is fully installed.