Conventional HDD

Design and Engineering

The success of every project is driven by the detail and full understanding of the clients project requirements  and the given site conditions at each individual location.  Each project’s designs start with the gathering of necessary information. This information includes the site survey, including locations of existing pipelines and services, geotechnical site investigation and local environmental conditions. These factors will drive the engineering design and determine the HDD methodology necessary to successfully plan and execute the project.

Pilot hole drilling

The 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 enlargement

In 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 back

Once 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.

Shore Crossings

While the basic steps of a shore approach remain the same as a conventional HDD crossing (i.e. pilot, ream, pullback), there are additional challenges in working within a marine environment.

Pilot hole drilling

The 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. Marine Support including vessel and dive crew management is essential on Shore Crossing Projects.

Hole enlargement

In 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 back

Once the drilled hole has been enlarged to the required diameter and cleaned adequately, the product pipe, which will have been preassembled offshore (or assembled onshore and then towed offshore), is readied for installation. The pipeline string is aligned behind the underwater borehole exit point and then pulled into the hole towards the onshore drill rig until installation is complete. Variations to this basic scenario may be needed to fit actual conditions.

Intersect HDD Installations

The intersect method is utilized when the length, the soil conditions, or a combination of the two do not allow the use of a single drilling rig to accomplish the bore. In an intersect HDD installation, two directional drilling rigs (a primary and secondary drilling rig) are placed at opposite ends of a project site and start drilling toward each other guided by a precision underground magnetic tracking device. Once the bores are within a pre-determined distance from each other, the primary rig advances its drill string, following behind the secondary rig’s retreating downhole assembly. The advancing drill string is then steered toward and ultimately “falls” into the vacated borehole produced by the retreating drill string, creating a continuous single borehole. The borehole is then reamed to the appropriate size and product pipe is pulled.