How Horizontal Directional Drilling Rigs Work


The development of horizontal directional drilling methods made it possible for oil, gas and pipeline companies to drill from a single pad location and move those resources directly into open tanks or large pipelines on the surface. This eliminates some of the costs associated with setting up multiple drilling locations to reach a single formation, since all drilling operations can be performed from one central location.

It is also used in geotechnical engineering projects such as the construction of landfills or underground storage tanks for oil and gas deposits. These projects also require boreholes to be drilled into various sub-surface levels. These are all feasible because of a horizontal directional drilling rig.

Drilling Methods Used In Horizontal Directional Drilling Rigs

Horizontal directional drilling is completed in three steps: pilot hole development, pilot hole enlargement, and hole conditioning.

Hydraulic fluids are fed into the hole and drill bits during the procedure to aid in breaking up soft soil, lubricate the bore, and cool the drill bits. While a tougher bit material such as Polycrystalline Diamond (PCD) or tungsten carbide alloys, along with hydraulic force is needed in rock formations.

A pilot hole drill is used to start the HDD installation. The pilot hole is drilled in a profile and alignment from the entry point to the exit point. Drill bits are initially used to make a smaller hole between the entry and exit points. The installer should create and program the profile and alignment.

A directional guidance system is utilized to navigate the pilot hole following its pre-designed profile during drilling. The drilling tools and rig equipment used for each operation are mostly influenced by the results of the geotechnical research, the crossing’s size (diameter and length), and the installer’s judgment.

The drill string is usually inserted at an angle of 8 degrees to 16 degrees, and is propelled forward by the rig’s rotation torque and push. This enables the operator to modify the direction of the pilot hole and move it along the pre-designed profile. Drill bits often have a slant-face and can be tailored to navigate through a variety of soils, including sands, clays, and rock.

By pulling back the pilot bore towards the entrance site, the drill bits are changed to a larger reamer at the exit site, enlarging the hole to the needed pipeline diameter. For small diameter crossings applications, the pipeline is installed directly into the pilot hole.

In most cases, though, the pilot hole will need to be enlarged, also known as “pre-reaming.” This process is needed to create a large enough bore diameter for the intended pipeline to be put in the drilled crossing. Depending on the final desired diameter and soil conditions, pre-reaming may entail one or more phases.

Following the completion of pre-reaming to the required diameter and adequate hole cleaning, pipe installation can begin. The pipeline is pre-assembled and placed on rollers as a single string. Pullback is the result of this configuration.

The drill pipe is fitted with a reamer for pullback. A swivel is also attached to the drill pipe, allowing the reamer to revolve without passing on the torque to the pipe. After that, the drill pipe is dragged back toward the entry site until the pipeline is completely installed. Using a swab instrument, the completed diameter is checked.

The Drill Hole

This method uses one drill bit that is rotated at high speed to make a small hole approximately 2 inches in diameter. The hole is then extended as the bit continues to cut into it. When drilling in this way, several holes are drilled to create a perforation pattern that allows for the best possible surface area to be penetrated around the wellbore.

Measurements can be taken at regular intervals so that well bore integrity and rock quality may be effectively evaluated. This information can be used to create a more effective drilling plan.

When the proper depth is achieved, casing (a pipe with holes bored through it) is run into and cemented in place within the wellbore. Casing prevents soil, rock or other debris from entering the borehole while still allowing fluids to flow toward the production casing. Casing is commonly used in vertical and directional drilling, while pipe is frequently used in horizontal wellbores.

Once the casing has been installed, the bit can be disconnected from the drill string and removed from the borehole. The next step is to prepare for perforating by running a series of smaller strings including conductor pipe, perforating guns, packers and parachutes into the wellbore.

Perforating is accomplished by running a high-pressure hydraulic fluid down the conductor pipe and into the perforators. This pressure causes air to be expelled from within the perforators, causing them to inflate like a balloon. At this point, the perforating guns can be used to break through the rock at various depths and create small openings connecting the wellbore with surrounding rock formations or strata. Alternatively, a perforator gun can fire a series of holes into an already perforated hole that haven’t been broken open. This is commonly done so that fluids may flow back up the wellbore by increasing the surface area of the hole.

Once perforating has been completed, the well is placed into production with a workstring that includes a packer and frac pump. A “frac” or hydraulic fracturing job is commonly used to stimulate or increase production within an existing borehole.

The job involves pumping high-pressure fluids into the drill string in order to break up surrounding rock and release trapped gases, liquids or oil. Fracking creates small fractures in the formation that extend from a wellbore upwards toward the surface. These tiny fissures allow for greater amounts of oil, gas or other substances to flow freely through the wellbore.


Depending on the application, horizontal directional drilling rig maintenance methods may differ. But, it normally follows three basic steps such as;

  • Service checking on a daily basis.
  • Maintenance of lubrication.
  • Clean-up at the end of the working day.

Service Inspections on a Daily Basis

Each rig has its own service handbook. Operators can use the manual to learn how to service hydraulic pumps, oils, fluids, coolant, and other components. There are also daily maintenance checks included in the instructions.

Not only will early diagnosis and maintenance save money,  time, and costly damages from any ignored faults, but it will also keep machines running at their best on the jobsite.

Maintenance of Lubrication

It’s critical to keep the drill rig properly lubricated and rotated. It will not only help your equipment last longer, but it will also improve its overall performance.

All manufacturers have their own lubrication standards, which is intended to improve thread compression and tolerance. Contractors can obtain adequate torque by maintaining automated greaser machines in order to maintain adequate hydraulic pressure. The risk of  the pipe unthreading and breaking downhole is also reduced.

End-of-Day Clean-Up

It is advised that each machine be cleaned at the conclusion of each work day to remove any blockages. Machines are frequently designed with a high-pressure pump that connects to the machine’s circuit system, allowing for a quick end-of-day wash down.

Maintenance duties may appear to be monotonous, but they are essential to the overall success of any project. Contractors can keep their machinery in top operating condition by doing these checks and routine maintenance, which saves time and money in the long run.

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