Horizontal Directional Drilling (HDD)
Horizontal directional drilling (HDD) technology originated from the oil fields in the 1970s and was evolved by merging technologies used in utilities and water well industries. HDD, one of the most common trenchless installation methods, is a steerable system used for the installation of pressure pipelines, cables and conduits in a shallow arc using a surface-launched drilling rig ( common brand name VERMEER, XCMG, GOODEN, APPOLO).
Horizontal Directional Drilling (HDD) has become a favorable method of pipeline installation in urban areas and for crossing obstacles such as rivers and roads.
Horizontal Directional
Drilling process is completed in two main stages which are followed;
1. Preconstruction Process
2. Installation Process
a) Pilot hole (Bore drilling
from entry to exit bore)
b) Pre-reaming (Enlarging
the bore)
c) Pull Back Operation (Installation of pipe)
Preconstruction Process.
At preconstruction process, a design plan and profile drawing must be prepared for each crossing. Then, site preparation is performed by setting up drilling rig at the proper location and preparing slurry to stabilize and lubricate the borehole. On the other side of the proposed alignment, pipeline, reamer, and storage space that are required for pre-reaming and pullback are prepared.
Figure 1. Horizontal Directional Drilling (HDD) construction procedure
The
first stage of an HDD installation is to advance a small diameter pilot hole
along the designed path with a drill bit attached at the front of a drill pipe
string. Drilling the pilot hole is the most important phase of an HDD project,
because it determines the ultimate position of the installed pipe. A small-diameter
(typically 1 to 5 in) drilling string penetrates the ground at the prescribed
entry point at a predetermined angle. The leading assembly used for steering,
survey and advancing the drill bit is called the Bottom Hole Assembly (BHA) and
consists of the drill bit, a bent sub or mud motor and non-magnetic drill
collar.
The
slight bend in the bent sub or mud motor provides a steering bias that can be
oriented in the desired direction of advancement to allow the pilot hole to be
advanced according to the designed alignment and profile. The drill path is
monitored by a special electronic tracking system (Digi-track) housed
in the pilot drill string near the cutting.
Once
the pilot hole is advanced along the desired path and the drill bit exits the
ground at the exit point, the BHA is then removed from the downhole drill pipe
string and replaced with a larger diameter reaming tool to enlarge the pilot
hole. This stage of reaming/enlarging the pilot hole may be completed in
several stages depending on the final diameter required to install the
pipeline. The reaming tool typically consists of a circular array of cutters
and drilling fluid jets tailored to the anticipated subsurface. In general, for
mini HDD, the final size of the bore should be at least 50% larger than the
outside diameter (OD) of the product pipe. This overcut is necessary to allow
for an annular void for the return of drilling fluids and spoils and to allow
for the bend radius of the pipeline.
Pull Back Operation.
After
the hole has been reamed to the targeted diameter, the hole is typically
swabbed (one or more times) with a reaming tool to check the hole condition
prior to pullback operations. Following the swab pass, the product pipe, which
is prefabricated, tested, supported by rollers and pipe handling equipment at
pipe side, is attached to a pullback assembly. The pullback assembly typically
includes a pull head, reaming tool, and swivel. A reamer is located between the
pull head and the drill string to ensure that the hole remains open and to
allow lubricating fluid to be pumped into the hole during the pullback.
At
the completion of HDD works, pipe log book indicating the horizontal and
vertical position at 10 or 20 meter interval along the pipe will be maintained.
This will include pipe number, size, depth, rig performance parameters etc. After
installation and jointing of Pipeline in each pipe length it
will be tested for sectional pressure and leakage test.
Finally, site will be cleaned and disposal of
excess earth then the reinstatement of work will be started to restore in original
road condition.
Some site photographs of HDD works
Pic. 1 HDD Machine
Pic. 2 Entry and exit pits excavation
Pic. 3 Jointing of HDPE pipes
Pic. 4 Piloting/Pre-reaming
Pic. 5 Tracking
Vid. Pipe Pulling
Pic. 6 Two hours continuous pressure and leak test
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