Paper - Challenges Faced in HDD
Paper - Challenges Faced in HDD
Paper - Challenges Faced in HDD
ABSTRACT
Horizontal Directional Drilling (HDD) is a steerable trenchless technology process for the installation
of an undeground pipeline which is accomplished in three stages namely – Pilot Hole, Pre-reaming
and Pull back. Today’s oil companies have the ability to drill horizontal bores to cross obstacles such
as rivers, mountains, roads and residential areas, as well as difficult terrain and nature protection
zones underground. HDD is increasingly becoming an economic, safe and time saving solution among
pipeline operators. Though HDD was evolved from the directional drilling method once adopted in oil
fields but the technique is increasingly becoming popular in sewage disposal, potable water supply
network, telecom operators, electricity / city gas networks and a wide range of other services.
Based on experience and observations, this paper discusses the challenges related to site accessibility,
difficulty in achieving bore profile, pipe installation, etc. which are generally faced during HDD.
1. INTRODUCTION
HDD is a high end technology transferred from practical problems crop up during the HDD
oil exploration industry to nowadays micro- execution. These challenges are listed in the
tunnelling for installation of utilities such as below table and can be divided into three
power cables, telecom conduits, water mains and categories:
gas mains, etc. This specialised technique is
featured with a drilling rig on surface and a mud Geo-technical During Bore During pipe
aspects preparation installation
motor to drive the cutting tools such as tri-cone
Space Loss of Damage to
bit and reamers. It is almost certain that problems constraints for circulation of carrier pipe
will occur in very carefully planned HDD string drilling fluid
operations. Understanding and anticipating preparation Obstructions
drilling problems, understanding their causes and along drill
planning solutions are necessary for overall- path
construction-cost control and for successfully Line and
reaching the target zone by achieving the desired grade
problem
pipeline profile and alignment. Before applying
Bore-hole
this technique, careful planning, design collapse
procedures, thorough site investigation (soil / Rocky area Surface Hydro-lock
water / topographic) and precise preparation is heave or
required to ensure a practical solution before humping
tendering, and more importantly, to ensure Dogleg
inclusion of all technical requirements and severity
Lost probe
concerns for the HDD works under the Contract
connection
for the Contractor to implement during the
Magnetic
construction stage. A dedicated pre-qualification interference
process can be helpful to assure properly Jam in drill
qualified HDD Contractors and materials for the bit nozzle
process. In spite of all the preparedness, some Table: 1
2. DISCUSSIONS: 2.1.3 Mitigation of Geo-technical challenges:
Pre-construction surveys during the
2.1 Challenges of Geo-technical aspects: design phase must be carried out which
may typically involve surface survey
2.1.1 Space constraint for string (Ground features like roadways, utility
preparation: As a convention, pull back poles, overhead power cables, culverts,
through HDD bore is done with a single etc., Structures like buildings, tanks,
pipeline string. However, due to bridges, hazardous material storage, etc.,
geographical constraints wherever space Flora spread like mature trees, crops and
for preparation of a single string and manmade slopes or retaining walls, etc.)
placement of same on rollers during pull and sub-surface survey (soil investigation
back is not possible, pipeline operators and underground utilities)
tend to pull the HDD string in sections by 2.1.4 Case study:
joining the sections with golden joints
(joints which aren’t subjected to 2.2 Challenges during Bore preparation:
hydrostatic test). Since the weld joint will Failure to complete the bore is often the
not be pressure tested, NDE is performed main concern globally for the executors
in lieu of pressure test. The best welders of HDD. The following are some of the
are to be deployed to weld these joints challenges / problems that are faced
because defects in such joints may cause during bore-hole preparation:
further delay in pipe pulling. Going for
Golden joints is also critical time has to 2.2.1 Loss of circulation of drilling fluid:
be given for completion of activities like During the HDD, loss in circulation of
welding, radiography and joint coating of drilling fluid (bentonite solution) may
golden joint during pipe pulling. occur by drilling through voids, highly
Probability of bore collapse in soft coarse fractured rock etc. An effective drilling
soil with low quality mud during this halt fluid at a suitable pumping rate and
period is also an additional challenge. In viscosity must be pumped for achieving
order to avoid such circumstance, bore the bore as per the subsurface conditions.
hole has to be filled with good quality These are critical factors for maintaining
drilling fluid / mud during clean pass. It circulation and bore-hole stability.
is better to make the golden joint away Circulation can be lost very quickly if
from the exit point so that pipe string can voids are encountered and cannot be
be pulled after the completion of each resumed until the void is filled or the
activity which reduces the chance of bore path to the void is sealed. In general,
collapse. viscosity of the drilling fluid shall be
2.1.2 Drilling in rocky areas: Execution of increased to seal the void / low resistant
HDD successfully in hard, rocky areas path.
has always been a challenge. The added 2.2.2 Obstructions along drill path:
time and tool wear seem to be the biggest Obstructions can cause a failed bore if
concern amongst drillers operating in the drill bit, reamer, or product pipe
these conditions. Drill bit with multiple cannot be advanced past the object. If
nozzles must be used to avoid jam identified during planning, the best
because of rock particles. Proper drill bit approach is to avoid the obstacle. Typical
with qualitative drilling fluid must be obstructions faced during HDD
used for achieving the required bore construction are cobbles and boulders,
profile. gravel beds, wood, bedrock, and
construction debris or foundations. There
might be chances of worn out drill bit if it 2.2.6 Surface Collapse: This is typically a
encounters hard rock along the drill path result of a significant over excavation
which would effect in even cutting soft above the bore hole, which can be caused
soil further. by large volumes of thin drilling fluid
2.2.3 Line and grade problems: These occur used at high velocities, incomplete filling
due to faulty tracking and steering or of the annulus with drilling fluids for a
subsurface conditions that prevent or large-diameter bore near the surface, or
hamper the proper steering. Improper leaks in high- pressure pipes after
matching of the down-hole tools to the installation, which erode the soil above
subsurface conditions can also cause line the bore hole.
and grade problems. 2.2.7 Dog Leg Severity (DLS): Dogleg
2.2.4 Bore-hole collapse: Bore hole collapse Severity is a measure of the amount of
severely impacts the chances of success change in the inclination, and/or azimuth
on any HDD project. Soft or loose soils of a borehole, usually expressed in
present a high risk of collapse during degrees per 100 feet. Since in a
HDD operations. When a bore hole directional well, we continuously have
collapses, there is an immediate increase changes in inclination and/or azimuth,
in rotary torque and pressure and a thus the presence of DLS is always there.
decrease or loss of circulation. Increasing The dogleg severity is low if the changes
the viscosity of drilling fluid might help in inclination and/or azimuth are small or
in reducing the chances of bore collapse. occur over a long interval of course
2.2.5 Surface heave or humping / Frac-out: length. The dogleg severity is high when
This is a condition that is usually a result the inclination and/or azimuth changes
of excess pumping of drilling fluids after quickly or occur over a short interval of
a loss of circulation. This condition can course length. At low inclinations a
quickly pressurize the formation and change in azimuth will have a small
cause a heave at the surface. Heaving can dogleg severity. As the inclination
also arise from reaming with a barrel increases, the dogleg severity will also
reamer without enough depth, which can increase for the same change in azimuth.
result in a displacement of soil towards Methods to reduce DLS: Once a severe
the surface. Heaving or humping the dogleg comes into play, its effect can be
surface is a far more common reduced by using lubricants in mud
occurrence. Several factors contribute to system. The lubricant reduces the
the development of surface heave coefficient of friction between the drill
including back ream rate, borehole string and the bore wall thereby reducing
pressure, down-hole tooling, depth of the tension in the drill string.
cover, annular space size, geotechnical
Problems associated with dogleg: As
properties, etc.
drilling continues, the drill string tension
in the dogleg increases which increases
the lateral force. The lateral force causes
the drill string to cut into the bore wall at
the dogleg (refer figure below). Repeated
abrasion by the drill string in a particular
location of the dogleg results in a
worn spot called a key seat, in which
the BHA (Bottom Hole
Assembly) components may
Figure: 1
become stuck as they are pulled through retrieve the drill pipe until he finds the
the section. Severe doglegs results in damaged joint. Hence, wire of good
worn of casing which can lead to collapse make& quality, experienced welder along
of hole in the casing. Casing string may with a robust solenoid machine to be
no longer easily fit through the curved deployed for soldering the wire line
section and casing may wear unusually joints.
quickly due to higher contact forces
between the drill string and the inner
diameter (ID) of
Figure: 3