The development of small HDD Rigs with
the power sources, drilling mud fluid pump and hydraulic pumps all mounted
on a mobile drill carriage then began, and manufacturers of self-contained HDD
move rapidly forward. Currently, a contractor can obtain mini-HDD rigs fully
selfcontained, including an on-board drilling water
supply to midi-HDD rigs supported only by an additional water/drilling mud source.
An outgrowth of oil well drilling technology, HDD has become the method of choice
for river, road and various other types of crossings.
A Staff Report
The directionally controlled horizontal drilling process was developed in the U.S., and has
become commonly used for installing pipelines under natural or manmade
obstacles, especially river crossings. This method has revolutionized
complicated river crossings for pipelines which were initially done by
conventional dredging methods or were rerouted through long distances and
crossed over at a bridge location.
The method, an outgrowth of the oil
well drilling technology, was reportedly first developed in
the early 1970s by Titan Construction, of Sacramento, California. The first
installation was accomplished in 1971 for Pacific Gas & Electric Co., and
involved the installation of approximately 600 If ( 180 m) of four-inch
diameter steel pipe under the Pajaro River near Watsonville, California. Prior
to 1979, the method was limited to the installation of short lengths. In 1979,
the method was acquired by Reading & Bates Construction Company (Now
Inarc Drilling, Inc.), Tulsa, Oklahoma. Since 1979, the method has
progressed to state-of-the art where long lengths of crossing with a wide
variety of pipe sizes can be accomplished.
From 1971 to 1979, only 36 crossings
were made using this method, all of them in the United States. However, in the
next seven years, over 175 crossings were made, with several accomplished in
South America, Europe, Africa and Asia. Currently, there are several firms
competing in the market, and the total number of crossings exceed well over
500.
For a time, horizontal directional drilling (HDD) was primarily used by the oil and gas
industry on large-diameter, cross-country pipeline transmission lines.
Increasingly, it is being approved and used for small-diameter gas distribution
lines in urban and suburban areas, as well for municipal water and
telecommunication cable crossings at airports, highways, and waterways.
HDD has become the preferred technique
of many pipeline and utility companies by virtue of its lower costs and
decreased surface disruption. Because it minimizes the negative impact of
construction on the surrounding areas, HDD provides a method of installation
that is unsurpassed in its ease and overall "friendly" nature.
Pipeline companies have been increasingly turned to HDD over traditional,
open-trench methods for underground construction projects.
Equipment and Systems
Introduced in the 1970s, the first HDD
rigs were considered difficult to operate. But improvements came quickly, and
more manufacturers developed products as utility companies and contractors
recognized the advantages offered by the technique.
A basic HDD system is highly user
friendly, and includes a drill frame, power source, hydraulics, drilling fluid and guidance systems. No starting pits are
needed; bores are launched from the surface and proceed downward at an angle
until the necessary depth is reached. Then the path of the bore is leveled, and
the bore head is steered to a designated exit point, where it is brought to the
surface.
As the bore progresses, lengths of drill
pipe are added. When the initial bore is complete, material to be installed is
attached to the drill string, often with a backreamer, to enlarge the diameter
of the borehole. The installation is made by pulling the product pipeline back
through the borehole, with drill pipe sections being removed as the drillstring
approaches the drill frame.
Drilling fluid is used in making the initial bore, and
during pullback. For utility work, bore lengths generally range from 50 to 600
ft, but, with some systems, can extend as far as 1,800 ft.
HDD equipment has evolved dramatically
over the past 10 years. The introduction of a reliable walk-over locating
system spawned the initial growth of the mini- and midi-class drills that use
high drilling fluid pressure (up to 5,000 psi) and low drilling fluid volume (2-10 gpm). This method of drilling is effective in soft to medium ground
conditions.
Initially, manufacturers custom-built
each drill, making improvements and design changes based on suggestions and
feedback from their customers. The next hurdle to overcome for the mini- to
midi-class drills was to be able to successfully bore in hard soil and solid
rock conditions.
A boom in oilfield horizontal drilling forced the development of smalldiameter downhole
mud motors. The maxi-class HDD rig operators had been using large-diameter mud
motors successfully for years. Industry demands led the manufacturers to
develop the necessary design changes, to enable the use of small-diameter,
lower-flow mud motors (minimum 30-40 gpm required). Having expanded the capacities
of the mini- and midiHDD rigs with higher flow mud pumps, the need to limit job
setup space or rig footprint led to the concept of self-contained HDD Rigs.
The development of small HDD Rigs with
the power sources, drilling mud fluid pump and hydraulic pumps all mounted
on a mobile drill carriage then began, and manufacturers of self-contained HDD
move rapidly forward. Currently, a contractor can obtain mini-HDD rigs fully
selfcontained, including an on-board drilling water
supply to midi-HDD rigs supported only by an additional water/drilling mud source.
Along with the development of these
higher flow output mini- and midi-class rigs, the need for a mud cleaning,
mixing and redrculating system began to evolve. Minimizing drilling mud spillage at the bore entry site while
lowering mud cost made the cleaning and mixing system a logical investment for
many contractors.
At the same time HDD rigs were evolving,
so were various downhole supporting tools. Drill pipe, once thought by many to
be a low-cost, expendable item, is now usually the second-highest dollar amount
on a purchase order for a new HDD rig. Early examples of pipe threads varied
widely - left-hand, right-hand, even "rope" threads have been
replaced with API-approved thread designs. Forged drill pipe has become
standard on most midi-class rigs.
The evolution of walk-over locating
systems has been almost as dramatic as that of the HDD rigs themselves. Early
systems were limited to very shallow depths, and information update times were
extremely slow by today's standards. Now, not only do contractors have a choice
of sondes to match their project scopes, but wireline steering tools have been
simplified. Walkover system status readouts that are broadcast back to the
driller's console enable the driller and locator to see the information
simultaneously.
The variety of drill bits or heads and
back reamers can be overwhelming to a contractor. Each style of bit or reamer
has a designated purpose. Most contractors will find a bit/reamer design that
consistently works in their typical soil conditions, and will employ that style
almost exclusively.
Currently, the trend in the industry is
contractor diversification. They want to have the capacity to not only be able
to bore in the service lines from the right-of-way to the house, but also be
able to handle longer, harder formation bores. Realistically, this type of
project work requires more than one class of machine. The development of the
mini-, self-contained drills has satisfied a majority of service-type work.
The midi-class of rigs has undergone big
changes in recent years. Various manufacturers have developed midi-rigs that
are relatively compact in size, yet powerful enough to tackle the occasional
difficult bore.
Some of the more experienced HDD
contractors have gained enough confidence to move into the maxi-class of rigs.
This move, according to some contractors, can be as overwhelming as buying
their first HDD rig. Larger projects require more planning, more time and more
support. However - assuming that no unexpected disaster occurs - the financial
reward is usually greater.
The use of HDD grew throughout the
1980s, but was still not as commonplace as it has become today. By the end of
the decade,directional drilling was a technique to be tried when other
construction methods could not be used.
But the technique saw tremendous growth
in the 1990s, as the need for environmentally friendly installation methods
grew. In 1996, about 30% of all underground work was completed with directional drillingequipment. That figure increased to close to 50% in
1999 and 2000, as demand from the telecommunications companies joined that of
pipelines and utilities.
That rapid growth has slowed with the
recent downturn in the telecommunications and internet-broadband industries.
But demand for trenchless installation techniques from pipeline companies and
utilities has remained strong, and is expected to increase in the future. This
is due to advantages HDD offers in the environmental, technical, contractual
and economic arenas.
Today, utilities and contractors often
make HDD their first choice. In the early days, the only obvious drawback to
choosing HDD was that the technology was so new, there was not a large pool of
experienced personnel to draw from. This has changed as well. In 2004, there is
a much larger amount of experience regarding HDD, on the part of operators,
contractors, public officials and regulators.
In no small part, this is because
contractors, equipment manufacturers, and service companies teamed together to
develop educational HDD programs. These programs aid in the development of
competent HDD employees. The initial learning curve of a new horizontal directional drill owner is dramatic in its rapid up-slope.
However, after the initial knowledge is attained, moving to the next level can
be difficult without support from the manufacturers, dealers and service
companies. Recognizing this need, schools and one-on-one training courses are
available from an increasing number of sources.
Utility construction, particularly in
the gas and telecommunications industries, ensures a growing demand for the use
of directional drilling techniques into the 21st century. The potential
for work spans the spectrum, from major river crossings to utility installation
in congested urban areas, to various types of environmental remediation.
Compact HDD systems can be used to
install service lines to residences, without damaging private or public
property, and other utility systems. These (usually smaller) rigs are able to
bore beneath driveways and sidewalks, existing utility lines, and underground
sprinkler systems. Larger directional
drilling equipment can be used to go under
parking lots, highways, freeways, and even rivers and lakes.
In addition, HDD offers unique solutions
to environmental problems. For example, directional systems
can install horizontal remediation wells to access contaminated soil
and ground water in areas where other procedures are uneconomical. Some in the
industry predict the environmental market for HDD will eventually be larger
that the utility market.
Overall, HDD reduces restoration time
and costs in both urban areas and residential neighborhoods. The public
appreciates the reduced inconvenience made possible by the use of directional drilling equipment.
Applications
Companies usually consider the
technical, contractual, and economic aspects of a project when determining
whether to use HDD. In the case of a river crossing, the project is determined
to be technically feasible if it can be installed using existing tools and
techniques, regardless of uncertainties surrounding installation cost. A
crossing is contractually feasible if the installation cost can be accurately
estimated in advance, allowing contractors to submit lump-sum bids. HDD is
economically feasible if installation cost is less than the cost of competing
construction methods.
Mini-HDD is a subsurface-launched
installation technique that typically uses either controlled-fluid cutting or
fluid-assisted mechanical cutting. However, this method can be use air for
cooling or dry boring assistance, or can be a dry process where
neither liquid (e.g., bentonite, water) nor air is used. Therefore, the choice
of fluid-assisted or dry cutting depends on the nature of work (normal utility
application or environmental application), size of the utility line (diameter
and length), subsurface conditions, and impact on the environment.
The feasibility for using the mini-HDD
technique should be initially established on the basis of diameter length, and
required/achievable degree accuracy in alignment and grade. Mini-HDD currently
is not practical for installing pipe to the precise alignment and grade
tolerances required for gravity sewer line. However, mini-HDD is suited for
installing new utility networks for water, gas, electric or telecommunication
lines in developed areas. It can also be used to install pressure sewer line.
The diameter of the product pipe or utility line to be installed using this
technique should be somewhere in the 2 to 10-in. range. The depth should be
less than 30 ft.
The dry system is suitable only for
small-diameter pipelines (typically less than 4 in.) and short (typically less
than 150 ft) utility line installations. It is useful for drilling through soft soil or drilling under a sensitive, contaminated site where the
probability of contamination movement to ground water or to the surface is
high. It may also be applicable where hazardous or toxic wastes have a high
probability of contaminating drillingfluids,
which would then require proper disposal.
The main drawbacks of dry boring are the limitation of pipe size and overheating
of the drill head as the bore diameter and the length of the bore increases.
Also, it should be remembered that the dry boring system (with or
without air) is usually less responsive to steering corrections than
fluid-assisted mechanical cutting.
Fluid-assisted mechanical boring is appropriate for most utility applications,
and the low drilling fluid volume used is unlikely to cause voids or
settlement problems. Moreover, the fluid assisted mechanical cutting systern is
very useful for coarse, saturated, sandy soils where drilling fluid stabilizes the borehole.
An important distinction between
fluid-assisted mechanical boring and water-jet boring is that the high fluid volumes and pressures
used in water-jet boring often cause erosion of the soil adjacent to the
borehole. Water-jet boring uses large volumes of water at pressures as high
as 15,000 psi for cutting the soil, while mini-HDD uses water pressure less
than 4,500 psi to assist in mechanical cutting by the drill head.
Another factor that should be considered
for selecting the method of installation is the steerability of different
techniques. Steerability is important for curved space alignment, or where the
clearance between the existing utility lines is small. It is important to
determine the minimum radius of curvature attainable with specified diameter
drill pipe for each method. The minimum radius of curvature is typically given
as 125 ft for 1.5-in. diameter pipe, although some manufacturers state that
radii of 42.5 ft for 1.25-in. pipe and 30 ft for 1.0-in. pipe are not unusual.
Drill rod life can be adversely affected by use of sharp bends.
The mini-HDD method is best suited for soils with some cohesion (i.e.,
clays). The method is also successfully used in sandy soils by adding bentonite
to the drilling fluid, to ensure borehole stability. Hard soils, caliche, shale,
limestone and other rocks typically reduce the drilling rate
and increase, and increase drilling head wear. The mini-HDD method is not well suited for gravelly
soils (greater than 25% gravel sizes).
Sumber : "History of Horizontal Directional Drilling". 1 Februari 2014. http://search.proquest.com/docview/214452369?accountid=31562
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