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| Source: ChevronTexaco
Corporation |
Drilling into the Earth in the hopes of uncovering
valuable resources is nothing new. In fact, the digging
of water and irrigation wells dates back to the beginning
of recorded history. At first, these wells were primarily
dug by hand, then by crude stone or wood tools. Metallurgy
brought about the use of iron and bronze tools to delve
beneath the Earth's surface, and innovations led to
more efficient ways of removing debris from the newly
dug hole. The first recorded instance of the practice
of 'drilling' holes in the ground came about around
600 B.C., when the Chinese developed a technique of
repeatedly pounding bamboo shoots capped with metal
bits into the ground. This crude technology was the
first appearance of what is now known as 'percussion
drilling'; a method of drilling that is still in use
today. Much advancement has been made since these first
bamboo drilling implements, with the realization of
the value and increased demand for subsurface hydrocarbons.
This section will cover the basics of modern onshore
natural gas drilling practices.
There are two main types of onshore drilling. Percussion,
or 'cable tool' drilling, consists of raising and dropping
a heavy metal bit into the ground, effectively punching
a hole down through the Earth. Cable tool drilling is
usually used for shallow, low pressure formations. The
second drilling method is known as rotary drilling,
and consists of a sharp, rotating metal bit used to
drill through the Earth's crust. This type of drilling
is used primarily for deeper wells that may be under
high downhole pressure.
Cable Tool Drilling
Cable tool, or percussion drilling is recognized by
many as the first drilling method employed to dig wells
into the Earth for the purpose of reaching petroleum
deposits and water. This method is still in use in some
of the shallow wells in the Appalachian Basin, although
rotary drilling has taken over the bulk of modern drilling
activities.
The basic concept for cable tool drilling consists
of repeatedly dropping a heavy metal bit into the ground,
eventually breaking through rock and punching a hole
through to the desired depth. The bit, usually a blunt,
chisel shaped instrument, can vary with the type of
rock that is being drilled. Water is used in the well
hole to combine with all of the drill cuttings, and
is periodically bailed out of the well when this 'mud'
interferes with the effectiveness of the drill bit.
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| Early Percussion Rigs in Pennsylvania
- Late 1800's |
| Source: Office of
Fossil Energy, DOE |
Cable tool drilling has historically taken many forms.
In the early days of percussion drilling, equipment was
very crude compared to today's technology. The 'springpole'
technique, used in the early 1800's, consisted of a flexible
pole (usually a tree trunk) anchored at one end, and laying
across a fulcrum, much like a diving board. The flexible
pole, or springpole, would have a heavy bit attached at
the loose end. In order to get the bit to strike the ground,
workers would use their own body weight to bend the pole
towards the ground, allowing the bit to strike rock. The
tension in the pole would spring the bit free, should
it become stuck in the ground.
Much advancement has been made since these early percussion
rigs. In fact, it was from cable tool drilling that
one of the most important drilling advancements was
made. In 1806, David and Joseph Ruffner were using the
springpole technique to drill a well in West Virginia.
In order to prevent their well from collapsing, they
used hollow tree trunks to reinforce the sides of the
well, and to keep water and mud from entering the well
as they dug. They are credited as the first drillers
to use a casing in their well - an advancement that
made drilling much more efficient and easily accomplished.
It is believed by many that 'Colonel' Drake's 1856 well
achieved success due to the use of steel casing to reinforce
the well. Drake's well was drilled using steam powered
cable tool drilling methods. For more information on
well casings, and well completion, click here.
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| A Modern, Mobile Cable Tool
Drilling Rig |
| Source: Anadarko
Petroleum Corporation |
Innovations, such as the use of steam power in cable
tool drilling, greatly increased the efficiency and
range of percussion drilling. Conventional man-powered
cable tool rigs were generally used to drill wells 200ft
or less, while steam powered cable tool rigs, consisting
of the familiar derrick design, had an average drilling
depth of 400 to 500 feet. The deepest known well dug
with cable tool drilling was completed in 1953, when
the New York Natural Gas Corporation drilled a well
to a depth of 11,145 ft.
Despite the historical significance of cable tool drilling,
modern drilling activity has shifted mainly towards
rotary drilling methods. However, the foundation of
knowledge laid by years of cable tool drilling is, in
many cases, directly transferable to the practice of
rotary drilling.
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