In 1900, while drilling an oil well in Spindletop,
Texas, workers ran a herd of cattle through a pit
filled with water. The mud that resulted, a viscous,
muddy slurry of water and clay, was pumped into the
borehole. Drilling fluids are still called mud, but
engineers no longer rely only on water and clay.
Instead, they carefully design compounds and mixtures
to meet specific needs under various drilling conditions.
Modern drilling fluids are truly the lifeblood of
the well. Today's deep wells could not exist without
them.
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Drilling fluids are referred to
as
mud. You can see why. |
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Rotary drilling from an offshore rig. |
Long ago, people were generally drilling for water, not for
oil. In fact, they were annoyed when they accidentally found
oil since it contaminated the water! Early wells were drilled
for water to be used for drinking, washing, irrigation and
for brine, which is used as a source of salt. It was only
in the 19th century that drilling for oil became widespread
as industrialization increased the need for petroleum products.
The earliest records of well drilling date back to the third
century BC in China. The technique - cable tool drilling -
involved dropping a heavy metal drilling tool and removing
the pulverized rock with a tubular container. The Chinese
were relatively advanced in this art and are credited with
the first intentional use of fluids in the process of drilling.
In this case the fluid was water. It softened the rock making
penetration easier and aided in the removal of the pieces
of pulverized rock known as cuttings. ( It is important to
remove the cuttings from the borehole so the drill bit is
free to dig further.)
In 1833 a French engineer named Flauville was watching a
cable tool drilling operation in which the drilling apparatus
struck water. He realized that the gushing water was very
effective in lifting the cuttings out of the well. The principle
of using moving fluid to remove cuttings from the well bore
was established. He conceived of an assembly in which water
would be pumped down the inside of a drilling rod and carry
cuttings with it as it returned to the surface in the space
between the drilling rod and the wall of the well bore. This
procedure remains standard today.
Rotary drilling has largely replaced cable tool drilling.
With this technique the drill bit is at the tip of a rotating
pipe. The process is similar to that used with a hand-held
electric drill or auger that you might use to drill into
a piece of wood. But instead of drilling a few inches or
centimeters into wood, modern oil wells may reach thousands
of feet or meters into the ground. When drilling wood the
cuttings are cleared out of the hole via spiral grooves
along the shaft. This works for a shallow hole, but not
a deep well. Instead, the cuttings are carried up to the
surface along with the circulating mud.
As wells get deeper, drilling fluids have taken
on increased importance, serving a number of purposes and
solving a variety of problems that vary greatly from place
to place.
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