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series of valves only under controlled conditions. But how do we
accomplish this? What are the basic techniques of oil well drilling?
Drilling a well is, in many ways, similar to drilling a hole
into a piece of wood using a rotating drill bit. The bit in this case is
much larger and is attached to the bottom of a hollow steel pipe
called a drill string (or drill pipe) that can be thousands of metres
long. The drill string is rotated by an engine at the surface [2].
Types of Drill Bits
There are a number of different types of drill bits. Steel
Tooth Rotary Bits are the most common types of drill bits, while
Insert Bits are steel tooth bit with tungsten carbide inserts.
Polycrystalline Diamond Compact Bits use synthetic diamonds
attached to the carbide inserts. Forty to 50 times stronger than steel
bits, Diamond Bits have industrial diamonds implanted in them to
drill extremely hard surfaces. Additionally, hybrids of these types
of drill bits exist to tackle specific drilling challenges.
Various drilling designs are also employed for different
results, including core bits, which gather formation cores for well
logging; mill bits, which help to remove cuttings from the well;
and fishtail bits, which enlarge the drill hole above the drill bit.
Different configurations work better on different
formations; so a number of different drill bits may be inserted and
used on one well. Additionally, drill bits have to be changed due to
wear and tear. Drilling engineers choose the drill bits according to
the type of formations encountered, whether or not directional
drilling is required, for specific temperatures, and if well logging is
being done.
When a drill bit has to be changed, the drill pipe (typically
in 30-feet increments) is hoisted out of the well, until the complete
drill string has been removed from the well. Once the drill bit has
been changed, the complete drill string is again lowered into the
well.
Rotary drilling uses two types of drill bits:
Roller-cone bits
Fixed-cutter bits
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