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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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