Machining, Rotary Drilling Methods


Cable tool method has its beginnings 4000 years ago in China. it was the earliest drilling method
and  has  been  in  continuous  use  for  about  4000  years.  The  Chinese  used  tools  constructed of
bamboo  and  well  depths  of  3000  ft  are  recorded.  However,  wells  of  these  depth  often  took
.generations to complete

Cable tool rigs are sometimes called pounders, percussion, spudder or walking beam rigs. They
operate repeatedly lifting and dropping a heavy string of drilling tools into the boreholes. The drill
bits  breaks  or  crushes  consolidate  rock  into  small  fragments.  When  drilling  in  unconsolidated
.formations, the bit primarily loosens material

Water, either from the formation or added by the driller, mixes the crushed or loosened into a
slurry at the bottom of the borehole. An experienced cable tool driller feels when the accumulated
slurry has reached the point where it is reducing bi penetration to an unacceptably slow level. At
this point the slurry is removed from the borehole by a bailer. Once the slurry is removed, the bit
.is reinserted into the hole and drilling continues

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Often  a  cable-tool  rig  drills  only  one-tenth  as  fast  as  a  rotary  rig  in  comparable  formations
However,  the  cost  of  a  cable-tool  rig  is  substantially  less  than  a  rotary  rig.  This  tends  to
compensate  for  its slower  drilling  rate. A distinct  disadvantage  of  the  cable-tool method  is  that
when high-pressure oil and gas formations are encountered, there is no fluid in the hole to control
them. The result is frequent blowouts. When a blowout occurs, the oil and gas from the subsurface
formation rush to the surface and flow uncontrolled. A blowout may spray
the oil and gas several hundred feet into the air, and there is always great danger of a fire. Because
of its slow penetration rate and the hazard of blowouts, the cable-tool method is seldom used on
wells deeper than (3000 ft or 900 meters). Even on shallower wells, this method has largely been
.replaced by the rotary method


In Rotary drilling, a bit used to cut the formation is attached to steel pipe called drillpipe. The bit is
lowered to the bottom of the hole. The pipe is rotated form the surface by means of a rotary table
through which is inserted a square or hexagonal piece called a kelly. The Kelly (in the top drive
system the rotary table and Kelly are not exist), connected to the drillpipe at the surface, passes
through the rotary table. The turning action oft the rotary table is applied to the Kelly, which is turn
rotate,   the   drillpipe   and   the   drilling   bit.   Routine   drilling   consists   of   continuously  drilling
increments the length of one joint of pipe, making connections or adding to the drillstring another
single joint of pipe, generally 30 or 45 ft long. This drilling continues until the drill bit must be
changed. Changing the bit is also called making a trip

The idea of rotary drill bit is not new. Archaeological records show that as early as 3000 B.C., the
Egyptians  may  have  been  using  a  similar  technique.  Leonardo  Di  Vinci,  as  early as  1500
developed   a design for a rotary drilling mechanism that bears much resemblance to technology
used today. Despite these precursors, rotary drilling did not rise in use or popularity until the early

Although  rotary  drilling  techniques  had  been  patented  as  early  as  1833,  most  of  these  early
attempts  at  rotary  drilling  consisted of  little  more  than  a  mule,  attached  to  a  drilling  device
walking in a circle! It was the success of the effort of captain 'Anthony Lucas' and 'Patillo Higgins
in drilling their 1901 'Spindltop' well in Texas that catapulted rotary drilling to the forefront   of
petroleum drilling technology

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