22 September 2009

Oil-well drill bit

The invention: Arotary cone drill bit that enabled oil-well drillers
to penetrate hard rock formations.
The people behind the invention:
Howard R. Hughes (1869-1924), an American lawyer, drilling
engineer, and inventor
Walter B. Sharp (1860-1912), an American drilling engineer,
inventor, and partner to Hughes
Digging for Oil
Arotary drill rig of the 1990’s is basically unchanged in its essential
components from its earlier versions of the 1900’s. A drill bit is
attached to a line of hollow drill pipe. The latter passes through a
hole on a rotary table, which acts essentially as a horizontal gear
wheel and is driven by an engine. As the rotary table turns, so do the
pipe and drill bit.
During drilling operations, mud-laden water is pumped under
high pressure down the sides of the drill pipe and jets out with great
force through the small holes in the rotary drill bit against the bottom
of the borehole. This fluid then returns outside the drill pipe to
the surface, carrying with it rock material cuttings from below. Circulated
rock cuttings and fluids are regularly examined at the surface
to determine the precise type and age of rock formation and for
signs of oil and gas.
Akey part of the total rotary drilling system is the drill bit, which
has sharp cutting edges that make direct contact with the geologic
formations to be drilled. The first bits used in rotary drilling were
paddlelike “fishtail” bits, fairly successful for softer formations, and
tubular coring bits for harder surfaces. In 1893, M. C. Baker and C. E.
Baker brought a rotary water-well drill rig to Corsicana, Texas, for
modification to deeper oil drilling. This rig led to the discovery of
the large Corsicana-Powell oil field in Navarro County, Texas. This
success also motivated its operators, the American Well and Prospecting
Company, to begin the first large-scale manufacture of rotary
drilling rigs for commercial sale.In the earliest rotary drilling for oil, short fishtail bits were the
tool of choice, insofar as they were at that time the best at being able
to bore through a wide range of geologic strata without needing frequent
replacement. Even so, in the course of any given oil well,
many bits were required typically in coastal drilling in the Gulf of
Mexico. Especially when encountering locally harder rock units
such as limestone, dolomite, or gravel beds, fishtail bits would typically
either curl backward or break off in the hole, requiring the
time-consuming work of pulling out all drill pipe and “fishing” to
retrieve fragments and clear the hole.
Because of the frequent bit wear and damage, numerous small
blacksmith shops established themselves near drill rigs, dressing or
sharpening bits with a hand forge and hammer. Each bit-forging
shop had its own particular way of shaping bits, producing a wide
variety of designs. Nonstandard bit designs were frequently modified
further as experiments to meet the specific requests of local drillers
encountering specific drilling difficulties in given rock layers.
Speeding the Process
In 1907 and 1908, patents were obtained in New Jersey and
Texas for steel, cone-shaped drill bits incorporating a roller-type
coring device with many serrated teeth. Later in 1908, both patents
were bought by lawyer Howard R. Hughes.
Although comparatively weak rocks such as sands, clays, and
soft shales could be drilled rapidly (at rates exceeding 30 meters per
hour), in harder shales, lime-dolostones, and gravels, drill rates of 1
meter per hour or less were not uncommon. Conventional drill bits
of the time had average operating lives of three to twelve hours.
Economic drilling mandated increases in both bit life and drilling
rate. Directly motivated by his petroleum prospecting interests,
Hughes and his partner, Walter B. Sharp, undertook what were
probably the first recorded systematic studies of drill bit performance
while matched against specific rock layers.
Although many improvements in detail and materials have been
made to the Hughes cone bit since its inception in 1908, its basic design
is still used in rotary drilling. One of Hughes’s major innovations
was the much larger size of the cutters, symmetrically distributed as a large number of small individual teeth on the outer face of
two or more cantilevered bearing pins. In addition, “hard facing”
was employed to drill bit teeth to increase usable life. Hard facing is
a metallurgical process basically consisting of wedding a thin layer
of a hard metal or alloy of special composition to a metal surface to
increase its resistance to abrasion and heat. A less noticeable but
equally essential innovation, not included in other drill bit patents,was an ingeniously designed gauge surface that provided strong
uniform support for all the drill teeth. The force-fed oil lubrication
was another new feature included in Hughes’s patent and prototypes,
reducing the power necessary to rotate the bit by 50 percent
over that of prior mud or water lubricant designs.
In 1925, the first superhard facing was used on cone drill bits. In
addition, the first so-called self-cleaning rock bits appeared from
Hughes, with significant advances in roller bearings and bit tooth
shape translating into increased drilling efficiency. The much larger
teeth were more adaptable to drilling in a wider variety of geological
formations than earlier models. In 1928, tungsten carbide was
introduced as an additional bit facing hardener by Hughes metallurgists.
This, together with other improvements, resulted in the
Hughes ACME tooth form, which has been in almost continuous
use since 1926.
Many other drilling support technologies, such as drilling mud,
mud circulation pumps, blowout detectors and preventers, and
pipe properties and connectors have enabled rotary drilling rigs to
reach new depths (exceeding 5 kilometers in 1990). The successful
experiments by Hughes in 1908 were critical initiators of these developments.


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