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.

Impact

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.