Well drilling

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Drilling rig head

Well drilling is the process of drilling a hole in the ground for the extraction of a natural resource such as ground water, natural gas, or petroleum. Drilling for the exploration of the nature of the material underground (for instance in search of metallic ore) is best described as borehole drilling, or 'drilling'.

The earliest water wells were probably shallow pits dug by hand in regions where the water table approached the surface, possibly with masonry walls lining the interior to prevent collapse. Modern drilling techniques utilize long drill shafts, producing holes much narrower and deeper than could be produced by digging.

Well drilling can be done either manually or mechanically and the nature of required equipment varies from extremely simple and cheap to very sophisticated.

[edit] Drill bits in mechanical drilling

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Depending on the soil condition different drill bits are utilised. There are three main categories: soft, medium and hard formation bits. Soft formation rock bits are used in unconsolidated sands, clays, soft lime stones, red beds and shale, etc. Medium formation bits are used in calcites, dolomites, lime stones, and hard shale, while hard formation bits are used in hard shale, calcites, mudstones, cherty lime stones and hard and abrasive formations.

Historically there were two types of drill bits used in oil or natural gas drilling rigs, a drag bit, and a rock bit:

a pdc bithammer bit is used for soft rocks, like sand and clay. The drill string is rotated along with pneumatic pressure, and nibs on the bit shear the rock.
a deep hole (also called a roller bit) consists of teeth on wheels which turn as the drill string is rotated. These teeth apply a crushing pressure to the rock, breaking it up into small pieces.

(However a new type of environmentally friendly type of drilling in soft ground called sonic is used) The original patent for the rotary rock bit was issued to Howard Hughes Sr. for his dual cone roller bit in 1909. It consisted of two interlocking wheels. Walter Benona Sharp worked very closely with Hughes in developing the Rock Bit. The success of this bit led to the founding of the Sharp-Hughes Tool Company.

a shallow Drag Bit consists of blades with tungsten carbide, made by Lone Star Drill Bits

In 1933 two Hughes engineers invented the tricone bit. This bit has three wheels and is still the dominant bit in the market today. The Hughes patent for the tricone bit lasted until 1951, after which time other companies started making similar bits. However, Hughes’ market share was still 40% of the world's drill bit market in 2000.

In today's modern industry the two main types of drill bits are now classed as PDC (polycrystalline Diamond Compact) and Roller Cone; although the tri-cone dominates, bi-cone and mono cone bits do exist. Natural and synthetic diamonds are used in coring bits, as well as for very hard rock drilling with mud motors and turbines. Drag bit type bits are used for mining and construction and also for oil and gas workover wells.

The technology of both bit types has advanced significantly to provide improved durability and rate of penetration of the rock. This has been driven by the economics of the industry, and by the change from the empirical approach of Hughes in the 1930s, to today's time domain Finite Element codes for both the hydraulic and cutter placement software.

In 2005 market shares were roughly 20% each for Hughes Christensen and Smith Bits, ReedHycalog with 37%, and the remainder of the market with Security-DBS, and smaller companies such as [1] DOWDCO, Varel, TSK,Focusrocbit, Sam(AOE), Walker-Mcdonald et al, Ulterra, PDC Logic, and Lone Star Drill Bits .

Tricone bit for well drilling (medium worn-out)	PDC bit for well drilling	Multiple Tricone Bits	Tricone Bit
Drill Bit	Damaged Drill Bit, pieces missing on the left hand cone

Evaluation of the dull bit grading is done by a uniform system promoted by the International Association of Drilling Contractors (IADC). See Society of Petroleum Engineers / IADC Papers SPE 23938 & 23940. See also PDC Bits