Well drilling

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Tricone rock bit

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 wells were water wells, 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.

Managed Pressure Drilling (MPD) is defined by the International Association of Drilling Contractors (IADC) as “an adaptive drilling process used to more precisely control the annular pressure profile throughout the wellbore." The objectives of MPD are “to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly."

Drill bits in mechanical drilling

Depending on the soil condition, different drill bits are used. There are three main categories: soft, medium and hard formation bits. Soft formation rock bits are used in unconsolidated sands, clays, soft limestones, red beds and shale, etc. Medium formation bits are used in calcites, dolomites, limestones, and hard shale. 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:

1. a polycrystalline diamond compact hammer bit (PDC 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.
2. 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.

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.

In 1933 two Hughes engineers, one of whom was Ralph Neuhaus, invented the tricone bit, which has three wheels. 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. The superior wear performance of PDC bits gradually eroded the dominance of roller cone bits and early in this century PDC drill bit revenues overtook those of roller cone bits.

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 2008 market shares were roughly 30% each for Hughes Christensen and Smith Bits, 20% for REEDHycalog with Security-DBS, and smaller companies such as Viper Bit VIPERBIT, Encore PDC Bits, DOWDCO, Varel, TSK, PDC Logis, Focusrocbit, Sam(AOE), Walker-Mcdonald et al., Ulterra,and Lone Star Drill Bits making up the rest.

sumber :

http://en.wikipedia.org/wiki/Well_drilling