Editing Well drilling (section)

== Drill bits in mechanical drilling ==
{{Main|Drill bit (well)}}
The factors affecting drill bit selection include the type of geology and the capabilities of the rig. Due to the high number of wells that have been drilled, information from an adjacent well is most often used to make the appropriate selection. Two different types of drill bits exist: fixed cutter and [[Roller cone bit|roller cone]]. A fixed cutter bit is one where there are no moving parts, but drilling occurs due to shearing, scraping or abrasion of the rock. Fixed cutter bits can be either [[polycrystalline diamond]] compact (PDC) or grit hot-pressed inserts (GHI) or natural diamond.  Roller cone bits can be either tungsten carbide inserts (TCI) for harder formations or milled tooth (MT) for softer rock. The manufacturing process and composites used in each type of drill bit make them ideal for specific drilling situations. Additional enhancements can be made to any bit to increase the effectiveness for almost any drilling situation.

A major factor in drill bit selection is the type of formation to be drilled. The effectiveness of a drill bit varies by formation type. There are three types of formations: soft, medium and hard. A soft formation includes unconsolidated [[sand]]s, [[clay]]s, soft [[limestone]]s, red beds and [[shale]]. Medium formations include [[Dolomite (rock)|dolomite]]s, limestones, and hard shale. Hard formations include hard shale, calcites, mudstones, cherty lime stones and hard and abrasive formations.

Until 2006, market share was divided primarily among [[Hughes Christensen]], Security-DBS ([[Halliburton]] Drill Bits and Services), Smith Bits (a subsidiary of [[Schlumberger]]), and ReedHycalog (acquired by [[National Oilwell Varco]] in 2008).

By 2014, Ulterra (then a subsidiary of [[ESCO Group|ESCO Corp.]]) and Varel International (a subsidiary of Swedish engineering group [[Sandvik]]) had together gained nearly 30% of the U.S. bit market and eroded the historical dominance of the Smith, Halliburton, and Baker Hughes. By 2018, Schlumberger, which acquired Smith in 2010,<ref>{{Cite web|url=https://www.ogj.com/general-interest/companies/article/17285367/schlumberger-to-acquire-smith-international|title = StackPath|website = OGJ| date=22 February 2010 }}</ref> became dominant in international markets thanks to packaging drill bits with their other tools and services, while Ulterra (owned by private equity firms [[Blackstone Inc.|Blackstone]] Energy Partners and [[American Securities]]) continued a Stark growth trend, becoming the market share leader in drill bits in the US according to Spears Research <ref>{{Cite web|url=https://spearsresearch.com/reports|title = Reports|website = Spears Research}}</ref> and Kimberlite Research.<ref>{{Cite web |title=MARKET SHARE REPORTS |url=https://www.kimberliteresearch.com/marketsharereports |access-date=2023-01-23 |website=KIBERLITE RESEARCH }}</ref>

<gallery widths="190px" heights="180px">
Image:Drill bit tricone worn.jpg|Tricone bit for well drilling (medium worn-out)
Image:Hughesbit.gif |PDC bit for well drilling
Image:Drill bits-italy.JPG | Multiple Tricone Bits
Image:Drill bit 2-italy.JPG | Tricone Bit
Image:Drill bit 3-italy.JPG | Drill Bit
Image:Damaged drill bit-italy.JPG | Damaged Drill Bit, pieces missing on the left hand cone
Image:Mudlogging.JPG|[[Mud log]] in process, a common way to study the lithology when drilling oil wells
</gallery>
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 [http://www.glossary.oilfield.slb.com/Display.cfm?Term=PDC%20bit PDC Bits]

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