When to Use Down-The-Hole Drilling Tools？

Method of extracting a natural resource

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Well drilling is the process of drilling a hole in the ground for the extraction of a natural resource such as ground water, brine, natural gas, or petroleum, for the injection of a fluid from surface to a subsurface reservoir or for subsurface formations evaluation or monitoring. Drilling for the exploration of the nature of the material underground (for instance in search of metallic ore) is best described as borehole drilling.

The earliest wells were water wells, shallow pits dug by hand in regions where the water table approached the surface, usually with masonry or wooden 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."

History

Earliest Record

The earliest record of well drilling dates from 347 AD in China.[1] Petroleum was used in ancient China for "lighting, as a lubricant for cart axles and the bearings of water-powered drop hammers, as a source of carbon for inksticks, and as a medical remedy for sores on humans and mange in animals."[2] In ancient China, deep well drilling machines were in the forefront of brine well production by the 1st century BC. The ancient Chinese developed advanced sinking wells and were the first civilization to use a well-drilling machine and to use bamboo well casings to keep the holes open.[3][4]

Modern Era

In the modern era, the first roller cone patent was for the rotary rock bit and was issued to American businessman and inventor Howard Hughes Sr. in . It consisted of two interlocking cones. American businessman 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 two Hughes engineers, one of whom was Ralph Neuhaus, invented the tricone bit, which has three cones. The Hughes patent for the tricone bit lasted until , after which other companies made similar bits. However, Hughes still held 40% of the world's drill bit market in . The superior wear performance of polycrystalline diamond compact (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. 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 s, to modern day domain Finite Element codes for both the hydraulic and cutter placement software.

Drill bits in mechanical drilling

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. 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 sands, clays, soft limestones, red beds and shale. Medium formations include dolomites, limestones, and hard shale. Hard formations include hard shale, calcites, mudstones, cherty lime stones and hard and abrasive formations.

Until , 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 ).

By , Ulterra (then a subsidiary of 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 , Schlumberger, which acquired Smith in ,[5] became dominant in international markets thanks to packaging drill bits with their other tools and services, while Ulterra (owned by private equity firms 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 [6] and Kimberlite Research.[7]

• 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

• Mud log in process, a common way to study the lithology when drilling oil wells

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 & . See also PDC Bits

See also

Manual well drilling methods

References

Bibliography

• Australian Drilling Industry Training Committee Ltd (). Drilling: the manual of methods, applications and management (4th ed.). CRC Press. ISBN 978-1--242-3.

Pneumatic tools have been used to drill through rock since the 19th century. Back then, drillers would suspend themselves from a rope over a quarry face to put a drill from the right position and use small diameter holes. The process was inefficient and dangerous. It could send rocks flying and the accuracy was subject as much to luck as it was skill. After a while, drilling crews started carrying jackhammers on masts, beautiful boreholes were misaligned, the explosives that followed could be even more dangerous.

Thankfully, we live in the modern era, where down the hole (DTH) drilling has become one of the most efficient and safest methods since its invention in the mid s. Let&#;s explore what DTH drilling is, why it&#;s such a successful technique, and how it might be the perfect process for your drilling operation.

What is DTH Drilling and how does it work?

DTH drilling is a drilling method that&#;s used to crush rock by using a drilling hammer to hit hard rock repeatedly. DTH drills are pneumatic tools that provide power by driving compressed air into a piston inside the hammer. This type of drilling has made it much easier to drill wells quickly and efficiently by allowing contractors to switch from dirt boring to rock boring simply by adding a compressor and hammer to a drill bit.

Before DTH became a widespread drilling technique, contractors would desert a dirt bore project after encountering hard rock, leaving it to a different set of drillers to continue. With DTH drilling, the same drilling team can work through multiple materials.

At its most basic level, DTH drilling involves attaching a drilling hammer to the bottom of a drill string. Small, percussive hammers are placed above the drill bit, allowing drill pipes to exert a feed force necessary to rotate the hammer and bit together with fluid (usually air, water, or mud). This actuates the hammer and flushes the cutting. Drill pipes are then added to the drill string as the hole gets deeper.

Because the air-powered piston strikes the bit directly, energy is transferred down the hole, minimizing any lost energy. This allows drilling to greater depths.

DTH Drilling is most often used in the mining industry, where blast hole drilling is necessary for projects like water well drilling, building construction, and oil and gas processes.

Types of DTH Drilling Hammers

DTH hammers are fully fluid actuated. There are two primary parts: a valve which controls the flow and a piston that strikes the impact surface. The hammer body allows for stable, straight guidance of the bit. There are three types of hammers that depend on the actuation fluid:

• Air hammers

  &#; These are typically limited to shallow holes of less than 200 meters.

• Water hammers

  &#; These require a lost water flow of between 55 and 744 L/min depending on hammer size to actuate the hammer. These allow for better borehole control and greater depth than air hammers.

• Drilling mud hammers

  &#;  These are the newest types of drilling hammers, but they&#;ve shown a lot of promise so far. They&#;re able to drill on every existing drilling rig by using classical mud composition. They are fantastic choices for drilling into hard rock in geothermal projects due to their ability to drill extremely deep.

What are the benefits of DTH drilling?

DTH drilling is extremely effective, which is why we&#;ve been using it for the past seven decades. Some of the major benefits include:

• The use of air is extremely efficient. You don&#;t have to buy, source, treat, or transport it for use.

• DTH systems are simple to adapt to most directional drills, and it doesn&#;t take long.

• Very little rotational torque is required to cut rock that will allow the hammer to drill straight.

• The same drill can be used to drill through both dirt and rock.

• There isn&#;t as much wear and tear on a drill bit since the hammer is doing most of the work.

• There is a smaller carbon footprint than other techniques due to the use of less drilling mud and additives that need to be disposed of.

• It can be used more often in cities because it produces less noise and vibrations than alternatives. 

• Fewer amounts of additives and drilling fluids are required than for alternatives.

• The rate of penetrations is up to five times greater than rotary drilling techniques.

OK Bit has the DTH Drill Bits you need

If you&#;ve decided DTH is the right drilling method for your project, OK Bit can supply you with whatever bits you need to get the job done. If you aren&#;t sure if DTH drilling is the best choice or if you need help choosing a specific hammer or bit, our expert staff will be happy to help. Contact us today.

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