A
drilling rig is a machine which creates holes (usually called
boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
s) and/or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill
water wellA water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a vertical turbine pump, a handpump or a mechanical pump...
s,
oil wellAn oil well is a general term for any boring through the earth's surface that is designed to find and produce petroleum oil hydrocarbons. Usually some natural gas is produced along with the oil. A well designed to produce mainly or only gas may be termed a gas well.-History:The earliest known oil...
s, or
natural gasNatural gas is a gas consisting primarily of methane. It is found associated with fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills...
extraction wells or they can be small enough to be moved manually by one person. They sample sub-surface mineral deposits, test rock, soil and groundwater physical properties, and also can be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures (such as
oil platformAn offshore platform, often referred to as an oil platform or an oil rig, is a large structure used to house workers and machinery needed to drill wells in the ocean bed, extract oil and/or natural gas, process the produced fluids, and ship or pipe them to shore...
s, commonly called 'offshore oil rigs' even if they don't contain a drilling rig). The term "rig" therefore generally refers to the complex of equipment that is used to penetrate the surface of the earth's
crustCrust may refer to:Geology and soil science:*Crust , the outer solid layer of a planet*Continental crust*Oceanic crust*Soil crust*the dough or pastry shell of pies, pizzas, etc.Music:*Crust punk, a hardcore punk / extreme metal fusion...
.
Drilling rigs can be:
- Small and portable, such as those used in mineral exploration drilling, water wells and environmental investigations.
- Huge, capable of drilling through thousands of meters of the Earth
Earth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's crustCrust may refer to:Geology and soil science:*Crust , the outer solid layer of a planet*Continental crust*Oceanic crust*Soil crust*the dough or pastry shell of pies, pizzas, etc.Music:*Crust punk, a hardcore punk / extreme metal fusion...
. Large "mud pumpA Mud pump is a reciprocating piston/plunger device designed to circulate drilling fluid under high pressure down the drill string and back up the annulus....
s" circulate drilling mud (slurry) through the drill bitDrill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....
and up the casing annulus, for cooling and removing the "cuttings" while a well is drilled. Hoists in the rig can lift hundreds of tonThe term ton or tonne generally refers to a unit of mass. However, there exists more than one measure of mass that are named "ton", so one has to be specific when using the term. While they do vary considerably, a ton is generally one of the heaviest units of mass referred to in colloquial speech...
s of pipeDrill pipe is hollow, thick-walled, steel tubing that is used on drilling rigs to facilitate the drilling of a wellbore and comes in a variety of sizes, strengths and weights but are typically 30 to 33 feet in length...
. Other equipment can force acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
or sand into reservoirs to facilitate extraction of the oil or natural gas; and in remote locations there can be permanent living accommodation and catering for crews (which may be more than a hundred). Marine rigs may operate many hundreds of miles or kilometres distant from the supply base with infrequent crew rotation.
Petroleum drilling industry
OilPetroleum or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.The term "petroleum" was first used in the treatise De Natura Fossilium, published in...
and
Natural GasNatural gas is a gas consisting primarily of methane. It is found associated with fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills...
drilling rigs can be used not only to identify geologic reservoirs but also to create holes that allow the extraction of
oilPetroleum or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.The term "petroleum" was first used in the treatise De Natura Fossilium, published in...
or
natural gasNatural gas is a gas consisting primarily of methane. It is found associated with fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills...
from those reservoirs. Primarily in onshore oil and gas fields once a well has been drilled, the drilling rig will be moved off of the well and a service rig (a smaller rig) that is purpose-built for completions will be moved on to the well to get the well on line. This frees up the drilling rig to drill another hole and streamlines the operation as well as allowing for specialization of certain services, i.e., completions vs. drilling.
History
Until
internal combustion engineThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable...
s came in the late 19th century, the main method for drilling rock was muscle power of man or animal. Rods were turned by hand, using clamps attached to the rod. The rope and drop method invented in
ZigongZigong , ancient name Ziliujing and Gongjing, is a prefecture-level city and the third largest city in Sichuan Province, in southwest China.-Geography:...
,
ChinaChina is a cultural region, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
used a steel rod or piston raised and dropped vertically via a rope. Mechanised versions of this persisted until about 1970, using a cam to rapidly raise and drop what, by then, was a steel cable.
In the 1970s, outside of the oil and gas industry, roller bits using mud circulation were replaced by the first efficient pneumatic reciprocating piston Reverse Circulation
RCRC, rc or R/C can mean:*Sanskrit ṛc "verse"In sport:*Roberto Carlos, brazilian footballer.In computing:* a filename extension for configuration files in UNIX-like environments, abbreviating "run commands"...
drills, and became essentially obsolete for most shallow drilling, and are now only used in certain situations where rocks preclude other methods. RC drilling proved much faster and more efficient, and continues to improve with better
metallurgyMetallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
, deriving harder, more durable bits, and compressors delivering higher air pressures at higher volumes, enabling deeper and faster penetration. Diamond drilling has remained essentially unchanged since its inception.
Mobile drilling rigs
In early oil exploration, drilling rigs were semi-permanent in nature and the derricks were often built on site and left in place after the completion of the well. In more recent times drilling rigs are expensive custom-built machines that can be moved from well to well. Some light duty drilling rigs are like a mobile crane and are more usually used to drill water wells. Larger land rigs must be broken apart into sections and loads to move to a new place, a process which can often take weeks.
Small mobile drilling rigs are also used to drill or bore piles. Rigs can range from 100
tonThe term ton or tonne generally refers to a unit of mass. However, there exists more than one measure of mass that are named "ton", so one has to be specific when using the term. While they do vary considerably, a ton is generally one of the heaviest units of mass referred to in colloquial speech...
continuous flight auger (CFA) rigs to small air powered rigs used to drill holes in quarries, etc. These rigs use the same technology and equipment as the oil drilling rigs, just on a smaller scale.
The drilling mechanisms outlined below differ mechanically in terms of the machinery used, but also in terms of the method by which drill cuttings are removed from the cutting face of the drill and returned to surface.
Drilling rig classification
There are many types and designs of drilling rigs, with many drilling rigs capable of switching or combining different drilling technologies as needed. Drilling rigs can be described using any of the following attributes:
by power used
- mechanical - the rig uses torque converters, clutches, and transmissions powered by its own engines, often diesel
- electric - the major items of machinery are driven by electric motors, usually with power generated on-site using internal combustion engines
- hydraulic - the rig primarily uses hydraulic power
- pneumatic - the rig is primarily powered by pressurized air
- steam - the rig uses steam-powered engines and pumps (obsolescent after middle of 20th Century)
by pipe used
- cable - a cable is used to raise and drop the drill bit
- conventional - uses metal or plastic drill pipe of varying types
- coil tubing - uses a giant coil of tube and a downhole drilling motor
vertical drilling machine $ horizontal drilling machine.
by height
- single - can drill only single drill pipes. The presence or absence of vertical pipe racking "fingers" varies from rig to rig.
- double - can hold a stand of pipe in the derrick consisting of two connected drill pipes, called a "double stand".
- triple - can hold a stand of pipe in the derrick consisting of three connected drill pipes, called a "triple stand".
by method of rotation or drilling method
- no rotation includes direct push rigs and most service rigs
- rotary table - rotation is achieved by turning a square or hexagonal pipe (the kelly) at drill floor level.
- top drive
A top drive is a mechanical device on a drilling rig that provides clockwise rotational force to the drill string to facilitate the process of drilling a borehole. It is an alternative to rotary table. It is located at the swivel place and allows a vertical movement up and down the derrick.-...
- rotation and circulation is done at the top of the drillstring, on a motor that moves in a track along the derrick.
- sonic - uses primarily vibratory energy to advance the drill string
- hammer - uses rotation and percussive force (see Down-The-Hole Drill
A Down-The-Hole Drill is either a pneumatic or hydraulic powered rock or ground drill placed on the bottom of a drill string.DTH is short for “down-the-hole”. Since the DTH method was originally developed to drill large-diameter holes downwards in surface-drilling applications, its name originated...
)
by position of derrick
- conventional - derrick
A derrick is a lifting device composed of one mast or pole which is hinged freely at the bottom. It is controlled by lines powered by some means such as man-hauling or motors, so that the pole can move in all four directions. A line runs up it and over its top with a hook on the end, like with a...
is vertical
- slant - derrick
A derrick is a lifting device composed of one mast or pole which is hinged freely at the bottom. It is controlled by lines powered by some means such as man-hauling or motors, so that the pole can move in all four directions. A line runs up it and over its top with a hook on the end, like with a...
is slanted at a 45 degree angle to facilitate horizontal drilling
Drill types
There are a variety of drill mechanisms which can be used to sink a
boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
into the ground. Each has its advantages and disadvantages, in terms of the depth to which it can drill, the type of sample returned, the costs involved and penetration rates achieved. There are two basic types of drills: drills which produce rock chips, and drills which produce
core sampleA core sample is a cylindrical section of a naturally occurring medium consistent enough to hold a layered structure. Most cores are obtained by drilling into the medium, for example sediment or rock, with a hollow steel tube called a corer. The hole made for the core sample is called a core hole....
s.
Auger drilling
Auger drilling is done with a
helicalA helix is a special kind of space curve, i.e. a smooth curve in three-space. As a mental image of a helix one may take the spring...
screw which is driven into the ground with rotation; the earth is lifted up the borehole by the blade of the screw. Hollow stem Auger drilling is used for environmental drilling, geotechnical drilling,
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
engineeringEngineering is the discipline, art and profession of acquiring and applying technical, scientific and mathematical knowledge to design and implement materials, structures, machines, devices, systems, and processes that safely realize a desired objective or inventions.The American Engineers' Council...
and
geochemistryThe field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and their...
reconnaissance work in exploration for
mineralA mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific...
deposits. Solid flight augers/bucket augers are used in construction drilling. In some cases,
mineMining is the extraction of valuable minerals or other geological materials from the earth, usually from an ore body, vein or seam. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash...
shafts are dug with auger drills. Small augers can be mounted on the back of a utility truck, with large augers used for sinking piles for bridge foundations.
Auger drilling is restricted to generally soft unconsolidated material or weak weathered
rockIn geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
. It is cheap and fast.
Percussion rotary air blast drilling (RAB)
RAB drilling is used most frequently in the mineral exploration industry. (This tool is also known as a
Down-The-Hole DrillA Down-The-Hole Drill is either a pneumatic or hydraulic powered rock or ground drill placed on the bottom of a drill string.DTH is short for “down-the-hole”. Since the DTH method was originally developed to drill large-diameter holes downwards in surface-drilling applications, its name originated...
.) The drill uses a pneumatic reciprocating piston-driven 'hammer' to energetically drive a heavy drill bit into the rock. The drill bit is hollow, solid steel and has ~20 mm thick tungsten rods protruding from the steel matrix as 'buttons'. The tungsten buttons are the cutting face of the bit.
The cuttings are blown up the outside of the rods and collected at surface. Air or a combination of air and
foamThe most general definition of foam is a substance that is formed by trapping many gas bubbles in a liquid or solid. It can also refer to anything that is analogous to such a phenomenon, such as quantum foam. Often the term is used in reference to polyurethane foam , XPS foam, Polystyrene, or many...
lift the cuttings.
RAB drilling is used primarily for
mineralA mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific...
explorationProspecting is the physical search for minerals, fossils, precious metals or mineral specimens, and is also known as fossicking.Prospecting is a small-scale form of mineral exploration which latter is an organised, large scale effort undertaken by mineral resource companies to find commercially...
, water bore drilling and blast-hole drilling in mines, as well as for other applications such as engineering, etc. RAB produces lower quality samples because the cuttings are blown up the outside of the rods and can be contaminated from contact with other rocks.
RAB drilling rarely achieves more than 150 metres depth as encountering water rapidly clogs the outside of the hole with debris, precluding removal of drill cuttings from the hole.
This can be counteracted, however, with the use of 'stabilisers' also known as 'reamers', which are large cylindrical pieces of steel attached to the drill string, and made to perfectly fit the size of the hole being drilled. These have sets of rollers on the side, usually with tungsten buttons, that constantly break down cuttings being pushed upwards.
The use of multiple high-powered air compressors, which push 900-1150cfm of air at 300-350psi down the hole also ensures drilling of a deeper hole up to ~1250m due to higher air pressure which pushes all rock cuttings and any water to the surface. This, of course, is all dependent on the density and weight of the rock being drilled, and on how worn the drill bit is.
Air core drilling
Air core drilling and related methods use hardened
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
or
tungstenTungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A steel-gray metal, tungsten is found in several ores, including wolframite and scheelite...
blades to bore a hole into unconsolidated ground. The drill bit has three blades arranged around the bit head, which cut the unconsolidated ground. The rods are hollow and contain an inner tube which sits inside the hollow outer rod barrel. The drill cuttings are removed by injection of compressed air into the hole via the annular area between the innertube and the drill rod. The cuttings are then blown back to surface up the inner tube where they pass through the sample separating system and are collected if needed. Drilling continues with the addition of rods to the top of the drill string. Air core drilling can occasionally produce small chunks of cored rock.
This method of drilling is used to drill the weathered
regolithRegolith is a layer of loose, heterogeneous material covering solid rock. The term is a combination of two Greek words: Rhegos , which means blanket, and Lithos , which means rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids,...
, as the drill rig and steel or tungsten blades cannot penetrate fresh rock. Where possible, air core drilling is preferred over RAB drilling as it provides a more representative sample. Air core drilling can achieve depths approaching 300 meters in good conditions. As the cuttings are removed inside the rods and are less prone to contamination compared to conventional drilling where the cuttings pass to the surface via outside return between the outside of the drill rob and the walls of the hole. This method is more costly and slower than RAB.
Cable tool drilling
Cable tool rigs are a traditional way of drilling
water wellA water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a vertical turbine pump, a handpump or a mechanical pump...
s internationally and in the United States. The majority of large diameter water supply wells, especially deep wells completed in
bedrockIn stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
aquifers, were completed using this drilling method. Although this drilling method has largely been supplanted in recent years by other, faster drilling techniques, it is still the most practicable drilling method for large diameter, deep bedrock wells, and in widespread use for small rural water supply wells. The impact of the drill bit fractures the rock and in many shale rock situations increases the water flow into a well over rotary.
Also known as ballistic well drilling and sometimes called "spudders", these rigs raise and drop a drill string with a heavy
carbideIn chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by chemical bonding type as follows: salt-like, covalent compounds, interstitial compounds, and "intermediate" transition metal carbides...
tipped drilling bit that chisels through the rock by finely pulverizing the subsurface materials. The drill string is comprised of the upper drill rods, a set of "jars" (inter-locking "sliders" that help transmit additional energy to the drill bit and assist in removing the bit if it is stuck) and the
drill bitDrill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....
. During the drilling process, the drill string is periodically removed from the borehole and a
bailerA bailer is a device used for removing water which has entered a boat. In the simplest case it is simply a container which can be filled manually and tipped over the side....
is lowered to collect the drill cuttings (rock fragments, soil, etc.). The bailer is a bucket-like tool with a trapdoor in the base. If the borehole is dry, water is added so that the drill cuttings will flow into the bailer. When lifted, the bailer closes and the cuttings are then raised and removed. Since the drill string must be raised and lowered to advance the boring, casing (larger diameter outer piping) is typically used to hold back upper soil materials and stabilize the borehole.
Cable tool rigs are simpler and cheaper than similarly sized rotary rigs, although loud and very slow to operate. The world record cable tool well was drilled in New York to a depth of almost 12,000 feet. The common Bucyrus Erie 22 can drill down to about 1,100 feet. Since cable tool drilling does not use air to eject the drilling chips like a rotary, instead using a cable strung bailer, technically there is no limitation on depth.
Reverse circulation (RC) drilling
RC drilling is similar to air core drilling, in that the drill cuttings are returned to surface inside the rods. The drilling mechanism is a pneumatic reciprocating piston known as a
hammer driving a tungsten-steel drill bit. RC drilling utilises much larger rigs and machinery and depths of up to 500 metres are routinely achieved. RC drilling ideally produces dry rock chips, as large air
compressorsA gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
dry the rock out ahead of the advancing drill bit. RC drilling is slower and costlier but achieves better penetration than RAB or air core drilling; it is cheaper than diamond coring and is thus preferred for most
mineral explorationMineral exploration is the process undertaken by companies, partnerships or corporations in the endeavour of finding ore to mine...
work.
Reverse circulation is achieved by blowing air down the rods, the differential pressure creating
air liftAn airlift pump is a simple pump which is powered by compressed air.-Principle:The only energy required is air.This air is usually compressed by a compressor or a blower....
of the water and cuttings up the
inner tube which is inside each rod. It reaches the
bell at the top of the hole, then moves through a sample hose which is attached to the top of the
cyclone. The drill cuttings travel around the inside of the cyclone until they fall through an opening at the bottom and are collected in a sample bag.
The most commonly used RC drill bits are 5-8 inches (12.7–20.32 cm) in diameter and have round metal 'buttons' that protrude from the bit, which are required to drill through
shaleShale is a fine-grained, clastic sedimentary rock composed of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable...
and abrasive rock. As the buttons wear down, drilling becomes slower and the rod string can potentially become bogged in the hole. This is a problem as trying to recover the rods may take hours and in some cases weeks. The rods and drill bits themselves are very expensive, often resulting in great cost to drilling companies when equipment is lost down the bore hole. Most companies will regularly 'sharpen' the buttons on their drill bits in order to prevent this, and to speed up progress. Usually, when something is lost (breaks off) in the hole, it is not the drill string, but rather from the bit, hammer, or stabiliser to the bottom of the drill string (bit). This is usually caused by a blunt bit getting stuck in fresh rock, over-stressed metal, or a fresh drill bit getting stuck in a part of the hole that is too small, owing to having used a bit that has worn to smaller than the desired hole diameter.
Although RC drilling is air-powered, water is also used, to reduce dust, keep the drill bit cool, and assist in pushing cutting back upwards, but also when
collaring a new hole. A
mud called
liqui-pol is mixed with water and pumped into the rod string, down the hole. This helps to bring up the sample to the surface by making the sand stick together. Occasionally, 'super-foam' (AKA 'quik-foam') is also used, to bring all the very fine cuttings to the surface, and to clean the hole. When the drill reaches hard rock, a
collar is put down the hole around the rods which is normally PVC piping. Occasionally the collar may be made from metal casing. Collaring a hole is needed to stop the walls from caving in and bogging the rod string at the top of the hole. Collars may be up to 60 metres deep, depending on the ground, although if drilling through hard rock a collar may not be necessary.
Reverse circulation rig setups usually consist of a support vehicle, an auxiliary vehicle, as well as the rig itself. The support vehicle, normally a truck, holds diesel and water tanks for resupplying the rig. It also holds other supplies needed for maintenance on the rig. The auxiliary is a vehicle, carrying an auxiliary engine and a booster engine. These engines are connected to the rig by high pressure air hoses. Although RC rigs have their own booster and
compressorThe air compressors seen by the public are used in 5 main applications:*To supply a high-pressure clean air to fill gas cylinders*To supply a moderate-pressure clean air to supply air to a submerged surface supplied diver...
to generate air pressure, extra power is needed which usually isn't supplied by the rig due to lack of space for these large engines. Instead, the engines are mounted on the auxiliary vehicle. Compressors on an RC rig have an output of around 1000
cfmCubic feet per minute is a non-SI unit of measurement of the flow of a gas or liquid that indicates how much volume in cubic feet pass by a stationary point in one minute...
at 500 psi (500 L·s
−1 at 3.4 MPa). Alternatively, stand-alone air compressors which have an output of 900-1150cfm at 300-350 psi each are used in sets of 2, 3, or 4, which are all routed to the rig through a multi-valve manifold.
Diamond core drilling
Diamond core drilling (
Exploration diamond drillingExploration diamond drilling is used in the mining industry to probe the contents of known ore deposits and potential sites. By withdrawing a small diameter core of rock from the orebody, geologists can analyze the core by chemical assay and conduct petrologic and mineralogic studies of the...
) utilises an annular diamond-impregnated drill bit attached to the end of hollow drill rods to cut a cylindrical core of solid rock. The diamonds used are fine to microfine industrial grade
diamondIn mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is the second most stable form of carbon, after graphite; however, the conversion rate from diamond to graphite is...
s. They are set within a matrix of varying hardness, from
brassBrass is any alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties. In comparison, bronze is principally an alloy of copper and tin. Despite this distinction, some types of brasses are called bronzes. Brass is a...
to high-grade steel. Matrix hardness, diamond size and dosing can be varied according to the rock which must be cut. Holes within the bit allow water to be delivered to the cutting face. This provides three essential functions; lubrication, cooling, and removal of drill cuttings from the hole.
Diamond drilling is much slower than reverse circulation (RC) drilling due to the hardness of the ground being drilled. Drilling of 1200 to 1800 metres is common and at these depths, ground is mainly hard rock. Diamond rigs need to drill slowly to lengthen the life of drill bits and rods, which are very expensive.
Core sampleA core sample is a cylindrical section of a naturally occurring medium consistent enough to hold a layered structure. Most cores are obtained by drilling into the medium, for example sediment or rock, with a hollow steel tube called a corer. The hole made for the core sample is called a core hole....
s are retrieved via the use of a
lifter tube, a hollow tube lowered inside the rod string by a winch cable until it stops inside the core barrel. As the core is drilled, the core lifter slides over the core as it is cut. An
overshot attached to the end of the winch cable is lowered inside the rod string and locks on to the
backend, located on the top end of the lifter tube. The winch is retracted, pulling the lifter tube to the surface. The core does not drop out the inside of the lifter tube when lifted because a "core lifter spring," located at the bottom of the tube allows the core to move inside the tube but not fall out.
Once a rod is removed from the hole, the core sample is then removed from the rod and catalogued. The Driller's offsider screws the rod apart using tube clamps, then each part of the rod is taken and the core is shaken out into core trays. The core is washed, measured and broken into smaller pieces using a hammer to make it fit into the sample trays. Once catalogued, the core trays are retrieved by geologists who then analyse the core and determine if the drill site is a good location to expand future mining operations.
Diamond rigs can also be part of a multi-combination rig. Multi-combination rigs are a dual setup rig capable of operating in either a reverse circulation (RC) and diamond drilling role (though not at the same time). This is a common scenario where exploration drilling is being performed in a very isolated location. The rig is first set up to drill as an RC rig and once the desired metres are drilled, the rig is set up for diamond drilling. This way the deeper metres of the hole can be drilled without moving the rig and waiting for a diamond rig to set up on the
padThe Drill Floor is the heart of any drilling rig and is also known as the pad. This is the area where the drill string begins its trip into the earth. It is traditionally where joints of pipe are assembled, as well as the BHA , drilling bit, and various other tools. This is the primary work...
.
Direct Push Rigs
Direct push technology includes several types of drilling rigs and drilling equipment which advances a drill string by pushing or hammering without rotating the drill string. While this does not meet the proper definition of drilling, it does achieve the same result - a
boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
. Direct push rigs include both
cone penetration testThe cone penetration test is an in situ testing method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils. Based on this history...
ing (CPT) rigs and direct push sampling rigs such as a PowerProbe or Geoprobe. Direct push rigs typically are limited to drilling in unconsolidated soil materials and very soft rock.
CPT rigs advance specialized testing equipment (such as electronic cones), and soil samplers using large hydraulic rams. Most CPT rigs are heavily ballasted (20 metric tons is typical) as a counter force against the pushing force of the hydraulic rams which are often rated up to 20kn. Alternatively, small, light CPT rigs and offshore CPT rigs will use anchors such as screwed-in ground anchors to create the reactive force. In ideal conditions, CPT rigs can achieve production rates of up to 250-300 meters per day.
Direct Push Drilling rigs use hydraulic cylinders and a hydraulic hammer in advancing a hollow core sampler to gather soil and groundwater samples. The speed and depth of penetration is largely dependent on the soil type, the size of the sampler, and the weight and power the rig. Direct push techniques are generally limited to shallow soil sample recovery in unconsolidated soil materials. The advantage of direct push technology is that in the right soil type it can produce a large number of high quality samples quickly and cheaply, generally from 50 to 75 meters per day. Rather than hammering, direct push can also be combined with sonic (vibratory) methods to increase drill efficiency.
Hydraulic-rotary drilling
Oil wellAn oil well is a general term for any boring through the earth's surface that is designed to find and produce petroleum oil hydrocarbons. Usually some natural gas is produced along with the oil. A well designed to produce mainly or only gas may be termed a gas well.-History:The earliest known oil...
drilling utilises tri-cone roller, carbide embedded, fixed-cutter diamond, or diamond-impregnated drill bits to wear away at the cutting face. This is preferred because there is no need to return intact samples to surface for assay as the objective is to reach a formation containing oil or natural gas. Sizable machinery is used, enabling depths of several kilometres to be penetrated. Rotating hollow drill pipes carry down
bentoniteBentonite is an absorbent aluminium phyllosilicate, generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na, Ca, and Al. As noted in several places in the geologic literature, there are some...
and
bariteBaryte, or barite, is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium...
infused
drilling muds to lubricate, cool, and clean the drilling bit, control downhole pressures, stabilize the wall of the
boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
and remove
drill cuttingsDrill cuttings refers to any material removed from a borehole while drilling petroleum wells. Although sand and shale make up the majority of the cuttings encountered while drilling a well, depending on the location, any number of formations will actually be encountered...
. The mud travels back to the surface around the outside of the drill pipe, called the
annulusAnnulus , being the Latin and French for "ring," is a term used to describe various ring or circle shaped objects :
. Examining rock chips extracted from the mud is known as
mud loggingMud logging, also known as hydrocarbon well logging, entails gathering technical data and creating a borehole well log, usually performed by a third-party mud logging company. This provides well owners and producers with information about the lithology and fluid content of the borehole while...
. Another form of well logging is electronic and is frequently employed to evaluate the existence of possible oil and gas deposits in the
boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
. This can take place while the well is being drilled, using
Measurement While DrillingMeasurement while drilling is a system developed to make drilling related measurements and transmit information to the surface while drilling the well. MWD tools are conveyed downhole as part of bottom hole assembly...
tools, or after drilling, by
lowering measurement toolsWell logging, also known as borehole logging is the practice of making a detailed record of the geologic formations penetrated by a borehole. The log may be based either on visual inspection of samples brought to the surface or on physical measurements made by instruments lowered into the hole...
into the newly-drilled hole.
The rotary system of drilling was in general use in Texas in the early 1900s. It is a modification of one invented by Fauvelle in 1845, and used in the early years of the oil industry in some of the oil-producing countries in Europe. Originally pressurized water was used instead of mud, and was almost useless in hard rock before the diamond cutting bit.. The main breakthrough for rotary drilling came in 1901, when
Anthony Francis LucasAnthony Francis Lucas was a Croatian-born mechanical engineer responsible for the first successful oil well at the Spindletop oil field in Southeast Texas, which made Beaumont, Texas one of the first oil boomtowns...
combined the use of a steam-driven rig and of mud instead of water in the
SpindletopSpindletop is a salt dome oil field located in south Beaumont, Texas in the United States. The Spindletop dome was derived from the Louann Salt evaporite layer of Jurassic age. On January 10, 1901, a well at Spindletop struck oil...
discovery well.
The drilling and production of oil and gas can pose a
safetySafety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...
risk and a hazard to the
environmentThe natural environment, commonly referred to simply as the environment, is a term that encompasses all living and non-living things occurring naturally on Earth or some region thereof....
from the ignition of the entrained gas causing dangerous fires and also from the risk of oil leakage polluting water, land and groundwater. For these reasons, redundant safety systems and highly trained personnel are required by law in all countries with significant production.
Sonic (vibratory) drilling
A sonic drill head works by sending high frequency resonant vibrations down the drill string to the drill bit, while the operator controls these frequencies to suit the specific conditions of the soil/rock geology. Vibrations may also be generated within the drill head. The frequency is generally between 50 and 120 hertz (cycles per second) and can be varied by the operator.
Resonance magnifies the amplitude of the drill bit, which fluidizes the soil particles at the bit face, allowing for fast and easy penetration through most geological formations. An internal spring system isolates these vibrational forces from the rest of the drill rig.
Limits of the technology
Drill technology has advanced steadily since the 19th century. However, there are several basic limiting factors which will determine the depth to which a bore hole can be sunk.
All holes must maintain
outer diameter; the diameter of the hole must remain wider than the diameter of the rods or the rods cannot turn in the hole and progress cannot continue. Friction caused by the drilling operation will tend to reduce the outside diameter of the drill bit. This applies to all drilling methods, except that in diamond core drilling the use of thinner rods and casing may permit the hole to continue. Casing is simply a hollow sheath which protects the hole against collapse during drilling, and is made of metal or
PVCPolyvinyl chloride, commonly abbreviated PVC, is the third most widely used thermoplastic polymer after polyethylene and polypropylene. In terms of revenue generated, it is one of the most valuable products of the chemical industry. Around the world, over 50% of PVC manufactured is used in...
. Often diamond holes will start off at a large diameter and when outside diameter is lost, thinner rods put down inside casing to continue, until finally the hole becomes too narrow. Alternatively, the hole can be reamed; this is the usual practice in oil well drilling where the hole size is maintained down to the next casing point.
For percussion techniques, the main limitation is air pressure. Air must be delivered to the piston at sufficient pressure to activate the reciprocating action, and in turn drive the head into the rock with sufficient strength to fracture and pulverise it. With depth, volume is added to the in-rod string, requiring larger compressors to achieve operational pressures. Secondly,
groundwaterGroundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in...
is ubiquitous, and increases in
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
with depth in the ground. The air inside the rod string must be pressurised enough to overcome this water pressure at the bit face. Then, the air must be able to carry the rock fragments to surface. This is why depths in excess of 500 m for reverse circulation drilling are rarely achieved, because the cost is prohibitive and approaches the threshold at which diamond core drilling is more economic.
Diamond drilling can routinely achieve depths in excess of 1200 m. In cases where money is no issue, extreme depths have been achieved because there is no requirement to overcome water pressure. However, circulation must be maintained to return the drill cuttings to surface, and more importantly to maintain cooling and lubrication of the cutting surface.
Without sufficient lubrication and cooling, the matrix of the drill bit will soften. While diamond is one of the hardest substances known, at 10 on the Mohs hardness scale, it must remain firmly in the matrix to achieve cutting. Weight on bit, the force exerted on the cutting face of the bit by the drill rods in the hole above the bit, must also be monitored.
A unique drilling operation in deep ocean water was named
Project MoholeProject Mohole was an ambitious attempt to drill through the Earth's crust into the Mohorovičić discontinuity, and to provide an Earth science complement to the high profile Space Race. It was led by the American Miscellaneous Society with funding from the National Science Foundation.Phase One was...
.
Causes of deviation
Most drill holes deviate from the vertical. This is because of the torque of the turning bit working against the cutting face, because of the flexibility of the steel rods and especially the screw joints, because of reaction to
foliationFoliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the typical sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss...
and structure within the rock, and because of
refractionRefraction is the change in direction of a wave due to a change in its velocity. This is most commonly observed when a wave passes from one medium to another...
as the bit moves into different rock layers of varying resistance. Additionally, inclined holes will tend to deviate upwards because the drill rods will lie against the bottom of the bore, causing the drill bit to be slightly inclined from true. It is because of deviation that drill holes must be surveyed if deviation will impact on the usefulness of the information returned. Sometimes the surface location can be offset laterally to take advantage of the expected deviation tendency, so the bottom of the hole will end up near the desired location. Oil well drilling commonly uses a process of controlled deviation called
directional drillingDirectional drilling is the practice of drilling non-vertical wells. It can be broken down into three main groups: Oilfield Directional Drilling, Utility Installation Directional Drilling and in-seam directional drilling .-History:Many prerequisites enabled this suite of...
(e.g., when several wells are drilled from one surface location).
Rig equipment
typically includes at least some of the following items: See
Drilling rig (petroleum)This article lists the main components of a petroleum drilling rig.The equipment associated with a rig is to some extent dependent on the type of rig but typically includes at least some of the items listed below.-List of items:#Mud tank#Shale shakers...
for a more detailed description.
- Blowout preventer
A blowout preventer is a large valve that can seal off at the surface wellhead a well being drilled or worked over. During drilling or well interventions, the valve may be closed if overpressure from an underground zone causes formation fluids such as oil or natural gas to enter the wellbore and...
s: (BOPs)
The equipment associated with a rig is to some extent dependent on the type of rig but (#23 & #24) are devices installed at the wellhead to prevent fluids and gases from unintentionally escaping from the
boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
. #23 is the Annular (often referred to as the
Hydril, which is one manufacturer) and #24 is the Pipe rams and Blind rams.
- Centrifuge
A centrifuge is a piece of equipment, generally driven by an electric motor , that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis...
: an industrial version of the device that separates fine silt and sand from the drilling fluid.
- Solids Control
Solids Control is used for well drilling to provide prepared drilling fluids for drilling rig. Drilling fluid maintenance cost, clean up & disposal cost as well as the over all cost of boring, can be reduced dramatically when proper solids control techniques are utilized...
: Solids Control Equipments for preparing drilling mud for the drilling rig.
- Chain tongs: wrench with a section of chain, that wraps around whatever is being tightened or loosened. Similar to a pipe wrench.
- Degasser
-Degasser:For small amount of entrained gas in a drilling fluid, the degasser can play a major role of removing small bubbles that a liquid film has enveloped and entrapped...
: a device that separates air and/or gas from the drilling fluidIn geotechnical engineering, drilling fluid is a fluid used to drill boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells...
.
- Desander
Desanders and desilters are drilling rig equipment with a set of hydrocyclones that separates sand and silt from the drilling fluid. Desander is installed after shakers and degasser but before desilter. Desander removes those abrassive solids from the drilling mud which cannot be removed by shakers...
/ desilter: contains a set of Hydrocyclones that separate sand and silt from the drilling fluid.
- Drawworks: (#7) is the mechanical section that contains the spool, whose main function is to reel in/out the drill line to raise/lower the traveling block
A ' is the free moving section of a block and tackle that contains a set of pulleys or sheaves through which the drill line is threaded or and is opposite the crown block ....
(#11).
- Drill Bit: (#26) device attached to the end of the drill string that breaks apart the rock being drilled. It contains jets through which the drilling fluid exits.
- Drill Pipe
Drill pipe is hollow, thick-walled, steel tubing that is used on drilling rigs to facilitate the drilling of a wellbore and comes in a variety of sizes, strengths and weights but are typically 30 to 33 feet in length...
: (#16) joints of hollow tubing used to connect the surface equipment to the bottom hole assembly (BHA) and acts as a conduit for the drilling fluidIn geotechnical engineering, drilling fluid is a fluid used to drill boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells...
. In the diagram, these are standsStands can refer to:*The Stands, an English rock band*The seating or standing areas at a sports venue *Stands, a supernatural power in the manga and anime JoJo's Bizarre Adventure....
of drill pipe which are 2 or 3 joints of drill pipe connected together and stood in the derrick vertically, usually to save time while Tripping pipe.
- Elevators
, as developed for the drilling industry, is a hinged device with handles that are used to wrap around the tool joint of drill pipe, casing or lift nipples to facilitate the lifting or lowering of them singly or of the drill string as a whole....
: a hinged device that is used to latch to the drill pipe or casing to facilitate the lowering or lifting (of pipe or casing) into or out of the boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
.
- Mud motor
Mud motor refers to a Progressive Cavity Positive Displacement Pump placed in the Drill string to provide additional power to the bit while drilling. The PCPD Pump uses Drilling Fluid to create eccentric motion in the power section of the motor which is transferred as concentric power to the...
: a hydraulically powered device positioned just above the drill bit used to spin the bit independently from the rest of the drill string.
- Mud pump
A Mud pump is a reciprocating piston/plunger device designed to circulate drilling fluid under high pressure down the drill string and back up the annulus....
: (#4) reciprocal type of pump used to circulate drilling fluid through the system.
- Mud tank
A mud tank is an open-top container, typically made of steel, to store drilling fluid on a drilling rig. They are also called mud pits, because they used to be nothing more than pits dug out of the earth....
s: (#1) often called mud pits, provides a reserve store of drilling fluid until it is required down the wellbore.
- Rotary table
A Rotary table is a mechanical device on a drilling rig that provides clockwise rotational force to the drill string to facilitate the process of drilling a borehole.In the diagram, #20 is the rotary table...
: (#20) rotates the drill string along with the attached tools and bit.
- Shale shaker: (#2) separates drill cuttings
Drill cuttings refers to any material removed from a borehole while drilling petroleum wells. Although sand and shale make up the majority of the cuttings encountered while drilling a well, depending on the location, any number of formations will actually be encountered...
from the drilling fluid before it is pumped back down the boreholeA borehole is the generalised term for any narrow shaft drilled in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation or environmental site...
.
See also
- Oil platform
An offshore platform, often referred to as an oil platform or an oil rig, is a large structure used to house workers and machinery needed to drill wells in the ocean bed, extract oil and/or natural gas, process the produced fluids, and ship or pipe them to shore...
- Oil well
An oil well is a general term for any boring through the earth's surface that is designed to find and produce petroleum oil hydrocarbons. Usually some natural gas is produced along with the oil. A well designed to produce mainly or only gas may be termed a gas well.-History:The earliest known oil...
- Boring
- Pumpjack
A pumpjack is the overground drive for a reciprocating piston pump installed in an oil well.It is used to mechanically lift liquid out of the well if there is not enough bottom hole pressure for the...
- Mineral exploration
Mineral exploration is the process undertaken by companies, partnerships or corporations in the endeavour of finding ore to mine...
- Subsea
Subsea is a general term frequently used to refer to equipment, technology, and methods employed to explore, drill, and develop oil and gas fields that exist below the ocean floors...
- Flame jet drill
The Flame Jet Drill is a type of drilling equipment whereby there is no contact with the drilling surface, therefore the drill never wears down....
External links
Drilling Rig Manufacturers
Drilling Rig Solids Control Manufacturers
Drilling Rig Photos
Drilling Rig Videos