Natural Gas Production and Processing Operations

There are two types of wells producing natural gas. Wet gas wells produce gas which contains dissolved liquids, and dry gas wells produce gas which cannot be easily liquefied

After natural gas is withdrawn from producing wells, it is sent to gas plants for processing. Gas processing requires a knowledge of how temperature and pressure interact and affect the properties of both fluids and gases. Almost all gas-processing plants handle gases that are mixtures of various hydrocarbon molecules. The purpose of gas processing is to separate these gases into components of similar composition by various processes such as absorption, fractionation and cycling, so they can be transported and used by consumers.

Absorption processes

Absorption involves three processing steps: recovery, removal and separation.

• Recovery.

Removes undesirable residue gases and some methane by absorption from the natural gas. Absorption takes place in a counterflow vessel, where the well gas enters the bottom of the vessel and flows upward through absorption oil, which is flowing downward. The absorption oil is “lean” as it enters the top of the vessel, and “rich” as it leaves the bottom as it has absorbed the desirable hydrocarbons from the gas. The gas leaving the top of the unit is called “residue gas.”

Absorption may also be accomplished by refrigeration. The residue gas is used to pre-cool the inlet gas, which then passes through a gas chiller unit at temperatures from 0 to –40 °C. Lean absorber oil is pumped through an oil chiller, before contacting the cool gas in the absorber unit. Most plants use propane as the refrigerant in the cooler units. Glycol is injected directly into the inlet gas stream to mix with any water in the gas in order to prevent freezing and formation of hydrates. The glycol-water mixture is separated from the hydrocarbon vapour and liquid in the glycol separator, and then reconcentrated by evaporating the water in a regenerator unit.

• Removal

The next step in the absorption process is removal, or demethanization. The remaining methane is removed from the rich oil in ethane recovery plants. This is usually a two-phase process, which first rejects at least one-half of the methane from the rich oil by reducing pressure and increasing temperature. The remaining rich oil usually contains enough ethane and propane to make reabsorption desirable. If not sold, the overhead gas is used as plant fuel or as a pre-saturator, or is recycled to the inlet gas in the main absorber.

• Separation.

The final step in the absorption process, distillation, uses vapours as a medium to strip the desirable hydrocarbons from the rich absorption oil. Wet stills use steam vapours as the stripping medium. In dry stills, hydrocarbon vapours, obtained from partial vaporization of the hot oil pumped through the still reboiler, are used as the stripping medium. The still controls the final boiling point and molecular weight of the lean oil, and the boiling point of the final hydrocarbon product mix.

Other Processes

• Fractionation.

Is the separation of the desirable hydrocarbon mixture from absorption plants, into specific, individual, relatively pure products. Fractionation is possible when the two liquids, called top product and bottom product, have different boiling points. The fractionation process has three parts: a tower to separate products, a reboiler to heat the input and a condenser to remove heat. The tower has an abundance of trays so that a lot of vapour and liquid contact occurs. The reboiler temperature determines the composition of the bottom product.

• Sulphur recovery.

Hydrogen sulphide must be removed from gas before it is shipped for sale. This is accomplished in sulphur recovery plants.

• Gas cycling.

Gas cycling is neither a means of pressure maintenance nor a secondary method of recovery, but is an enhanced recovery method used to increase production of natural gas liquids from “wet gas” reservoirs. After liquids are removed from the “wet gas” in cycling plants, the remaining “dry gas” is returned to the reservoir through injection wells. As the “dry gas” recirculates through the reservoir it absorbs more liquids. The production, processing and re circulation cycles are repeated until all of the recoverable liquids have been removed from the reservoir and only “dry gas” remains.

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TYPES OF CASING PIPE

Casing Pipe for Oil Gas Well

In practice, it would be much cheaper to drill a hole to total depth (TD), probably with a small

diameter drill bit, and then case the hole from surface to TD. However, the presence of high pressured zones at different depths along the wellbore, and the presence of weak, unconsolidated formations or sloughing, shaly zones, necessitates running casing to seal off these troublesome zones and to allow the drilling to TD. Thus, different sizes of casing are employed and this arrangement gives a tapered shape to the finished well. 

The types of casing currently in use are as follows:

1. Stove Pipe

Stove pipe (or marine-conductor, or foundation-pile for offshore drilling) is run to prevent washouts of near-surface unconsolidated formations, to provide a circulation system for the drilling mud and to ensure the stability of the ground surface upon which the rig is sited. This pipe does not usually carry any weight from the wellhead equipment and can be driven into the ground or seabed with a pile driver. A typical size for a stove pipe ranges from 26 in. to 42 in.

    2. Conductor Pipe

Conductor pipe is run from the surface to a shallow depth to protect near surface unconsolidated formations, seal off shallow-water zones, provide protection against shallow gas flows, and provide a conduit for the drilling mud. One or more BOPs may be mounted on this casing or a diverter system if the setting depth of the conductor pipe is shallow. In the Middle East, a typical size for a conductor pipe is either 18 5/8 in. (473 mm) or 20 in. (508 mm). In North Sea exploration wells, the size of the conductor pipe is usually 26 or 30 in also in most of Iraqi wells. Conductor pipe is always cemented to surface. It is used to support subsequent casing strings and wellhead equipment or alternatively the pipe is cut off at the surface after setting the surface casing.

 3. Surface Casing

Surface casing is run to prevent caving of weak formations that are encountered at shallow

depths. This casing should be set in competent rocks such as hard limestone. This will ensure that formations at the casing shoe will not fracture at the high hydrostatic pressures which may be encountered later. The surface casing also serves to provide protection against shallow blowouts, hence BOPs are connected to the top of this string. The setting depth of this casing string is chosen so that troublesome formations, thief zones, water sands, shallow hydrocarbon zones and build-up sections of deviated wells may be protected. A typical size of this casing is l3 3/8 in. (240 mm) in the Middle East and 18 5/8 in. or 20 in. in North Sea operations.

4. Production Casing

Production casing is the last casing string. It is run to isolate producing zones, to provide reservoir fluid control and to permit selective production in multizone production. This is the string through which the well will be completed. The usual sizes of this string are 4 1/2, 5 and 7 in.

6. Liners

A liner is a string of casing that does not reach the surface. Liners are hung on the intermediate casing by use of a liner-hanger. In liner completions both the liner and the intermediate casing act as the production string. Because a liner is set at the bottom and hung from the intermediate casing, the major design criterion for a liner is usually the ability to withstand the maximum expected collapse pressure.

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TRAVELLING BLOCK Drilling Rig

The set of sheaves that move up and down in the derrick. The wire rope threaded through them is threaded (or "reeved") back to the stationary crown blocks located on the top of the derrick. This pulley system gives great mechanical advantage to the action of the wire rope drilling line, enabling heavy loads (drillstring, casing and liners) to be lifted out of or lowered into the wellbore. A traveling block is a multisheave pulley used to raise or lower the drill string and casings into a well bore. 

The blocks typically consist of four to six individual sheaves over which the steel cables used to suspend the traveling black are passed. The cables are then attached to the

fixed crown block at the top of the derrick, leaving the lower block free to move up and down the cable fall. A shock absorber and crane hook are attached to the bottom of the traveling block and are used to suspend the drill string. These block assemblies are most frequently encountered in the oil drilling applications and are often capable of handling loads in excess of 1,000,000 pounds (454,000 kg).

Pulley of Travelling Block

Lowering, lifting, and controlling the drill string in deep well bores generally requires an extraordinarily robust hoist arrangement. These hoists usually consist of a crown block mounted in a fixed position at the top of the well derrick and a traveling block at the bottom of the fall of rope. The travelling block sheaves are flat disks with a deep groove machined around their circumference. When grouped together, as they are in the traveling block, they are collectively referred to as a pulley.

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RIG POWER SYSTEM

Most rig power is consumed by hoisting and fluid circulating systems. The other rig systems have much smaller power requirements. Fortunately, the hoisting and circulating systems generally are not used simultaneously, so that the same engines perform both functions.

Total power requirements for most rigs are from 1000 to 3000 hp provided by one or more engines depending on well depth and rig design. Power requirements vary for different drilling jobs, shallow or moderate depth drilling rigs need 500 - 1,000 HP, heavy-duty rigs for 20,000 foot (6000 meters) holes usually need 3,000 hp, Auxiliary power requirements for lighting, etc., may be 100 - 500 hp.

The early drilling rigs were powered primarily by steam. However, because of high fuel consumption and lack of portability of the large boiler plants required, steam-powered rigs have become impractical. 

Modern rigs are powered by internal-combustion diesel (or gas) engines .engines and sub-classified depending on the method used to transmit power to the various rig systems as:

1-Diesel electric type.

2-Direct drive type.

Diesel electric rigs are those in which the main rig engines are used to generate electricity. Electric power is transmitted easily to the various rig systems(the diesel engines generate and deliver electric power by cables to electrical then to electric motors attached to the involved equipments) switch gear then to , where the required work is accomplished through use of electric motors. Direct-current motors can be wired to give a wide range of speed-torque characteristics.

That are extremely well-suited for the hoisting and circulating operations. The rig components can be packaged as portable units that can be connected with plug-in electric cable connectors. There is considerable flexibility of equipment placement, allowing better space utilization and weight distribution. In addition, electric power allows the use of relatively simple and flexible control system. The driller can apply power smoothly to various rig components, thus minimizing shock and vibration problems.

Direct drive rigs accomplish power transmission from the internal-combustion engines using system of pulleys, gears, chains, belts, and clutches rather than generators and motors. The initial cost of a direct-drive power system generally is considerably less than that of a comparable diesel-electric power system. The development of hydraulic drive has improved greatly the performance of this type of power system. Hydraulic drives reduce shock and vibrational problems of the direct drive power system. Torque convertors, which are hydraulic drives designed so that the output torque increases rapidly with output load, are now used to extend the speed-torque characteristics of the internal-combustion engine over greater ranges that are better suited to drilling applications. The use of torque convertors also allows selection of engines based on running conditions rather than starting conditions. Power-system performance characteristics generally are stated in terms of output horsepower, torque and fuel consumption for various engine speeds.

3000hp =2237099.615 watt equal to the power operates 22371 house lamps.

The power on modern rigs is most commonly generated by diesel-electric power units. The power produced is AC current which is then converted to DC current by the use of SCR (Silicon Controlled Rectifier).

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Exploration Drilling

Exploration drilling is a procedure in which several test holes are perforated in order to evaluate the soil content in a particular area. It was conducted to find out whether the valuable materials are present, and to evaluate the quality of these materials. There are a number of industries that use drilling exploration in their work, sometimes with their own drilling crews, and sometimes through companies offering hire of drilling services.

A common reason for drilling exploration to do is in mining prospecting. Once a potential site is identified, drilling exploration can be used to determine whether the site has material of interest ranging from metallic minerals to diamonds, and to evaluate the quality and quantity of such materials. 

In the first drilling exploration phases, several test holes can be excavated for carotage covering a large area. Once site value is confirmed, additional holes can be drilled and people can learn more about site quality. The company has to determine whether exploiting the site will generate profits that exceed the costs of drilling and the ongoing site maintenance costs once it is active. A site with potentially poor returns could be too expensive to invest, leading the company to pull out.

The oil industry also uses exploration to pervade suspect oil deposits. Drill samples are analyzed to determine the quality of the crude, while geologists work on estimates of how much oil can be available at the site. People are sometimes surprised to learn that crude oil actually enters into quality ranges that determine what can be done on the market by analyzing oil deposits on a critical site.

Geologists can use drilling exploration to learn more about geological layers without the specific target of exploiting mineral resources. Carotages can provide a great deal of information about geological composition of a site and history. These samples can also be picked up by ice and mud deposits to collect layers of stored data that provides climatic information; Pollen displacement can indicate change in time, for example, while increases in deposits of certain chemicals can sometimes be related to geological or human activity.

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Rig Service

A service facility is a piece of material that is used for the maintenance of wells such as oil and gas wells. Service facilities are not intended for drilling, but for completing other tasks related to oil and gas wells. Some well-maintained wells maintain their own service facilities, while others prefer to rent them because they can be very expensive. Specialists performed service facilities when they are needed for routine maintenance and emergencies.

Once a well is perforated and productive, it requires periodic maintenance. This is where a service facility enters. When components have to be replaced or a well has to be cleaned, it is done with a service facility. Likewise, when a well is to be closed for any reason, the crew uses a service facility to complete the tasks associated with shutting down the good and fixing it for safety.

Service facilities are loaded on large vehicles that carry them to the site well. The drilling rig is in itself a telescopic tower fixed with tie rods, which keep it in place. Attachments can be mounted on the rig service to complete various tasks related to the activities of the wells. In special circumstances, attachments may be added to a service facility so that it may puncture.

Also known as completions of installations, workover systems, or traction units, service facilities are managed by a crew of people. The crew members gather the rig, confirm it is safe and it works properly, and complete the task assigned to the good. It is necessary to have more people, both for security and why some activities can not be completed by a single person. People who are just beginning are known as thugs and work their way into more advanced positions as tool dealers.

Working on a service desk can be dangerous. The equipment is large and heavy, and when it is not installed and maintained properly, it may pose a safety risk. People are also at risk of electric shock when working with good maintenance equipment and may be endangered by environmental toxins that may be present around oil and gas wells. In recognition of the dangers, oil and gas occupations can come with very high salaries along with the benefits. Employers usually have to pay high civil liability and disability insurance because workers' claims are much more likely than other trades.

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What is Seismic Drilling

Seismic drilling, also known as drilling, is perforation conducted as part of a seismic survey of geological formation. In such studies, the team uses a series of controlled vibrations to generate a map of underground structures. This map can determine where deposited material is to be found and how accessible it will be drilling equipment. Seismic surveys are an important part of oil and gas, and are also used by researchers who want to map geological formations for scientific purposes.

In seismic drilling, a company uses a drill specially designed to dig a hole at the desired depth. Air and water cutters are both available for this purpose, and are often mounted on slides or mobile platforms. This allows the team to quickly move the drill between the positions, which may be critical on a large survey. The time it takes to establish a drilling platform and stabilize it can add considerably the overall time required for the survey, and as a result teams try to use mobile drills where it is possible to do so.

After sinking a hole, team members can mount explosives inside. These explosives cause ground vibrations when they go out. With the use of seismic equipment, the team can follow the movement and reflection of vibrations. This information can help build a map of underground features and formations. The seismic drilling team may include geologists, explosive experts, and other personnel with training in seismic surveys.

A permit is usually required for seismic drilling. The process can be disruptive and can cause problems for plants, animals, or residents in the region. Permission seekers must describe the area they want to work and what they will do there. While on the site, team members usually follow business protocols set to make the site as secure as possible. They also check waste material to keep the site clean and tidy.

If seismic drilling suggests that training is workable, the team can locate some locations for drilling wells. The company may sink some test wells to confirm the results before starting large-scale production on the site. This survey and exploration can be expensive, especially when companies believe that not all land sites will produce usable deposits. Some sites may not have any useful material, while other deposits may be visible on a seismic survey, but essentially unavailable due to their depth or configuration.

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CONVENTIONAL OIL

Definition Oil is a hydrocarbon formed over thousands of years from the decomposition of dead plants and organisms. Intense heat and pressure on this material triggers a reaction, which leads to the creation of oil

Conventional oil is a term used to describe oil that can be produced (extracted from the ground) using traditional drilling methods.  It is liquid at atmospheric temperature and pressure conditions, and therefore flows without additional stimulation.  This is opposed to unconventional oil, which requires advanced production methods due to its geologic formations and/or is heavy and does not flow on its own. 

You may have heard of these terms used to distinguish different types of oil:

​Light vs. Heavy - this refers to the density of oil and its ability to flow.  Lighter oil can be refined with minimal processing due to higher fractions of light hydrocarbons.

Sweet vs. Sour - this refers to the sulphur content of the oil, sulphur must be removed prior to refining.  When oil has sulphur greater than 0.5% it is referred to as "sour."

Because of these variations, oil quality is a spectrum and the distinction between conventional and unconventional is not always black and white. Generally, however, if traditional drilling techniques are used in the oil production it is considered conventional regardless of its physical properties.

Conventional oil is produced using drilling technologies that utilize the natural pressure of an underground reservoir.  Production of a conventional oil well has four main phases[2]:

Exploration: Geological exploration is a series of technologies that are used by geologists and geophysicists to predict the location and extent of underground oil reservoirs.

Drilling: Once a reservoir has been located with sufficient certainty, a drilling rig is used to bore a hole from the surface to the oil reservoir.  Piping is then inserted, allowing the oil to be brought to the surface.  Some of the oil in the reservoir will be produced using the natural pressure of the reservoir.  

Pumping: Gradually the pressure of the well will decrease as oil is produced. At this point a pump will be connected to allow the remaining oil to be extracted.

Abandoning: After all the economically viable oil has been extracted from the well, the well is filled with cement to prevent any hydrocarbons from escaping and a special cap is placed over it to protect the area[3].

Context

Conventional oil tends to be less expensive and complex to extract than unconventional oil due to the routine nature of the production techniques.  This oil is also the most valuable in global markets because it requires the smallest amount of processing prior to refining to create value-added products. Consequently, many of our global conventional oil supplies have already been extracted, limiting the availability of these source for future extraction[2].

Generally, drilling and well abandonment are well-understood and regulated processes but there are always risks with such industrial operations. In drilling, pressure must be regulated carefully to avoid accidents and immediate environmental impacts like land disturbance must be carefully monitored.  After abandonment, well leaks can occur if improper procedures were taken.  

As with all fossil fuel production, there are also concerns with greenhouse gas emissions from their combustion 

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Oil Exploration

Crude oil is usually located deep below the earth's surface, without any visible traces of being present.

In the early years of the oil industry, one could easily find small amounts of oil in the vicinity of the oil urinating drilling. "Oil Lakes" are small amounts of oil that come up on the surface or in water.

However, a well drilling is very expensive; Therefore, alternative methods have been sought in order to locate oil. Today, geologists determined using a range of techniques where oil could be found. They make use of include seismic and visual observation techniques to determine the geological formations could contain oil.

• Seismic surveys

this case a small amount of underground explosive is detonated. In addition, to be sensitive instruments used which register the shock waves moving across the ground and which are reflected by rock walls. On the basis of the speed and direction of the waves geologists can identify the type of rock formations, and to detect the types of which are known to oil or hydrocarbons (such as gas) may contain.

• Vibro-seismic survey

, with special vibrating trucks are used, which is a controlled signal to submit the bottom. Although this method is more complicated, it is often used in places where explosives can not be used for practical reasons.

• Geophysical research

, this method is used to measure the thickness of sediment and in order to map out the shape of the structures within the sediment. In this way, often underground structures could be located in the last 30 years where oil had gathered.

• Research based on aerial photographs

on the basis of aerial photos, maps can be established in which the main geological properties are shown of an area. The photos are also used to determine oil field pipelines and infrastructure very closely. This information is of great value for planning seismic surveys and other projects.

• Surface Research

Here, specific localized areas on the ground and it is determined their height. One of the tools used therewith, is a theodolite, which is equipped with a telescope that measurement angles horizontally and vertically.

• Gravity investigation

In this method, there is used a highly sensitive gravimeter, which is analyzed to gravity variations. These variations may indeed indicate hidden geological structures. The study is usually performed in an early stage of exploration. The researchers thereby identify areas that may be potentially interesting. At these zones is then carried out, a more detailed seismic survey.

Drilling for oil

When certain areas of potential interest are labeled, are drills used to dig wells. Seismic research shows that the best places to look for oil. In this way, the risk of finding dry wells ( "dry hole") is limited. They contain no oil.

A drill is guided straight into the ground. If the rig can not be drawn directly on the surface, it is placed next to it and is drilled at an angle. The horizontal drilling technology is used to drill into the portion of the source which horizontally through the oil (the "output section") passes along the path from the oil reservoir.

Oil Transport

Crude oil is transported by pipeline from the drilling rig to tank farms. Since the oil is stored in huge tanks. The crude oil is then transported by pipeline to a local refinery or an oil tanker to an overseas refinery.

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Vertical Well

A well that is not converted into horizontally in depth, allowing access to the oil and gas reserves are located directly below the point of surface access. Historically, natural gas and oil exploration has involved the use of vertical wells because the directional drilling technology was expensive and complicated. Drilling of vertical wells is considered a conventional method.

Vertical shafts differ directional wells, such as horizontal wells, deep because they require the use of directional drilling. This makes them less expensive to develop, although less productive because of their limited range.

While vertical wells may be less complicated to bring in line of directional wells, their limited angles make them less able to reach a wider part of the underground area. Because a vertical shaft can access only the reserves of petroleum and natural gas directly under, making a large manufacturing industry requires the drilling of many vertical wells. They are especially handy in case of reserve thin layers located over a wide area. Since a vertical well can be drilled in a single direction, the exploration company must estimate the most productive portion of the reserve from the beginning; a vertical drilled well can go right through the reserve, drawing only a portion of the available energy.

horizontal wells usually starting with the drilling of a vertical well. Drilling vertically allows engineers to examine rock fragments at different levels, in order to determine where the reserves are located. horizontal wells are then "kicked off" from the primary vertical shaft.

The extraction of oil and gas from unconventional sources such as shale rock, often requires the use of horizontal drilling technologies because the source can be executed in the horizontal direction. If the reserves are located in a residential area, well vertical drilling would require both the displacement of residents or require them to live next to a tower.

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What Mud Fluid in drilling for ?

The drilling mud are primarily for:

1. to lubricate and cool the drill drilling that would otherwise warming, for the friction with the rock , quickly arrive at break.
2. Pipe on the surface of earth and rock fragments (commonly known by the English technical term for cutting ) produced by the action of the chisel.
3. Exercise a counter pressure hydrostatic hole at the bottom and along its walls discoveries (ie not tubate) to contain the leakage of the fluid layer and to avoid the risk of kick or in more severe cases the real eruption of the well.
4. Supporting walls of the hole (thanks to the pressure exerted by the hydrostatic load), in order to prevent landslides and loss of the punched hole. This feature is said that the mud must do "panel" that must practically "plaster" the walls of the well.
5. The most important properties of the drilling mud must be the "thixotropy", namely the characteristic that, at the time that the circulation in the pit stops, the sludge to be gelled fluid holding imprisoned in suspension the cutting resulting from the drilling. Otherwise these debris, stopping the circulation of the fluid, would fall to the bottom hole imprisoning the chisel and the "battery terminal part" drilling.

In the oil exploration monitoring geological of drilling muds, by analyzing the microscope of fragments of rock it allows to recognize the stratigraphy of the perforated rocky succession and provides the first indications of the characteristics petrophysical properties of the reservoir . 

Furthermore, the analysis by means of gas chromatographs , of the fluids contained in the outgoing mud from the well, provides important clues for the detection and recognition of mineralized levels to hydrocarbons.

In some cases similar muds are used temporarily to support the walls of trenches or over works of excavation of civil engineering within loose soil, prior to the implementation of their final completion.

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Drilling Rig

A drilling rig is a machine that creates holes in the earth sub-surface. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person and are called augers. Drilling rigs can 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 platforms, 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 crust.

Small to medium-sized drilling rigs are mobile, such as those used in mineral exploration drilling, blast-hole, water wells and environmental investigations. Larger rigs are capable of drilling through thousands of metres of the Earth's crust, using large "mud pumps" to circulate drilling mud (slurry) through the drill bit and up the casing annulus, for cooling and removing the "cuttings" while a well is drilled. Hoists in the rig can lift hundreds of tons of pipe. Other equipment can force acid 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 thousands of miles distant from the supply base with infrequent crew rotation or cycle.

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Drilling Rigs Type

There are many different types of drilling rigs. Which rig selected depends on the specific requirements of each drill site. Roll your mouse over each picture to see what kind of rig it is.Its a good for drilling knowledge

Land Based Drilling Rigs - The land-based drilling rig is the most common type used for exploration. This site is using a conventional, land-based drilling rig that is smaller and more efficient than those used in the past.

Slim Hole Drilling Rig - A conventional drill bore might be 18 inches in diameter; a slimhole bore can be as little as 6 inches. A slimhole well drilled to 14,760 feet may produce one-third the amount of rock cuttings generated by a standard well. The size of the drill site can be as much as 75 percent smaller, since slimhole equipment requires less space than conventional equipment. However, slimhole drilling is not technically feasible in all environments.

Coiled Tubing Drill Rig - Conventional wells are drilled using sections of rigid pipe to form the drill string. In some cases, coiled tubing technology can replace the typical drill string with a continuous length of pipe stored on a large spool. This approach has many benefits, including reduced drilling waste and minimized equipment footprints, so it is especially useful in environmentally sensitive areas. This technology is best suited to re-entering existing wells, and when multiple casing wells are unnecessary.

Jackup Drill Rigs – These rigs may be used in relatively shallow water -- less than 300 feet deep. A jackup rig is a floating barge containing the drilling structure that is outfitted with long support legs that can be raised or lowered independently of each other. The jackup, as it is known informally, is towed onto location with its legs up and the barge section floating on the water. Once at the drilling location, the legs are jacked down onto the seafloor, and then all three legs are jacked further down. Since the legs will not penetrate the seafloor, continued jacking down of the legs raises the jacking mechanism attached to the barge and drilling package, and slowly lifts the entire barge and drilling structure to a predetermined height above the water. These rigs are extremely strong, since they have to withstand ocean storms and high waves. These rigs are moved by simply by moving the legs up and down, which makes them cost-effective and easily shifted out of harm's way during storms.

Semi-Submersible Rigs – Drilling in water deeper than 300 feet demands some kind of floating platform to hold the rig. Semi-submersible rigs are floating vessels supported on large pontoon-like structures that are submerged below the sea surface. As with jackup rigs, the operating decks are elevated as much as 100 or more feet above the pontoons on large steel columns. This design has the advantage of submerging most of the area of components in contact with the sea and minimizing loading from waves and wind. Semisubmersibles can operate in a wide range of water depths, including deep water. Semi-submersibles can either be attached to the ocean bottom using strong chains and wire cables or may utilize dynamic positioning to remain stationary during drilling without anchors.

Drill Ship - For exploration targets farther offshore, specially designed rigs mounted on ships can drill a well in water depths up to 10,000 feet. These rigs float and can be attached to the ocean bottom using traditional mooring and anchoring systems, or utilize dynamic positioning to remain stationary during drilling without anchors.

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Drilling for oil

After the drilling of one exploration well, designed to confirm the presence of oil and other wells are drilled to delineate the deposit. Most wells are drilled using a drill bit, a cutting tool on the end of a set of drill pipe supported by a metal tower called derrick. The drill bit is rotated. The drilling speed varies greatly depending on the nature of the rocks traversed. Of the "drilling mud" (a mixture of clay with water and chemicals) is continuously injected inside the stems. It goes back into the space between the rods and the walls of the well. The mud serves to cool the drill bit and remove the cuttings. Back on the surface, the slurry is filtered and reinjected into the well. Analysis of the debris can qualify the rocks traversed. 

Advances in drilling techniques now allow the completion of drilling small diameter boreholes deviated (obliques), horizontal multidrains, etc ... This progress has allowed the exploitation of deposits that were previously unprofitable, for technical reasons and / or economic. 

For offshore deposits (offshore), is generally used for pumping platform independent. Special ships can be used to exploit deposits of lower capacity.

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