Drilling fluid

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In geotechnical engineering, drilling fluid is used to help drill a borehole into the earth. Often used when drilling oil and gas wells and on exploratory drilling rigs, drilling fluid is also used for simpler drill holes, such as water wells. Liquid drilling fluid is often called drilling mud . The three main categories of drilling fluids are water-based (dispersible and non-dispersible) sludge, non-aqueous sludge, usually called oil-based sludge, and gas drilling fluid, where various gases can be used..

The main functions of the drilling fluid include providing hydrostatic pressure to prevent formation fluid from entering the wellbore, keeping the drill cool and clean during drilling, drilling and suspending drill cuttings while drilling is suspended and when drilling assembly is brought in and out of the hole. Drilling fluid used for a particular job is selected to avoid formation damage and to limit corrosion.

Video Drilling fluid

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Many types of drilling fluids are used everyday. Some wells require different types to be used on different parts of the hole, or some types are shared with others. Different types of fluids generally fall into several broad categories:

• Air: The compressed air is pumped downward in the annular space of the drill hole or down the drill string itself.
• Air/water: Same as above, with water added to increase viscosity, flush holes, provide more cooling, and/or to control dust.
• Air/polymer: Specially formulated chemicals, most commonly referred to as polymer types, added to water & amp; air mixture to create certain conditions. The foaming agent is a good example of polymer.
• Water: Water by itself is sometimes used. On the high seas, sea water is usually used when drilling the top of the hole.
Water-based mud (WBM): Most mud-based water based systems start with water, then clay and other chemicals are fed into water to create a homogeneous mixture that resembles something between milk chocolate and malt (depending on the viscosity). Clay is usually a combination of native clay suspended in liquid during drilling, or certain clay types that are processed and sold as additives for WBM systems. The most common of these is bentonite, often referred to in oil fields as "gel". Gel tends to refer to the fact that when the liquid is pumped, it can be very thin and free-flowing (like milk chocolate), although when pumping is stopped, static fluid builds a flow-resistant "gel" structure. When an adequate pumping force is applied to "break the gel", the flow returns and the liquid returns to its previously free flow state. Many other chemicals (eg potassium formation) are added to the WBM system to achieve various effects, including: viscosity control, shale stability, increased penetration drilling rate, refrigeration and equipment lubrication.
• Oil-based mud (OBM): Oil-based mud is a sludge in which basic liquids are oil products such as diesel. Oil-based mud is used for many reasons, including increased lubrication, increased inhibition of shale, and greater cleaning ability with less viscosity. Oil-based mud also retains greater heat without damaging it. The use of oil-based sludge has special consideration, including cost, environmental considerations such as proper cuttings disposal, and exploration losses using oil-based sludge, especially in wildcat wells. Using oil-based slurries interferes with the geochemical analysis of cuttings and cores and with the determination of API gravity because the base fluid is indistinguishable from the oil returning from the formation.
• Synthetic-based fluids (SBM) (otherwise known as Low Poison Based Oil or LTOBM): Synthetic-based liquids are sludges where the liquid is essentially synthetic oil. It is most commonly used on offshore rigs because it has oil-based sludge properties, but the vapor toxicity of liquids is much less than oil-based liquids. This is important when men work with fluids in enclosed spaces such as offshore drilling rigs. Synthetic based fluids cause the same environmental and analytical problems as oil-based liquids.

On drilling rigs, the mud is pumped from the mud hole through a drill strap where it sprays the nozzle on the drill bit, cleans and cools the drill in the process. The sludge then carries rocks that are crushed or cut ("cut") onto the circular space ("annulus") between the drill string and the sides of the drilled holes, rising through the surface of the casing where it reappears to the surface. The cuttings are then filtered with a shale shaker, or newer shale conveyor technology, and the mud returns to the mud hole . The mud holes let the drilled "fines" settle; pit also where the liquid is treated by adding chemicals and other substances.

Returning mud can contain natural gas or other combustible materials to be collected in and around the shaker/conveyor shift area or in other work areas. Due to the risk of fire or explosion if they are on, special monitoring sensors and anti-explosion certified equipment are generally installed, and workers are advised to take safety precautions. The sludge is then pumped back into the hole and then recirculated. After testing, the mud is periodically treated in the mud pit to ensure optimizing properties and improve drilling efficiency, drill stability, and other requirements listed below.

Maps Drilling fluid

Function

The main functions of drilling mud can be summarized as follows:

Remove pieces from well

Drilling fluid brings rocks dug by the drill bit to the surface. His ability to do so depends on the size of the cut, shape, and density, and the speed of the liquid that goes to the well (circular velocity). This consideration is analogous to the ability of flow to carry sediment; Large grains of sand in a slow-moving stream settle to the bottom of the river, while small grains of sand in a fast-moving stream are brought along with water. Sludge viscosity is another important property, since the cuttings will settle at the bottom of the well if the viscosity is too low.

Other properties include:

• Most drilling mud is thixotropic (increase in viscosity during static conditions). This characteristic makes cuttings delayed when the mud does not flow during, for example, maintenance.
• Fluids that have high shear depletion and high viscosity are efficient for purging.
• Higher annular velocity increases cutting transport. Transportation ratio (transport speed/lowest annular speed) should be at least 50%.
• High density liquids can clean out holes adequately even with lower circular velocities (by increasing the floating force that works on cuttings). But it may have a negative impact if the weight of the sludge is more than necessary to balance the surrounding rock pressure (formation pressure), so the sludge weight usually does not increase for clearance purposes.
• The higher drill-string rotational speed introduces a circular component to the annular flow path. The helical flow around the bor-string causes a drill bit near the wall, where a poor pit cleansing condition occurs, to move to a higher transport area of ​​the annulus. Increased rotation is one of the best methods to improve clearance of holes in high angle and horizontal wells.

Suspend and undo the

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• Must suspend drill cuttings, heavy materials and additives under various conditions.
• A precipitated drill cut can cause bridges and filling, which can cause pipes to jam and loss of circulation.
• Heavily precipitated materials are referred to as sag, this causes a wide variation in well density, this is more common at high angles and hot wells.
• High concentrations of high drill disadvantage:
  • Drilling efficiency (causing an increase in mud weight and viscosity, which in turn increases maintenance costs and increases dilution)
  • Rate of Penetration (ROP) (increase horse power needed to circulate)
  • The suspended mud properties must be offset by the properties in cutting removal with solids control equipment
• For effective solids control, the solid drill must be removed from the sludge on circulation 1 of the well. When recirculated, the cuttings break into smaller pieces and are more difficult to remove.
• Perform testing to compare the mud sludge content at the flow line and the suction hole (to determine if the cuttings have been removed).

Control formation pressures

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• If the formation pressure increases, the sludge density must also be increased to balance the pressure and keep the wellbore stable. The most common weighting material is barite. The unbalanced formation pressure will cause an unexpected entry (also known as kick) of formation fluid in the wellbore that may cause an explosion of the formation of the pressed liquid.
• Hydrostatic pressure = drilling fluid density * actual vertical depth * acceleration of gravity. If the hydrostatic pressure is greater than or equal to the formation pressure, the formation fluid will not flow into the wellbore.
• Good control means no flow of formation fluid flows into the wellbore.
• Hydrostatic pressures also control the pressure caused by tectonic forces, this can make the borehole unstable even when the formation fluid pressure is balanced.
• If under-normal formation pressure, air, gas, fog, rigid foam, or low-density slurry (oil base) may be used.
• In practice, the sludge density should be limited to the minimum required for well control and wellbore stability. If it's too good it can break formation.

Seal permeable formation

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• The mud column pressure must exceed the formation pressure, in which case the filtrate mud invades the formation, and the mud filter cake is deposited on the wellbore wall.
• Mud is designed to deposit a thin low permeability filter cake to limit the invasion.
• Problems occur if a thick filter cake is formed; strict hole conditions, poor log quality, jammed pipes, lost circulation and formation damage.
• In highly permeable formations with large bore necks, the entire mud can attack the formation, depending on the size of the solid slurry;
  • Use a liaison agent to block a large opening, then the mud solid can form a seal.
  • For effectiveness, the contacting agent should be more than half the size of the pore/fracture space.
  • Bridging agents (eg calcium carbonate, cellulose soil).
• Depending on the sludge system used, some additives may increase the filter cake (eg, bentonite, synthetic & natural polymers, bitumen and gilsonite).

Maintaining the stability of the wellbore

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• The chemical composition and sludge properties should be combined to provide a stable wellbore. The weight of the mud should be within the range required to balance the mechanical strength.
• Wellbore instability = formation decay, which can cause rigid hole conditions, bridges and travel filling (same symptoms indicate hole-clearing problems).
• Wellbore stability = hole maintains the size and shape of the cylinder.
• If the hole is enlarged, it becomes weak and difficult to stabilize, resulting in problems such as annular low velocity, poor pit clearance, solid loading and poor formation evaluation
• In sand and sandstone formations, hole enlargement can be done by mechanical action (hydraulic strength & blade speed). Formation damage is reduced by conservative hydraulics. A good quality filter cake containing bentonite is known to limit bore drill enlargement.
• In flakes, the weight of the mud is usually enough to balance the formation stress, since the well is usually stable. With basic water sludge, chemical differences can cause interactions between sludge & amp; shale that causes the softening of the original stone. Very cracked, dry, fragile fragments can be very unstable (leading to mechanical problems).
• Various chemical inhibitors can control the interaction of the mud/crust (calcium, potassium, salt, polymer, asphalt, glycol and oil - best for water sensitive formations)
• Oils (and synthetic oils) based on drilling fluid are used to drill the most water sensitive Shales in areas with difficult drilling conditions.
• To increase inhibition, the pharmaceutically precipitated water phase (calcium chloride) is used to reduce water activity and create an osmotic force to prevent water adsorption by Shales.

Minimize formation damage

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• Skin damage or reduction in porosity of natural formation and permeability (washout) is a formation damage
• Skin damage is the accumulation of residue on perforation and that causes a decrease in pressure through them.
• The most common damage;
  • Mud or solid drill attacks formation matrices, reduces porosity and causes skin effect
  • Swelling of formation clay in the reservoir, reducing permeability
  • Solid precipitation due to mixing of mud filtrate and formation liquids resulting in precipitation of insoluble salts
  • Mud filtrate and formation fluid form emulsions, reducing reservoir porosity
• Fluid or specially designed liquid and workaround solutions, minimizing formation damage.

Cool, lubricate and support bit assembly and drilling

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• Heat is generated from mechanical and hydraulic forces in bits and when drill strings rotate and rub against casing and wellbore.
• Cool and transfer heat from source and lower to temperature than bottom hole.
• Otherwise, bits, drill strings and mud motor will fail faster.
• Lubrication based on coefficient of friction. ("Friction coefficient" is how much friction on the side of the wellbore and the size of the collar or the size of the drill pipe to pull the retained pipe.) Oil-based and synthetic sludge generally lubricates better than the slurry-based (but the latter can be increased with the addition of lubricants).
• The amount of lubrication provided by the drilling fluid depends on the type & amp; amount of drill solid and heavy material of the chemical composition of the system.
• Bad lubrication causes high torque and drag, hot checks on drill string, but this problem is also caused by the main seat, poor pit clearance and the wrong bottom hole assembly design.
• Liquid drilling also supports part of the drill-string or casing through buoyancy. The suspension in the drilling fluid, supported by a force equal to the weight (or density) of the sludge, thus reducing the load of the hook on the crane.
• The weight of the crane can be supported by the limited mechanical capacity, increasing the depth so that the drill-string and casing weight are increased.
• When running a long string, weight or casing, floating power allows to run a string casing that weighs more than the load capacity of the rig hook.

Transferring hydraulic energy to tools and bits

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• Hydraulic energy provides power for sludge motors for bit rotation and for MWD tools (drilling measurements) and LWD (logging while drilling). The hydraulic program is based on nozzle bits for available mud pump power to optimize the impact of jets in the lower wells.
• Limited to:
  • Horsepower pump
  • Loss of pressure inside drillstring
  • Maximum permissible surface pressure
  • Optimal flow rate
  • Drill press strain loses higher in liquids with higher density, viscosity and plastic solids.
• Low solids, dilution fluid that flows like a polymeric liquid, is more efficient at emitting hydraulic energy.
• The depth can be extended by controlling the nature of the mud.
• Transfer information from MWD & amp; LWD surfaces by pressure pulse.

Make sure adequate formation evaluation

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• The chemical and physical mud properties and drilling well conditions after drilling affect formation evaluation.
• The mud loggers examine the pieces for mineral composition, visual hydrocarbon marks and record logs of sludge, lithology, ROP, gas detection or geological parameters.
• The size of Wireline logging - electrical resonance, sonic, nuclear, and magnetic.
• Potential productive zones are isolated and tested for formation and testing of drill rods.
• Mud helps not to dissolve cuttings and also increases cutting transport for the muddy loggers determines the depth of the cuttings originated.
• Mud, lubricants, oil-based asphalt will cover hydrocarbon indications.
• So the mud for the drill core is selected based on the type of evaluation to be performed (many coring operations determine the mixture of sludge with minimum additive).

Corrosion control (at an acceptable level)

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• Bor-string and casing in continuous contact with drilling fluid can cause corrosion.
• Dissolved gas (oxygen, carbon dioxide, hydrogen sulphide) causes serious corrosion problems;
  • The cause of a rapid catastrophic failure
  • May be deadly for humans after a short time
• Low pH (acid) aggravates corrosion, so use corrosion coupons to monitor the corrosion type, price and to tell the correct chemical inhibitor is used in the right amount.
• Other aeration conditions of mud, foaming, and O ₂ cause corrosion damage in a short time.
• When drilling high H ₂ S, increase the pH of the chemical liquid of sulphide (zinc) cleanser.

Facilitate cementing and completion

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• Cementing is critical for effective zones and good solutions.
• During the running casing, the sludge must remain liquid and minimize the spike in pressure so that fracture caused loss of circulation does not occur.
• The water temperature used for cement should be within the tolerance of the duty of cement implementation, usually 70 degrees, especially in winter conditions.
• Mud should have a thin, slippery sieve, with minimal solids in a cake filter, wellbore with minimal cuttings, caving or bridges will prevent a good casing from flowing down. Circulate well until clean.
• To cement and complete the operation properly, the mud is removed with flushes and cement. For effectiveness;
  • Hole near the gauge, use proper hole cleaning technique, pumping sweep in TD, and travel eraser to shoe.
  • Low viscosity of sludge, sludge parameters should be tolerant of drilled formation, and drilling fluid composition, turbulent flow - high flow rate of low viscosity, high viscosity laminar flow, high pump rate.
  • Non progressive gel strength of mud

Minimize impact on the environment

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Mud, in varying degrees, is toxic. It is also difficult and expensive to dispose of it in an environmentally friendly way. The Vanity Fair article describes the conditions at Lago Agrio, a large oil field in Ecuador where drillers are effectively unregulated.

Water-based drilling fluids have very little toxicity, made of water, bentonite and barite, all clay from mining operations, usually found in Wyoming and in Lunde, Telemark. There are certain chemicals that can be used in water-based drilling fluids that themselves can be corrosive and toxic, such as hydrochloric acid. However, when mixed into a water-based drilling fluid, hydrochloric acid only lowers the pH of the water to a more manageable level. Caustic (sodium hydroxide), anhydrous lime, soda ash, bentonite, barite and polymer are the most common chemicals used in water-based drilling fluids. Mud Base Oil and synthetic drilling fluid can contain high levels of benzene, and other chemicals

The most common chemicals added to OBM Muds:

• Barite
• Bentonit
• Diesel
• Emulsifiers
• Water

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Composition of drilling mud

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Water-based drilling mud generally consists of bentonite clay (gel) with additives such as barium sulfate (barite), calcium carbonate (lime) or hematite. Various thickeners are used to influence the viscosity of the liquid, eg xanthan gum, guar gum, glycol, carboxymethylcellulose, polyanionic cellulose (PAC), or starch. In turn, deflocculants are used to reduce the clay-based sludge viscosity; Anionic polyelectrolytes (eg acrylate, polyphosphate, lignosulfonate (Lig) or tannic acid derivatives such as Quebracho) are often used. Red mud is the name for the Quebracho-based mixture, named after the color of the red tannic acid salt; it was typically used in the 1940s until the 1950s, then made obsolete when lignosulfonate became available. Other components are added to provide specific functional characteristics as listed above. Some other common additives include lubricants, shale inhibitors, fluid loss additives (for controlling drilling fluid losses into permeable formations). Weighing agents such as barite are added to increase the overall density of the drilling fluid so that sufficient bottom hole pressure can be maintained thus preventing unwanted (and often harmful) influx of fluid formation.

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Factors affecting drilling fluid performance

The three factors that affect the performance of the drilling fluid are:

• Changes in viscosity of drilling fluid
• Drilling fluid density change
• Changes in pH sludge
• Corrosion or fatigue of drill string
• The thermal stability of the drilling fluid
• Spin differential

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Drilling mud classification

They are classified by their liquid phase, alkalinity, dispersion and type of chemicals used.

Dissolved system

• fresh water mud : Low pH mud (7.0-9.5) which includes mud, bentonite, natural, processed phosphate, organic sludge and organic colloidal slurry. high pH sludge samples treated with alkaline bases above 9.5 in pH.
• Water-based drilling mud that suppresses hydration and clay dispersion - There are 4 types: high pH lime slurries, low pH gypsum, seawater and saturated brine sludge.

System not dispersed

• Low solids mud : This mud contains less than 3-6% solids by volume and weighs less than 9.5 pounds/gal. Much of this type of mud is water based with different amounts of bentonite and polymer.
• Emulsion : The two types used are oil in water (oil emulsion sludge) and water in oil (reversing oil emulsion sludge).
  • Oil-based mud : Oil-based mud contains oil as a continuous phase and water as a contaminant, and not an element in the sludge design. They usually contain less than 5% (by volume) of water. Oil-based mud is usually a mixture of diesel and bitumen, but can be based on crude oil and mud production

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Mud Technician

"Mud Technician" shall be the name given to an individual oilfield service company charged with the maintenance of a drilling fluid or a liquid solution system on an oil and/or gas drilling rig. These individuals usually work for companies that sell chemicals for the work and are specially trained with these products, although independent mud engineers are still common. The role of the mud engineer, or more precisely the drilling fluid engineer, is essential for all drilling operations because even a small problem with mud can stop all operations on the rig. The internationally accepted shift pattern in offshore drilling operations is personnel (including mud engineers) working on a 28-day shift pattern, where they work for 28 days continuously and rest the next 28 days. In Europe, this is more commonly a 21 day shift pattern.

In offshore drilling, with new technology and a high total day cost, wells are drilled very quickly. Having two mud engineers makes economic sense to prevent down time due to drilling fluid difficulties. Two mud engineers also reduced insurance costs for oil companies for environmental damage borne by oil companies during drilling and production. A senior mud engineer usually works during the day, and a young mud engineer at night.

The cost of drilling fluids is usually about 10% (may vary greatly) from the total cost of drilling the well, and demanding competent mud engineers. The results of great cost savings when mud and fluid engineers work well.

The mud technicians are not to be confused with the mudloggers, the service personnel who monitor the gas from the mud and collect the wellbore samples.

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Compliance engineer

The compliance engineer is the most common name for a relatively new position in oil fields, emerging around 2002 due to new environmental regulations on synthetic mud in the United States. Previously, synthetic sludge is set equal to water-based sludge and can be disposed offshore due to low toxicity to marine organisms. The new regulations limit the amount of synthetic oil that can be removed. This new regulation creates a significant burden in the form of tests required to determine "ROC" or retention on cuttings, sampling to determine the percentage of crude oil in drilling mud, and extensive documentation. It should be noted that no type of oil-based/synthetic sludge (or drilled pieces contaminated with OBM/SBM) can be disposed of in the North Sea. The well-contaminated mud must be sent back to the shore at pass or processed on the rig.

A new monthly toxicity test is also now performed to determine the sediment toxicity, using amphipod Leptocheirus plumulosus . Various concentrations of drilling mud were added to the captive environment of L. plumulosus to determine its effect on animals. This test is controversial for two reasons:

1. These animals are not from many of the territories they are in, including the Gulf of Mexico
2. The test has a very large standard deviation and poorly failed samples can easily escape during retesting

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See also

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References

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Further reading

• ASME Shale Shaker Committee (2005). Drilling Fluid Handbook . ISBNÃ, 0-7506-7775-9.
• Kate Van Dyke (1998). Liquid Drilling, Slurry Pumps, and Conditioning Equipment .
• G. V. Chilingarian & amp; P. Vorabutr (1983). Drilling and Drilling Fluid .
• G. R. Gray, H. C. H. Darley, & amp; W. F. Rogers (1980). Composition and Properties of Oil Well Drilling Fluids .
• DCS Shale Shaker SUPPLIER. Disposal Fluid Cleaning System .

Source of the article : Wikipedia