Drilling Fluid Functions

The following is the function of Drilling Fluid: 

1. Cool the drill bit and lubricates its teeth: one of the prime functions of the drilling fluid or mud is to cool the drill bit and lubricate its teeth. The drilling action requires a considerable amount of mechanical energy in the form of weight on bit, rotation, and hydraulic energy. A large proportion of this energy is dissipated as heat, which must be remove to allow the drill bit to function properly, the drilling mud also helps the removing of the rock cuttings from the space between the bit teeth, thereby preventing bit balling which is one of the common problems in drilling process. 
2. Lubricates and cool the drillstring: a rotary drillstring generates a considerable amount of heat which must be dissipated outside the hole. The drilling mud helps to cool the drillstring by absorbing the heat and releasing it, by convection and radiation, to air surrounding the surface mud tanks (pits). The mud also, provides lubrication by reducing friction between drillstring and borehole walls. Lubrication is usually achieved by the addition of bentonite, oil, graphite, etc.
3. Control formation pressure: for safe drilling, high formation pressure must be contained within the hole to prevent damage to equipment and injury to personnel. The drilling mud achieves this by providing a hydrostatic pressure just greater than the formation pressure. For effective drilling, the difference between the hydrostatic pressure and formation pressure should be zero. the hydrostatic pressure depends on the mud weight which, in turn, depends on the type of solids added to the fluid making up the mud and the density of the continuous phase. In practice, an overbalance,(Where the pressure in the wellbore in higher than the pressure in the formation), 100 to 200 psi (trip margin) is normally used to provide an adequate safe guard against well kick. The pressure overbalance sometimes referred to as chip hold down pressure (CHDP), and its value directly influences penetration rate. In general, penetration rate decreases as (CHDP) increases. When an abnormally pressured formation is encountered, the (CHDP) becomes negative and sudden increase in penetration rate is observed. This is normally taken as an indication of a well kick.
4. Carry cuttings out of the hole: for effective drilling, cuttings generated by the bit must be removed immediately. The drilling mud carries these cuttings up the hole and to the surface, to be separated from the mud. The removal of cuttings depends on the viscous properties called "Yield Point" which influences the carrying capacity of the flowing mud and "gels" which help to keep the cuttings in suspension when the mud is static to prevent them from accumulating on the bottom of the hole and causing pipe sticking. The flow rate of mud is also critical in cleaning the hole.
5. Stabilize the wellbore and prevent it from caving in: the formation of a good mud cake helps to stabilize the walls of plaster to interior walls (like plastering a room walls to keep them from flaking). The pressure differential between hydrostatic pressure of mud and that of the wellbore stable. Shale stability is largely dependent on the type of mud used To minimise the swelling stresses caused by the reaction of the mud with the shale formations. This reaction can cause hole erosion or cavings resulting in an unstable wellbore. Minimisation of wellbore instability is provided by the "inhibition" character of the drilling mud.. At last it should be noted that the best way to keep a hole stable is to reduce time during which the hole is kept open.
6. Helps in the evaluation and interpretation of well logs: wire line logs are run in mud-fills holes in order to ascertain the existence and size of hydrocarbons zones. Open hole logs are also run to determine porosity, boundaries between formations, location of geopressured (or abnormally pressured) formations and the site for the next well. Hence, the drilling mud must possess such properties that it will aid the production of good logs (Log response may be enhanced through selection of specific fluids and conversely, use of a given fluid may eliminate a log from use. Drilling fluids must be evaluated to assure compatibility with the logging program).
7. Limiting the corrosion of drilling equipment: the drilling mud in most cases will have water that contains dissolved salts as its base liquid. This serves as a medium in which corrosion takes place. If corrosion is suspected, then the cause should be determined and steps taken to prevent damage of the equipment. It has been found that in muds containing oil as the continuous phase, little or no corrosion occurs.
8. Transmit Hydraulic Horsepower to Bit: Hydraulic horsepower generated at the bit is the result of flow volume and pressure drop through the bit nozzles. This energy is converted into mechanical energy which removes cuttings from the bottom of the hole and improves the rate of penetration.

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Mud Tank

A mud tank is a large container used to contain drilling fluid reserves, also known as drilling mud, for a drilling rig. Drilling fluid is used to reduce the friction on the drilling components to allow them to work faster and faster with less risk of breaking. Many companies produce and restructure mud tanks of various shapes and sizes for industrial use, and entrepreneurs specializing in cleaning tanks and other drilling equipment are also available. The cost for tanks and associated services varies greatly, especially when personal designs are involved.

Historically, wells in the soil near a well have been used to contain sludge, and mud tanks are sometimes referred to as mud wells in a reference to this. A modern mud tank is a large container, usually open over and divided into different compartments. In some situations, a plan can be used to reduce the risk of worker accidents, with a parapet and a gangway, allowing people to look into the tank to control the level and consistency of the drilling fluid.

New fluid can be periodically added, and components can be mixed in to modify the formulation if it is deemed necessary. Perforation mud acts as a lubricant and coolant and the demands placed on it are very high. It is essential to maintain a constant flow in a puncture site to prevent stoppages. If a plant runs out of fluid, closing it temporarily can be extremely expensive.

Several drilling fluid blends are used, depending on the type of drilling, the geology, and the equipment in use. The fluid tank to pump mud on and through the drill. Mud baths can be set to receive recycled drilling fluid, a common practice in many sites. In these situations, the fluid is pumped from the puncture site, passed through a series of tanks to separate the fluid from rocks and other debris, and then routed back into a mud tank.

These tanks can eventually become in-crusted with drilling mud and can be corroded by fluid components. For this reason, waste companies and periodically clean their tanks with high pressure cleaners and other equipment. A large company run their own mud tank cleaning and maintenance, while smaller companies can call a company to clean their mud tanks and prepare them for continuous service in the field.

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Mud Weight in Drilling Operation

Mud weight is a term used to express the amount of drilling fluids used in sinking wells, especially in the exploration and extraction of crude oil industry. The weight of the mud of a drilling fluid is generally expressed in pounds per gallon (ppg), even if more than one unit of measurement is used, including kilograms per cubic meter (kg / m 3). The drilling fluids are used to cool the tips, to remove drilling debris from the shaft, and to avoid collision wrap. A mud scale, consisting of a level sliding scale, is generally used to determine the weight of the mud.

Considering the rugged environment that generally surrounds pit drilling, the process is even more complex and delicate. Tips work at great depths and are subject to extreme conditions, like the other components involved in the process. One of the elements used to reduce the voltage on these components is the drilling fluid within which the tip operates. These sludges, as are commonly known, cool the tip, and help in the removal of drilling debris. They also suspend cuts during breaks in the drilling process and hydrostatic pressure control inside the well.

Several means are used as drilling sludges, including water, oil, and gas-based fluids. The type of drilling mud used in a particular drilling site is carefully formulated to meet specific environmental conditions with different wells, rarely using the same mixture of mud. One of the most important variables in formulating drilling fluids is mud or fluid density. Wrong mud weight values ​​can cause several serious problems, such as circulation leakage. The density of these fluids is controlled by the addition of barites or, less frequently, halite and calcium carbonate.

A specially designed sliding scale known as a mud equilibrium is used to calculate the weight of mud drilling fluids. This instrument consists of a cursor equilibrium beam equipped with a type bubble leveling system. A sealed container is attached to one end of the beam where the sample of the drilling fluid is placed. The slider is moved along the bar to determine the density of the fluid.

Mud weight values ​​are generally expressed in pounds per gallon or ppg. Other units are used if, including kg per cubic meter (kg / m 3) and grams per cubic centimeter (g / cm 3). The weighing and test procedures used to measure sludge weight values ​​are set out in a set of globally recognized standards published by the American Petroleum Institute.

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Ultrasonic Mixers for Drilling Muds and Fluid Packers

Drilling liquid (drilling mud) is used to aid drilling of oil wells, natural gas wells, exploration wells (wildcat wells) or water wells. Ultrasonic reactors are an effective technology for emulsifying blending, dispersing and degassing water-based mud (WBM, aqueous), oil-based mud (OBM, non-aqueous) or mud-based synthetic (SBM ). 

The formulation and the persistence of the quality of drilling sludge is a key factor in drilling operations today. The mud composition and characteristics affect well-drilled stability, lubrication, cooling and drilling penetration rate. Even small problems with the puncture fluid can stop the whole drilling operation. Derivatives from too dense or too heavy drilling mud excessive pressure can cause significant leakage. 

It allowed it to be generally made of fresh water, sea water, or (saturated or formiated) brine and natural clay and polymers. OBM and SBM Inverti-emulsion systems that have an oil base (diesel, mineral oil) or synthetic base (olefins and paraffins) such as continuous (external) and brine as the dispersed phase (internal). The emulsion must be sufficiently stable to withstand the addition of the water flow from the well. Less common than water in oil (Inverted oil sludge emulsion) are oil in water (oil emulsion sludges). Ultrasonic faecemulsification works for both types of emulsion and achieves good internal stability, water, or brine. 

Ultrasonic reactors are very effective and intense cavitation cutting mixers for use in production. Generally, ultrasonic reactors are used inline for high throughput single step transformation or batch processing recirculated. 

Ultrasonic can mixing for 

Manufacture of additives 

Masterbatch with high concentration to prepare 

Mix ready-to-use drilling fluids or packer fluids 

Degas drilling sludge 

Develop and formulate better sludge drilling 

Production of drilling mud additives The manufacture of chemicals and additives such as liquid polymer sludge benefits from high-capacity processing and ultrasonic cutting flexibility. Ultrasonic mixing unleashes all the potential of additives, such as viscosifiers, filter reducers or polymer additives. Ultrasonic cavitation moisturizes powders quickly and completely during drilling mud mixing. For mixing liquid / liquid emulsions, It improves in-line mixing of the two phases in the intense cavitation cutting zone.

Ultrasonic mixing improves the mass transfer to particles in liquids or boundary layers. This reduces the time needed to prepare the brine or brine, eg. calcium chloride brine, calcium bromide brine, zinc bromide brine or brine of potassium formate and cesium. 

Masterbatches of clay or additives 

Mixing ultrasonic cutting can be used to make high concentrations or high density compounds (eg calcium carbonate (plaster), deflocculents or saprophagous organisms) before adding these to the final drilling mud formulation. 

Production of Fluids and Packers Fluid Drilling 

Drilling mud performance, such as shrinkage stability, viscosity, cooling or lubrication, depends on many factors. Uniformity and consistency in quality of the utmost importance. Ultrasonic cutting mixing is very effective in the production of uniform size distribution distributions and therefore better dispersion and emulsion stability. This prevents phase separation or settling during storage, transport, or while mud wells. 

Today specific mud drilling changes frequently. Hielscher ultrasonic reactors are highly adaptable to changes in the perforation liquid formulation. By changing from a traditional mixing line to single-pass mixing ultrasonic mixing, several types of perforating mud can be made on the same ultrasonic machine. This helps reduce storage time for inventory and shelf. 

The dispersion of conventional clay (eg bentonite) and organofile clay specially treated in the fluid produces sludges and highly viscous, thixotropic or trimming-thinning gel. When exposed to high ultrasonic cutting, the viscosity drops to a flow-free state. This facilitates dispersion and manipulation. For this reason, sonication is very effective for mixing thixotropic sewage and fluidizing the cutting. Sonification results in better dispersion of bentonite / platelet particles and improved gelling characteristics. Ultrasonic dispersion of bentonite (performed with ultrasonic mixer UIP2000hdT) 

Rheological, thickening and stabilizing agents (eg gums, glycols, carboxymethylcellulose, polyanionic cellulose (PAC) or starch) require good dispersion for maximum effectiveness. 

Agents, such as weight barite (baritine) sulfite, must not separate from mud during storage, transport or perforation. In accordance with Stokes law, smaller particles of sediment slower or not at all. Dispersion ultrasound avoids larger agglomerates, which can cause dispersion instability. A dispersing system can increase the tolerance for solids, making it possible to weigh up to 20 pounds / gallon (US) or 2.4 g / cm 3 . 

Degassing of mud 

When preparing sludge drilling, clay powder and other additive powders introduce a lot of air into the circulation mud. This gas is trapped inside liquid systems and can cause loss and separation of emulsifying or stabilizing performance. Repeated compression (high pressure cycles) and rarefaction (low pressure cycles) during sonication allow decomposed gas to migrate and form small microbubbles. Ultrasonic waves then force the coalescence gas microbubbles. Ultrasonic high cavitation cutting reduces thinning cut viscosity and thixotropic drilling fluids. This way the air bubbles rise faster. This leads to the best separation of gas in reservoirs downstream of the separator or degassing under vacuum. Degassing increases mud weight, reduces viscosity and separation problems. Less gas bubbles reduce the use of emulsifiers, stabilizers, surfactants and dispersing agents. This reduces the cost per barrel. A reduction in gas content can curb aerobic microbial growth, too. 

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9 Distinct Mud Systems

For mud to manage its many tasks, a broad range of different fluid systems have been developed. 9 distinct mud systems are defined here. 

The first seven are water-based, while the eighth is oil-based. The ninth category is a specialized one in which air or gas is the continuous fluid. 

The 9 categories are:

1. Non dispersed. These may consist of spud muds, natural muds and other lightly treated systemsgenerally used for shallow wells or top-hole drilling.

2. Dispersed. At greater depths or where hole-conditions may be problematic, muds are often dispersed, typically by means of lignosulphonates or other deflocculants. These and similar products are also effective filtrate reducers.

3. Calcium treated. Divalent cations such as calcium and magnesium, when added to a mud, inhibit the swelling of formation clays and shale, and are therefore added to control sloughing shale, hole enlargement and to prevent formation damage. Hydrated lime, gypsum (calcium sulphate) and calcium chloride are principal ingredients of calcium systems. Gyp systems (note: Gyp = gypsum) usually have a pH of 9.5 to 10.5 and an excess gyp concentration of 2 to 4 lb/ bbl; Lime systems have an excess lime concentration of 1 to 15 lb/bbl and a pH of 11.5 to 12.0.

4. Polymer. Muds incorporating long-chain, high-molecular-weight chemicals are effective in increasing viscosity, flocculating muds, reducing filtrate loss and stabilizing the formation. Various types of polymers are available for this purpose, including Bentonite extenders. Bio polymers and cross-linked polymers are also used and have good shear-thinning properties at low concentrations.

5. Low solids. This includes systems in which the amount and type of solids are controlled. Total solids should not range higher than about 6% to 10% by volume (and clay < 3% by volume). One primary advantage of low-solids systems is that they significantly improve the rate of penetration.

6. Saturated salt. Include several groups: Saturated salt systems have a chloride ion concentration of 189 000 ppm. Saltwater systems have a chloride content from 6 000 to 189 000 ppm, and at its lower level are usually referred to as brackish or seawater systems.

7. Workover. Completion and workover fluids are specialized systems designed to minimize formation damage, and be compatible with acidizing and fracturing operations (acid soluble) and capable of inhibiting swelling clays that reduce formation permeability. Density is obtained  through dissolved salt to avoid long term settling.

8. Oil/synthetic. Oil-based fluids are used for high temperature wells, deviated holes and wells where pipe sticking and hole stabilization is a problem.

 They consist of two types of systems:

1) Invert emulsion muds are water-in-oil fluids and have water as the dispersed phase and oil as the continuous phase. They may contain up to 50% water in the liquid phase. Emulsifier (commonly fatty acids amine derivatives, high-molecular-weight soaps), and water concentrations are varied to control rheological and electrical stability;

2) Synthetic fluids are designed to duplicate the performance of oil-based muds, without the environmental hazards. Primary types of synthetic fluids are esters, poly alpha olefins and food grade paraffin. They are environmentally friendly, can be discharged offshore and are non-sheening and biodegradable.

9. Air, mist, foam and gas. Four basic operations are included in this specialized category according

to the IADC. These include:

1) Dry air drilling, which involves injecting dry air or gas into the wellbore at rates capable of achieving annular velocities that will remove cuttings;

2) Mist drilling involves injecting a foaming agent into the air stream, which mixes with produced water and lifts drill cuttings;

3) Stable foam uses chemical detergents and polymers and a foam generator to carry cuttings in fast-moving air stream;

4) Aerated fluids rely on mud with injected air (which reduces the hydrostatic head) to remove drilled solids from the wellbore.

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