Drilling fluids processing glossary C

Cable tool drilling. A method of drilling a well by allowing a weighted bit (or chisel) at the bottom of a cable to fall against the formationbeing penetrated. The cuttings are then bailed from the bottom of thewell bore with a bailer. See: rotary drilling.
Cake consistency. According to API RP 13B, can be described as hard,soft, tough, rubbery, firm, etc.
Cake thickness. (1) A measurement of the thickness of the filter cake deposited by a drilling fluid against a porous medium, usually filter paper, according to the standard API filtration test. Cake thickness is usually reported in 32nds of an inch or millimeters. (2) A parameter of the filter cake deposited on the wall of the borehole. See: filter cake,wall cake.
Calcium. One of the alkaline earth elements with a valence of 2 and an atomic weight of about 40. Calcium compounds are a common cause of the hardness of water. Calcium is also a component of lime, gypsum, limestone, etc.
Calcium carbonate. (1) CaCO3. An acid soluble calcium salt sometimes used as a weighting material (limestone, oyster shell, etc.) in specializeddrilling fluids. (2) A term used to denote a unit and/or standard to report hardness. See: limestone.
Calcium chloride. CaCl2. A very soluble calcium salt sometimes added to drilling fluids to impart special inhibitive properties, but used primarily to increase the density of the liquid phase (water) in completion fluids and as an inhibitor to the water phase of invert oil emulsion drilling fluids.
Calcium contamination. Dissolved calcium ions in sufficient concentration to impart undesirable properties in a drilling fluid, such as flocculation, reduction in yield of bentonite, increase in fluid loss, etc. See: calcium sulfate, gyp, anhydrite, lime, calcium carbonate.
Calcium hydroxide. Ca(OH)2. The active ingredient of slaked lime. It isalso the main constituent in cement (when wet) and is referred to as‘‘lime’’ in field terminology. See: lime.
Calcium sulfate. Anhydrite, CaSO4, plaster of Paris, CaSO4
12H2O, and gypsum, CaSO4
2H2O. Calcium sulfate occurs in drilling fluids as a contaminant or may be added as a commercial product to certain drilling fluids to impart special inhibitive properties. See: gypsum,anhydrite.
Calcium-treated drilling fluids. Drilling fluids to which quantities of soluble calcium compounds have been added or allowed to remain from the formation drilled in order to impart special inhibitive properties to the drilling fluid.
Calendered wire cloth. Wire cloth that has been passed through a pair of heavy rollers to reduce the thickness of the cloth or flatten the intersections of the wire and produce a smooth surface. This process is usually done to the coarser backing cloths. See: market grade cloth,mill grade cloth.
Capacity. The maximum volume flow rate at which a solids-control device is designed to operate without detriment to separation. See: feed capacity, solids discharge capacity.
Cascade. Gravity-induced flow of fluid from one unit to another.
Cascade shaker arrangement. System that processes the drilling fluid through two or more shakers in series.
Casing. Steel pipe placed in an oil or gas well to prevent the wall of the hole in a drilled interval from caving in, as well as to prevent movement of fluids from one formation to another.
Cation. The positively charged particle in the solution of an electrolyte,which, under the influence of an electrical potential, moves toward the cathode (negative electrode). Examples are Naþ, Hþ, NH4þ, Caþ,Mgþþ, and Alþþþ.
Cation exchange capacity. The total amount of cations adsorbed on the basal surfaces or broken bond edges of a clay sample, expressed in milliequivalents per 100 grams of dry clay. See: base exchange,methylene blue titration, methylene blue test, MBT, CEC.
Caustic. See: sodium hydroxide.
Caustic soda. See: sodium hydroxide.
Cave in. A severe form of sloughing. See: sloughing.
Cavernous formation. A formation having voluminous voids, usually the result of dissolution by formation waters that or may not be still present.
Caving. Caving is a severe form of sloughing. See: sloughing, heaving.
Cavitation. Cavitation is the formation and collapse of low-pressure bubbles in a liquid. In centrifugal pumps it occurs when the pressure within the impeller chamber decreases below the vapor pressure of the liquid. As these vapor bubbles move to the impeller tip and into a higher-pressure region, they implode or collapse. The pressure at the suction entry may be considerably below atmospheric pressure if the pressure loss in the suction line is too large, if the flow rate from the pump is too large for the inlet size, or if the fluid must be lifted to excessive heights. As the bubbles move out to the tips of the impeller, they implode, releasing a large amount of energy that can actually chip metal pieces from the impeller blade. Cavitation frequently sounds like the centrifugal pump is pumping gravel. See:centrifugal pump.
CEC. See: cation exchange capacity.
Cement. A mixture of calcium aluminates and silicates made by combining lime and clay while heating. Slaked cement containsabout 62.5% calcium hydroxide, which can cause a major problem when cement contaminates drilling fluid.
Centipoise (cP). Unit of viscosity equal to 0.01 Poise. Poise equals 1 dynesecond per square centimeter. The viscosity of water at 20Celsius is 1.005 cP
(1 cP¼0.000672 lb/ft sec).
Centrifugal force. That force which tends to impel matter outward from the center of rotation. See: g force.
Centrifugal pump. A machine for moving fluid by spinning it using a rotating impeller in a pump casing with a central inlet and a tangential outlet. The path of the fluid is an increasing spiral from the inlet at the center to the outlet, tangent to the annulus. In the annular space between the impeller vane tips and the casing wall, the fluid velocity is roughly that of the impeller vane tips. Useful work is produced by the pump when some of the spinning fluid flows out of the casing tangential outlet into the pipe system. Power from the motor is used to accelerate the fluid coming into the inlet up to the speed of the fluid in the annulus. (Some of the motor power is expended as friction of thefluid in the casing and impeller.)
Centrifugal separator. A general term applicable to any device using centrifugal force to shorten and/or control the settling time required to separate a heavier mass from a lighter mass.
Centrifuge. A centrifugal separator, specifically a device rotated by an external force for the purpose of separating materials of different masses. This device is used for the mechanical separation of solids from a drilling fluid. Usually in a weighted drilling fluid, it is used to eliminate colloidal solids. In an unweighted drilling fluid, it is used to remove solids larger than colliods. The centrifuge uses high-speed mechanical rotation to achieve this separation, as distinguished from the cyclone type of separator, in which the fluid energy alone provides the separating force. See: hydrocyclone, desander, desilter.
Ceramics. A general term for heat-hardened clay products, which resist abrasion; used to extend the useful life of wear parts in pumps and hydrocyclones.
Check/suction section. The last active section in the surface system. It provides a location for the rig pump and drilling-fluid hopper suction.This section should be large enough to check and adjust drilling-fluid properties before the drilling fluid is pumped downhole.
Chemical barrel. A container in which soluble chemicals can be mixed with a limited amount of fluid prior to addition to the circulating system.
Chemical treatment. The addition of chemicals (such as caustic,thinners, or viscosifiers) to the drilling fluid to adjust the drillingfluid properties.
Chemicals. In drilling-fluid terminology, a chemical is any material that produces changes in the low-shear-rate viscosity, yield point, gel strength, fluid loss, pH, or surface tension.
Choke. An opening, aperture, or orifice used to restrict a rate of flow or discharge.
Chromate. A compound in which chromium has a valence of 6, for example, sodium dichromate. Chromate may be added to drilling fluids either directly or as a constituent of chrome lignites or chrome lignosulfonates to assist with rheology stabilization. In certain areas,chromate is widely used as an anodic corrosion inhibitor, often inconjunction with lime.
Chrome lignite. Mined lignite, usually leonardite, to which chromate has been added and/or reacted. The lignite can also be causticized with either sodium or potassium hydroxide. The chrome lignite is used for rheology stabilization and filtration control of the drilling fluid.
Circular motion. A shale shaker screen moves in a uniform circular motion when the vibrator is located at the center of gravity of the vibrating basket.
Circulation. The movement of drilling fluid through the flow system on a drilling or workover rig. This circulation starts at the suction pit and goes through the mud pump, drill pipe, bit, annular space in the hole, flowline, fluid pits, and back again to the suction pit. The time involved is usually referred to as circulation time. See: reverse circulation.
Circulation rate. The volume flow rate of the circulating drilling fluid, usually expressed in gallons per minute or barrels per minute. See:flow rate.
Clabbered. A slang term used to describe moderate to severe flocculation of drilling fluid due to various contaminants. See: gelled up.
Clarification. Any process or combination of processes the primary purpose of which is to reduce the concentration of suspended matter in liquid.
Clay. (1) A soft, variously colored earth, commonly hydrous silicatesof alumina, formed by the decomposition of feldspar and other aluminum silicates. Clay minerals are essentially insoluble in water but disperse under hydration, grinding, or velocity effects. Shearing forces break down the clay particles to sizes varying from submicron particles to particles 100 microns or larger.  (2) Solids particles of less than 2 micrometer equivalent spherical diameter. See: attapulgite clay, bentonite, high yield clay, low yield clay, and natural clays.
Clay extender. Substances, usually high-molecular-weight organic compounds, that when added in low concentrations to a bentonite or to other specific clay slurries, will increase the low-shear-rate viscosity of the system. An example would be polyvinyl acetate-maleic anhydride copolymer. See: low solids drilling fluids.
Clay-size particles. See: clay.
Closed loop mud systems. A drilling-fluid processing system that minimizes the liquid discard. Usually as much as possible of the liquid phase normally separated with drilled solids is returned to the active system.
Closed loop systems (pressurized). In underbalanced drilling, this refers to a system in which formation fluid is contained in tanks and not exposed to the atmosphere until sent to the flare line or the holding tank.
CMC. Ceramic matrix compound(s). See: sodium carboxymethylcelluose.
Coagulation. The destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of a floc-forming agent. See: floc.
Coalescence. (1) The change from a liquid to a thickened curdlike state by chemical reaction. (2) The combination of globules in an emulsion caused by molecular attraction of the surfaces.
Coarse solids. Solids larger than 2000 microns in diameter.
Coating. (1) A material adhering to a surface to change the properties of the surface. (2) A condition in which material forms a film that covers the apertures of the screening surface. See: blinding, plugging.
Cohesion. The attractive forces between molecules of the same kind, that is, the force that holds the molecules of a substance together.
Colloid. A particle smaller than 2 microns. The size and electrical charge of these particles determine the different phenomena observed with colloids, for example, Brownian movement. See: clay, colloidal solids.
Colloidal composition. A colloidal suspension containing one or more colloidal constituents.
Colloidal matter. Finely divided solids that will not settle but may be removed by coagulation.
Colloidal solids. Particles smaller than 2 microns. These are so small that they do not settle out when suspended in a drilling fluid. Commonly used as a synonym for clay. See: clay, colloid.
Colloidal suspension. Finely divided particles that are so small that they remain suspended in a liquid by Brownian movement.
Combining weight. See: equivalent weight.
Conductance. The permeability of a shaker screen per unit thickness of the screen, measured in units of kilodarcys/millimeter, while the screen is stationary.
Conductivity. Measure of the quantity of electricity transferred across unit area per unit potential per unit time. It is the reciprocal of resistivity.Electrolytes may be added to a fluid to alter its conductivity. See: resistivity.
Cone. See: hydrocyclone, hydroclone.
Connate water. Water trapped within sedimentary deposits, particularly as hydrocarbons displaced most of the water from a reservoir.
Consistometer. A thickening time tester having a stirring apparatus to measure the relative thickening time for drilling fluid or cement slurries under predetermined temperatures and pressures. See: API RP 10B.
Contamination. In a drilling fluid, the presence of any material that may tend to harm the desired properties of the drilling fluid.
Continuous phase. (1) The fluid phase that completely surrounds the dispersed phase. (2) The fluid phase of a drilling fluid: either water, oil, or synthetic oil. The dispersed (noncontinuous) phase may be solids or liquid.
Controlled aggregation. The condition in which the clay platelets are maintained stacked by a polyvalent cation, such as calcium.
Conventional drilling fluid. A drilling fluid containing essentially clay and water. Also called conventional mud.
Conventional shale shakers. Usually refers to device that vibrates screens with a circular or an unbalanced elliptical motion. These shale shakers are usually limited to processing drilling fluid through screens up to 100 mesh.
Conveyor. A mechanical device for moving material from one place to another. In a decanting centrifuge, this is a hollow hub fitted with flights rotating in the same direction but at a different speed than the centrifuge bowl. These flights are designed to move the coarse solids out of the bowl and are part of the conveyor.
Copolymer. A substance formed when two or more substances polymerize at the same time to yield a product that is not a mixture of separate polymers but a complex substance having properties different from either of the base polymers. Examples are polyvinylacetate-maleic anyhdride copolymer (clay extender and selective
flocculant), acrylamide-carboxylic acid copolymer (total flocculant),etc. See: polymer.
Corrosion. A chemical degradation of a metal by oxygen in the presence of moisture. An oxide is the by-product of corrosion.
Corrosion inhibitor. An agent that, when added to a system, slows down or prevents a chemical or corrosion. Corrosion inhibitors are used widely in drilling and producing operations to prevent corrosion of metal equipment exposed to hydrogen sulfide, carbon dioxide, oxygen,saltwater, etc. Common inhibitors added to drilling fluids are filming amines, chromates, and oxygen scavengers.
Crater. The formation of a large funnel-shaped cavity at the top of a hole resulting from either a blowout or from caving.
Creaming of emulsions. The settling or rising of particles from the dispersed phase of an emulsion as observed by a difference in color shading of the layers formed. This separation can be either upward or downward, depending on the relative densities of the continuous and dispersed phases.
Created fractures. Induced fractures by means of hydraulic or mechanical pressure exerted on the formation by the drill string and/or circulating fluid.
Critical velocity. That velocity at the transitional point between laminar and turbulent types of fluid flow. This point occurs in the transitional range of Reynolds numbers between approximately 2000 to 3000.
Crown. The curvature of a screen deck or the difference in elevation between its high and low points. See: bow.
Cryogenic (nitrogen). Nitrogen in its liquid form.
Cubic centimeter (cc). A metric-system unit for the measure of volume. A cube measuring 1 centimeter on each side would have a volume of 1 cubic centimeter. It is essentially equal to the milliliter, with which it is commonly used interchangeably. One cc of water at room temperature weighs approximately 1 gram.
Cut point. Cut point curves are developed by dividing the mass of solids in a certain size range removed by the total mass of solids in that size range that enters the separation device. A cut point usually refers to the size of particle that has a 50% chance of being discarded. See median cut.
Cutt points (pronounced ‘‘Koot’’). The equivalent spherical diameters corresponding to the ellipsoidal volume distribution of a screen’s opening sizes, as determined by image analysis. See: API RP 13E.
Cuttings. The pieces of formation dislodged by the bit and brought to the surface in the drilling fluid. Field practice is to call all solids removed by the shaker screen ‘‘cuttings,’’ although some can be sloughed material from the wall of the borehole. See: drilled solids, low-gravity solids, samples.
Cyclone. A device for the separation of solid particles from a drilling fluid. The most common cyclones used for solids separation are a desander or desilter. In a cyclone, fluid is pumped tangentially into a cone, and the fluid rotation provides enough centrifugal force to separate particles by mass (weight). See: desander, desilter, hydrocyclone,hydroclone.
Cyclone bottom. See: apex, apex valve.

Drilling fluids processing glossary B

Backpressure. The frictional or blocking pressure opposing fluid flow ina conduit. See: differential pressure.

Back tank. The compartment on a shale shaker that receives drillingfluid from the flowline. See: possum belly, mud box.

Backing plate. The plate attached to the back of screen cloth(s) for support.

Backup screen. See: support screen.

Baffles. Plates or obstructions built into a compartment to change thedirection of fluid flow.

Balanced design hydrocyclone. A hydrocyclone that has the lower apex adjusted to the diameter of the cylinder of air formed within the cone by the cyclonic forces of drilling fluid spinning within cone. This tends to minimize liquid discharge when there are no separable solids.

Balanced elliptical motion. An elliptical motion of a shale shaker screen such that all ellipse axes are tilted at the same angle toward the discharge end of the shale shaker.

Ball valve. A valve that uses a spherical closure with a hole through its center and rotates 90 to open and close.

Barite. Natural barium sulfate, BaSO4, is used for increasing the density of drilling fluids. The API standard requires a minimum of 4.20 specific gravity. Commercial barium sulfate ore can be produced from a single ore or a blend of ores and may be a straight-mined product or processed by flotation methods. It may contain minerals other than barium sulfate. Because of mineral impurities, commercial barite may vary in color from off-white to gray to red or brown. Common accessory minerals are silicates such as quartz and chert, carbonate compounds such as siderite and dolomite, and metallic oxide and sulfide compounds.

Barite recovery efficiency. Barite recovery efficiency is the ratio of the mass flow rate of barite returning to a drilling fluid from a solids control device divided by the mass flow rate of barite in the feed to the solids-control device.

Barium sulfate. BaSO4. See: barite.

Barrel (bbl). A volumetric unit of measure used in the petroleum industry consisting of 42 U.S. gallons.

Barrel equivalent. One gram of material in 350 ml of fluid is equivalent to a concentration of 1 lb of that material in an oilfield barrel of fluid.See: barrel, pound equivalent.

Base. A compound of a metal, or a metal-like group, with hydrogen and oxygen in the proportions that form an OH– radical, when ionized in an aqueous solution, yielding excess hydroxyl ions. Bases are formed when metallic oxides react with water. Bases increase the pH. Examples of bases are caustic soda, NaOH; and lime, Ca(OH)2.

Base exchange. The replacement of the cations associated with the surface of a clay particle by another species of cation, for example,the substitution of sodium cations by calcium cations on the surface of a clay particle. See: methylene blue titration, methylene blue test, MBT, cation exchange capacity, CEC.

Basicity. pH value above 7. Ability to neutralize or accept protons from acids. See: pH.

Basket. That portion of a shale shaker containing the deck upon which the screen(s) is mounted; supported by vibration isolation members connected to the bed.

Beach. Area between the liquid pool and the solids discharge ports in a decanting centrifuge or hydrocyclone.

Bed. Shale shaker support member, consisting of mounting skid or frame with or without bottom, flow diverters to direct screen underflow to either side of the skid, and mountings for vibration isolation members.

Bentonite. A colloidal clay, largely made up of the mineral sodium montmorillonite, a hydrated aluminum silicate. Used for developing a low shear rate viscosity and/or good filtration characteristics in water-based drilling fluids. The generic term ‘‘bentonite’’ is not an exact mineralogical name, nor is the clay of definite mineralogical

composition. See: gel, montmorillonite.

Bentonite (clay) extender. Additive that interacts with clay in a drilling fluid to boost viscosity; usually this at a low to moderate concentration of polymer and depends on the polymer/clay ratio.

Bernoulli Principle. One means of expressing Newton’s Second Law of Physics, that is, concerning conservation of energy. Roughly stated,this principle demonstrates that the sum of pressure and velocity through or over a device represents equal quantities, neglecting the effects of losses due to friction and/or increases by adding energy with external devices such as pumps.

Bicarb. See: sodium bicarbonate.

Bingham model. A mathematical description that relates shear stress to shear rate in a linear manner. This model requires only two constants (plastic viscosity and yield point) and is the simplest rheological model possible to describe a non-Newtonian liquid. It is very useful for analyzing drilling fluid problems and treatment. See: viscosity, pseudoplastic fluid, plastic viscosity, yield point, gel strength.

Blade. See: flight, flute.

Blinding: A reduction of open area in a screening surface caused by coating or plugging. See: coating, plugging.

Blooie line. The flowline for air or gas drilling.

Blowout. An uncontrolled escape of drilling fluid, gas, oil, or water from the well caused by the formation pressure being greater than the hydrostatic head of the fluid being circulated in the well bore. See: kick, kill fluid.

Bonded screens. Multiple screens bonded together with plastic to form a multilayered screen or screens bonded to a metal support plate.

Bonding material. Material used to secure screen cloth to a backing plate or support screen.

Bottom flooding. The behavior of a hydrocyclone when the underflow discharges whole drilling fluid rather than separated solids.

Bound liquid. Adsorbed liquid. See: absorb, absorption, adsorb, adsorption, adsorbed liquid.

Bow. See: crown.

Bowl. The outer rotating chamber of a decanting centrifuge.

Brackish water. Water containing low concentrations of any soluble salts.

Break circulation. To start movement of the drilling fluid after it has been quiescent in a borehole.

Bridge. An obstruction in a well formed by the intrusion of subsurface formations and/or cuttings or material, which prevents a tubular string from moving down a borehole.

Brine. Water containing a high concentration of common salts such as sodium chloride, calcium chloride, calcium bromide, zinc bromide, etc.

Bromine value. The number of centigrams of bromine that are absorbed by 1 gram of oil under certain conditions. The bromine check is a test for the degree of unsaturation of a given oil.

Brownian movement. Continuous, irregular motion exhibited by particles suspended in a liquid or gaseous medium, usually as a colloidal dispersion.

BS&W. Base sediment and water.

Buffer. Any substance or combination of substances that, when dissolved in water, produces a solution that resists a change in its hydrogen ion concentration upon the addition of an acid or base.

Drilling fluids processing glossary A

Abnormal pressure. A formation pore pressure that is higher than that
resulting from a water gradient.
Absolute temperature. Temperature related to absolute zero, the
temperature at which all molecular activity ceases. Calculated by
adding 460F to the temperature in Fahrenheit to obtain the absolute
temperature in degrees Rankine or by adding 273C to the
temperature in degrees Celsius to obtain the absolute temperature in
degrees Kelvin.
Absorb. To take in and make part of an existing whole. See: absorption,
adsorption, adsorb, adsorbed liquid, bound liquid.
Absorption. The penetration or apparent disappearance of molecules or
ions of one or more substances into the interior of a solid or liquid.
For example, in hydrated bentonite, the planar water that is held
between the mica-like layers is the result of absorption. See: absorb,
adsorption, adsorb, adsorbed liquid, bound liquid.
Acid. Any chemical compound containing hydrogen capable of being
replaced by elements or radicals to form salts. In terms of the dissociation
theory, it is a compound, which, on dissociation in solution,
yields excess hydrogen ions. Acids lower the pH. Examples of acids or
acidic substances are hydrochloric acid (HCl), sodium acid pyrophosphate
(SAPP), and sulfuric acid (H2SO4). See: pH, acidity.
Acidity. The relative acid strength of liquid as measured by pH. A pH
value below 7. See: pH, acid.
Across-the-line-start. A motor startup method that provides full line
voltage to the motor windings.
Active system. The volume of drilling fluid being circulated to drill
a hole. It consists of the volume of drilling fluid in the hole plus the
volume of drilling fluid in the surface tanks through which the fluid
circulates.
Additions section. A (or the) compartment(s) in a drilling-fluid system
between the removal section and the suction section that provide(s)
a well-agitated location within the fluid circulation system for the
addition of commercial materials.
Adhesion. The force that holds unlike molecules together.
Adsorb. (1) The liquid on the surface of a solid particle that cannot
be removed by draining or centrifugal force. (2) To hold a liquid on
the surface of a solid particle that cannot be removed by draining or
centrifugal force. See: absorption, adsorption, adsorb, adsorbed liquid,
bound liquid.
Adsorbed liquid. The liquid film adhering to the surfaces of solids
particles that cannot be removed by draining, even with centrifugal
force. See: absorb, absorption, adsorption, adsorb, bound liquid.
Adsorption. A surface phenomenon exhibited by a solid (adsorbent) to
hold or concentrate gases, liquids, or dissolved substances (adsorptive)
upon its surface, a property due to adhesion. For example, water, held
to the outside surface of hydrated bentonite, is adsorbed water.
Adsorption refers to liquid that is on the outside of some material,
and absorbed refers to the liquid that becomes part of the material.
See: absorb, absorption, adsorb, adsorbed liquid, bound liquid.
Aerated fluid. Drilling fluid to which air or gas has been deliberately
added to lighten the fluid column.
Aeration. (1) The technique of injecting air or gas in varying amounts
into a drilling fluid for the purpose of reducing hydrostatic head.
(2) The inadvertent mechanical incorporation and dispersion of air
or gas into a drilling fluid. If not selectively controlled, it can be very
harmful. See: air cutting, gas cut.
Agglomerate: The larger groups of individual particles usually originating
in sieving or drying operations.
Agglomeration. A group of two or more individual particles held together
by strong forces. Agglomerates are stable to normal stirring, shaking,
or handling as powder or a suspension. They may be broken by drastic
treatment such as the ball milling of a powder or the shearing of a
suspension.
Aggregate. To gather together, to clump together. A flocculated drilling
fluid will aggregate if flocculent is added.
Aggregation. (1) Formation of aggregates. (2) In drilling fluids, aggregation
results in the stacking of the clay platelets face to face. As a
consequence, the viscosity and gel strength of the fluid decreases.
Agitation. The process of rapidly moving a slurry within a tank to
obtain and maintain a uniform mixture.
Agitator. A mechanically driven impeller used to stir the drilling fluid to
assist in the suspension of solids, blending of additives, and maintenance
of uniform consistency.
Air cutting. The inadvertent mechanical incorporation and dispersion of
air into a drilling fluid system. See: aeration, gas cut.
Airlock. A condition causing a centrifugal pump to stop pumping
because of a large bubble of air or gas in the center of the pump
impeller. This prevents the liquid from entering the pump suction.
Airlocking. See: airlock.
Alkali. Any compound having pH properties higher than the neutral
state. See: base.
Alkalinity. The combining power of a base measured by the maximum
number of equivalents an acid with which it can react to form a salt. In
water analyses, it represents the carbonates, bicarbonates, hydroxides,
and occasionally the borate, silicates, and phosphates in the water.
It is determined by titration with standard acid to certain datum
points. See API RP 13B for specific directions for determination
of phenolphthalein (Pf) and methyl orange (Mf) alkalinities of the
filtrate in drilling fluids and the (Pm) alkalinity of the drilling fluid
itself. See: alkali, base, Pf, Mf, and Pm.
Alum. Aluminum sulfate, Al2(SO4)3, a common inorganic coagulant.
Aluminum stearate. An aluminum salt of stearic acid used as a defoamer.
See: stearate.
Amorphous. The property of a solid substance that does not crystallize
and is without any definite characteristic shape.
Ampere. The measurement of electric flow per second.
Amplitude. The distance from the mean position to the point of maximum
displacement. In the case of a vibrating screen with circular
motion, amplitude would be the radius of the circle. In the case of
straight-line motion or elliptical motion, amplitude would be one half
of the total movement of the major axis of the ellipse; thus, one-half
stroke. See: stroke.
Anhydrite. A mineral compound, CaSO4, that is often encountered
while drilling. It may occur as thin stringers or massive formations.
See: calcium sulfate, gypsum.
Anhydrous. Without water.
Aniline point. The lowest temperature at which equal volumes of freshly
distilled aniline and an oil sample that is being tested are completely
miscible. This test gives an indication of the characteristics (paraffinic,
naphthenic, asphaltic, aromatic, etc.) of the oil. The aniline point of
diesels or crude oils used in drilling fluid is also an indication of
the deteriorating effect that these materials may have on natural or
rubber. The lower the aniline point of a particular oil, the greater its
propensity for damaging rubber parts.
Anion. A negatively charged atom or radical, such as Cl–, OH– , SO–4,
etc., in solution of an electrolyte. Anions move toward the anode
(positive electrode) under the influence of an electrical potential.
Annular pressure loss. The pressure on the annulus required to pump
the drilling fluid from the bottom of the hole to the top of the hole in
the annular space. See: ECD.
Annular velocity. The velocity of a fluid moving in the annulus, usually
expressed in ft/min or m/min.
Annulus. The space between the drill string and the wall of the hole or
the inside surface of the casing. Also called annular space.
Antifoam. A substance used to prevent foam by increasing the surface
tension of a liquid. See: defoamer.
Aperture. (1) An opening in a screen surface. (2) The opening between
the wires in a screen cloth. See: mesh.
Apex. The lower end (conical tip) of a hydrocyclone. See: underflow
opening.
Apex valve. See: apex underflow opening.
API Bulletin RP 13E. Recommended practice for shaker screen cloth
design. Published by the American Petroleum Institute. This is an
alternative method for screen description, which is no longer used by
the industry.
API RP 10B. Recommended Practice (RP) for Testing Well Cement.
Published by the Petroleum Institute (API).
API RP 13B. Recommended Practice for Standard Procedure for
Testing Drilling Fluids at the rig. Published by the American
Petroleum Institute.
API RP 13C. Recommended Practice for Drilling Fluid Systems Process
Evaluation. Published by the American Petroleum Institute.
API filter press. A device used to measure API fluid loss conditions.
See: API fluid loss.
API fluid loss. This fluid loss is measured under ambient conditions.
Usually these are room temperature and 100 psi differential pressure.
API gravity. The gravity (weight per unit volume) of crude oil or other
related fluids as measured by a system recommended by the American
Petroleum Institute (API). It is related to specific gravity by the
following formula:
degree API=[141:5/specific gravity]-131:5
API sand. Solids particles that are too large to pass through a U.S.
Standard No. 200 screen (74-micron openings). Note that particle size
is the only standard. Particles larger than 74 microns are classified
as sand even though they may be shale, limestone, wood, or any other
material. See: API RP 13B, sand, sand content.
Apparent viscosity. The apparent viscosity in centipoise, as determined
by the direct-indicating viscometer is equal to one-half the 600-rpm
reading. It is the viscosity of a fluid at a shear rate of 1022 sec1.
See: viscosity, plastic viscosity, yield point, API RP 13B.
Aromatic hydrocarbons. Hydrocarbons that include compounds containing
aliphatic or aromatic groups attached to aromatic rings.
Benzene is the simplest example. See: live oil.
Asphalt. A natural or mixed blend of solid or viscous bitumen found in
natural beds or obtained as a residue from petroleum distillation.
Asphalt, blends containing asphalt, and altered air-blown, chemically
modified, etc.) asphaltic materials have been added to drilling fluids
for purposes such as lost circulation, emulsification, fluid loss control,
lubrication, seepage loss, shale stability, etc.
Atom. The smallest quantity of an element capable of entering into
chemical combination or that can exist alone.
Atomic weight. The relative weight of an atom of any element as
compared with the weight of 1 atom of oxygen. The atomic weight of
oxygen is 16.
Attapulgite clay. A colloidal, viscosity-building clay used principally in
saltwater drilling fluids to the low shear viscosity. Attapulgite, a special
fuller’s earth, is a hydrous magnesium aluminum silicate that has long,
needle-like platelets, as opposed to the broader, more symmetrical
platelets of bentonite.
Axial flow. Flow from a mechanical agitator in which the fluid first
moves along the axis of the impeller shaft (usually down toward the
bottom of a tank) and then away from the impeller. See: radial flow.