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.
