Salt. A class of compounds formed when the hydrogen of an acid is partially or wholly replaced by a metal or a metallic radical. Salts are formed by the action of acids on metals, or oxides and hydroxides, directly with ammonia and by other methods. See: sodium chloride.
Saltwater drilling fluid. A water-based drilling fluid whose external liquid phase contains sodium chloride or calcium chloride.
Saltwater mud. See: saltwater drilling fluid.
Samples. Cuttings obtained for geological information from the drilling fluid as it emerges from the hole. They are washed, dried, and labeled as to the depth.
Sand. (1) Particle-size classification for solids larger than 74 microns. (2) A loose, granular material resulting from the disintegration of rocks with a high silica content. See: API RP 13B, API sand.
Sand content. The solids particles retained on a U.S. Standard No. 200 test screen, expressed as the bulk percentage by volume of the drilling fluid slurry sample. The opening in this screen is 74 microns. The retained solids may be of any mineral or chemical composition and characteristic. For example, barite, shale, mica, silica, steel, chert, etc., larger than 74 microns are called API sand. See. API sand.
Sand trap. The first compartment and the only unstirred compartment in a well-designed drilling-fluid system intended as a settling compartment.
Scalping shakers. The first set of shale shakers after the flowline in a cascade shaker arrangement. These shakers are usually circular or elliptical motion shakers with coarse mesh screens that are used to remove the bulk of the large-diameter drilled solids or gumbo. This initial fluid preparation allows the second set of fine-screen shale shakers in the series to operate more efficiently with less possibility of flooding. See: fine-screen shale shakers, flooding, blinding.
Screen cloth. A type of screening surface, woven in square, rectangular, or slotted openings. See: wire cloth.
Screen support rubbers. Elastomers that cushion the contact between screens and shale shaker frames.
Screen underflow. The discharge stream from a screening device that contains a greater percentage of liquids than does the feed. See: liquid discharge.
Screening. A mechanical process resulting in a division of particles on the basis of size by their acceptance or rejection by a screening surface.
Screening surface. The medium containing the openings for passage of undersize material.
Scroll. See: flute.
Self-lubricating. Units that provide their own means of lubrication.
Separation potential. Separation potential of a shale shaker screen is the size distribution of equivalent spherical volumes calculated by determining the equivalent ellipsoidal volumes of at least 1500 openings in a screen as determined by image analysis. Also called the Cutt point distribution. See: Cutt point.
Separator. A tank in which mixed water, oil, and gas are allowed to separate by gravity or enhanced force.
Separator (open/atmospheric). A separator for drilling fluid/formation fluid that is open to atmospheric pressure.
Separator (closed/pressurized). A separator for drilling fluid/formation fluid that is closed and pressurized.
Separator (West Texas). A type of open separator. A large tank at atmospheric or 1–3 psi gauge that is used to separate gas from drilling fluid at the flowline.
Settling velocity. The velocity a particle achieves in a given fluid when gravity forces equal friction forces of the moving particle, that is, when the particle achieves its maximum velocity.
Shale. Stone of widely varying hardness, color, and compaction that is formed of clay-sized grains (less than two microns). See: natural clay.
Shale shaker. Any of several mechanical devices for removing cuttings and other large solids from drilling fluid. Common examples are the vibrating screen and rotating cylindrical screen.
Shale stabilizer. Drilling-fluid additive that reduces the rate of interaction of water with the clays in shale. Also known as shale shaker inhibitor.
Sharpness of cut. The slope of a straight line drawn between the solids separated at the 84% point and the 16% point on a graph of the percentage of solids separated versus particle size. The more vertical the slope, the sharper the cut. Also known as sharpness of separation.
Shear rate. The change of velocity with respect to the distance perpendicular to the velocity changes. See: rate of shear.
Shear stress. The force per unit of an area parallel to the force that tends to slide one surface past another. See: viscosity, Bingham model, plastic viscosity, yield point, gel strength.
Shear thinning. Opposite of dilatant. The apparent viscosity decreases instantaneously with increasing shear rate. See: apparent viscosity, viscosity, Bingham model, plastic viscosity, yield point, gel strength.
Short circuiting. A hydraulic condition existing in parts of the tank basin, reservoir, or hydrocyclone in which the time of travel of liquid/ solids is less than the normal flowthrough time—for instance, if the surface tanks contain very viscous fluid, but the returns from the flowline have a very low viscosity; the flowline returns might tend to channel across the top of the surface system toward the pump suction. In this case the flowline returns would be ‘‘short circuiting’’ or bypassing the solids-separation equipment. In hydrocyclones, separable solids that pass directly from the feed inlet and out through the vortex finder without passing through the cone section of the
hydrocyclone have ‘‘short circuited’’ the hydrocyclone processing system.
Shute. In a woven cloth, the direction of the wires running perpendicular to the loom or running across the roll of cloth. In wire cloth production, these are the short or transverse wires. See: weft.
Sieve. See: testing sieve.
Sieve analysis. The mass classification of solid particles passing through or retained on a sequence of screens of increasing mesh count. Analysis may be by wet or dry methods. See: particle size distribution.
Silencer. A tank or pit used to muffle the sound at the blooie line.
Silt. Materials whose particle size generally falls between 2 and 74 microns. A certain portion of dispersed clays and barite fall into this particle size range, as well as drilled solids.
Size distribution. See: particle size distribution.
Slip. The difference between synchronous speed and operating speed compared with synchronous speed, expressed as a percentage. If expressed in rpm, slip is the difference between synchronous speed and operating speed.
Sloughed solid. A solid entering the well bore from the exposed formation; not a drilled solid.
Sloughing. A situation in which portions of a formation fall away from the walls of a hole, as a result of incompetent unconsolidated formations, tectonic stresses, high angle of repose, wetting along internal bedding planes, or swelling of formations. See: caving, cuttings, heaving.
Slug. A small volume of weighted fluid pumped into the drill string to keep the drilling fluid liquid level below the rig floor while pulling drill pipe during a trip. This prevents drilling fluid from spilling on the rig floor as the pipe is pulled. See: pill.
Slug tank. A small compartment (normally adjacent to the suction compartment) used to mix special fluids to pump downhole. The most common use is to prepare a slug or a small volume of weighted mud before a trip. See: pill tank.
Slurry. A mixture or suspension of solid particles in one or more liquids.
Sodium bicarbonate. NaHCO3. A material used extensively for treating cement contamination and occasionally other calcium contamination of drilling fluids. It is the half-neutralized salt of carbonic acid. See: bicarb.
Sodium carboxymethylcelluose. An organic polymer, available in various grades of purity, used to control filtration, suspend weight material, and build low-shear-rate viscosity in drilling fluids. It can be used in conjunction with bentonite where low-solids drilling fluids (muds) are desired. See: CMC, low-solids drilling fluids.
Sodium chloride. NaCl. Commonly known as salt. Salt may be present in the drilling fluid as a contaminant or may be added purposely for inhibition. See: salt.
Sodium chromate. Na2CRO4. See: chromate.
Sodium hydroxide. NaOH. Commonly referred to as ‘‘caustic’’ or ‘‘caustic soda.’’ A chemical used primarily to raise pH.
Sodium polyacrylate. A synthetic, high-molecular-weight polymer of acrylonitrile used primarily for fluid loss control.
Sodium silicate drilling fluids. Special class of inhibited chemical drilling fluid using sodium silicate, saltwater, and clay.
Solid. A firm substance that holds its form; not gaseous or liquid.
Solids. All particles of matter in the drilling fluid, that is, drilled formation cuttings, barite, bentonite, etc.
Solids content. The total amount of solids in a drilling fluid. This is usually determined by distillation that measures the volume fraction of both the dissolved and the suspended, or undissolved, solids. The suspended solids content may be a combination of high– and low– specific gravity solids and native or commercial solids. Examples of dissolved solids are the soluble salts of sodium, calcium, and magnesium.
Suspended solids make up the wall cake; dissolved solids remain in the filtrate. The total suspended and dissolved solids contents are commonly expressed as percentage by volume and less commonly as percentage by weight. See: retort.
Solids discharge. That stream from a liquid/solids separator containing a higher percentage of solids than does the feed.
Solids discharge capacity. The maximum rate at which a liquid/solids separation device can discharge solids without overloading.
Solids removal equipment efficiency. A measure of the performance of surface equipment in removing drilled solids from the drilling fluid. It is a calculation based on a comparison of the dilution required to maintain the desired drilled-solids content with that which would have been required if no drilled solids were removed. Also called solids removal equipment performance and drilled solids removal system performance.
Solids separation equipment. Any and all of the devices used to remove solids from liquids in drilling, that is, shale shaker, desander, desilter, mud cleaner, and centrifuge.
Solubility. The degree to which a substance will dissolve in a specific solvent.
Solute. A substance that is dissolved in another (the solvent).
Solution. A mixture of two or more components that form a homogeneous single phase. An example of a solution is salt dissolved in water.
Solvent. Liquid used to dissolve a substance (the solute).
Souring. A term commonly used to mean fermentation.
Specific gravity (SG). The weight of a specific volume of a liquid, solid, or slurry in reference to the weight of an equal volume of water at a reference temperature of 3.89oC (water has a density of 1.0 g/cc at this temperature).
Specific heat capacity. The number of calories required to raise 1 g of a substance one degree Celsius.
Spray bar. A pipe located over the bed of a shale shaker through which dilution fluid is sprayed onto the screen surface during separation of the drilled solids. In practice, spray bars may supply a mist or small amount of liquid, not a hard spray, to prevent washing fine solids through the screen panels and back into the circulating system.
Spray discharge. See: spray underflow.
Spray underflow. The characteristic underflow of certain balanced hydrocyclones discharging to the atmosphere and not overloaded with separable solids.
Spud mud. The drilling fluid used when drilling starts at the surface often a thick bentonite-lime slurry.
Spudding in. The initiating of the drilling operations in the first top-hole section of a new well.
Spurt loss. The flux of fluids and solids that occurs in the initial stages of any filtration before pore openings are bridged and a filter cake is formed. See: surge loss.
Square mesh. Screen cloth with the same mesh count in both directions.
Square weave. See: square mesh.
Squeeze. A procedure whereby slurries of cement, drilling fluid, gunk plug, etc., are forced into the formation by pumping into the hole while maintaining a backpressure. This is usually achieved by closing the blowout preventers or by using a retrievable downhole packer.
Squirrel-cage motor. An induction motor that gets its name from the rotor assembly that looks like a squirrel cage, typical of those used earlier in the twentieth century. The cage consists of rotor bars secured at each end to the shorting rings. An induction motor is one in which there is no physical electrical connection to the rotor. Current in the rotor is induced by the magnetic field of the stator.
Stability meter. An instrument to measure the breakdown voltage of oil-based drilling fluids. This gives an indication of the emulsion stability.
Stacking a rig. Storing a drilling rig upon completion of a job when the rig is to be withdrawn from service for a period of time.
Starch. A group of carbohydrates occurring in plant cells. Starch is specially processed (pregelatinized) for use in drilling fluids to reduce filtration rate and occasionally to increase the viscosity. Without proper preservative, starch can ferment.
Static. Not moving, or at rest. Opposite of dynamic. See: quiescence.
Stearate. Salt of stearic acid, which is a saturated, 18-carbon fatty acid. Certain compounds, such as aluminum stearate, calcium stearate, and zinc stearate, have been used in drilling fluids for defoaming, lubrication, air drilling in which a small amount of water is encountered, etc.
Stiff foam. A foam in which a bentonite or long-chain polymer has been added.
Stirrer. See: agitator, mechanical agitator.
Stokes’ law. Stokes’ law states that the terminal settling velocity of a spherical particle is proportional to the square of the particle diameter, the acceleration of gravity, and the density difference between the density of the particle and the density of the liquid medium; the terminal settling velocity is inversely proportional to the viscosity of the liquid medium:
VT =[ gDP^2(ρS-ρL)(10^-6)]/116ρ
VT=terminal settling velocity, in in./sec
DP=particle diameter, in microns
ρS=density of the solids, in g/cm3
ρL=density of the liquid, in g/cm3
μ=viscosity of the feed slurry, in centipoise
Stormer viscometer. A rotational shear viscometer used for measuring the viscosity and gel strength of drilling fluids. This instrument has been largely replaced by the direct-indicating viscometer.
Streaming potential. The electrokinetic portion of the spontaneous potential (SP) electric-log curve that can be significantly influenced by the characteristics of the filtrate and filter cake of the drilling fluid.
Streamline flow. See: laminar flow.
Stroke. The distance between the extremities of motion or total displacement normal to the screen; that is, the diameter of a circular motion or twice the amplitude. See: amplitude.
Stuck. A condition whereby the drill pipe, casing or any other device inserted into the well bore inadvertently becomes lodged in the hole. Sticking may occur while drilling is in progress, while casing is being run in the hole, or while the drill pipe is being tripped. Frequently a fishing job results.
Stuck pipe. See: differential pressure sticking, stuck.
Suction compartment. (1) The area of the check/suction section from which drilling fluid is picked up by the suction of the mud pumps. (2) Any compartment from which a pump moves fluids.
Sump. (1) A disposal compartment or earthen pit for holding discarded liquids and solids. (2) The pan or compartment below the lowest shale shaker screen.
Supersaturation. If a solution contains a higher concentration of a solute in a solvent than would normally correspond to its solubility at a given temperature, a state of supersaturation exists. This is an unstable condition, because the excess solute separates when the solution is seeded by introducing a crystal of the solute. The term is frequently used erroneously for hot salt drilling fluids.
Support screen. A heavy, wire mesh either plain or calendered that supports a finer mesh screen for use in filtering or screen separation. See: backup screen.
Surface active materials. See: surfactant.
Surface tension. Generally the cohesive forces acting on surface molecules at the interface between a liquid and its own vapor. This force appears as a tensile force per unit length along the interface surface and is usually expressed in units of dynes per centimeter. Since the surface tension is between the liquid and the air, it is common practice to refer to values measured against air as surface tension, and to use the term ‘‘interfacial tension’’ for measurements at an interface between two liquids or a liquid and a solid. See: interfacial tension, emulsion.
Surfactant. Material that tends to concentrate at an interface of an emulsion or a solid/liquid interface. Used in drilling fluids to control degree of emulsification, aggregation, dispersion, interfacial tension, foaming, defoaming, wetting, etc.
Surfactant drilling fluid. A drilling fluid that contains a surfactant, usually to effect control over the degree of aggregation and dispersion or emulsification.
Surge. The pressure increase in a well bore caused by lowering tubulars. Viscous drilling fluid flowing up the annulus, displaced by drill pipe, tubing, or casing, creates the pressure surge.
Surge loss. This is a colloquial term used to describe a spurt of filtrate and solids that occurs in the initial stages of any filtration before pore openings are bridged and a filter cake is formed. The preferred term is ‘‘spurt loss.’’ See: spurt loss.
Suspensoid. A mixture that consists of finely divided colloidal particles floating in a liquid. The particles are so small that they do not settle but are kept in motion by the moving molecules of the liquid (Brownian movement).
Swabbing. When pipe is withdrawn from the hole in a viscous drilling fluid or if the bit is balled, a decrease in pressure in the well bore can cause formation fluid to flow into the well.
Swelling. See: hydration.
Synergism. Term describing an effect obtained when two or more products are used simultaneously to obtain a certain result. Rather than the result of each product being additive to the other, the result is a multiple of the effects.
Synergistic properties. See: synergism.