Ultra-fine solids. Particles whose diameter is between 2 and 44 microns.
Ultra-fine wire cloth. A group of industrial wire cloth specifications with lighter than normal wire. The wire diameter of this grade produces the highest percentage of open area of all other grades for any specific mesh size. This cloth is used in multiple layer screens. See: market grade cloth, mill grade cloth, tensile bolting cloth, and calendered.
Ultraviolet light. Light waves shorter than the visible blue and violet waves of the spectrum. Crude oil, colored distillates, residium, a few drilling-fluid additives, and certain minerals and chemicals fluorescein the presence of ultraviolet light. These substances, when present in drilling fluid, may cause the drilling fluid to fluoresce.
Unbalanced elliptical motion. An elliptical motion of a shale shaker screen such that the ellipse axes at the feed end are tilted toward the discharge end of the screen and the ellipse axes at the discharge end are tilted toward the feed end. Usually these screens are tilted downward to assist solids removal from the end of the screen. The vibrator is usually located above the center of gravity of the shaker basket.
Underflow. (1) Centrifugal separators: the discharge stream from centrifugal separators that contains a higher percentage of solids than does the feed. (2) Screen separators: the discharge stream from screen separators that contains a lower percentage of solids than does the feed.
Underflow header. A pipe, tube, or conduit into which two or more hydrocyclones discharge their underflow.
Underflow opening. See: apex, apex valve.
Undersize solids particles. (1) Particles, in a given situation, that will pass through the mesh of the screen in use. (2) Particles, in a given situation, that will remain with the liquid phase when subjected to centrifugal force.
Underslung. Field terminology denoting that the support ribs for the shaker screen are located above the screen surface. See: overslung.
Tannic acid. The active ingredient of quebracho and other quebracho substitutes such as mangrove bark, chestnut extract, hemlock, etc.
Temperature survey. An operation to determine temperatures at various depths in the well bore. This survey is used to find the location of inflows of water into the borehole or where proper cementing of the casing has taken place.
Tensile bolting cloth. A group of industrial wire cloth specifications woven of extremely smooth and durable stainless steel in a square mesh pattern. The wire diameter is lighter than mill grade cloth, producing a higher percentage of open area. See: market grad cloth, mill grade cloth, ultra-fine wire cloth, and calendered.
Tensioning. The stretching of a screening surface of a shale shaker within the vibrating frame, to the proper tension.
Testing sieve. A cylindrical or traylike container with a screening surface bottom of standardized apertures. See: sieve.
Thermal decomposition. Chemical breakdown of a compound or substance by temperature into simple substances or into its constituent elements. Starch thermally decomposes in drilling fluids as the temperature approaches 300 F.
Thinner. Any of the various organic agents (e.g., tannins, lignins, lignosulfonates, etc.) and inorganic agents (pyrophosphates, tetraphosphates, etc.) that are added to a water-based drilling fluid to reduce the low-shear-rate viscosity and/or thixotropic properties by deflocculation.
Thixotropy. The ability of a fluid to develop gel strength with time. That property of a fluid at rest that causes it to build up a rigid or semirigid gel structure if allowed to remain at rest. The fluid can be returned to a liquid state by mechanical agitation. This change is reversible. See: gel strength.
Thrust. A force that pushes; for example. as solids experience a thrust on a shale shaker screen.
Tighten-up emulsion. Jargon describing condition in oil-based drilling fluids in which either chemicals or shear or both are used to emulsify water in oil into smaller droplets to prevent the emulsion from breaking, or coming apart. Also known as tighten-up emulsion mud.
Titration. The process of using a standard solution in order to determine of the amount of some substance in another solution. The known solution is usually added in a definite quantity to the unknown until a reaction is complete.
Tool joint. A drill-pipe coupler consisting of a threaded pin and a box of various designs and sizes.
Torque. (1) The turning effort caused by a force acting normal to the radius at a specified distance from the axis of rotation. Torque is expressed in pound-feet (pounds at a radius of one foot). Torque, lb-ft¼force, lbs lever arm, ft. (2) Drill string connections require a specific torque to be properly tightened. The drill string in a borehole experiences a frictional force as it is rotated. This causes a torque in the drill string. Torque reduction can usually be accomplished by the addition of various drilling-fluid additives.
Total depth (TD). The greatest depth reached by the drill bit in a particular well.
Total dilution. The volume of drilling fluid that would be built to maintain a specified fraction of drilled solids over a specified interval of footage if there were no solids-removal system.
Total head. The sum of all the heads within a system (total head= velocity head + pressure head + elevation head).
Total nonblanked area. The net unblocked area, in square feet, that will permit the passage of fluid through a screen. Some screen designs can eliminate as much as 40% of the gross screen panel area from fluid flow due to backing plate and bonding material blockage.
Tour. Pronounced like ‘‘tower.’’ A person’s turn in an orderly schedule, designating the shift of a drilling crew.
Trenchless drilling. Excavating material near the surface for tunnels, cables, pipelines, etc., by drilling instead of digging ditches.
Trip. The process of pulling the drill string from the hole and running it back to the bottom again. One way (either in or out) is referred to as a half-trip. See: round trip.
Trip tank. A gauged and calibrated vessel used to account for fill and displacement volumes as pipe is pulled from and run into the hole. Close observation allows early detection of formation fluid entering the well bore and of drilling fluid loss to a formation.
Turbidity. A condition in a clear fluid that causes a lack of clarity caused by the presence of suspended matter, resulting in the scattering and absorption of light rays.
Turbulent flow. Fluid flow in which the velocity at a given point changes constantly in magnitude and the direction of flow; pursues erratic and continually varying courses. See: critical velocity, Reynolds number.
Twist-off. The severing or failure of a joint of drill pipe caused by excessive torque.
