Glossary
Drilling fluids glossary
Plain definitions of the terms used in drilling fluid work, written for buyers, investors and anyone new to the subject. Where a term relates to part of the range supplied by Galaxy Drilling Fluids Pvt Ltd, it links to that page.
- Annulus
- The space between the drill string and the wall of the hole or casing. Mud returns to surface through it.
- Barite
- A dense mineral, barium sulfate, added to raise the density of a drilling fluid.
- Barite sag
- Settling of weighting material in the mud, most often in deviated wells, which leaves the density uneven along the hole.
- Bentonite
- A swelling clay used in water-based mud to build viscosity and filter cake.
- Bit balling
- Sticky clay packing onto the bit and slowing the rate of drilling. See Surfactants
- Bridging
- Sealing pores or fractures in the rock with solid particles sized to lodge in the openings. See LCM
- Continuous phase
- The liquid in which everything else in a drilling fluid is mixed or suspended. It gives each type of mud its name.
- Cuttings
- Pieces of rock broken off by the bit and carried to surface by the mud.
- Differential sticking
- Pipe held against the filter cake by the difference between mud pressure and the lower pressure in the rock. See Spotting Fluids
- Dispersant
- A chemical that breaks up clay structures in water-based mud to lower its viscosity. See Dispersants
- Electrical stability
- A test of how strong an invert emulsion is, measured by the voltage needed to break it. See Emulsifiers
- Emulsifier
- A chemical that holds droplets of one liquid stable within another, such as brine within oil. See Emulsifiers
- Equivalent circulating density (ECD)
- The effective density the rock feels while mud is circulating. It is higher than the static mud weight because of friction in the annulus.
- Filter cake
- The thin layer of solids left on the wall of the hole as liquid from the mud leaks into the rock. See Filter Cake Breaker
- Filtrate
- The liquid that passes through the filter cake into the rock.
- Flat rheology
- Flow properties that stay nearly even as temperature and pressure change along the well.
- Fluid loss
- Leakage of liquid from the mud into the rock. Additives that limit it are called fluid loss control. See Fluid Loss Control
- Gel strength
- How firmly mud sets when it stops moving, which decides how well it holds solids while the pumps are off.
- HPHT
- High pressure, high temperature: wells or test conditions severe enough to demand specially stable fluids.
- Hydrostatic pressure
- The pressure exerted by the weight of the column of mud in the hole.
- Invert emulsion
- A fluid in which droplets of brine are held in a continuous phase of oil or synthetic base. Oil-based and synthetic-based muds are built this way. See Emulsifiers
- Kick
- An unplanned flow of formation fluid into the well, which happens when mud pressure falls below the pressure in the rock.
- Lost circulation
- Mud escaping into the rock instead of returning to surface. See Loss Circulation
- Lost circulation material (LCM)
- Particles, flakes and fibres added to the mud to seal the paths through which it is being lost. See LCM
- Mud weight
- The density of a drilling fluid, which sets the hydrostatic pressure it applies at any depth.
- Oil-to-water ratio
- The proportion of oil to brine in the liquid part of an invert emulsion.
- Overbalance
- Mud pressure higher than the pressure of the fluids in the rock, the usual condition while drilling.
- PHPA
- Partially hydrolysed polyacrylamide, a polymer that thickens water-based mud and coats cuttings and shale. See Viscosifier
- Pill
- A small volume of specially mixed fluid pumped to a particular point in the well to do one job.
- Plastic viscosity
- The part of the resistance to flow caused by friction among the solids and liquid in the mud.
- Rheology
- How a fluid flows and deforms. In drilling, it describes how mud behaves at different pump rates and at rest.
- Scavenger
- A chemical that reacts with a harmful substance in the mud, such as hydrogen sulfide or oxygen, and removes it. See Specialities
- Shale inhibition
- Keeping water-sensitive shale from taking up water, swelling and falling into the hole. See Shale Inhibitors
- Spotting fluid
- A fluid placed around stuck pipe to help release it. See Spotting Fluids
- Spud mud
- The simple fluid used to start a well and drill its shallow top section.
- Thinner
- A chemical that lowers the viscosity of a mud that has become too thick. See Thinners
- Viscosifier
- An additive that thickens the mud so it can lift cuttings and hold solids in suspension. See Viscosifier
- Wellbore strengthening
- Treating the hole so that the rock resists fracturing, which helps prevent losses. See Well Bore Strengthening Both for WBM & OBM
- Wetting agent
- A chemical that keeps solids coated with oil in an invert emulsion, so they stay dispersed instead of clumping. See Wetting Agents
- Yield point
- A measure of the force needed to start mud flowing, which reflects how strongly its particles attract one another and bears on hole cleaning.