Viscosity – liquid and gaseous substances’ capability to resist mutual drift of adjacent layers (inner friction). Most often viscosity depends on pressure and temperature. In most cases viscosity of liquids slightly grows with increase of pressure and decreases with increase of temperature.

Viscosity is defined by two factors: dissolved gas breakout leading to increase of residual oil viscosity, and volumetric expansion of oil at decrease of pressure leading to viscosity reduction. The first factor has stronger impact. Viscosity of gases goes up significantly with increase of both pressure and temperature.

Viscosity is one of the most important technical parameters of oil, refined products, gas condensates and fractions. Viscosity determines the choice of oil production methods, technologies used for lifting it to the surface, field gathering and pre-processing of crude and gas, conditions of transportation and pumping of petroleum products, flow resistance during their transportation via pipelines, etc. For some types of fuels and lubricants viscosity is a proscriptive indicator.

In the processes of solid commercial minerals separation viscosity impacts the particles’ movement speed in a suspended matter and is the key dense separation parameter. Viscosity depends not only on suspended matter density (ration between solid and liquid matters), but also on the size and hydrophilic properties of the particles.