Turbulent flow, on the other hand, is characterized by an intense local oscillating motion perpendicular to the tube axis. Although the fluid moves in a net forward direction, the transfer perpendicular to the net axial motion causes an increase in the shear stress exerted on the fluid and, thus, increases the energy loss due to friction. Due to the nature of the equipment and the flow rates used in oilfield applications, frictional losses may ultimately exceed the pressure and horsepower limitations of the pumping equipment.
The mechanism of drag reduction is not well understood, but certain polymer characteristics beneficial to drag reduction have been determined. Polymers with long chair “backbones” and a high degree of flexibility are most effective. Linear polymers are more effective than branched polymers with the same structural units and molecular weight. Guar reduces fluid friction because of its high molecular weight and highly extended structure. The amount of drag reduction is dependent on polymer concentration and can range from 20% to 70% .
