Pressure Loss in the Drillstring
Once passed the surface equipment, the fluid will flow through the drillstring. In hydraulic calculations, these parts of the circulating system are considered circular pipes. In typical field operations, fluid velocities are in the order of 1000 ft/min (300 m/min). At such velocities, the fluid is in turbulent flow.
The pressure required to circulate fluid in turbulent flow varies by approximately 1.8 power of the flowrate. Doubling the flowrate would increase the pressure drop in the drillstring by approximately 3.5 times. Typically, the pressure losses in the drillstring are about 35 percent of the total pump pressure.
With this in mind, it will be necessary to know how much pressure will be required to pump the fluid through the drillstring, at a given rate.
