Surge
While running in the drill string or casing in the well, the downward motion of the string forces the drilling fluid out of the flowline. This upward flow causes frictional force with the wellbore wall and pipe that acts downwards. At the same time, the fluids immediately adjacent to the string are dragged downwards. This creates a piston effect and adds additional pressure to the hydrostatic pressure. This additional pressure is called 'Surge Pressure'. Excessive surge pressures can increase the Bottom hole pressure to high levels and induce losses.
More Topics and Illustrations in Upstream Oil & Gas
e-Learning Resources on Surge and Swab Pressures while drilling