The displacement of drilling fluid by the movement of the drill string or casing pipes produces pressure variations in the borehole. The velocity of this displacement governs the magnitude of the pressure change which can add or subtract to the hydrostatic pressure of the mud to produce surge or swab pressure, respectively.

The surge or swab pressure computation techniques presented in this paper are based on sound, easy to follow, step-by-step analysis of steady laminar couette flow of non-Newtonian power-law fluids through a concentric annular wellbore. The annular geometry is made of a stationary outer pipe and a steady axial motion of an inner pipe.

By employing the computed surge pressures, in combination with family of curves, the maximum velocities at which the casing pipes can be run in the hole without the danger of fracturing the formation are obtained. The results obtained from these analysis will aid in proper design and optimization of drilling programs.

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