An easy to use transient surge swab model has been developed. The model takes into account dampening of pressure peaks due to fluid compression and elasticity of open hole and casing. Contributions from acceleration are included. The model is fully discretised allowing pressure and temperature dependent fluid properties, and a large number of changes in drill string and casing diameters. The model will help drilling engineers to avoid getting outside the pore and fracture pressure window during tripping operations without slowing down more than necessary. Controlled field measurements have been made in two North Sea HPHT wells, one with water based and one with oil based drilling fluid. Surge and swab pressures were measured at different hook velocities, both with open string and when pumping. The effect of rotating before pulling drill string to break gel was investigated. The transient model reproduced relevant measured data with adequate accuracy when there is little gel strength in the fluid. When the drilling fluid is gelled up after a long static period, measured pressure peaks are significantly above calculated pressure. The observed effects are expected to be of importance when drilling any critical well, which may be deep water, HPHT, or extended reach wells.

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