Surge Pressure in Conduits Containing Non-Newtonian Drilling Fluids: A Comparative Study on Impact of in Situ Thermal Conditions, Salinity, and Measurement Apparatus

Surge and swab pressure are two well-known parameters limiting velocity of pipe movement in various drilling operations. The detailed information about the effect of thermal conditions, fluid properties, and measurement approach on surge pressure, however, has not been deeply addressed yet. This paper compares the behavior of surge pressure of sepiolite-based mud against bottom-hole temperature for different salinities and rheological models (Herschel-Bulkley (HB), Bingham plastic (BP), and power law (PL)). As a non-Newtonian fluid, seven samples of sepiolite-based mud, a thermally stable drilling fluid, were used to measure their rheological constants by both a high pressure-high temperature (HTHP) dynamic rheometer and a classical viscometer. To calculate surge pressure, a computer code was developed in which the experimentally measured rheological constants and frictional pressure loss equations, available in the literature, were used as input data and governing equations, respectively. Surge pressures calculated based on viscometer's measurements were relatively higher than those based on rheometer measurements. Even though viscometer is usually used in field measurements, the results of this study emphasize the privilege of using rheometer data to successfully predict surge pressure. In drilling fluids with NaCl intrusion, unlike viscometer, rheometer was able to catch the true behavior of surge pressure against temperature. This study also shows that fresh water sepiolite-based mud delivers higher surge pressure compared to salt (NaCl) semi- and fully saturated muds, but no remarkable difference was observed between the results of semisaturated and fully saturated sepiolite-based muds.