Critical Liquid Velocities for Low Concentration Sand Transport

Abstract

The transport of solid particles is a concern for several industries and has been the source of extensive research for many years. One topic that has been studied is the critical velocity required to transport particles, but the transport behavior used to determine the critical velocity can be different. For example, one commonly defined critical velocity is the minimum velocity necessary to keep the particles fully suspended. However, this study examined the sand behavior with two different definitions for critical velocity. The first definition simply requires the sand to move enough to prevent a permanent bed from forming. The sand behavior when this velocity requirement is met can be described as intermittent scouring and stopping. All particles do not need to move continuously. The second definition of critical liquid velocity requires the sand particles to continuously move along the bottom of the pipe. The sand behavior when this velocity requirement is met is described as continuous scouring and not fully suspended. Numerous past experiments have amassed a significant amount of slurry data, but the majority of the data is for particle volume concentrations greater than 1%. However for many cases such as in oil and gas production, particle concentrations much below 1% are present. So to examine transport for lower concentrations, experiments were conducted for volume concentrations of 0.01%, 0.1%, and 1%. Three different sand diameters and two different liquid viscosities were also used to observe their effects on the critical liquid velocities. All tests were conducted in transparent, horizontal pipe to observe particle behavior. Results have shown that as particle size, concentration, and liquid viscosity increase, the required critical liquid velocity also increases. Experimental results are compared to existing data and models to examine the effect of concentration, focusing on volume concentrations below 1%.