(61a) Experimental and Modeling Investigation of Sand Dune and Sand Bed Transition

Solid particles are encountered in oil and gas pipelines when producing from unconsolidated reservoirs. Particle deposition occurs most often in stratified flow regime due to low phase velocities. This accumulation can cause several difficulties in production fluid such as increased pressure loss, erosion, corrosion, production decline etc. Particles that stop moving and accumulate along pipes do so either as separated stationary dunes or as a continuous stationary bed. The objective of this paper is to investigate experimentally and theoretically the conditions that result in the transition of the sand bed flow regime from separated dunes to stationary bed.

The experimental data is acquired in a 10 cm (4 in.) ID pipe, utilizing air as the gas phase, water-PAC, and water as the liquid phases. Effect of particle size (glass beads) is measured by using particles of specific gravity of 2.65 and three different sizes, namely, 45-90, 125-250 and 425-600 µm, with concentrations up to 10,000 PPM. The effect of superficial velocities as well as viscosity on the sand bed flow patterns are also measured. The experimental data show that formation of dunes and bed is strongly dependent on particle concentration, particle size, phase velocities and liquid viscosities.

A mechanistic modeling is developed to predict the transition between separated dune and stationary bed, sand bed flow regimes. The model developed includes rolling and saltation mechanisms for particles located between two sand piles. If these particles are salted or rolled up on a pile, transition to separated dunes occur, otherwise, stationary bed exits along the pipe. The comparison between the model and experimental data confirms an averaged uncertainty less than 20% for all conditions.