Minimum sand transport conditions in gas-solid-liquid three-phase stratified flow in horizontal pipelines

Producing sand during oil and gas production is unavoidable. Sand is produced along with oil and gas and its deposition in pipelines is a significant risk as it can cause pipe corrosion and flow assurance difficulties. It is therefore key that flow conditions are sustained to guarantee lack of deposition of sand particles. The minimum combination of mixture velocities that guarantee continuous sand motion is known as the minimum transport condition (MTC). Here, we investigate the effect both of sand concentration and particle diameter on MTC in a horizontal pipeline in the stratified flow regime. Non-intrusive conductivity probes were utilised for the detection of sand. These sensors are commonly used for the measurement of film thickness in gas and liquid flows, but we demonstrate their use here for sand detection after suitable calibration. It was observed that at the ultra-low sand concentrations of our experiments, MTC increases with both sand particle diameter and concentration. We developed a new correlation based on Thomas's lower model but included a sand concentration correction term that also applies at low particle concentrations. The correlation's predictions compared favourably with our measurements at MTC as well as data obtained from the open literature at medium concentrations.