Sand Transport Modeling in Multiphase Pipelines

Abstract

Abstract Prediction of the critical flow rate that will result in sand bed formation in multiphase flow is a critical aspect of multiphase production. Many correlations have been developed for solids transportation in multiphase flow; however, all of them treat the multiphase flow in an ad hoc way that does not respect the complexity of the phenomenon. Further, many approaches rely on correlations that have been developed for much higher solids loading than would occur in oil and gas production. In this paper, first a correlation for liquid-solid transport is developed, based on data taken in the SINTEF STRONG JIP. A good fit to both sand bed height and measured pressure drop is obtained. A critical aspect of the model is the assumption that there is a critical slip velocity between the sand and liquid which remains relatively constant over a wide range of flow velocities. Second, the particle diameter is used to augment the surface roughness. A critical velocity correlation is developed, based on solid and fluid properties, and pipe diameter. An essential feature of the model is that the critical slip between the liquid and solid phases is unaffected by the presence of gas. Good fit to the data is obtained. A sand model is developed using OLGA2000 which does a good job in fitting sand hold-up against the experimental data. Such a model can be used to predict sand bed formation potential in field lines. Introduction Sand is often produced out of the reservoir in both onshore and offshore production systems, particularly in reservoirs that have a low formation strength. Sand production may be continuous, or sudden - as when a gravel pack fails. In the case that no downhole sand control is done, or that a sandcontainment strategy fails, a sand-management strategy must be employed, with operations designed to tolerate a certain amount of sand production. Deposition of sand beds poses several risks, including increased frictional pressure losses, increased risk of corrosion due to microbial attack under the sand bed, and increased risk of equipment failure due to sand. Sand transport in near-horizontal pipelines has four main regimes, depending on the fluid flow rate. Below a critical velocity, sand will drop out of the carrier fluid and form a stable, stationary sand bed. As the sand bed builds over time, the fluid above the bed is forced into a smaller cross-sectional area, causing the fluid velocity to increase. When the velocity reaches a critical value, sand is transported in a thin layer along the top of the sand bed. A steady-state is reached, such that the sand eroded from the top of the bed is replaced by new sand production from upstream. At higher velocities, the sand bed begins to break up into a series of slow-moving dunes, with sand particles transported from the upstream to the downstream side of the dune. As the flow velocity increases still further, the dunes break up entirely, and the sand forms a moving bed along the bottom of the pipe.