A Semi-Mechanistic Model for Predicting Sand Erosion Threshold Velocities in Gas and Multiphase Flow Production

Abstract Sand production causes many operational problems for the oil and gas industry and can cause erosion of production equipment, well tubing, elbows and fittings. Operators would like to predict a threshold operational flow condition below which erosion failure is minimized. The API RP 14 E provides a guide to calculate a "threshold erosional velocity" in multiphase flow production, but this guideline is not intended for sand erosion! As an alternative to API RP 14E, a modified model for calculation of erosion in multiphase flow is presented that considers the effects of particle velocities in gas and liquid phases upstream of the elbow. Local fluid velocities in multiphase flow are used as a basis to determine representative particle impact velocities. Additionally, the effects of turbulent eddies near the elbow walls are considered through a particle Stokes number. Erosion experiments are also conducted on elbows in a 2 to 4-inch large scale multiphase flow loop with gas, liquid and sand flowing in vertical and horizontal test sections. Based on the experimental data for different flow regimes including slug, wet gas and annular flow, a method for improving a previous model has been discussed and is implemented to predict erosion rates in multiphase flow. The results from the model are compared to a variety of data and also to a state-of-the-art Computational Fluid Dynamics (CFD) erosion calculation model for multiphase flow for cases where data is available. The results from the current predictions are also compared to CFD calculation models for larger diameter pipes and higher pressure conditions, and the model predictions are found to be in good agreement with CFD results. The current model is by far much simpler than CFD methods that are utilized by some operators to predict erosion in elbows and tees. Yet the model predictions match CFD results for larger diameter pipes and field conditions. Additionally, this model can be used to determine threshold erosional velocity and thus is a potential candidate to replace the guideline provided by the API RP 14E.

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