Predicting Sand Erosion in Slug Flows Using a Two-Dimensional Mechanistic Model

Slug flow is a very common flow regime encountered in the oil and gas industry.  With sand entrained, slug flow is also one of the most erosive flow regimes due to its relatively high gas flow rate.  The design of oil and gas production equipment to withstand erosive conditions and optimize the production rate, while keeping the piping system operating safely, requires a reliable erosion prediction tool.  Chen et al. (2006) proposed a comprehensive approach for estimating the erosion rate in slug flows.  This approach is a combination of mechanistic analysis and computation fluid dynamics (CFD).  Shirazi et al. (1994) and McLaury et al. (2010) presented a mechanistic model that calculates representative particle impact velocity, which is used along with an erosion equation to predict the erosion rate.  This model accounts for  essential parameters, such as flow geometry and dimensions, fluid properties, flow conditions, particle size, target material types.    It has been successfully applied to predict erosion caused by relatively large sand particles (>50 to 100 microns).   However, when very small sand particles (~20 microns) are present, this model under-predicts the erosion rate dramatically.  The main reason is that this model calculates the representative impact velocity in a one-dimensional manner.  The current authors (2010) presented an improved model by introducing a two-dimensional particle tracking module.  It has been shown that for gas/solid or liquid/solid flows, the 2-D mechanistic model performs very well in predicting erosion caused by both large and small sand sizes.  This 2-D mechanistic model is being extended for handling gas/liquid/solid flows.  This paper explains its application in slug flows.  Results from the 2‑D mechanistic model and the previous 1-D model are compared with experimental data.  It is shown that the 2-D mechanistic model performs much better for slug flow, especially when very small sand is involved.