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Facilities Sand Management: Critical Sizes of Produced Solids (B-FSM031)

A.K. Cousens, Fitzwilliam College, "The Erosion of Ductile Metals by Solid Particle Impact", February 1984, PhD Dissertation

Not all solids should be treated as equal.

Prime Directive of Facilities Sand Management

The primary purpose is to ONLY treat, remove, or modify only the solids that are interfering with hydrocarbon production. Principally this is reducing/eliminating erosion or preventing settling in low velocity zones.

With this in mind, the goal should be to target removal of critical particles only and not overdesign the Facilities Sand management system.

You don’t need to remove all the solids – only the problem ones.

Example: The practical removal size limit for cyclonic technology is 10-15 microns. Removal down to 5 microns requires filtration, however filters are 5-10X the size, weight, and cost of cyclones. If particles >25 microns are interfering with hydrocarbon production, then don’t over-design by using filtration.

Effect of Particle Size on Erosion

Based on the U of Tulsa ECRC model (discussed in article B-FSM-27) there is a threshold particle size below which erosion is negligible. See Figure 7 from the McLaury et al. paper (SPE 38842).

The curves are shown for sand particle size versus penetration rate in elbows. The lower curve is for water (20 ft/s) while the upper curve is for methane (4000 psi & 250°F at 100 ft/s). The threshold particle size is fluid dependent. In water sand below 100 microns has steep drop-off in erosion, while sand in gas has a threshold around 20 microns.

These curves indicate that in their respective flow regimes, only particles above this threshold should be removed – the smaller sizes are not significant in the design. The larger particle sizes are easy to remove, thus simplifying the Facilities Sand Management system.

Effect of Sand Morphology on Erosion

Sharp angular particles create a higher erosion rate than round shape. This shouldn’t be a surprise to anyone. However, the magnitude of the difference is surprising.

Data from Cousens (1984), whose photographs are shown in the header shows >100X the erosive rate of crushed glass compared to spherical glass beads. Clearly particle shape has a strong impact.

Work at U of Tulsa ECRC shows the same ranking, albeit at a smaller magnitude difference. The McLaury and Shirazi paper from 1999 (SPE 56812) incorporates sand sharpness factors (Fs) into the erosion model. Rounded, spherical glass beads have only 20% the erosive power of sharp cornered, angular sand.

This leads me to the question – can sharpness of sand particles be reduced in-situ? Some ideas we’ve researched include particle coating and partial chemical dissolution (increasing curvature or sharpness increases chemical potential). These topics are still in the R&D stage and will be published in the future.

The next article will discuss hazardous solids from oil and gas production.

References

  1. Cousens, A.K. 1984. Fitzwilliam College, “The Erosion of Ductile Metals by Solid Particle Impact”, PhD Dissertation.
  2. McLaury, B.S. and Shirazi, S.A. 1999., Generalization of API RP 14E for Erosive Service in Multiphase Production, SPE 56812 https://doi.org/10.2118/56812-MS
  3. McLaury, B.S., Wang, J., Shirazi, S.A., Shadley, J.R., Rybicki, E.F. 1997. “Solid particle erosion in long radius elbows and straight pipes,” Paper 38842 presented at the SPE Annual Technical Conference and Exhibition, San Antonio, TX, 5-8 Oct. https://doi.org/10.2118/38842-MS

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