Low shear pump study highlight

Introduction

 

This article presents a short overview of two papers: SPE-18204 “Droplet Size Analysis: A New Tool for Improving Oilfield Separations” by Flanigan et al. (1988) and SPE-19743-PA “Use of Low-Shear Pumps and Hydrocyclones for Improved Performance in the Cleanup of Low-Pressure Water” by Flanigan et.al. (1992).

 

 

Experimental study

 

The purpose of this study was to evaluate the pump performance and their effect on oil droplets in produced water. The first paper investigated the effect of various pump types and other process equipment on oil droplet size in produced water flow. Once-through oil-water experimental test set-up was used to observe the effect of various pumps on droplet shearing. Flanigan et al. used seven different pumps in their study:

 

  • Progressive cavity pump
  • Small progressive cavity pump
  • Twin lobe pump
  • Sliding rotary vane pump
  • Large progressive cavity pump
  • Centrifugal pump
  • Twin screw pump

 

The low shear pump type was defined as one that simply does not cause large droplets to be degraded into smaller ones. The results given in Fig. 1 show the droplet shearing effect of tested pumps as a function of differential head. Mean inlet droplet size during the tests was kept constant at 24 μm. The results demonstrate that all pump shear inlet oil droplet to a certain degree. The progressive cavity pumps had the best performance regarding the low shear operation.

 

Figure 1. – The effect of droplet shearing as a function of differential head for various types of pumps.

Figure 1. – The effect of droplet shearing as a function of differential head for various types of pumps.

 

 

 

Field tests

 

Based on preliminary experimental study the progressive cavity pump type was chosen as the one that causes the lowest degree of shear. Both onshore and offshore tests were performed with this pump type.

 

Actual produced fluids from the production wells were used during the field tests. Oil concentration in produced water varied between 100 and 550 ppm on the inlet side. Fig. 2  shows the results of droplet shearing by progressive cavity pump. Increased concentration of oil droplets smaller than 16 μm indicated the effect of droplet degradation.

 

Figure 2. – Droplet size distribution curve for the pump inlet, pump outlet (Vortoil (Hydrocyclone) inlet) and the outlet from the hydrocyclone (clean water outlet).

Figure 2. – Droplet size distribution curve for the pump inlet, pump outlet (Vortoil (Hydrocyclone) inlet) and the outlet from the hydrocyclone (clean water outlet).

 

 

An offshore test was performed to validate the results of the previous study. A large progressive cavity pump located upstream the hydrocyclones was chosen for the test. The inlet oil droplet sizes ranged between 11 and 17 μm during the performance test. The sampling of the produced water downstream the pump showed that the average droplet size on the outlet flow was around 95% of the inlet droplet size. The droplet shearing by the progressive pump was concluded to be minimal.

 

 

Paper source:

 

Flanigan, D.A., Stolhand, J.E., Scribner, M.E., et.al. 1988. “Droplet Size Analysis: A New Tool for Improved Oilfeld Separations”, presented at SPE Annual Technical Conference and Exhibition, 2-5 October, Houston, TX. https://doi.org/10.2118/18204-MS

 

Flanigan, D.A., Stolhand, J.E., Shimoda, E., et.al. 1992. “Use of Low-Shear Pumps and Hydrocyclones for Improved Performance in the Cleanup of Low-Pressure Water”, SPE Production Engineering, 7(3): 295-300. https://doi.org/10.2118/19743-PA

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