# Assessment of Changes in the Abrasiveness of Solid Particles in Hydraulic Mixtures Pumped with ESPs
## 4 Discussion  
In the Russian and foreign practices of designing ESP installations for the oil industry, the following ways of protecting working stages from hydroabrasive wear are known:  
* Insertion of wear-resistant rings in interstage seals;
* Application of hard coatings on the surfaces of guide vanes and impellers;
* Use of stages with enlarged cross-sections of flow channels and protective ribs on the upper disk of the guide apparatus in the cavity under the impeller;
* Use of stages with holes in the upper disk of the guide apparatus to remove abrasive particles from the cavity under the impeller. Increased flow through sections of stages (without any change in nominal-stage flow rate) results in decreased hydromechanical mixture velocity, which would determine the decrease in hydroabrasive-wear intensity. However, in this case, the ESP-unit size and cost would increase, and the wear rate of interstage seals would remain at the same level. The presence of protective ribs on the upper disk of the guide apparatus in the cavity under the impeller changes the character of the eddy-current-formation process. Moving abrasive particles hit the radially located ribs and lose kinetic energy. Destruction of the body of the guide apparatus begins only after the wearing of the protective ribs, which increases its operating time by 30-40%. However, the obtained positive effect is often insufficient for operation of electric centrifugal pumps in complicated well conditions after hydraulic fracturing. Placement of holes in the upper disc of the guide apparatus causes reduction in the working stage head due to additional fluid overflow through the holes, which reduces the energy efficiency of ESP operations as a whole. Today, one of the most cost-effective and efficient ways to protect ESPs from the impact of mechanical impurities is the use of preinjection devices: filters and mechanical-impurity separators. Figure 7: Change in the wear value, S, of wheel thrust washers depending on the location of the stage of the pumping section in the direction of the water–abrasive mixture flow. The analysis of the results of the studies given in this article allowed estimation of the changes in abrasiveness of mechanical impurities pumped with model fluid flow through ESP stages. It was shown that coarse particles of mechanical impurities of natural origin, when in contact with the metal of the working stages, were subjected to intensive grinding to a value of \(D_{f}=0.25\,\dots\,0.3\) mm, after which the particle size remained practically unchanged; that is, the particles were not ground and their abrasiveness did not increase. It follows from the above that ESP-unit filters should be selected with a main focus on a cleaning fineness of 0.25... 0.3 mm. Particles with an initial size greater than \(D_{i}=0.3\) mm would be ground, and the destruction products of such particles would be characterized with high abrasiveness. Fine filters undergo intensive colmatation and are characterized with lower dirt capacity and low operating time in downhole conditions. An increase in the abrasiveness index of mechanical impurities as they pass through working stages causes an increase in the intensity of wear of the wheel-support washers and interstage seals along the flow of the hydraulic abrasive mixture (from the inlet to the outlet of the pumping section). Uneven hydroabrasive wear of working stages determines the possibility of using electric centrifugal pumps of combined assembly, in which the first stages in the flow direction are of normal design, followed by stages with wear-resistant design [38; 39]. The seals in such wear-resistant stages can be made of materials with increased hardness. Use of labyrinth seals, for example, of the type described in the patent is promising [40].