TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractProgressive Cavity Pump (PCP) performance has been traditionally modeled as a composition of Couette flow and Poiseuille flow, represented by pump displacement and internal slip respectively. Pump displacement can be easily calculated from pump components geometry, but calculating internal slip is not a trivial problem. Previous studies have proposed to use Hagen-Poiseuille equation for modeling internal slip flow, assuming a constant interference value. In these studies slippage gap area is not clearly defined, so great results have not been reached.This study introduces a new approach for modeling single lobe PCP performance. Slip flow is modeled as the result of two components, one of them due to the movement of the rotor and the other one due to the differential pressure between cavities, assuming that slippage gap area depends on the stator material. This assumption is based on the analysis of metallic, elastomer and PTFE stator PCP characteristic curves, obtained from experimental data of previous works.The existence of a strong relationship between slippage gap area and differential pressure, related to mechanical properties of stator material, is demonstrated. Thus, internal deformation of stator is identified as the main parameter to be understood before predicting PCP performance. For a polymer stator PCP this relationship approximates to a quadratic form, while in a metallic stator PCP a constant gap area can be assumed.Although the proposed model is not able to fit data for any PCP models, its results agree with the ideas proposed above and documented PCP performance theory. In order to obtain a definitive model, future investigation is needed to improve expressions for calculating friction factor inside the pump and also to define a procedure for obtaining gap area relationships for any type of stator material.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractProgressive cavity pump metal to metal has its two elements, rotor and stator, made from a metallic material. It has been demonstrated that this pump can reach an acceptable volumetric efficiency with high viscosity fluids. However, the performance of the pump with two-phase flow has never been investigated. There are not field or experimental tests which provide tools to predict the behavior of the pump in such applications. If progressive cavity pump metal to metal were able to handle high viscosity fluids with gas void fractions, as well as conventional progressive cavity pumps, it could be found a range of application for using this pump in heavy oil production. Its advantages would be valious, since it doesn't have the problems due to the use of elastomer stators.In this research the progressive cavity pump metal to metal performance has been studied. Characteristic curves and instantaneous pressure profiles along the pump with singlephase and two-phase flow have been obtained experimentally. The results show that the internal slip with two-phase flow is a function of gas void fraction, differential pressure and rotational speed. Under some conditions an increase in volumetric efficiency occurs when the gas void fraction is increased. Instantaneous pressure profiles explain the changes of internal sealing lines when gas void fraction changes, also show that longitudinal pressure distribution along the pump have a linear behavior for single-phase and twophase pumping.The knowledges acquired with this research are useful for understanding the progressive cavity pump metal to metal performance in two-phase pumping applications and also can be used in the future for theorical modeling of the pump.
Head deterioration observed in electrical submersible pumps (ESPs) under two-phase flow is mild until a sudden performance breakdown is observed in the pump head curve at a certain volumetric gas fraction. This critical condition is termed surging. Consequently, the head that the pump generates with two-phase flow depends on whether the stages operate under conditions before (mild performance deterioration) or after (severe performance deterioration) the surging point.The surging, for engineering purposes, can be predicted by published correlations, but the lack of a theoretical basis is a limiting factor for their application. Mechanistic models seem to be the proper alternative. However, the poor understanding of the physical mechanism that causes the surging hinders the development of such mechanistic models. This paper reviews some of these correlations and mechanistic models by comparing the correlation predictions against experimental data acquired in a closed loop with water and air using a commercial 24-stage ESP. The data cover a wide range of volumetric gas fractions, rotational speeds, and intake pressures. As a consequence of this analysis, a new correlation has been formulated. This correlation predicts the initiation of the surging as a function of rotational speed and fluid properties.
This paper presents electric-submersible-pump (ESP) -stage performance handling air and water in a laboratory setup. Experimental data gathered shows the effect of volumetric gas flow rate and intake-stage pressure for different rotational speeds. The presence of gas mildly deteriorates the stage performance at low volumetric gas flow rates. A sudden reduction in the stage-pressure increment is observed at this operation condition for a certain critical liquid flow rate, which marks the initiation of surging on the stage performance as mentioned by Lea and Bearden (1982). The surging initiates at lower liquid flow rates as the volumetric gas flow rate increases, which demonstrates the relationship between the surging initiation and liquid flow rate. It is also observed that the initiation of the surging moves toward lower liquid flow rates by increasing the rotational speed or the stage intake pressure.A two-phase stage-performance map was recently introduced, defining boundaries for five pump-performance regimes: homogenous, mild-performance deterioration, performance reverse slop, server performance deterioration, and nil performance (Gamboa and Prado 2011b). The current work shows that these performance regime boundaries are affected by rotational speed and intakestage pressure. Experimental ProgramExperimental Facility Layout. The tests are conducted in the facility described by Gamboa and Prado (2011b). The ESP tested
Experiments with a seven-stage Electrical Submersible Pump (ESP) have been carried out to study the effect of liquid viscosity on the gas-liquid two-phase stage performance. The experimental tests provided data about the stage pressure increment as a function of the liquid flow rate at constant rotational speed, inlet pressure, and volumetric gas flow rate. Two different mineral oils were used so that the ESP two-phase stage performance was measured for 1 cP, 1.2 cP and 8.5 cP liquid viscosities, and for 8 different gas flow rates. The experimental results demonstrate that the increase of liquid viscosity causes gas surging in the stage to initiate at lower normalized gas flow rates, reducing the gas handling capability of the stage. Increasing the liquid viscosity also causes the stage to reach a zero pressure increment at a higher normalized liquid flow rate. The pressure increment deterioration caused by the gas worsens with increased liquid viscosity. The performance map is analyzed and compared with that of another pump (GC-6100) with a higher inlet stage pressure.
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