Experimental and CFD Simulation of a Helico-Axial Pump
Abstract
Multiphase flows are encountered in the majority of crude oil wells. Electrical Submersible Pumps (ESPs) are used to pump the crude oil in wells that do not have sufficient pressure head. Conventional ESPs are mixed or radial flow pumps which have limited gas handling capabilities. For handling high GVF (Gas Volume Fraction) fluids, advanced gas handlers (a type of ESP) were used in series before the conventional ESPs. These homogenize the flow and eliminate gas lock occurrence. The behavior of ESPs (Advanced Gas Handlers) under two phase flows was not widely understood. To better understand the behavior, a helico-axial pump capable of handling fluids up to 90% GVF has been investigated.
Using the high pressure closed loop test facility at the Turbo Machinery Laboratory, a 4-stage helico-axial pump has been tested experimentally using water and air as test fluids for varying conditions such as inlet pressure, flow rate, GVF, and rotating speed. Performance maps of the pump along with vibrational characteristics have been obtained to identify the Best Efficiency Point (BEP) and stable operating regimes. The head degradation of the pump under two phase flow conditions as a function of stage has been obtained. From the head degradation results, the number of advanced gas handler stages to be used before conventional ESPs in an actual assembly has been identified to improve the total system efficiency when used in the field. Based on the experimental data, a new empirical model is developed to predict the stage by stage performance under multi-phase flow conditions.
To understand the two-phase flow behavior in the pump, flow visualization was performed on a full scale single stage pump that was designed and built using transparent Polycarbonate material. Flow visualization was performed using a laser and a high speed camera. The visualization has provided much insight into how the flow goes through the pump: showing recirculation zones, back flow, vortices, and impeller diffuser blade interaction. The bubble diameter obtained from the flow visualization is being used as one of the inputs to allow two phase CFD Simulations.
The efficiency of Advanced Gas Handlers is less than conventional ESPs. To better understand the flow behavior, 3-D single- and two-phase flow through the pump was modeled numerically using the commercial software ANSYS. The pump flow model was validated using the experimental data. From the single-phase simulations, regions of improvement were identified to increase the efficiency of the pump. Different diffuser designs were evaluated to improve the performance of the pump. Two-phase simulations are performed to study the homogeneity of the flow and to identify head degradation. Head degradation can be improved by identifying the regions where the phases tend to separate in the flow path and eliminating them.
Citation
Gudigopuram, Sujan Reddy (2016). Experimental and CFD Simulation of a Helico-Axial Pump. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /187330.