Modeling Gerotor Pump Performance in Artificial Lift for Single-Phase and Multiphase Conditions

Abstract

Summary Gerotors are positive displacement pumps and candidates for artificial lift in the oil and gas industry. This study evaluates the performance of a unique gerotor pump design under single-phase and multiphase conditions. The gerotor pump performance is modeled with computational fluid dynamics (CFD) to develop a virtual prototype of the multiphase performance behavior. The gas/liquid flow is modeled using a homogeneous multiphase approach. A prototype 3D model of a 400 series gerotor pump suitable for application in a 5½-in. casing is developed. The pump volume displacement is consistent with that to be used in subsequent laboratory experimental tests and field prototype testing. Transient 3D CFD is used to simulate the gerotor pump performance under single-phase and multiphase flow conditions. The complex gerotor motion is modeled in CFD using a dynamic meshing technique. Pump rotor speeds applicable to the range of testing conditions were applied. The gas and liquid phase properties correspond to mineral oil and air at the prototype test conditions. The results of the gerotor pump performance are presented for single-phase and multiphase conditions over a range of gas volume fractions (GVFs) from 0 to 0.75. The CFD results show that the flow rate decreases approximately linearly with pump differential pressure, which is typical of positive displacement pumps. Pump performance and efficiency curves are developed relating the pump differential pressure and flow rate. The CFD model methodology is presented with consideration to appropriate selection of the numerical methods, multiphase model, mesh design, dynamic mesh motion, and other aspects to improve the reliability of the numerical simulations. For the same differential pressure, increasing the GVF decreases the gerotor total pumping volume rates. The results establish a first baseline for the pumping system for subsequent comparison with physical model testing to ascertain gas/liquid handling capability of the pump for further optimization for field application. This study evaluates and highlights the potential applicability of gerotors as an alternative artificial lift technology for multiphase pumping. This technology with further development in addition to its inherent mechanical simplicity and compactness can serve as a promising candidate for surface and downhole multiphase pressure boosting for production in the oil and gas industry.