Abstract

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 and multiphase conditions in a downhole configuration. The gerotor pump performance is modeled with computational fluid dynamics (CFD) to develop a virtual prototype of the multiphase performance behavior prior to physical testing.

A prototype 3D model of a 400 series gerotor pump suitable for application in a 5½-in. casing was developed. The pump volume displacement is consistent between the initial laboratory experimental tests and future field testing. A transient 3D CFD was used to simulate the gerotor pump performance under single-phase and multiphase flow conditions. The complex gerotor motion was 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 zero to 0.75. The CFD results show that the flow rate decreases approximately linearly with discharge pressure, which is typical of positive displacement pumps. Pump performance and efficiency curves are developed relating the delivery 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 delivery pressure, increasing the GVF decreases the gerotor pumping rates. Recommendations are proposed for improving the multiphase pumping capacity through pump geometry modifications. The modifications effectively tailor the gerotor to improving gas-liquid pumping in specific oil field operating conditions.

This study highlights the potential for gerotors as an alternative artificial lift technology for multiphase pumping. This technology with the inherent mechanical simplicity and compactness provides cost-effective surface and downhole multiphase pressure boosting for production in the oil and gas industry.

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