Abstract
Since the invention of the progressing cavity pump (PCP), there has been a desire to accurately model its downhole performance. This work aims to improve the pump performance model by proposing a preliminary correction factor that can be used to estimate the effect of produced fluid viscosity on downhole pump fluid slippage.
Previous efforts to model the effect of fluid viscosity on pump fluid slippage have required precise knowledge of the pump's downhole geometry. Those efforts assumed that pump fluid slippage can be modelled as Poiseuille flow, such as is found in pipes or between parallel plates, where the rate of pump fluid slippage is presumed to be inversely proportional to the fluid viscosity. This work proposes a different approach where pertinent experimental test data is collected for elastomeric and all-metal PCPs that were tested with fluids of varying viscosities and analyzed to create a simplified correction factor that can be used to estimate the effect of fluid viscosity on pump fluid slippage without needing to know the exact downhole pump geometry. It also looks to ascertain if the assumption that Poiseuille flow is a valid model for modelling fluid viscosity effects on pump fluid slippage or whether an alternative mathematical relationship better represents the relationship between fluid viscosity and pump fluid slippage.
The analysis of experimental test data gathered from various pumps that were operated at varying speeds and with fluids of varying viscosities, conducted at C-FER Technologies and with available published test data, enables the development of a preliminary viscosity correction factor, which challenges the conventional belief in an inversely proportional relationship between fluid viscosity and pump fluid slippage. Based on the resulting preliminary viscosity correction factor, the authors propose an alternative relationship between fluid viscosity and pump fluid slippage. The preliminary fluid viscosity correction factor serves as a tool for estimating the impact of changes in fluid viscosity on downhole pump fluid slippage and, thus, pump efficiency.
The proposed preliminary viscosity correction factor can be used to estimate how the downhole pump efficiency can change based on changes in the produced fluid viscosity. This viscosity correction factor can be used to help users of PCP systems optimize the design and operation of their PCP systems.
