Flow Assurance: Reliable and Accurate Prediction of the Viscosity of Natural Gas

Abstract

Abstract Modern viscosity prediction methods have to satisfy the requirements for flow assurance and reliable reservoir characterization by demonstrably predicting accurate, reliable and internally consistent viscosity data. The best way to achieve this is by employing predictive methods based on the best available theory, simplified, just sufficiently to allow ready application and validated against a critical set of primary experimental data of proven accuracy. The presented VW methodology is one such method, that is based on the kinetic theory of rigid spheres, modified to take into account the behavior of real fluids. It has no adjustable parameters, and requires no dense mixture viscosity data. In this work, the VW method was validated against a new set of natural gas viscosity data of very high accuracy. The experimental data were predicted with an rms deviation of the order of 0.5%-1%, commensurate with the experimental accuracy of the data. Overall, it is estimated that the VW method can predict the viscosity of natural gas within ±2% in the temperature region 260 K - 400 K and pressures up to 200 bars, with the accuracy deteriorating slightly at higher pressures and lower temperatures. It can be used to predict the viscosity of CO2-rich, sour and wet natural gas.