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Because of its simple principle and high adaptability to severe operational conditions, the capillary-tube viscometer has been widely used for viscosity measurement. However, difficulties in accurately correcting the end effect induced measurement deviation will result in great uncertainty for measurement results. In order to solve this problem, in this work, we studied factors affecting the end effect by conducting the high pressure nitrogen viscosity measurement at low flow velocity with an improved capillary-tube viscometer. The experimental results indicated that the influence of the end effect became less significant with the decrease in flow velocity (v) and tube inner diameter (d) and varied inversely with the length of tube (L). We defined the ratio of measured viscosity to standard viscosity obtained from the NIST database as the viscosity deviation coefficient (Ce). From the Ce vs v, Ce vs d, and Ce vs L curves, we have observed that there existed a threshold velocity (vthreshold), a threshold diameter (dthreshold), and a threshold length (Lthreshold) at which Ce got closer to 1.0. It suggested that under certain experimental conditions, the influence of the end effect on gas viscosity measurement became negligible. Based on that, we established end effect free capillary-tube viscometry and compared the nitrogen viscosity results measured by this method with the data provided by the NIST database. The results presented a good match with error within 1.2%. These insights will contribute to improving the accuracy of a capillary-tube viscometer especially under high pressure.

The evaluation of the ease to generate emulsions and emulsions stability of oil−water system is essential for the investigation and application of chemical flooding technology for the enhanced oil recovery (EOR). However, the previous characterization methods have mainly focused on emulsion stability. To fill this gap, this study designed a novel instrument for visualizing the presence of emulsions and the separation of an oil−water system. Thereafter it also proposed quantitative methods: the emulsification index (EI) for characterizing the ease of surfactants to generate emulsions with crude oil and the demulsification index (DI) for describing emulsion stability. The results show that EI and DI can accurately characterize the dynamic characteristics of emulsions generation and demulsification, respectively. On the basis of the numerous test data composed by three crude oils and seven surfactants with different concentrations, the emulsifying capability and emulsion stability of different oil−water samples can be quantitatively determined. More importantly, these differences between various oil−water samples caused by surfactant concentration, surfactant types and crude oil property can also be accurately distinguished. Besides, the core flooding tests also provide support for the EI and DI and are reasonable parameters for characterization of the emulsification capability and emulsion stability of oil−water systems. Therefore, the overall investigations ultimately revealed that the parameters EI and DI can be used to determine ease of emulsion generation and separation of oil−water systems with an acceptable level of accuracy. The findings of this study provide a novel method for preparing effective chemical agents, which is useful for EOR fields with economic returns.