Exploring the Temperature and Pressure Dependence of the Viscosities of Two Potential Deepwater Viscosity References

Deeper drilling for hydrocarbon fuels has elevated the need for viscosity reference fluids for the purpose of calibrating and validating of viscometers and rheometers at high temperatures and high pressures. The International Association for Transport Properties (IATP) established the nominal value of the high-pressure viscosity standard at about 20 cP at a temperature of 200^oC and pressure of 200 MPa. The desirable attributes of the high-pressure viscosity standard candidate include thermal stability, inertness, insensitivity to UV radiation, hydrophobicity, monodispersity, lot-to-lot consistency, occurrence as a liquid at ambient conditions and commercial availability. Further, the candidate should be safe to use in the laboratory and it should be environmentally benign. DuPont’s perfluoropolyether oil Krytox GPL 102 was proposed by our team and several members of the high pressure transport property community as a viable deepwater viscosity standard (DVS) that meets most of the aforementioned requirements. However, lot-to-lot variation of this polydisperse perfluoropolyether could be a serious hurdle preventing its long term acceptance as a viscosity standard. Tris(2-ethylhexyl) trimellitate (TOTM) has also been proposed by Diogo and coworkers as a promising alternative to Krytox GPL 102. This study explores the viability of Krytox GPL 102 and tris(2-ethylhexyl) trimellitate (TOTM) as deepwater viscosity standards. High-pressure viscosity measurements for both fluids are reported at pressures between 7 and 242 MPa and temperatures between 314 and 527 K with an expanded uncertainty of 3% at a 95% confidence level. In addition, the viscosity results are correlated with an empirical temperature/pressure-dependent function and a modified Vogel-Fulcher-Tammann (VFT) Equation.