Exploratory Characterization of a Perfluoropolyether Oil as a Possible Viscosity Standard at Deepwater Production Conditions of 533 K and 241 MPa

DuPont’s perfluoropolyether oil Krytox $^{\textregistered }$ GPL 102 is a promising candidate for the high-temperature, high-pressure Deepwater viscosity standard (DVS). The preferred DVS is a thermally stable liquid that exhibits a viscosity of roughly 20  $\hbox {mPa} \cdot \hbox {s}$ at 533 K and 241 MPa; a viscosity value representative of light oils found in ultra-deep formations beneath the deep waters of the Gulf of Mexico. A windowed rolling-ball viscometer designed by our team is used to determine the Krytox $^{\textregistered }$ GPL 102 viscosity at pressures to 245 MPa and temperatures of 311 K, 372 K, and 533 K. At 533 K and 243 MPa, the Krytox $^{\textregistered }$ GPL 102 viscosity is $(27.2 \pm 1.3)\,\hbox {mPa} \cdot \hbox {s}$ . The rolling-ball viscometer viscosity results for Krytox $^{\textregistered }$ GPL 102 are correlated with an empirical 10-parameter surface fitting function that yields an MAPD of 3.9 %. A Couette rheometer is also used to measure the Krytox $^{\textregistered }$ GPL 102 viscosity, yielding a value of $(26.2 \pm 1)\,\hbox {mPa} \cdot \hbox {s}$ at 533 K and 241 MPa. The results of this exploratory study suggest that Krytox $^{\textregistered }\, \hbox {GPL}$ 102 is a promising candidate for the DVS, primarily because this fluoroether oil is thermally stable and exhibits a viscosity closer to the targeted value of 20 mPa $\cdot $ s at 533 K and 241 MPa than any other fluid reported to date. Nonetheless, further studies must be conducted by other researcher groups using various types of viscometers and rheometers on samples of Krytox GPL $^{\textregistered }$ 102 from the same lot to further establish the properties of Krytox GPL $^{\textregistered }$ 102.     

Equation of state modeling of high-pressure, high-temperature hydrocarbon density data

Experimental densities are reported for n-pentane, n-octane, cyclooctane, 2,2,4-trimethylpentane, n-decane, and toluene to ∼280 MPa and ∼250 °C. These densities are in good agreement with available literature data that typically cover lower pressure and temperature ranges than those reported here. The data are modeled with the Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) cubic equations, the temperature-dependent, volume-translated SRK equation, the temperature- and density-dependent SRK equation, and the SAFT and PC-SAFT equations. Mean absolute percentage deviation (MAPD) values between densities calculated with the PR equation and literature data are 4.55 for n-pentane, 2.91 for n-octane, 3.68 for cyclooctane, 3.98 for 2,2,4-trimethylpentane, 5.58 for n-decane, and 1.99 for toluene. With the exception of 2,2,4-trimethylpentane, these MAPD values are substantially better than those obtained with the SRK and modified SRK equations. Although both SAFT-based models have MAPD values significantly lower than those with the PR equation, the PC-SAFT equation provides the lowest MAPD values.