Viscosity Measurements of Two Potential Deepwater Viscosity Standard Reference Fluids at High Temperature and High Pressure

Abstract

This paper reports high-pressure viscosity measurements for Krytox GPL 102 lot K2391 and tris­(2-ethylhexyl) trimellitate (TOTM). These two viscous liquids have recently been suggested as potential deepwater viscosity standard (DVS) reference fluids for high temperature, high pressure viscosity studies associated with oil production from ultradeep formations beneath the deepwaters of the Gulf of Mexico. The measurements are performed using a windowed, variable-volume, rolling-ball viscometer 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. The viscosity results are correlated using an empirical temperature/pressure-dependent function and a modified Vogel–Fulcher–Tammann (VFT) Equation. The present viscosity data for TOTM and Krytox GPL 102 lot K2391 are in good agreement with the available reported data in the literature at lower temperatures and pressures. The viscosity values of TOTM and Krytox GPL 102 lot K2391 are 9.5 mPa·s and 25 mPa·s, respectively, at 473 K and 200 MPa, whereas the desired DVS viscosity value at this condition is 20 mPa·s. Although the viscosity of Krytox GPL 102 lot K2391 is closer to the targeted value, a comparison of the present viscosity results with data obtained for lot K1537 indicates a very large lot-to-lot variation of the viscosity for this polydisperse perfluoropolyether oil, which represents a significant deficiency for a DVS.

In Pursuit of a High-Temperature, High-Pressure, High-Viscosity Standard: The Case of Tris(2-ethylhexyl) Trimellitate

“…It is also worth noting that minor changes in the color of aged samples were observed when the samples were heated in the presence of air. However, Baled et al have made viscosity measurements up to 523 K (points up to 477 K contribute to the present reference viscosity correlation) and did not report any alterations in the TOTM samples. In addition, Bamgbade et al measured the density up to 523.5 K using a different view cell, and they also did not notice any changes in color or odor of the TOTM sample.…”

“…The values reported by Diogo et al, 15,23 with a nominal uncertainty of ±2.0−3.0%, deviate from eq 8 by less than −4.9% with rms deviation equal to 1.6%; the majority of their results have deviations from the correlation of approximately ±2.0%; only nine points have deviations of approximately 5% for the 21 have reported viscosity data for TOTM at pressures between 7 and 242 MPa and temperatures between 314 and 527 K with an expanded uncertainty of 3%. The deviations encountered from eq 9 for their entire data set used in the present correlation vary from −4.88 to +3.3%, which is within the overall uncertainty of the experimental method.…”

“…Five viscosity measurement sets on compressed liquid TOTM have been reported by Diogo et al, 15,23 Bair, 12 Baled et al, 21 and Linẽira del Ri ́o et al 25 Diogo et al measured the viscosity of two lots, A 15 and B, 23 using a vibrating-wire viscometer. Baled et al 21 measured the viscosity of lot C of TOTM using a windowed, variable-volume, rolling ball viscometer.…”

“…Five viscosity measurement sets on compressed liquid TOTM have been reported by Diogo et al, 15,23 Bair, 12 Baled et al, 21 and Linẽira del Ri ́o et al 25 Diogo et al measured the viscosity of two lots, A 15 and B, 23 using a vibrating-wire viscometer. Baled et al 21 measured the viscosity of lot C of TOTM using a windowed, variable-volume, rolling ball viscometer. Two more viscosity data sets of TOTM lot C were reported, one by Linẽira del Ri ́o et al 25 using a falling body viscometer and another by Bair 12 using a falling body viscometer.…”

“…Assuming a 95% confidence level, we have withdrawn 18 possible outlying data points with corresponding deviations larger than twice the rms deviation. In particular, the following experimental points were withdrawn: two values from the highest pressures measured by Bair 12 and six points from the highest viscosity data obtained by Baled et al 21 In addition, we have eliminated seven points from the data of Linẽira del Ri ́o et al, 25 which include their results for the highest viscosities; finally, three points from the set reported by Assael and Tsolakidou 32 were excluded because they deviate more from the correlation than the uncertainty of their measurements.…”