568 r2011 American Chemical Society pubs.acs.org/EF Energy Fuels 2011, 25, 568–572 : DOI:10.1021/ef101213x Published on Web 01/18/2011 Study of Live Oil Wax Precipitation with High-Pressure Micro-Differential Scanning Calorimetry † Priyanka Juyal, ‡ Tran Cao, ‡ Andrew Yen, ‡ and Rama Venkatesan* ,§ ‡ Nalco Energy Service, 7705 Highway 90-A, Sugar Land, Texas 77478, United States, and § Chevron Energy Technology Company, 1400 Smith Street, Houston, Texas 77002, United States Received September 7, 2010. Revised Manuscript Received December 3, 2010 For live oils, the effect of pressure (amount of dissolved gas) on the wax appearance temperature (WAT) can be quite pronounced. Here, we describe the use of high-pressure micro-differential scanning calorimetry (HP-μDSC) as an effective technique to determine the WAT for live oils. The effect of increas- ing equilibration time on WAT is described and compared to predictions from a thermodynamic model. Introduction Paraffins can precipitate out of a crude oil during produc- tion operations when the oil is cooled because of heat loss to the surroundings. The deposition of paraffinic waxes in pipelines poses a significant challenge during petroleum production. 1-5 Ensuing production losses because of down- time and remediation operations may cost millions of dollars and even lead to abandoning of off-shore wells. 6-8 As the oil industry expands into deeper offshore oil and gas prospects, flow assurance takes on a new shift driven by the combination of a hostile environment, challenging fluid properties, and system reliability targets in deep-water production systems. The problem of wax deposition increases in severity in extreme subsea environments, where the surrounding temperature is colder and because of the deployment of subsea tie-backs over longer distances. In such remote environments, the cost of remediation also increases manifold. An understanding of the rheology and crystallization be- havior of the crude oil is critical to manage wax deposition during oil production, transportation, and end-use applica- tions. Wax appearance temperature (WAT) is an important measure of the crystallization behavior of a crude oil. 9-12 At temperatures lower than the WAT, the paraffin molecules in a crude oil start to precipitate as wax crystals, which is the first step toward both wax gelation and deposition. The WAT and amount of wax precipitated at temperatures below the WAT are thus important indicators in determining if wax deposition and gelation will occur. Estimation of the WAT and amount of wax precipitated is crucial information for the design of flow lines and the production system and also the wax control strategy. Several procedures are employed to study wax phase transitions in crude oil systems, such as viscometry, 1,13-15 cross-polar microscopy (CPM), 1,13 differential scanning cal- orimetry (DSC), 10,13,15 densitometry, 16 near-infrared (NIR) spectroscopy, 11,17 centrifugation, and filtration, that provide information on the WAT and amount of wax precipitated as a function of the temperature. 12 Most of these techniques measure the WAT of dead crude oil; the effects of the pres- sure and amount of dissolved gas in the live oil are not taken into account. The effect of the pressure on wax pre- cipitation for reservoir fluids with a high gas/oil ratio (GOR) can be quite pronounced. 18-23 The lighter components at reservoir conditions are able to dissolve a significant amount of wax molecules. Both the WAT and amount of wax precipitated will be reduced with an increasing amount of † Presented at the 11th International Conference on Petroleum Phase Behavior and Fouling. *To whom correspondence should be addressed. E-mail: vrama@chevron.com. (1) Roenningsen, H. P.; Bjoerndal, B.; Hansen, A. B.; Pedersen, W. B. Energy Fuels 1991, 5 (6), 895–908. (2) Pauly, J. P.; Daridon, J. L.; Coutinho, J. A. P. Fluid Phase Equilib. 1998, 149, 191–207. (3) Thanh, N. X.; Hsieh, M.; Philip, R. P. Org. Geochem. 1999, 30, 119–132. (4) Coto, B.; Martos, C.; Espada, J. J.; Robustillo, M. D.; Pe~ na, J. L. Fuel 2010, 89, 1087–1094. (5) Venkatesan, R.; Singh, P.; Fogler, H. S. SPE J. 2002, 7, 349–352. (6) Nguyen, A. D.; Fogler, H. S.; Sumaeth, C. Ind. Eng. Chem. Res. 2001, 40, 5058. (7) Singh, P.; Venkatesan, R.; Fogler, H. S.; Nagarajan, N. R. AIChE J. 2000, 46, 1059. (8) Moritis, G. Oil Gas J. 2001, 99, 66. (9) Pedersen, W. B.; Hansen, A. B.; Larsen, E.; Nielsen, A. B.; Roenningsen, H. B. Energy Fuels 1991, 5 (6), 908–913. (10) Hansen, A. B.; Larsen, E.; Pedersen, W. B.; Nielsen, A. B.; Roenningsen, H. B. Energy Fuels 1991, 5 (6), 914–923. (11) Roehner, R. M.; Hanson, F. V. Energy Fuels 2001, 15, 756–763. (12) Meray, V. R.; Volle, J.; Schranz, C. J. P.; Marechal, P. L.; Pasteur, U. L.; Behar, E. Proceedings of the 68th Annual Technical Conference and Exhibition; Houston, TX, Oct 3-6, 1993; SPE 26549. (13) Kok, M. V.; Letoffe, J. M.; Claudy, P.; Martin, D.; Garcin, M.; Volle, J. L. Fuel 1996, 75, 787–790. (14) Singh, P.; Fogler, H. S.; Nagarajan, N. J. Rheol. 1999, 43, 1437– 1459. (15) Elsharkawy, A. M.; Al-Sahhaf, T. A.; Fahim, M. A. Fuel 2000, 79, 1047–1055. (16) Kruka, V. R.; Cadena, E. R.; Long, T. E. J. Pet. Technol. 1995, 47, 681–687. (17) Alex, R. F.; Fuhr, B. J.; Klein, L. L. Energy Fuels 1991, 5, 866– 868. (18) Brown, T. S.; Niesen, V. G.; Erickson, D. D. Proceedings of the 69th Annual Technical Conference and Exhibition; New Orleans, LA, Sept 25-28, 1994; SPE 28505. (19) Pan, H.; Firoozabadi, A. Proceedings of the Annual Technical Conference and Exhibition; Denver, CO, Oct 6-9, 1996; SPE 36740. (20) Coutinho, J. A. P. Proceedings of the 13th European Petroleum Conference; Aberdeen, Scotland, Oct 29-31, 2002; SPE 78324. (21) Daridon, J.; Pauly, J.; Coutinho, J. A. P.; Montel, F. Energy Fuels 2001, 15, 730–735. (22) Pauly, J.; Daridon, J.; Coutinho, J. A. P.; Dirand, M. Fuel 2005, 84, 453–459. (23) Tackett, J. E. Comparison of Cloud Point Methods, DeepStar Report (CTR 907); DeepStar: Houston, TX, 1997.