PARTIAL RECOVERY OF WAX GEL STRENGTH: QUANTITATIVE AND QUALITATIVE ANALYSES Kyeongseok Oh, Mark Jemmett, Pankaj Tiwari Jules Magda and Milind Deo University of Utah, Salt Lake City, UT 84112 Abstract Waxy components in a crude oil start to precipitate when the surrounding temperature is lower than wax appearance temperature (WAT). While the wax deposition can be initiated during the flow, wax gel formation occurs primarily under static conditions. When the wax gel develops within a relatively short time, certain pressure is needed to overcome the yield strength of the gel along the pipeline for restart. It was found that paraffinic components contribute to the evolving gel strength continuously while the oil is cooled below pour point (PP). Gel strength depends on wax amount and wax composition in the gel network. It has been reported that the gel properties depend on various factors: temperature, cooling rate, cooling time, shear history, and a diverse combination of factors. This study explores gel strength by stress exertion below the PP followed by further cooling. Model oil used in this study was prepared by mixing mineral oil and well-characterized wax. The measurements of WAT and PP were performed using the ASTM methods. A controlled-stress rheometer equipped with a cone-and-plate geometry and a Peltier plate device was employed to determine the yield stress and the measurement of creep response. The cooling was scheduled after applying stresses in the creep range. Yield behavior was compared after applying varying stresses and cooling to lower temperatures. Key words: wax, gel strength, yield stress, creep compliance Introduction High molecular paraffinic waxes in a crude oil start to precipitate when the surrounding temperature is lower than the wax appearance temperature (WAT). Pour point is another important characteristic temperature usually determined by ASTM D97 (1), which represents a transition from flow to no flow. Flow discontinuity occurs in due to either wax deposition or wax gel formation. While the wax deposition can be initiated during flow, wax gel formation occurs primarily under static conditions caused by either planned or emergency shutdown. When the wax gel develops within a relatively short time, certain level of pressure application upstream is necessary to overcome the yield stress of the gel along the pipeline for restart (2, 3). Various rheological studies of gelled waxy oil have been published. Boger and coworkers (4, 5) discussed the existence of three definite characteristic responses, which they categorized as elastic, creep and fracture when the gel was subjected to shear. In the elastic region, the gel strength is fully recovered after sufficiently low shear is applied to the gel regardless of duration time over which the shear is applied. Prior to the static yield stress (the point at which the gel fractures), a creep region is observed, in which the gel strength is partially recovered once the applied stress is released. The gel yields at shorter times, when higher shear is applied. In case of fracture, the gel breakage occurs when the loading stress is high enough to deform the gel network.