Effects of shear and temperature on wax deposition: Coldfinger investigation with a Gulf of Mexico crude oil

The ability to determine the severity of wax deposition is an extremely important issue for the petroleum industry, particularly in the design and development of deepwater fields. Unfortunately, wax deposition is a complex process for which the mechanism is not fully understood. Furthermore, although much progress has been made in the last few decades in better understanding this complex process, the ability to accurately account for all the factors that affect deposition does not currently exist in the wax deposition simulators used in industry today. This paper examines the effects of two factors on the deposition process: shear and temperature. The effects are illustrated through results from coldfinger experiments, which are often used as a simple means to approximate the deposition process in flow lines. Shown are the effects in influencing both the amount of deposition occurring and nature of deposits formed from a medium-gravity Gulf of Mexico crude oil. Although the results do not directly represent flow-line deposition data, the data provide a relatively comprehensive set of illustrative examples on how deposition can vary with changing conditions. In the study, increases in shear have been observed to result in decreases in the amount of total deposition, primarily through a reduction in the amount of entrained crude oil contained in the deposits. The amount of wax in the deposits was determined to be relatively constant, within the range of variation in shear examined. However, the concentration of wax increased as the shear increased, because of the reduction in entrained crude oil. The effect of increasing the temperature differential (between bulk oil and cold surface) led to an expected increase in total deposition. Both the amount of wax and entrained crude oil increased. The concentration of entrained crude oil in the deposits was observed to increase at a greater rate. Hence, higher entrained oil concentrations occurred with larger temperature differentials.