Investigating Non-Uniformity of Wax Appearance Temperature of Crude Oil in Nigeria

Abstract

A significant sample of crude oil found in Niger Delta have between moderate to high wax content which makes flow process sometimes difficult at low temperatures due to the formation of gel-like structure which increases viscosity of the fluid. Removal of wax from flowlines and reservoirs can account for significant additional operating costs. To evaluate these potential costs, the operating conditions that allow waxes to precipitate at any point in the production line be identified, and deposition rates must also be estimated to determine the implications associated with removal of wax deposits. This project investigates the non-uniformity in wax appearance temperature of crude oil in the Niger delta and the flow behavior of waxy crude oil under variation in the temperature of the external environment of the flow. The temperature at which the first wax crystals appear during cooling is known as the wax appearance temperature. once below the WAT, the crude oil can form the gel like structure. Breaking down this structure to restart and maintain the flow often require energy and cost intensive approach. This project focuses on characterizing different waxy crude oil samples using thermal and compositional analysis, specifically with measurement of WAT in the context of the field of flow assurance. The test is based on the experimental design technique, and the behavior of the fluids evaluated based on the variation generated by the flow. The carbon distribution of oil samples and their corresponding wax components were analyzed by high temperature gas Chromatography. The crude oil properties determined include wax content, Aromatics, asphaltene, saturates and resin content by HPLC, pour point, wax appearance temperature by optical microscopy and paraffin carbon number distribution of whole oil and wax precipitate by GC- FID. Asphaltene and resin content were found to influence the oil cloud point, while saturates content, paraffin carbon number of crystallizing waxes and wax content control its low temperature flow properties including the wax appearance temperature. This study shows that the seven Niger delta crude oil studied have wax content between 4.5 to 22.1 weight percent with WAT in the range of -19oC to 27.5oC the results showed that the aromatics and asphaltene interaction had a significant impact on the wax appearance temperature (WAT) and hence largely responsible for the variations on the WAT of crude oil samples.