Prediction of Wax Deposition in Crude Oil by Small- and Wide-angle X-ray Scattering

BAVA YANINA BELÉN; KHALIL JORI; FERNANDO PSCHUNDER; GIOVANETTI LISANDRO

Campinas, San Pablo

Congreso; XVIII International Small-Angle Scattering Conference 2022; 2022

The Brazilian Synchrotron Light Laboratory is part of the Brazilian Center for Research in Energy and Materials (CNPEM)

Waxes are complex mixtures of high molecular weight or high carbon number alkanes that consist of straight, branched, and cyclic chains. Petroleum waxes are generally categorized into two groups, paraffin wax (straight chain saturated hydrocarbons with carbon atoms ranging from C18 to C36) and microcrystalline wax (branched and cyclic hydrocarbons with carbon atoms ranging from C30 to C60), present in petroleum distillates and residues. [1] Many crude oils in the world contain significant quantities of wax (3?44%) that crystallizes during the oil production, transportation, and storage. [2] This is known as wax deposition and it is one of the chronic problems during oil production, transportation, and storage. [3] The temperature that at which n-paraffins start to solidify and may deposit on the pipe walls is defined as wax appearance temperature (WAT) and its appropriate determination is fundamental for the wax deposition problems that leads to significant additional production costs. Additionally, the development of operational remediation techniques such as pigging or chemical inhibition requires a deep understanding of the complex behavior of waxy crude oils. [4]In order to a better understanding of the problem, we studied structural behavior of petroleum paraffin directly in crude oils by small- and wide-angle X-ray scattering (SAXS/WAXS). We explore de SAXS and WAXS images from one crude oil, the paraffins extracted from it and the dewaxed crude oil, cooling the sample between 130 to 0 °C on the Linkam temperature-controlled sample holder. Paraffin extraction was carried out by cold fractional precipitation of the crude oil sample. This procedure is a modification of the UOP Method 46-85 standard.[5] Then, all samples were filled into glass capillaries and placed on the Linkam and heated for a few minutes to 130 °C. Finally, the scattered intensities were measure whereas the temperature was cooled down from 130 to 0 °C.The recomposed 1D curves obtained at only a few temperatures for the crude oil and extracted samples are shown in Figure 1. There it is possible to observe the simple WAT determination as the temperature at which the most intense narrow Bragg peaks appear[H1] . These peaks were attributed to an orthorhombic crystal system. Furthermore, it was possible to adjust the form of the crystals such as discs or lamellae and determine the maximum crystallite size, in direction c, is found to be of the order of 100 Å in thecrude oil. These sizes are typical of anisotropic objects, which is in good agreement with lamellar crystals.So, these techniques provide information on crystals interarrangement, their size, and shape. The knowing of these properties enable a better characterization of wax deposit structure and a deeper understanding of the different mechanisms that lead to wax deposit formation. Up to now, this is the promising technique for wax deposition problems. Actually we are working in the calibration curve, to determine de paraffins concentration and realize a complete comparison with the differential scanning calorimetry (DSC) ASTM-D-4419 test method currently employed in petroleum industry.