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

JORI, KHALIL; BAVA, YANINA; PSCHUNDER, FERNANDO; GIOVANETTI, LISANDRO J.

Campinas, SP, BRAZIL

Conferencia; XVIII edition of the International Small-Angle Scattering Conference (SAS2022); 2022

CNPEM

Waxes are complex mixtures of high molecular weight or high carbon number alkanes that consist ofstraight, branched, and cyclic chains. Petroleum waxes are generally categorized into two groups, paraffinwax (straight chain saturated hydrocarbons with carbon atoms ranging from C18 to C36) andmicrocrystalline 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 quantitiesof wax (3–44%) that crystallizes during the oil production, transportation, and storage. [2] This is knownas 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 definedas wax appearance temperature (WAT) and its appropriate determination is fundamental for the waxdeposition problems that leads to significant additional production costs. Additionally, the development ofoperational remediation techniques such as pigging or chemical inhibition requires a deep understandingof the complex behavior of waxy crude oils. [4]In order to a better understanding of the problem, we studied structural behavior of petroleum paraffindirectly in crude oils by small- and wide-angle X-ray scattering (SAXS/WAXS). We explore de SAXSand WAXS images from one crude oil, the paraffins extracted from it and the dewaxed crude oil, coolingthe sample between 130 to 0 °C on the Linkam temperature-controlled sample holder. Paraffin extractionwas carried out by cold fractional precipitation of the crude oil sample. This procedure is a modificationof the UOP Method 46-85 standard.[5] Then, all samples were filled into glass capillaries and placed onthe Linkam and heated for a few minutes to 130 °C. Finally, the scattered intensities were measure whereasthe 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 areshown in Figure 1. There it is possible to observe the simple WAT determination as the temperature atwhich the most intense narrow Bragg peaks appear[H1] . These peaks were attributed to an orthorhombiccrystal system. Furthermore, it was possible to adjust the form of the crystals such as discs or lamellae anddetermine 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 knowingof these properties enable a better characterization of wax deposit structure and a deeper understanding ofthe different mechanisms that lead to wax deposit formation. Up to now, this is the promising techniquefor wax deposition problems. Actually we are working in the calibration curve, to determine de paraffinsconcentration and realize a complete comparison with the differential scanning calorimetry (DSC) ASTMD-4419 test method currently employed in petroleum industry.