1/23/2024 0 Comments Petroleum wax![]() ![]() Another inherent problem is that the cloud-point measurement sees the precipitation of the most insoluble paraffin, not the mass of lower-molecular-weight paraffins that might contribute the major amount of wax deposit. Measured cloud-point data should only match field results for wells producing at low shear (high shear rates tend to delay the deposition of waxes). ![]() Of more importance, is how well laboratory-measured cloud points anticipate WATs found in the field. In testing, cloud points, measured by each of the four methods, agreed with the average value of all methods within 3 to 5☏. A comparison/review of these methods is found in Monger-McClure, et al. Fourier transform infrared energy scattering (FTIR) - detects the cloud point by measuring the increase in energy scattering associated with wax solidificationĮach of these techniques has its advantages and disadvantages.Filter plugging (FP) - measures the increase in differential pressure across a filter, which can be attributed to wax-crystal formation.Cross polarization microscopy (CPM) - exploits the fact that insoluble wax crystals rotate polarized light, but liquid hydrocarbons do not.Differential scanning calorimetry (DSC) - measures the heat released by wax crystallization.See Wax precipitation for additional information.Ī variety of experimental methods have been used to obtain this number. Occurrence of nucleating materials such as asphaltenes, formation fines, and corrosion products.The WAT (or “cloud point”) is highly specific to each crude. The primary chemical parameter to establish is the critical temperature at which these wax nuclei form-the wax appearance temperature (WAT). Prior to solidification, the solid wax crystals in the liquid oil change the flow properties from a Newtonian low viscosity fluid to a very-complex-flow behavior gel with a yield stress. High-molecular-weight waxes tend to deposit in the higher-temperature sections of a well, while lower-molecular-weight fractions tend to deposit in lower-temperature regions. Paraffin deposits will be harder, if longer-chain n-paraffins are present. The wax deposits vary in consistency from a soft mush to a hard, brittle material. Wax deposition onto the production system (“growth”) generally requires a “nucleating agent,” such as asphaltenes and inorganic solids. This insoluble wax itself tends to disperse in the crude. Nucleation is the forming of paraffin clusters of a critical size (“nuclei”) that are stable in the hydrocarbon fluid. The deposition process involves two distinct stages: nucleation and growth. More information on the characteristics of waxes in crude oil can be found in Asphaltenes and waxes.Īs the temperature of the crude drops below a critical level and/or as the low-molecular-weight hydrocarbons vaporize, the dissolved waxes begin to form insoluble crystals. ![]() These heavy organics have interactions with the crude, which can either prevent wax-crystal formation or enhance it. “Regular waxy crudes” contain other heavy organics in addition to the waxes (e.g., asphaltenes and resins). 1) are more likely to be included in a wax deposit than the more highly branched alkanes.Ī “clean waxy crude” is defined as a crude oil that consists of only hydrocarbons and wax as the heavy organic constituents. The iso-paraffins of the 2-methyloctane type ( Fig. For example, waxes derived from several Venezuelan crudes showed n -paraffin/(cyclo + iso paraffin) ratios ranging from 1.28 to 0.23. Waxes isolated from crudes can contain various amounts of all classes: n-paraffins, naphthenes, and iso-paraffins. 1-Structures of hydrocarbon classes involved in wax deposition. The drawings illustrate the type of structures involved.įig. These specific n-paraffins and naphthenes are too small to crystallize as wax deposits (i.e., outside the carbon-number range specified above). The n-heptane structure is an example of a “normal” paraffin 2-methyloctane is an “iso” paraffin and n-butylcyclopentane is a naphthene. 1 shows the generic molecular structures of n-paraffins, iso-paraffins, and naphthenes. This wax material is referred to as “macrocrystalline wax.” Naphthenic hydrocarbons (C18 to C36) also deposit wax, which is referred to as “microcrystalline wax.” Macrocrystalline waxes lead to paraffin problems in production and transport operations microcrystalline waxes contribute the most to tank-bottom sludges. Paraffin wax produced from crude oil consists primarily of long chain, saturated hydrocarbons (linear alkanes/ n-paraffins) with carbon chain lengths of C18 to C75+, having individual melting points from 40 to 70☌. ![]()
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