Crude oil, determination

The crude oil used by Bennett and Barter (1997) was a typical North Sea oil generated from Upper Jurassic, Kimmeridge clay formation source rocks. The alkylphenol distribution in a sample of (Miller) crude oil, determined using solid phase extraction (SPE), is shown in Fig. 16.21. The crude oil is dominated by phenol and cresol and contains appreciable quantities of dimethylphenols. The concentrations of 2,3-, 3,4-, and 3,5-dimethylphenol also include a contribution from 2-, 3-, and 4-ethylphenols, because they coelute under the conditions employed (Bennett et ah, 1996). 

The losses could be quite substantial and produce inaccurate results when standard extraction methods are used for the analysis of waste-waters containing crude oils. In our experience, typical recoveries for crude oils were in the 50%—60% range when Standard Extraction Method 502B (I) was used. This was in sharp contrast to crude oil determination by the Total Organic Carbon (TOC) method (modified for analysis of oil in water) where TOC recoveries were close to 100%. 

Table II. Accuracy of Crude Oil Determination by the Freon Extraction—IR Method of Analysis...

J. L. Epler, J. A. Young, A. A. Hardigree, T. K. Tao, M. R. Guerin, I. B. Rubin, C.-h. Ho, and B. R. Clark, Analytical and biological assessment of test materials from the synthetic fuel technologies. I. Mutagenicity of crude oils determined by the Salmonella typhimurium microsomal activation system, Mutat. Res. 57, 265-276 (1978). 

Knowledge of a crude oil s overall physical and chemical characteristics will determine what kind of initial treatment —associated gas separation and stabilization at the fi ld of production— transport, storage, and of course, price. 

The water content of crude oils is determined by a standardized method whose procedure is to cause the water to form an azeotrope with an aromatic (generally industrial xylene). Brought to ambient temperature, this azeotrope separates into two phases water and xylene. The volume of water is then measured and compared with the total volume of treated crude. 

The water and sediment contents of crude oils is measured according to the standard methods NF M 07-020, ASTM D 96 and D 1796, which determine the volume of water and sediments separated from the crude by centrifuging in the presence of a solvent (toluene) and of a demulsifylng agent Table 8.13 gives the bottom sediment and water content of a few crude oils. 

The determination of properties for each cut enables curves to be obtained for yields and properties as well as curves for iso-properties that are useful in the economic analyses of crude oils. 

Simple conventional refining is based essentially on atmospheric distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used. 

To type crude oils (see Figure 2.13). This method uses an extremely accurate compositional analysis of crudes to determine their source and possible migration route. As a result of the accuracy It is possible to distinguish not only the oils of individual accumulations in a region, but even the oils from the different drainage units within a field. If sufficient samples were taken at the exploration phase of a field, geochemistry allows one to verify cross flow and preferential depletion of units during later production. 

Production Controls The nature of the produc tion control logic differs greatly between continuous and batch plants. A good example of produc tion control in a continuous process is refineiy optimization. From the assay of the incoming crude oil, the values of the various possible refined products, the contractual commitments to dehver certain products, the performance measures of the various units within a refinery, and the hke, it is possible to determine the mix of produc ts that optimizes the economic return from processing this crude. The solution of this problem involves many relationships and constraints and is solved with techniques such as linear programming. 

Naphthenic acid is a collective name for organic acids present in some but not all crude oils. In addition to true naphthenic acids (naphthenic carboxylic acids represented by the formula X-COOH in which X is a cycloparaffin radical), the total acidity of a crude may include various amounts of other organic acids and sometimes mineral acids. Thus the total neutralization number of a stock, which is a measure of its total acidity, includes (but does not necessaiily represent) the level of naphthenic acids present. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize one gram of stock as determined by titration using phenolphthalein as an indicator, or as determined by potentiometric titration. It may be as high as 10 mg KOH/gr. for some crudes. The neutralization number does not usually become important as a corrosion factor, however, unless it is at least 0.5 mg KOH/gm. 

Similarly, in processes where the listed toxic chemical occurs at a concentration below the de minimis level and is processed to a concentration above the de minimis level, the portion of the process where the toxic chemical is present above the de minimis level must be considered lor threshold and release determinations, lor example, an impurity contained in a solvent that is concentrated to above the de minimis level in a process. Beneficiation activities involving listed toxic chemicals present in ores, natural gas, and crude oil are an exception and require threshold and release determinations regardless of concentration of the listed toxic chemical(s) involved in the beneficiation process. 

Nevertheless, a number of gas chromatographic applications exist, epecially those for the determination of crude oil indicators. Such indicators are used as geochemical parameters for the thermal history of the crude as well as to indicate the possible relationship between crudes from different wells. These indicators comprise a number of isomeric aromatic species, such as the individual alkylnaphthalenes (44, 45), the individual Cio-mono-aromatics or the individual C9-mono-aromatics. The ratio between these isomers gives a definite indication of the crude oil. In general, these systems use a Deans switching unit to make a heart-cut, which then is focused, reinjected and separated on a second column with a different polarity. 

After field processing of wellhead products is complete, the oil and gas production phase of the industry passes into the refining stage, where the crude oil and field gas are further processed to make the products that ultimate users will purchase. The prices that refiners will pay determine the maximum allowable costs for oil and gas exploration and production. An oil or gas producer must be able to provide the product at a competitive price. For a vertically integrated oil company, no actual sale may take place, but the economics are much the same. 

FCC feedstocks contain sulfur in the form of organic-sulfur compounds such as mercaptan, sulfide, and thiophenes. Frequently, as the residue content of crude oil increases, so does the sulfur content (Table 2-5). Total sulfur in FCC feed is determined by the wavelength dispersive x-ray fluorescence spectrometry method (ASTM D-2622), The results are expressed as elemental sulfur. 

This input to design refers to the long-term stability of the raw material sources for the plant. It is only of importance where the raw materials can or do contain impurities which can have profound effects on the corrosivity of the process. Just as the design should cater not only for the norm of operation but for the extremes, so it is pertinent to question the assumptions made about raw material purity. Crude oil (where HjS, mercaptan sulphur and napthenic acid contents determine the corrosivity of the distillation process) and phosphate rock (chloride, silica and fluoride determine the corrosivity of phosphoric acid) are very pertinent examples. Thus, crude-oil units intended to process low-sulphur crudes , and therefore designed on a basis of carbon-steel equipment, experience serious corrosion problems when only higher sulphur crudes are economically available and must be processed. 

The classic method for the determination of corrosion inhibitors in oil field brines is the dye transfer method. This method is basically sensitive to amines. Within this method, there are many variations that the analyst may use to determine the amount of corrosion inhibitor in either water or crude oil. Unfortunately these methods detect all amines present as corrosion inhibitors [1174]. 

Interfacial rheologic properties of different crude oil-water systems were determined in wide temperature and shear rate ranges and in the presence of inorganic electrolytes, surfactants, alkaline materials, and polymers [1056]. 

Caustic Waterflooding. In caustic waterflooding, the interfacial rheologic properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior, and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration, and aging time. The interfacial viscosity drastically... 

The effectiveness of a crude oil demulsifier is correlated with the lowering of the shear viscosity and the dynamic tension gradient of the oil-water interface. The interfacial tension relaxation occurs faster with an effective demulsifier [1714]. Short relaxation times imply that interfacial tension gradients at slow film thinning are suppressed. Electron spin resonance experiments with labeled demulsifiers indicate that the demulsifiers form reverse micellelike clusters in the bulk oil [1275]. The slow unclustering of the demulsifier at the interface appears to be the rate-determining step in the tension relaxation process. 

The performance of demulsifiers can be predicted by the relationship between the film pressure of the demulsifier and the normalized area and the solvent properties of the demulsifier [1632]. The surfactant activity of the demulsifier is dependent on the bulk phase behavior of the chemical when dispersed in the crude oil emulsions. This behavior can be monitored by determining the demulsifier pressure-area isotherms for adsorption at the crude oil-water interface. 

H. U. Khan, J. Handoo, K. M. Agrawal, and G. C. Joshi. Determination of wax separation temperature of crude oils from their viscosity behaviour. Erdol Erdgas Kohle, 107(l) 21-22, January 1991. 

R. M. Matherly, J. Jiao, J. S. Ryman, and D. J. Blumer. Determination of imidazoline and amido-amine type corrosion inhibitors in both crude oil and produced brine from oilfield production. In Proceedings Volume. 50th Annu NACE Int Corrosion Conf (Corrosion 95) (Orlando, FL, 3/26-3/31), 1995. 

Kline WF, Wise SA, and May WE (1985) The apphcation of perdeuterated polycydic aromatic hydrocarbons (PAH) as internal standards for the liquid chromatc aphic determination of PAH in petroleum crude oil and other complex mixtures. J Liq Chromatogr 8 223-237. 

NMR spectroscopy is one of the most widely used analytical tools for the study of molecular structure and dynamics. Spin relaxation and diffusion have been used to characterize protein dynamics [1, 2], polymer systems[3, 4], porous media [5-8], and heterogeneous fluids such as crude oils [9-12]. There has been a growing body of work to extend NMR to other areas of applications, such as material science [13] and the petroleum industry [11, 14—16]. NMR and MRI have been used extensively for research in food science and in production quality control [17-20]. For example, NMR is used to determine moisture content and solid fat fraction [20]. Multi-component analysis techniques, such as chemometrics as used by Brown et al. [21], are often employed to distinguish the components, e.g., oil and water. 

The pore geometry described in the above section plays a dominant role in the fluid transport through the media. For example, Katz and Thompson [64] reported a strong correlation between permeability and the size of the pore throat determined from Hg intrusion experiments. This is often understood in terms of a capillary model for porous media in which the main contribution to the single phase flow is the smallest restriction in the pore network, i.e., the pore throat. On the other hand, understanding multiphase flow in porous media requires a more complete picture of the pore network, including pore body and pore throat. For example, in a capillary model, complete displacement of both phases can be achieved. However, in real porous media, one finds that displacement of one or both phases can be hindered, giving rise to the concept of residue saturation. In the production of crude oil, this often dictates the fraction of oil that will not flow. 

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