An explanation for solid-liquid-liquid-vapour phase behaviour in reservoir fluids

The appearance of solid-liquid-liquid-vapour phase equilibria in reservoir fluids is explained as an extension of the phase behaviour of binary asymmetric fluids. The theoretical approach is demonstrated for the model condensate-rich reservoir-fluid ethane (10 mole %) butane (40 mole %) phenanthrene (50 mole %), to which propane is added. Extant solid-liquid-liquid-vapour phase equilibrium data for reservoir fluids, which include asphaltenes, are found to be consistent with the phase behaviour of this model fluid. The implications for the prediction of asphaltene “precipitation” are discussed.     

UNUSUAL RETROGRADE CONDENSATION AND ASPHALTENE PRECIPITATION IN A MODEL HEAVY OIL SYSTEM

ABSTRACT

A partial phase diagram for the system athabasca bitumen vacuum bottoms (ABVB) (24.6 wt% / 2 mole % ) + dodecane (73.8 wt. % / 47 mole % ) + hydrogen (1.6 wt % / 51 mole % ) was constructed in the temperature range 425 K to 725 K and the pressure range 2 MPa to 7 MPa using an X-ray view cell apparatus. This fluid system is shown to exhibit two phase L₁V and three phase L₁ L₂ V phase behaviour over parts of this P-T region. The shape of the low temperature boundary between the L₁V and L₁ L₂ V zones is characteristic of dilute asymmetric mixtures where a heavy liquid phase, L₂ appears then disappears within the light liquid phase L₁ on isothermal compression. Such phase behaviour is referred to as unusual retrograde condensation and is of both practical and theoretical interest. Transitions between the multiphase regions were found to be reversible at temperatures less than 660 K., in all cases. At higher temperatures irreversible “ asphaltene precipitation” arose within the L₂ phase “ Asphaltene precipitation” did not arise in the absence of the L₂ phase, i.e.: within the L₁ V region, even at temperatures in excess of 700 K. These data provide a strong link between “ asphaltene precipitation” and multiphase behaviour, and demonstrate a physical rather than kinetic basis for asphaltene precipitation at elevated temperatures     

New Generalized One-Parameter Vapor Pressure Formula of Homologous Pure Hydrocarbon Series

Generalized formula has been developed to calculate vapor pressure of pure hydrocarbon series (C_nH_2n+2) from C₁₁H₂₄ to C₃₅H₇₂ based on one parameter “carbon number” only. As a result this technique is considered to be useful for prediction of vapor pressure of pure hydrocarbons, since it is possible to use this formula depending on simple parameter “carbon number”.     

CHARACTERIZATION OF PETROLEUM RESIDUA THROUGH REDUCTIVE CHEMISTRY

Distillation residua from petroleum, containing 26 — 32% aromatic carbon (f_a), are reduced by K⁰ in tetrahydrofuran to form anions which are then alkylated by alkyl iodides. Consumption of potassium in 24 hours at room temperature is in the range 4 to 5 mmol K per gram resid, of which 19—23% goes to the formation of “K₂S” from the removal of sulfur from the resid. The anions of the resid are characterized by alkylation of the resid with ¹³C enriched methyl iodide followed by examination by heteronuclear correlated two—dimensional nuclear magnetic resonance of ¹H and ¹³C spins. Analysis of proton and carbon shifts of individual methyls demonstrates that attachment of methyls to carbon atoms of the resid is the principal chemistry of the reductive methylation.     

COMMENT ON THE STUDY OF ASPHALTENES BY X-RAY DIFFRACTION

In the x-ray diffraction of carbonaceous materials, there is no logical reason to assume an interrelation between the intensity of the (002) peak, reflecting intermolecular “stacking” order of aromatic planes, and the fractional aromaticity f_a measured by carbon nuclear magnetic resonance. Approaches to the calculation of a diffraction-based aromaticity f₀₀₂ by comparing the intensity of the (002) peak to that of the γ-band at 450 pm, reflecting intermolecular order of saturated chain hydrocarbons, are fundamentally flawed. The use of diffraction linewidth data for peaks near 210 pm (“(100)”) and near 120 pm (“(110)”) to infer an aromatic diameter has difficulties in systems containing hydroaromatic molecules (e.g., tetralin) because the naphthenic moiety contributes to diffraction peaks in the 210 and 120 pm regions.     

Evaluation of Effects of Selected Wax Inhibitors on Wax Appearance and Disappearance Temperatures

In this investigation, a light transmittance method was used to evaluate the wax appearance temperatures (WAT) and wax disappearance temperatures (WDT) of model paraffin compounds (n-C₂₄H₅₀ (C₂₄) and n-C₃₆H₇₄ (C₃₆)) in n-decane (C₁₀) solutions both with and without wax inhibitors. The change in WAT at different paraffin concentrations in the presence of an inhibitor behaves as though there is a constant amount of paraffin removed by the inhibitor. However, the amount of apparent paraffin reduction by an inhibitor (e.g. 160 g of C₂₄ by one gram of an inhibitor) indicates that the inhibition mechanism cannot easily be explained by a simple “sequestering” effect. Wax inhibitors that decrease the WAT tend to also increase the WDT. Most of the wax inhibitors tested at a dosage of 100 ppm did suppress the WAT of lower molecular weight paraffin (C₂₄) solutions, but had little or no effect for higher molecular weight paraffin (C₃₆) solutions. Side-chain length of polymethacrylate wax inhibitors is an important performance parameter. Of the three polymethacrylate wax inhibitors tested, the one with the longest alkyl side-chain (C₁₈) had the most effect on suppressing the WAT and increasing the WDT of the binary mixtures (n-C₁₀-n-C₂₄ solutions).     

准噶尔盆地南缘井筒堵塞物中沥青质分子组成研究

采用傅里叶变换离子回旋共振质谱分析技术,分析了准噶尔盆地南缘高探1井原油及井筒堵塞物抽提物中沥青质化学组成及差异,探讨了沥青质的组成及结构与沥青质沉积关系,对于沥青质聚集理论研究具有重要意义.研究结果显示,高探1井原油及井筒堵塞物抽提物中沥青质分子主要为N1、N1 O1、O1、O2、O3和O4类化合物,但堵塞物抽提物中...     

Oxidehydrogenation of Ethylbenzene Over Supported TiO2 Catalysts

Six different metals as active components of catalyst for dehydrogenation of ethylbenzene were supported over TiO₂ using isovolumetric impregnation method. In the bench scale experiment at 623 K an effective catalyst V₁/TiO₂ was found, 18.8% ethylbenzene with 100% styrene selectivity acquired. Various characterization techniques, physisorption, SEM/EDX, XRD, TGA, and particle size analyzer, were employed to analyze the features of catalysts. Results showed that lower calcined temperatures helped to increase the selectivity of styrene when V₁/TiO₂ was calcined at 523 K while the reaction temperature was 623 K. The pore distribution was concentrated and the growth of active components crystalline grains in V₁/TiO₂ catalyst could be effectively controlled when it was calcined in lower temperature during preparation. The agglomeration of V on the surface of V₁/TiO₂ catalyst during reaction leads to the decrease of ethylbenzene conversion.     

PdCl2 CATALYZED OXIDATION OF STYRENE TO ACETOPHENONE UNDER MILD CONDITIONS

PdCl₂ exhibits very high catalytic activity and acetophenone selectivity for liquid-phase oxidation of styrene under mild conditions at 55 °C, H₂O₂/styrene = 1.15 (mole ratio) and acetone as cosolvent. The effect of cosolvents and phase transfer reagents on the reaction is investigated. The results show that the use of acetone as cosolvent or sodium dodecyl sulfate as phase-transfer reagent can accelerate the reaction. The conversion of styrene is high when the mole ratio of styrene to PdCl₂ over the range of 400∼1500. The selectivity for acetophenone decreases significantly by adding some chelating ligands to the catalytic system. The selectivity for benzaldehyde decreases significantly by adding some radical inhibitor to the catalytic system. These results show that that benzaldehyde may be produced through radical auto-oxidation mechanism while acetophenone may be produced through coordination catalysis mechanism.     

X-RAY DIFFRACTION USED TO MEASURE LEVELS OF SP2 AND SP3 CARBON IN FOSSIL FUELS: A MICROCOSM OF THE 1990'S, WORKING HARDER AND GETTING LESS

The proposition that a diffraction peak can be “far too intense to be caused by amorphous scattering and far too broad to be caused by conventional diffraction” is analyzed and found to be in error. Theoretically, Debye peaks arising from intermolecular interference in liquids and conventional Bragg peaks are part of a continuum. Experimentally, with respect to the “(002)” peak in benzenoid materials, not all aromatic carbons need contribute to an intermolecular interference peak, so that determinations of sp² or sp³ carbon abundance based on analysis of only the “(002)” peak are necessarily flawed. As a separate but related matter, journal citation trends of relevance to the court case Gordon and Breach v. AIP are analyzed     

THERMAL STABILITY ANALYSIS OF THE LIQUID PHASE METHANOL SYNTHESIS REACTOR

The effect of addition of an inert liquid phase on the rate of heat generation in the catalytic synthesis of methanol from syngas has been studied. Gas compositions typical of product gases from Lurgi and Koppers-Totzek gasifiers, represented by H₂-rich and CO-rich syngas respectively, were used to experimentally verify the “slope” and “dynamic” critria in a three-phase fixed bed recycle reactor. The liquid medium, witco-40 oil, has been effective in controlling the rate of heat generation and in preventing catalyst overheating, signifying that the liquid phase synthesis is thermally far more stable than the vapor phase synthesis. The experimental thermal stability study provides crucial and valuable information in commercializing the liquid phase methanol synthesis process. The current approach of thermal stability analysis does not require any a priori assumption or predetermined reaction kinetics.     

Rheological evidence of structural phase transitions in asphaltene-containing petroleum fluids

The aim of this paper is to provide data on the rheological/structural properties of “synthetic oils,” composed of light hydrocarbons (toluene) and a heavy fraction, containing asphaltenes (vacuum residue, VR). Samples with asphaltene concentrations 20–85 g/l have been studied at temperatures 0–60 °C and shear rates up to 1500 s⁻¹. The non-Newtonian flow curves were approximated by the Bingham and the Herschel–Bulkley models to determine the apparent yield stress and the shear-rate exponent as functions of the asphaltene concentration and the temperature. Sharp variations of these parameters were attributed to formation/destruction of extended ordered structures in asphaltene colloid suspensions. Structural changes were observed in the temperature range 20–30 °C, particularly important for industrial processes of reservoir development and pipeline transportation. A molecular model of the observed macroscopic effects takes into account possible first-order structural phase transitions in the nanometer-size resin/asphaltene colloid microparticles.     

SHALE OIL UPGRADING IN SUPERCRITICAL WATER SOLUTIONS

A supercritical water/HCl system was studied for upgrading Paraho shale oil (SO) at 400-425^°C. The key process parameters were water density (ρw) and HC1 loading. Increases in ρw increased the selectivity to distillate-range products at the expense of gas and coke products. Increases in ρw also enhanced the ability of HCl to catalyze N-removal. However, coke and gas make also increased with increases in HCl loading. Optimal or “best case” results and conditions were 897% N-removal and 75% distillate yield, at T = 425^°C, ρw = 0.2 g/cc, and HCl/SO = 0.05g/g. The underlying chemical mechanisms appeared to involve SCF solvent cage effects and hcterolytic N-removal brought about by dissociation of HCl.     

STUDY ON PROCESSING SCHEME OF HIGH VISCOUS CRUDE FROM NO.1 SHUGUANG ZONE OF LIAOHE OIL

The characteristics of the high viscous crude from No.1 Shuguang Zone of Liaohe Oil Field are similar to those of residue distillates of general crude such as high density (ρ₂₀ = 0.9977 g.cm^-3), high viscidity (ν₁₀₀ = 1223.9 mm².s^-1) and high solidifying point(SP = 48°C). It contains no gasoline distillate and diesel yield is just 7.19%. And now it is only used as fuel. In order to make full use of this oil, the high viscous crude from No.1 Shuguang Zone of Liaohe Oil Field is evaluated comprehensively. And the properties of various distillates from the crude are analyzed and evaluated respectively. The results indicate that this oil contains less wax, but rich in resin and asphaltene, which belongs to low sulfur naphthene-base crude oil and can be used as feedstock to produce high paving asphalt. According to its characteristics, the optimum processing scheme is put forward and the high grade paving asphalts are produced by using the distillates higher than 350°C.     

Production of High-Grade Asphalt from Liaoshu Crude Oil

The high viscous crude oil for Shuguang No. 1 zone of Liaohe oilfield has the characteristics of high density (ρ₂₀ = 0.9977 g.cm^-3), high viscidity (ν₁₀₀ = 1,223.9 mm².s^-1), and high solidifying point (SP = 48°C), which belongs to low sulfur naphthene-base crude oil. The comprehensive evaluations indicate that this oil has no gasoline fraction and the diesel oil is only 7.19%. In addition, the lubricating oil distillate is not suited to produce lubricating oil and heavy oil is not good feedstock for catalytic cracking. However, the low wax and high resin, as well as asphaltene content, make it an ideal raw material for producing paving asphalt. The vacuum residue of this crude acted as base oil and three kinds of waste oil with high aromatics and low wax content were selected as blenders. Various brands of high-grade paving asphalts meeting GB/T15180-94 (China) specification were produced by blending method. The blending effects were investigated and corresponding mathematics models were set up.     

页岩储层CO2驱沥青质沉淀特征及影响因素分析

为明确CO2在页岩储层纳米孔隙中的流动机理及其对沥青质沉淀的影响,采用自主研发的高温高压过滤容器和复合纳米滤膜,进行纳米滤膜过滤实验,模拟了单(多)层岩石切片作用下的CO2驱替过程,开展储层参数和注入参数对CO2驱替效果及沥青质沉淀的影响研究.研究结果表明:CO2驱会引发沥青质沉淀,导致剩余油中的沥青质含量远大于产出油...     

Determination of cadmium and lead in fruit juices by stripping chronopotentiometry and comparison of two sample pretreatment procedures

A method for the determination of cadmium and lead in apple and pear fruit juices by stripping chronopotentiometry (SCP) is described. The results obtained after previous digestion of the sample with concentrated sulphuric acid and dry-ashing (sample pretreatment procedure “A”) and after a treatment with concentrated hydrochloric acid followed by heating in hot water bath (sample pretreatment procedure “B”) were compared. The sample pretreatment procedures were tested on real fruit juice samples and all data confirmed that the efficiency of procedure A was greater than procedure B. In particular, for samples treated with procedure A, good linearity was obtained in the range of examined concentration as is shown by the determination coefficients that were 0.998 (n = 4) for cadmium and 0.996 (n = 4) for lead. Recoveries of 86–104% for cadmium and of 87–102% for lead were obtained from a sample spiked at different levels. The accuracy was also evaluated by means of a matching reference sample of spiked skim milk powder (BCR 150—Community Bureau of Reference) to prove the reliability of the method. The detection limits were 2.0 ng g⁻¹ for cadmium and 4.8 ng g⁻¹ for lead. The relative standard deviations (mean of nine determinations), evaluated on a real sample, were 7.8% and 6.5% respectively. The average content was in the range not detectable–3.0 ng g⁻¹ for cadmium and 8.2–21.3 ng g⁻¹ for lead.     

The Asphaltene and Wax Deposition Envelopes

Asphaltene and wax phase behavior is quite different than the conventional “PVT” phase behavior. Asphaltenes exhibit a behavior at some thermodynamic states called flocculation. That is, asphaltene particles or micelles aggregate or flocculate into larger aggregates or flocs. The locus of all thermodynamic points in a P-T-x phase diagram at which flocculation occurs is called the Asphaltene Deposition Envelope (ADE). Paraffin waxes, on the other hand, at some thermodynamic states, exhibit the phenomenon of crystallization. The locus of all thermodynamic points in a P-T-x phase diagram at which wax crystallization occurs is called the Wax Deposition Envelope (WDE). Asphaltene flocculation can be both reversible and irreversible (as expected from the asphaltene colloidal nature). Wax crystallization is generally a reversible process. However, paraffin waxes more than often precipitate together with resins and asphaltenes (which are said to be responsible for the observed irreversible thermodynamic phenomena). Hence, some wax precipitation is occasionally reported as irreversible. Measurement of the ADE and WDE boundaries, at in-situ conditions, is a challenging task. Measurement of asphaltene and wax solubility at in-situ conditions inside the ADE and WDE is even more challenging. The ADE and WDE data have practical significance and are very useful for modeling of reservoir fluid behavior. Asphaltene and wax data for a number of oils are presented and analyzed. This paper introduces and compares two powerful thermodynamic diagrams that summarize the phase behavior of asphaltenes and waxes, the ADE and WDE.     

An explanation for solid-liquid-liquid-vapour phase behaviour in reservoir fluids

ABSTRACT

The appearance of solid-liquid-liquid-vapour phase equilibria in reservoir fluids is explained as an extension of the phase behaviour of binary asymmetric fluids. The theoretical approach is demonstrated for the model condensate-rich reservoir-fluid ethane (10 mole %) butane (40 mole %) phenanthrene (50 mole %), to which propane is added. Extant solid-liquid-liquid-vapour phase equilibrium data for reservoir fluids, which include asphaltenes, are found to be consistent with the phase behaviour of this model fluid. The implications for the prediction of asphaltene “precipitation” are discussed.     

NEW TECHNIQUES AND METHODS FOR THE STUDY OF AGGREGATION, ADSORPTION, AND SOLUBILITY OF ASPHALTENES. IMPACT OF THESE PROPERTIES ON COLLOIDAL STRUCTURE AND FLOCCULATION

The solubility of Furrial asphaltene in toluene was 57g L^-1. However, using a new technique, based on the precipitation of this sample by the phenol PNP, we found that a fraction [2], comprising 47% of the asphaltene, is of low solubility. This suggested that this material constitutes the colloidal phase, and the rest acts as the dispersing fraction. This technique allowed the fractionation of asphaltenes in fractions A₁, A₂, and A₃ according to solubility, going from practically insoluble (A₁) to low (A₂, 1 g L^-1) to high (A₃, around 57 g L^-1). The adsorption isotherms of asphaltenes on glass and silica in toluene consist of a sequence of steps or step-wise adsorption. The first layer or first step is formed by the adsorption of free asphaltene molecules and by small aggregates (aggregation number between 3 and 6) which saturate the glass or silica surface in the usual manner (L-type or H-type isotherms). However, we suggest that the second, third, and other asphaltene layers adsorb sequentially according to the above differences in solubility. The very slow changes with time and the negligible desorption from the surface measured for the above isotherms were interpreted as the effect of packing or the building up of a well packed layer. This would be achieved by the slow formation and rupture of bonds between neighboring molecules at the surface. Thus, molecules with difficulties to pack, adsorbed by a kinetically controlled process, are either rejected or relocated in a thermodynamic controlled process. The above results and ideas were used to improve the models for asphaltene and petroleum colloids and to underscore the importance of surfaces and colloid dispersants in asphaltene precipitation during the production of crude oils. For instance, the results described below suggest that colloids are constituted by a well packed and insoluble asphaltene core, impervious to the solvent, and by a loose packed periphery which, by allowing solvent penetration, keep the colloid in solution. According to this model, desorption of compounds in the above loosely packed periphery, such as the one promoted by a surface, would be the main cause of asphaltene precipitation from crude oils. In this case, solubility reductions caused by pressure drops during oil production would have a minor effect. Also, preliminary number average molecular weights M_n for four asphaltenes, obtained using a new procedure, are presented here. The M_n values obtained ranged from 780 to 1150 g/mol.