The morphology and structure of wax crystals are among the factors dominating rheological characteristics of a waxy crude oil at temperatures below the wax appearance temperature (WAT). In several reported researches fractal dimensions were employed in describing the waxy crude oil microstructures; however, they were all determined via the indirect approach, i.e. deduced from the rheological data. This paper presents a direct fractal characterization approach based on micrographs of wax crystals. The box-counting method is applied to the wax crystal images of three waxy crude oils beneficiated with and without pour-point-depressants (PPDs), and for the fractal measurements the t-distribution tests of hypothesis on linear regression are performed at the significance level of 0.01. It is demonstrated that the boundary fractal dimensions from micrographs of different visual fields of a specimen are almost identical, with the maximum and minimum relative ranges being 9.97% and 1.88% respectively, and with the standard deviation ranging from 0.0549 to 0.0107. Then the wax crystal structures are determined as fractal at the confidence level of 99%. All the listed absolute t-statistics with the minimum of 29.568 are much higher than the corresponding t-quantiles with the maximum of 3.4995. The results also show that the larger value of the boundary box dimension represents the higher complexity and irregularity of the wax crystal morphology. The box dimension increases with decreasing oil temperature for each waxy crude oil. After the oil is beneficiated with a PPD, the box dimension increases at each given temperature. Thus, it is feasible to use fractal dimensions to characterize the waxy crude oil microstructures. This helps to probe the rheology–microstructure relation.

Venezuela heavy oil under various hydrogen pressures has been hydrocracked to investigate the variation of asphaltene components during reaction. Asphaltenes have been isolated from the product and analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR). The experimental data revealed that the interlamellar spacing and interchain spacing of the asphaltenes increased while the layer diameter decreased with the hydrogen pressure increasing. At the same time, the amount of aromatic carbon and alkyl carbon of the asphaltenes decreased gradually and the amount of naphthenic carbon increased. As the hydrogen pressure increased, the substitution ratio and the condensation degree parameter (H AU /C A ) of the aromatic system in the periphery increased gradually and the replacement index and peri-position condensation index of asphaltenes decreased obviously.

We study the complex dynamics of a two-dimensional suspension comprising non-motile active particles confined in an annulus. A coarse-grained liquid crystal model is employed to describe the nematic structure evolution, and is hydrodynamically coupled with the Stokes equation to solve for the induced active flows in the annulus. For dilute suspensions, coherent structures are captured by varying the particle activity and gap width, including unidirectional circulations, travelling waves and chaotic flows. For concentrated suspensions, the internal collective dynamics features motile disclination defects and flows at finite gap widths. In particular, we observe an intriguing quasi-steady-state at certain gap widths during which $+1/2$-order defects oscillate around equilibrium positions accompanying travelling-wave flows that switch circulating directions periodically. We perform linear stability analyses to reveal the underlying physical mechanisms of pattern formation during a concatenation of instabilities.

The composition, structure, and colloidal stability of hydrocracked products at various hydrogen pressures were analyzed to investigate the role of hydrogen pressure in slurry-phase hydrocracking of Venezuela heavy oil. Experimental data showed that the formation of gas, naphtha, and coke was suppressed by a high hydrogen pressure during the slurry-phase hydrocracking. In addition, the maximum of light oil per coke ratio was observed at 8 MPa of hydrogen. The desulfurization and denitrogenation were promoted by the increase of hydrogen pressure. However, the influence of hydrogen pressure on the desulfurization rate was reduced at higher pressure, while the influence on the denitrogenation rate was still obvious. With the increase of hydrogen pressure, the Conradson carbon residue (CCR) of the vacuum residue (VR) product decreased. Meanwhile, the coking inducing period of the atmospheric residue (AR) product prolonged, which means that the colloidal stability of the AR product was enhanced by a high hydrogen pressure. Structural parameters of asphaltene were studied according to the reference of the Fourier transform infrared (FTIR) spectroscopy method of kerogen structure studying. The cracking and hydrogenation saturation of asphaltene were promoted by a high hydrogen pressure, which lead to the increase of the A factor (infrared absorption intensity ratio of saturated aliphatic carbon and aromatic carbon) and n CH 2 /n CH 3 of asphaltene products as well as the decrease of the Y factor (condensation index of asphaltene) and Z factor (discriminative index of the side-chain fracture situation of asphaltene).

A new statistical approach to assessing the friction factor correlations was presented. Fourteen correlations, published from 1959 to 2003, were collected to calculate friction factors for power law fluids in turbulent pipe flow. A series of Fanning friction factors, f, were computed from these equations. Then the relations between the calculated values of f and Re MR (Metzner-Reed Reynolds number) were analyzed, when the rheological behavior index, n, was given. To verify the foregoing analysis result, in addition, the relations between the calculated values of f and n were analyzed, when Re MR was given. The f value calculated from each equation was compared with each mean value of all the f values from the 14 equations, when each combination (n, Re MR ) (n ranging from 0.4 to 1.4 and Re MR from 4 000 to 100 000) was set. The comparison results were surveyed in the relative deviation table of the calculated f values. It shows that the overall mean relative deviation (OMRD) of the Dodge-Metzner correlation is the minimum, 1.5%. Therefore, the Dodge-Metzner correlation is recommended for predicting the friction factors for the turbulent pipe flow of power law fluids.

No abstract

It is important and profound to quantitatively study the relation between rheology and microstructure for development of the microstructural mechanism of crude oil rheology and even for the waxy crude oil pipelining. However, due to the high complexity and irregularity of wax crystal morphology, quantitative characterization is hard to achieve. This has hampered further study on the rheology-microstructure relationship. A new approach combined the fractal geometry and the stereology theory is presented for quantifying the intricate wax crystal morphology and structure. Based on the characterization, the effects of microstructures and oil composition on the waxy crude viscosities are analyzed quantitatively. It further validates the previous qualitative research and enriches understanding into the microstructural mechanism of waxy crude oil rheology.

No abstract