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[en] As a result of the interplay between advances in computer hardware, software, and algorithm, we are now in a new era of large-scale reservoir simulation, which focuses on accurate flow description, fine reservoir characterization, efficient nonlinear/linear solvers, and parallel implementation. In this paper, we discuss a multilevel preconditioner in a new-generation simulator and its implementation on multicore computers. This preconditioner relies on the method of subspace corrections to solve large-scale linear systems arising from fully implicit methods in reservoir simulations. We investigate the parallel efficiency and robustness of the proposed method by applying it to million-cell benchmark problems.
[en] Multi-element gamma-ray spectrum logging requires standard spectra of individual elements for its interpretation. Since the standard element spectra are usually derived using Monte Carlo simulation of either a pure element or its oxide, we synthesized the standard neutron captured γ spectra (as would be observed using a NaI(Tl) detector) of elements H, Si, Ca and Fe from each element and its oxide. To compare the standard spectra from the elements and oxides, we operated three simulations of sandstone, limestone and mixed formation of sandstone and limestone each with ten different porosities, and used the two kinds of standard spectra to analyze the mixed spectra modeled from sandstone and limestone formations. The results show that the standard element spectra from oxides have more prominent energy peaks than the standard spectra from pure elements. The calculated formation element contents are close to the theoretical values when the standard element spectra from oxides are used to analyze the formation mixed spectra. Therefore, the formation element standard spectra should be calculated from oxide models in the analysis of neutron captured γ spectra by logging tools.
[en] Phase spectrum estimation of the seismic wavelet is an important issue in high-resolution seismic data processing and interpretation. On the basis of two patterns of constant-phase rotation and root transform for wavelet phase spectrum variation, we introduce six sparse criteria, including Lu’s improved kurtosis criterion, the parsimony criterion, exponential transform criterion, Sech criterion, Cauchy criterion, and the modified Canchy criterion, to phase spectrum estimation of the seismic wavelet, obtaining an equivalent effect to the kurtosis criterion. Through numerical experiments, we find that when the reflectivity is not a sparse sequence, the estimated phase spectrum of the seismic wavelet based on the criterion function will deviate from the true value. In order to eliminate the influence of non-sparse reflectivity series in a single trace, we apply the method to the multi-trace seismogram, improving the accuracy of seismic wavelet phase spectrum estimation.
[en] In this paper, we analyze the seismic signal in the time-frequency domain using the generalized S-transform combined with spectrum modeling. Without assuming that the reflection coefficients are random white noise as in the conventional resolution-enhanced techniques, the wavelet which changes with time and frequency was simulated and eliminated. After using the inverse S-transform for the processed instantaneous spectrum, the signal in the time domain was obtained again with a more balanced spectrum and broader frequency band. The quality of seismic data was improved without additional noise.
[en] Biodiesel is one of the most popular prospective alternative fuels and can be obtained from a variety of sources. Waste frying oil is one such source along with the various raw vegetable oils. However, some specific technical treatments are required to improve certain fuel properties such as viscosity and calorific value of the biodiesel being obtained from waste cooking oil methyl ester (WCOME). Various treatments are applied depending on the source and therefore the composition of the cooking oil. This research investigated the performance of WCOME as an alternative biofuel in a four-stroke direct injection diesel engine. An 8-mode test was undertaken with diesel fuel and five WCOME blends. The best compromise blend in terms of performance and emissions was identified. Results showed that energy utilization factors of the blends were similar within the range of the operational parameters (speed, load and WCOME content). Increasing biodiesel content produced slightly more smoke and NOx for a great majority of test points, while the CO and THC emissions were lower.
[en] In this study, an enthalpy-concentration method was applied in order to model a steady state continuous benzene-toluene mixture distillation column. For a distillation tower such as the benzene-toluene splitter, there are relatively few degrees of freedom that can be manipulated in order to minimize the total annualized cost. The reflux ratio can influence the steady-state operating point and therefore influence the total annualized cost. The trade-offs between reflux ratios and total annualized cost were discussed. The Cuckoo optimization algorithm was applied to obtain a correlation for the optimum value of the reflux ratio as a power function of the economic parameters of energy price and capital cost. The results show that, at low energy price or high capital cost, the optimum reflux factor is high.
[en] Petroleum refinery wastewater (PRW) containing hydrocarbon is highly toxic to the environment and the surrounding ecosystem. Proper treatment of the PRW effluent is necessary to remove the pollutants before discharge. Bioremediation is considered to be a promising approach as it is eco-friendly and efficient. The exopolysaccharide (EPS) produced by the O. anthropi acts as a bioemulsifier and showed the highest emulsification activity of 60% on diesel. An EPS yield of about 0.42 g/L was obtained under optimized conditions. The carbohydrate and protein content of the EPS was found to be 71.1% and 19.7% respectively, showing the glycoprotein nature. The structural properties of EPS were analyzed by FT-IR and 1H NMR. The batch degradation of oil in PRW by O. anthropi was studied gravimetrically, and showed about 53% degradation in 7 days, indicating the strong ability of the isolated strain to degrade the hydrocarbons in PRW.
[en] In this paper, cationic polyacrylamide microspheres (CPAM) were synthesized using acrylamide (AM) and methacryloyloxyethyl trimethyl ammonium chloride (TMAEMC) as monomers, ammonium sulfate as dispersant, poly(acryloyloxyethyl trimethyl ammonium chloride) (PAETAC) as dispersion stabilizer, and ammonium persulfate as initiator. The synthetic method was dispersion polymerization. The effects of monomer ratio (AM/TMAEMC), dispersant concentration, and dispersion stabilizer dosage on dispersion polymerization were systematically studied to determine the optimal preparation conditions. The structure and viscosity of the synthesized polymer were characterized by FTIR and capillary viscometry, respectively, and the particle sizes and distribution of the polymer microspheres were characterized by microscopy and dynamic light scattering, respectively. Finally, flow tests were conducted to measure the permeability reduction performance of the microspheres at various concentrations in sand packs with different permeability. Results show that CPAM emulsion of a solids content of lwt% has excellent performance in low-to-medium permeability formations (< 1,000 mD), and the efficiency may reach above 90%.
[en] The oxidation kinetics, surface morphology and phase structure of oxide films grown on 25Cr20Ni alloy in air-H2O and H2-H2O atmospheres at 900 °C for 20 h were investigated. The anti-coking performance and resistance to carburization of the two oxide films were compared using 25Cr20Ni alloy tubes with an inner diameter of 10 mm and a length of 850 mm in a bench scale naphtha steam pyrolysis unit. The oxidation kinetics followed a parabolic law in an air-H2O atmosphere and a logarithm law in a H2-H20 atmosphere in the steady-state stage. The oxide film grown in the air-H2O atmosphere had cracks where the elements Fe and Ni were enriched and the un-cracked area was covered with octahedral-shaped MnCr2O4 spinels and Cr1,3Fe0.7O3 oxide clusters, while the oxide film grown in the H2-H2O atmosphere was intact and completely covered with dense standing blade MnCr2O4 spinels. In the pyrolysis tests, the anti-coking performance and resistance to carburization of the oxide film grown in the H2-H2O atmosphere were far better than that in the air-H20 atmosphere. The mass of coke formed in the oxide film grown in the H2-H2O atmosphere was less than 10% of that in the air-H2O atmosphere. The Cr1.3Fe0.7O3 oxide clusters converted into Cr23C6 carbides and the cracks were filled with carbon in the oxide film grown in the air-H2O atmosphere after repeated coking and decoking tests, while the dense standing blade MnCr2O4 spinels remained unchanged in the oxide film grown in the H2-H2O atmosphere. The ethylene, propylene and butadiene yields in the pyrolysis tests were almost the same for the two oxide films.
[en] To investigate the effect of texture structure on the desulfurization performance in the Ni/ZnO reactive adsorption desulfurization (RADS) system, two kinds of ZnO porous materials with rod-shaped morphology were synthesized and their structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption/desorption. The formation mechanisms of hierarchical porous ZnO (ZnO with meso and macro pores) were also studied. Their application performance was evaluated in the RADS process over Ni/ZnO absorbent. Due to the difference in structure between the two kinds of ZnO, the two ZnO based adsorbents showed different desulfurization activity.