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The low permeability reservoir perfect an important role of energy replacement in petroleum industry. Aiming at the problem of low prediction accuracy of the deep profile control in low permeability reservoirs and the lack of theoretical basis for the tracking and adjustment of projects, the variation characteristics of relaxation time are determined based on the viscoelastic experiments of movable gels with different concentrations, shear rates and angular velocities. The viscoelastic mobile gel apparent viscosity model considering the relaxation time kinetics is established based on the Maxwell theory and the pressure prediction model for the expanded granular/mobile gel deep profile control in low permeability reservoirs is established. Finally, the real production data of profile control wells in Yushulin oilfield in China is taken as an example, the application effects of the new pressure prediction model considering the viscoelasticity, the pressure model without viscoelasticity and the numerical simulation model are compared and verified. The results show that the gel exhibits viscoelasticity at high shear rate, and when the gel concentration is increased from 500 mg/L to 1500 mg/L, the relaxation time decreases from 1.04 s to 0.08 s and from 6.3 s to 0.8 s before and after gelation, respectively. The application effects of the models show that the new model takes into account the viscoelasticity of the gel, which is 12.3 percentage points higher than that of the traditional pressure model based on the reservoir engineering method and 10.6 percentage points higher than that of the numerical simulation model. [ABSTRACT FROM AUTHOR]

With the growing demand for oil energy and a decrease in the recoverable reserves of conventional oil, the development of viscous oil, bitumen, and shale oil is playing an important role in the oil industry. Bohai Bay in China is an offshore oilfield that was developed through polymer flooding process. This study investigated the pore-scale displacement of medium viscosity oil by hydrophobically associating water-soluble polymers and purely viscous glycerin solutions. The role and contribution of elasticity on medium oil recovery were revealed and determined. Comparing the residual oil distribution after polymer flooding with that after glycerin flooding at a dead end, the results showed that the residual oil interface exhibited an asymmetrical “U” shape owing to the elasticity behavior of the polymer. This phenomenon revealed the key of elasticity enhancing oil recovery. Comparing the results of polymer flooding with that of glycerin flooding at different water flooding sweep efficiency levels, it was shown that the ratio of elastic contribution on the oil displacement efficiency increased as the water flooding sweep efficiency decreased. Additionally, the experiments on polymers, glycerin solutions, and brines displacement medium viscosity oil based on a constant pressure gradient at the core scale were carried out. The results indicated that the elasticity of the polymer can further reduce the saturation of medium viscosity oil with the same number of capillaries. In this study, the elasticity effect on the medium viscosity oil interface and the elasticity contribution on the medium viscosity oil were specified and clarified. The results of this study are promising with regard to the design and optimum polymers applied in an oilfield and to an improvement in the recovery of medium viscosity oil. [ABSTRACT FROM AUTHOR]

In the feed industry, through crushing, mixing and conditioning, feedstuffs are pelleted by mechanical equipment to obtain pellet products. In this compression process, the feed material particles are overlapped and staggered with each other, and the granular system is changed from the loose state into the curing bond with squeeze flow and the gap flow occurs synchronously. The mechanism for the pelleting process appears to be a regular relationship of stress and strain and other mechanical properties. Therefore, it is necessary to learn the stress-strain relationship and rheology properties of the feedstuffs during the compression process, and it is of theoretical significance to analyze the forming rules of granules and optimize the pelleting process and equipment. In this paper, based on characteristics and nonlinear properties of wheat as a feedstuff, a nonlinear visco-elasto-plastic constitutive model for characterization of rheological properties was constructed. Based on the experiment, and establishment and verification of the numerical model, the rheological properties such as viscoelasticity and plasticity of the feedstuff were analyzed by the model coefficients, and the influence of material properties and processing parameters on the rheological properties is studied. Also, the relationship between the rheological coefficients of the materials and the quality of the pellet is learned, which provides a new methodology for the study on the compression process of pellet feed. According to the process of pelleting, the factors in compression trials were selected including moisture, particle size (i.e., mesh size) and forming temperature, compression load. During the initial stage of the compression process, air between the particles was extruded by pressure and relative positions of particles are rearranged under the action of the inertial force. With the process progressing, the gap gradually decreases to infinitely small and the relative positions of the particles cease to change significantly, after which the deformation of the material can be considered as caused by its own viscoelastic properties, and therefore the compression process is divided into inertial deformation stage and visco-elasto-plastic compression stage for better description. According to the theory of rheology, the feedstuffs properties exhibited during the compression process are summarized as elastic-plastic, viscous and particle-wall friction, and represented by the strain hardening spring element, Newton viscous dashpot element, and Coulomb friction element, respectively. The elastic modulus shows the flexibility of the elastic element or the difficulty of compression. It turns out that the larger the coefficient, the more difficult the deformation and the stronger the stiffness of the material, which can stand for the strength and deformation properties. The improvement of the plastic strain showed by combined plastic exponent, which is coupled by plastic modulus and strain hardening exponent, indicates that the deformation can be maintained after the removal of the compressive stress, which has a special meaning on the quality control of the pellet feed. The viscous coefficient is mainly characterized by the ability of the particles to be bonded in the process of pelleting, thus reflecting the capacity of the formed pellet to stay stable under external force without significant damage in the current state. Meantime, the frictional loss factor can reflect the characteristics of energy dissipation, which mainly includes the friction and adhesion between the particles or the particles and the die wall. The compression stage was divided into 5 even ranges in order to study the various material properties along with the process. The numerical results of the constitutive model of wheat were obtained under 15% material moisture content, 2. 0 mm mesh size, 80 °C forming temperature and 3 kN compression load, which showed that the determination coefficients (R2) in all stress ranges were beyond 0.99 and the mean relative error values were 3.883%, 1.798%, 2.992%, 1.496%, and 6.721% in the ranges of 1-5, respectively. The comparative curve showed a good fit between the actual test value and model value; besides, the χ2 examination showed that the χ2 values of the data in each range were much smaller than the standard values in the degree of freedom of 130 and the significance of 0.001. Based on the above criteria, this constitutive model possesses a good performance that can be used to characterize the rheological properties of wheat. The constitutive model coefficients and the rheological properties of the feedstuff were characterized by regular changes, which showed obvious stress function: The elastic modulus increased with the increase of stress, indicating the deformation performance of the material was gradually weakened and the overall compressibility of the material decreased step by step to reach the end of forming, and the stiffness increased significantly. The increases of combined plastic exponent showed that the plastic deformation of the material increased gradually with a sudden downside in the last range. The absolute value of the viscosity coefficient increased gradually, which means that the bonding force among the material particles is enhanced with the progress of the forming, and the connection between the particles is strengthened therewith. For the influence of various forming factors, results were showed as follows: The increase in forming temperature can improve the elastic modulus, which means a better compression deformation capacity; with preferable softening, and bonding effect on the compressibility, higher moisture content can improve the combined plastic exponent and viscosity coefficient at the same time; the decrease of the particle size increases the absolute value of the viscosity coefficient, indicating its significant positive effect on the particle bonding force. The correlation relations between the pellet quality index and the constitutive model coefficients show that the pellet density, the pellet forming ratio and the pellet hardness were correlated with the viscous coefficient, plastic modulus, and elastic modulus respectively (P<0.001), which owned the highest correlation coefficients that were all above 0.80, illustrating the close relationship between pellet product quality and feedstuff rheological properties. The nonlinear visco-elasto-plastic constitutive model constructed in this paper can provide a new methodology and perspective for the research of the process of feed pelleting, and provide theoretical basis for analyzing the particle forming characteristics, and product quality from the view of material rheology, which give contribution to the efficient and low-cost pellet production and the improvement of product quality. [ABSTRACT FROM AUTHOR]

This study focuses on the M ≥ 6.7 earthquakes that have occurred since 1816 on the Xianshuihe fault zone in southwest China. The interseismic Coulomb stress accumulation and the Coulomb stress changes caused by coseismic dislocation and postseismic viscoelastic relaxation of the previous shocks were computed for different periods on the relevant fault segments. Based on these results, we analyzed the relationship between time-adjacent strong shocks and the Coulomb stress evolution before every earthquake. The analysis suggests that strong earthquakes mostly occurred in the Coulomb stress enhancement region caused by coseismic dislocation and postseismic viscoelastic relaxation of the last earthquake. Considering the Coulomb stress evolution at the fault planes of the epicentral area before earthquakes, we found that the Coulomb stress accumulation caused by the interseismic tectonic loading was dominant for most strong earthquakes. For some other earthquakes the stress changes caused by coseismic dislocation and postseismic viscoelastic relaxation of surrounding earthquakes were very significant, which may be equivalent to the effect of interseismic tectonic loading lasting hundreds of years. Based on the time-dependent probabilistic risk model and the Dieterich (1994) model, we estimate the background seismic activity and the future earthquake probability for different fault segments, using long term seismic activity and strong earthquake recurrence cycles. It is shown that the Bamei, Selaha, and Kangding segments of the Xianshuihe fault zone have high earthquake probability, and are likely to have strong earthquakes. If energy is accumulated up to the year 2050, the magnitude of an event on these three segments could reach M w 7.2, M w 7.0, and M w 7.1 respectively, while if the S7 and S8 cascades rupture, the event on these segments could reach a magnitude of up to M w 7.2. [ABSTRACT FROM AUTHOR]

We investigate in this study the impact of the Tohoku-Oki earthquake on Eastern China, and particularly focus on postseismic relaxation processes. We first invert for postseismic slip on the fault plane based on the GPS measurements of GEONET in Japan. Then, we use a layered rheological model to theoretically investigate the deep viscoelastic relaxation process. The Tohoku-Oki mainshock produced significant strain changes in Eastern China, dominantly east-west-oriented extension with a level close to or higher than the tectonic strain rates at the east border of China. The strain due to the postseismic stress relaxations has similar patterns as those produced by the mainshock, but with smaller magnitudes. The Tohoku-Oki earthquake impacts Eastern China for decades, but dominantly in the first 2-3 years after the mainshock and caused an apparent displacements and decrease of seismicity rate in Northeast China. For a long-term of 100 years, the Tohoku-Oki earthquake produces about 10 % of the tectonic strain rates in Eastern China, due to viscoelastic relaxation at the deep depth. [ABSTRACT FROM AUTHOR]

• Dynamic stiffness tests for a two-stage rail fastener has been conducted. • Corrections are proposed to minimise effects of artefacts on measured results. • Dynamic properties of the fastener are determined from individual components. The dynamic stiffness of rail fasteners has a significant effect on the noise radiated by the rails as well as the vibration transmitted to the underlying structures, such as bridges, tunnels or track at grade. This study investigates the load- and frequency-dependence of a WJ-2A fastener which is commonly used in urban rail transit systems in China. This is a two-stage fastener with a rail pad and a baseplate pad separated by a steel plate. Results are obtained using the indirect measurement method in the frequency range 30 to 1000 Hz. The dynamic stiffness of the individual components is investigated as well as that of the whole fastener system and the combined stiffness of the components is verified by comparison with the whole fastener system. A numerical model of the test rig is used to provide understanding of various artefacts that are observed in the measurements and corrections are proposed to minimise their effects on the measured results. These allow for the differences between the response at the measurement positions and at the ideal positions at the interfaces between the fastener system and the rig. The stiffness magnitude of the rail pad, baseplate pad, and whole fastener system increases strongly with increasing static preload and increases weakly with increasing frequency; it is important to take these effects into account in prediction models for noise and vibration. The damping loss factors are not strongly dependent on preload or frequency. To describe the frequency-dependence, a fractional derivative Kelvin-Voigt (FDKV) model is introduced and is fitted to the dynamic stiffness with the help of a genetic algorithm method. The dynamic stiffness of the whole fastener system is influenced by both the rail pad and the lower baseplate pad. It is important to take account of both of them, as well as the internal resonance of the baseplate assembly which appears at around 1 kHz. [ABSTRACT FROM AUTHOR]

Abstract: We examine the distribution of Coulomb stress before and following the M=7.9 Wenchuan earthquake and model the time dependent components of the stress field into the future. Our modelling shows that the combined (coseismic plus postseismic viscoelastic) stress change due to the preceding large events (M≥6.7) at the hypocentral area of the Wenchuan earthquake is negative which may have led to a delay on its occurrence between 16 and 95yr depending on the rake of the rupture. On the other hand coseismic stress modelling of the Wenchuan earthquake shows strong interaction, particularly with the faults close to its SW and NE ends; such interactions have previously been shown to trigger further large earthquakes. In addition, redistribution of stresses due to continuing postseismic deformation will potentially increase the stress levels not only on these faults but also on the distant faults such as the Xianshuihe, Kunlun and Tazang faults. Postseismic viscoelastic stress load on these distant faults over the next 22yr since the earthquake could be up to 2.5 times larger than that of the coseismic stress increase alone. This would potentially advance these faults in their seismic cycle and thereby encourage future earthquakes, resulting in clustering of large earthquakes in the region. This behaviour, however, strongly depends on the stage that these faults are in their seismic cycle which is not known currently. Given the high density of population in the area with several cities, Chengdu, Guangyuan and Hanzhong, of more than 1million inhabitants, our results indicate a need for detailed paleoseismic studies to help elucidate the state of the stressed faults. [Copyright &y& Elsevier]

Abstract: The 1600-km-long Kunlun Fault striking E–W to WNW–ESE had long been recognized as one of the major left-lateral strike-slip faults bounding the Tibetan Plateau, and ranked one of the most active faults in China continent. During the past hundred years, over twenty strong earthquakes occurred along and near the Kunlun Fault, including six large earthquakes (M >7). Since some major highly-populated and industrialized cities are close to the Kunlun Fault, understanding of stress transfer and earthquakes migration along the Kunlun Fault is most important for assessing seismic hazard in this region. In this study, by integrating coseismic effect, viscoelastic relaxation and tectonic loading, we studied the evolution of the regional Coulomb stress field by analyzing a sequence of strong earthquakes along the Kunlun Fault. We studied the stress evolution over one century by analysing a sequence of five earthquakes (M ≥7) that occurred along the Kunlun Fault since 1937. The model of dislocation sources embedded in a mixed elastic/inelastic layered half-space was used, and the layered model and relevant parameters were constrained by seismic studies. Fault rupture locations and geometry, as well as slip distribution of earthquakes were taken from field observations and seismic studies. Numerical results showed a good correlation between stress transfer, accumulation and earthquakes occurrence. All four studied earthquakes occurred after the 1937 Tuosuo Lake quake were encouraged by the preceding earthquakes with positive stress loading. In subject to the choice of the earthquake source parameter two or three out of four events occurred in regions that experienced previous coseismic and postseismic stress changes of at least 0.01 MPa, suggesting that earthquake triggering due to stress transfer has occurred along the Kunlun Fault. The total stress change since 1937 of the Kunlun Fault region has lead to high levels of stress accumulated on the Xidatan–Dongdatan segment and Maqin–Maqu segment, which have not experienced any significant large earthquake over at least several hundred or several thousand years. The accumulated stress raises the potential earthquake hazard in these areas. Our study demonstrated the crucial importance of postseismic viscoelastic relaxation in the stress transfer and accumulation following large earthquakes. [Copyright &y& Elsevier]

In order to improve the dissatisfied oil displacement results of conventional low molecular weight polymers in some thin and poor reservoirs of the Daqing Oilfield in China, two new polymers with low molecular weight are introduced. A series of laboratory experiments were performed to evaluate the performance index and oil displacement results of the novel polymers. The results show that the new polymers have the characteristics of higher viscosity, better salt and shearing resistance, and better solubility than conventional polymers, and the viscoelasticity and shearing resistance of the new polymers increases with a decrease in molecular weight. Bench-scale oil displacement experiments indicate that the oil displacement results of the new polymers are better than those of the conventional polymers with the same molecular weight and the performance will be better with a decrease in molecular weight. Novel polymers have a favorable matching relationship with low-permeability reservoirs that are fit for wide application in thin and poor reservoirs. [ABSTRACT FROM AUTHOR]

Pulse dye laser has been used with variable degrees of success in the treatment of hypertrophic scars, and although earlier reports suggested a significant degree of improvement, more recent studies have raised concern about its effectiveness. Furthermore, most previous studies examined its use in patients with light skin types, and the use of pulse dye laser in dark-skinned patients for the treatment of hypertrophic scars is not well established. The objective was to assess the role of pulsed dye laser therapy in the treatment and prevention of hypertrophic scars in Chinese persons. Twenty-nine patients (35 scars) who had scars for less than 6 months were recruited into the prevention group, and 27 patients (36 scars) who had scars for more than 6 months were recruited into the treatment arm of the study. Each received pulse dye laser treatment (585 nm, 1.5-msec pulse duration, 5-mm spot size, 7–8 J/cm2) for three to six treatments at 8-week intervals. Half of the scar was treated with the laser and the other half was used as a control. All patients were assessed for subjective improvement with the use of a structured questionnaire and objectively with ultrasonography for thickness and a cutometer for viscoelasticity. Scars were marked on every patient and mapped with a translucent paper at the first appointment to ensure the consistency of location. At the end of the study, 15 patients from the prevention group (15 scars) and 23 patients from the treatment group (34 scars) agreed to return for spectrophotometer assessment. Fifty-four percent of patients in the prevention group and 66% of patients in the treatment group considered their scars to be better or much better. For both groups of patients, there was significant improvement in term of pruritics after laser treatment. For objective assessment, although scar thickness reduced significantly compared to baseline in the treatment group, such change was not significant when changes in the control side were taken into consideration. There was insignificant change in viscoelasticity. Spectrophometer assessment indicated a significant degree of lightening in the treatment group. Our study indicated that although there was significant symptomatic improvement, there was an insignificant degree of objective improvement in terms of scar thickness and viscoelasticity in the prevention group compared to the control group. Our findings are in line with several previous controlled studies and contradict the results of several others. Such differences can be due to differences in assessment methodology, laser settings, skin type, and scar location. Suprapurpuric pulsed dye laser should not be considered as the standard of practice for the treatment and prevention of hypertrophic surgical scars especially in the chest in Asians patients. HENRY H. CHAN, DAVID S. Y. WONG, W. S. HO, L. K. LAM, AND W. WEI HAVE INDICATED NO SIGNIFICANT INTEREST WITH COMMERCIAL SUPPORTERS. [ABSTRACT FROM AUTHOR]

Studies the viscoelastic effect of dilute heteropolymer solutions on the formation of meso-globular phases. Key issues of interest; Analysis of pertinent topics and relevant issues; Implications on Chinese studies of polymer science.

The article focuses on the study regarding the crustal stress in the Northern South China Sea (NSCS). Topics discussed include the development of various stress measurement methods such as hydraulic fracturing in coastal zone, stress observation, and interpretation of Formal Micro-Imager (FMI) logs from oil and gas fields, the various aspects of the conducted in situ stress test, and the calculation of the stress through finite element numerical simulation and viscoelastic model.