Search

We systematically investigate the plugging performance and oil-displacement efficiency of the novel bilayer-coating microspheres (BCMS) designed for in-depth conformance control within heterogeneous hydrocarbon reservoirs. Visualization experiments on various glass models, as well as one- and two-phase core floods have been carried out at reservoir temperature and fluid salinity. Our results demonstrate that the rigid outer layer of BCMS can successfully protect its adhesive inner coating, enabling BCMS to transport deeply into porous media. Increasing particle concentration yields higher collision probability, leading to the formation of particle assembly that could effectively block pore throats in high-permeability channels and achieve more oil recovery in the low-permeability zones. It is also shown that as the BCMS slug size increases, the oil recovery asymptotically reaches a maximum value. A larger slug size cannot highly enhance the plugging performance yet significantly increase the resistance factor. A smaller permeability ratio of parallel cores leads to a narrower difference between the fractional flow rates. When the permeability ratio is two or lower, the fractional flow rates of parallel cores are both around 50%, yielding the best oil-displacement efficiency. BCMS exhibits promising application potential in production enhancement under reservoir conditions.

A novel concept of treating oil reservoirs by nanofluids is being developed to improve oil recovery and reduce the trapped oil in hydrocarbon reservoirs. Nanoparticles show great potential in enhancing oil recovery under ambient conditions. In this paper, the approaches of wettability alteration by using nanofluid, stability of nanofluids, and the most reliable wettability alteration mechanisms associated with variant types of nanoparticles have been reviewed. Moreover, the parameters that have a significant influence on nanofluid flooding have been discussed. Finally, the recent studies of the effect of nanoparticles on wettability alteration have been summarised and analysed. Furthermore, this paper presents possible opportunities and challenges regarding wettability alteration using nanofluids.

Oleic acid-modified titania (OA-TiO2) nanoparticles are synthesized for the application of enhanced oil recovery (EOR) in low-permeability reservoirs. The oleic acid is grafted onto the surface of ...

We report a new type of nano-optical tip, the quantum dot decorated nano-pyramid fiber tip, for scanning near-field optical microscopy. The nano-pyramid tip has a large apex angle (70.5 degree), and consequently exhibits a significant improvement (17-fold) of the signal collection efficiency compared to conventional tapered fiber tips. Moreover, thanks to the template-based fabrication method and the surface treatment technique, the quantum-dot decorated nano-pyramid tip enjoys a clean and smooth surface, and can be produced with high accuracy and high reproducibility. Experimental results show that, with the nano-pyramid tip, the optical field distribution of a photonic nanostructure can be mapped with a 20 nm resolution ( λ /20). It provides a powerful and reliable tool for near-field optical measurements.

To obtain the ultrafine pigment for ink-jet printing, ultrafine spherical Pr-ZrSiO4 pigment was prepared by sol-gel-microemulsion method (S-G-M). In the emulsion, ZrO2 and SiO2 sols are used as water phase, cyclohexane serves as oil phase, Triton X-100 and 1-hexanol are chosen as surfactant and co-surfactant, respectively. The results show that without the introduction of demulsifier, the sol/oil microemulsion system is demulsified automatically due to the transformation of liquid/liquid to solid/liquid interface following the transformation from sol to gel. The obtained Pr-ZrSiO4 pigment owns uniform spherical particles with the average particle size of about 0.785 μm, which is suitable for the ink-jet printing. The CIE coordination of the pigment is L* = 87.63, a* = −3.82, b* = 65.68, which shows bright lemon yellow. Hence, the ultrafine pigment in this work has the good application prospects.

Microparticles covered with double-layered coatings are developed for in-depth conformance control to enhance oil recovery within heterogeneous reservoirs. The proposed bilayer-coating microspheres (BCMS) can transport deeply into a porous media, owing to the rigid outer layer designed for protecting the adhesive inner coating. The objective of the present work is to characterize the adhesion property and the plugging behavior of BCMS at reservoir temperature and fluid salinity. A series of static and coreflood tests are conducted. BCMS exhibits resistance to high temperature and high salinity and shows a great ability of deep transport into porous media. A mathematical model for the deep-bed filtration of BCMS in porous media is developed, accounting for the limited retention concentration and the velocity difference between the suspended particles and the carrier fluid. Modeling results match the measured pressure drop histories in coreflood tests with high accuracy, which validates the proposed analytical model. BCMS shows promising potential for application in production enhancement in hydrocarbon reservoirs.

Fines migration with consequent well productivity reduction is a well-known phenomenon occurring during exploitation of geothermal reservoirs. Laboratory corefloods with piecewise constant decreasing ionic strength have been performed with measurements of the pressure drop along the core and the accumulated effluent particle concentration. The tests were performed under ambient conditions with further results re-calculation for high geothermal temperatures. Permeability stabilises after injection of numerous pore volumes, suggesting slow drift of mobilised particles if compared with the carrier water velocity. SEM-EDX analysis of the produced fine particles shows that kaolinite and illite/chlorite are the major minerals responsible for the permeability damage. The competitive effects of decreasing water viscosity and weakening electrostatic attraction on the attached particle concentration during temperature increase have been observed. The micro modelling of the fine particle mechanical equilibrium shows that the electrostatic attraction effect on the fines attachment dominates. It results in increased fines detachment and permeability decline at high temperatures, suggesting that geothermal fields are more susceptible for fines migration formation damage than the conventional oilfields and aquifers. A new “ionic strength- velocity” translation procedure is developed for determining velocity dependency of the maximum retention function from laboratory coreflood tests with varying ionic strength. Experiment-based evaluation of velocity- and temperature-dependencies on the maximum retention function is demonstrated for specific conditions of geothermal resevoirs. We discuss well inflow performance with fines migration, and derive an exact solution for axi-symmetric water-flow towards the well. The solution includes explicit formulae for attached, suspended and strained fines, and well productivity. The analytical model along with the obtained laboratory data allows successful matching of the well discharge history (Salamander geothermal field, Australia).

During micro-scale tracer flow in porous media, the permeability and fluid velocity significantly affect the fluid dispersion properties of the media. However, the relationships between the dispersion coefficient, permeability, and fluid velocity in core samples are still not clearly understood. Two sets of experiments were designed to study the effects of tracer fluid flow velocity and porous medium permeability on the dispersion phenomenon in a core environment, using natural and sand-filled cores, respectively. From experimental data-fitting by a mathematical model, the relationship between the dispersion coefficient, flow velocity, and permeability was identified, allowing the analysis of the underlying mechanism behind this phenomenon. The results show that a higher volumetric flow rate and lower permeability cause a delay in the tracer breakthrough time and an increase in the dispersion coefficient. The core experimental results show that the dispersion coefficient is negatively correlated with the permeability and positively correlated with the superficial velocity. The corresponding regression equations indicate linear relations between the dispersion coefficient, core permeability, and fluid velocity, resulting from the micron scale of grain diameters in cores. The combination of high velocity and low permeability yields a large dispersion coefficient. The effects of latitudinal dispersion in porous media cannot be ignored in low-permeability cores or formations. These findings can help to improve the understanding of tracer flow in porous media, the design of injection parameters, and the interpretation of tracer concentration distribution in inter-well tracer tests.

Foam-assisted steam flooding is a promising technique to alleviate gas channeling and enhance sweep efficiency in heterogeneous heavy-oil reservoirs. However, long-term foam stabilization remains problematic at high temperatures. Three-phase foam (TPF), containing dispersed solid particles, has been proposed to improve foam stability under harsh reservoir conditions. We fabricated a novel TPF system by adding ultrafine fly ash particles, as well as high-temperature resistant microspheres with an adhesive coating layer. This work aims at assessing the ability of the generated TPF in controlling steam channeling and enhancing oil recovery. Static and core flood tests were performed to evaluate foam strength and stability. Our results suggested a stronger foamability at a lower consolidation agent concentration, while a longer half-life period of foam and settling time of solid particles at a larger consolidation agent concentration were observed. Bubbles suspended independently in the liquid phase, with sizes varying from 10 to 100 μm, smaller than that of the conventional foam, suggesting a significant enhancement of foam dispersity and stability. The plugging rate was close to 90% when the temperature was as high as 300 °C, demonstrating a well-accepted plugging effect under high temperatures. A larger pore volume injection of TPF yielded a higher EOR in parallel cores, which substantiated the effectiveness of the three-phase foam system in sealing high-permeability channels.

Studying manganite superlattices ${[{(\mathrm{LCMO})}_{2n}/{(\mathrm{PCMO})}_{n}]}_{t}$ made of ${\mathrm{La}}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_{3}$ (LCMO) and ${\mathrm{Pr}}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_{3}$ (PCMO), we found an unexpected behavior varying the period $n$. At small $n$, the ensemble is a three-dimensional ferromagnetic metal due to interfacial charge transfer. At large $n$, the LCMO layers dominate transport. However, rather than a smooth interpolation between these limits a sharp transport and magnetic anomaly is found at an intermediate critical PCMO thickness ${n}^{*}$. Magnetic force microscopy reveals that the phase-separation length scale also maximizes at ${n}^{*}$ where, unexpectedly, it becomes comparable to that of the ${({\mathrm{La}}_{1--y}{\mathrm{Pr}}_{y})}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_{3}$ (LPCMO) alloy. We conjecture the phenomenon originates in a disorder-related length scale: Large charge-ordered clusters as in LPCMO can only nucleate when Pr-rich regions reach a critical size related to ${n}^{*}$.

Free amino acids (FAAs) are key components of the global nitrogen cycle and important disinfection byproduct (DBP) precursors. The knowledge gap of FAA occurrence in source and engineered water is discussed in this paper. Solid phase extraction and post column derivatization was combined with gas chromatography&ndash, mass spectrometry to simultaneously detect &mu, g/L concentrations of FAAs. This method efficiently detects alanine (Ala), threonine (Thr), serine (Ser), valine (Val), leucine (Leu), isoleucine (Ile), proline (Pro), aspartic (Asp), phenylalanine (Phe), and glutamic acid (Glu) with good linearity, accuracy, and precision. An investigation of FAAs in surface waters in Zhejiang Province found concentrations of 1.48&ndash, 14.73 &mu, g/L Ala, 0.20&ndash, 2.39 &mu, g/L Thr, 0.41&ndash, 7.84 &mu, g/L Val, 0.21&ndash, 6.86 &mu, g/L Ser, 0.11&ndash, 4.16 &mu, g/L Leu, 0.57&ndash, 1.54 &mu, g/L Ile, 0.24&ndash, 8.06 &mu, g/L Pro, 0.42&ndash, 4.73 &mu, g/L Asp, 0.30&ndash, 3.01 &mu, g/L Phe, and 0.12&ndash, 3.83 &mu, g/L Glu. Phe and tyrosine (Tyr) exhibited higher trichloromethane (TCM) formation (1029&ndash, 1148 &mu, g/mmolAA) than dichloroacetonitrile (DCAN) formation (333&ndash, 347 &mu, g/mmolAA). Asp and Glu demonstrated the opposite trend: higher DCAN (570&ndash, 1106 &mu, g/mmolAA) formation than TCM (137&ndash, 506 &mu, g/mmolAA).

As a globally important artificial sweetener, sucralose (SUC) is a persistent emerging contaminant in global aquatic environments. This research comprehensively track the fate and transport of SUC throughout an urban water cycle; to perform laboratory experiments to determine chlorinated disinfection by-products (DBPs) of SUC sebsequent to advanced oxidation with ozone; and to perform a risk evaluation of SUC related DBPs.; The results demonstrated that SUC was consistently present throughout the urban water cycle, including consumer's tap water. The inluent to the municipal wastewater treatment plant contained 1033.4-2626.3 ng/L SUC, and as expected for this non-biodegradable artificial sweetener, the concentration in the effluent was slightly reduced to 917.6-2031.2 ng/L. The concentration of SUC varied in surface waters with a peak value of 2070.0 ng/L. In finished drinking water 288.1–505.3 ng/L SUC was found, and values of 177.7–409.7 ng/L were present in the distribution system. Up to 16.3% of SUC concentration discharged as municipal wastewater was delivered to residents in their drinking water. While conventional treatment little removed SUC, the mean removal efficiency of SUC with ozonation followed by activated carbon filtration was 39.6% at a full-scale drinking water treatment plant. The fate and transformation of SUC in drinking water treated by ozonation and chlorination were investigated in laboratory experiments. Ozonation partially degraded SUC; however, intermediates reacted with chlorine to generate DBPs, including trichloromethane (TCM), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA). Peak 7-days potential formation of TCM, DCAA and TCAA were 0.016, 0.51 and 23.34 μ g/mg SUC, respectively. DBP yields increased with increasing chlorine dosage, chlorination time, temperature, and solution pH. The presence of ammonia nitrogen in water facilitated dichloroacetonitrile (DCAN) production up to 0.78 μ g/mg SUC, while simultaneously reducing the yield of TCM, DCAA and TCAA. Human exposure analysis revealed that carcinogenic risks of DBPs caused only by SUC ozonation were in the range of 1.86 × 10−12-6.12 × 10−9, while non-carcinogenic risks were in the range of 6.0 × 10−9-4.37 × 10−6. The pervasive occurrence of SUC in an urban water cycle, couple to its resistance to biological and chemical treatment, confirms that SUC is a persistent contaminant in the aquatic system, including tap water.

Non-uniform solar flux distribution in a parabolic trough concentrator (PTC) causes large temperature gradients on absorber tube surface, making the PTC inefficient and damaged. To solve the problem, a novel method is proposed for designing the additional secondary reflector (SR) in a PTC to improve uniform heat flux distribution on absorber tube surface. In the design, the heat flux between upper and lower surfaces of absorber tube is well balanced by optimizing the location of absorber. Then, the SR with segmented broken-line type composed of multiple plane mirrors is delicately designed with local heat flux compensation strategy. Two case studies are conducted to compare the performances of the newly designed SRs with other existing SR designs. It is shown that the uniformity of heat flux distribution can be improved to over 90% for present SR design, much higher than those for other existing SR designs. Also, the optical efficiency of the PTC with present SR design is also increased as compared with other designs. The results indicate that this proposed method is competent for designing SR in a PTC with uniform heat flux distribution.

The paper discusses migration of natural reservoir fines lifted by high-rate or low-salinity water injection. The previous papers used linear analytical model, which is valid for low retention of mobilised fine particles in order to determine the model parameters from breakthrough fines concentration and pressure drop across the core during laboratory corefloods. The current work derives exact analytical solutions for the nonlinear case of high retention-concentration fines migration. The solution exhibits uniform profiles of suspended and retained concentrations ahead of the particle front and steady-state retained concentration behind the front. The obtained type curves allow distinguishing between linear and nonlinear fines migration. The laboratory data exhibit close agreement with the nonlinear model predictions, whereas the linear model poorly matches the laboratory data.

Low-cost porous ceramic from fly ash with alumina as the pore-forming agent was produced. The effect of the alumina content on line shrink, bulk density, mechanical strength, porosity, and phase composition of porous ceramic were investigated in detail. The results showed that the addition of alumina can help to improve the porosity and then it can change the pore structure of porous ceramic. Meanwhile, the addition of alumina can react with SiO2 in fly ash which can form the mullite. With the increase of alumina content, the content of quartz decreased gradually, while the alumina and mullite increased. Furthermore, the pore size becomes uniform and the permeability increased gradually. After sintering at 1250 ℃ for 0.5 h, the porous ceramic has been obtained the bending strength of ≥ 35MPa and the porosity of ≥ 28% with the addition content of alumina (25 wt%).

In recent years, there has been a great interest in integrating crowdsourced API documents that are often dispersed across multiple places. Because of the complexity of natural language, however, automatically synthesized documents often fall short on quality and completeness compared to those authored by human experts. We develop a complementary “human-assensors” approach to document integration that generates API FAQs based on users’ help-seeking behavior and history. We investigated the benefits and limitations of this approach in the context of programming education. This paper describes a prototype system called COFAQ and a controlled experiment with 18 novice programmers. The study confirms that the generated FAQs effectively fosters knowledge transfer between the programmers and significantly reduce the need for repeated search. It also discovers several difficulties novice programmers encountered when seeking API help as well as the strategies they used to seek and utilize API knowledge.

Hole defects and uneven membrane thicknesses can lead to poor performance, especially in the separation stability of ceramic membranes. This paper uses a one-step sintering method, which avoids hole defects and uneven membrane thicknesses, for the preparation of high-performance and defect-free ceramic membranes. For this purpose, two kinds of ceramic membrane slurry with high or low viscosities were prepared by alumina particles, as raw materials. Both the effects of the two coating process with a one-step coating method for low-viscosity slurry, and the two-step coating method with a high viscosity flush after a low viscosity coating, on the surface properties of a ceramic membrane, were studied in detail. The result shows that the properties of ceramic membranes can be improved by a two-step coating method, with a high viscosity flush after a low viscosity coating, A high-performance and defect-free ceramic membrane was obtained by one-step sintering at 1450 &deg, C for 2 hr with 7 wt % solid content and a coating time of 11 s.

In this paper, vanadium ion (V4+) doped ZrO2 pigment (Vx-ZrO2) and vanadium/yttrium ions (V4+/Y3+) co-doped ZrO2 pigment (VxYy-ZrO2) were synthesized via inorganic sol-gel route. The Vx-ZrO2 and VxYy-ZrO2 pigments with the low V4+ content still have excellent color performance, because the gel network is conducive to immobilize coloring ions which to reduce the loss of coloring ions. The results show that the Vx-ZrO2 pigment has the optimal chromatic parameters of L∗ = 68.40, a∗ = 7.93, b∗ = 43.72 when the x-value is 0.04. The measurement of EDS indicates the actual doping amount of V4+ is up to 3.14 mol%. The introduction of Y3+ in a moderate amount can increase the doping amount of V4+ in the V–ZrO2 pigment, because of Y3+ can activate zirconia lattice. Therefore, with the introduction of 1 mol% Y3+ in the ZrO2 lattice, the chromatic parameter of the pigment (i.e. V0.04Y0.01-ZrO2) is optimized to L∗ = 58.57, a∗ = 19.39, b∗ = 40.02, where the actual doping amount of V4+ increased to 3.48 mol%. Meanwhile, there is a synergy/competition mechanism in the process of V4+ and Y3+ co-doped into ZrO2 lattice. After applying on high-temperature ceramic glaze, the V0.04-ZrO2 and V0.04Y0.01-ZrO2 pigment present superior tinting strength, high thermal stability and excellent chemical stability, indicating they are attractive application in ceramic decoration.

Groundwater infiltration through cracked sewer pipes has caused significant economic losses. This paper presents a three-dimensional analytical expression for calculating the steady-state groundwater infiltration rate into sewer systems. As an extension of the previously developed two-dimensional model by the author, this new model can be used to simulate the infiltration through an orifice defect. The derived analytical expression has been validated with experimental results. The new model incorporates all the related resistances during the infiltration process, including the soil head loss and the orifice loss. The soil head loss is assessed with Ergun equation, which involves an inertial loss term in addition to the viscous loss. This has significantly extended the application range of the new expression. A new OS number (the ratio of orifice loss to soil loss) expression is also presented. The order analysis of the OS number expression has demonstrated that in most real cases, the head loss through the soil layer dominates the whole infiltration process.

Fines migration involving particle detachment in natural reservoirs usually exhibits significant permeability damage. This occurs due to mobilization and migration of detached colloidal or suspended fines that were strained in thin pore throats. Numerous laboratory coreflood tests show that the time for permeability stabilization accounts for hundreds of injected pore volumes. However, classical filtration theory assumes that the released fines are transported by the bulk of the carrier fluid, thus stabilizing the permeability after the injection of one pore volume. The current paper attributes the stabilization delay to the slow drift of the mobilized fines near the pore walls. We propose basic flow equations for single-phase particle transport in porous media with velocity lower than the carrier fluid velocity. We derive an analytical model for one dimensional flow with particle release and straining under piecewise-constant increasing velocity. The laboratory data are in high agreement with the results of mathematical modelling. The effective particle speed is 500–1000 times lower than the water velocity.

A new computational methodology is presented for the dynamic analysis of multibody systems with multiple clearance joints by vector form intrinsic finite element method. A joint model is developed to simulate the motion of ideal and clearance joints for multibody systems. The dynamic behaviour of a four-bar mechanism with three clearance joints in continuous contact mode is analysed. The results show that the dynamic performance of the mechanism with three clearance joints in continuous contact mode is not similar to that with ideal joints and is fluctuating and affected by the clearance size of the joints and input crank speed.

Laboratory-based mathematical modelling of fines migration allows predicting well productivity reduction during the geothermal reservoir exploitation. The analytical model for one-dimensional flow with ionic strength alteration has been derived. Good adjustment of the permeability and breakthrough concentration data from coreflood test by the analytical model has been achieved, and the tuned model coefficients fall in the common ranges. The obtained maximum retention function of multi-sized fines allows calculating their size distribution. During the temperature rise, weakening of electrostatic attraction on fines attached to rock surface overwhelms the reduction of detaching drag force due to water viscosity decrease. It leads to increased fines detachment and more severe permeability decline at elevated temperatures, typical for geothermal fields.

Foam has been widely used as a proven technology in enhanced oil recovery by improving the mobility of the injected gas. However, its further application has been retarded owing to the limited stability in high salinity, high temperature and crude oil conditions. Traditional agents for foam stabilization including surfactants, polymers are unable to stabilize foam for long term under harsh conditions. In this work, the nanogel particles with high viscoelasticity were synthesized to stabilize foam for more than one year through a free radical reaction method using α-starch, acrylamide, N,N′-methylene bisacrylamide, potassium persulfate. The diameter of nanogel particles was 30 nm. The stability of foam stabilized by nanogel particles was evaluated by using foam volume and T90 as indicators at temperature of 30–120 °C, salinity of 0–240 g/L and oil percentage of 0–50 wt%. Moreover, the rheological properties of foam were also measured to study the mechanisms of foam stability under different conditions. The results demonstrated that foam stabilized by nanogel particles exhibited excellent resistance to high salinity, high temperature and crude oil. Thus, the synthesized nanogel particles can be used as a potential candidate for stabilizing foam in enhanced oil recovery.

High-performance submicron ZrSiO4 powder is prepared by a sol-gel-microemulsion-hydrothermal method (S-G-M-H). In this method, the transformation from sol to gel is constrained in the droplets of the microemulsion and accelerated by the hydrothermal process. The interface change of sol/oil to gel/oil makes the emulsion automatic demulsificate without demulsifiers, which means that the organic solvents can be recycled. The preparation process is low-cost and environmentally friendly. The results show that the synthesized ZrSiO4 powder owns the optimized median diameter (D50) of 0.67 μm under the optimized preparation condition of hydrothermal treatment at 150 °C for 7 h. The ZrSiO4 particles are the agglomeration of the primary particles with a size of about 100 nm. As an opacifier, 15 wt% submicron ZrSiO4 powder added give a whiteness value of 85 to the opaque glaze, which is significantly better than commercial ZrSiO4 powder with the same amount added. Meanwhile, the obtained submicron powder has excellent sintering activity. After sintered at 1300 °C for 2 h, the ZrSiO4 pellets has the density of 4.32 g cm−3 and the porosity of 0.31%.

TiO2 is usually used as a sintering aid to lower the sintering temperature of porous alumina membrane support. Two ways of the addition of TiO2 are chosen: in-situ precipitation and in-situ hydrolysis. The results show that the distribution status of TiO2 has an important effect on the property of porous alumina membrane support. In in-situ hydrolysis method, the nano-meter scale TiO2 distributes evenly on the alumina particles&rsquo, surface. The bending strength of the support increases sharply and the pore size distribution changes more sharply along with the content of TiO2 which slightly increases from 0.3 wt.% to 0.4 wt.%. The distribution of the nano-meter scale TiO2 is not so even added by in-situ precipitation method. Neither the bending strength nor the pore size distribution of the support is worse than that of the support added by in-situ hydrolysis even if the content of TiO2 is high to 2 wt.%. The permeating flux has a similar tendency. Consequently, the porous alumina membrane support has the porosity of 30.01% and the bending strength of 77.33 MPa after sintering at 1650 &deg, C for 2 h with the optimized TiO2 content of 0.4 wt.% added by the in-situ hydrolysis method.

Migration of natural reservoir fines is one of the main causes of formation damage in oil and gas fields. Yet, fines migration can be employed for enhancing reservoir sweep and water production control. Permeability decline due to fine particles’ detachment from reservoir rocks, mobilisation, migration and straining has been widely reported in the petroleum industry since the 1960s and is being researched worldwide. The topic of colloidal-suspension flows with particle detachment is also of wide interest in environmental, chemical and civil engineering. The current work begins with a detailed introduction on laboratory and mathematical modelling of fines migration, along with new mathematical models and experimental results. Each of the next three sections explores a particular cause of fines mobilisation, migration and straining. Section 2 covers high flow velocity that causes particle detachment accompanied by consequent permeability decline. Section 3 covers low-salinity water injection, where the decreased electrostatic attraction leads to particle mobilisation. Section 4 covers the effect of high temperature on production rate and low-salinity water injection in geothermal reservoirs. We attribute the long permeability stabilisation period during coreflooding with fines migration, to slow fines rolling and sliding and to diffusive delay in particle mobilisation. We derive the analytical models for both phenomena. Laboratory fines-migration coreflood tests are carried out, with the measurement of breakthrough fines concentration and pressure drop across the whole core and the core’s section. Treatment of the experimental data and analysis of the tuned coefficients show that the slow-particle model contains fewer coefficients and exhibits more typical strained concentration dependencies of the tuned parameters than does the delay-release model.

For heavily curtailed wind power caused by the coexistence of large-scale wind power and high-penetration combined heat and power (CHP) units, especially during the winter heating period in...

Free-form gesture passwords have been introduced as an alternative mobile authentication method. Text passwords are not very suitable for mobile interaction, and methods such as PINs and grid patterns sacrifice security over usability. However, little is known about how free-form gestures perform in the wild. We present the first field study (N=91) of mobile authentication using free-form gestures, with text passwords as a baseline. Our study leveraged Experience Sampling Methodology to increase ecological validity while maintaining control of the experiment. We found that, with gesture passwords, participants generated new passwords and authenticated faster with comparable memorability while being more willing to retry. Our analysis of the gesture password dataset indicated biases in user-chosen distribution tending towards common shapes. Our findings provide useful insights towards understanding mobile device authentication and gesture-based authentication.

To lower the sintering temperature of Al 2 O 3 microfiltration membrane support, Al 2 O 3 powders with particle size distribution of tri-modal are chosen. The results show that the function of fine Al 2 O 3 grains depends on their agglomeration state: if fine Al 2 O 3 grains distribute discretely, the bending strength of the support increases along with a slight increase in porosity; however, the aggregated fine grains are harmful to both bending strength and pore size distribution of the support. The bridging of medium Al 2 O 3 grains between coarse grains contributes to increase the bending strength, but has less effect on porosity. The addition of medium (and/or fine) Al 2 O 3 powder has less effect on the pore size distribution of the support if only coarse Al 2 O 3 grain forms the support's framework, which suggests a new way to prepare the support with both high bending strength and high porosity at low temperature.

The interpolation error of an optical encoder is largely determined by the imperfections in the electrical signals, such as amplitude error, phase-shift error, DC error and higher harmonic distortion. In this paper, an optimized optical encoder based on generalized grating imaging is presented. We first describe the basic principle and configuration of the optical encoder. To achieve four electrical signals with equal amplitudes, equal DC contents and accurate 90° electrically phase-shift, a photodiodes array is adopted as the photo-detector. The photodiodes array offers the advantage of single-field scanning. Then, to solve the remaining problem of higher harmonic distortion, a slit-width-modulated index grating is proposed to suppress the dominant third order and fifth order harmonics simultaneously, and the cell's width of the photodiodes array is optimized to further reduce the fifth order harmonic. Experiments have been carried out to verify the theoretical results. The feasibility and effectiveness of the proposed optimizing methods have been confirmed from the experimental results.

Fines mobilisation and straining by changing the ionic strength of the reservoir water results in a significant permeability reduction, and is a well known mechanism of formation damage. The phenomenon occurs during drilling and completion, where the fluid invasion with fines lifting may cause significant productivity damage. The paper experimentally investigates the permeability damage of natural sandstone rocks in order to select ionic compositions for drilling and completion fluids. Two sandstone rock cores from the same production well from the Birkhead Formation in the area of underlying Patchawarra Trough (Eromanga Basin, Australia) were chosen to study formation damage during successively decreasing (piece-wise) the ionic strength of injected fluid using a three point pressure measurement method along the core. Effluent particle concentration and electrolytic conductivity were measured for effluent streams. It was observed that formation damage in the studied rock cores after their contact with low-ionic strength fluid is caused by fines mobilisation, their migration in the porous medium and straining in thin pores. Each coreflood is characterised by decreased rock permeability with stabilisation times significantly exceeding one pore volume, suggesting that mobilised particle’s drift velocity is significantly lower than that for a carrier fluid. The electrolytic conductivity profile shows that the fluid front in porous medium is not piston-like, rather diffusion driven, suggesting that there is an additional reason behind long permeability stabilisation time – a delayed contact of rock with low ionic strength fluid.