Low Filtration Research Articles

Research and Application of Fast Plugging Method for Fault Zone Formation in Tarim Basin, China

The Silurian strata in the Shunbei No. 5 fault zone have the characteristics of long open holes, easy leakage and complex leakage. In the early stages, plugging technologies and methods such as bridging plugging, cement, chemical consolidation and high-water-loss plugging have poor effects and low plugging efficiency. Plugging slurry directly prepared with drilling fluid has low filtration characteristics, and the main reason is that the plugging material cannot filter quickly after the fluid enters the fracture. Based on the basic principle of fast filtration, the main plugging fluid M-Fluid, the micro-elastic high-strength main plugging agent M-Block and the filling agent Filling-Seal have been developed. In combination with the water-loss and wall-building properties of the circulating drilling fluid after plugging, a fast plugging technology for fractured volcanic rock formation has been established. The laboratory evaluation experiment showed that the filtration rate increased rapidly with the increase of temperature, and the filtration rate was about 0.31~0.79 mL/s, while the filtration rate of the drilling fluid was 0.0067 mL/s under the same conditions. The pressure-bearing capacity of various plugging evaluation methods, such as the simulated fracture of a large-grain sand bed, artificial fracture of small core and full-size core and multi-form fracture of double core, all exceed 5 MPa, and the system has a good plugging effect for complex fractures.

Resistance of domestic plum tree rootstocks against periodic overwatering of floodplain soils

This work investigates the effect of domestic plum rootstocks on the stability and productivity of Stanley plum plants. The main factor limiting the productivity of fruit crops in the floodplain soils of the foothill horticultural area of Krasnodar Oblast was found to be an unfavorable water-air regime of these soils in wet periods. The main geogenic factors that negatively affect the state and productivity of plum plants include the following: the presence of layers of low fertility and medium-clay granulometric composition in the soil profile. Depression and death of trees is promoted by prolonged overwatering of the upper part of the soil profile, caused by low filtration capacity of soil layers in combination with heavy granulometric composition and conditions of laying on the terrain (absence of horizontal surface runoff). A different degree of plum trees resistance to these unfavorable geogenic conditions depending on the type of rootstock was revealed. The lowest degree of depression under prolonged overwatering of the root-containing soil layer was observed in plum trees on the PK SK2 rootstock, which demonstrated the highest vegetative mass growth under the smallest number of dead plants. Stanley plum trees on rootstock AP1 were subjected to the greatest depression. The different degree of plum tree stability on different rootstocks is mainly related to the location of potentially active roots in the soil. The root system of plum trees on rootstock PK SK2 is characterized by the concentration of the main part (about 65 %) of potentially active roots in the upper soil layer of 0–40 cm. In plum trees on AP1 rootstock, potentially active roots penetrate to greater depths, with about 60% of the roots located in the soil layer of 40-80 cm. During wet periods and after abundant precipitation, when the soil below the 40 cm level is saturated with moisture, more than half of potentially active roots of plum trees on AP1 rootstock have to survive in unfavorable conditions.

FEATURES OF THE STRUCTURE, FUNCTIONING AND RECONSTRUCTION OF THE LANDFILL NIZHNEKAMSKNEFTEKHIM PUBLIC JOINT STOCK Co.

PJSC Nizhnekamskneftekhim is one of the largest petrochemical companies in Europe. Industrial production was launched there in 1967. Production waste is stored in a sludge reservoir and waste landfill. The landfill has been operating since 1982. It is equipped with systems of surface and underground drainage, impervious curtains, and two belts of observation wells. More than 0.5 million m3 of mostly solid waste III-V classes of hazard has been accumulated there. The landfill capacity is depleted by more than 80%. Its operation has led to a significant groundwater level rise (4.0–4.5 m) and groundwater pollution, the water salinity reaching 12.75 g/l, and hardness, 73.9 mmol/l. These negative hydrogeoecological effects are primarily due to increased atmospheric recharge of groundwater and the active interaction of atmospheric precipitation with the waste substance. There is plan to reconstruct the landfill. It involves encapsulating the waste in a watertight reservoir confined by artificial geosynthetic materials with extremely low filtration properties. Hydrodynamic and balance methods were used to determine the infiltration supply of groundwater in natural and disturbed conditions, productivity of underground drainage; the continuously formed flow rate of polluted groundwater, which is not intercepted by drainage system (with the flow discharge equal to 116.7 m3/day); as well as modern and predicted (postreconstruction) water balances. The effectiveness of the existing engineering protective structures of the landfill was assessed. It is shown that the planned reconstruction should lead to a decrease in the groundwater level and its pollution degree. In this case, the concentrations of organic substances, which are the priority pollutants, will decrease most intensely. The geological environment of the landfill site is characterized by significant buffer (protective) properties. They control just local spreading of contaminated groundwater. According to the data of numerous different-time sampling at a distance of 1.0–1.5 km from the landfill in the direction of groundwater current spreading, no signs of pollution caused by the landfill operation are registered. The main processes determining the self-purification of groundwater are as follows: dilution of polluted water by pure infiltration nutrition, the minimum layer of which is 67.6 mm/year; chemo- and biodestruction of pollutants, their sorption, diffusion-dispersion scattering and precipitation as pH–Eh conditions change.

Microplastics pollution in the rivers of a metropolitan city and its estimated dependency on surrounding developed land

The spatial distribution and abundance of suspected microplastics (SMPs) in the surface water of a metropolitan city, as represented by four Hong Kong rivers, was studied during the dry season. Shing Mun River (SM), Lam Tsuen River (LT), and Tuen Mun River (TM) are located in urbanized areas, and SM and TM are tidal rivers. The fourth river, Silver River (SR) is situated in a rural area. TM had a significantly higher SMP abundance (53.80 ± 20.67 n/L) than the other rivers. The SMP abundance increased from upstream to downstream in non-tidal rivers (LT and SR), but not in tidal rivers (TM and SM), probably due to the tidal influence and a more homogeneous urban development along the tidal rivers. Inter-site differences in the SMP abundance were strongly correlated with the built area ratio (defined as the percentage of surrounding developed land area), human activities, and the nature of the river. About half (48.72 %) of the SMPs were <250 μm. Fibers and fragments were most abundant (>98 %), with most of them being transparent (58.54 %), black (14.68 %), or blue (12.12 %). Polyethylene terephthalate (26.96 %) and polyethylene (20.70 %) were the most common polymers. However, the MP abundance could be overestimated due to the presence of natural fibers. By contrast, an underestimation of the MP abundance could result from a smaller volume of water samples collected, due to a low filtration efficiency caused by high organic content and particle concentrations in the water. A more effective solid waste management strategy and upgrading of the sewage treatment facilities for removing microplastics are recommended to ameliorate the microplastic pollution in local rivers.

Transition to unstable oscillatory flames in porous media combustion

The flames inside porous burners with low filtration velocity are prone to oscillatory behavior similar to unstable combustion in narrow channels but accompanied by complicated dynamics due to the irregularity of porous structure, flow field, and thermal gradient formed as a result of heat recuperation. This work is a numerical study within the framework of the pore-scale simulation approach devoted to investigating the flame oscillation mechanisms and characteristics in a two-dimensional pseudo-irregular packed bed of particles generated using the Voronoi tessellation algorithm with constant pore size. The results demonstrate that unstable flame oscillations like flames with repetitive extinction and ignition (FREI) lead to the velocity pulsation in adjacent pore channels, where the stable flame fragments are exposed to the hydrodynamically-driven fluctuations. In the case of the flow rate close to the stability threshold, the flow pulses can reach a magnitude enough to shift the stable flame in the upstream quenching zone, promoting its oscillations with repetitive extinction and ignition. Results of parametric simulation with a variation of the particle diameter and flow velocity were summarized in the regime diagram revealing the transition between stable normal flame, FREI, and stable weak flame with the velocity reduction. The pulsating transitional regime was detected between the stable normal flame and the FREI. The amplitude and intensity of such pulsations increase monotonically with the flow rate reduction in a narrow range. Oscillations of the unstable flame and hydrodynamically-driven flame pulsations are similar in dynamics but different in their physical mechanisms. However, in irregularly packed beds of particles, both these phenomena unavoidably coexist and interfere significantly with each other due to the connectivity of the pore channels.

Optimization of the operating parameters in a membrane bioreactor operated in direct-flow mode by assessing threshold flux for compressibility

Direct-flow filtration (i.e., without membrane aeration during the filtration phase) is a challenging operation strategy in membrane bioreactors (MBRs). This study aims to provide a comprehensive approach for assessing optimal values for the main operating parameters (filtration time between backwashes and permeate flux) through the determination of the threshold flux for compressibility (Jth,c). A pilot-scale tertiary MBR was used for conducting filtration tests. Flux-step trials revealed the crucial role of cake compressibility in fouling deposition and reversibility. Accordingly, the compressible cake model was used to investigate Jth,c under different operating conditions and suspension characteristics. Based on this approach, lower filtration times (5–7 min) are recommended so that sustainable process productivity can be maximized. Specifically, decreasing filtration times from 12 to 7 min results in net permeate flux increase of more than 50%. A significant effect of suspension properties (biopolymer cluster content, BPC) on Jth,c was also found which decreased from 41.9 to 13.0 L/h m2 when increasing BPC from 0.3 to 4.6 mg/L. Long-term tests, under temporized and variable filtration time modes, demonstrate the feasibility of using the Jth,c as a guideline for optimizing filtration performance.

Aramid-based highly conductive composite films by incorporating graphene for electromagnetic interference shielding and Joule heating applications

With the development of modern electronic devices, high-performance polymer-based conductive composites are urgently needed. However, the poor thermal stability of most polymers, the high content of conducive fillers, and the unsatisfied performance efficiency of most composites limited their application in high high-end areas. Both aramid and graphene are fantastic engineering materials, their composites are expected to have desirable performances. Herein, we demonstrate the preparation of polymerization-induced aramid nanofiber (PANF)/reduced graphene oxide (rGO) composite films through a simple yet efficient strategy. The assembly of the two components were achieved by a low cost and scalable vacuum-assisted filtration method. With PANFs serving as the matrix and rGO serving as the filler, PANF/rGO composite films with multilayer structure, excellent mechanical property, superior thermal stability and flame retardancy were obtained. The electrical conductivity of composite films can reach 4.8 × 103 S/m with a rGO content of 20%. Correspondingly, the composite films show excellent electromagnetic interference shielding performance and the shielding effectiveness of PANF/rGO composite film with a thickness of 30 μm can reach 33.6 dB. Furthermore, the composite films also exhibit excellent Joule heating performance with a wide heating temperature range (30–180 °C). These advantages can promote the practical engineering applications of aramid and graphene.

How do three-layer surgical masks prevent SARS-CoV-2 aerosol transmission?

The three-layer surgical mask was recognized by the World Health Organization as an effective-protection tool for reducing SARS-CoV-2 transmission during the COVID-19 pandemic; however, the contribution of each layer of this mask to the particle size–dependent filtration performance resistance remains unclear. Here, both experimental work and numerical simulation were conducted to study the role of each mask layer in particle size–dependent filtration and respiratory resistance. By using scanning electron microscopy images of a commercial three-layer mask, composed of two spun-bond and one melt-blown nonwoven polypropylene fabric layers, four representative models were constructed, in which the computational fluid dynamics of multiphase flow were performed. The pressure drop of all models under different flow conditions was measured next. Numerical simulation was then verified by comparing the experimental results in the present study and other theoretical works. The filtration efficiency of the spun-bond polypropylene nonwoven fabric layer was much lower than that of the melt-blown nonwoven polypropylene fabric layer for the particle diameter in the range of 0.1–2.0 μm. Both the spun-bond and melt-blown nonwoven polypropylene fabric layers demonstrated extremely low filtration efficiency for particles was<0.3 μm in diameter, with the maximum filtration efficiency being only 30%. The present results may facilitate rational design of mask products in terms of layer number and structural design.

A novel temperature-resistant fracturing fluid for tight oil reservoirs: CO2-responsive clean fracturing fluid

With the increasing demand for oil and gas resources, deep tight oil and gas reservoirs have gradually become the focus of global oil and gas exploration and development. Hydraulic fracturing technology based on water-base fracturing fluid plays a more and more important role in improving the recovery of tight oil reservoirs. Under the background of global CO2 emission reduction, a CO2-responsive clean fracturing fluid with controllable gelling/gel breaking at high temperatures was constructed in this paper. The system was not only friendly to the reservoir and environment, but also overcame the shortcomings of the traditional clean fracturing fluid with undesirable temperature resistance. The viscosity characteristics and viscoelastic behavior of temperature-resistant clean fracturing fluid were investigated through high-temperature rheology experiments. The interaction between fluid and rock was investigated through the core flow experiment. The results showed that the clean fracturing fluid had the characteristics of good CO2 responsiveness, excellent shear resistance at high temperatures, high drag reduction, satisfactory gel breaking performance, low filtration and low core damage. The complex three-dimensional network structure formed by the intertwined micelles and vesicles improves the temperature resistance of the clean fracturing fluid. It is expected that the fluid can not only be used to improve oil recovery in tight oil reservoirs, but also be used to solve the leakage problem in CO2 storage underground.

The association between visceral adiposity index and decreased renal function: A population-based study.

We aimed to investigate the association of visceral adiposity index (VAI) with decreased renal function in US adults. Cross-sectional data were analyzed for 35,018 adults in the National Health and Nutrition Examination Survey (NHANES) 2005-2018. VAI was determined using waist circumference, body mass index (BMI), triglycerides (TGs) and high-density lipoprotein-cholesterol. Albuminuria was defined as urinary albumin-to-creatinine ratio (ACR) >30 mg/g. A low estimated-glomerular filtration rate (eGFR) was defined as an eGFR lower than 60 ml/min/1.73 m2. Chronic kidney disease (CKD) was defined as either albuminuria or low-eGFR. A multivariable logistic regression analysis was utilized to explore the relationship of VAI with albuminuria, low-eGFR and CKD. Subgroup analysis and interaction tests were also conducted. A total of 35,018 participants were enrolled with albuminuria, low-eGFR, and CKD prevalence rates of 5.18, 6.42, and 10.62%, respectively, which increased with the higher VAI tertiles. After full adjustment, a positive association of VAI with albuminuria (OR = 1.03, 95% CI: 1.00, 1.06) and CKD (OR = 1.04, 95% CI: 1.02, 1.06) was observed. Participants in the highest VAI tertile had a significantly 30% increased risk for albuminuria (OR = 1.30, 95% CI: 1.07, 1.58) and a 27% increased risk for CKD (OR = 1.27, 95% CI: 1.08, 1.49) compared with those in the lowest VAI tertile. No statistically significant association between VAI and low-eGFR was detected. Subgroup analysis and the interaction term indicated that there was no significant difference among different stratifications. Visceral adiposity accumulation evaluating by VAI was associated with increased likelihood of the decline in renal function.

Optimization and Performance Evaluation of Foam Acid Systems for Plugging Removal in Low Pressure Oil and Gas Reservoirs

Foam acidization has unique advantages such as low damage, low filtration, low friction, high efficiency, excellent retardation, and fast liquid discharge rate, which is suitable for stimulation and reconstruction of low-pressure oil and gas reservoirs that have been developed over many years. It is obtained that the main chemical components of downhole plugging materials include vegetable oil, fatty acids and their esters, silicone oil, amide polymers, and additional organic components, as well as non-organic components, elemental sulfur, ferrous sulfide, iron disulfide, silicon dioxide, mineral salts, etc. The performance of foam acid was investigated by experiments, including the effective range of action of active acids, reducing filtration, increasing temperature resistance and high-temperature stability of foam acid deep wells. The new foam acid system is developed and optimized to suitable for low-pressure deep well acidification operations. Experimental evaluation optimized the acid foaming agent and foam stabilizer and developed a new foam acid formulation with foam stability, filter loss reduction, temperature resistance, and easy backflow performance. The experimental condition is that the temperature is 90 °C, the foam quality can reach more than 70% when mixed for more than 30 s, the average half-life is 38.75 min, and the liquid separation rate is 19.90 s/mL. Its suspension is better than that of conventional hydrochloric acid, its corrosion rate is 1.872 g/m2·h, and the flowback rate of foam acid residue reaches 97%. Experimental evaluation has shown that the developed foam acid features high surface activity, stable foam, strong temperature resistance, significant speed and corrosion suppression, and excellent drainage assist performance. Dynamical simulation evaluation of reservoir core foam acidification demonstrated that the foam features long-life, strong suspension capacity, excellent rheology, low filtration, and significant acidization and plug removal effects, and can be used in stimulating the medium-deep, high-temperature, and low-pressure oil and gas reservoirs.

Polymer-flooding produced water treatment using an electro-hybrid ozonation-coagulation system with novel cathode membranes targeting alternating filtration and in situ self-cleaning

Polymer-flooding produced water is more difficult to treat for reinjection compared with normal produced water because of the presence of residual hydrolyzed polyacrylamide (HPAM). A novel cathode membrane integrated electro-hybrid ozonation-coagulation (CM-E-HOC) process was proposed for the treatment of polymer-flooding produced water. This process achieved in situ self-cleaning by generated microbubbles in the cathode membrane. The CM-E-HOC process achieved a higher suspended solid (SS), turbidity and PAM removal efficiency than the CM-EC process. The SS in the CM-E-HOC effluent was ≤ 20 mg/L SS, which met the reinjection requirements of Longdong, Changqing Oilfield, China (Q/SYCQ 08,011–2019) at different current densities (3, 5 and 10 mA/cm2). The CM-E-HOC process greatly mitigated both reversible and irreversible membrane fouling. Therefore, excellent flux recovery was obtained at different in situ self-cleaning intervals during the CM-E-HOC process. Furthermore, alternating filtration achieved continuous water production during the CM-E-HOC process. On one hand, the effective removal of aromatic protein-like substances and an increase in oxygen-containing functional groups were achieved due to the enhanced oxidation ability of the CM-E-HOC process, which decreased membrane fouling. On the other hand, the CM-E-HOC process showed improved coagulation performance because of the increased oxygen-containing functional groups and polymeric Fe species. Therefore, larger flocs with higher fractal dimensions were generated, and a looser and more porous cake layer was formed on the membrane surface during the CM-E-HOC process. Consequently, the CM-E-HOC process exhibited better in situ self-cleaning performance and lower filtration resistance than the CM-EC process.

Efficiency of a gravity-driven membrane in a water treatment plant

Abstract Membrane filtration technology is widely applied in conventional surface water treatment plants because of its low power load and high filtration accuracy. This study follows the transition from a power-driven to a gravity-driven siphon-submerged ultrafiltration membrane system in a drinking water treatment plant in Shandong Province, China. The proportion of space membrane areas in the tank was further developed, by increasing the membrane areas of a single tank to 1.6 times that before the transformation, and the design production capacity of a single tank is increased from 10,000 m3/d before the transformation to 16,700 m3/d. The recovery rate of a single tank was also increased from 96.28 to 97.77%. The energy consumption per ton of water decreased from 0.06 to 0.017 MJ. The annual carbon emissions reduction reached 197.13 tons per tank. In terms of the water quality, the algae removal rate from surface water by the ultrafiltration membrane reached 100%. Further, the removal rates of 2 μm particles, turbidity, and chlorophyll were above 99%. Our results suggest that gravity-driven siphon-submerged ultrafiltration promotes environmental protection, energy conservation, and emissions reduction. This technology introduces a new development direction for membrane filtering in drinking water treatment plants.

Application of BiVO4/TiO2/CNT Composite Photocatalysts for Membrane Fouling Control and Photocatalytic Membrane Regeneration during Dairy Wastewater Treatment

This study aimed to investigate the performance of composite photocatalytic membranes fabricated by incorporating multiple nanoparticles (TiO2, carbon nanotubes, BiVO4) into polyvinylidene fluoride membrane material for real dairy wastewater treatment. The composite photocatalytic membranes exhibited superior antifouling behavior, lower filtration resistance, better flux, and higher flux recovery ratio than the pristine membrane. Salinity, pH, and lactose concentration are determinant factors that affect filtration resistance and rejection performance during the ultrafiltration of dairy wastewater. Generally, higher irreversible and total resistances and slightly lower chemical oxygen demand (COD) rejections were found at higher salinity (expressed by electric conductivity values of &gt;4 mS/cm) than lower salinity (&lt;4 mS/cm) levels. The presence of lactose in dairy wastewater increased irreversible resistance and severely reduced COD rejection during ultrafiltration due to the ability of lactose to pass through the membranes. It was ascertained that membranes require further treatment after filtrating such wastewater. Lower resistances and slightly better COD rejections were observed at pH 7.5 and pH 9.5 compared to those observed at pH 4. Photocatalytic membranes fouled during the ultrafiltration of real dairy wastewater were regenerated by visible light irradiation. The membrane containing all constituents (i.e., TiO2, carbon nanotubes, and BiVO4) showed the best regeneration performance, exceeding that of the pristine membrane by 30%.

Assessing the impact of granular anaerobic membrane bioreactor intensification on treatment performance, membrane fouling and economic balance

Anaerobic membrane bioreactors (AnMBRs) have attracted much attention for mainstream domestic wastewater treatment. However, membrane fouling, operating costs, energy consumption and low filtration flux are important challenges slowing the scale-up of the technology. In this study and for the first time, granular sludge, submerged membrane, no gas sparging and low permeate flux were chosen to mitigate membrane fouling and to improve the energy and economic balance of an AnMBR. A granule-based AnMBR (G-AnMBR) was operated under four organic loading rates (between 0.5 and 1.6 kgCOD.m–3.d–1) with hydraulic retention times ranged from 13.9 to 4.9 h, and instantaneous permeate flux levels (Jp20,inst) ranged from 2.8 to 6.0 LMH to evaluate OLR impact on anaerobic digestion performance, membrane fouling extent and economic balance. Results show that COD removal rates above 83 % were achieved during the four experimental periods. Membrane fouling was directly correlated to the flux and OLR and increased from 0.03 to 2.86 kPa.d–1 as the Jp20,inst increased from 2.8 to 6.0 LMH and the OLR increased from 0.5 to 1.6 kgCOD.m–3.d–1, respectively. In all the periods, macromolecules and colloidal proteins were the major foulants deposited on the membrane. Most of the fouling was reversible and was easily removed by physical cleaning (>97.7 %). A preliminary economic assessment revealed that the permeate flux and OLR are key economic drivers for the G-AnMBR economic balance and allowed to define the satisfactory compromise between membrane purchase and chemical consumption for the long-term control of membrane fouling.

Advanced ceramics in radical filtration: TiO2 layer thickness effect on the photocatalytic membrane performance

Membranes with advanced oxidation processes (AOPs) are a promising combination to separate and degrade organic pollutants in a single system. In this work, we describe the fabrication and characteristics of nine membranes with different TiO2 top layer thicknesses (from 0.26 to 21.9 μm), giving attention to the critical catalyst thickness and the formation of defects. We also report the optimum photocatalyst thickness for our single-layer membranes (∼2.74 μm), after which more titanium dioxide does not improve the degradation. However, an increase in degradation for membranes with multiple TiO2 layers was still possible. These results and the comparisons with the literature suggested that the optimal catalyst thickness is closely related to the material morphology. We obtained a maximum degradation at the lower filtration rate (1.6 L m−2 h−1) of 72% with a single layer membrane of 3.4 μm and 82% with a membrane with six layers of 21.9 μm. Furthermore, a 1D mass transport and reaction model that describes the coating thickness effect was developed and fitted with the experimental data. Other parameters are also discussed, such as light penetration limitations, surface area, and surface reaction rate constant. These results and analysis provide a better understanding of the fabrication and optimization of photocatalytic membranes.

Multi-stage hydraulic fracturing technology in a well with horizontal working face

At present, hydraulic fracturing (HF) is still the most effective method of stimulating hydrocarbon flow and enhancing oil recovery in certain types of wells, particularly those with horizontal endings. In many regions, this is the only technology that enables development of fields with hard-to-recover reserves confined to low-permeability, poorly drained, heterogeneous and dissected reservoirs, which significantly increases hydrocarbon production and makes well construction economically viable. In this work, the authors have developed a new technology for interval hydraulic fracturing in a well with a horizontal target area, with the ability to inject fracturing fluid and hold excess pressure on either side of the fracturing unit by means of flap-type check valves. The fracturing is performed through a transport unit that runs directly through the casing and protects the plug from the abrasive effects of the gel-propellant mixture. After fracturing is complete, the transport unit is removed from the plug, and the rear cut-off valves are closed. No re-entry is possible after the adaptor has been removed from the well. For the next interval, the work cycle of plug, activation and fracturing is repeated using a new transport unit. For each repetition, the newly stimulated interval remains isolated until the fracturing operation is complete and all downstream plugs have been fractured. All installed plugs are drilled out before development. During all phases of the work, it is assumed that the well is prepared without the use of coiled tubing. The novelty and innovation lie in the technological solution of delivery to the target area and using easy-to-drill plugs to guarantee open interval separation and perform selective fracturing. Potential candidates are wells with 114 mm diameter casings with single- or multiple-acting fracturing sleeves to open-close after the horizontal part of the well has been prepared (the ‘equal-pass’ section requirement is for a 95 mm diameter bit). The proposed technical means and technology, in the opinion of the authors, will increase the efficiency of field development, reservoir conditions in which are characterized by low filtration parameters, high viscosity properties, etc. The authors do not think that the proposal will generally solve the problem of intensification of the inflow of reservoir fluid to the well and thereby increase oil recovery from the reservoir, but according to in their opinion, in some respects it will contribute to this. The final results will be obtained based on the results of extensive production tests.

Filtering Efficiency of Sustainable Textile Materials Applied in Personal Protective Face Mask Production during Pandemic.

The COVID-19 outbreak increased demand for personal protective respirator masks. Textile masks based on cloth materials appeared to be a sustainable, comfortable, and cost-effective alternative available in global communities. In this study, we used laser-based particle counting for mask material qualification to determine the concentration filtering efficiency in general, everyday community use. The efficiencies of eleven different commercially available textile materials were measured in single-, double-, and triple-layer configurations according to their grammage, mesh (XY), and inter-yarn gap. It was found that in the single-layer configurations, most materials were well below the acceptable standards, with a wide variation in filtering efficiency, which ranged from 5% to ~50%. However, when testing the fabrics in two or three layers, the efficiency increased significantly, exceeding or approaching the standard for medical masks. Three layers of natural silk was able to produce a level of filtration efficiency of 84.68%. Two-layered natural silk achieved 70.98%, cotton twill achieved 75.6%, and satin-weave viscose achieved 69.77%. Further options can also be considered in cases where lower filtration is acceptable It was statistically shown that applying a second layer was more significant in terms of overall filtering than increasing the layer count to three. However, layer stacking limited the breathability. The paper presents measurement-based qualitative and quantitative recommendations for future textile applications in face mask manufacturing.

Size-selective accretion of dust on to CPDs: low CPD masses and filtration of larger grains

ABSTRACT The major satellites of Jupiter and Saturn are believed to have formed in circumplanetary discs (CPDs), which orbit forming giant protoplanets. Gas and dust in CPDs have different distributions and affect each other by drag, which varies with grain size. Yet simulations of multiple dust grain sizes with separate dynamics have not been done before. We seek to assess how much dust of each grain size there is in CPDs. We run multifluid 3D hydrodynamical simulations including gas and four discrete grain sizes of dust from 1 μm to 1 mm, representing a continuous distribution. We consider a 1MJup protoplanet embedded in a protoplanetary disc around a 1 M⊙ star. Our results show a truncated MRN (Mathis-Rumpl-Nordsieck) distribution at smaller grain sizes, which starts to tail off by a = 100 μm and is near zero at 1 mm. Large dust grains, which hold most of the dust mass, have very inefficient accretion to the CPD, due to dust filtration. Therefore, CPDs’ dust masses must be small, with mass ratio ∼ a few × 10−6 to the protoplanet. These masses and the corresponding millimetre opacities are in line with CPD fluxes observed to date.

Особенности проведения ремонтновосстановительных работ в газовых скважинах месторождений Западной Сибири, находящихся на стадии падающей добычи

Introduction. The article discusses the features of carrying out repair and restoration work in gas wells of Western Siberian fields that are at the stage of declining production. The compositions of process fluids used to block the bottomhole formation zone during well killing, to isolate the inflow of formation waters in various mining and geological conditions are given. The compositions of process fluids used in repair and restoration work in certain fields of Western Siberia are presented. They are easily removed when inducing inflow from the formation, and allow providing the required pressure at the bottomhole, as well as maintaining the reservoir properties of the productive formation and preventing its destruction. Materials and research methods. Based on the generalization of field experience in killing wells, fields at the stage of declining production, the results of their own theoretical, laboratory and bench studies. Research results and their discussion. When killing wells with temporary blocking of the bottomhole formation zone, the choice of the composition of process fluids with high stability, low filtration, in a wide range of adjustable density and rheological properties, allows creating the necessary repression on the formation and carrying out various operations in the well without complications. Technological fluids for killing wells, which are direct-type emulsion systems based on a composite reagent, are pseudo-plastic systems in terms of rheological parameters, where the density range is 900-1000 kg/m3. The properties of the emulsion solution based on the kill fluid reagent are determined by the complex effect of the reagents included in its composition. Filler-based blocking fluids are used to temporarily block the bottomhole formation zone of wells, and are prepared by introducing the calculated amount of the reagent into the required volume of killing fluid based on the killing fluid reagent. As a water-insulating composition for creating an insulating barrier in the reservoir, a formulation of a gel-forming composition based on a reagent – a dry mixture for carrying out repair and restoration work and a gelforming reagent – is considered. Conclusions. Based on the study, it was determined that the most promising technology for killing wells under conditions of abnormally low formation pressures is the technology of preliminary blocking of the bottomhole formation zone using blocking fluids with filler. To ensure high efficiency of repair and restoration work, preliminary calculations of the process fluids used are necessary, taking into account the mining and geological conditions of the reservoir and the geometric parameters of the well.