Proppant embedment, which occurs at depths in rock formations, is a key proppant downhole mechanism which can result in rapid decline in hydrocarbon production. The current review study reveals that ...both rock formation characteristics and proppant characteristics significantly determine the embedment mechanism. Importantly, the review shows that embedment can occur in any formation, whatever the type of rock, leading to conductivity loss in siltstone of 78.42%, in mudstone of 81.89%, in conglomerate of 91.55%, and in shale of 78.05%. The present study investigated the importance of the creep phenomenon (a function of confinement and temperature), the percentage of clay content, and surface roughness on proppant embedment. Other dynamics, such as time, temperature and fracture fluid, can also impact the rate of proppant embedment as they help to alter the softness (young's modulus) of the fracture surface. This study reveals that curable resin-coated sand (embedment of 44 μm) is very tolerant of the embedment process compared with lightweight ceramics (113 μm) and uncoated fracture sand (106 μm). Similarly, higher proppant concentration, greater proppant size, uniform proppant distribution and a greater number of proppant layers can minimize the embedment process to a great extent, ensuring the effective extraction of oil/gas from hydraulically fractured wells. This paper also reviews some existing numerical and analytical models on proppant embedment which enable forecasting of the fracture conductivity loss undergone in downhole fracture treatments. Finally, the paper summarizes some of the case studies emphasized on proppant embedment effect and various research recommendations are suggested to minimize the proppant embedment.
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Tributyltin (TBT) is a toxic organotin compound that belongs to the group of Persistent Organic Pollutants (POPs) and it is documented to cause severe sexual disorders development in aquatic fauna. ...According to the present study, The TBT concentration in coastal water ranged from 303 ± 7.4 ngL−1 to 25 ± 4.2 ngL−1 wherein sediment was from 107 ± 4.1 ngKg−1 to 17 ± 1.4 ngKg−1. TBT in Perna viridis was found to range from 4 ± 1.2 ngKg−1 to 42 ± 2.2 ngKg−1 wet weight and in ascending order of the body weight. The highest TBT level in water and sediment was found in the Colombo port where the highest level of TBT in P. viridis (42 ± 2.2 ngKg−1) was recorded from the Dikkowita fishery harbor. A positive correlation between the number of male P. viridis and TBT level (p < 0.05) suggests possible reproductive impairment in aquatic animals exposed continuously to a high concentration of TBT.
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•Solid Phase Micro Extraction is a sensitive, cost effective and novel precise method to identify and quantify TBT•The highest TBT concentration in water and sediment indicate that high amount of TBT inputs are occurring in Colombo port•Positive correlation between numbers of male P. viridis and TBT concentration suggest that possible reproductive impairment•Marinas in fishery and commercial harbors are likely sources of TBT contamination in Sri Lanka•Dietary consumption of contaminated seafood would be the main pathway of TBT exposure in the environmental biota
The inability to achieve satisfactory production targets from unconventional oil/gas deposits is a foremost concern for many hydraulic fracturing projects. One potential reason for recovery ...difficulties is the lack of a clear understanding of the severity of proppant damage mechanisms in fractures exposed to extreme reservoir environments. In this comprehensive laboratory-scale experimental analysis, we evaluate the significance of one such proppant damage mechanism: proppant embedment, which occurs in fractures over extended time frames, and its ultimate effect on fracture permeability and the reduction of fracture aperture. The results reveal that a significant reduction of fracture permeability occurred after only 36 h of exposure to confining stresses in uniformly (49%) and partially (29%) proppant-distributed fractures. Importantly, by 144 h, permeability reductions of 92.3% and 54.6% were observed for uniformly- and partially-distributed fractures. However, improved permeability results were obtained for multilayer proppant-distributed fractures. The effect of creep-induced proppant embedment was comprehensively studied. In uniformly and partially proppant-distributed specimens, both elastic and creep deformation dominate the embedment process. However, in multilayer proppant-distributed fractures, the embedment process is predominantly governed by the initial elastic embedment mechanism. CT scanning of uniformly and partially proppant-distributed fractures confirmed the substantial reduction in fracture aperture due to proppant embedment combined with fracture asperity damage. Nevertheless, CT scanning revealed only a minor degree of proppant embedment in multilayer proppant-distributed fractures, although significant proppant-re-arrangement occurs in multilayer proppant packs under high-stress conditions. Importantly, for both following scenarios: (1) high confining pressures (30 MPa) at lower testing times (12 h), and (2) low confining pressures (20 MPa) at longer testing times (144 h), the impact of the presence of either a uniform or partial proppant arrangement is minimal, as both proppant arrangements lead to significantly lower fracture permeability and aperture.
We make publicly available a catalog of calibrated environmental measures for galaxies in the five 3D-Hubble Space Telescope (HST)/CANDELS deep fields. Leveraging the spectroscopic and grism ...redshifts from the 3D-HST survey, multiwavelength photometry from CANDELS, and wider field public data for edge corrections, we derive densities in fixed apertures to characterize the environment of galaxies brighter than mag in the redshift range . By linking observed galaxies to a mock sample, selected to reproduce the 3D-HST sample selection and redshift accuracy, each 3D-HST galaxy is assigned a probability density function of the host halo mass, and a probability that it is a central or a satellite galaxy. The same procedure is applied to a z = 0 sample selected from Sloan Digital Sky Survey. We compute the fraction of passive central and satellite galaxies as a function of stellar and halo mass, and redshift, and then derive the fraction of galaxies that were quenched by environment specific processes. Using the mock sample, we estimate that the timescale for satellite quenching is it is longer at lower stellar mass or lower redshift, but remarkably independent of halo mass. This indicates that, in the range of environments commonly found within the 3D-HST sample ( ), satellites are quenched by exhaustion of their gas reservoir in the absence of cosmological accretion. We find that the quenching times can be separated into a delay phase, during which satellite galaxies behave similarly to centrals at fixed stellar mass, and a phase where the star formation rate drops rapidly ( Gyr), as shown previously at z = 0. We conclude that this scenario requires satellite galaxies to retain a large reservoir of multi-phase gas upon accretion, even at high redshift, and that this gas sustains star formation for the long quenching times observed.
High tolerance of ticks to acaricides is increasingly becoming a problem to cattle farmers. Resistance status of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)from two cattle farms of Sri ...Lanka were determined against different concentrations of pyrethroid permethrin, organophosphate malathion, organochlorine DDT and carbamate propoxur using Larval Packet Test (LPT) as recommended by Food and Agriculture Organization (FAO). Mechanisms of acaricide resistance were studied by conducting biochemical and PCR assays. Tick larvae were tested for the activity levels of acaricide metabolizing enzymes i.e.esterases, glutathione S-transferases (GSTs) and monooxygenases, and for altered target sites i.e.acetylcholinesterase (target site of organophosphates and carbamates) and sodium channel regulatory proteins (target site of pyrethroids and DDT). According to discriminating dosages specified by FAO for ticks both populations were 24–56% resistant to DDT. LC values showed that the both populations were susceptible to permethrin and resistant to malathion. Moderate insensitivity of AChEs and knock-down resistance (kdr) mutations were found as resistance mechanisms. GSTs and monooxygenases were not elevated. The kdr type mutation G72V (G215T in the gene) found in the sodium channel regulatory protein of R. (B.) microplus samples may be responsible for DDT resistance. Systematic and sophisticated insecticide resistance monitoring programmes and a better understanding on the mechanisms which govern resistance development are vital for future tick control programmes.
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•Sri Lankan Rhipicephalus (B.) microplus is resistant to DDT, malathion and propoxur•Tick populations are ‘susceptible’ to permethrin•Organophosphorus and carbamate target site AChE is moderately insensitive•Knock-down resistance (kdr) gene mutation G215T is present•Activity of the enzymes which provide metabolic resistance to acaricides are assessed for two Rhipicephalus (B.) microplus populations.
Naphthalene (NAP) and phenanthrene (PHE) are prevalent Polycyclic Aromatic Hydrocarbons (PAHs) in the environment. High-Performance Liquid Chromatography (HPLC) analysis was performed on marine water ...samples (n = 57) collected from 19 locations. Molecular screening of the aromatase (CYP19) gene expression was examined using quantitative Reverse Transcriptase PCR (qRT-PCR). The findings of the study showed a significant range of naphthalene concentrations along the coastline, spanning from 1.70 to 15.05 mg/L, where phenanthrene concentrations varied from undetectable to a maximum of 5.36 mg/L. The relative expression of the CYP19 gene ranged from 0.5 to 13.9 in the sampling sites. The ANOVA analysis showed a significant positive correlation (p < 0.05) between the concentrations of PAHs and CYP19 gene expression. The study concluded that the CYP19 gene could be useful in detecting contaminants such as naphthalene and phenanthrene in water. This study may help develop effective strategies to detect and mitigate PAH pollution in coastal areas.
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•The highest PAH concentrations were detected in Southern coastal water.•Naphthalene concentrations along the coastline ranged from 1.70 to 15.05 mg/L.•Phenanthrene concentrations varied from zero to 5.36 mg/L along the coastal zone.•A positive correlation was observed between PAH concentration and gene expression.
River basins are logical units interacting with geological formations and anthropological footprints while providing many rewards to humans and the associated ecosystems. Yan Oya is the primary ...surface water source in the North Central Province of Sri Lanka. The timely study focused on analyzing the present status of surface water quality in the Yan Oya river basin to evaluate the impacts of anthropological activities. Forty surface water samples were collected in wet and dry seasons in 2019. Principal component analysis (PCA) was employed to evaluate the similarities and dissimilarities of the water quality between three different zones of the Yan Oya river basin. At the same time, GIS was applied to show the spatial distribution of water quality parameters. According to the Sri Lankan Standards for drinking water, pH, DO, NO
3−
, NO
2−
, NH
4
+
, TP, fluoride, Na
+
, K
+
, and trace metal concentrations remained within permissible limits. Electric conductivity (EC), total dissolved solids (TDS), chemical oxygen demand (COD), turbidity, total hardness (TH), fecal coliform, and total coliform were exceeded the allowable threshold levels. PCA analysis revealed that the significance of geomorphological catchment factors and land use features on broad-scale water quality patterns and the study identified that spatial variations in cations (Na
+
, K
+
, Ca
2+
, Mg
2+
), TH, EC, and TDS. High FC contamination was the most important factor variable for COD and turbidity in the Yan Oya river. The results yielded spatiotemporal patterns of contamination divided along anthropogenic footprints, serving as a benchmark for future studies, particularly basins that have reservoirs constructed to facilitate better human consumption of water.
The Open University's My Digital Life course offers a learning infrastructure that allows complete novices to experiment with, and learn about, Internet-of-Things technologies by engaging in a range ...of activities that include collaborative and collective programming of real-world sensing applications. The first Web extra at http://youtu.be/JUpkHqivXp4 is a video presentation in which Arosha Bandara, a lecturer in computing at the Open University, explains how embedded, interconnected devices have grown to affect our lives. The second Web extra at http://youtu.be/VL37sjj_I1sis a video demonstration of Sense from the Open University's My Digital Life course. Sense is a newly developed visual programming language and programming environment based on SenseBoard, an embedded networked sensor device that supports active learning and experimentation with sensing, actuation, and networking by students at home.
This research presents a low-cost, easy-to-assemble nondispersive infrared (NDIR) device for monitoring N2O gas concentration in agricultural soils during field and laboratory experiments. The study ...aimed to develop a cost-effective instrument with a simple optic structure suitable for detecting a wide range of soil N2O gas concentrations with a submerged silicone diffusion cell. A commercially available, 59 cm path-length gas cell, microelectromechanical systems (MEMS)-based infrared emitter, pyroelectric detector, two anti-reflective (AR) coated optical windows, and one convex lens were assembled into a simple instrument with secure preciseness and responsivity. Control of the IR emitter and data recording processes was achieved through a microcontroller unit (MCU). Tests on humidity tolerance and the saturation rate of the diffusion cell were carried out to test the instrument function with the soil atmosphere. The developed calibration model was validated by repeatability tests and accuracy tests. The soil N2O gas concentration was monitored at the laboratory level by a specific experimental setup. The coefficient of determination (R2) of the repeatability tests was more than 0.9995 with a 1–2000 ppm measurability range and no impact of air humidity on the device output. The new device achieved continuous measuring of soil N2O gas through a submerged diffusion cell.
Diatom frustules are incorporated into multilayer photoelectrodes intending to enhance efficiency in dye-sensitized solar cells utilizing their light interaction properties. A specific, but ...ubiquitous in all oceans, pennate-type diatom frustules were used to form the composite layers. Single, double, and triple-layer photoelectrodes were constructed with pure TiO2 (control measurements) as well as with a TiO2/diatom frustule composite. The electrodes were prepared using TiO2 nanoparticles of two sizes (13 and 21 nm) and were analyzed using UV visible absorption and XRD spectra. The morphology of frustules and electrodes were analyzed using scanning electron microscopy. The performance for each photoanode configuration was measured by assembling photoelectrochemical solar cells fabricated with a Pt counter electrode and a gel polymer electrolyte that excludes volatile solvents. The efficiency of the control cell is 3.37%. After replacing the topmost TiO2 layer with a TiO2/diatom frustule composite layer, efficiency increases to 6.78%. This is an impressive efficiency enhancement of 101%. The short circuit current density of frustule-incorporated three-layer cells is 18.1 mA cm−1 while for the control cell it is 8.98 mA cm−1. The enhanced efficiency of cells made with TiO2/diatom frustule composite electrodes and a polyethylene oxide-based gel polymer electrolyte can be attributed to the improved light absorption by the photoanode due to optical scattering and light-trapping effects caused by the presence of diatom frustules. Frustules also can assist in enhancing dye adsorption by increasing the effective specific surface area of the composite photoelectrode due to their nanoporous structure.
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•Diatom frustules are infused into TiO2 multilayer photoanodes to enhance DSSC efficiency.•Photoelectrodes with up to 3 layers of TiO2/diatom frustule were constructed.•101% efficiency boost is noted when frustules are impregnated to the topmost TiO2 layer.•Cells showed good short-term stability due to the use of apt gel polymer electrolyte.•Nanostructures of biological origin can be utilized to harness solar energy efficiently.
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