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Groundwater is the main source of drinking water for the rural population in the chronic kidney disease of unknown etiology (CKDu) zone of the North Central Province (NCP) in Sri Lanka. In this study, a total of 334 groundwater samples (311 dug wells, 21 tube wells and 2 springs) during the wet season from two aquifers in the NCP were collected, and investigated their chemical characteristics and evaluate their water quality, including groundwater chemistry, main ion sources, the corrosion and scaling potential of groundwater. The results showed that the two hydrochemical types of groundwater in the NCP were mainly of the Ca-HCO 3 , Na·Ca-HCO 3 types, with the main HCO 3 −, Na+ and Ca2+ ions in both types of groundwater originating from silicate and evaporite salt dissolution and influenced by alternating cation adsorption, while the presence of NO 3 − was mainly anthropogenic. Evaluation of water stability using namely Langelier saturation index (LSI), Ryznar stability index (RSI), Puckorius scaling index (PSI) and Larson-Skold index (LS), indicated that most groundwater presents corrosion potential and has corrosion behavior tendency of metals to some degrees. The water quality of Polonnaruwa was better than that of Anuradhapura in the NCP, and when the groundwater was worse than the "good" grade, which must be properly treated before it is used as drinking water. [ABSTRACT FROM AUTHOR]

To predict the process states of nonlinear distributed parameter systems (DPS) using various process variables, a novel multi-source spatiotemporal modeling method is proposed in this paper to improve conventional temporal modeling methods. To tackle the challenge of modeling industrial process data of DPS with multi-source spatiotemporal characteristics, a multi-source spatiotemporal network (MS-STN) model, which is the integration of a long short-term memory (LSTM) network to extract information containing temporal characteristics and a convolutional long short-term memory (ConvLSTM) network to extract information containing spatiotemporal characteristics, is constructed. The comprehensive use of various process information is beneficial to improving the fitting accuracy of the model, and the generalization ability of the model can be enhanced at the same time. To prevent the gradient vanishing or gradient explosion in presenting complex spatiotemporal data due to the increase of network layers, a model structure of the residual network based on ConvLSTM is proposed in performing model training. Finally, the industrial ethylene oxychlorination reaction process is taken as an example. The experimental results of predicting the temperature of the reaction tube well demonstrate the effectiveness of the proposed method. • Temporal models cannot meet requirements of distributed parameter system (DPS). • The multi-source spatiotemporal modeling method enhances state prediction of DPS. • LSTM and ConvLSTM extract temporal and spatiotemporal information, respectively. • ConvLSTM-based residual networks prevent gradient vanishing or gradient explosion. [ABSTRACT FROM AUTHOR]

The Salto–Arapey Aquifer System (SAAS) represents a complex hydrogeological framework composed of a detrital aquifer that lays over a fissured one in the Chaco-Paraná Basin. To enhance our understanding of this underground system, an initiative was undertaken to characterize a specific sector of the SAAS utilizing a geophysical methods known as Audiomagnetotelluric sounding. The primary outcomes of this endeavor include the geoelectrical characterizations of key formations and the development of a 2.5D geological-geophysical model. This endeavor significantly advances our geological and geophysical comprehension of the targeted sector, thereby offering substantial societal and economic benefits. Although the method did not allow differences between sedimentary formations, it did allow the recognition of altered basalts, which would facilitate the identification of areas with considerable potential for the productive development of water wells. Notably, this investigation holds significant local relevance as it presents a replicable methodology to characterize the rest of the system, or even aquifers sharing similar characteristics. [ABSTRACT FROM AUTHOR]

Concerns about the over-extraction of groundwater and the environmental effects of that have increased the need to change mental patterns about water consumption. This study is aimed on the psychological analysis of the blockage of unauthorized water wells in the agricultural sector of Iran through the integration of PMT and TPB models. The research model was tested with 384 farmers. A questionnaire was used for data collection, the validity and reliability of which were obtained to be at an optimal level. For testing the research hypotheses Smart-PLS4 software was used. The research findings showed that the effects of six variables being attitude, subjective norm, perceived severity, response cost, response efficacy, and self-efficacy on intention were significant; however, the effect of perceived vulnerability on intention was not significant. Based on structural equation modeling results, the intention variable mediates significantly the relationship between dependent and independent variables. The independent and mediating variables were able to explain 49 % of the variance of farmers' behavior toward blockage of unauthorized water wells. Other than providing a new theoretical perspective toward understanding the blocking behavior of unauthorized water wells, the present study findings provide valuable insights for enhancing conservation behavior. To encourage people to participate in conservation behaviors, practical suggestions are provided for relevant policy-makers and planners as well as water conservation advocates. • The study addresses the critical issue of groundwater depletion in Iran. • FCB and the determining factors of blocking unauthorized wells were identified. • IN is the most important variable influencing FCB. • The independent and mediating variables show the explanatory power of the model in optimal level. • The results showed that PV has no significant effect on IN. [ABSTRACT FROM AUTHOR]

• A framework integrates borehole and AEM data to map saltwater in aquifers. • Cokriging fuses AEM resistivity data obtained from different EM systems. • A power law converts electrical resistivity into chloride concentration in aquifers. • High-resolution 3D saltwater distribution is derived for the MRVA. Salinity in groundwater reduces crop productivity, drinking water quality, and economics. Saltwater plume mapping can provide crucial information for groundwater management. However, delineating saltwater plumes in aquifers is challenging and highly uncertain due to a lack of water quality data from water wells. This study introduces an integrated framework to map saltwater plumes in the agriculturally intensive Mississippi River Valley alluvial aquifer (MRVA) in northeast Louisiana using airborne electromagnetic (AEM) resistivity data. However, AEM resistivity data cannot distinguish saline sands from fine-grained sediments as both exhibit low resistivity values. To overcome this ambiguity, a lithofacies model is first constructed using borehole data through indicator kriging. Then, a 3D resistivity model is constructed for sand facies by fusing AEM resistivity data from two different airborne EM systems through a cokriging method. Finally, chloride concentration distribution in the MRVA is inferred by a resistivity-to-chloride concentration regression formula that is established using nearly collocated wells and AEM data points. The resistivity model shows the stratified pattern with low resistivity at the MRVA base, which resembles saltwater stratification. The salinity model shows that the highest chloride concentration zone coincides with the Jurassic Mississippi Salt Basin, indicating saltwater originates from the deep saline formations. Additionally, saline river water may also contribute salinity to the alluvial aquifer through surface water-groundwater interactions. The delineated saltwater plumes reveal saltwater upconing and proximity to pumping wells, providing unprecedented information to the agriculture sector. [ABSTRACT FROM AUTHOR]

In this paper, we propose a non-pretrained deep supervision network (NPD-Net) for polyp segmentation. Unlike previous deep supervision networks that rely on ground truth (GT) or pre-training with GT to supervise deep features(the prediction maps from decoder), we propose a novel deep supervision strategy that directly utilizes the GT encoder (that encodes GT to get its maps) after initialization to mitigate overfitting and enhance generalization ability without pre-training, in other words, a non-pretrained. This strategy makes up the gap of directly using GT for deep supervision while mitigates the risk of overfitting due to leverage the well-train pre-trained weights on a small polyp datasets. In addition, we introduce a simple and efficient parallel dual attention module (PDA) to enhance the global modeling ability. PDA executes spatial and channel attention in parallel, and adopts implicit positional encoding and transpose operation to reduce computational complexity. Finally, NPD-Net is able to effectively supervise deep features, expand the range of context information acquisition and improve segmentation performance, particularly in terms of generalization ability. Our experimental results on five benchmark datasets demonstrate that NPD-Net outperforms other state-of-the-art methods. The code will be available at https://github.com/guobaoxiao/NPD-Net. • We propose a novel non-pretrained deep supervision strategy for polyp segmentation. • We design a parallel dual attention module to enhance the global modeling ability. • The method has been evaluated widely, outperforming state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Sinkholes play a critical role in groundwater systems by facilitating both recharge and discharge of groundwater, serving as indicators of underlying geologic processes, shaping subsurface hydrology, and influencing water quality. Therefore, studying karst groundwater systems is essential for effective groundwater management, especially in areas with limestone sequences. Spatial variations of water isotopes (δ2H, δ18O), dissolved inorganic and organic carbon (DIC and DOC), including their isotopes alone with pH, EC, alkalinity and chloride were determined in surface- and groundwater of the Mulankavil karst aquifer basin in the northwest of Sri Lanka. Twenty-seven groundwater wells, one offshore spring and two sinkholes were selected for sampling. The contribution of sinkhole water and seawater to karst aquifers was calculated using δ18O and chloride as tracers. In addition, deuterium excess (d-excess) values were used to determine groundwater evaporative loss before infiltration. Near the Mulankavil sinkhole area, the mixing of surface water and infiltrating rainwater was found to vary between 26 and 60%, with an average of 56%. In contrast, surface water mixing in the Nagapadduvan and Vellankulam sinkholes was about 41–59% and 33–70%, respectively. In near coastal wells, these values fell to 20% due to the influence of seawater intrusion. During the dry season, groundwater d-excess varied between −5.0 and + 10.8‰, while surface water in sinkholes showed values between +1.8 and −9.4‰. Groundwater wells near the Mulankavil sinkhole showed lower DIC (<5.5 mmol/L) with enriched δ13C DIC (>-14‰). The karst aquifer systems in northern Sri Lanka exhibit two main recharge mechanisms: (a) selective recharge by surface water at sinkholes and (b) diffuse recharge by direct rainfall over the study area. Seawater intrusion near the coast can be prevented by artificially recharging rainwater during the monsoon season. [Display omitted] • The Mulankavil Karst groundwater basin is a vital freshwater reserve in Sri Lanka. • A geochemical proxy approach was used to quantify water fluxes from different sources. • The mixing of evaporated sinkholes and seawater determines the geochemistry of groundwater. • Conversion of DOC to DIC was evident in the studies of karst aquifer systems. [ABSTRACT FROM AUTHOR]

• Paper 5 of Hawaii play fairway project: results of slim-hole drilling on Lanai. • Lanai temperature gradient of 42 °C/km, bottom hole temperature at ∼1 km of 66 °C. • Detailed analyses of Lanai drill core, including stratigraphic column. • Successful community outreach on Lanai. This paper builds on four earlier papers detailing the results of the Hawai'i Play Fairway (PF) project's first two phases. In Phase 3 the project deepened a water well on the rim of the caldera of Lāna'i Volcano to a maximum depth of just over 1 km. Due to funding constraints, the project deepened an already existing water well that was proximal to our area of highest resource probability within the caldera. Drilling preparation included: completion of an Environmental Assessment, lowering a camera down the well, deviation logging, coordinating site preparation, procure and shipping, and participating in multiple community meetings. Drilling occurred 24/7 the entire month of June 2019. The project deepened Lāna'i Well 10 from 427 m to 1057 m, while collecting continuous core, and measured a roughly linear temperature gradient averaging 42 °C/km and a maximum bottom hole temperature of 66 °C. This gradient is more than twice the background for Hawai'i and within a range of gradients measured in this depth range for some exploration wells within the volcanically active East Rift Zone of Kīlauea Volcano. Geothermal gradient determinations and computed chemical geothermometer temperatures indicate that accessible temperatures within Lāna'i Well 10 are 130–200 °C between 2 and 3 km depth. This paper includes a summary of detailed core logging, which found pervasive hydrothermal alteration. We recommend drilling a slim hole within Lāna'i's caldera to ∼2 km, where considerably higher temperatures may be encountered. The positive implications this project's results have for the island of O'ahu are substantial. The shield stage of O'ahu's volcanoes ended 1–2 Million years earlier, however O'ahu uses more electricity than the rest of the islands combined. [ABSTRACT FROM AUTHOR]

In the US, violations of drinking water regulations are highest in lower-income rural areas overall, and particularly in Central Appalachia. However, data on drinking water use, quality, and associated health outcomes in rural Appalachia are limited. We sought to assess public and private drinking water sources and associated risk factors for waterborne pathogen exposures for individuals living in rural regions of Appalachian Virginia. We administered surveys and collected tap water, bottled water, and saliva samples in lower-income households in two adjacent rural counties in southwest Virginia (bordering Kentucky and Tennessee). Water samples were tested for pH, temperature, conductivity, total coliforms, E. coli , free chlorine, nitrate, fluoride, heavy metals, and specific pathogen targets. Saliva samples were analyzed for antibody responses to potentially waterborne infections. We also shared water analysis results with households. We enrolled 33 households (83 individuals), 82% (n = 27) with utility-supplied water and 18% with private wells (n = 3) or springs (n = 3). 58% (n = 19) reported household incomes of <$20,000/year. Total coliforms were detected in water samples from 33% (n = 11) of homes, E. coli in 12%, all with wells or springs (n = 4), and Aeromonas , Campylobacter , and Enterobacter in 9%, all spring water (n = 3). Diarrhea was reported for 10% of individuals (n = 8), but was not associated with E. coli detection. 34% (n = 15) of saliva samples had detectable antibody responses for Cryptosporidium spp. , C. jejuni , and Hepatitis E. After controlling for covariates and clustering, individuals in households with septic systems and straight pipes had significantly higher likelihoods of antibody detection (risk ratios = 3.28, 95%CI = 1.01–10.65). To our knowledge, this is the first study to collect and analyze drinking water samples, saliva samples, and reported health outcome data from low-income households in Central Appalachia. Our findings indicate that utility-supplied water in this region was generally safe, and individuals in low-income households without utility-supplied water or sewerage have higher exposures to waterborne pathogens. [ABSTRACT FROM AUTHOR]

The Be Well Home Health Navigator Program is a prospective, randomized controlled trial (RCT) implemented to compare a community health navigator program to usual care program to reduce contaminants in drinking water. This 4-year two-armed RCT will involve well owners in Oregon that have private drinking water wells that contain arsenic, nitrate, or lead above maximum contaminant levels. The intervention leverages the trusted relationship between Cooperative Extension Service (CES) Community Educators and rural well owners to educate, assist and motivate to make decisions and set actionable steps to mitigate water contamination. In this study, CES will serve as home health navigators to deliver: 1) individualized feedback, 2) positive reinforcement, 3) teach-back moments, 4) decision-making skills, 5) navigation to resources, 6) self-management, and 7) repeated contact for shaping and maintenance of behaviors. Usual care includes information only with no access to individual meetings with CES. Pre-specified primary outcomes include 1) adoption of treatment to reduce exposure to arsenic, nitrate, or lead in water which may include switching to bottled water and 2) engagement with well stewardship behaviors assessed at baseline, and post-6 and 12 months follow-up. Water quality will be measured at baseline and 12-month through household water tests. Secondary outcomes include increased health literacy scores and risk perception assessed at baseline and 6-month surveys. The results will demonstrate the efficacy of a domestic well water safety program to disseminate to other CES organizations. Trial registration number: NCT05395663 • Approximately 25% of private wells in the United States that are used for drinking water contain contaminants that are known to increase the risk of chronic diseases. • Homeowners are responsible for maintaining the quality of the drinking water provided by their private wells. • This intervention leverages the trusted relationships of Cooperative Extension Service Community Educators within local communities to educate, assist, and motivate well owners. [ABSTRACT FROM AUTHOR]

This paper describes development of a nitrate decision support tool for groundwater wells (GW-NDST) that combines nitrate leaching and groundwater lag-times to compute well concentrations. The GW-NDST uses output from support models that simulate leached nitrate, groundwater age distributions, and nitrate reduction rates. The support models are linked through convolution to simulate nitrate transport to wells. Spatially distributed parameters were adjusted through calibration to 34,255 nitrate sample targets. Prediction uncertainty is illustrated via Monte Carlo realizations informed during calibration. Over 78% of target concentrations were within the simulated range of results from 450 realizations. An example forecasting scenario illustrates that a range of feasible outcomes exist and should be considered when interpreting forecasts for decision making. Uncertainty in forecasting is unavoidable; the intent of characterizing uncertainty in the GW-NDST is to facilitate decision making by increasing insight into the response of nitrate contamination to physical and chemical processes. • This Decision Support Tool assists resource managers improve drinking water quality. • The flexible Reduced-Complexity framework matched nitrate concentrations in wells. • An Iterative Ensemble Smoother (IES) generated 450 posterior parameter realizations. • IES realizations were informed through Monte Carlo methods during calibration. • Six leaching reduction scenarios use uncertainty in nitrate concentration forecasts. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) contamination has been reported in all environmental compartments, but very limited information is available at higher-altitude lakes. Nainital Lake, located at a high altitude in the Indian Himalayas, has various ecosystem services and is the major source of water for Nainital town, but the MP abundance is still unknown. This study presents the first evidence of the abundance and distribution of MP in Nainital Lake. Surface water and sediment samples were analysed from 16 different sites in and around the catchment area of Nainital Lake. The MP were observed in all the samples, and their abundance in surface water was 8.6–56.0 particles L−1 in the lake and 2.4–88.0 particles L−1 in hotspot sites. In the surface sediment, MP abundance ranged from 0.4–10.6 particles g−1, while in the hotspot sediment, the mean abundance was 0.6 ± 0.5 particles g−1. Fibers were the dominant MP, while 0.02–1 mm were the predominant size of MP particles. The results of chemical characterization showed the presence of six polymers, among which high-density polyethylene was the most abundant. The Polymer Hazard Index assessment classified the identified polymers as low-to high-risk categories, with a higher abundance of low- (polypropylene) and medium- (polyethylene)-risk polymers. Tourist activities and run-off catchments can be considered the major sources of MP, which can affect the ecosystem. Minimal concentrations of MP were observed in the tube well and drinking water, which depicts the direct risks to humans and, thus, the need for remedial measures to prevent MP contamination in drinking water. This study improves the knowledge of MP contamination in the higher-altitude freshwater lake, which can be the major pathway for the transport of MP to the rivers, and also emphasizes the need for waste management in Nainital town. [Display omitted] • This is the first evidence of microplastics in the Nainital Lake in the Indian Himalayas. • The study observed that there is a significant amount of microplastic particles in and around Nainital Lake. • The chemical composition of microplastics was determined by SEM-EDX. • The possible sources were identified as domestic discharge and tourist activities. • The lake provides drinking water, and its contamination causes human health risks. [ABSTRACT FROM AUTHOR]

• Unique setup of rooftop rainwater harvesting and infiltration wells was tested. • Specific Infiltration Capacity parameter (SIC) was defined for dry and wet wells. • Wet well SIC was high and constant, while dry well SIC improved with time. • Both dry and wet wells were suitable to cope with amount of harvested rainwater. • Single wet well can be applied for several buildings in parallel. In urban environments there is a severe reduction of infiltration and groundwater recharge due to the existence of large impervious areas. During rain events, large volumes of water that could have recharged groundwater and surface water bodies are diverted into the municipal drainage system and lost from the freshwater storage. Moreover, extreme rain events impose high peak flows and large runoff volumes, which increase the risk of urban floods. Recent studies have suggested the use of rainwater harvesting for groundwater recharge, as a plausible solution for these challenges in dense urban environments. While the benefits of this approach are well understood, research on its practical, engineering, and hydrological aspects is relatively limited. The objective of the present study was to examine the use of infiltration wells for groundwater recharge with harvested rainwater collected from building rooftops under Mediterranean climate conditions. Two types of wells with similar hydraulic and technical properties were examined: a well that reaches the groundwater (wet well); and a well that discharges the harvested water into the unsaturated zone (dry well). Infiltration capacities of the wells were compared in controlled experiments conducted during summer months, and in operational recharge of harvested rainwater, during winter. Both dry and wet wells were found to be suitable for purposes of groundwater recharge with rooftop-harvested rainwater. Infiltration capacity of the wet well was about seven times greater than the infiltration capacity of the dry well. While the infiltration capacity of the wet well was constant throughout the entire length of the study (∼10 m3/h/m), the dry well infiltration capacity improved during winter (from 0.5 m3/h/m to 1.5 m3/h/m), a result of development of the dry well with time. Considering Tel-Aviv, Israel, as a case study for a dense modern city in a Mediterranean climate, it is demonstrated herein that the use of infiltration wells may reduce urban drainage by ∼40 %. [ABSTRACT FROM AUTHOR]

[Display omitted] • Regional faults control the groundwater flow along granular and fractured aquifers. • Local, intermediate, and regional flow systems were identified in groundwater. • Groundwater geochemical evolution shows significant water–rock interaction. • Baseline water quality is important for groundwater supply planning and management. Groundwater is the main source for domestic drinking water supply, irrigation, and industrial activities in Zacatecas in central Mexico, a good example for numerous semiarid regions worldwide, however, there is insufficient information about characterization and evolution of the baseline water quality to create hydrogeological conceptual models, fundamentals for the future planning of new sources of groundwater supply for the population, especially under ongoing global climate change conditions. By a multi-method analysis that included geological, geophysical, hydrochemical and isotopic tools this investigation allowed the identification of: a) local flows, represented by shallow groundwater and shallow wells, hosted over basin fill sediments with low average temperatures (≈ 23.3 °C), variation in water types related to anthropogenic activities, low trace elements concentrations, δ18O and δ2H signatures indicating surface water and tritium being present in this system, b) intermediate flows (25 °C), identified in wells with depths of 100 to 200 m, water circulating through the basin fill sediments and the sequence of volcanic rocks characterized by intermediate concentrations of trace elements, and groundwater ages calculated for this system vary from 1,000 to 6,000 years, c) regional flows in volcanic rocks, characterized by groundwater from wells with depths of more than 200 m, high temperatures (up to 31.5 °C) and elevated concentrations of trace elements. The δ18O and δ2H signals are more homogenous and the 14C residence times for this flow system are greater than 8,000 years, and d) regional flows in Cretaceous rocks, with depths greater than 400 m, the highest temperatures (≈ 43.7 °C) and intermediate concentrations of trace elements. The δ18O and δ2H signals are homogenous and δ13C can widely be associated with carbonate shales. The hydrogeochemical evolution has been documented along a 62 km flow line to develop a robust conceptual model, reflecting the water–rock interaction in the system. Physicochemical parameters, as well as major and trace element concentrations, reflect a distinct evolution according to the flow paths and their increase is generally proportional to the residence time. Likewise, processes of dissolution of feldspars and some clay minerals from initial weathering in the basin fill sediments, as well as devitrification of the glassy matrix in the volcanic rocks are taking place in the evolution of the system. The results obtained through the analysis of water–rock interaction in this research can be applied to other semi-arid regions with geogenically impacted aquifers, due to the geological and climatic similarity with numerous volcano-sedimentary basins around the world. [ABSTRACT FROM AUTHOR]

• Nonparametric kernel density estimator was used to calculate SGI. • Significant spatial variation in groundwater drought was observed across the region. • Groundwater drought is weakly connected to meteorological and agricultural droughts. • Agricultural irrigation and groundwater extraction influence groundwater drought. Groundwater drought is a significant type of hydrological drought and manifests as abnormal groundwater shortages as a result of prolonged drought propagation. This type of drought typically exhibits a longer duration than meteorological and agricultural droughts and can be severe in arid and semiarid regions. Human activities like pumping can further complicate the detection and characterization of groundwater drought. This study used long-term groundwater level monitoring data from 1991 to 2018 for the Yinchuan region to calculate a standardized groundwater level index and applied hierarchical clustering and the run theory to assess groundwater drought. Additionally, the relationship between groundwater and meteorological/agricultural droughts were investigated, and the factors driving groundwater drought were analyzed. Based on the results, regional groundwater droughts are becoming increasingly severe. In this study, there are regional differences in the trends of the standardized groundwater level index, which could be divided into three clusters (C1, C2, and C3). Wells in C2 are located near the Yellow River and show a shorter groundwater drought duration (mean value: 3.16 months), which means that these wells can recover from drought more quickly than those in the other clusters. Meteorological and agricultural droughts show a weak correlation with groundwater drought (with average cross-correlation coefficients of 0.03 and 0.25, respectively), and human activities most likely were the causes of regional groundwater droughts. Thus, a comprehensive understanding of regional groundwater droughts should consider human activities, in addition to the geographical location and natural environments. This research establishes a scientific foundation for managing regional groundwater resources and offers novel insights for future groundwater drought studies in the context of human activities. [ABSTRACT FROM AUTHOR]

In this paper we provide a local well posedness result for a quasilinear beam-wave system of equations on a one-dimensional spatial domain under periodic and Dirichlet boundary conditions. This kind of systems provides a refined model for the time-evolution of suspension bridges, where the beam and wave equations describe respectively the longitudinal and torsional motion of the deck. The quasilinearity arises when one takes into account the nonlinear restoring action of deformable cables and hangers. To obtain the a priori estimates for the solutions of the linearized equation we build a modified energy by means of paradifferential changes of variables. Then we construct the solutions of the nonlinear problem by using a quasilinear iterative scheme à la Kato. [ABSTRACT FROM AUTHOR]

A study was conducted to analyze the electrical resistivity structure of the Triassic Sandstone Aquifer in southeastern Tunisia in regions without constraints from nearby well data. The aim was to determine how the geometry, depth, thickness, and lateral extension of the aquifer within the Medenine region. Seven profiles, including two-dimensional profiles and vertical electrical soundings, were collected, with electrodes spaced between 4 and 5 m apart depending on the desired depth penetration. Geological outcrops and stratigraphic data from nearby water wells were used to constrain the final models, however these wells could only be used roughly as most of them were too far from a given profile. The models from two-dimensional inversions showed that the alluvium in the upstream region of Oued Nagueb had a maximum thickness of about 10 m, whereas in the downstream reaches, the thickness decreased to 4 m. The models indicated that the sandy clays of the alluvium may reduce the infiltration of surficial water into the Triassic Sandstone aquifer. The study area has a gradual thinning of the sedimentary cover from west to east, causing the Triassic Sandstone aquifer to deepen toward the west. The fine-grained sandstone which is characteristic of the Triassic Sandstone aquifer was detected at depths of approximately 40 m in the eastern region and more than 77 m in the western region of the study area. The electrical resistivity models imaged the Medenine fault, which may influence the structural configuration of the Triassic Sandstone aquifer. One model (ERT7) indicated that the Medenine fault acts as a water barrier and retards the groundwater movement of the aquifer. These findings provide information on the extent and depth of the aquifer for future groundwater exploration in the area and can serve as a reference model for analyzing aquifers in northeastern Tunisia. • Variation of thickness of the alluvium deposits in the upstream of Oued-Nagueb. • The sandy clays decrease the filtration of superficial water into the Aquifer. • The sedimentary cover thins from west to east, the aquifer is at 70m depth. • The aquifer is characterized by a fine-grained sandstone. • The Medenine fault is a structural barrier, it deforms the geometry of the rocks contains the aquifers. [ABSTRACT FROM AUTHOR]

With the increasing number of shale gas wells being hydraulically fractured with recycled flowback and produced water to reduce the consumption of fresh water, geochemical indicators of hydraulic fracturing flowback fluids (HFFFs) from such wells need to be found to evaluate the potential pollutants caused by shale gas development. To fill this knowledge gap, we analysed 64 HFFF samples from 3 Changning wells (fracked with recycled wastewater) to form a time series and compared them to HFFF samples from 3 Weiyuan wells (fracked with fresh water). We also made comparisons of HFFFs from two types of wells in the Appalachian Basin with reported data. The results indicated that regardless of the fracturing fluid being used, the water‒rock reaction caused by the hydraulic fracturing process resulted in the release of exchangeable phase elements, such as lithium, boron, with relatively depleted δ7Li and δ 11B, and strontium with relatively enriched 87Sr/86Sr values on the shale surface, into the HFFFs. The composition of the injected fracturing fluid affected the strength of the water‒rock reaction, but the effect is negligible, as the fracturing process can still form the unique Sr, Li, and B isotope ratios of the HFFF. Thus, the elemental signatures (B/Cl and Sr/Cl) and isotopic fingerprints (δ 11B, δ7Li, and 87Sr/86Sr) derived from HFFFs can be used to distinguish between HFFFs from wells hydraulically fractured by either fresh water or recycled wastewater and flowback water from conventional oil and gas wells. The results are important for the environmental evaluation of the large number of wells being fracked with recycled wastewater each year. [Display omitted] • δ 11B and 87Sr/86Sr can be used as indicator for HFFF in Changning field. • Hydraulic fracturing caused the release of minerals enriched in 10B, 6Li, and 87Sr. • Shale formation water composition determined the ratio between Na, Ca, Cl, and Br. • Fracturing fluid composition impact the major elements of HFFFs in the first dozens of days. [ABSTRACT FROM AUTHOR]

The second cohomology group of a left skew brace with coefficients in a trivial left brace with non-trivial actions is defined, its connection with extensions of a left skew brace by a trivial brace is established and a Wells' like exact sequence relating the second cohomology group with inducible automorphisms of an extension of left skew braces is constructed. [ABSTRACT FROM AUTHOR]

• OMZs developed in intermediate water of SE Levantine basin during early Holocene. • Oxygen status of overlying water defined by benthic forams, Fe speciation and RSTM. • Overlying water was anoxic non-sulphidic not euxinic as found in deep water at that time. • SEDEX P showed P was recycled into overlying water and fixed as apatite in sediment. • Speculated that modern OMZs possibly adjacent to major rivers could develop similarly. Oxygen Minimum Zones (OMZs) are expanding in modern oceans due to anthropogenically-driven climate and environmental change. In the Eastern Mediterranean Sea (EMS), OMZs developed in the early Holocene as a result of decreased intermediate water ventilation, increasing temperature, and increased Nile discharge and primary productivity. Here, we report benthic foraminiferal numbers (BFN) and species abundances, together with redox-sensitive trace metals (RSTM), and iron and phosphorus speciation from two sediment cores sampled at intermediate depths (1200 and 1430 m) from the SE Levantine shelf. The main aim of our study is to better understand the sequence of redox changes during sapropel S1 deposition caused by biogeochemical processes affecting the sapropel intermediate water mass. The use of benthic foraminifera indices (diversity and oxygen) together with iron speciation and RSTM (V, Mo and U) enables detailed description of the changing oxygen/redox status of the overlying water. Prior to sapropel S1 deposition at ∼10.2 ka BP, RSTM suggest that the overlying water was well oxygenated, but benthic foraminifera numbers (BFN) suggest that oxygen levels had already begun to decrease. There was then a pulse of increased export carbon from the enlarged Nile flood plume, as shown by increased BFN at the beginning of sapropel S1. Shortly after, RSTM and Fe-S systematics suggest that the water column transitioned from dysoxic to anoxic, non-sulfidic. Anoxic conditions then persisted at 1200 m depth, but RSTM and benthic foraminifera indices suggest that deeper waters at 1430 m were more likely dysoxic, until the 8.2 ka BP global cooling event. The benthic foraminifera and inorganic redox proxies then suggest a second period of anoxic, non-sulfidic conditions, with a gradual return to well ventilated waters at the end of sapropel deposition at ∼6 ka BP. There was enhanced burial of authigenic P throughout sapropel deposition, derived from the deposition and subsequent release of organic-P and iron bound-P during diagenesis. Phosphorus recycling from the sediment and in the overlying water column added reactive P to these mid-depth waters, a process which has the potential to result in a positive feedback in systems where such waters are upwelled into the photic zone. The past EMS thus represents a template which can be used to predict biogeochemical changes in settings that evolve towards anoxic, non sulfidic conditions, which may occur in some areas as modern climate and environment change causes the continued expansion of modern OMZs and hypoxic areas adjacent to modern major rivers. [ABSTRACT FROM AUTHOR]

Identification of paleowater in aquifers tapped for the public water supply is important both for sound water management, because paleowater is likely to be withdrawn unsustainably in high demand regions in the absence of large scale artificial recharge operations, and for contamination susceptibility assessment, because paleowater is typically isolated from contamination sources. In this study, paleowater, which herein includes pre-Holocene groundwater and also water that recharged well before the onset of significant human alteration of the hydrologic system in California, is identified using three key isotopic indicators of groundwater residence time: tritium (3H), radiocarbon (14C), and radiogenic helium-4 (4He rad). We compared results of these three tracers from a unique data set of more than 2000 wells that are predominantly long-screened drinking water production wells. Although considerable uncertainty is associated with calculated apparent ages for individual samples, non-parametric statistical tests indicate that the composite set of isotopic indicators support classification of samples into categories that allow identification of wells most likely to produce paleowater. Approximately 7% of the wells included in the study show strong evidence for producing paleowater, with screens extending greater than 146 m below ground surface, in which 3H activity is less than 1 pCi/L, 14C activity is less than 40.9 pmC, and 4He rad concentration exceeds 7.4 × 10−8 cm3STP/g water. An additional 22% of wells produce mixed-age water with a component of paleowater, with screens extending greater than 95 m below ground surface, in which 3H is less than 5 pCi/L, and 14C activity is less than 95.91 pmC. Wells in desert basins of southeastern California and wells in the southwestern quadrant of the Central Valley are most likely to produce paleowater that is pre-Holocene in age. Very few wells in the northwestern portion of the state, the foothills and Sierra Nevada regions, and coastal basins with intensive artificial recharge activities are categorized as producing paleowater. Climate is the primary control on paleowater occurrence, with arid portions of the state that were wetter during the Pleistocene having the largest number of wells categorized as producing paleowater. Secondarily, paleowater is found at the end of very long flow paths in confined aquifers, e.g., in the center of the Northern Sacramento Valley. In contrast, paleowater may be masked in areas where unconfined or semi-confined conditions allow substantial mixing between modern recharge and paleowater. Modern, artificially recharged water has replaced very old groundwater on a large scale in urban coastal basins. [ABSTRACT FROM AUTHOR]

Microbialites and abiogenic carbonates of the closed-basin hypersaline lake Laguna Negra (Catamarca Province, Argentina) are highly enriched in both 13C and 18O. These carbonates precipitate in the zone of recharge where lake water mixes with groundwater. We examined the processes controlling the isotopic evolution of input waters in order to better interpret the isotopic compositions of the carbonates. Large enrichments of 13C in dissolved inorganic carbon and 18O in water occur as input groundwater chemically evolves. These enrichments can be explained through the abiotic processes of water-equilibration, evaporation, degassing, and carbonate precipitation. The 13C and 18O contents of lake carbonates are consistent with equilibrium precipitation from lake water indicating that the currently ongoing processes can explain the isotopic patterns observed in carbonates. Isotopic compositions of these microbialites are largely unrelated to the biological processes controlling microbialite formation – a pattern that may be generalizable to other settings. However, the isotopic compositions of these microbialites record information about their depositional environment. [ABSTRACT FROM AUTHOR]

The hydrothermal geothermal heating depends heavily on the existence of hot water reservoir and the shallow ground source heat pump occupies large area. Here a single well geothermal heating (SWGH) technology is shown, which does not depend on the existence of hot water reservoir. An experimental research on SWGH is carried out and a mathematical model describing the heat transfer through surrounding rock to well tube as well as inside the geothermal well is developed. The mathematical model validated by experimental data is then used to predict the performance of SWGH. It is found that the average extracted thermal output is respectively 448.49 and 413.63 kW in the first and tenth heating seasons. By changing the injection water temperature and velocity, SWGH system can meet the requirement of building heating load varying with the outdoor air temperature and adjust the imbalance of the extracted thermal output among different heating seasons. Understanding these will enable us to better apply SWGH technology. • The experimental and simulation researches on single well geothermal heating are carried out. • A model describing the heat transfer has been validated against experimental data. • Well spacing should be more than 100 m with 10 years run for avoiding interference. • Well depth has important influence on the extracted thermal output. • The thermal output can be adjusted by changing injection temperature and velocity. [ABSTRACT FROM AUTHOR]

• Borehole temperature logs, the thermal parameters and five high-quality heat-flow values were reported. • The relationship between high heat flow in the Lu-zong Basin and high heat production in the upper crust were discussed. • The relationship between 350 °C isotherm along the STLFZ and the maximum depth of recorded seismicity were discussed. • The geodynamic implications of these heat-flow data were discussed. We present new heat flow and heat production data to constrain the lithospheric thermal structure along the southern Tan-Lu Fault Zone (STLFZ), a continuous active deep crustal fault zone in East Asia, and use these thermal data to infer how the thermal structure of the STLFZ influences regional focal depths. We report five new high-quality heat flow measurements derived from temperature–depth profiles at five well sites and detailed thermal conductivity measurements of 13 outcrop samples and 115 dry core samples from five wells along the STLFZ. We analyze these new data in combination with published data to derive a thermal profile along the STLFZ and map the 350 °C isotherm along the STLFZ, which correlates well with the maximum depth of recorded seismicity. The results indicate that: (1) the thermal gradient along the STLFZ increase from 22.2 °C km–1 in the south to 34.8 °C km–1 in the north; (2) heat flow values are in the 44.0–75.4 mW m–2 range along the STLFZ, with a mean value of 59.9 ± 10.5 mW m–2; (3) the highest heat flow value is located in Lu-Zong Basin, with extremely high radioactive heat production of 15–20 μW m–3 in the upper crust that may be related to local ore bodies; and (4) the bottom boundary of the shallow-earthquake seismic zone in the STLFZ coincides with the 350 °C isotherm. [ABSTRACT FROM AUTHOR]

Application of Aquifer Thermal Energy Storage with High Temperatures (HT-ATES) ranging from 60–90 ° C is a promising technique to store large amounts of energy in urban areas. However, these areas typically lack information on hydrogeological and thermal parameters of the subsurface to determine the potential for energy storage. Moreover, conventional exploration methods as pumping tests do not account for the variation in density caused by the high temperature gradients or changes in salinity as encountered in HT-ATES operation. The objective of this study is therefore to develop best practices for characterizing the hydrogeological and thermal properties of groundwater wells and their surrounding formation that determine the potential performance of HT-ATES-systems. In addition to conventional pumping tests, a set of Push–Pull tracer Tests (PPTs) with cold and hot water are proposed and scrutinized using Berlin as case study. There, the research well Gt BChb 1/2015, which is characterized by a reservoir temperature of 17 ° C at a depth between 220 und 230 m below ground surface was tested. In 2017, seven Slug-Withdrawal Tests (SWTs), a Step-Rate-Test (SRT), a production tests, and two Push–Pull tracer Tests (PPTs) with hot and cold water were performed during a period of 40 days. These tests were accompanied by Distributed-Temperature-Sensing (DTS) monitoring. The temperature measurements provide indications of injection areas based on the warmback period during a PPT with 81 ° C hot water. The determined aquifer transmissibility T = 3. 2 × 1 0 − 5 m 2 / s , the related Productivity Index (P I = 2. 0 m 3 / (h bar)), and maximum flow rates of about 5 m 3 / h indicate that the aquifer has potential for HT-ATES. However, the PPT and the DTS monitoring revealed cross flow between the target aquifer and an overlying aquifer. Thus, a new well with a design avoiding cross flow is required to utilize the aquifer's energy storage potential. A set of best practices for characterizing HT-ATES potential was derived from the experiences in this study. • A test program for the thermal-hydraulic-chemical characterization of ATES was developed. • With this test program, the charging and discharging periods, storage capacity and sustainability of the ATES can be proven. • Other methods such as DTS monitoring and numerical simulation support the aforementioned ATES characterization. [ABSTRACT FROM AUTHOR]

Asphaltene precipitation and its subsequent deposition always remain a major concern for Oil industry. Formulation of a comprehensive and reliable risk management system for asphaltene prone wells and fields is a challenging task because of the influence of diverse factors. In this study, a decision support system is developed for the asphaltene risk assessment in wells and fields. Since, the data present in the literature is scarce and not consistent, therefore, a hypothetical data of fields and their wells was considered to conduct the study comprehensively. Three hypothetical fields namely; Field A, Field B and Field C were assumed and in each field ten wells were taken into consideration. A decision support system for assessing the risk of asphaltene prone wells was developed using one of the popular and powerful multi-criteria decision making technique i.e. Fuzzy Technique for Order of Preference by Similarity to Ideal Solution (Fuzzy TOPSIS) coupled with Analytic Hierarchy process (AHP). The risk of wells was evaluated using three criteria namely; Detection, Severity and Controls. These criteria were further sub-divided into sub-criteria and their data was assumed. The assumed data was transformed into Triangular fuzzy numbers for calculations. According to the final outcomes, Field A was proved be the most risky field followed by Field B and in the last comes Field C. The outcomes were further validated by other method namely; Fuzzy Complex Proportional Assessment (COPRAS) and all TOPSIS outcomes were found in good relationship with Fuzzy COPRAS. The proposed methodology proposed in this study will be landmark in risk ranking of asphaltene prone wells and fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Precipitation, pumping, and tidal modules were designed to quantify GWL variation. • Transfer-function models and wavelet analysis were integrated to model 3 stresses. • Climate forcings can explain most of the GWL fluctuation in the unconfined aquifer. • Groundwater withdrawal is the dominant driver of GWLs in the confined aquifer. • The influence of tides on GWLs is minor compared to the other two stresses. In coastal aquifers, dynamic stresses such as climate forcings, groundwater withdrawals, and ocean tidal fluctuations cause nonlinear responses to groundwater levels. Such responses to the stresses impact groundwater resources and related flooding and infrastructure risks at multiple scales. We used time-series models such as transfer-function models and wavelet analysis to quantify the relative contribution of these stresses to groundwater-level fluctuation in wells from the unconfined and confined aquifers in an Atlantic coastal aquifer. Climate forcings, such as precipitation and temperature, explained most of the groundwater-level variation for wells in the unconfined aquifer, whereas groundwater withdrawals were the dominant driver of groundwater levels for wells in the confined aquifer. The impact of groundwater withdrawals also was detected in several wells in the unconfined aquifer. Although the influence of ocean tides on groundwater levels commonly is observed in coastal aquifers, we found that daily groundwater withdrawals can obscure the semi-diurnal coherence signal of the two series. The magnitude of groundwater-level fluctuation that could be explained solely by tides was minor compared to that explained by climate or withdrawal stresses. Transfer-function modeling showed seasonal withdrawals from wells in confined aquifers had a significant, yet heterogeneous influence on groundwater levels in coastal aquifers, which highlights climate and withdrawals as key compounding stresses in coastal hydrology. This study demonstrates the value of time-series approaches to advance characterization of groundwater systems in areas with limited hydrogeologic parameter information. [ABSTRACT FROM AUTHOR]

Spatial and temporal variations have been found in the levels of arsenic (As) throughout the groundwater of the Ghaghara basin. Fifteen out of twenty-five districts in this basin are reported to be affected by As, where the levels of As in groundwater and soil exceed the permissible limits set by the WHO (10 μgl−1) and FAO (20 mgkg−1) respectively. These districts include a total of four municipalities in Nepal and eighty-six blocks in India, all of which have varying degrees of As contamination. Approximately 17 million people are at risk of As poisoning, with more than two orders of magnitude higher potential lifetime incremental cancer risk, constituting over 153 thousand potential additional cases of cancer due to As-contaminated drinking water. Out of the 90 As-contaminated blocks in the Ghaghara basin, 4 blocks have about 7-fold higher potential risk of developing cancer, 49 blocks have 8–37-fold higher risk, and 37 blocks have up to 375-fold higher risk compared to the upper limit of the USEPA acceptable range, which is 1 × 10−6-1 × 10−4. High accumulation of As has been reported in the nails, hair, and urine of local inhabitants, with higher levels observed in females than males. The toxicity of As is manifested in terms of a higher occurrence of various diseases. Reproductive endpoints, such as increased incidences of preterm birth, spontaneous abortion, stillbirth, low-birth weight, and neonatal death, have also been reported in the basin. The level of As in tube wells has been found to be negatively correlated with the depth (r = −0.906), and tube wells with high levels of As (>150 μgl−1) are generally located within close proximity (<10 km) to abandoned or present meander channels in the floodplain areas of the Ghaghara river. In addition to As contamination, the water quality index (WQI) in the Ghaghara basin is poor according to the BIS standards for drinking water. Groundwater in six out of fifteen districts is unsuitable for drinking purposes, with a WQI exceeding 100. The levels of As in agricultural soil in many villages of Ballia, Bahraich, and Lakhimpur Kheri districts have exceeded the FAO limit. Water from deep tube wells has been found to be relatively safe in terms of As content, and thus can be recommended for drinking purposes. However, the use of surface water needs to be encouraged for irrigation purposes in order to preserve soil health and reduce As contamination in the food chain, thereby minimizing the risk of cancer. [Display omitted] • More than 17 million people are at risk of arsenic poisoning in the Ghaghara basin. • Potential cancer risk is more than two orders of magnitude higher than USEPA limit. • Arsenic accumulation is higher in hair and nails of female compared to males. • Area within 10 km distance from midstream of Ghaghara river is most contaminated. • Groundwater arsenic levels and depth of tube wells are inversely related. [ABSTRACT FROM AUTHOR]

• Global groundwater models predicted consistent heads for the Mediterranean basin. • Models performed better at low elevations than in mountainous areas. • Global models reproduced well the observed head trends in the Iberian Peninsula. • A geostatistical approach conditioning global models on observations is proposed. • Model conditioning with observations density of 3/1000 km2 or more is recommended. Groundwater is a strategic freshwater resource that is over-exploited in the Mediterranean region mainly for agricultural uses, leading to severe groundwater depletion in many aquifers. Uncertainties in groundwater availability are further exacerbated by climate change and its associated impacts. To address these challenges and ensure the longevity of this resource, sustainable groundwater management is essential. Unfortunately, our knowledge of groundwater status at the regional Mediterranean scale is limited due to the lack of consistent in-situ monitoring and data sharing. Groundwater modelling at the global scale offers a tool to evaluate the status of data-scarce regions. This study aims to assess steady-state water table depth in the Mediterranean region and its uncertainty by examining the simulations of three global gradient-based groundwater models. To examine these models' agreement with observed data, we focused for demonstration purposes on the Iberian Peninsula for its climatic diversity similar to that of the Mediterranean region and for its relatively high density of in-situ data. Results showed that the models represented reasonably well the observed groundwater heads of the Iberian Peninsula (R2 = 0.70–0.74). The models performed better at low elevations than in mountainous areas. To overcome the limitations of the regional models, a geostatistical approach is proposed to downscale the average of the three models for different subsets of the observed data (i.e., 10, 30, 50, and 70 %). Results revealed that when the average simulated groundwater depth was conditioned with at least 50 % of observations (equivalent to about three wells per 1000 km2), the spatial groundwater patterns in the Iberian Peninsula were well reproduced (R2 ≥ 0.65). Overall, this study shows that despite their underlying assumptions, global models can be used to map regional groundwater resources as long as they are conditioned on observed data. [ABSTRACT FROM AUTHOR]

Understanding water flow through discontinuities in rock masses is essential for ensuring the safety of engineering works, understanding the transport of contaminants, and directing the prospection and production of water in fractured aquifers. Investigation methods such as boreholes are expensive and not always effective. An alternative can be indirect investigation with electrical geophysical methods, such as Electrical Resistivity (ER) and Streaming Potential (SP), owing to their technical feasibility, low cost, and speed of execution. Although well established, doubts remain about these surveys owing to field limitations. In this sense, simulations in reduced physical models, where the internal and boundary conditions tend to be known, are ideal for testing these surveys. In this study, a rock mass model was developed with vertical fracturing patterns covered by soil; the entire set was saturated, thus reproducing the conditions common to areas of the crystalline basement with a tropical climate. With the use of ER and SP, the objective was to map the preferential flow directions with and without deep tube well influences and estimate fissure porosity. ER results showed an efficiency of 85% in the estimation of porosity, clearly distinguishing the main directions of anisotropy by the fractures. With SP, it was possible to identify flow directions through the fractures and define the geometry of the depression cone caused by pumping a deep tube well. Overall, these findings demonstrate the feasibility of physical models for understanding media with fissural porosity. Outcome of the SP survey in the reduced physical model of the fractured aquifer (a), with the simulation of pumping groundwater in a deep tube well, from the center (x = 0.25 m; y = 0.16 m). In the electrical potential isovalue map (b), the direction of the (blue) flow lines were interpreted by the J1 and J2 fracture sets. Red arrows emphasize the proximity of the well. The approximate elliptical area of influence (yellow) of the drawdown was plotted. The major axis "E", with 0.09 m-long, is oriented N-NE. [Display omitted] • The Wenner and Quadratic arrays of the azimuthal technique are efficient for identifying anisotropy. • The Azimuthal Technique is good for estimating fissural porosity. • ER integrated with SP determines the directions of groundwater flow. • The area and radius of influence of a deep tube well were estimated using the SP. [ABSTRACT FROM AUTHOR]

In the last decades, the intensification of agricultural practices has deeply altered nitrogen (N) and water cycles. Climate change and drought events are expected to further increase the human impacts on the hydrological and biogeochemical cycles, and these impacts are gaining the attention of the scientific community. Here we show how the Chiese River watershed (Lombardy Region, Italy) represents an interesting opportunity to analyse the effects of traditional irrigation practices on N contamination in the context of water scarcity. During summer, flood irrigation is mostly sustained by groundwater withdrawal. Additional water withdrawals from the river contribute to the dry out of the Chiese River. The use of wells for irrigation over permeable and fertilized soils and the percolation of nitrate (NO 3 -) from the vadose zone to groundwater result in the accumulation of NO 3 - in groundwater and limited N losses via denitrification due to dominant oxic conditions. These practices contrast other measures targeting the reduction of N excess over arable land. In the Chiese River watershed, the N surplus from Soil System Budget calculations decreased by 43% since the early 2000 s but NO 3 - concentration in groundwater remained high and stable (up to 98.0 mg NO 3 - L−1). The dried-out Chiese River gains groundwater and NO 3 - concentration at the river mouth approaches 32.2 mg NO 3 - L−1. Our results suggest how the mismanagement of the watershed (overabundant fertilization and flood irrigation using groundwater) increases the N concentration both in the river and groundwater, leading to the violation of both Nitrate and Water Framework directives. We anticipate our assay to be a starting point for the conversion of the northern Po Plain to more efficient irrigation and fertilization practices to contrast severe droughts driven by climate change like the one who struck the Po Plain in summer 2022. [Display omitted] • Variations in nitrate concentrations in a sub-basin of the Po Plain were evaluated. • The nitrogen input decreased from the 2000′s but contamination did not. • The irrigation practices promote the contamination of surface and groundwater. • Climate change and watershed mismanagement foster environment degradation. [ABSTRACT FROM AUTHOR]

The present study is to investigate resistance of an ITER divertor module against typical seismic loads. Two kinds of complex finite element (FE) models, which consists of cassette body, inner and outer vertical targets, dome and stabilizers, were developed; one is 1- or 2-layer simplified models without consideration of inner tubes. The other is a 3-layer detailed model with the inner tubes as well as cooling water. Modal analyses to predict dynamic characteristics were conducted in use of block-Lanczos algorithm for all the FE models. Subsequently, response spectrum analyses were performed by employing three modal combination techniques and taking into account different seismic magnitudes. Analysis results from the detailed model led to higher von-Mises stresses than those obtained from the simplified model. Moreover, calculated stress intensities at critical locations were compared with corresponding design stress intensities, according to ITER structural design criteria for in-vessel components, which satisfied sufficiently the structural assessment requirement. [ABSTRACT FROM AUTHOR]

• Analyzed well leakage risk at a brownfield geologic carbon storage site. • Considered several well leakage scenarios and risk mitigation strategies. • Used well attribute data to inform monitoring and mitigation decisions. • Presented a workflow for determining a risk-based post-injection site care period. • Found risk-based well leak mitigation strategy to be robust to uncertainty. Potential geologic carbon storage (GCS) sites with a history of oil and gas production have well-characterized injectivity and storage capacity, but the presence of legacy wells increases leakage risk. Thus, the success of GCS operations at sites with many wells will require a thorough leakage risk assessment and a robust strategy for managing well leakage risk over the lifetime of the project. In this study, we demonstrate a workflow that uses the National Risk Assessment Partnership's open-source Integrated Assessment Model to quantify well leakage risks and test the performance of various leakage risk management strategies at a heavily drilled GCS site. Our model simulates a 50-year basin-scale injection of CO 2 at a hypothetical site based on the Kimberlina Project Site in the Southern San Joaquin Valley of California. Brine and CO 2 leakage through 1000 legacy wells into a USDW are stochastically simulated as a proxy for risk. We consider multiple scenarios that explore the efficacy of various well leakage risk management strategies with changes in well leakage behavior, reservoir behavior, and post-injection site care (PISC) length. Predicted leakage at the site after 100 years was small with a maximum CO 2 leakage of 102.1 tonnes (4.08 × 10−5% of the 250 Mt injected) and a maximum brine leakage of 2.4 tonnes. Leakage risk management strategies based on accurate prior information about well leak probability reduced leakage risks more effectively at the modeled site and were more robust with respect to reservoir uncertainty than strategies based on the distance of the legacy well from the injector. The importance of the PISC period length was not clear as it had a negligible impact on CO 2 leakage risk but a sizable impact on brine leakage risk in our model. [ABSTRACT FROM AUTHOR]

A defect-free ZIF-8 membrane on a porous ceramic tube was well prepared by the self-conversion of ZnO nanorods in a zinc-free 2-methylimidazole (Hmim) water-solvent solution. In the synthesis, the ZnO nanorods grown on the substrate provide the zinc source and act as the nucleation and growth sites for the ZIF-8 membrane, thus contributing to the formation of a high-quality ZIF-8 membrane with the ideal selectivity of over 40 for H 2 /CH 4. Most importantly, it is found that after the one-time membrane synthesis, the used solution could be still recycled for the self-conversion of ZnO nanorods to ZIF-8 membranes. The results show that each self-converted synthesis merely consumed around 0.005 M ligand for achieving a continuous ZIF-8 membrane, and thus the solution with the ligand concentration of 0.5 M could be repeatedly used for at least 50 times for preparing compact ZIF-8 membranes without any treatment. Moreover, when the synthesis solution of around 0.2 M produced after the recycling for 60 times is recovered to the one of 0.5 M by adding fresh Hmim ligand, the obtained solution of 0.5 M could again act as the membrane synthesis one for the self-conversion of ZnO nanorods into the compact ZIF-8 membrane. Moreover, it could be also recycled for another 50 times for the synthesis of ZIF-8 membrane as the first-stage recycling, thus realizing a sustainable synthesis without any wastewater discharge. The present strategy is an environmental friendly and low-cost method for the scalable preparation of a ZIF-8 tubular membrane and of potential in practical applications. Image 1 • A ZnO nanorods self-converted strategy was employed to prepare a compact ZIF-8 membrane in a Zn-free water-solvent solution. • The synthesis solution could be recycled for over 50 times for growing dense ZIF-8 membranes without any treatment. • The strategy is a recyclable environmentally friendly synthesis process without any wastewater discharge. [ABSTRACT FROM AUTHOR]

Water injection is widely performed to enhance oil recovery in fossil energy development. The fracture initiation pressure (FIP) is a key parameter for designing the reasonable injection pressure for micro-fracturing water injection (MFWI). In this work, a modified method was presented to accurately predict the FIP, in which the thermal effect and plugging effect were considered; moreover, the stress around perforations was analyzed. To validate our method, the field tests, including a step rate test (SRT) and a well test, were conducted to obtain the actual FIP for perforated water injection wells, and then the FIP calculated by our method was compared with a low relative error of about 1.7%. Results show that (i) a greater temperature difference between the injected water and the formation forms a greater thermal stress around perforations, resulting in a greater change in the FIP; (ii) a larger skin factor causes a greater pressure drop for the injected water flowing through a plugged area, resulting in a stronger effective stress reduction around perforations and further producing a larger FIP. Therefore, our present work illustrates a better understanding of the stress distribution around a perforated wellbore, and paves a path for a more accurate prediction of the FIP in perforated water injection wells. • A model for predicting FIP in perforated water injection wells is proposed. • A step rate test and well tests were conducted. • A method for obtaining the actual FIP in perforated water injection wells is discussed. • The proposed method performs with a lower relative error than the existing models. [ABSTRACT FROM AUTHOR]

This study was aimed to investigate the potentially harmful elements (PHE) contamination and provenance in water and sediments of Zhob and Loralai valleys, northern Sulaiman fold belt (SFB), Baluchistan province, Pakistan. For this purpose, groundwater (springs, dug wells, bore wells and tube wells), surface water (Zhob River, Loralai River and tributaries) and sediments samples were collected and analyzed for physicochemical parameters including PHE. The concentrations of PHE including iron (Fe2+), nickel (Ni2+), lead (Pb2+), cobalt (Co2+), chromium (Cr3+) and cadmium (Cd2+) surpassed the world health organization (WHO) drinking water guidelines in 71%, 76%, 71%, 57%, 67% and 45% of samples in Zhob valley, respectively. Determined PHE concentrations in drinking water were evaluated for the potential risk assessment through average daily intake (ADI) and hazard quotient (HQ). Among PHE, the highest mean (0.12 mg/kg-day) ADI values were noted for Fe2+ and HQ for Cr3+ (1.95), surpassed the safe threshold limit in Zhob valley. Highest contamination factor (CF) values were found for Fe2+, Mn2+, Ni2+, Cu2+, Co2+, Cr3+ and Cd2+ in Zhob valley, while Zn and Pb in Loralai valley. Statistical analysis such as inter-metals correlation, one-way ANOVA and principal component analysis (PCA) showed that major sources of PHE contamination are geogenic. • Drinking water was analyzed for potentially harmful elements (PHE). • Certain PHE surpassed the WHO drinking water guidelines. • Chromium has HQ values >1 in Zhob valley. • Zhob valley has higher contamination level than Loralai valley. [ABSTRACT FROM AUTHOR]

• Nine groundwater level time-series with records of more than 100 years were analyzed. • First study of aquifer responses to the teleconnections AMO and ENSO in Europe. • Results are a valuable contribution to longer-term forecasting of groundwater levels. Groundwater is an important resource for drinking water supply, and is subject to natural variation as well as climate change effects. It has been shown that long-term natural variations of groundwater levels can often be attributed to climatic oscillations. Long-term groundwater level records are rare, but of special importance for the detection of longer, decadal to multi-decadal periodicities, which are vital for predictions of future development of groundwater levels and the distinction between natural variation and climate change effects. We have examined periodicities of nine groundwater level time-series with records of more than 100 years, as well as possible impacts of climatic teleconnections (NAO, AMO and ENSO) with wavelet analysis. The monitoring wells are located in Germany, Netherlands, UK and Denmark and cover different depths to groundwater, different aquifer types and hydraulic conditions. Our results show that all evaluated monitoring wells exhibit significant relations to long-term climatic periodicities of NAO, AMO and ENSO. Among the wells in phreatic porous aquifers, there is a signal damping, which can be related to the thickness of the unsaturated zone. Further, the damping is higher in the lower permeable aquifers and there is less damping in the karstic aquifers compared to the porous aquifers, in spite of a much thicker unsaturated zone. [ABSTRACT FROM AUTHOR]

• Water level in response to periodic loadings in two closely wells were compared. • Two wells show different response characteristics to different periodic loadings. • Permeability and noise perturbations lead to the different response sensitivity. Groundwater well can be used as a seismograph or as strainmeter, since the well water level is sensitive to seismic waves and other crustal strains through mechanical coupling between rock and groundwater. The use of the groundwater level in monitoring tectonic strain, however, is hindered by the enigmatic response discrepancy among wells (different responses may be recorded by even closely clustered wells). Therefore, understanding the factors that control the sensitivity of well-aquifer systems in response to different periodic loadings is important. In this paper, we analyzed two closely located wells that show no response to seismic waves and respond differently to earth tides and barometric pressure. We discuss these wells' sensitivity of response to periodic loadings by using the spectrum, barometric response function, tidal response, and slug test methods. Our results show that the different response characteristics are due to the differences in permeability and confinement of the well-aquifer systems. Well-aquifer systems with a low permeability cannot record coseismic responses, even if they can record clear tidal and barometric signals. In addition, periodic loading signals in shallow aquifers will be easily masked by the interference from the surface, for example rainfall or pumping, which diminishes the signal-to-noise ratio of the tectonic activity. Thus, the hydrogeological and tectonic settings are the two key factors that should be considered in choosing a suitable monitoring well location for tectonic strain monitoring. [ABSTRACT FROM AUTHOR]

• CO 2 gas bubbles are completely dissolved within 2 m above the seabed. • CO 2 is not emitted into the atmosphere but retained in the North Sea. • Dissolved CO 2 is rapidly dispersed by tidal currents in the North Sea. • Harmful effects on benthic biota occur in the direct vicinity of the leak. • Monitoring has to be performed at the seabed and close to the leak. Existing wells pose a risk for the loss of carbon dioxide (CO 2) from storage sites, which might compromise the suitability of carbon dioxide removal (CDR) and carbon capture and storage (CCS) technologies as climate change mitigation options. Here, we show results of a controlled CO 2 release experiment at the Sleipner CO 2 storage site and numerical simulations that evaluate the detectability and environmental consequences of a well leaking CO 2 into the Central North Sea (CNS). Our field measurements and numerical results demonstrate that the detectability and impact of a leakage of <55 t yr−1 of CO 2 would be limited to bottom waters and a small area around the leak, due to rapid CO 2 bubble dissolution in seawater within the lower 2 m of the water column and quick dispersion of the dissolved CO 2 plume by strong tidal currents. As such, the consequences of a single well leaking CO 2 are found to be insignificant in terms of storage performance. Only prolonged leakage along numerous wells might compromise long-term CO 2 storage and may adversely affect the local marine ecosystem. Since many abandoned wells leak natural gas into the marine environment, hydrocarbon provinces with a high density of wells may not always be the most suitable areas for CO 2 storage. [ABSTRACT FROM AUTHOR]

The geochemical response of produced water from coalbed methane (CBM) well group with multiple coal seams has rich geological significance. Taking 8 CBM wells of Songhe well group in western Guizhou as an example, the geochemical response characteristics and productivity significance of the CBM well group with multiple coal seams when inter-well interference or inter-layer interference appears have been examined mainly based on analyzing conventional ions, hydrogen and oxygen isotopes (δD and δ18O) of 7 batches of produced water samples in the stable production period of 1 year and 4 months, and dissolved inorganic carbon (DIC) stable isotopes (δ13C DIC) of 5 batches of produced water samples by cluster analysis and geological analysis methods. The study found that the change in dynamic fluid level has a good correlation with the Q-type clustering of δD-δ18O of produced water in the process of forming inter-well interference. With the formation of inter-well interference, the δD and δ18O clustering coefficient gradually decreases, and the fluids produced from the wells become more and more similar in property. In addition to the influence of drainage time, another main geological factor affecting inter-well interference is the buried depth of the coal seam. The larger the buried depth is, the larger the cumulative production of water, the faster the water circulation, the larger the Cl− concentration in produced water, the smaller the d-excess value (δD surplus index), and the smaller the cumulative production of CBM will be. In commingled CBM production of multiple coal seams, with larger span and multiple layers, inter-layer interference is likely to occur, resulting in unbalanced productivity contribution of the layers hard to tell. Because the δ13C DIC value in produced water from a well has a positive anomaly, the producing coal seams in the well are in the middle-upper layer of coal bearing strata; these coal seams have better permeability and higher water content, higher CO 2 concentration and lower heavy hydrocarbon gas concentration offsetting each other, together with other geological conditions, it is concluded that the relatively large amount of CO 2 formed by microbial reduction is the main cause of the positive δ13C DIC abnormality. Taking this well as the calibration well, combined with the Q-type clustering result of the δ13C DIC in produced water from the well group, considering the distribution of the developed coal seams and the change of the dynamical liquid level during the stable production period of the well group, the contribution of multi-coal layers in each well were estimated. If the cluster distance between the calibration well and another well is farther, the lower layer makes a larger contribution to the CBM productivity. If the cluster distance between the calibration well and another well is closer, the middle and upper layer contribute more to the CBM productivity, and it is mainly the production layers under the liquid level that produce CBM. This provides a unique hydrogeochemical analysis method for analyzing and identifying the contribution of production layers. • The change of dynamic fluid level in CBM group has a good correlation with the Q-type clustering of δD-δ18O of produced water in the process of forming inter-well interference • The larger the buried depth of CBM well is, the larger the cumulative production of water, the faster the water circulation, the larger the Cl- concentration in produced water, the smaller the d-excess value, and the smaller the cumulative production of CBM will be. • The δ13C DIC value of produced water is negative in wells in which deep production layers make more contribution to productivity; while the δ13C DIC value of produced water is positive and larger in wells in which shallow production layers make more contribution to productivity. [ABSTRACT FROM AUTHOR]

Highlights • Multi-level wells in multiple rock types were temporally sampled for δ2H and δ18O. • Isotopic periodicity in all rock types indicates strong surface connections. • Isotopic attenuation is highest with increased depth and matrix porosity. • Snowmelt recharge occurs through both long, slow and short, rapid flow paths. • Multi-level wells are vital for resolving flow and recharge processes in bedrock. Abstract The use of stable isotopes from precipitation as tracers in unconsolidated porous media can be limited due to attenuation in the unsaturated zone, yet this process has been poorly constrained in fractured rock. The complexities of fractured rock systems necessitate the use of multi-level monitoring wells for the measurement of isotopic tracers with depth. These methods, however, are rarely employed in groundwater flow and recharge studies, particularly involving temporal isotope measurements in multiple rock types. To understand the attenuation of isotopic snowmelt tracers in fractured rock and explore surface connections and recharge, an investigation was undertaken at three geologically-distinct field sites in south-eastern Ontario, Canada. Results of constant head injection tests at 2-m intervals were used to identify and isolate high transmissivity zones (2–3 in each well) for the construction of eight multi-level wells (22 intervals) used for groundwater sampling. Deuterium and oxygen-18 were measured in rain (n = 64), snow (n = 67), soil water (n = 118) and groundwater (n = 594) on a bi-weekly to monthly basis over two seasonal snowmelt cycles (>1.5 years). In combination with stable isotopes, measurements of hydraulic head, groundwater temperature, specific conductance and two rounds of tritium sampling contributed to the development of a conceptual model for snowmelt recharge and flow in sandstone, limestone and crystalline rock. Seasonal variation of δ2H and δ18O was observed in all rock types indicating recent recharge and strong surface connections. The dampening and residence time of the snowmelt tracer increased with depth in crystalline rock. Tracer attenuation was highest in higher-porosity sedimentary rock and strong confining conditions were observed to inhibit recent recharge. Substantial isotopic attenuation measured in the overburden indicated that the strong snowmelt signal measured in groundwater stemmed from water infiltrating through areas with thin or no overburden. Identification of the periodic trends and distinct isotopic horizons in this study would not have been possible without the use of multi-level wells. [ABSTRACT FROM AUTHOR]

Abstract The vulnerability of engineering barrier and the toxicity of leachate increase the need to maintain a certain buffering distance between landfill and drinking water sources. In order to provide decision-making support and technical guidance for the determination, and management of buffering distance, this paper coupled the dose-response model, leakage estimation model, exponential decay source model, and the advection-dispersion model for contaminants transportation and transformation in vadose and aquifer groundwater, and constructed an integral risk-based framework to help to calculate the buffering distance in shallow aquifers against the leachate contamination. Based on the framework and method, a case study is carried out. The results indicate that Zn and Ni have experience a similar dilution and attention process, but due to its smaller RDAF (required dilution and attenuation factor, equal to the ratio of initial concentration to limit concentration) value, Ni needs only a vertical separation distance (VSD) of 4 m (a 4 m vadose zone with saturated conductivity of 1 × 10-5 cm/s) without additional requirement on horizontal buffering distance. While, Zn requires an additional buffering distance of 380 m in addition to the VSD to achieve to be diluted/attenuated to a risk-acceptable level. 2,4-D has larger RDAF than Zn, but due to its difference in degradation characteristics from Zn, it also needs a smaller buffering distance (135 m) than Zn; Further studies shown that the sensitivity of the dilution and attenuation of heavy metals to distance is relatively weak, especially when the distance is greater than 800 m; organic pollutants are more sensitive to distance, even more than 800 m; for the landfill site to dispose organic pollutants, the buffering distance of 400 m is a conservative choice, while for sites to dispose heavy metal wastes, 400 m may be a risky decision and needs further calculation and demonstration. Highlights • Buffering distance, if properly set, helpful to prevent drinking well pollution. • Ni need no horizontal buffering distance, for its small requirement on DAF. • It increases to 380 m for Zn, for its required DAF is 2 times smaller than Ni. • 2,4-D, though large in required DAF, needs only 135 m for its high degradability. • For impractical larger distance, reduction on initial concentration is an alternative. [ABSTRACT FROM AUTHOR]

Highlights • Analytical model for describing drawdown induced by constant-head test at partially penetrating well are developed. • The three different outer boundaries of the aquifer system are considered. • The wellbore flow rate and pumping induced leakage rate(volume) solutions are obtained. • Characteristics of the drawdown, wellbore flowrate and leakage rate (volume) are discussed. • Sensitivity analysis for the change of the each of aquifer parameters on drawdown and wellbore flowrate is performed. Abstract An analytical model for describing pumping induced drawdown by constant-head test at a partially penetrating well in a leaky confined aquifer is developed by treating the leakage of aquitard storage as an interface phenomenon rather than an volumetric effect, which is the novel and never developed so far. Three different cases of remote lateral boundaries are considered in the model. The new drawdown solution in Laplace space is obtained and inverted into time-domain solution utilizing the Stehfest method. The (semi-)analytical solutions for well discharge are then obtained under three different cases. Analytical solutions in Laplace and time domains are developed for calculating the (total) leakage rate and volume across the aquitard-aquifer interface due to constant-head test at a partially penetrating well in a leaky confined aquifer, and such solutions are of great use for groundwater resource management. Based on the newly developed solutions, the distribution of wellbore flowrate and aquitard leakage are explored and the sensitivity analysis is conducted to identify the most important controlling factor. The sensitivity analysis shows that the wellbore flowrate and the drawdown in infinite (Case 1), finite (Case 2), and closed (Case 3) leaky confined aquifer systems are both sensitive to the variation of well partial penetration, well radius, and aquifer anisotropic ratio during the whole pumping period and they are most sensitive to the change of outer boundary distance at late time for Case 3. The effect of the outer boundary on the drawdown or wellbore flowrate is more significant for a shorter outer boundary distance. [ABSTRACT FROM AUTHOR]

Abstract In order to investigate the noise reduction effect of barrier with multi-well on its top. The effect of the layout of the wells was investigated by the 2D boundary element method (BEM). Results show that, the layout of the well would affect the noise reduction effect on receiver which is high from the ground, mainly in the mid frequency range. And the mainly concerned well should better be located close to the source side. Besides, the noise reduction effect relies on the sound diffraction around the top of the barrier, so, the layout of the walls of the wells also plays an important role to improve the performance of the barrier. Different kinds of layouts of the walls of the wells were also calculated and compared. Results show that, the noise reduction effect of the barrier is greatly affected by the layout of the walls of the wells. The performance of barrier which the layout of walls of the wells in ascending order of the heights from the source side to the receiver side is better than that in descending order. Experiments were also carried out in a semi-anechoic chamber, the experimental results agree well with the calculation results. [ABSTRACT FROM AUTHOR]

Abstract The article deals with geological and geomorphological conditions of the construction and functioning of wells from the Roman period of the Iron Age in a settlement on the Amber Road. This settlement is located in Central Poland (in the vicinity of Kwiatków village), on a flat surface of the lower terrace of the Warta River valley, among the dry channels of numerous streams cutting the terrace, which developed in three generations, from the Younger Dryas onwards. In the Holocene, the area was characterised by an abundance of flowing water in a multichannel system and the stability of the groundwater table. Among the archaeological features discovered there, the most interesting is a large complex of well-preserved wells dated to the early Roman period. The structures of the wells were based or dug in an organic series which constituted the terrace profile at a depth of between 2.0 and 2.5 m, dated to the late Alleröd and the Younger Dryas. In the study, the authors focus on the purpose of locating a large number of wells within a relatively small area abundant with numerous streams. The authors used a range of methods, including lithological and textural analyses, a geochronological analysis and a geochemical examination to describe the properties of the deposits and the quality of the waters. The characteristics of the wells were provided from dendrochronological studies. The archaeological approach included an analysis of the features morphology and the stage of technological advancement, as well as the diversity of the wells' casings. The spatial and functional relationships of the locations of the wells were also given special attention. [ABSTRACT FROM AUTHOR]

Abstract The downhole weight on bit (WOB) measurement sensor can produce significant inaccuracies in its readings owing to the effects of temperature variation and well pressure differential. To improve the accuracy of downhole WOB measurement, the impacts of temperature variation and pressure differential on WOB measurement were studied via theoretical derivations, laboratory experiments, and field experiments. Based on the constitutive equations of thermoelastic materials and the strain theory of strain gauge, the equation of error induced by temperature variation was deduced. Through laboratory experiments, the conventional temperature compensatory method, and the new compensatory temperature method proposed herein were compared. The experimental results show that the proposed new temperature compensatory method performed better in eliminating the effects of temperature variation. The shortcoming of the conventional WOB correction method for eliminating the pressure differential impact is that it does not consider the pressure drop in the drill motor. A new WOB correction method is proposed based on the momentum equation of flowing fluid and floating body theory. The field experimental results indicate that the measurement error of the conventional correction method could reach up to 80 kN. The work presented herein can serve as guidance for the downhole WOB measurement. Highlights • A new method for removing strain errors due to temperature variation was proposed. • A new correction method for eliminating pressure differential's impact on WOB measurement was proposed. • Laboratory and field experimental results indicated that the new methods performed better in WOB measurement. [ABSTRACT FROM AUTHOR]

Abstract Liquid loading is a serious issue in the production of gas wells. In order to recognize liquid loading, the flow regime and the transition criteria of the gas-liquid two-phase in the wellbore were obtained by theoretical analysis. The prediction correlation for the size of the entrained droplet was given for every flow pattern. Based on the force balance condition of the largest droplet in the gas core, the dimensionless critical gas mass flow rate was defined to recognize liquid loading along the whole wellbore. The influence of different factors on liquid loading was analyzed by an example. The results show that there are three kinds of flow regime in the wellbore, which are co-current annular flow with disturbance wave torn off, co-current annular flow with bag breakup and churn-annular flow with wave under-cut. The maximum size of the droplet in the gas core depends on the droplet breakup process under co-current annular flow and droplet entrainment process under churn-annular flow. The dimensionless critical gas mass flow rate decreases with the increase of gas flow rate and the decrease of tube diameter, which reduces the possibility of liquid loading. Liquid loading can be avoided by the decrease of surface tension. The viscosities of the gas and liquid phases have slight influence on the dimensionless critical gas mass flow rate. Highlights • Whole wellbore liquid loading recognition model was developed. • Dimensionless critical gas mass flow rate was defined to recognize liquid loading. • The maximum droplet size depends on both droplet entrainment and breakup process. • The size of the entrained droplet was predicted for each flow regime. [ABSTRACT FROM AUTHOR]

Abstract The Permian shale reservoir in southern Anhui province, East China is regarded as a promising target for shale gas exploration. In order to investigate the characteristics of shale pore structures and their controlling factors, total organic carbon (TOC), Rock-eval, organic petrology, X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), nitrogen gas adsorption (N 2 GA), mercury intrusion porosimetry (MIP) and helium pycnometry were conducted on the Permian shales collected from two shale gas parameter wells. The results indicate that the BET surface areas determined by N 2 GA method vary between 1.05 and 49.25 m2/g. The porosities derived from MIP and helium pycnometry tests are in the range of 0.68%–8.9% and 1.15%–9.79%, respectively. FE-SEM reveals that organic matter (OM) pores and cracks are well developed in the Permian shales, though some OM grains contain few pores, which might be related to the maceral composition. At a high maturity stage, vitrinite do not develop secondary OM pores, and sapropelinite generally develop abundant OM pores. However, solid bitumen occupies interparticle space between minerals grains, and generally contains a small amount of pores documented in studied samples. The TOC contents have a positive relationship with the BET surface areas, suggesting OM is a primary factor in micropore and fine mesopore (<10 nm) development. TOC content has a positive relationship with porosity for samples with TOC<6.16%, but samples with TOC>6.16% usually have a low porosity probably due to compaction and/or different organic fractions. Residual bitumen (S 1) is weakly and negatively correlated with Hg-porosity, due to residual bitumen filling in OM and mineral pores and reducing the total porosity. In addition, BET surface area decreases with increasing clay mineral content and Hg-porosity decreases with increasing quartz content, illustrating that clay mineral is unfavorable to the development of micropores and fine mesopores and high content of quartz may reduce macropore space. Finally, the shales of the Gufeng and Dalong Formations display a higher TOC content and a better physical property than the Longtan Formation shales and appear to be superior prospective shale gas exploration potential. Highlights • TOC content plays a complex role in pore structure affected by organic maceral and/or compaction. • Higher TOC sample generally contains more micropores and fine mesopores but less macropores. • Residual bitumen has a negative effect on pore system due to filling in OM and mineral pores. • The Dalong and Gufeng Formations have a better physical property than the Gufeng Formation. [ABSTRACT FROM AUTHOR]

Abstract A wellbore strengthening model for CBM drilling was analytically established based on the fracture mechanics, considering the cleat system. In this model, the stress field induced by the multi-cleats opened was firstly solved based on the fracture mechanics and the principle of the linear superposition. Especially, a failure criterion was introduced to judge whether the cleat was opening or closed. Then, the total stress was obtained by superimposing the stresses induced by the drilling fluid pressure, the formation pressure, the in-situ stress and the opened cleat. More importantly, the cleat-tip stress intensity factors before and after strengthening were calculated and compared to elaborate the validity of the wellbore strengthening. The results show that the cleat-tip stress intensity factors decreases obviously after the wellbore strengthening. Meanwhile, the analytical model shows an agreement to the finite element results for the stress distribution and the cleat-tip stress intensity factor. Finally, the parametric analysis was performed to reveal that: the smaller distance from the location of LCMs to the wellbore wall and the higher sealing efficiency of LCMs are positive for the wellbore strengthening; the larger number of cleats and the longer length of the opened cleat are harmful to the wellbore strengthening. This research has a contribution on establishing the wellbore strengthening model with multi-cleats. Highlights • Wellbore strengthening model is proposed considering complex distribution of cleat system. • The results of analytical model show a good agreement to those of finite element model. • Wellbore strengthening technology was verified by comparing stress intensity factor. • The parametric analysis on the cleat-tip stress intensity factor is performed. [ABSTRACT FROM AUTHOR]

[Display omitted] • In large-scale karst areas, COPK was modified to assess source vulnerability. • The spatial aggregation of groundwater vulnerability has been evaluated. • We used BI-LISA to assess the spatial relationship between vulnerability and nitrate. Groundwater protection and sustainable utilization of wells in large-scale karst areas face many challenges due to the complexity of numerous groundwater basins and aquifers. Therefore, scientific evidence is needed for groundwater management in these areas. A method combining source vulnerability, spatial autocorrelation, and bivariate spatial autocorrelation is proposed for groundwater management research. Based on the COP method (composed of flow Concentration, Overlying layers, and Precipitation regime), the COPK method is modified by replacing the sinkhole distance with sinkhole density, and incorporating land use and karst network development. The modified COPK method is used to evaluate the vulnerability of nitrate in groundwater in large-scale karst areas. Guizhou Province in China, which is a typical karst region, was evaluated as a study area. Comparatively to the classical COP method, the revised vulnerability map shows more areas of high vulnerability, mainly in the middle of the study area. According to the receiver operating characteristic curve (ROC) analysis, the modified method had a higher accuracy than the classical COP algorithm. Based on the accurate vulnerability index, vulnerability was classified using the natural break method, and the spatial autocorrelation of vulnerability clustering characteristics was studied. The source vulnerability was divided into High-High (HH), High-Low (HL), Low-High (LH), Low-Low (LL), and Not Significant (NS) clusters. This result can clarify the vulnerability clustering of groundwater in specific areas, thereby helping to improve groundwater management accuracy and efficiency. In addition, bivariate spatial autocorrelation was used to study the nitrate content of wells and source vulnerability. The bivariate local Moran's index showed a spatial negative correlation between the two. Similarly, the BI-LISA map can be used to characterize the spatial aggregation of nitrate content and well vulnerability. This result can help groundwater managers develop reasonable measures to protect water wells. [ABSTRACT FROM AUTHOR]