Repository for Oil and Gas Energy Research (ROGER)

Abstract:
This paper is the first of a two-part series designed to assess and summarize extant knowledge regarding hydraulic fracturing water and wastewater management practices using a comparative, multidisciplinary approach. To provide context for both papers, the water and wastewater practices are summarized for the four focus plays: Montney, Duvernay, Barnett, and Marcellus. In Alberta and British Columbia, which host the less-studied Duvernay and Montney plays, play-scale unconventional water and wastewater data are extracted and combined from three databases: FracFocus.ca, geoSCOUT, and AccuMap. A reasonable picture of hydraulic fracturing water use and practices in western Canada emerges from the over 4,000 wells studied. From late 2011 to early 2014, the average number of fracturing stages reported increased from 7 to over 14, while reported cumulative water use approached approximately 15 million m3 in 2013, the first year for which full data in all three databases was available. The majority of wells consuming 10,000 to 50,000 m3 of water are slickwater type, located largely in the two target plays; however, several wells using >50,000 m3 of water appear in the Horn River Formation in BC. While it is possible to identify in the databases wastewater treatment facilities and deep wastewater injection wells, it is at present difficult to constrain wastewater disposal practices and chemistry in Alberta and British Columbia. The analysis points to the need for further coordination between academics, industry, and governmental agencies to develop publicly available, searchable databases that carefully document water sourcing, wastewater recycling/reuse/disposal, and chemistry, in order to properly form hydraulic fracturing water management strategies.

Abstract:
The present study explores the feasibility of using the electrocoagulation (EC) process for the treatment and reuse of wastewater produced during shale gas recovery by hydraulic fracturing. The electrocoagulation process has been evaluated for the removal of suspended solids, total organic carbon (TOC) and scale (hardness) causing divalent cations, which, if untreated, can clog the gas well. Experiments were performed with actual shale gas wastewater (ASWW), synthetic shale gas wastewater prepared with low concentration of dissolved salts (SSWW – LDS) and synthetic shale gas wastewater prepared with a high concentration of dissolved salts (SSWW – HDS). EC is found to be effective for removing TOC and hardness from both the actual and synthetic shale gas wastewaters. The electric energy required per unit mass (EEM) for removal of TOC for ASWW, SSWW – LDS and SSWW – HDS are 243, 102 and 70 kWh/kg respectively. The EEM for removal of hardness for ASWW, SSWW – LDS and SSWW – HDS are 303, 104 and 25 kWh/kg respectively. The high conductivity of SSWW – HDS helps in achieving higher currents and hence the lower reported EEM values for SSWW – HDS. Also, under alkaline conditions, the performance of EC increases significantly. Combination of aeration with EC is also found to increase the performance of EC, especially for wastewater containing high concentrations of chloride ions.

Abstract:
Shale gas has emerged as a potential resource to transform the global energy market. Nevertheless, gas extraction from tight shale formations is only possible after horizontal drilling and hydraulic fracturing, which generally demand large amounts of water. Part of the ejected fracturing fluid returns to surface as flowback water, containing a variety of pollutants. For this reason, water reuse and water recycling technologies have received further interest for enhancing overall shale gas process efficiency and sustainability. Water pre-treatment systems (WPSs) can play an important role for achieving this goal. This paper introduces a new optimization model for WPS simultaneous synthesis, especially developed for flowback water from shale gas production. A multistage superstructure is proposed for the optimal WPS design, including several water pre-treatment alternatives. The mathematical model is formulated via generalized disjunctive programming (GDP) and solved by reformulation as a mixed-integer nonlinear programming (MINLP) problem, to minimize the total annualized cost. Hence, the superstructure allows identifying the optimal pre-treatment sequence with minimum cost, according to inlet water composition and wastewater-desired destination (i.e., water reuse as fracking fluid or recycling). Three case studies are performed to illustrate the applicability of the proposed approach under specific composition constraints. Thus, four distinct flowback water compositions are evaluated for the different target conditions. The results highlight the ability of the developed model for the cost-effective WPS synthesis, by reaching the required water compositions for each specified destination.

Abstract:
We report the 5,425,832 bp draft genome of Pseudomonas sp. strain BDAL1, recovered from a Bakken shale hydraulic fracturing-produced water tank metagenome. Genome annotation revealed several key biofilm formation genes and osmotic stress response mechanisms necessary for survival in hydraulic fracturing-produced water.

Abstract:
Rapid growth in unconventional oil and gas (UOG) has produced jobs, revenue, and energy, but also concerns over spills and environmental risks. We assessed spill data from 2005 to 2014 at 31 481 UOG wells in Colorado, New Mexico, North Dakota, and Pennsylvania. We found 2–16% of wells reported a spill each year. Median spill volumes ranged from 0.5 m3 in Pennsylvania to 4.9 m3 in New Mexico; the largest spills exceeded 100 m3. Seventy-five to 94% of spills occurred within the first three years of well life when wells were drilled, completed, and had their largest production volumes. Across all four states, 50% of spills were related to storage and moving fluids via flowlines. Reporting rates varied by state, affecting spill rates and requiring extensive time and effort getting data into a usable format. Enhanced and standardized regulatory requirements for reporting spills could improve the accuracy and speed of analyses to identify and prevent spill risks and mitigate potential environmental damage. Transparency for data sharing and analysis will be increasingly important as UOG development expands. We designed an interactive spills data visualization tool (http://snappartnership.net/groups/hydraulic-fracturing/webapp/spills.html) to illustrate the value of having standardized, public data.

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This paper introduces a new optimization model for the single and multiple-effect evaporation (SEE/MEE) systems design, including vapor recompression cycle and thermal integration. The SEE/MEE model is specially developed for shale gas flowback water desalination. A superstructure is proposed to solve the problem, comprising several evaporation effects coupled with intermediate flashing tanks that are used to enhance thermal integration by recovering condensate vapor. Multistage equipment with intercooling is used to compress the vapor formed by flashing and evaporation. The compression cycle is driven by electricity to operate on the vapor originating from the SEE/MEE system, providing all the energy needed in the process. The mathematical model is formulated as a nonlinear programming (NLP) problem optimized under GAMS software by minimizing the total annualized cost. The SEE/MEE system application for zero liquid discharge (ZLD) is investigated by allowing brine salinity discharge near to salt saturation conditions. Additionally, sensitivity analysis is carried out to evaluate the optimal process configuration and performance under distinct feed water salinity conditions. The results highlight the potential of the proposed model to cost-effectively optimize SEE/MEE systems by producing fresh water and reducing brine discharges and associated environmental impacts.

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Management of shale gas wastewater treatment, disposal, and reuse has become a significant environmental challenge, driven by an ongoing boom in development of U.S. shale gas reservoirs. Systems-analysis based decision support is helpful for effective management of wastewater, and provision of cost-effective decision alternatives from a whole-system perspective. Uncertainties are inherent in many modeling parameters, affecting the generated decisions. In order to effectively deal with the recourse issue in decision making, in this work a two-stage stochastic fracturing wastewater management model, named TSWM, is developed to provide decision support for wastewater management planning in shale plays. Using the TSWM model, probabilistic and nonprobabilistic uncertainties are effectively handled. The TSWM model provides flexibility in generating shale gas wastewater management strategies, in which the first-stage decision predefined by decision makers before uncertainties are unfolded is corrected in the second stage to achieve the whole-system’s optimality. Application of the TSWM model to a comprehensive synthetic example demonstrates its practical applicability and feasibility. Optimal results are generated for allowable wastewater quantities, excess wastewater, and capacity expansions of hazardous wastewater treatment plants to achieve the minimized total system cost. The obtained interval solutions encompass both optimistic and conservative decisions. Trade-offs between economic and environmental objectives are made depending on decision makers’ knowledge and judgment, as well as site-specific information. The proposed model is helpful in forming informed decisions for wastewater management associated with shale gas development.

Abstract:
Hydraulic fracturing used for natural gas extraction from unconventional onshore resources generates large quantities of produced water that needs to be managed efficiently and economically to ensure sustainable development of this industry. Membrane distillation can serve as a cost effective method to treat produced water due to its low energy requirements, especially if waste heat is utilized for its operation. This study evaluated the performance of commercially available hydrophobic microfiltration membranes in a direct contact membrane distillation system for treating very high salinity (i.e., up to 300,000 mg/L total dissolved solids) produced water. Polypropylene and polytetrafluoroethylene membranes yielded the highest permeate flux with membrane distillation coefficient of 5.6 l/m2/hr/kPa (LMH/kPa). All membranes showed excellent rejection of dissolved ions, including naturally occurring radioactive material (NORM), which is a significant environmental concern with this high salinity wastewater. Analysis of membranes after extended testing with actual produced waters revealed unevenly distributed inorganic deposits with significant iron content. A key finding of this study is that the iron oxide fouling layer had negligible effect on membrane performance over extended period of time despite its thickness of up to 12 µm. The results of this study highlight the potential for employing membrane distillation to treat high salinity wastewaters from unconventional gas extraction.

Abstract:
The purpose of the study was to separate and identify the unknown surfactants present in flowback and produced water from oil and gas wells in the Denver-Julesburg Basin (Niobrara Formation) in Weld County, Colorado, USA. Weld County has been drilled extensively during the last five years for oil and gas between 7000–8000 feet below land-surface. Polypropylene glycols (PPGs) and polyethylene glycols carboxylates (PEG-Cs) were found for the first time in these flowback and produced water samples. These ethoxylated surfactants may be used as friction reducers, clay stabilizers, and surfactants. Ultrahigh-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry (UHPLC/QTOF-MS) was used to separate and identify the different classes of PPGs, PEG-Cs, and their isomers. The Kendrick mass scale was applied along with mass spectrometry/mass spectrometry (MS-MS) with accurate mass for rapid and unequivocal identification. The PPGs and their isomers occur at the ppm concentration range and may be useful as “fingerprints” of hydraulic-fracturing. Comparing these detections to the compounds used in the fracturing process from FracFocus 3.0 (https://fracfocus.org), it appears that both PPGs and polyethylene glycols (PEGs) are commonly named as additives, but the PEG-Cs have not been reported. The PEG-Cs may be trace impurities or degradation products of PEGs.

Abstract:
Microbial activity in the produced water from hydraulically fractured oil and gas wells may potentially interfere with hydrocarbon production and cause damage to the well and surface infrastructure via corrosion, sulfide release, and fouling. In this study, we surveyed the microbial abundance and community structure of produced water sampled from 42 Marcellus Shale wells in southwestern Pennsylvania (well age ranged from 150 to 1846 days) to better understand the microbial diversity of produced water. We sequenced the V4 region of the 16S rRNA gene to assess taxonomy and utilized qPCR to evaluate the microbial abundance across all 42 produced water samples. Bacteria of the order Halanaerobiales were found to be the most abundant organisms in the majority of the produced water samples, emphasizing their previously suggested role in hydraulic fracturing related microbial activity. Statistical analyses identified correlations between well age and biocide formulation and the microbial community, in particular the relative abundance of Halanaerobiales. We further investigated the role of the order Halanaerobiales in produced water by reconstructing and annotating a Halanaerobium draft genome (named MDAL1), using shotgun metagenomic sequencing and metagenomic binning. The recovered draft genome was found to be closely related to the species H. congolense, an oil-field isolate, and Halanaerobium sp. T82-1, also recovered from hydraulic fracturing produced water. Reconstruction of metabolic pathways revealed Halanaerobium sp. MDAL1 to have the potential for acid production, thiosulfate reduction, and biofilm formation, suggesting it have the capability to contribute to corrosion, souring, and biofouling events in the hydraulic fracturing infrastructure. Importance There are an estimated 15,000 unconventional gas wells in the Marcellus Shale region, each generating up to 8000 liters of hypersaline produced water per day throughout their lifetime (1-3). Microbial activity in produced waters could lead to issues with corrosion, fouling, and souring, potentially interfering with hydraulic fracturing operations. Previous studies have found microorganisms contributing to corrosion, fouling, and souring to be abundant across produced water samples from hydraulically fractured wells (4-12); however, these findings were based on a limited number of samples and six total well sites. In the current paper we investigate the microbial community structure in produced water samples from 42 unconventional Marcellus Shale wells, confirming the dominance of the genus Halanaerobium in produced water and its metabolic potential for acid and sulfide production and biofilm formation.

Abstract:
Wastewaters from oil and gas development pose largely unknown risks to environmental resources. In January 2015, 11.4 M L (million liters) of wastewater (300 g/L TDS) from oil production in the Williston Basin was reported to have leaked from a pipeline, spilling into Blacktail Creek, North Dakota. Geochemical and biological samples were collected in February and June 2015 to identify geochemical signatures of spilled wastewaters as well as biological responses along a 44-km river reach. February water samples had elevated chloride (1030 mg/L) and bromide (7.8 mg/L) downstream from the spill, compared to upstream levels (11 mg/L and < 0.4 mg/L, respectively). Lithium (0.25 mg/L), boron (1.75 mg/L) and strontium (7.1 mg/L) were present downstream at 5–10 times upstream concentrations. Light hydrocarbon measurements indicated a persistent thermogenic source of methane in the stream. Semi-volatile hydrocarbons indicative of oil were not detected in filtered samples but low levels, including tetramethylbenzenes and di-methylnaphthalenes, were detected in unfiltered water samples downstream from the spill. Labile sediment-bound barium and strontium concentrations (June 2015) were higher downstream from the Spill Site. Radium activities in sediment downstream from the Spill Site were up to 15 times the upstream activities and, combined with Sr isotope ratios, suggest contributions from the pipeline fluid and support the conclusion that elevated concentrations in Blacktail Creek water are from the leaking pipeline. Results from June 2015 demonstrate the persistence of wastewater effects in Blacktail Creek several months after remediation efforts started. Aquatic health effects were observed in June 2015; fish bioassays showed only 2.5% survival at 7.1 km downstream from the spill compared to 89% at the upstream reference site. Additional potential biological impacts were indicated by estrogenic inhibition in downstream waters. Our findings demonstrate that environmental signatures from wastewater spills are persistent and create the potential for long-term environmental health effects.

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Fracturing waste liquid (FWL) generates during shale gas extraction and contains high concentrations of suspended solid, salinity and organic compounds, which needs well management to prevent excessive environmental disruption. Biological treatment of the FWL was attempted in this study using membrane coupled internal circulation aerobic biological fluidized bed (MC-ICABFB) after being treated by coagulation. The results showed that poly aluminium chloride (PAC) of 30 g/L, polyacrylamide (PAM) of 20 mg/L and pH of 7.0 were suitable choices for coagulation. The pretreated FWL mixed with synthetic wastewater at different ratios were used as the influent wastewater for the reactor. The MC-ICABFB had relatively good performance on COD and NH4+-N removal and the main residual organic compound in the effluent was phthalates according to the analysis of GC-MC profiles. In addition, a suitable pretreatment process for the FWL to facilitate biological treatment of the wastewater needs further research.

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Membrane distillation (MD), often integrated with crystallization (MDC), is an attractive treatment option for shale gas produced water (SGPW) because of its ability to handle high salinity as well as the inherent geothermal heat available to this process. To evaluate the feasibility of applying MD process for SGPW treatment, membrane fouling and wetting, which are barrier to its practical application, were systematically examined by varying organic and inorganic constituents, simulating the SGPW from Marcellus shale (USA). The liquid entry pressure (LEP) was first measured to predict the possibility of wetting by the chemical constituents of SGPW, and then a series of lab-scale MD and MDC experiments were performed to elucidate membrane wetting mechanisms. The results revealed that membrane wetting became more pronounced in the presence of oil and grease. The inorganic scaling induced by multivalent ions, such as barium and calcium in SGPW, also enhanced membrane wettability and led to poor permeate water quality. By integrating with crystallization, scalant loading was reduced properly and thus membrane wetting was mitigated effectively. As a result, adopting this MDC process increased total recovery up to 62.5%. Our experimental observations demonstrated that MD could be sustainably operated for SGPW treatment through optimized crystallization for scaling removal as well as effective pre-treatment for organic removal.

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We provide a critical review of existing research and information regarding the sources of risk associated with on-site shale gas and tight oil wastewater storage in the United States, the gaps that exist in knowledge regarding these risks, policy and technology options for addressing the risks, and the relative merits of those options. Specifically, we (a) identify the potential risks to human and ecological health associated with on-site storage of shale gas and tight oil wastewater via a literature survey and analysis of data on wastewater spills and regulatory violations, (b) provide a detailed description of government regulations or industry actions that may mitigate these risks to human and ecological health, and (c) provide a critical review of this information to help generate progress toward concrete action to make shale gas and tight oil development more sustainable and more acceptable to a skeptical public, while keeping costs down.

Abstract:
A holistic risk assessment of surface water (SW) contamination due to lead-210 (Pb-210) in oil produced water (PW) from the Bakken Shale in North Dakota (ND) was conducted. Pb-210 is a relatively long-lived radionuclide and very mobile in water. Because of limited data on Pb-210, a simulation model was developed to determine its concentration based on its parent radium-226 and historical total dissolved solids levels in PW. Scenarios where PW spills could reach SW were analyzed by applying the four steps of the risk assessment process. These scenarios are: (1) storage tank overflow, (2) leakage in equipment, and (3) spills related to trucks used to transport PW. Furthermore, a survey was conducted in ND to quantify the risk perception of PW from different stakeholders. Findings from the study include a low probability of a PW spill reaching SW and simulated concentration of Pb-210 in drinking water higher than the recommended value established by the World Health Organization. Also, after including the results from the risk perception survey, the assessment indicates that the risk of contamination of the three scenarios evaluated is between medium-high to high.

Abstract:
Hydraulic fracturing is an industrial process allowing for the extraction of gas or oil. To fracture the rocks, a proprietary mix of chemicals is injected under high pressure, which later returns to the surface as flowback and produced water (FPW). FPW is a complex chemical mixture consisting of trace metals, organic compounds, and often, high levels of salts. FPW toxicity to the model freshwater crustacean, Daphnia magna, was characterized utilizing acute (48 h median lethal concentrations; LC50) and chronic (21 d) exposures. A decrease in reproduction was observed, with a mean value of 18.5 neonates produced per replicate over a 21-d chronic exposure to 0.04% FPW, significantly decreased from the average of 64 neonates produced in controls. The time to first brood was delayed in the highest FPW (0.04%) treatment. Neonates exhibited an LC50 of 0.19% of full-strength FPW, making them more sensitive than adults, which displayed an LC50 value of 0.75%. Quantitative PCR highlighted significant changes in expression of genes encoding xenobiotic metabolism (cyp4) and moulting (cut). This study is the first to characterize chronic FPW toxicity and will help development of environmental monitoring and risk assessment of FPW spills.

Abstract:
Microorganisms present in production facilities of shale gas can cause substantial increases in production costs and complicate water management. Here, an uncommon microbial distribution was observed at six gas-gathering stations of deep shale wells (average depth: 4162 m) in Sichuan Basin, China. Employing Illumina MiSeq 16S rRNA gene sequencing and quantitative polymerase chain reaction (qPCR), the majority of bacterial communities in gas-water separators and water storage tanks sampled belonged to the genus Shewanella (accounting for 60.67% of total bacterial sequences detected) as well as Marinobacter, Marinobacterium, Arcobacter, Acetobacterium, Alkalibacter that were encountered in previously reported shale produced water. Archaea were mainly methylotrophic and halotolerant methanogenic genera, including Methanolobus, Methanohalophilus, and Methanocalculus. For the first time, fungi (primarily Ascomycota and Basidiomycota) were detected in the produced water from production facilities, and some genera, such as Cladosporium, may be associated with corrosion. Apart from Shewanella, other sulfidogenic taxa mainly belonging to Dethiosulfovibrio, Dethiosulfatibacter and acid producers belonging to Acetobacterium were also encountered. Microbial communities in storage tanks were more abundant and diverse than that in separators. Notably, detection of biocorrosive sulfate-reducing bacteria (SRB), increased from separators (0.39%) to storage tanks (2.37%). This study expands our knowledge about microbial diversity in production facilities of shale gas and the findings may have implications in guiding wastewater management during shale gas production.

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The logistical issues surrounding the timing and transport of flowback generated by each shale gas well to the next is a big challenge. Due to more and more flowback being stored temporarily near the shale gas well and reused in the shale gas development, both transportation cost and storage cost are the heavy burden for the developers. This research proposed a theoretical cost optimization model to get the optimal flowback distribution solution for regional multi shale gas wells in a holistic perspective. Then, we used some empirical data of Marcellus Shale to do the empirical study. In addition, we compared the optimal flowback distribution solution by considering both the transportation cost and storage cost with the flowback distribution solution which only minimized the transportation cost or only minimized the storage cost.

Abstract:
Hydrocarbons produced via hydraulic fracturing of shale formations frequently contain elevated quantities of Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) that are difficult to dispose of and can be harmful to the environment. This research investigates the elemental composition of seven major shale formations at the bulk and microstructural scale to better understand the relationship between major naturally occurring radioactive elements (NORM) and organic phases within shales. Bulk mineralogy analysis was performed via powder X-ray diffraction to identify which shales were ideal for hydraulic stimulation based on the content of ductile and brittle minerals. To complement the XRD, Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN®) was performed to identify non-crystalline phases and provide spatial mapping of the minerals through the shale samples. In addition, XRD and QEMSCAN were used to determine the total sulfur and carbonate content as this greatly contributes to the acidity of the shale and subsequently, U and Th migration. Select samples were characterized by scanning electron microscopy - energy dispersive x-ray spectroscopy (SEM/EDX) to reveal the presence of heavy metals (i.e. U, Pb) near hydrocarbon-rich regions of the shale. The NORM content and organic content were also correlated using gamma well logging.

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Abstract:
Fluids injected into shale formations during hydraulic fracturing of black shale return with extraordinarily high total-dissolved-solids (TDS) and high concentrations of barium (Ba) and radium (Ra). Barite, BaSO4, has been implicated as a possible source of Ba as well as a problematic mineral scale that forms on internal well surfaces, often in close association with radiobarite, (Ba,Ra)SO4. The dissolution of barite by abiotic processes is well quantified. However, the identification of microbial communities in flowback and produced water necessitates the need to understand barite dissolution in the presence of bacteria. Therefore, we evaluated the rates and mechanisms of abiotic and microbially-mediated barite dissolution under anoxic and hypersaline conditions in the laboratory. Barite dissolution experiments were conducted with bacterial enrichment cultures established from produced water from Marcellus Shale wells located in northcentral Pennsylvania. These cultures were dominated by anaerobic halophilic bacteria from the genus Halanaerobium. Dissolved Ba was determined by ICP-OES and barite surfaces were investigated by SEM and AFM. Our results reveal that: 1) higher amounts of barium (up to ∼5 × ) are released from barite in the presence of Halanaerobium cultures compared to brine controls after 30 days of reaction, 2) etch pits that develop on the barite (001) surface in the presence of Halanaerobium exhibit a morphology that is distinct from those that form during control experiments without bacteria, 3) etch pits that develop in the presence of Halanaerobium exhibit a morphology that is similar to the morphology of etch pits formed in the presence of strong organic chelators, EDTA and DTPA, and 4) experiments using dialysis membranes to separate barite from bacteria suggest that direct contact between the two is not required in order to promote dissolution. These results suggest that Halanaerobium increase the rate of barite dissolution in anoxic and high ionic strength solutions. Additionally, the increase in rate occurs without direct microbe-mineral contact suggesting that metabolites secreted by the bacteria may be responsible for promotion of dissolution. The findings of this study have implications for understanding barium cycling in marine/hypersaline environments, release of barium (and associated radium) from waste solids generated from energy and mining industries, as well as potential for developing new anti-scaling chemicals.

Abstract:
Over the past 60 years, road deicers (i.e. road salt) have been applied to roadways in high latitudes to improve road conditions in winter weather. However, the dissolution of road deicers in highway runoff creates waters with high concentrations of sodium, which can mobilize soil metals via soil cation-exchange reactions. While several studies have detailed the interactions of road salt-rich solutions and surface and ground waters, less attention has been given to how local hydrologic flowpaths can impact the delivery of these solutions to near-road soils. Between 2013 and 2014, soil water samples were collected from a roadside transect of lysimeter nests in Pittsburgh, Pennsylvania (USA). Soil water samples were analysed for metal concentrations and resulting data used to examine cation dynamics. While patterns in soil water calcium and magnesium concentrations follow patterns in soil water sodium concentrations, additional processes influence patterns in soil water potassium concentrations. Specifically, we observe the highest calcium and magnesium concentrations in the deepest lysimeters, suggesting divalent cations are mobilized to, and potentially accumulate in, deeper soil horizons. In contrast, soil water potassium concentrations do not follow this pattern. Additionally, in all examined elements (Ca, Mg, K, Na, and Cl), the timing of concentration peaks appears be influenced by a combination of both distance from the roadside and sampling depth. These relationships not only suggest that multiple soil water flowpaths interact with our study transect but also confirm that road salt plumes persist and migrate following the road salting season. Characterizing the interactions of sodium-rich solutions and roadside soil cation pools clarifies our understanding of metal dynamics in the roadside environment. A deeper understanding of these processes is necessary to effectively restore and manage watersheds as high total dissolved solid solutions (e.g. road deicing melt, unconventional natural gas brines, and marginal irrigation water) continue to influence hydrological systems. Copyright (C) 2016 John Wiley & Sons, Ltd.

Abstract:
Hydraulic fracturing consumes billions of gallons of water each year to extract oil and natural gas from the ground. The resulting wastewater contains sand, salts, metals, gel, diluted acid, and other unknown proppants, and does not meet the EPA standards for environmental release. With the goal of treating the hydraulic fracturing water to meet the highest possible EPA standards for water quality, a benchtop water purification process was designed, built, and tested. The treatment process consisted of an activated charcoal adsorption column filter, a reverse osmosis membrane and ion exchange columns. Produced water from Eagle Ford Shale was pumped through the system and samples were collected before and after each unit operation. The water, treated with this system, was pumped through the system a second time; samples were collected and analyzed using the same methodology from the first iteration to analyze the potential benefits of a second iteration. In order to assess the effectiveness of each unit operation and iteration in the wastewater treatment system, a series of experiments were designed to monitor the flow ratio, metal & salt content, pH, and change in organic content. Inductively coupled plasma optical emission spectrometry was implemented as a means to measure the metal and salt content present in the water at various purification steps. The produced waters initial metal content was determined to be 184.45 ppm, and the initial salt content was determined to be 2,262.26 ppm. After the first iteration of treatment, the final metal and salt contents were determined to be 0.32 ppm and 1.39 ppm respectively. Gas chromatography was used to monitor organic content. The total organic content of the produced water was reduced by 83.5% by the treatment process. The initial pH of the produced water was 4.25, and after the first iteration of treatment, the final pH was 5.31. The produced water treated in our process in a single iteration met the EPA standards for metal and salt content for potable water; however the pH is at the lower end of the standard. The second iteration analysis showed that the pH of the twice treated water was raised to acceptable levels for potable water, however the concentration of the other pollutants changed negligibly. Based on the average national price for electricity, a treatment system that operated for 10 years would cost $1.68 per day, including the capital costs. The performance analysis indicated that the treatment system has commercial applications for home use in areas with groundwater affected by hydraulic fracturing wastewater.

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The inorganic geochemistry of hydraulic fracturing fluids is reviewed with new insights on the role of entrapped formation waters in unconventional shale gas and tight sand formations on the quality of flowback and produced waters that are extracted with hydrocarbons. The rapid increase of the salinity of flowback fluids during production, combined with geochemical and isotopic changes, indicate mixing of the highly saline formation water with the injected water. The salinity increase suggests that the volume of the injected water that is returned to the surface with the flowback water is much smaller than previous estimates, and thus the majority of the injected water is retained within the shale formations. The high salinity of the flowback and produced water is associated with high concentrations of halides, ammonium, metals, metalloids, and radium nuclides that pose environmental and human health risks upon the release of the hydraulic fracturing fluids to the environment.

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The management and disposal of flowback and produced waters (FP water) is one of the greatest challenges associated with unconventional oil and gas development. The development and production of unconventional natural gas and oil is projected to increase in the coming years, and a better understanding of the volume and quality of FP water is crucial for the safe management of the associated wastewater. We analyzed production data using multiple statistical methods to estimate the total FP water generated per well from six of the major unconventional oil and gas formations in the United States. The estimated median volume ranges from 1.7 to 14.3millionL (0.5 to 3.8milliongal) of FP per well over the first 5-10years of production. Using temporal volume production and water quality data, we show a rapid increase of the salinity associated with a decrease of FP production rates during the first months of unconventional oil and gas production. Based on mass-balance calculations, we estimate that only 4-8% of FP water is composed of returned hydraulic fracturing fluids, while the remaining 92-96% of FP water is derived from naturally occurring formation brines that is extracted together with oil and gas. The salinity and chemical composition of the formation brines are therefore the main limiting factors for beneficial reuse of unconventional oil and gas wastewater.

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Shale gas produced water is a hypersaline wastewater that is generated during the shale gas development process called as a hydraulic fracturing. The produced water contains many substances including inorganic salts, organic compounds, and particulates. The treatment process of the produced water is mainly composed of four parts: oil and water separation, removal of suspended solids, removal of organics, and salts removal. This study focuses on the total dissolved salts removal through applying three different desalination techniques - membrane distillation (MD), reverse osmosis (RO), and evaporative crystallization (EC). The experiments were conducted using synthetic shale gas produced water to understand the changes of chemical properties in permeate and concentrate. In the permeate solution, MD and EC showed more than 99% of salts removal efficiency for all ions, but RO showed relatively low efficiency. In the concentrate solution, the concentrations of all ions varied according to the type of ions and applied treatment methods.

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The produced water, which could be a complex mixture of different organic and inorganic compounds (mostly salts, minerals and oils) is a major wastewater stream generated during oil and gas production processes. Due to increase oil and gas exploration and production, especially from unconventional resources like shale oil and gas reservoirs, the volume of this effluent production is increasing around the world and its discarding to the environment is one of the global concerns. There are various physical and chemical methods to treat the produced water. However, a comprehensive and deep understanding of each issue can lead to a better and more efficient solution. In this study, various physical and chemical treatment methods for produced water have been reviewed based on the latest findings and recently published articles on this topic. Moreover, challenges and opportunities of each of these treatment methods have been fully discussed. Also potential applications for reusing the treated PW have been suggested and discussed finally.

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A dramatic increase in unconventional drilling that utilizes hydraulic fracturing to extract oil/gas over the past decade has led to concern over handling and management of produced/ flowback water (PFW; hydraulic-fracturing wastewater) because the potential exists for its accidental release into the environment. This PFW contains high amounts of total dissolved solids acquired from interaction with the reservoir formation. Development and testing of geochemical methods, such as strontium (Sr) isotope ratio (87Sr/86Sr) analysis, to determine the origin of dissolved solids in an environment would be valuable. Samples acquired from different sources in Texas overlying and within the Barnett Shale, such as surface/ground water and PFW, contain unique Sr concentrations and 87Sr/86Sr values, with the potential to be used as a geochemical fingerprint. This study shows that because of the very high concentration of Sr in PFW and its high 87Sr/86Sr value, when as little as 1% of a sample is PFW, the sample experiences a measurable change in 87Sr/86Sr. To determine which phase within the reservoir rock imparts its 87Sr/86Sr to the PFW, sequential extractions were performed on powdered Barnett Shale core samples. Results of the extractions show varying geochemical affinities and distinct 87Sr/86Sr values by leaching solution. However, a direct link to the PFW sample was not conclusive, likely because of the unknown location of the PFW sample and the spatially variable 87Sr/86Sr of the Barnett Shale. Future work requires further cooperation with industry or federal agencies that could provide a more complete set of samples.

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The environmental impact of shale oil and gas production by hydraulic fracturing (fracking) is of increasing concern. The biggest potential source of environmental contamination is flowback and produced water, which is highly contaminated with hydrocarbons, bacteria and particulates, meaning that traditional membranes are readily fouled. We show the chemical functionalisation of alumina ceramic microfiltration membranes (0.22 μm pore size) with cysteic acid creates a superhydrophilic surface, allowing for separation of hydrocarbons from frac and produced waters without fouling. The single pass rejection coefficients was >90% for all samples. The separation of hydrocarbons from water when the former have hydrodynamic diameters smaller than the pore size of the membrane is due to the zwitter ionically charged superhydrophilic pore surface. Membrane fouling is essentially eliminated, while a specific flux is obtained at a lower pressure (<2 bar) than that required achieving the same flux for the untreated membrane (4–8 bar).

Abstract:
The large volume of wastewater produced during unconventional oil and gas (UOG) extraction is a significant challenge for the energy industry and of environmental concern, as the risks due to leaks, spills, and migration of these fluids into natural waters are unknown. UOG wastewater is often hypersaline, and contains myriad organic and inorganic substances added for production purposes and derived from the source rock or formation water. In this study, we examined the organic composition and toxicology of water and sediments in a stream adjacent to an underground injection disposal facility that handles UOG wastewaters. We sampled water and streambed sediments from an unnamed tributary of Wolf Creek upstream from the disposal facility, near the injection well, and downstream. Two sites downstream from the disposal facility contained organic compounds in both water and sediments that were consistent with a source from UOG wastewater. These compounds included: 2-(2-butoxyethoxy)-ethanol, tris(1-chloro-2-propyl)phosphate, α, α-dimethyl-benzenemethanol, 3-ethyl-4-methyl-1H-pyrrole-2,5-dione, and tetrahydro-thiophene-1,1-dioxide in water, diesel fuel hydrocarbons (e.g. pentacosane, Z-14-nonacosane), and halogenated hydrocarbons (e.g., 1-iodo-octadecane, octatriacontyl trifluoroacetate, dotriacontyl pentafluoropropionate) in sediments. Concentrations of UOG-derived organic compounds at these sites were generally low, typically 4 to <1 μg/L in the water, and <70 μg/g (dry wt.) in the sediment. In addition, water and sediment at a site immediately downstream from the facility contained many chromatographically unresolved and unidentified hydrocarbons. In contrast, sites upstream from the facility or in nearby watersheds not influenced by the disposal well facility contained primarily natural (biologically produced) organic substances from the local environment. Toxicological assays of human cell line exposures to water and sediment showed minimal effects. Results indicate that UOG wastewater has entered the stream and that UOG-derived organic substances are present. The contamination level, however, is low and appears to be restricted to sites immediately downstream from the disposal facility at this time.

Abstract:
Nanoscale zero-valent iron (nZVI) was tested for the removal of Cu(II), Zn(II), Cr(VI), and As(V) in model saline wastewaters from hydraulic fracturing. Increasing ionic strength (I) from 0.35 to 4.10 M (Day-1 to Day-90 wastewaters) increased Cu(II) removal (25.4–80.0%), inhibited Zn(II) removal (58.7–42.9%), slightly increased and then reduced Cr(VI) removal (65.7–44.1%), and almost unaffected As(V) removal (66.7–75.1%) by 8-h reaction with nZVI at 1–2 g L−1. The removal kinetics conformed to pseudo-second-order model, and increasing I decreased the surface area-normalized rate coefficient (ksa) of Cu(II) and Cr(VI), probably because agglomeration of nZVI in saline wastewaters restricted diffusion of metal(loid)s to active surface sites. Increasing I induced severe Fe dissolution from 0.37-0.77% in DIW to 4.87–13.0% in Day-90 wastewater; and Fe dissolution showed a significant positive correlation with Cu(II) removal. With surface stabilization by alginate and polyvinyl alcohol, the performance of entrapped nZVI in Day-90 wastewater was improved for Zn(II) and Cr(VI), and Fe dissolution was restrained (3.20–7.36%). The X-ray spectroscopic analysis and chemical speciation modelling demonstrated that the difference in removal trends from Day-1 to Day-90 wastewaters was attributed to: (i) distinctive removal mechanisms of Cu(II) and Cr(VI) (adsorption, (co-)precipitation, and reduction), compared to Zn(II) (adsorption) and As(V) (bidentate inner-sphere complexation); and (ii) changes in solution speciation (e.g., from Zn2+ to ZnCl3− and ZnCl42−; from CrO42− to CaCrO4 complex). Bare nZVI was susceptible to variations in wastewater chemistry while entrapped nZVI was more stable and environmentally benign, which could be used to remove metals/metalloids before subsequent treatment for reuse/disposal.

Abstract:
Scale-up of microalgal biotechnology to provide large quantities of biofuel, lipids, and coproducts is not fully developed because of the large needs for nutrients, water, land, solar insolation, and CO2/carbon supplies. Wastewaters, including oil and gas produced water (PW), may supply a portion of these needs in regions with insufficient fresh water resources. PW is a challenging water resource for this use because of variable salinity, geochemical complexity, and the presence of biologically toxic components. In this paper we review PW volumes, quality, and use in media for microalgae production in the southwestern US, Australia, and Oman. We also include data from the southwestern US, referencing previously unpublished results from the National Alliance for Biofuels and Bioproducts (NAABB) consortium research project. We include a Supplementary Information section that explores cultivation of multiple microalgae species in PW and examines the carbon utilization process, all work performed in support of the NAABB field program. Strains of algae tested in the reviewed papers include Nannochloropsis, Dunalliella, Scenedesmus, and several mixed or unknown cultures. We conclude that the use of PW in algae cultivation is feasible, if the additional complexity of the water resource is accounted for in developing media formulations and in understanding metals uptake by the algae. We recommend additional work to standardize growth testing in PW, better and more thorough chemical analysis, and geochemical modeling of the PW used in media. Expanded strain testing in PW media will identify improved strains tolerant of PW in algae cultivation.

Abstract:
Produced water is a type of wastewater generated from hydraulic fracturing, which may pose a risk to the environment and humans due to its high ionic strength and the presence of elevated concentrations of metals/metalloids that exceed maximum contamination levels. The mobilization of As(V) and Se(VI) in produced water and selected soils from Qingshankou Formation in the Songliao Basin in China were investigated using column experiments and synthetic produced water whose quality was representative of waters arising at different times after well creation. Temporal effects of produced water on metal/metalloid transport and sorption/desorption were investigated by using HYDRUS-1D transport modelling. Rapid breakthrough and long tailings of As(V) and Se(VI) transport were observed in Day 1 and Day 14 solutions, but were reduced in Day 90 solution probably due to the elevated ionic strength. The influence of produced water on the hydrogeological conditions (i.e., change between equilibrium and non-equilibrium transport) was evidenced by the change of tracer breakthrough curves before and after the leaching of produced water. This possibly resulted from the sorption of polyacrylamide (PAM (-CH2CHCONH2-)n) onto soil surfaces, through its use as a friction reducer in fracturing solutions. The sorption was found to be reversible in this study. Minimal amounts of sorbed As(V) were desorbed whereas the majority of sorbed Se(VI) was readily leached out, to an extent which varied with the composition of the produced water. These results showed that the mobilization of As(V) and Se(VI) in soil largely depended on the solution pH and ionic strength. Understanding the differences in metal/metalloid transport in produced water is important for proper risk management.

Abstract:
After the completion of hydraulic fracturing, some part of injected fluids mixed with the formation brines - so called flowback brine, migrate back through the well to the surface. Our autoclave experiments were aimed to reproduce and evaluate the chemical composition of the flowback brine derived from CO2-energized fluid fracturing of shale gas of the Baltic province (Poland).Results show the flowback composition is controlled mainly by the interactions between fracturing fluids and original pore water, and to a lesser extent with the reservoir rock.

Abstract:
The current California drought has reduced freshwater availability, creating tensions between water users across the state. Although over 518 million m 3 of water were produced during fossil fuel production in California in 2014, the majority was disposed into Class II injection wells. There have been few attempts to assess the feasibility of using produced water for beneficial purposes, due in part to the difficulties of accessing, synthesizing and analyzing data regarding produced water quality and quantity. This study addresses this gap and provides a techno-economic assessment of upgrading produced water from California’s oil and natural gas activities and moving it to adjacent water-stressed regions. Results indicate that the four population centers facing the greatest water shortage risk are located in the Central Valley within a 161 km (100 mile) radius of 230 million m 3 of total treatable produced water. This volume can supply up to one million people-years worth of potable water. The cost of desalinating and transporting this water source is comparable in magnitude to some agricultural and local public water supplies and is substantially lower than bottled water. Thus, utilizing reverse osmosis to treat produced water might be a feasible solution to help relieve water scarcity in some drought-stricken regions of California.

Abstract:
Produced water is a significant waste stream that can be treated and reused; however, the removal of production chemicals—such as those added in hydraulic fracturing—must be addressed. One motivation for treating and reusing produced water is that current disposal methods—typically consisting of deep well injection and percolation in infiltration pits—are being limited. Furthermore, oil and gas production often occurs in arid regions where there is demand for new water sources. In this paper, hydraulic fracturing chemical additive data from California are used as a case study where physical-chemical and biodegradation data are summarized and used to screen for appropriate produced water treatment technologies. The data indicate that hydraulic fracturing chemicals are largely treatable; however, data are missing for 24 of the 193 chemical additives identified. More than one-third of organic chemicals have data indicating biodegradability, suggesting biological treatment would be effective. Adsorption-based methods and partitioning of chemicals into oil for subsequent separation is expected to be effective for approximately one-third of chemicals. Volatilization-based treatment methods (e.g. air stripping) will only be effective for approximately 10% of chemicals. Reverse osmosis is a good catch-all with over 70% of organic chemicals expected to be removed efficiently. Other technologies such as electrocoagulation and advanced oxidation are promising but lack demonstration. Chemicals of most concern due to prevalence, toxicity, and lack of data include propargyl alcohol, 2-mercaptoethyl alcohol, tetrakis hydroxymethyl-phosphonium sulfate, thioglycolic acid, 2-bromo-3-nitrilopropionamide, formaldehyde polymers, polymers of acrylic acid, quaternary ammonium compounds, and surfactants (e.g. ethoxylated alcohols). Future studies should examine the fate of hydraulic fracturing chemicals in produced water treatment trains to demonstrate removal and clarify interactions between upstream and downstream processes.

Abstract:
To find out the impact of chemical potential difference between the low salinity fracturing fluid and the high salinity formation water on fracturing fluid flowback, a chemical potential difference expression of fracturing fluid and formation water was deduced, on this basis, a mathematical model which considers viscous force, capillary force and osmosis pressure driven gas-water flow in matrix-fracture system was built, the flow back performance of fracturing fluid driven by chemical potential difference was simulated, and the formation water saturation and salt concentration profile with flow back time were analyzed. The results show that in the process of flow back, the water molecules in the matrix driven by the chemical potential difference continually migrated to the deeper reservoirs, while salt ions in the matrix constantly spread to the fractures. After 168 h of fracturing-fluid flow back, the migration distance of water was up to 40 cm, and the salt concentration near the fracture surface increased by 0.841%, and the cumulative flowback ratio of the gas well was only 22.1%. The cumulative flowback ratio would be 23.5%, 32.4% and 41.1% respectively, without taking into account the effect of gas absorption, chemical osmosis or capillary imbibition. The capillary imbibition and chemical osmosis seriously hindered the fracturing-fluid flow back, therefore, the two factors should be fully considered in the post-fracturing evaluation of shale gas wells.

Abstract:
Determination of in situ formation water chemistry is an essential component of reservoir management. This paper details the use of thermodynamic computer models to calculate reservoir pH and restore produced water analyses for prediction of scale formation. Bakken produced water samples were restored to formation conditions and calculations of scale formation performed. In situ pH is controlled by feldspar-clay equilibria. Calcite scale is readily formed due to changes in pH during pressure drop from in situ to surface conditions. The formation of anhydrite and halite scale, which has been observed, was predicted only for the most saline samples. In addition, the formation of anhydrite and/or halite may be related to the localized conditions of increased salinity as water is partitioned into the gas phase during production.

Abstract:
The rapidly increasing implementations of oilfield technologies such as horizontal wells and multistage hydraulic fracturing, particularly in unconventional formations, have expanded the need for fresh water in many oilfield locations. In the meantime, it is costly for services companies and operators to properly dispose large volumes of produced water, generated annually at about 21 billion barrels in the United States alone. The high operating costs in obtaining fresh water and dealing with produced water have motivated scientists and engineers, especially in recent years, to use produced water in place of fresh water to formulate well treatment fluids. The objective of this brief review is to provide a summary of the up-to-date technologies of reusing oilfield produced water in preparations of a series of crosslinked fluids implemented mainly in hydraulic fracturing operations. The crosslinked fluids formulated with produced water include borate- and metal-crosslinked guar and derivatized guar fluids, as well as other types of crosslinked fluid systems such as crosslinked synthetic polymer fluids and crosslinked derivatized cellulose fluids. The borate-crosslinked guar fluids have been successfully formulated with produced water and used in oilfield operations with bottomhole temperatures up to about 250 °F. The produced water sources involved showed total dissolved solids (TDS) up to about 115,000 mg/L and hardness up to about 11,000 mg/L. The metal-crosslinked guar fluids prepared with produced water were successfully used in wells at bottomhole temperatures up to about 250 °F, with produced water TDS up to about 300,000 mg/L and hardness up to about 44,000 mg/L. The Zr-crosslinked carboxymethyl hydroxypropyl guar (CMHPG) fluids have been successfully made with produced water and implemented in operations with bottomhole temperatures at about 250+ °F, with produced water TDS up to about 280,000 mg/L and hardness up to about 91,000 mg/L. In most of the cases investigated, the produced water involved was either untreated, or the treatments were minimum such as simple filtration without significantly changing the concentrations of monovalent and divalent ions in the water. Due to the compositional similarity (high salinity and hardness) between produced water and seawater, crosslinked fluids formulated with seawater for offshore and onshore jobs were also included. The crosslinked guar and derivatized guar fluids have been successfully formulated with seawater for operations at bottomhole temperatures up to about 300 °F. Operating costs have been significantly reduced when produced water or seawater is used to formulate fracturing fluids in place of fresh water. With various challenges and limitations still existing, the paper emphasizes the needs for new developments and further expansion of produced water reuse in oilfield operations.

Abstract:
Naturally occurring radioactive materials (NORM) in solid waste or “drill cuttings” produced from unconventional drilling for natural gas extraction wells potentially pose environmental contamination risks; however, the composition and mobility of NORM in these solid wastes are poorly understood. In this study, the composition of NORM, including uranium, thorium, radium, lead, and polonium isotopes, was evaluated in three samples of drill cuttings extracted from a well drilled into the Marcellus Shale formation. Leachability of NORM in drill cuttings was characterized by leaching the solid waste with dilute acetic acid at four different pH values. The uranium-series radionuclides in cuttings and leachate samples displayed isotopic disequilibrium, suggesting some environmental mobility of radionuclides in these shale formations. Our results indicate that isotopic analysis of uranium-series radionuclides is needed for a more complete understanding of the potential environmental contamination risks associated with these solid wastes.

Abstract:
Flowback water generated during shale gas extraction in Pennsylvania is mostly reused for hydraulic fracturing operation. Abandoned mine drainage (AMD), one of the most widespread threats to water quality in Pennsylvania, can potentially serve as a make-up water source to enable flowback water reuse. This study demonstrated co-treatment of flowback water and AMD produced in northeastern Pennsylvania in a pilot-scale system consisting of rapid mix reactor, flocculation tank and sedimentation tank. Sulfate concentration in the finished water can be controlled at a desired level (i.e., below 100 mg/L) by adjusting the ratio of flowback water and AMD in the influent. Fe3+ contained in the AMD can serve as a coagulant to enhance the removal of suspended solids, during which Fe2+ is co-precipitated and the total iron is reduced to a desirable level. Solid waste generated in this process (i.e., barite) will incorporate over 99% of radium present in the flowback water, which offers the possibility to control the fate of naturally occurring radioactive materials (NORM) brought to the surface by unconventional gas extraction. Sludge recirculation in the treatment process can be used to increase the size of barite particles formed by mixing flowback water and AMD to meet specifications for use as a weighting agent in drilling fluid. This alternative management approach for NORM can be used to offset the treatment cost and promote flowback water reuse, reduce environmental impacts of AMD and reduce pressure on fresh water sources.

Abstract:
The toxicity of shale gas fracturing flowback fluid in the eastern Sichuan Basin was investigated and proven to be nontoxic. Based on the water quality characteristics of the fracturing flowback fluid in this area, an experimental study of treatment processes was conducted considering the coagulation–Fenton oxidation processes. Orthogonal and single-factor experiments were carried out for the coagulation and Fenton oxidation processes, respectively. The appropriate values of the various factors affecting the coagulation and Fenton oxidation experiments were determined according to the results. Subsequently, the water quality of the effluent treated by the coagulation–Fenton oxidation processes was evaluated, and the result showed that the water quality requirements for underground injection were met. Finally, the performances of slick water prepared by the effluent were evaluated, and the results showed that the slick water met the demands of fracturing operations and could be reused for further fracturing jobs.

Abstract:
Shale with high clay content has caused instability from hydration during the hydraulic fracturing process. Macro-level migration phenomenon of water molecules is induced by the chemical potential difference between low-salinity fracturing fluid and high-salinity formation brine. This study aims to establish the equation for the chemical potential difference between fracturing fluid and formation brine by theoretical deduction in order to investigate the effect of the aforementioned phenomenon on fracturing flowback. Accordingly, a mathematical model was established for the gas–water two-phase flow which driven by the chemical potential difference. Viscous force, capillarity and chemiosmosis were considered as the driving forces. A numerical simulation of fracturing fluid flowback with or without considering of the effect of chemiosmosis was performed. A simulation analysis of the water saturation and salinity profiles was also conducted. Results show that capillarity and chemiosmosis hinder fracturing fluid flowback in different degrees. As the condition worsens, they inhibit more than 80% of water to flow back out of the formation, forming a permanent water lock. This study contributes to improvement of the theory on shale gas–water two-phase flow, establishment of a flowback model that suitable for shale gas wells, and accurate evaluation of the fracturing treatment.

Abstract:
Flowback/produced water reuse cannot be optimized without a thorough understanding of the quality of the water that needs to be treated for reuse, including the temporal variability. Samples for flowback/produced water were collected over a 200-day period (day 0 refers to when flowback began) from two wells. One of the frac fluids had an initial pH greater than 10 and used a guar-based gel and the second fluid contained a non-guar polysaccharide based polymer with an initial pH of less than 6. Total dissolved solids (TDS) and total organic carbon (TOC) were used as macro-indicators and key ions (barium, calcium, chloride, magnesium, sodium, strontium, boron and iron) were compared to TDS with the different frac fluids and there were significant positive correlations observed between the key ions and TDS with relatively high values of the coefficient of determinant (over 0.85). The concentrations of calcium, chloride, sodium and strontium are statistically equivalent between the two fluids. A mass balance approach was applied to evaluate the quantity of mass of injected additives that was recovered over the 200-day period. Recoveries of zirconium, potassium and aluminum ranged from 3% to 33% after 200 days, and notable differences were observed between frac fluids.

Abstract:
Surface water is at risk from Marcellus Shale operations because of chemical storage on drill pads during hydraulic fracturing operations, and the return of water high in total dissolved solids (up to 345 g/L) from shale gas production. This research evaluated how two commercial, off-the-shelf water quality sensors responded to simulated surface water pollution events associated with Marcellus Shale development. First, peak concentrations of contaminants from typical spill events in monitored watersheds were estimated using regression techniques. Laboratory measurements were then conducted to determine how standard in-stream instrumentation that monitor conductivity, pH, temperature, and dissolved oxygen responded to three potential spill materials: ethylene glycol (corrosion inhibitor), drilling mud, and produced water. Solutions ranging from 0 to 50 ppm of each spill material were assessed. Over this range, the specific conductivity increased on average by 19.9, 27.9, and 70 μS/cm for drilling mud, ethylene glycol, and produced water, respectively. On average, minor changes in pH (0.5–0.8) and dissolved oxygen (0.13–0.23 ppm) were observed. While continuous monitoring may be part of the strategy for detecting spills to surface water, these minor impacts to water quality highlight the difficulty in detecting spill events. When practical, sensors should be placed at the mouths of small watersheds where drilling activities or spill risks are present, as contaminant travel distance strongly affects concentrations in surface water systems.

Abstract:
Microporous membranes fabricated from hydrophobic polymers such as polyvinylidene fluoride (PVDF) have been widely used for membrane distillation (MD). However, hydrophobic MD membranes are prone to wetting by low surface tension substances, thereby limiting their use in treating challenging industrial wastewaters, such as shale gas produced water. In this study, we present a facile and scalable approach for the fabrication of omniphobic polyvinylidene fluoride (PVDF) membranes that repel both water and oil. Positive surface charge was imparted to an alkaline-treated PVDF membrane by aminosilane functionalization, which enabled irreversible binding of negatively charged silica nanoparticles (SiNPs) to the membrane through electrostatic attraction. The membrane with grafted SiNPs was then coated with fluoroalkylsilane (perfluorodecyltrichlorosilane) to lower the membrane surface energy. Results from contact angle measurements with mineral oil and surfactant solution demonstrated that overlaying SiNPs with ultralow surface energy significantly enhanced the wetting resistance of the membrane against low surface tension liquids. We also evaluated desalination performance of the modified membrane in direct contact membrane distillation with a synthetic wastewater containing surfactant (sodium dodecyl sulfate) and mineral oil, as well as with shale gas produced water. The omniphobic membrane exhibited a stable MD performance, demonstrating its potential application for desalination of challenging industrial wastewaters containing diverse low surface tension contaminants.

Abstract:
Since the beginning of this millennium, shale gas extraction by horizontal drilling and hydraulic fracturing has boosted U.S. gas production, changing the global energy markets and leading to low natural gas and oil prices. Following the expansion of this industry, other countries such as U.K., Poland or China are exploring and supporting its extraction as a way to secure energy independence in an increasingly unstable geopolitical context and as an effective transition substitute for coal while moving towards a renewable energy market. However, there are important environmental concerns associated to shale gas production including atmospheric pollution and air quality issues, risks of water pollution and nuisance to the population caused by road traffic and noise. Water management is one of the most challenging problems since hydraulic fracturing requires millions of liters of water and produces high volumes of liquid effluents at variable compositions and rates. The present review focuses on the characteristics of this wastewater and the options existing to minimize its environmental impacts. At the moment, deep well injection and re-use are the most commonly employed strategies for this wastewater in the U.S. but the stricter regulations in other regions will require further treatment. Partial treatment and reuse is the preferred option where feasible. Otherwise, techniques such as mechanical vapor compression, thermal distillation or forward osmosis may be needed in order to meet the requirements for discharge.

Abstract:
A review of the literature published in 2015 on topics relating to public and environmental health risks associated with wastewater treatment, reuse, and disposal is presented. This review is divided into the following sections: wastewater management, microbial hazards, chemical hazards, wastewater treatment, wastewater reuse, agricultural reuse in different regions, greywater reuse, wastewater disposal, hospital wastewater, industrial wastewater, and sludge and biosolids.

Abstract:
Summary Fracture fluid is composed of fresh water, proppant, and a small percentage of other additives, which support the hydraulic-fracturing process. Excluding situations in which flowback water is recycled and reused, the total dissolved solids (