Repository for Oil and Gas Energy Research (ROGER)

Abstract:
This study investigated the removal of organic compounds from shale gas fracturing flowback water (FFW) by an integrated electro-coagulation and electro-peroxone (EC-EP) process in a divided electrochemical reactor. During the EC-EP process, electricity was efficiently utilized to produce both aluminum ion (Al3+) from electrochemical oxidation of an aluminum anode in the anodic compartment and hydrogen peroxide (H2O2) from oxygen reduction at a carbon-based cathode in the cathodic compartment. The in-situ generated H2O2 then reacted with ozone (O3) sparged in the cathodic compartment to produce hydroxyl radicals (•OH) for pollutant oxidation. The results showed that by sequentially treating the selected FFW by the EC and EP process in the anodic and cathodic compartment for 30 min, respectively, the EC-EP process effectively removed ~95% of total organic carbon (TOC) from the FFW, meeting the wastewater discharge standard for TOC (≤30 mg/L) with a low specific energy consumption of 0.11–0.21 kWh/g TOC removed. In contrast, individual EC and EP process, as well as the previously investigated ECP process that combined the EC and EP process in an undivided reactor, removed only ~76%, 32%, and 80% TOC from the FFW under similar reaction conditions, and thus could not meet the wastewater discharge standard. These results demonstrate that the EC-EP process successfully integrates the merit of the EC and EP process and may thus provide a cost-effective way to remove organic compounds for FFW disposal and reuses.

Abstract:
Understanding the speciation and fate of radium during operational discharge from the offshore oil and gas industry into the marine environment is important in assessing its long term environmental impact. In the current work, 226Ra concentrations in marine sediments contaminated by produced water discharge from a site in the UK were analysed using gamma spectroscopy. Radium was present in field samples (0.1–0.3 Bq g−1) within International Atomic Energy Agency activity thresholds and was found to be primarily associated with micron sized radiobarite particles (≤2 μm). Experimental studies of synthetic/field produced water and seawater mixing under laboratory conditions showed that a significant proportion of radium (up to 97%) co-precipitated with barite confirming the radiobarite fate pathway. The results showed that produced water discharge into the marine environment results in the formation of radiobarite particles which incorporate a significant portion of radium and can be deposited in marine sediments.

Abstract:
The oilfield produced water is a major waste stream in places where shale-gas production is growing rapidly. The reuse of produced water merits consideration because this practice helps reduce freshwater demand for fracking and moderates water pollution. Knowledge about the chemistry of produced water is needed to develop sustainable treatment/reuse strategies and set standards for acceptable levels of treatment of produced water. Thus, the author performed the first comprehensive analysis of oilfield produced water collected from the Bakken shale play in the U.S. state of North Dakota that represents the nation's third-largest net increase in proven crude oil reserves. The concentrations of a total of 36 elements in 13 IUPAC groups were determined. Among them, a few metals that are critical to the economy of the United States were detected at elevated concentrations (median, mg/L): K (7,620), Mg (2780), Sr (1610), Li (69), and Mn (33). Heavy metals essential for plants and animals, including Cu, Zn, and Mn, were detected at ppm levels. Measurable concentrations of highly toxic metal ions such as Cd and Pb were not detected. Concentrations of rare earth elements and platinum group metals were below respective detection limits. The produced water samples had very high total dissolved solids (237,680 ± 73,828 mg/L) and total hardness (>31,000 mg/L as CaCO3) but an extremely low alkalinity (152.4 ± 184.9 mg/L as CaCO3); therefore, softening by lime and soda was ineffective. Softening by caustic soda removed 99.5% hardness ions (Ca and Mg) under alkaline conditions. This study provides vital insight into the chemistry and treatability of produced water containing various metals.

Abstract:
Diluted bitumen, also known as dilbit, is transported by rail and pipeline across Canada and the United States. Due to the fewer number of studies characterizing the toxicity of dilbit, a dilbit spill poses an unknown risk to freshwater aquatic ecosystems. In the following study, we compared the impact of early-life exposure to conventional and unconventional crude oils on the optomotor behavior, reproductive success, and transgenerational differences in gene expression in zebrafish and their progeny. For exposures, water accommodated fractions (WAFs) of crude oil were generated using a 1:1000 oil to water ratio for 3 different crudes; mixed sweet blend (MSB), medium sour composite (MSC) and dilbit. All three oils generated unique volatile organic compound (VOC) and polycyclic aromatic compound (PAC) profiles. Of the WAFs tested, only dilbit decreased the eye size of 2 dpf larvae, and only MSB exposed larvae had an altered behavioral response to a visual simulation of a predator. Early-life exposure to crude oil had no lasting impact on reproductive success of adult fish; however, each oil had unique impacts on the basal gene expression of the somatically exposed offspring. In this study, the biological effects differed between each of the oils tested, which implied chemical composition plays a critical role in determining the sublethal toxicity of conventional and unconventional crude oils in freshwater ecosystems.

Abstract:
Despite the growing body of studies on the various fracturing phrases, the research on the differences between subterranean and surface microorganisms at shale gas drilling sites is still limited. Generally, shale gas development and the production process are divided into drilling and fracturing. The distribution of microbial communities in the latter has been paid some attention, but a deficit remains in terms of our understanding of the microbial community in the former, especially for the phase of drilling flowback and drilling flowback surface. In this study, four drilling flowback fluids (DFFs) (H230-flowback drilling cuttings, H23G-flowback drilling mud, H240-flowback drilling sediment, and H21F-flowback drilling water) from the outlet of subterranean pipeline to the inlet of storage tank were successively collected from H2 shale gas field during its initial drilling in Sichuan, China. Natural mountain water (H10W) used as the injection water of H2 was also sampled. Illumina MiSeq 16S rRNA gene sequencing revealed a total of 8 phyla, 17 classes, 35 orders, 61 families, and 98 genera that were recovered from these samples with uneven distribution. The majority of the obtained sequences belonged to the phyla Proteobacteria (75.36%), Bacteroidetes (10.75%), and Firmicutes (5.64%), with significant differences found in DFFs and injection water. The richness of microorganisms gradually increased with the increasing flowback flowing distance (H230< H23G< H240< H21F< H10W), which was employed to reveal a rapid change in microbiota that was evident in samples along the flow path aboveground from a depth of 3548 m. The findings of this study could expand our understanding of the ecological role of microorganisms during the shale gas drilling phase. Furthermore, the study highlights the temporal-spatial trajectory of microbial communities from subterranean environments to the surface in a short period of 30 days.

Abstract:
Understanding the behavior and composition of fracturing flowback water (FFW) can provide insight into in situ water–rock interactions, assessment of the success of the fracturing operations. FFW was collected from three wells (Z202-H1, Z203, and Z205) for up to 108 days after fracturing in the same area of western Chongqing, China. The samples were analyzed for the concentrations of various ions (Na+, K+, Ca2+, Mg2+, Ba2+, Sr2+, Cl−, SO42−, Br−, HCO3−, etc.) and for the stable isotope composition (δD and δ18O) of water. With increasing flowback time, the ionic concentration and total salinity increased (e.g., from 315 mg/L to 37117 mg/L after 38 days for well Z203), stable isotopic ratios became heavier (e.g., δD values changed from −23.59‰ to −14.32‰, δ18O values changed from −3.91‰ to −1.92‰). The total salinity of the FFW is shown to be the result of mixing of the highly saline formation water and the low-salinity fracturing water. FFW from Z205 had higher concentrations of Li+ and NO3−, heavier stable isotope compositions, larger Na+/Cl− ratio, smaller (Cl−-Na+)/Mg2+ ratio, and larger SO42− × 100/Cl− ratio compared to the other two wells. All these phenomena revealed that Z205 is more likely to contact with active aquifers which is not conducive to natural gas preservation, because Z205 is close to (less 300 m from) a grade II fault. The RITS and RSIH with flowback time in Z203 were higher than Z202-H1, which shows that FFW from Z203 contained a greater fraction of formation water released from pores or fractures due to complex the network fractures formed by fracturing. Therefore, the fracturing operations of Z203 is better than Z202-H1. This result can reveal the reason for the production difference of adjacent wells, which is difficult to explain by similar total SRV.

Abstract:
Flowback/Produced fluid samples were collected from several wells from two Utica/Point Pleasant (UPP) sites (UPPW and UPPS) in Ohio, and one Marcellus (Marcellus Shale Energy and Environment Laboratory (MSEEL)) site in West Virginia over a period of approximately two years. Although these formations have different ages, depositional environments, diagenetic histories, and geochemical and mineralogical compositions (i.e. the UPP is significantly more carbonate rich than the Marcellus which is more siliceous), analysis of trends in fluid species over time shows that, overall, the TDS and major solubilized elements (Na, Ca, Cl) in the UPP and Marcellus brines are remarkably similar. Total dissolved solutes (TDS) in these brines ranged from approximately 40 to 250 g/L salt, and in general, concentrations increased with time elapsed since natural gas well completion and stimulation. The behavior of Na, Br, and Cl suggests that the produced water signatures from these formations are largely derived from the native formational brines which display evidence of originating from evaporated seawater. There is a strong correlation between Cl and Br, indicating that both species behave conservatively, and the similarity among each of these brines suggests no appreciable contribution of salt from halite dissolution because Br is excluded from the halite structure. Cl/Br ratios in the brines range from ~80 to 120 (mg/L/mg/L). Other elements, such as K, which readily reacts between fluids and ion exchange sites on clays, generally exhibit conservative behavior for an individual site, but show significant variations among each of the different well pads. The concentrations of Sr and Ba vary dramatically among well sites, and increase with respect to Cl− over time, suggesting increasing solubilization, presumably from desorption from clay minerals or dissolution of carbonates or sulfates from the source formation(s). The UPPW well site has very low Ba due to high-sulfate input fluid, which resulted in precipitation of barite/celestite in the brines. In contrast the UPPS well site had elevated Sr (~ 3500 mg/L), presumably due to the use of Sr-rich recycled brine used in hydraulic fracturing. The Marcellus site had the highest Ba concentrations (up to 10 g/L) and highest Ba/Sr ratios in the fluids, due to the high concentration of barium in the Marcellus target (~ 1000 ppm, as compared to ~200 ppm in the UPP). These observations suggest that solutes in the FP fluids are derived from native brines, water-rock interactions that have occurred over geologic time scales, as well as some contribution from contemporaneous reactions in the subsurface. The results also show that the composition of the injected fluid can influence flowback fluid chemistry and possibly production efficiency.

Abstract:
Oilfield flowback and produced water (FPW) is a waste stream that may offer an alternative source of water for multiple beneficial uses. One practice gaining interest in several semi-arid states is the reuse of FPW for agricultural irrigation. However, it is unknown if the reuse of FPW on edible crops could increase health risks from ingestion of exposed food, or impact crop growth. A greenhouse experiment was conducted using wheat (Triticum aestivum) to investigate the uptake potential of select hydraulic fracturing additives known to be associated with health risks. The selected chemicals included acrylamide, didecyldimethylammonium chloride (DDAC), diethanolamine, and tetramethylammonium chloride (TMAC). Mature wheat grain was extracted and analyzed by liquid chromatography-triple quadrupole mass spectrometry (LC-QQQ) to quantify chemical uptake. Plant development observations were also documented to evaluate impacts of the chemicals on crop yield. Analytical results indicated that TMAC and diethanolamine had significantly higher uptake into both wheat grain and stems than control plants which were not exposed to the four chemicals under investigation. Acrylamide was measured in statistically higher concentrations in the stems only, while DDAC was not detected in grain or stems. Growth impacts included lodging in treated wheat plants due to increased stem height and grain weight, potentially resulting from increased nitrogen application. While analytical results show that uptake of select hydraulic fracturing chemicals in wheat grain and stems is measurable, reuse of FPW for irrigation in real world scenarios would likely result in less uptake because water would be subject to natural degradation, and often treatment and dilution practices. Nonetheless, based on the outstanding data gaps associated with this research topic, chemical specific treatment and regulatory safeguards are still recommended.

Abstract:
The large-scale extraction of unconventional resources from shale reservoirs utilizing horizontal hydraulic fracturing has significantly improved economic development in U.S. However, the increased well production has been accompanied by rising concerns about potential impact resulting from excessive freshwater usage and wastewater generation. Currently, water issues have become increasingly challenging with the development of shale reservoirs. In this paper, technical, economic, and environmental challenges encountered during energy production are reviewed with a focus on water issues due to hydraulic fracturing in the U.S. Moreover, the detailed discussion of characteristics and contaminant sources of wastewater indicates the wastewater composition is complicated and varies over time and location. Understanding these factors contributed to high contaminant levels of wastewaters is important to grow awareness of the impacts of hydraulic fracturing on water quality for both operators and the public. Furthermore, pertinent wastewater management strategies for different purposes are highlighted. Although there is no one-size-fits-all solution, understanding the advantages and limitations of different treatment methods is critical for decision-makers to develop appropriate management system. The aim behind this review is to provide a reference for selecting better and practical solutions for current wastewater issues and identifying key issues for future research.

Abstract:
This research assessed the efficacy of UV and UV advanced oxidation processes (UV/AOPs) to reduce dissolved organic carbon (DOC), total petroleum hydrocarbons (TPH), and microorganisms in hydraulic fracturing produced water. To improve water quality conditions before UV treatment with and without added hydrogen peroxide (UV/H2O2), produced water was treated with coagulation, flocculation, and sedimentation (CFS) and biologically activated carbon filtration (BACF). BACF was more effective than CFS as a pre-UV and UV/AOP treatment strategy and reduced DOC, TPH, and absorbing species by over 70% which, subsequently, resulted in the highest hydroxyl radical steady-state concentrations during UV and UV/H2O2 experiments. UV alone minimally degraded DOC, while UV/H2O2 improved DOC and TPH degradation by 9% to 36%. Interestingly, UV without added H2O2 created an in situ AOP by generating hydroxyl radicals with similar steady-state concentrations to that of UV/H2O2. UV was found to be highly effective for the inactivation of microorganisms that were cultured in produced water by reducing microbial communities dominated by Citrobacter by 4 logs after only 30 mJ/cm2. Together, these results demonstrate UV/AOP as a potential strategy to not only improve the treatment and reuse of produced water but also reduce biocide use in fracturing fluids.

Abstract:
This review focuses on recent developments in electrochemical technology (with special emphasis on electrocoagulation, electro-oxidation, and electro-Fenton) to treat petroleum industry effluents (offshore and hydraulic fracturing extraction, as well as refinery effluents). In addition, an overview is given of what these processes face to position themselves as consolidated technologies.

Abstract:
Hydraulic fracturing of unconventional hydrocarbon resources involves the sequential injection of a high-pressure, particle-laden fluid with varying pH’s to make commercial production viable in low permeability rocks. This process both requires and produces extraordinary volumes of water. The water used for hydraulic fracturing is typically fresh, whereas “flowback” water is typically saline with a variety of additives which complicate safe disposal. As production operations continue to expand, there is an increasing interest in treating and reusing this high-salinity produced water for further fracturing. Here we review the relevant transport and geochemical properties of shales, and critically analyze the impact of water chemistry (including produced water) on these properties. We discuss five major geochemical mechanisms that are prominently involved in the temporal and spatial evolution of fractures during the stimulation and production phase: shale softening, mineral dissolution, mineral precipitation, fines migration, and wettability alteration. A higher salinity fluid creates both benefits and complications in controlling these mechanisms. For example, higher salinity fluid inhibits clay dispersion, but simultaneously requires more additives to achieve appropriate viscosity for proppant emplacement. In total this review highlights the nuances of enhanced hydrogeochemical shale stimulation in relation to the choice of fracturing fluid chemistry.

Abstract:
Produced water (PW) generation has been increasing recently due to the expansion of fossil fuel extraction and the aging of oil wells worldwide and especially in the United States (US). The adverse health risks, seismicity, and environmental impacts associated with PW have become a challenging concern. Therefore, there is increased demand for improved PW treatment and reuse management options. There are multiple methods for treating PW; this article focuses on treatment through membrane filtration. Moreover, this mini review aims to summarize statistics on PW abundance, trends in PW generation over time, to briefly call attention to health-related issues, highlight some treatment challenges, and mention potential purposes for reuse with an emphasis on the US, the largest generator of PW worldwide.

Abstract:
Hydraulic fracturing has become widely used in recent years to access vast global unconventional sources of oil and gas. This process involves the injection of proprietary mixtures of water and chemicals to fracture shale formations and extract the hydrocarbons trapped within. These injection fluids, along with minerals, hydrocarbons, and saline waters present within the formations being drilled into, return to the surface as flowback and produced water (FPW). FPW is a highly complex mixture, containing metals, salts and clay, as well as many organic chemicals, including polycyclic aromatic hydrocarbons such as phenanthrene. The present study sought to determine the effects of temperature on the accumulation of phenanthrene in rainbow trout (Oncorhynchus mykiss). This model organism resides in rivers overlapping the Montney and Duvernay formations, both highly developed formations for hydraulic fracturing. Rainbow trout acclimated to temperatures of 4, 13 and 17°C were exposed to either 5% or 20% FPW, as well as saline mixtures representing the exact ionic content of FPW to determine the accumulation of radiolabelled 14C phenanthrene within the gill, gut, liver and gallbladder. FPW exposure reduced the overall accumulation of phenanthrene in a manner most often similar to high salinity exposure, indicating that the high ionic strength of FPW is the primary factor affecting accumulation. Accumulation was different at the temperature extremes (4 and 17°C), although no consistent relationship was observed between temperature and accumulation across the observed tissues. These results indicate that several physiological responses occur as a result of FPW exposure and water temperature change which dictate phenanthrene uptake, particularly in the gills. Temperature (and seasonality) alone cannot be used to model the potential accumulation of polycyclic aromatic hydrocarbons after FPW spills.

Abstract:
Releases of oil and gas (OG) wastewaters can have complex effects on stream-water quality and downstream organisms, due to sediment-water interactions and groundwater/surface water exchange. Previously, elevated concentrations of sodium (Na), chloride (Cl), barium (Ba), strontium (Sr), and lithium (Li), and trace hydrocarbons were determined to be key markers of OG wastewater releases when combined with Sr and radium (Ra) isotopic compositions. Here, we assessed the persistence of an OG wastewater spill in a creek in North Dakota using a combination of geochemical measurements and modeling, hydrologic analysis, and geophysical investigations. OG wastewater comprised 0.1 to 0.3% of the stream-water compositions at downstream sites in February and June 2015, but could not be quantified in 2016 and 2017. However, OG-wastewater markers persisted in sediments and pore water for 2.5 years after the spill and up to 7.2-km downstream from the spill site. Concentrations of OG wastewater constituents were highly variable depending on the hydrologic conditions. Electromagnetic measurements indicated substantially higher electrical conductivity in groundwater seeps below the streambed 7.2 km downstream from the spill site. Geomorphic investigations revealed mobilization of sediment is an important contaminant transport process. Labile Ba, Ra, Sr, and ammonium (NH4) concentrations extracted from sediments indicated sediments are a long-term reservoir of these constituents, both in the creek and on the floodplain. Using the drivers of ecological effects identified at this intensively studied site we identified 41 watersheds across the North Dakota landscape that may be subject to similar episodic inputs from OG wastewater spills. Effects of contaminants released to the environment during OG waste management activities remain poorly understood; however, analyses of Ra and Sr isotopic compositions, as well trace inorganic and organic compound concentrations at these sites in pore-water provide insights into potentials for animal and human exposures well outside source remediation zones.

Abstract:
Hydraulic fracturing flowback and produced water (FPW) is a highly complex and heterogenous wastewater by-product of hydraulic fracturing practices. To date, no research has examined how FPW exposure to freshwater biota may affect energetic homeostasis following subsequent induction of detoxification processes. Rainbow trout (Oncorhynchus mykiss) were acutely exposed for 48 h to either 2.5% or 7.5% FPW, and hepatic metabolism was assessed either immediately or following a 3-week recovery period. Induction of xenobiotic metabolism was observed with an 8.8-fold increase in ethoxyresorufin-O-deethylase (EROD) activity after 48 h exposure to 7.5% FPW, alongside a 10.3-fold increase in the mRNA abundance of cyp1a, both of which returned to basal level after three weeks. Glucose uptake capacity was elevated by 6.8- and 12.9-fold following 2.5% and 7.5% FPW exposure, respectively, while alanine uptake was variable. Activity measurements and mRNA abundance of key enzymes involved in hepatic metabolism indicated that aerobic metabolism was maintained with exposure, as was glycolysis. Gluconeogenesis, as measured by phosphoenolpyruvate carboxykinase (PEPCK) activity, decreased by ~30% 48 h following 2.5% FPW exposure and ~20% 3 weeks after 7.5% FPW exposure. The abundance of pepck mRNA activity followed similar, yet non-significant, trends. Finally, a delayed increase in amino acid catabolism was observed, as glutamate dehydrogenase (GDH) activity was increased 2-fold in 7.5% FPW exposed fish when compared to saline control fish at the 3-week time point. We provide evidence to suggest that although hepatic metabolism is altered following acute FPW exposure, metabolic homeostasis generally returns 3-weeks post-exposure.

Abstract:
The Utica and Marcellus Shale Plays in the Appalachian Basin are the fourth and first largest natural gas producing plays in the United States, respectively. Hydrocarbon production generates large volumes of brine (“produced water”) that must be disposed of, treated, or reused. Though Marcellus brines have been studied extensively, there are few studies from the Utica Shale Play. This study presents new brine chemical analyses from 16 Utica Shale Play wells in Ohio and Pennsylvania. Results from Na–Cl–Br systematics and stable and radiogenic isotopes suggest that the Utica Shale Play brines are likely residual pore water concentrated beyond halite saturation during the formation of the Ordovician Beekmantown evaporative sequence. The narrow range of chemistry for the Utica Shale Play produced waters (e.g., total dissolved solids = 214–283 g/L) over both time and space implies a consistent composition for disposal and reuse planning. The amount of salt produced annually from the Utica Shale Play is equivalent to 3.4% of the annual U.S. halite production. Utica Shale Play brines have radium activities 580 times the EPA maximum contaminant level and are supersaturated with respect to barite, indicating the potential for surface and aqueous radium hazards if not properly disposed of.

Abstract:
Hydraulic fracturing is often criticized due in part to the potential degradation of ground and surface water quality by high-salinity produced water generated during well stimulation and production. This preliminary study evaluated the response of the freshwater mussel, Elliptio complanata, after exposure to produced water. A limited number of adult mussels were grown over an 8-week period in tanks dosed with produced water collected from a hydraulically fractured well. The fatty tissue and carbonate shells were assessed for accumulation of both inorganic and organic pollutants. Ba, Sr, and cyclic hydrocarbons indicated the potential to accumulate in the soft tissue of freshwater mussels following exposure to diluted oil and gas produced water. Exposed mussels showed accumulation of Ba in the soft tissue several hundred times above background water concentrations and increased concentrations of Sr. Cyclic hydrocarbons were detected in dosed mussels and principle component analysis of gas chromatograph time-of-flight mass spectrometer results could be a novel tool to help identify areas where aquatic organisms are impacted by oil and gas produced water, but larger studies with greater replication are necessary to confirm these results.

Abstract:
Unconventional shale gas production in the United States has been largely improved due to the development of hydraulic fracturing technology and is projected to rapidly grow in the coming years. However, the acquisition of freshwater and management of flowback and produced (FP) water associated with hydraulic fracturing operation are two of the greatest challenges in shale gas development, especially in arid regions. For efficient and sustainable water management, a better understanding of freshwater consumption and FP water production for shale gas wells is necessary to appropriately expand and upgrade the existing water network and shale gas network. To achieve this, we first collected water-use volume and monthly FP water production volume data for shale gas wells drilled in the Eagle Ford and Marcellus shale regions. Next, after integrating the data from multiple database sources, the water recovery ratio was calculated as the ratio of cumulative FP water volume to water-use volume and used as a metric to characterize the wells in these two shale regions. Then, we analyzed the obtained water recovery ratio data according to the location and production history to study the spatiotemporal variations across multiple counties and time periods. It shows that around 30% of the collected wells drilled in the Eagle Ford region have the water recovery ratio greater than 1; however, only 1% of the collected wells drilled in the Marcellus region have the water recovery ratio greater than 1. Besides, the water recovery ratios vary significantly across the counties in each shale region. To demonstrate how different water recovery ratio may affect shale gas development, a shale gas supply chain network (SGSCN) optimization model from the literature was utilized to perform two case studies in the Marcellus region. The optimal results suggest that different configurations of SGSCN are required for economically desirable and practically feasible management of shale gas wells with different water recovery ratios.

Abstract:
Fertilizer drawn forward osmosis (FDFO) was proposed to extract fresh water from flowback and produced water (FPW) from shale gas extraction for irrigation, with fertilizer types and membrane orientations assessed. Draw solution (DS) with NH4H2PO4 displayed the best performance, while DS with (NH4)2HPO4 resulted in the most severe membrane fouling. DS with KCl and KNO3 led to substantial reverse solute fluxes. FDFO operation where the active layer of the membrane was facing the feed solution outperformed that when the active layer was facing the DS. Diluted DS and diluted FPW samples were used for irrigation of Cherry radish and Chinese cabbage. Compared to deionized water, irrigation with diluted DS (total dissolved solid (TDS) = 350 mg·L-1) promoted plant growth. In contrast, inhibited plant growth was observed when FPW with high salinity (TDS = 5000 mg·L-1) and low salinity (TDS = 1000 mg·L-1) was used for irrigation of long-term (8-week) plant cultures. Finally, upregulated genes were identified to illustrate the difference in plant growing. The results of this study provide a guide for efficient and safe use of FPW after FDFO treatment for agricultural application.

Abstract:
The increased water consumption for hydraulic fracturing and the volume of wastewater generated from shale gas and tight oil exploration are major environmental challenges associated with unconventional energy development. Recycling of the flowback and produced water for hydraulic fracturing is one of the solutions for reducing the water footprint of hydraulic fracturing and removing highly saline oil and gas wastewater. Here we investigated the implications of recycling saline wastewater for hydraulic fracturing by monitoring the natural gas production, flowback water volume, and the water quality of generated flowback water in shale gas wells from Changning gas field in Sichuan Basin, China. A comparison of two sets of shale gas wells, with six wells in each sub-group, from the same location in Changning gas field shows lower (~20%) natural gas production and higher flowback water volume (~18%) in wells that were fracked with recycled saline wastewater relative to wells that were fracked with fresh water after a year of production. Geochemical analysis suggests that hydraulic fracturing with saline wastewater increases the salinity of the wastewater and reduces the magnitude of water-shale rock interactions. In spite of the direct economic consequences in reduction in natural gas production from recycling of wastewater for hydraulic fracturing, in areas where water scarcity could become a limiting factor for future large-scale shale gas development, hydraulic fracturing with recycled flowback water can be more beneficial than utilization of limited freshwater resources, as long as the higher saline flowback water is fully recycled.

Abstract:
A linear programming (LP) model is presented to investigate optimal shale gas wastewater management strategies for Marcellus shale play in Pennsylvania (PA) focusing on membrane distillation (MD) as the treatment technology. The optimization framework established in this study incorporates (1) detailed treatment cost obtained from techno-economic assessment (TEA) of MD, (2) cost of wastewater transportation from shale gas sites to treatment or disposal facilities, and (3) cost of injection into salt water disposal (SWD) wells. The optimization model is applied to four case study areas with significant shale gas extraction: Greene and Washington counties in Southwest PA and Susquehanna and Bradford counties in Northeast PA. The results reveal that onsite treatment in combination with shale gas wastewater treatment at natural gas compressor stations (NG CS) where available waste heat can be utilized for the treatment process are the most economically advantageous management options. The optimal solution could result in over 60% benefit over direct disposal in SWD, which translates to over $16 million/year savings in the counties in Northeast PA. Furthermore, the results of sensitivity analysis indicate that transportation cost is a major contributor to the overall cost of shale gas wastewater management.

Abstract:
Produced water (PW) is a major waste-product of oil and gas production that some consider a viable agricultural irrigation water source. However, the presence of petroleum hydrocarbons, toxic metals and potentially high salinity of PW may be deleterious for soil health. Thus, we irrigated wheat with minimally treated PW to investigate effects on soil health, wheat growth, and the soil microbiome. Irrigation treatments included control irrigation water (IW), 1% and 5% PW dilutions (1% PW, 5% PW), and a saltwater solution with salinity equivalent to the 5% PW dilution (SW). Wheat was irrigated three times a week, for a total of 2.1 L per pot by harvest. During wheat growth, we measured plant physiological parameters, soil electrical conductivity, as well as profiled soil microbial diversity by performing 16S ribosomal ribonucleic acid (rRNA) gene analysis. Soil health parameters were measured after harvest, including chemical, biological, physical, and nutrient properties that were used to calculate an overall soil health index (SQI). SQI analysis revealed that the SW and 5% PW treatments had significantly reduced soil health as compared to the control. Furthermore, the 16S rRNA gene analysis showed that the microbial community membership and structure was significantly different between irrigation treatments, highlighting shifts in the soil microbiome which may impact soil biochemical cycling. Both the SW- and 5% PW-treated wheat had reduced yields as compared to the control. Our results indicate that irrigating wheat with minimally treated PW may result in yield decreases, as well as reducing both overall soil health and soil microbial community diversity. Future large-scale field studies are needed to determine the long-term soil health effects of PW on different soil types and crops.

Abstract:
As global exploration of shale gas reserves increases, there is a need for accurate and efficient approach to proper water management, which is one of the vital problems related to shale gas production. This study looks at the effect of using multiple or hybrid treatment technologies in maximizing hydraulic fracturing wastewater reuse, whilst ensuring sustainability of the process in terms of energy and associated cost. The study considers ultrafiltration and membrane distillation processes as possible pre-treatment and desalination technologies for flowback water management. It also considers the possibility of supplying the electrical and thermal energy requirements of these regenerators using flared gas. Two different scenarios are considered based on flowback water composition in hydraulic fracturing in terms of salinity. Application of the proposed model to a case study leads to 24.13 % reduction in the quantity of water needed for fracturing. In terms of energy requirements, the approach yields 31.6 % reduction in the required thermal energy in membrane distillation and 8.62 % in energy requirement for ultrafiltration. For flowback water with moderate total dissolved solids concentration, 93.6 % of wastewater reuse comes from pre-treated water by ultrafiltration and 6.4 % from membrane distillation. However, as the flowback water salinity becomes higher, the percentage of pre-treated reusable water reduces to 81.1 % and the percentage supply through membrane distillation increases to 18.9 %. In all cases, the results indicate that the decision to allow the pre-treated water to pass through desalination technology strictly depends on the quantity of water required by a wellpad and the salinity of the wastewater.

Abstract:
Uranium and other radionuclides are prominent in many unconventional oil/gas shales and is a potential contaminant in flowback/produced waters due to the large volumes/types of chemicals injected into the subsurface during stimulation. To understand the stability of U before and after stimulation, a geochemical study of U speciation was carried out on three shales (Marcellus, Green River, and Barnett). Two types of samples for each shale were subjected to sequential chemical extractions: unreacted and shale reacted with synthetic hydraulic fracture fluid. A significant proportion of the total U (20-57%) was released from these three shales after reaction with fracture fluid, indicating that U is readily leachable. The total U released exceeds labile water soluble and exchangeable fractions in unreacted samples, indicating that fluids leach more recalcitrant phases in the shale. Radiographic analysis of unreacted Marcellus shale thin sections shows U associated with detrital quartz and the clay matrix in the shale. Detrital zircon and TiO2 identified by electron microprobe could account for the hotspots. This study shows that significant proportions of U in three shales are mobile upon stimulation. In addition, the extent of mobilization of U depends on the U species in these rocks.

Abstract:
Large amounts of fracturing flowback and wastewater with complex compositions are produced during hydraulic fracturing. Characterization of hydraulic fracturing flowback and produced water (HF-FPW) is an important initial step in efforts to determine a suitable treatment method for this type of wastewater. In the present study, fracturing flowback and produced water samples were obtained from well CN-F and well CN-E in the prophase and anaphase stages of the Changning shale gas mining area. Chemical characterization of inorganic and organic substances was then conducted. Metal contents were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES), and all inorganic anions involved were determined by ion chromatography. The organic pollutant components were analyzed in detail by combining Fourier transform infrared spectrometer (FTIR) and gas chromatography-mass spectrometer (GC-MS). Results showed that samples contained salt (TDS = 30,000–50,000 mg/L), metals (e.g., 650 ± 50 mg/L calcium), and total organic carbon (TOC = 32–178 mg/L). The organic substances detected in all samples could be divided into six categories, alkanes, aromatics, halogenated hydrocarbons, alcohols, esters, and ketones. C6–C21 straight-chain alkanes and C7–C13 naphthenes had the highest amount of organic matter, reaching more than 48%. The organic matter contained fracturing fluid additives, such as surfactants (e.g., ethylene glycol), and nitrotrichloromethane, which is a chlorinated product of some additives. These results provide information on the chemical composition of HF-FPW in Sichuan, China, as well as a basis for subsequent processing.

Abstract:
Produced water is the largest waste stream associated with oil and gas operations. This complex fluid contains petroleum hydrocarbons, heavy metals, salts, naturally occurring radioactive materials and any remaining chemical additives. In the United States, west of the 98th meridian, the federal National Pollutant Discharge Elimination System (NPDES) exemption allows release of produced water for agricultural beneficial reuse. The goal of this study was to quantify mutagenicity of a produced water NPDES release and discharge stream. We used four mutation assays in budding yeast cells that provide rate estimates for copy number variation (CNV) duplications and deletions, as well as forward and reversion point mutations. Higher mutation rates were observed at the discharge and decreased with distance downstream, which correlated with the concentrations of known carcinogens detected in the stream (e.g., benzene, radium), described in a companion study. Mutation rate increases were most prominent for CNV duplications and were higher than mutations observed in mixtures of known toxic compounds. Additionally, the samples were evaluated for acute toxicity in Daphnia magna and developmental toxicity in zebrafish. Acute toxicity was minimal, and no developmental toxicity was observed. This study illustrates that chemical analysis alone (McLaughlin et al., 2020) is insufficient for characterizing the risk of produced water NPDES releases and that a thorough evaluation of chronic toxicity is necessary to fully assess produced water for beneficial reuse.

Abstract:
While development of the Utica/Point Pleasant Shale (UPP) is extensive in Ohio (U.S.) and increasing in Pennsylvania and West Virginia, few studies report the chemistry of produced waters from UPP wells. These data have important implications for developing best management practices for handling and waste disposal, or identifying the fluid in the event of accidental spill events. Here, we evaluated the elemental and isotope chemistry of UPP produced waters from 26 wells throughout Ohio, Pennsylvania, and West Virginia to determine any unique fluid chemistries that could be used for forensic studies. Compared to the Marcellus, UPP produced waters contain higher activities of total radium (226Ra + 228Ra) and higher 228Ra/226Ra ratios. As with the Marcellus Shale, elemental ratios (Sr/Ca) and isotope ratios (87Sr/86Sr) can distinguish UPP produced waters from many conventional oil and gas formations. Sr/Ca and 87Sr/86Sr ratios can fingerprint small fractions (∼0.1%) of UPP produced water in freshwater. However, because Marcellus and UPP produced waters display similar major elemental chemistry (i.e., Na, Ca, and Cl) and overlapping ratios of Sr/Ca and 87Sr/86Sr, 228Ra/226Ra ratios may be the best tracer to distinguish these waters.

Abstract:
Unconventional methods of oil and natural gas extraction have been a growing part of North America's energy sector for the past 20-30 years. Technologies such as horizontal hydraulic fracturing have facilitated the exploitation of geologic reserves that were previously resistant to standard drilling approaches. However, the environmental risks associated with hydraulic fracturing are relatively understudied. One such hazard is the wastewater by-product of hydraulic fracturing processes: flowback and produced water (FPW). During FPW production, transport, and storage, there are many potential pathways for environmental exposure. In the current review, toxicological hazards associated with FPW surface water contamination events and potential effects on freshwater biota are assessed. This review contains an extensive survey of chemicals commonly associated with FPW samples from shale formations across North America and median 50% lethal concentration values (LC50) of corresponding chemicals for many freshwater organisms. We identify the characteristics of FPW which may have the greatest potential to be drivers of toxicity to freshwater organisms. Notably, components associated with salinity, the organic fraction, and metal species are reviewed. Additionally, we examine the current state of FPW production in North America and identify the most significant obstacles impeding proper risk assessment development when environmental contamination events of this wastewater occur. Findings within this study will serve to catalyze further work on areas currently lacking in FPW research, including expanded whole effluent testing, repeated and chronic FPW exposure studies, and toxicity identification evaluations.

Abstract:
Mixing of acid mine drainage (AMD) and hydraulic fracturing flowback fluids (HFFF) could represent an efficient management practice to simultaneously manage two complex energy wastewater streams while reducing freshwater resource consumption. AMD discharges offer generally high sulfate concentrations, especially from the bituminous coal region of Pennsylvania; unconventional Marcellus shale gas wells generally yield HFFF enriched in alkaline earth metals such as Sr and Ba, known to cause scaling issues in oil and gas (O&G) production. Mixing the two waters can precipitate HFFF-Ba and -Sr with AMD-SO4, therefore removing them from solution. Four AMD discharges and HFFF from two unconventional Marcellus shale gas wells were characterized and mixed in batch reactors for 14 days. Ba could be completely removed from solution within 1 day of mixing in the form BaxSr1–xSO4 and no further significant precipitation occurred after 2 days. Total removal efficiencies of Ba + Sr + SO4 and the proportion of Ba and Sr in BaxSr1–xSO4 depended upon the Ba/Sr ratio in the initial HFFF. A geochemical model was calibrated from batch reactor data and used to identify optimum AMD–HFFF mixing ratios that maximize total removal efficiencies (Ba + Sr + SO4) for reuse in O&G development. Increasing Ba/Sr ratios can enhance total removal efficiency but decrease the efficiency of Ra removal. Thus, treatment objectives and intended beneficial reuse need to be identified prior to optimizing the treatment of HFFF with AMD.

Abstract:
Shale gas extraction processes generate a large amount of hypersaline wastewater, whose spills or discharges may significantly increase the bromide levels in downstream water supplies and result in the formation of brominated disinfection byproducts (DBPs) upon chlorination. Although a few studies have investigated selective bromide removal from produced water, the low removal efficiencies and complex system setups are not desirable. In this study, we examined a simple cost-effective approach for selective bromide removal from produced water relying on the oxidation by un-activated peroxymonosulfate (PMS). More than 95% of bromide was removed as Br2(g) in less than 10 min under weakly acidic conditions without significant formation of Cl2(g) even when the chloride concentration was more than two orders of magnitude higher. A kinetic model considering the involved reactions was then developed to describe the process well under various reaction conditions. The organic compounds in produced water neither noticeably lowered bromide removal efficiency nor reacted with the halogen species to form halogenated byproducts. The tests in batch and continuously-stirred tank reactor systems suggested that it was feasible to achieve both high bromide removal and neutral effluent pH such that further pH adjustment was not necessary before discharge. After the treatment, the effect of the produced water on DBP formation was largely eliminated.

Abstract:
Produced water is a byproduct of oil and gas production. The chemistry of produced water may provide information about the source of the fluid and its evolution, leading to an improved understanding of the hydrology of petroleum systems. In this study, samples from 19 wells from the Tuscaloosa Marine Shale (TMS) in Mississippi and Louisiana, USA were analyzed for their major and trace element compositions. Data obtained from produced waters from the TMS were compared to existing chemical data from produced waters collected from nearby hydrocarbon reservoir rocks within the Gulf Coast Basin. The results show that produced waters from the TMS are highly saline, with a mean concentration of 15.9 g/L of total dissolved solids. Comparison of the chemistry of produced water from the TMS to early flowback waters demonstrated a rapid shift from the more dilute fracturing fluid to the formation water endmember composition. Most of the trace metals showed a moderate to strong correlation with the overall salinity of the waters. Concentrations of Cu and V showed a moderate correlation with the amount of oil produced from the TMS wells, suggesting that these elements are strongly affiliated with the kerogen and subsequent dissolved (<0.45 μm) organic phases. Analysis of the volume of produced water compared to the volume of water used during hydraulic fracturing indicates that 15%–110% of the water volume used for fracking had been returned to the surface over the 2–5 year production period of the sampled wells. Chloride to bromide ratios suggest that the formation water in the TMS was derived from evaporated seawater. Comparison to historical data for produced waters in other formations in and around the Mississippi Salt Basin showed that waters in all the formations had a consistent origin (bitterns likely derived from the formation of the Louann salt). This implies that over geologic time periods fluids migrated through the TMS despite its low permeability present-day. The TMS also exhibited lower concentrations of dissolved transition metals such as Zn and Pb relative to those described in adjacent formations. This observation may suggest the presence of larger amounts of H2S, limiting the solubility of sulfide phases, in the shale unit relative to adjacent reservoir units.

Abstract:
The data in this report are associated with https://doi.org/10.1016/j.scitotenv.2020.137085 and include data on water volumes and water quality related to the major unconventional oil and gas plays in the U.S.. The data include volumes of water co-produced with oil and gas production, county-level estimates of annual water use volumes by various sectors, including hydraulic fracturing water use, and the quality of produced water. The data on volumes of produced water and hydraulic fracturing water volumes were obtained from the IHS Enerdeq and FracFocus databases. Water use in other sectors were obtained from the U.S. Geological Survey water use database. Data on produced water quality were obtained from the USGS produced waters database.

Abstract:
Waters co-produced with hydrocarbons from unconventional oil and gas reservoirs such as the hydraulically fractured Marcellus Shale in the Appalachian Basin, USA, contain high levels of total dissolved solids (TDS), including Ba, which has been variously ascribed to drilling mud dissolution, interaction with pore fluids or shale exchangeable sites, or fluid migration through fractures. Here we show that Middle Devonian Marcellus Shale produced waters contain some of the heaviest Ba (high 138Ba/134Ba) measured to date (δ138Ba = +0.4‰ to +1.5‰ ±0.06‰), and are distinct from overlying Upper Devonian/Lower Mississippian reservoirs (δ138Ba = -0.8‰ to -0.5‰). Marcellus Shale produced water values do not overlap with drilling mud barite (δ138Ba ≈ 0.0‰), and are significantly offset from Ba reservoirs within the producing portion of the Marcellus Shale, including exchangeable sites and carbonate cement. Precipitation, desorption and diffusion processes are insufficient or in the wrong direction to produce the observed enrichments in heavy Ba. We hypothesize that the produced water is derived primarily from brines adjacent to and most likely below the Marcellus Shale, although such deep brines have not yet been obtained for Ba isotope analysis. Barium isotopes show promise for tracking formation waters and for understanding water-rock interaction under downhole conditions.

Abstract:
Unconventional oil and natural gas extraction (UOG) combines directional drilling and hydraulic fracturing and produces billions of liters of wastewater per year. Herein, we review experimental studies that evaluated the potential endocrine-mediated health impacts of exposure to a mixture of 23 UOG chemicals commonly found in wastewater. The purpose of this manuscript is to synthesize and summarize a body of work using the same UOG-mix but with different model systems and physiological endpoints in multiple experiments. The studies reviewed were conducted in laboratory animals (mice or tadpoles) and human tissue culture cells. A key feature of the in vivo studies was the use of four environmentally relevant doses spanning three orders of magnitude ranging from concentrations found in surface and ground water in UOG dense areas to concentrations found in UOG wastewater. This UOG-mix exhibited potent antagonist activity for the estrogen, androgen, glucocorticoid, progesterone, and thyroid receptors in human tissue culture cells. Subsequently, pregnant mice were administered the UOG-mix in drinking water and offspring were examined in adulthood or to tadpoles. Developmental exposure profoundly impacted pituitary hormone concentrations, reduced sperm counts, altered folliculogenesis, and increased mammary gland ductal density and preneoplastic lesions in mice. It also altered energy expenditure, exploratory and risk-taking behavior, the immune system in three immune models in mice, and affected basal and antiviral immunity in frogs. These findings highlight the diverse systems affected by developmental EDC exposure and the need to examine human and animal health in UOG regions.

Abstract:
Membrane-based desalination system under consideration for shale gas fracturing flowback wastewater treatment involves ultrafiltration (UF), reverse osmosis (RO) and storage tanks. The membrane unit (UF, RO) consists of online washing, operation and offline chemical washing sub-units. These sub-units operate in semi-continuous mode and have the similar characteristics as batch water-using processes. Based on their semi-continuous behaviors, the models of UF and RO sub-units are developed. The objective is to maximize the total water production ratio and profit while minimize storage tank capacity. Three nonlinear programming optimization models are developed for optimal design of UF-RO treatment system for shale gas fracturing flowback wastewater. Two scenarios – fixed schedule and fixed operating period for UF/RO treatment sub-units are investigated. Results show that with the increasing the operation duration of treatment sub-units, the water production ratio and profit will increase. The schedule of treatment sub-units has significant impact on the water-storage profiles, without adversely affecting the water production ratio. The proposed approach can guide the design of UF-RO desalination system.

Abstract:
The organic composition of produced waters (flowback and formation waters) from the middle member of the Bakken Formation and the Three Forks Formation in the Williston Basin, North Dakota were examined to aid in the remediation of surface contamination and help develop treatment methods for produced-water recycling. Twelve produced water samples were collected from the Bakken and Three Forks Formations and analyzed for non-purgeable dissolved organic carbon (NPDOC), acetate, and extractable hydrocarbons. NPDOC and acetate concentrations from sampled wells from ranged from 33-190 mg per liter (mg/L) and 16–40 mg/L, respectively. Concentrations of individual extractable hydrocarbon compounds ranged from less than 1 to greater than 400 μg per liter (μg/L), and included polycyclic aromatic hydrocarbons (PAHs), phenolic compounds, glycol ethers, and cyclic ketones. While the limited number of samples, varying well production age, and lack of knowledge of on-going well treatments complicate conclusions, this report adds to the limited knowledge of organics in produced waters from the Bakken and Three Forks Formations.

Abstract:
Produced water is the largest volume of waste product generated during oil and natural gas exploration and production. The traditional method to dispose of produced water involves deep well injection, but this option is becoming more challenging due to high operational cost, limited disposal capacity, and more stringent regulations. Meanwhile, large volumes of freshwater are used for hydraulic fracturing. The goal of this study is to develop cost-effective technologies, and optimize system design and operation to treat highly saline produced water (120–140 g/L total dissolved solids) for hydraulic fracturing. Produced water was collected from a salt water disposal facility in the Permian Basin, New Mexico. Chemical coagulation (CC) using ferric chloride and aluminum sulfate as coagulants was compared with electrocoagulation (EC) with aluminum electrodes for removal of suspended contaminants. The effects of coagulant dose, current density, and hydraulic retention time during EC on turbidity removal were investigated. Experimental results showed that aluminum sulfate was more efficient and cost-effective than ferric chloride for removing turbidity from produced water. The optimal aluminum dose was achieved at operating current density of 6.60 mA/cm2 and 12 min contact time during EC treatment, which resulted in 74% removal of suspended solids and 53%–78% removal of total organic carbon (TOC). The energy requirement of EC was calculated 0.36 kWh/m3 of water treated. The total operating cost of EC was estimated $0.44/m3 of treated water, which is 1.7 or 1.2 times higher than CC using alum or ferric chloride as the coagulant, respectively. The EC operating cost was primarily associated with the consumption of aluminum electrode materials due to faradaic reactions and electrodes corrosions. EC has the advantage of shorter retention time, in situ production of coagulants, less sludge generation, and high mobility for onsite produced water treatment. The fine particles and other contaminants after coagulation were further treated in continuous-flow columns packed with different filter media, including agricultural waste products (pecan shell, walnut shell, and biochar), and new and spent granular activated carbon (GAC). Turbidity, TOC, metals, and electrical conductivity were monitored to evaluate the performance of the treatment system and the adsorption capacities of different media. Biochar and GAC showed the greatest removal of turbidity and TOC in produced water. These treatment technologies were demonstrated to be effective for the removal of suspended constituents and iron, and to produce a clean brine for onsite reuse, such as hydraulic fracturing.

Abstract:
There is increasing interest in beneficial uses of large volumes of wastewater co-produced with oil and gas extraction (produced water, PW) because of water scarcity, potential subsurface disposal limitations, and regional linkages to induced seismicity. Here we quantified PW volumes relative to water demand in different sectors and PW quality relative to treatment and reuse options for the major U.S. shale oil and gas plays. PW volumes from these plays totaled ~600 billion liters (BL, 160 billion gallons, Bgal) in 2017. One year of PW is equal to ~60% of one day of freshwater use in the U.S. For these plays, the total irrigation demand exceeded PW volumes by ~5× whereas municipal demand exceeded PW by ~2×. If PW is reused for hydraulic fracturing (HF) within the energy sector, there would be no excess PW in about half of the plays because HF water demand exceeds PW volumes in those plays. PW quality can be highly saline with median total dissolved solids up to 255 g/L in the Bakken play, ~7× seawater. Intensive water treatment required for PW from most unconventional plays would further reduce PW volumes by at least 2×. Desalination would also result in large volumes of salt concentrates, equivalent to ~3000 Olympic swimming pools in the Permian Delaware Basin in 2017. While water demands outside the energy sector could accommodate PW volumes, much lower PW volumes relative to water demand in most regions would not substantially alleviate water scarcity. However, large projected PW volumes relative to HF water demand over the life of the play in the Permian Delaware Basin may provide a substantial new water source for beneficial use in the future. Large knowledge gaps in PW quality, lack of appropriate regulations, and economic factors currently preclude beneficial uses outside the energy sector in most regions.

Abstract:
Hydraulic fracturing of shale gas extraction generates numerous flowback and produced water (FPW), which will cause huge pollution if not properly treated. Gravity-driven membrane with economic advantages was applied as a pretreatment for desalinating this wastewater. The effects of membrane materials (polyvinylidene fluoride (PVDF) and polyvinylchloride (PVC)) with different mean pore sizes, porosities, contact angles, and pure water permeabilities and hydrostatic pressures (40 and 120 mbar) were investigated. The setups were operated for 90 days and the fluxes stabilized at about 0.87–1.00 L/(m2 h). PVDF membranes with higher price, had 6 % higher stable fluxes than PVC membranes, and the extracellular polymeric substances (EPS) contents in fouling layer of PVDF membranes were 10 %–20 % lower than those of PVC membranes. At higher pressures, the stable fluxes increased by only 8 %, but the total resistances increased by nearly 180 %, and there were more EPS, dissolved organic carbon, Na+, Ca2+, Mg2+, Cl− and NO3− on the fouling layer at 120 mbar. A denser cake layer was formed at a higher hydrostatic pressure, as observed by a scanning electron microscope and energy dispersive spectroscopy. Membrane properties and pressures had no significant effect on permeate quality (p > 0.05).

Abstract:
The worldwide expansion of shale gas production and increased use of hydraulic fracturing have raised public concerns about safety and risks of groundwater resources in shale gas extraction areas. China has the largest shale gas resources in the world, most of which are located in the Sichuan Basin. Shale gas extraction in the Sichuan Basin has been increasing rapidly in recent years. However, the potential impact on shallow groundwater quality has not yet been systematically investigated. In order to evaluate the possible impact of shale gas extraction on groundwater quality, we present, for the first time, the hydrochemistry and Sr isotopic data of shallow groundwater, as well as flowback and produced water (FP water) in the Changning shale gas field in Sichuan Basin, one of the major shale gas fields in China. The Changning FP water is characterized by high salinity (TDS of 13,100–53,500 mg/L), Br/Cl (2.76 × 10−3) and 87Sr/86Sr (0.71849), which are distinguished from the produced waters from nearby conventional gas fields with higher Br/Cl (4.5 × 10−3) and lower 87Sr/86Sr (0.70830–0.71235). The shallow groundwater samples were collected from a Triassic karst aquifer in both active and nonactive shale gas extraction areas. They are dominated by low salinity (TDS of 145–1100 mg/L), Ca-HCO3 and Ca-Mg-HCO3 types water, which are common in carbonate karst aquifers. No statistical difference of the groundwater quality was observed between samples collected in active versus nonactive shale gas extraction areas. Out of 66 analyzed groundwater, three groundwater samples showed relatively higher salinity above the background level, with low 87Sr/86Sr (0.70824–0.7110) and Br/Cl (0.5–1.8 × 10−3) ratios relatively to FP water, excluding the possibility of contamination from FP water. None of the groundwater samples had detected volatile organic compounds (VOCs). The integration of geochemical and statistical analysis shows no direct evidence of groundwater contamination caused by shale gas development.

Abstract:
In the United States, onshore oil and gas extraction operations generate an estimated 900 billion gallons of produced water annually, making it the largest waste stream associated with upstream development of petroleum hydrocarbons. Management and disposal practices of produced water vary from deep well injection to reuse of produced water in agricultural settings. However, there is relatively little information with regard to the chemical or toxicological characteristics of produced water. A comprehensive literature review was performed, screening nearly 16,000 published articles, and identifying 129 papers that included data on chemicals detected in produced water. Searches for information on the potential ecotoxicological or mammalian toxicity of these chemicals revealed that the majority (56%) of these compounds have not been a subject of safety evaluation or mechanistic toxicology studies and 86% lack data to be used to complete a risk assessment, which underscores the lack of toxicological information for the majority of chemical constituents in produced water. The objective of this study was to develop a framework to identify potential constituents of concern in produced water, based on available and predicted toxicological hazard data, to prioritize these chemicals for monitoring, treatment, and research. In order to integrate available evidence to address gaps in toxicological hazard on the chemicals in produced water, we have catalogued available information from ecological toxicity studies, toxicity screening databases, and predicted toxicity values. A Toxicological Priority Index (ToxPi) approach was applied to integrate these various data sources. This research will inform stakeholders and decision-makers on the potential hazards in produced water. In addition, this work presents a method to prioritize compounds that, based on hazard and potential exposure, may be considered during various produced water reuse strategies to reduce possible human health risks and environmental impacts.

Abstract:
Abstract. The response of microbial communities to releases of hydraulic fracturing flowback and produced water (PW) may influence ecosystem functionalities. H

Abstract:

Abstract:
Interest in both environmental impact and potential beneficial uses of produced water (PW) has increased with growth in unconventional oil and gas production, especially in semi-arid regions, e.g. the Permian Basin, the most productive tight-oil region in the USA. Characterization of PW compositional variability is needed to evaluate environmental impact, treatment, and reuse potential. Geochemical variability of PW from Guadalupian (Middle Permian) to Ordovician formations was statistically and geostatistically evaluated in the western half of the Permian Basin (Delaware Basin, Central Basin Platform, and Northwest Shelf) using the US Geological Survey’s Produced Waters Geochemical Database and the New Mexico Water and Infrastructure Data System. Mean total dissolved solids (TDS) of PW increased with depth in the Delaware Basin and Central Basin Platform to the Delaware and Wolfcamp formations (Guadalupian age). Mean TDS decreased with further increases in depth. In contrast, the mean salinity of PW was significantly higher within the shallow, younger formations (largest mean TDS in the Artesia Formation); TDS decreased with depth below Guadalupian age formations in the Northwest Shelf. Kriged contour maps of TDS and major ions illustrated spatial variability across the three geo-structural regions as a function of depth. The occurrence of meteoric waters in upper and deeper formations across the three regions was significant, and was attributed to Laramide Orogeny and Basin and Range extension uplifting and tilting effects and recent water flooding. These results quantify PW composition variability, and suggest that upon treatment, PW would support some uses such as onsite reuse and mining.

Abstract:
Limited understanding of wastewater streams produced from shale oil and gas wells impedes best practices of wastewater treatment and reuse. This study provides a comprehensive and comparative analysis of flowback and produced water from three major and newly developed shale plays (the Bakken shale, North Dakota; the Barnett shale, Texas; and the Denver-Julesburg (DJ) basin, Colorado) in central and western United States. Geochemical features that included more than 10 water quality parameters, dissolved organic matter, as well as microbial community structures were characterized and compared. Results showed that wastewater from Bakken and Barnett shales has extremely high salinity (∼295 g/L total dissolved solids (TDS)) and low organic concentration (80–252 mg/L dissolved organic carbon (DOC)). In contrast, DJ basin showed an opposite trend with low TDS (∼30 g/L) and high organic content (644 mg/L DOC). Excitation-emission matrix (EEM) fluorescence spectra demonstrated that more humic acid and fluvic acid-like organics with higher aromaticity existed in Bakken wastewater than that in Barnett and DJ basin. Microbial communities of Bakken samples were dominated by Fe (III)-reducing bacteria Geobacter, lactic acid bacteria Lactococcus and Enterococcus, and Bradyrhizobium, while DJ basin water showed higher abundance of Rhodococcus, Thermovirga, and sulfate reducing bacteria Thermotoga and Petrotoga. All these bacteria are capable of hydrocarbon degradation. Hydrogenotrophic methanogens dominated the archaeal communities in all samples.

Abstract:
Although multistage hydraulic fracturing is routinely performed for the extraction of hydrocarbon resources from low permeability reservoirs, the downhole geochemical processes linked to the interaction of fracturing fluids with formation brine and reservoir mineralogy remain poorly understood. We present a geochemical dataset of flowback and produced water samples from a hydraulically fractured reservoir in the Montney Formation, Canada, analyzed for major and trace elements and stable isotopes. The dataset consists in 25 samples of flowback and produced waters from a single well, as well as produced water samples from 16 other different producing wells collected in the same field. Additionally, persulfate breaker samples as well as anhydrite and pyrite from cores were also analyzed. The objectives of this study were to understand the geochemical interactions between formation and fracturing fluids and their consequences in the context of tight gas exploitation. The analysis of this dataset allowed for a comprehensive understanding of the coupled downhole geochemical processes, linked in particular to the action of the oxidative breaker. Flowback fluid chemistries were determined to be the result of mixing of formation brine with the hydraulic fracturing fluids as well as coupled geochemical reactions with the reservoir rock such as dissolution of anhydrite and dolomite; pyrite and organic matter oxidation; and calcite, barite, celestite, iron oxides and possibly calcium sulfate scaling. In particular, excess sulfate in the collected samples was found to be mainly derived from anhydrite dissolution, and not from persulfate breaker or pyrite oxidation. The release of heavy metals from the oxidation activity of the breaker was detectable but concentrations of heavy metals in produced fluids remained below the World Health Organization guidelines for drinking water and are therefore of no concern. This is due in part to the co-precipitation of heavy metals with iron oxides and possibly sulfate minerals.

Abstract:
Hydraulic fracturing (HF) flowback and produced water (FPW) can be toxic to aquatic life but its chemical content is largely unknown, variable and complex. Seven FPW samples were collected from a HF operation in the Duvernay Formation (Alberta, Canada) over 30 days of flowback and characterized by a nontarget workflow based on high performance liquid chromatography - high resolution mass spectrometry (HRMS). A modified Kendrick mass defect plot and MS/MS spectral interpretation revealed seven series of homologues composed of ethylene oxide (i.e. -CH2CH2O-), among which a series of aldehydes was proposed as degradation products of polyethylene glycols, and two series of alkyl ethoxylate carboxylates could be proprietary HF additives. Many other ions were confidently assigned a formula by accurate mass measurement and were subsequently prioritized for identification by matching to records in ChemSpider and the US EPA's CompTox Chemistry Dashboard. Quaternary ammonium compounds, amine oxides, organophosphorous compounds, phthalate diesters and hydroxyquinoline were identified with high confidence by MS/MS spectra (Level 3), matching to reference spectra in MassBank (Level 2) or to authentic standards (Level 1). Temporal trends showed that most of the compounds declined in abundance over the first nine days of flowback, except for phthalate diesters and hydroxyquinoline that were still observed on Day 30 and had disappearance half-lives of 61 and 91 days, respectively. All the compounds followed first-order disappearance kinetics in flowback, except for polyoxygenated acids which followed second-order kinetics. This analysis and the workflow, based largely on public on-line databases, enabled profiling of complex organic compounds in HF-FPW, and will likely be useful for further understanding the toxicity and chemical fate of HF-FPW.

Abstract:
Oil and gas (O&G) production in the United States is expected to grow at a substantial rate over the coming decades. Environmental sustainability related to water consumption during O&G extraction can be addressed through treatment and reuse of water returning to the surface after well completion. Water quality is an important factor in reuse applications, and specific treatment technologies must be utilized to remove different contaminants. Among others, biological active filtration can remove dissolved organic matter as a pre-treatment for surface discharge or to facilitate reuse in such applications as hydraulic fracturing, dust suppression, road stabilization, and crop irrigation. Yet, the formation of byproducts during treatment of O&G wastewater remains a concern when evaluating reuse applications. In this study, we investigated the previously unnoticed biotic formation of iodinated organic compounds (IOCs) such as triiodomethane during biological treatment of O&G wastewater for beneficial reuse. Iodide and several IOCs were quantified in O&G produced water before and after treatment in biological active filters filled with different media types over 13 weeks of operation. While iodide and total IOCs were measured at concentrations <53 mg/L and 147 μg/L, respectively, before biological treatment, total IOCs were measured at concentrations close to 4 mg/L after biological treatment. Triiodomethane was the IOC that was predominantly present. IOC formation had a negative strong correlation (r = −0.7 to −0.8, p < 0.05, n = 9) with iodide concentration in the treated O&G wastewater, indicating that iodide introduced to the biological active filter system was utilized in various reactions, including biologically mediated halogenation of organic matter. Additionally, iodide-oxidizing bacteria augmented in the treated produced water pointed towards potential negative environmental implications when releasing biologically treated halide-rich wastewater effluents to the aquatic environment.

Abstract:
Radium measurements in high total dissolved solids (TDS) fluids from oil and gas extraction can have unfavorable precision and accuracy, in part because these high-level impurities incur attenuation. γ spectroscopy is often recommended for determining radium activities in these fluids, but even this method can produce a range of reported activities for the same sample. To reduce measurement duration and to maintain or improve accuracy, we propose a method to rapidly assess both 226Ra and 228Ra and to account for the self-attenuation of γ rays in high-TDS oil and gas fluids when they are monitored by a well detector. In this work, comparisons between a NaCl-only and a multi-cation-chloride synthetic brine spiked with known amounts of 226Ra and 228Ra indicated that both the TDS concentration and the type of TDS (i.e., Na only vs Na–Mg–Ba–Ca–Sr) influenced self-attenuation in well-detector γ spectroscopy, thus highlighting the need to correct for this TDS-influenced self-attenuation. Radium activities can be underestimated if the correction is not applied. For instance, 226Ra activities could be ∼40% lower in a sample when measured directly at the 186 keV energy level if the attenuation of the high TDS of the fluid is not considered. We also showed that using a NaCl-only brine to match the matrix of high-TDS oil and gas brines is inadequate to produce accurate measurements, rather, the full set of cations should be included.