Repository for Oil and Gas Energy Research (ROGER)

Abstract:
Wastewater from shale oil and gas wells contains high levels of organic and inorganic compounds, and the beneficial reuse of produced water requires some level of treatment to remove emulsified oil and grease, suspended solids, and multivalent ions. It is important to identify the quantity and makeup of solids in produced water, so that an optimized reuse or treatment approach can be achieved. This study provides a qualitative and quantitative characterization of solids in frac flowback and produced water from five horizontal wells at two separate sites in the Wattenberg field of Northern Colorado. Difference in solids from wells fractured with fresh water and recycled water is compared in this study, and their distribution and characterization are identified by particle size distribution measurement and X-ray photoelectron spectroscopy (XPS). Results show that particle sizes were smaller and more uniform in produced water samples collected during the first week of production from the wells fractured with recycled water, suggesting that the recycled water was more compatible with the shale formation and wells fractured with recycled water tend to clean out faster.

Abstract:
Controlling microbial activity is a primary concern during the management of the large volumes of wastewater (produced water) generated during high-volume hydraulic fracturing. In this study we analyzed the transcriptional activity (metatranscriptomes) of three produced water samples from the Marcellus Shale. The goal of this study was to describe active metabolic pathways of industrial concern for produced water management and reuse, and to improve understanding of produced water microbial activity. Metatranscriptome analysis revealed active biofilm formation, sulfide production, and stress management mechanisms of the produced water microbial communities. Biofilm-formation and sulfate-reduction pathways were identified in all samples. Genes related to a diverse array of stress response mechanisms were also identified with implications for biocide efficacy. Additionally, active expression of a methanogenesis pathway was identified in a sample of produced water collected prior to holding pond storage. The active microbial community identified by metatranscriptome analysis was markedly different than the community composition as identified by 16S rRNA sequencing, highlighting the value of evaluating the active microbial fraction during assessments of produced water biofouling potential and evaluation of biocide application strategies. These results indicate biofouling and corrosive microbial processes are active in produced water and should be taken into consideration while designing produced water reuse strategies.

Abstract:
Gas shale fracturing relies on a method known as horizontal fracturing to remove gas trapped within the impermeable facies. Conventional vertical and unconventional horizontal fracturing requires a large amount of water to be injected downhole under high pressure. These fracturing fluids can contain high concentrations of petroleum hydrocarbons with known adverse health effects. The development of reuse technologies that reduce the need of potable water requires an accurate understanding of petroleum hydrocarbon loading during key points in the fracturing process. In this study, flowback water quality from both horizontally and vertically fractured wells within the Marcellus Shale region in Pennsylvania and West Virginia were analyzed. Flowback data made available by the Shale Network were collected using geographic information systems. Flowback sample analytes of interest were diesel range organic (DRO) and gasoline range organic (GRO) compounds. Noticeable patterns were present in DRO and GRO flowback data. Flowback water results showed differences between horizontally and vertically fractured well DRO patterns. Vertically fractured wells showed a sharp decrease in DRO concentrations following fracture events. Horizontally fractured wells exhibited a peak in loading when flowback water shifted to produced water. This pattern suggests the method of completion may affect DRO loading. GRO loadings appeared to not be effected by the method of completion. A horizontally fractured well and vertically fractured well within 16 km showed similar loading patterns. GRO data suggest factors such as geographic location may be responsible for VOC loading trends.

Abstract:
Summary Natural-gas recovery from low-permeability unconventional reservoirs--enabled by advanced horizontal drilling and multistage hydraulic-fracture treatment--has become a very important energy resource in the past decade. While evaluation of ea

Abstract:
There is growing interest in possible options for treatment or reuse of flowback and produced waters from natural gas processing. Here we investigated the fouling characteristics during microfiltration of different flowback and produced waters from hydraulic fracturing sites in the Marcellus shale. All samples caused severe and highly variable fouling, although there was no direct correlation between the fouling rate and total suspended solids, turbidity, or total organic carbon. Furthermore, the fouling of water after prefiltration through a 0.2 μm membrane was also highly variable. Low fouling seen with prefiltered water was mainly due to removal of submicron particles 0.4-0.8 μm during prefiltration. High fouling seen with prefiltered water was mainly caused by a combination of hydrophobic organics and colloidal particles <100 nm in size (quantified by transmission electron microscopy) that passed through the prefiltration membranes. The small colloidal particles were highly stable, likely due to the surfactants and other organics present in the fracking fluids. The colloid concentration was as high as 10(11) colloids/ml, which is more than 100 times greater than that in typical seawater. Furthermore, these colloids were only partially removed by MF, causing substantial fouling during a subsequent ultrafiltration. These results clearly show the importance of organics and colloidal material in membrane fouling caused by flowback and produced waters, which is of critical importance in the development of more sustainable treatment strategies in natural gas processing.

Abstract:
Concerns have been raised about potential public health effects that may arise if hydraulic fracturing-related chemicals were to impact drinking water resources. This study presents an overview of the chronic oral toxicity values?specifically, chronic oral reference values (RfVs) for noncancer effects, and oral slope factors (OSFs) for cancer?that are available for a list of 1,173 chemicals that the United States (US) Environmental Protection Agency (EPA) identified as being associated with hydraulic fracturing, including 1,076 chemicals used in hydraulic fracturing fluids, and 134 chemicals detected in flowback or produced waters from hydraulically fractured wells. EPA compiled RfVs and OSFs using six governmental and intergovernmental data sources. 90 (8%) of the 1,076 chemicals reported in hydraulic fracturing fluids and 83 (62%) of the 134 chemicals reported in flowback/produced water had a chronic oral RfV or OSF available from one or more of the six sources. Furthermore, of the 36 chemicals reported in hydraulic fracturing fluids in at least 10% of wells nationwide (identified from EPA?s analysis of the FracFocus Chemical Disclosure Registry 1.0), 8 chemicals (22%) have an available chronic oral RfV. The lack of chronic oral RfVs and OSFs for the majority of these chemicals highlights the significant knowledge gap that exists to assess the potential human health hazards associated with hydraulic fracturing.

Abstract:
Naturally-occurring radioactive materials (NORM) associated with unconventional drilling produced fluids from the Marcellus Shale have raised environmental concerns. However, few investigations into the fundamental chemistry of NORM in Marcellus Shale produced fluids have been performed. Thus, we performed radiochemical experiments with Marcellus Shale produced fluids to understand the partitioning behavior of major radioelements of environmental health concern (uranium (U), thorium (Th), radium (Ra), lead (Pb), and polonium (Po)). We applied a novel radiotracer, 203Pb, to understand the behavior of trace-levels of 210Pb in these fluids. Ultrafiltration experiments indicated U, Th, and Po are particle reactive in Marcellus Shale produced fluids and Ra and Pb are soluble. Sediment partitioning experiments revealed that >99% of Ra does not adsorb to sediments in the presence of Marcellus Shale produced fluids. Further experiments indicated that although Ra adsorption is related to ionic strength, the concentrations of heavier alkaline earth metals (Ba, Sr) are stronger predictors of Ra solubility.

Abstract:
Waters that return to the surface after injection of a hydraulic fracturing fluid for gas and oil production contain elements, including regulated metals and metalloids, which are mobilized through interactions between the fracturing fluid and the shale formation. The rate and extent of mobilization depends on the geochemistry of the formation and the chemical characteristics of the fracturing fluid. In this work, laboratory scale experiments investigated the influence of water chemistry on element mobilization from core samples taken from the Bakken formation, one of the most productive shale oil plays in the US. Fluid properties were systematically varied and evaluated with regard to pH, oxidant level, solid:water ratio, temperature, and chemical additives. Element mobilization strongly depended on solution pH and redox conditions and to a lesser extent on the temperature and solid:water ratio. The presence of oxygen and addition of hydrogen peroxide or ammonium persulfate led to pyrite oxidation, resulting in elevated sulfate concentrations. Further, depending on the mineral carbonates available to buffer the system pH, pyrite oxidation could lower the system pH and enhance the mobility of several metals and metalloids.

Abstract:
Growth in unconventional oil and gas has spurred concerns on environmental impact and interest in beneficial uses of produced water (PW), especially in arid regions such as the Permian Basin, the largest U.S. tight-oil producer. To evaluate environmental impact, treatment, and reuse potential, there is a need to characterize the compositional variability of PW. Although hydraulic fracturing has caused a significant increase in shale-oil production, there are no high-resolution organic composition data for the shale-oil PW from the Permian Basin or other shale-oil plays (Eagle Ford, Bakken, etc.). PW was collected from shale-oil wells in the Midland sub-basin of the Permian Basin. Molecular characterization was conducted using high-resolution solid phase micro extraction gas chromatography time-of-flight mass spectrometry. Approximately 1400 compounds were identified, and 327 compounds had a >70% library match. PW contained alkane, cyclohexane, cyclopentane, BTEX (benzene, toluene, ethylbenzene, and xylene), alkyl benzenes, propyl-benzene, and naphthalene. PW also contained heteroatomic compounds containing nitrogen, oxygen, and sulfur. 3D van Krevelen and double bond equivalence versus carbon number analyses were used to evaluate molecular variability. Source composition, as well as solubility, controlled the distribution of volatile compounds found in shale-oil PW. The salinity also increased with depth, ranging from 105 to 162 g/L total dissolved solids. These data fill a gap for shale-oil PW composition, the associated petroleomics plots provide a fingerprinting framework, and the results for the Permian shale-oil PW suggest that partial treatment of suspended solids and organics would support some beneficial uses such as onsite reuse and bio-energy production.

Abstract:
A new method that rapidly pre-concentrates and measures 226Ra from hydraulic fracturing wastewater samples was developed in the Savannah River Environmental Laboratory. The method improves the quality of 226Ra measurements using gamma spectrometry by providing up to 100 × pre-concentration of 226Ra from this difficult sample matrix, which contains very high levels of calcium, barium, strontium, magnesium and sodium. The high chemical yield, typically 80–90 %, facilitates a low detection limit, important for lower level samples, and indicates method ruggedness. Ba-133 tracer is used to determine chemical yield and correct for geometry-related counting issues. The 226Ra sample preparation takes <2 h.

Abstract:
Hydraulic fracturing has advanced the development of shale gas extraction, while inadvertent spills of flowback water may pose a risk to the surrounding environment due to its high salt content, metals/metalloids (As, Se, Fe and Sr), and organic additives. This study investigated the potential impact of flowback water on four representative soils from shale gas regions in Northeast China using synthetic flowback solutions. The compositions of the solutions were representative of flowback water arising at different stages after fracturing well establishment. The effects of solution composition of flowback water on soil ecosystem were assessed in terms of metal mobility and bioaccessibility, as well as biological endpoints using Microtox bioassay (Vibrio fischeri) and enzyme activity tests. After one-month artificial aging of the soils with various flowback solutions, the mobility and bioaccessibility of As(V) and Se(VI) decreased as the ionic strength of the flowback solutions increased. The results inferred a stronger binding affinity of As(V) and Se(VI) with the soils. Nevertheless, the soil toxicity to Vibrio fischeri only presented a moderate increase after aging, while dehydrogenase and phosphomonoesterase activities were significantly suppressed with increasing ionic strength of flowback solutions. On the contrary, polyacrylamide in the flowback solutions led to higher dehydrogenase activity. These results indicated that soil enzyme activities were sensitive to the composition of flowback solutions. A preliminary human health risk assessment related to As(V) suggested a low level of cancer risk through exposure via ingestion, while holistic assessment of environmental implications is required.

Abstract:
Subsurface processes alter the physical and chemical properties of fluid injected for hydraulic fracturing, with implications for its transport and fate in fractured or porous media. Models used to evaluate potential hydraulic fracturing-fluid migration lack formation-specific data to constrain temporal and thermal variation of the physical parameters that govern fluid movement. Density increases of 9.8% and viscosity increases of 26.5% were observed in produced water samples from three horizontally-drilled wells in the Marcellus shale, Pennsylvania, USA over a period of 11 months after hydraulic fracturing. Fluid density and viscosity rapidly increased during the first two weeks after fluid injection because of greater concentrations of dissolved inorganic ions, and plateaued within two months. When experimentally subjected to formation-relevant temperatures, mean density and viscosity decreased by up to 2.7 and 44.4%, respectively, between 20 and 60 degrees C. These measurements yield new data to better constrain constitutive relations in flow and transport models evaluating the migration of hydraulic-fracturing fluid between a wellbore terminus and other subsurface locations. (C) 2015 American Society of Civil Engineers.

Abstract:
Hydraulically fractured shales are becoming an increasingly important source of natural gas production in the United States. This process has been known to create up to 420 gallons of produced water (PW) per day, but the volume varies depending on the formation, and the characteristics of individual hydraulic fracture. PW from hydraulic fracturing of shales are comprised of injected fracturing fluids and natural formation waters in proportions that change over time. Across the state of Pennsylvania, shale gas production is booming; therefore, it is important to assess the variability in PW chemistry and microbiology across this geographical span. We quantified the inorganic and organic chemical composition and microbial communities in PW samples from 13 shale gas wells in north central Pennsylvania. Microbial abundance was generally low (66–9400 cells/mL). Non-volatile dissolved organic carbon (NVDOC) was high (7–31 mg/L) relative to typical shallow groundwater, and the presence of organic acid anions (e.g., acetate, formate, and pyruvate) indicated microbial activity. Volatile organic compounds (VOCs) were detected in four samples (∼1 to 11.7 μg/L): benzene and toluene in the Burket sample, toluene in two Marcellus samples, and tetrachloroethylene (PCE) in one Marcellus sample. VOCs can be either naturally occurring or from industrial activity, making the source of VOCs unclear. Despite the addition of biocides during hydraulic fracturing, H2S-producing, fermenting, and methanogenic bacteria were cultured from PW samples. The presence of culturable bacteria was not associated with salinity or location; although organic compound concentrations and time in production were correlated with microbial activity. Interestingly, we found that unlike the inorganic chemistry, PW organic chemistry and microbial viability were highly variable across the 13 wells sampled, which can have important implications for the reuse and handling of these fluids.

Abstract:
Drill cuttings generated during unconventional natural gas extraction from the Marcellus Shale, Appalachian Basin, U.S.A., generally contain a very large component of organic-rich black shale because of extensive lateral drilling into this target unit. In this study, element concentrations and Pb isotope ratios obtained from leached drill cuttings spanning 600 m of stratigraphic section were used to assess the potential for short and long term environmental impacts from Marcellus Shale waste materials, in comparison with material from surrounding formations. Leachates of the units above, below and within the Marcellus Shale yielded Cl/Br ratios of 100–150, similar to produced water values. Leachates from oxidized and unoxidized drill cuttings from the Marcellus Shale contain distinct suites of elevated trace metal concentrations, including Cd, Cu, Mo, Ni, Sb, U, V and Zn. The most elevated Mo, Ni, Sb, U, and V concentrations are found in leachates from the lower portion of the Marcellus Shale, the section typically exploited for natural gas production. In addition, lower 207Pb/206Pb ratios within the lower Marcellus Shale (0.661–0.733) provide a distinctive fingerprint from formations above (0.822–0.846) and below (0.796–0.810), reflecting 206Pb produced as a result of in situ 238U decay within this organic rich black shale. Trace metal concentrations from the Marcellus Shale leachates are similar to total metal concentrations from other black shales. These metal concentrations can exceed screening levels recommended by the EPA, and thus have the potential to impact soil and water quality depending on cuttings disposal methods.

Abstract:
Fluids co-produced with methane from hydraulically fractured organic-rich shales of the Marcellus Formation (USA) are characterized by high total dissolved solids (TDS), including elevated levels of Ba, Sr and Br. To investigate the source and geologic history of these high-TDS fluids and their dissolved constituents, we carried out a series of sequential extraction experiments on dry-drilled cuttings extracted within, below and above the Marcellus Shale from a well in Tioga County, New York State. The experiments were designed to extract (1) water soluble components, (2) exchangeable cations, (3) carbonate minerals, and (4) hydrochloric acid-soluble constituents. The geochemistry of the resultant leachates highlights the different geochemical reservoirs for extractable elements within the shale; notably, Na and Br were largely water-soluble, while Ba was extracted primarily from exchangeable sites, and Ca and Sr were found both in exchangeable sites and carbonate. Strontium isotope ratios measured on the leachates indicate that each of the element reservoirs has a distinct value. Measured 87Sr/86Sr ratios in the water soluble component are similar to those of Marcellus produced water, while the ion exchange reservoir yields lower ratios, and carbonate Sr is lower still, approaching Devonian-Silurian seawater values. Despite the isotopic similarity of water leachates and produced water, the total water chemistry argues against generation of produced water by interaction of hydraulic fracturing fluid with “dry” shale. The high-TDS produced water is most likely trapped formation water (within and/or adjacent to the shale) that is released by hydraulic fracturing. The formation water was affected by multiple processes, possibly including basin scale, tectonically-driven fluid flow. Significant chemical and isotopic differences between Marcellus Shale produced water and overlying Upper Devonian/Lower Mississippian produced waters suggests a hydrologic barrier has been maintained in parts of the Appalachian Basin since the late Paleozoic.

Abstract:
Development of unconventional shale gas wells can generate significant quantities of drilling waste, including trace metal-rich black shale from the lateral portion of the drillhole. We carried out sequential extractions on 15 samples of dry-drilled cuttings and core material from the gas-producing Middle Devonian Marcellus Shale and surrounding units to identify the host phases and evaluate the mobility of selected trace elements during cuttings disposal. Maximum whole rock concentrations of uranium (U), arsenic (As), and barium (Ba) were 47, 90, and 3333 mg kg−1, respectively. Sequential chemical extractions suggest that although silicate minerals are the primary host for U, as much as 20% can be present in carbonate minerals. Up to 74% of the Ba in shale was extracted from exchangeable sites in the shale, while As is primarily associated with organic matter and sulfide minerals that could be mobilized by oxidation. For comparison, U and As concentrations were also measured in 43 produced water samples returned from Marcellus Shale gas wells. Low U concentrations in produced water (<0.084–3.26 μg L−1) are consistent with low-oxygen conditions in the wellbore, in which U would be in its reduced, immobile form. Arsenic was below detection in all produced water samples, which is also consistent with reducing conditions in the wellbore minimizing oxidation of As-bearing sulfide minerals. Geochemical modeling to determine mobility under surface storage and disposal conditions indicates that oxidation and/or dissolution of U-bearing minerals in drill cuttings would likely be followed by immobilization of U in secondary minerals such as schoepite, uranophane, and soddyite, or uraninite as conditions become more reducing. Oxidative dissolution of arsenic containing sulfides could release soluble As in arsenate form under oxic acidic conditions. The degree to which the As is subsequently immobilized depends on the redox conditions along the landfill flow path. The results suggest that proper management of drill cuttings can minimize mobilization of these metals by monitoring and controlling Eh, pH and dissolved constituents in landfill leachates.

Abstract:
The Middle Devonian age Marcellus Shale contains one of the largest shale gas plays in North America. Hydrocarbon production in the eastern part of the play is mostly “dry gas,” consisting of essentially pure methane. Production of natural gas liquids (condensate) increases toward the west, which is the area currently, being targeted by developers. Two Marcellus Shale cores from West Virginia were analyzed to compare the isotopic and geochemical characteristics of a liquids-prone well (WV-7) in Wetzel County with a gas-prone well (WV-6) in Monongalia County. The contrasts between the cores indicate that the conditions of the Marcellus Shale deposition were different between the two sites. The dominant organic matter preserved in each core is isotopically different; δ13Corg values are lighter on average in WV-6 compared with WV-7. A possible explanation is that a larger fraction of terrestrial organic matter was preserved in the WV-6 core, whereas WV-7 may contain a greater percentage of marine organic matter. Clastic-influx proxies (e.g. Ti/Al, Ca/Al and Mg/Al) also suggest that the WV-6 core site received a higher siliciclastic input compared to WV-7, consistent with a more proximal location to dry land and the delivery of greater amounts of terrestrial organic matter. Depleted δ13Ccarb values, low concentrations of redox sensitive elements (e.g. V, Cr, Ni and U), and high variability δ15N values in the WV-6 core all suggest the presence of higher dissolved oxygen concentration and short term shifts in an oxic/anoxic boundary near the sediment–water interface during deposition. These lines of evidence indicate that the depositional conditions were favorable for the accumulation of predominantly gas-prone Type III kerogen in the Marcellus Shale at the WV-6 site. In contrast, the Marcellus Shale at the WV-7 site was deposited in a more distal area that received a low terrestrial sediment supply, organic matter primarily derived from marine algae, and bottom water conditions that were dominantly anoxic. Such conditions were favorable for the accumulation of Type II kerogen that has a greater capacity to generate liquid hydrocarbons. Differences between the liquids-prone and gas-prone parts of the Marcellus Shale play have been largely ascribed to depth-of-burial and thermal maturation history; this study indicates that depositional environment and sedimentary facies may have played significant roles as well.

Abstract:
Hydraulic fracturing of shale for gas production in Pennsylvania generates large quantities of wastewater, the composition of which has been inadequately characterized. We compiled a unique data set from state-required wastewater generator reports filed in 2009?2011. The resulting data set, comprising 160 samples of flowback, produced water, and drilling wastes, analyzed for 84 different chemicals, is the most comprehensive available to date for Marcellus Shale wastewater. We analyzed the data set using the Kaplan?Meier method to deal with the high prevalence of nondetects for some analytes, and compared wastewater characteristics with permitted effluent limits and ambient monitoring limits and capacity. Major-ion concentrations suggested that most wastewater samples originated from dilution of brines, although some of our samples were more concentrated than any Marcellus brines previously reported. One problematic aspect of this wastewater was the very high concentrations of soluble constituents such as chloride, which are poorly removed by wastewater treatment plants; the vast majority of samples exceeded relevant water quality thresholds, generally by 2?3 orders of magnitude. We also examine the capacity of regional regulatory monitoring to assess and control these risks.

Abstract:
Natural gas extraction from Marcellus Shale generates large quantities of flowback water that contain high levels of salinity, heavy metals, and Naturally Occurring Radioactive Material (NORM). This water is typically stored in centralized storage impoundments or tanks prior to reuse, treatment or disposal. The fate of Ra-226, which is the dominant NORM component in flowback water, in three centralized storage impoundments in southwestern Pennsylvania was investigated during a 2.5-year period. Field sampling revealed that Ra-226 concentration in these storage facilities depends on the management strategy but is generally increasing during the reuse of flowback water for hydraulic fracturing. In addition, Ra-226 is enriched in the bottom solids (e.g., impoundment sludge) where it increased from less than 10 pCi/g for fresh sludge to several hundred pCi/g for aged sludge. A combination of sequential extraction procedure (SEP) and chemical composition analysis of impoundment sludge revealed that barite is the main carrier of Ra-226 in the sludge. Toxicity characteristic leaching procedure (TCLP) (EPA Method 1311) was used to assess the leaching behavior of Ra-226 in the impoundment sludge and its implications for waste management strategies for this low-level radioactive solid waste. Radiation exposure for on-site workers calculated using the RESRAD model showed that the radiation dose equivalent for the baseline conditions was well below the NRC limit for the general public.

Abstract:
Hydraulic fracturing (HF) has been used with horizontal drilling to extract gas and natural gas liquids from source rock such as the Marcellus Shale in the Appalachian Basin. Horizontal drilling and HF generates large volumes of waste water known as flowback. While inorganic ion chemistry has been well characterized, and the general increase in concentration through the flowback is widely recognized, the literature contains little information relative to organic compounds and radionuclides. This study examined the chemical evolution of liquid process and waste streams (including makeup water, HF fluids, and flowback) in four Marcellus Shale gas well sites in north central West Virginia. Concentrations of organic and inorganic constituents and radioactive isotopes were measured to determine changes in waste water chemistry during shale gas development. We found that additives used in fracturing fluid may contribute to some of the constituents (e.g., Fe) found in flowback, but they appear to play a minor role. Time sequence samples collected during flowback indicated increasing concentrations of organic, inorganic and radioactive constituents. Nearly all constituents were found in much higher concentrations in flowback water than in injected HF fluids suggesting that the bulk of constituents originate in the Marcellus Shale formation rather than in the formulation of the injected HF fluids. Liquid wastes such as flowback and produced water, are largely recycled for subsequent fracturing operations. These practices limit environmental exposure to flowback.

Abstract:
A suite of analytical tools was applied to thoroughly analyze the chemical composition of an oil/gas well flowback water from the Denver–Julesburg (DJ) basin in Colorado, and the water quality data was translated to propose effective treatment solutions tailored to specific reuse goals. Analysis included bulk quality parameters, trace organic and inorganic constituents, and organic matter characterization. The flowback sample contained salts (TDS = 22,500 mg/L), metals (e.g., iron at 81.4 mg/L) and high concentration of dissolved organic matter (DOC = 590 mgC/L). The organic matter comprised fracturing fluid additives such as surfactants (e.g., linear alkyl ethoxylates) and high levels of acetic acid (an additives' degradation product), indicating the anthropogenic impact on this wastewater. Based on the water quality results and preliminary treatability tests, the removal of suspended solids and iron by aeration/precipitation (and/or filtration) followed by disinfection was identified as appropriate for flowback recycling in future fracturing operations. In addition to these treatments, a biological treatment (to remove dissolved organic matter) followed by reverse osmosis desalination was determined to be necessary to attain water quality standards appropriate for other water reuse options (e.g., crop irrigation). The study provides a framework for evaluating site-specific hydraulic fracturing wastewaters, proposing a suite of analytical methods for characterization, and a process for guiding the choice of a tailored treatment approach.

Abstract:
Treatment of produced water, i.e. wastewater from hydraulic fracturing, for reuse or final disposal is challenged by both high salinity and the presence of organic compounds. Organic compounds in produced water may foul physical-chemical treatment processes, or support microbial corrosion, fouling, and sulfide release. Biological approaches have potential applications in produced water treatment, including reducing fouling of physical-chemical treatment processes and decreasing biological activity during produced water holding; however, conventional activated sludge treatments are intolerant of high salinity. In this study, a biofilm treatment approach using constructed microbial mats was evaluated for biodegradation performance, microbial community structure, and metabolic potential in both simulated and real produced water. Results demonstrated that engineered microbial mats are active at total dissolved solids (TDS) concentrations up to at least 100,000 mg/L, and experiments in real produced water showed a biodegradation capacity of 1.45 mg COD/gramwet-day at a TDS concentration of 91,351 mg/L. Additionally, microbial community and metagenomic analyses revealed an adaptive microbial community that shifted based upon the sample being treated and has the metabolic potential to degrade a wide array of contaminants, suggesting the potential of this approach to treat produced waters with varying composition.

Abstract:

Abstract:
Elevated concentration of naturally occurring radioactive material (NORM) in wastewater generated from Marcellus Shale gas extraction is of great concern due to potential environmental and public health impacts. Development of a rapid and robust method for analysis of Ra-226, which is the major NORM component in this water, is critical for the selection of appropriate management approaches to properly address regulatory and public concerns. Traditional methods for Ra-226 determination require long sample holding time or long detection time. A novel method combining Inductively Coupled Mass Spectrometry (ICP-MS) with solid-phase extraction (SPE) to separate and purify radium isotopes from the matrix elements in high salinity solutions is developed in this study. This method reduces analysis time while maintaining requisite precision and detection limit. Radium separation is accomplished using a combination of a strong-acid cation exchange resin to separate barium and radium from other ions in the solution and a strontium-specific resin to isolate radium from barium and obtain a sample suitable for analysis by ICP-MS. Method optimization achieved high radium recovery (101±6% for standard mode and 97±7% for collision mode) for synthetic Marcellus Shale wastewater (MSW) samples with total dissolved solids as high as 171,000 mg/L. Ra-226 concentration in actual MSW samples with TDS as high as 415,000 mg/L measured using ICP-MS matched very well with the results from gamma spectrometry. The Ra-226 analysis method developed in this study requires several hours for sample preparation and several minutes for analysis with the detection limit of 100 pCi/L with RSD of 45% (standard mode) and 67% (collision mode). The RSD decreased to below 15% when Ra-226 concentration increased over 500 pCi/L.

Abstract:
Flowback and produced wastewaters from unconventional hydraulic fracturing during oil and gas explorations typically brings to the surface Naturally Occurring Radioactive Materials (NORM), predominantly radioisotopes from the U238 and Th232 decay chains. Traditionally, radiological sampling are performed by sending collected small samples for laboratory tests either by radiochemical analysis or measurements by a high-resolution High-Purity Germanium (HPGe) gamma spectrometer. One of the main isotopes of concern is Ra226 which requires an extended 21-days quantification period to allow for full secular equilibrium to be established for the alpha counting of its progeny daughter Rn222. Field trials of a sodium iodide (NaI) scintillation detector offers a more economic solution for rapid screenings of radiological samples. To achieve the quantification accuracy, this gamma spectrometer must be efficiency calibrated with known standard sources prior to field deployments to analyze the radioactivity concentrations in hydraulic fracturing waste products.

Abstract:
The number of Marcellus Shale gas wells drilled in the Appalachian basin has increased rapidly over the past decade, leading to increased interest in the highly saline water produced with the natural gas which must be recycled, treated, or injected into deep disposal wells. New geochemical and isotopic analyses of produced water for 3 time-series and 13 grab samples from Marcellus Shale gas wells in southwest and north central Pennsylvania (PA) are used to address the origin of the water and solutes produced over the long term (>12 months). The question of whether the produced water originated within the Marcellus Shale, or whether it may have been drawn from adjacent reservoirs via fractures is addressed using measurements of and activity. These parameters indicate that the water originated in the Marcellus Shale, and can be more broadly used to trace water of Marcellus Shale origin. During the first 1–2 weeks of production, rapid increases in salinity and positive shifts in values were observed in the produced water, followed by more gradual changes until a compositional plateau was reached within approximately 1 yr. The values and relationships between Na, Cl, and Br provide evidence that the water produced after compositional stabilization is natural formation water, the salinity for which originated primarily from evaporatively concentrated paleoseawater. The rapid transition from injected water to chemically and isotopically distinct water while of the injected water volume had been recovered, supports the hypothesis that significant volumes of injected water were removed from circulation by imbibition.

Abstract:
Hydraulic fracturing fluids contain a mix of organic and inorganic additives in an aqueous media. The compositions of these mixtures vary according to the region or company use, thus making the process of identifying individual compounds difficult. The analytical characterization of such mixtures is important in order to understand the transport, environmental fate and ultimate potential health impact in various water compartments associated with hydraulic fracturing. Organic compound classes include solvents, gels, biocides, scale inhibitors, friction reducers, surfactants and other related compounds. These contaminants are usually present in trace amounts, so sophisticated analytical methodologies are needed in order to fully characterize the chemical composition of fracking fluids. The current state of knowledge of chemical components and approaches for their analysis is reviewed here. In recent years, modern analytical methodologies, such as gas chromatography–mass spectrometry (GC–MS) have been specifically used to identify organic chemical components of fracking fluids and/or flowback and produced waters associated with the process of hydraulic fracturing. Other techniques such as liquid chromatography–mass spectrometry (LC–MS) have not been explored in detail yet. In this review a detailed description of chemical constituents present in hydraulic fracturing waters will be given, as well as an evaluation of the analytical techniques used for their unequivocal determination.

Abstract:
The expansion of unconventional shale gas and hydraulic fracturing has increased the volume of the oil and gas wastewater (OGW) generated in the U.S. Here we demonstrate that OGW from Marcellus and Fayetteville hydraulic fracturing flowback fluids and Appalachian conventional produced waters is characterized by high chloride, bromide, iodide (up to 56 mg/L), and ammonium (up to 420 mg/L). Br/Cl ratios were consistent for all Appalachian brines, which reflect an origin from a common parent brine, while the I/Cl and NH4/Cl ratios varied among brines from different geological formations, reflecting geogenic processes. There were no differences in halides and ammonium concentrations between OGW originating from hydraulic fracturing and conventional oil and gas operations. Analysis of discharged effluents from three brine treatment sites in Pennsylvania and a spill site in West Virginia show elevated levels of halides (iodide up to 28 mg/L) and ammonium (12 to 106 mg/L) that mimic the composition of OGW and mix conservatively in downstream surface waters. Bromide, iodide, and ammonium in surface waters can impact stream ecosystems and promote the formation of toxic brominated-, iodinated-, and nitrogen disinfection byproducts during chlorination at downstream drinking water treatment plants. Our findings indicate that discharge and accidental spills of OGW to waterways pose risks to both human health and the environment.

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The objective of the present study was to investigate the feasibility of stretching an arc discharge in produced water to increase the volume of produced water treated by plasma. Produced water is the wastewater generated by hydraulic fracturing of shale during the production phase in shale-oil or shale-gas exploration. The electric conductivity of produced water is in the range of 50-200 mS/cm, which provides both a challenge and opportunity for the application of plasmas. Stretching of an arc discharge in produced water was accomplished using a ground electrode and two high-voltage electrodes: one positioned close to the ground electrode and the other positioned farther away from the ground. The benefit of stretching the arc is that the contact between the arc and water is significantly increased, resulting in more efficient plasma treatment in both performance and energy cost.

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Electrocoagulation has been used to remove solids and some metals from both water and wastewater sources for decades. Additionally, chemical softening is commonly employed in water treatment systems to remove hardness. This paper assesses the combination and sequence of softening and EC methods to treat hydraulic fracturing flowback and produced water from shale oil and gas operations. EC is one of the available technologies to treat produced water for reuse in frac fluids, eliminating not only the need to transport more water but also the costs of providing fresh water. In this paper, the influence of chemical softening on EC was studied. In the softening process, pH was raised to 9.5 and 10.2 before and after EC, respectively. Softening, when practiced before EC was more effective for removing turbidity with samples from wells older than one month (99% versus 88%). However, neither method was successful in treating samples collected from early flowback (1-day and 2-day samples), likely due to the high concentration of organic matter. For total organic carbon, hardness, Ba, Sr, and B removal, application of softening before EC appeared to be the most efficient approach, likely due to the formation of solids before the coagulation process.

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Microbial activity in produced water from hydraulic fracturing operations can lead to undesired environmental impacts and increase gas production costs. However, the metabolic profile of these microbial communities is not well understood. Here, for the first time, we present results from a shotgun metagenome of microbial communities in both hydraulic fracturing source water and wastewater produced by hydraulic fracturing. Taxonomic analyses showed an increase in anaerobic/facultative anaerobic classes related to Clostridia, Gammaproteobacteria, Bacteroidia and Epsilonproteobacteria in produced water as compared to predominantly aerobic Alphaproteobacteria in the fracturing source water. The metabolic profile revealed a relative increase in genes responsible for carbohydrate metabolism, respiration, sporulation and dormancy, iron acquisition and metabolism, stress response and sulfur metabolism in the produced water samples. These results suggest that microbial communities in produced water have an increased genetic ability to handle stress, which has significant implications for produced water management, such as disinfection.

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A detailed analysis is reported of the organic composition of produced water samples from typical shale gas wells in the Marcellus (PA), Eagle Ford (TX), and Barnett (NM) formations. The quality of shale gas produced (and frac flowback) waters is a current environmental concern and disposal problem for producers. Re-use of produced water for hydraulic fracturing is being encouraged; however, knowledge of the organic impurities is important in determining the method of treatment. The metal content was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Mineral elements are expected depending on the reservoir geology and salts used in hydraulic fracturing; however, significant levels of other transition metals and heavier main group elements are observed. The presence of scaling elements (Ca and Ba) is related to the pH of the water rather than total dissolved solids (TDS). Using gas chromatography mass spectrometry (GC/MS) analysis of the chloroform extracts of the produced water samples, a plethora of organic compounds were identified. In each water sample, the majority of organics are saturated (aliphatic), and only a small fraction comes under aromatic, resin, and asphaltene categories. Unlike coalbed methane produced water it appears that shale oil/gas produced water does not contain significant quantities of polyaromatic hydrocarbons reducing the potential health hazard. Marcellus and Barnett produced waters contain predominantly C6–C16 hydrocarbons, while the Eagle Ford produced water shows the highest concentration in the C17–C30 range. The structures of the saturated hydrocarbons identified generally follows the trend of linear > branched > cyclic. Heterocyclic compounds are identified with the largest fraction being fatty alcohols, esters, and ethers. However, the presence of various fatty acid phthalate esters in the Barnett and Marcellus produced waters can be related to their use in drilling fluids and breaker additives rather than their presence in connate fluids. Halogen containing compounds are found in each of the water samples, and although the fluorocarbon compounds identified are used as tracers, the presence of chlorocarbons and organobromides formed as a consequence of using chlorine containing oxidants (to remove bacteria from source water), suggests that industry should concentrate on non-chemical treatments of frac and produced waters.

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Two series of ethylene oxide (EO) surfactants, polyethylene glycols (PEGs from EO3 to EO33) and linear alkyl ethoxylates (LAEs C-9 to C-15 with EO3 to EO28), were identified in hydraulic fracturing flowback and produced water using a new application of the Kendrick mass defect and liquid chromatography/quadrupole-time-of-flight mass spectrometry. The Kendrick mass defect differentiates the proton, ammonium, and sodium adducts in both singly- and doubly-charged forms. A structural model of adduct formation is presented and binding constants are calculated, which is based on a spherical cage-like conformation, where the central cation ( NH4+ or Na+) is coordinated with ether oxygens. A major purpose of the study was the identification of the ethylene oxide (EO) surfactants and the construction of a database with accurate masses and retention times in order to unravel the mass spectral complexity of surfactant mixtures used in hydraulic fracturing fluids. For example, over five hundred accurate mass assignments are made in a few seconds of computer time, which then is used as a fingerprint chromatogram of the water samples. This technique is applied to a series of flowback and produced water samples to illustrate the usefulness of ethoxylate ?fingerprinting?, in a first application to monitor water quality that results from fluids used in hydraulic fracturing.

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Flowback water is the solution that returns to the surface following completion of the hydraulic fracturing process during natural gas extraction. This study examines and analyzes the constituents that make up flowback waters collected from various drilling sites in Marcellus shale formation in the states of Pennsylvania, New York, and West Virginia. Flowback sampling data were collected from four different sources (the Environmental Protection Agency, Gas Technology Institute; Pennsylvania Department of Environmental Protection; Bureau of Oil and Gas Management; and the New York Department of Environmental Conservation) and compiled into one database with a total of 35,000 entries. Descriptive statistical analysis revealed high concentrations of chlorinated solvents, disinfectants, dissolved metals, organic compounds, radionuclides, and total dissolved solids. A one-way ANOVA test revealed that over 60% of the constituents tested displayed significant differences (significance level=0.05) in mean concentrations among the four data sources. Relative prioritization scores were developed for 58 constituents by dividing observed mean concentrations by the maximum contamination level (MCL) guidelines for drinking water. The following constituents were found to have mean concentrations over 10 times greater than the MCL: 1,2-dichloroethane, antimony, barium, benzene, benzo(a)pyrene, chloride, dibromochloromethane, gross alpha, iron, manganese, pentachlorophenol, radium, thallium, and vinyl chloride. Concentrations of anthropogenic chemicals are tightly correlated with each other, but not with chloride concentrations, and not with naturally occurring inorganics and radionuclides.

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This study considers the flux of radioactivity in flowback fluid from shale gas development in three areas: the Carboniferous, Bowland Shale, UK; the Silurian Shale, Poland; and the Carboniferous Barnett Shale, USA. The radioactive flux from these basins was estimated, given estimates of the number of wells developed or to be developed, the flowback volume per well and the concentration of K (potassium) and Ra (radium) in the flowback water. For comparative purposes, the range of concentration was itself considered within four scenarios for the concentration range of radioactive measured in each shale gas basin, the groundwater of the each shale gas basin, global groundwater and local surface water. The study found that (i) for the Barnett Shale and the Silurian Shale, Poland, the 1 % exceedance flux in flowback water was between seven and eight times that would be expected from local groundwater. However, for the Bowland Shale, UK, the 1 % exceedance flux (the flux that would only be expected to be exceeded 1 % of the time, i.e. a reasonable worst case scenario) in flowback water was 500 times that expected from local groundwater. (ii) In no scenario was the 1 % exceedance exposure greater than 1 mSv-the allowable annual exposure allowed for in the UK. (iii) The radioactive flux of per energy produced was lower for shale gas than for conventional oil and gas production, nuclear power production and electricity generated through burning coal.

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The most problematic hydrocarbons in hydraulic fracturing waste waters consist of fused, isolated, bridged, and spiro ring systems, the latter of which have been poorly studied with respect to biodegradation, prompting the testing here of six major ring structural sub-classes using a well-characterized bacterium and a silica encapsulation system previously shown to enhance biodegradation. The direct biological oxygenation of spiro ring compounds was demonstrated here for the first time. These and other hydrocarbon ring compounds have previously been shown to be present in flowback and produced waters from hydraulic fracturing operations. Pseudomonas sp. strain NCIB 9816-4 containing naphthalene dioxygenase was selected for its broad substrate specificity and it was demonstrated here to oxidize fundamental ring structures that are common in shale-derived waters but not previously investigated with this or related enzymes. Pseudomonas sp. NCIB 9816-4 was tested here in the presence of a silica encasement, a protocol that has been shown previously to protect bacteria against the extremes of salinity present in fracking waste waters. These studies demonstrate degradation of highly hydrophobic compounds by a silica-encapsulated model bacterium, demonstrate what it may not degrade, and contribute to a knowledge of the full range of hydrocarbon ring compounds that can be oxidized using Pseudomonas sp. NCIB 9816-4.

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This paper presents a compilation of published mineralogic and trace element data from nine gas shales in the United States. Formations analyzed include the Antrim, Bakken, Barnett, Eagle Ford, Haynesville, Marcellus, New Albany, Utica and Woodford. These mineralogic and trace element data can be used to assess the potential for environmental impacts during hydraulic fracturing. Impacts addressed in this study include: 1) the potential for acid rock drainage generation during gas shale weathering, 2) the distribution of trace elements in gas shales and comparison with regulatory guidelines, and 3) the implications for environmental management of well cuttings. The use of the mineralogic data to assess the fracability of the gas shales is also considered. Compilations of the mineralogy and geochemistry of gas shales can be a valuable resource for managing real and perceived environmental problems associated with their exploitation. Comprehensive environmental assessment to fully address these issues, in addition to other potential environmental impacts, will require collection and collation of additional data on the mineralogy and trace element geochemistry of gas and other hydrocarbon producing shales.

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The production of natural gas and natural gas liquids from unconventional tight shale formations involves hydraulic fracturing and subsequent removal of fluids co-produced with the gas. The chemistry of the returning fluid reflects the original composition of the injection water, mobilized constituents in the shale formation, and co-mingled formation waters liberated by hydraulic fracturing. Produced water from unconventional gas wells tapping the Middle Devonian Marcellus Formation is characterized by high total dissolved solids (TDS), including very high strontium concentrations. In this study, the strontium isotope composition (87Sr/86Sr) was measured in produced waters from four horizontally drilled, hydraulically fractured Marcellus shale gas wells in southwestern Pennsylvania, sampled from the first day after commencement of flowback to as much as 27 months later. The 87Sr/86Sr of the waters tended to change rapidly over the first few days of water return, and then approached (but did not reach) a constant range of values from 0.7113 to 0.7114, which appears to be characteristic of this part of the Marcellus play. In contrast, the concentration of Sr rose more slowly and appeared to hit a steady state value (up to 3000 mg/L) by the end of the first year. Taken together with results from earlier work, these data suggest mixing between injected frac fluid and high-TDS formation water, highly enriched in Sr, and isotopically relatively uniform throughout the Marcellus shale gas play. This brine could exist within porous lenses of organic matter in the shale, in pre-existing fractures within the shale, and/or originate from fluids that migrated from adjacent formations at some point during the post-depositional history of the basin.

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Organic substances in produced and formation water from coalbed methane (CBM) and gas shale plays from across the USA were examined in this study. Disposal of produced waters from gas extraction in coal and shale is an important environmental issue because of the large volumes of water involved and the variable quality of this water. Organic substances in produced water may be environmentally relevant as pollutants, but have been little studied. Results from five CBM plays and two gas shale plays (including the Marcellus Shale) show a myriad of organic chemicals present in the produced and formation water. Organic compound classes present in produced and formation water in CBM plays include: polycyclic aromatic hydrocarbons (PAHs), heterocyclic compounds, alkyl phenols, aromatic amines, alkyl aromatics (alkyl benzenes, alkyl biphenyls), long-chain fatty acids, and aliphatic hydrocarbons. Concentrations of individual compounds range from < 1 to 100 μg/L, but total PAHs (the dominant compound class for most CBM samples) range from 50 to 100 μg/L. Total dissolved organic carbon (TOC) in CBM produced water is generally in the 1–4 mg/L range. Excursions from this general pattern in produced waters from individual wells arise from contaminants introduced by production activities (oils, grease, adhesives, etc.). Organic substances in produced and formation water from gas shale unimpacted by production chemicals have a similar range of compound classes as CBM produced water, and TOC levels of about 8 mg/L. However, produced water from the Marcellus Shale using hydraulic fracturing has TOC levels as high as 5500 mg/L and a range of added organic chemicals including, solvents, biocides, scale inhibitors, and other organic chemicals at levels of 1000 s of μg/L for individual compounds. Levels of these hydraulic fracturing chemicals and TOC decrease rapidly over the first 20 days of water recovery and some level of residual organic contaminants remain up to 250 days after hydraulic fracturing. Although the environmental impacts of the organics in produced water are not well defined, results suggest that care should be exercised in the disposal and release of produced waters containing these organic substances into the environment because of the potential toxicity of many of these substances.

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A majority of well pads for unconventional gas wells that are drilled into the Marcellus shale (northeastern USA) consist of multiple wells (in some cases as many as 12 wells per pad), yet the influence of the evolution of well pad development on the extent of environmental violations and wastewater production is unknown. Although the development of multi-well pads (MWP) at the expense of single well pads (SWP) has been mostly driven by economic factors, the concentrated nature of drilling activities from hydraulic fracturing and horizontal drilling operations on MWP suggests that MWP may create less surface disturbance, produce more volumes of wastewater, and generate more environmental violations than SWP. To explore these hypotheses, we use geospatial techniques and statistical analyses (i.e., regression and Mann-Whitney tests) to assess development of unconventional shale gas wells, and quantify environmental violations and wastewater volumes on SWP and MWP in Pennsylvania. The analyses include assessments of the influence of different types of well pads on potential, minor and major environmental events. Results reveal that (a) in recent years, a majority of pads on which new wells for unconventional gas were drilled are MWP, (b) on average, MWP have about five wells located on each pad and thus, had the transition to MWP not occurred, between two and four times as much land surface disturbance would have occurred per year if drilling was relegated to SWP, (c) there were more environmental violations on MWP than SWP, but when the number of wells were taken into account, fewer environmental violations per well were observed on MWP than on SWP, (d) there were more wastewater and recycled wastewater volumes per pad and per well produced on MWP than on SWP, and (e) the proportion of wastewater that was recycled was higher on MWP than SWP. This study sheds light on how the evolution from SWP to MWP has influenced environmental violations and wastewater production in a field that has undergone rapid development in recent years.

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Microorganisms play several important roles in unconventional gas recovery, from biodegradation of hydrocarbons to souring of wells and corrosion of equipment. During and after the hydraulic fracturing process, microorganisms are subjected to harsh physicochemical conditions within the kilometer-deep hydrocarbon-bearing shale, including high pressures, elevated temperatures, exposure to chemical additives and biocides, and brine-level salinities. A portion of the injected fluid returns to the surface and may be reused in other fracturing operations, a process that can enrich for certain taxa. This study tracked microbial community dynamics using pyrotag sequencing of 16S rRNA genes in water samples from three hydraulically fractured Marcellus Shale wells in Pennsylvania, USA over a 328-day period. There was a reduction in microbial richness and diversity after fracturing, with the lowest diversity at 49 days. Thirty-one taxa dominated injected, flowback, and produced water communities, which took on distinct signatures as injected carbon and electron acceptors were attenuated within the shale. The majority (>90%) of the community in flowback and produced fluids were related to halotolerant bacteria associated with fermentation, hydrocarbon oxidation, and sulfur-cycling metabolisms, including heterotrophic genera Halolactibacillus, Vibrio, Marinobacter, Halanaerobium, and Halomonas, and autotrophs belonging to Arcobacter. Sequences related to halotolerant methanogenic genera Methanohalophilus and Methanolobus were detected at low abundance (<2%) in produced waters several months after hydraulic fracturing. Five taxa were strong indicators of later produced fluids. These results provide insight into the temporal trajectory of subsurface microbial communities after ?fracking?, and have important implications for the enrichment of microbes potentially detrimental to well infrastructure and natural gas fouling during this process.

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Flowback water from natural gas extraction in Marcellus Shale contains very high concentrations of inorganic salts and organic chemicals. Potential reuse of this water in subsequent hydraulic-fracturing operations may be limited by high concentrations of divalent cations (e. g., Ba, Sr, and Ca). Kinetics of barite and celestite precipitation in flowback waters from different well sites was evaluated in this study. Ba reacted rapidly with sulfate and reached equilibrium within 30 min, whereas Sr reacted slowly and took days to reach equilibrium. Equilibrium concentrations of Ba and Sr predicted by thermodynamics models were compared with experimental results. Activity corrections based on the Pitzer equation provided the best agreement with experimental data for both Ba and Sr. Comparison of barite and celestite precipitation kinetics in actual and synthetic flowback water revealed that there was no observable impact of organics and other minor components in actual flowback water on barite precipitation rate. This was primarily due to the fact that barite precipitation occurred relatively quickly at the high saturation levels utilized in this study. By contrast, lattice poisoning and complexation with organic matter had a profound impact on the comparatively slower celestite precipitation. The presence of organic matter in actual flowback water increased Ba and Sr concentrations in solution, and contributed to the discrepancy between measured and predicted equilibrium concentrations. (C) 2014 American Society of Civil Engineers.

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Radium occurs in flowback and produced waters from hydraulic fracturing for unconventional gas extraction along with high concentrations of barium and strontium and elevated salinity. Radium is often removed from this wastewater by co-precipitation with barium or other alkaline earth metals. The distribution equation for Ra in the precipitate is derived from the equilibrium of the lattice replacement reaction (inclusion) between the Ra2+ ion and the carrier ions (e.g., Ba2+ and Sr2+) in aqueous and solid phases and is often applied to describe the fate of radium in these systems. Although the theoretical distribution coefficient for Ra?SrSO4 (Kd = 237) is much larger than that for Ra?BaSO4 (Kd = 1.54), previous studies have focused on Ra?BaSO4 equilibrium. This study evaluates the equilibria and kinetics of co-precipitation reactions in Ra?Ba?SO4 and Ra?Sr?SO4 binary systems and the Ra?Ba?Sr?SO4 ternary system under varying ionic strength (IS) conditions that are representative of brines generated during unconventional gas extraction. Results show that radium removal generally follows the theoretical distribution law in binary systems and is enhanced in the Ra?Ba?SO4 system and restrained in the Ra?Sr?SO4 system by high IS. However, the experimental distribution coefficient (Kd?) varies widely and cannot be accurately described by the distribution equation, which depends on IS, kinetics of carrier precipitation and does not account for radium removal by adsorption. Radium removal in the ternary system is controlled by the co-precipitation of Ra?Ba?SO4, which is attributed to the rapid BaSO4 nucleation rate and closer ionic radii of Ra2+ with Ba2+ than with Sr2+. Carrier (i.e., barite) recycling during water treatment was shown to be effective in enhancing radium removal even after co-precipitation was completed. Calculations based on experimental results show that Ra levels in the precipitate generated in centralized waste treatment facilities far exceed regulatory limits for disposal in municipal sanitary landfills and require careful monitoring of allowed source term loading (ASTL) for technically enhanced naturally occurring materials (TENORM) in these landfills. Several alternatives for sustainable management of TENORM are discussed.

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The rapid proliferation of horizontal drilling and hydraulic fracturing for natural gas mining has raised concerns about the potential for adverse environmental impacts. One specific concern is the radioactivity content of associated ?flowback? wastewater (FBW), which is enhanced with respect to naturally occurring radium (Ra) isotopes. Thus, development and validation of effective methods for analysis of Ra in FBW are critical to appropriate regulatory and safety decision making. Recent government documents have suggested the use of EPA method 903.0 for isotopic Ra determinations. This method has been used effectively to determine Ra levels in drinking water for decades. However, analysis of FBW by this method is questionable because of the remarkably high ionic strength and dissolved solid content observed, particularly in FBW from the Marcellus Shale region. These observations led us to investigate the utility of several common Ra analysis methods using a representative Marcellus Shale FBW sample. Methods examined included wet chemical approaches, such as EPA method 903.0, manganese dioxide (MnO2) preconcentration, and 3M Empore RAD radium disks, and direct measurement techniques such as radon (Rn) emanation and high-purity germanium (HPGe) gamma spectroscopy. Nondestructive HPGe and emanation techniques were effective in determining Ra levels, while wet chemical techniques recovered as little as 1% of 226Ra in the FBW sample studied. Our results question the reliability of wet chemical techniques for the determination of Ra content in Marcellus Shale FBW (because of the remarkably high ionic strength) and suggest that nondestructive approaches are most appropriate for these analyses. For FBW samples with a very high Ra content, large dilutions may allow the use of wet chemical techniques, but detection limit objectives must be considered.

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The Antrim Shale in the Michigan Basin is one of the most productive shale gas formations in the U.S., but optimal resource recovery strategies must rely on a thorough understanding of the complex biogeochemical, microbial, and physical interdependencies in this and similar systems. We used Illumina MiSeq 16S rDNA sequencing to analyze the diversity and relative abundance of prokaryotic communities present in Antrim shale formation water of three closely spaced recently fractured gas-producing wells. In addition, the well waters were incubated with a suite of fermentative and methanogenic substrates in an effort to stimulate microbial methane generation. The three wells exhibited substantial differences in their community structure that may arise from their different drilling and fracturing histories. Bacterial sequences greatly outnumbered those of archaea and shared highest similarity to previously described cultures of mesophiles and moderate halophiles within the Firmicutes, Bacteroidetes, and δ- and ε-Proteobacteria. The majority of archaeal sequences shared highest sequence similarity to uncultured euryarchaeotal environmental clones. Some sequences closely related to cultured methylotrophic and hydrogenotrophic methanogens were also present in the initial well water. Incubation with methanol and trimethylamine stimulated methylotrophic methanogens and resulted in the largest increase in methane production in the formation waters, while fermentation triggered by the addition of yeast extract and formate indirectly stimulated hydrogenotrophic methanogens. The addition of sterile powdered shale as a complex natural substrate stimulated the rate of methane production without affecting total methane yields. Depletion of methane indicative of anaerobic methane oxidation (AMO) was observed over the course of incubation with some substrates. This process could constitute a substantial loss of methane in the shale formation.

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Hydraulic fracturing for natural gas extraction from shale produces waste brine known as flowback that is impounded at the surface prior to reuse and/or disposal. During impoundment, microbial activity can alter the fate of metals including radionuclides, give rise to odorous compounds, and result in biocorrosion that complicates water and waste management and increases production costs. Here, we describe the microbial ecology at multiple depths of three flowback impoundments from the Marcellus shale that were managed differently. 16S rRNA gene clone libraries revealed that bacterial communities in the untreated and biocide-amended impoundments were depth dependent, diverse, and most similar to species within the taxa -proteobacteria, -proteobacteria, -proteobacteria, Clostridia, Synergistetes, Thermotogae, Spirochetes, and Bacteroidetes. The bacterial community in the pretreated and aerated impoundment was uniform with depth, less diverse, and most similar to known iodide-oxidizing bacteria in the -proteobacteria. Archaea were identified only in the untreated and biocide-amended impoundments and were affiliated to the Methanomicrobia class. This is the first study of microbial communities in flowback water impoundments from hydraulic fracturing. The findings expand our knowledge of microbial diversity of an emergent and unexplored environment and may guide the management of flowback impoundments.

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Microbial communities associated with produced water from hydraulic fracturing are not well understood, and their deleterious activity can lead to significant increases in production costs and adverse environmental impacts. In this study, we compared the microbial ecology in prefracturing fluids (fracturing source water and fracturing fluid) and produced water at multiple time points from a natural gas well in southwestern Pennsylvania using 16S rRNA gene-based clone libraries, pyrosequencing, and quantitative PCR. The majority of the bacterial community in prefracturing fluids constituted aerobic species affiliated with the class Alphaproteobacteria. However, their relative abundance decreased in produced water with an increase in halotolerant, anaerobic/facultative anaerobic species affiliated with the classes Clostridia, Bacilli, Gammaproteobacteria, Epsilonproteobacteria, Bacteroidia, and Fusobacteria. Produced water collected at the last time point (day 187) consisted almost entirely of sequences similar to Clostridia and showed a decrease in bacterial abundance by 3 orders of magnitude compared to the prefracturing fluids and produced water samplesfrom earlier time points. Geochemical analysis showed that produced water contained higher concentrations of salts and total radioactivity compared to prefracturing fluids. This study provides evidence of long-term subsurface selection of the microbial community introduced through hydraulic fracturing, which may include significant implications for disinfection as well as reuse of produced water in future fracturing operations.

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Brines generated from oil and natural gas production, including flowback water and produced water from hydraulic fracturing of shale gas, may contain elevated concentrations of bromide (similar to 1 g/L). Bromide is a broad concern due to the potential for forming brominated disinfection byproducts (DBPs) during drinking water treatment. Conventional treatment processes for bromide removal is costly and not specific. Selective bromide removal is technically challenging due to the presence of other ions in the brine, especially chloride as high as 30-200 g/L. This study evaluates the ability of solid graphite electrodes to selectively oxidize bromide to bromine in flowback water and produced water from a shale gas operation in Southwestern PA. The bromine can then be outgassed from the solution and recovered, as a process well understood in the bromine industry. This study revealed that bromide may be selectively and rapidly removed from oil and gas brines (similar to 10 h(-1) m(-2) for produced water and similar to 60 h(-1) m(-2) for flowback water). The electrolysis occurs with a current efficiency between 60 and 90%, and the estimated energy cost is similar to 6 kJ/g Br. These data are similar to those for the chlor-alkali process that is commonly used for chlorine gas and sodium hydroxide production. The results demonstrate that bromide may be selectively removed from oil and gas brines to create an opportunity for environmental protection and resource recovery. (C) 2013 Elsevier Ltd. All rights reserved.