Characterization of the chemicals used in hydraulic fracturing fluids for wells located in the Marcellus Shale Play

Interactions between microbial communities and polymers in hydraulic fracturing water cycle: A review

Hydraulic fracturing (HF) has substantially boosted global unconventional hydrocarbon production but has also introduced various environmental and operational challenges. Understanding the interactions between abundant and diverse microbial communities and chemicals, particularly polymers used for proppant delivery, thickening, and friction reduction, in HF water cycles is crucial for addressing these challenges. This review primarily examined the recent studies conducted in China, an emerging area for HF activities, and comparatively examined studies from other regions. In China, polyacrylamide (PAM) and its derivatives products became key components in hydraulic fracturing fluid (HFF) for unconventional hydrocarbon development. The microbial diversity of unconventional HF water cycles in China was higher compared to North America, with frequent detection of taxa such as Shewanella, Marinobacter, and Desulfobacter. While biodegradation, biocorrosion, and biofouling were common issues across regions, the mechanisms underlying these microbe-polymer interactions differed substantially. Notably, in HF sites in the Sichuan Basin, the use of biocides gradually decreased its efficiency to mitigate adverse microbial activities. High-throughput sequencing proved to be a robust tool that could identify key bioindicators and biodegradation pathways, and help select optimal polymers and biocides, leading to more efficient HFF systems. The primary aim of this study is to raise awareness about the interactions between microorganisms and polymers, providing fresh insights that can inform decisions related to enhanced chemical use and biological control measures at HF sites.

Toxicity and chemical characterization of shale gas wastewater discharged to the receiving water: Evidence from toxicity identification evaluation

Flowback and produced water (FPW) generated from shale gas extraction is a complex mixture consisting of injected drilling fluid, deep formation water, and byproducts of downhole reactions. Limited knowledge is available regarding the impact of discharged FPW on surface water in China. With the development of shale gas exploitation, this emphasizes an urgent need for comprehensive assessments and stringent regulations to ensure the safe disposal of shale gas extraction-related wastewater. Herein, we explored potential impacts of treated shale gas wastewater discharged into a local river in southwest China through toxicity identification evaluation (TIE). Results revealed that organics and particulates significantly contributed to the overall toxicity of the treated FPW wastewater. Through target and suspect chemical analyses, various categories of organic contaminants were detected, including alkanes, aromatic hydrocarbons, biocides, phenols, and phthalates. Furthermore, non-target analysis uncovered the presence of surfactant-related contaminants in tissues of exposed organisms, but their contribution to the observed toxicity was unclear due to the lack of effect data for these compounds. Higher toxicity was found at the discharge point compared with upstream sites; however, the toxicity was rapidly mitigated due to dilution in the receiving river, posing little impact on downstream areas. Our study highlighted the importance of monitoring toxicity and water quality of FPW effluent even though dilution could be a viable approach when the water volume in the discharge was small.

Identifying persistent, mobile and toxic (PMT) organic compounds detected in shale gas wastewater

Shale gas exploitation is a water-intensive process, generating flowback and produced water (FPW) with complex chemical compositions. Reuse, disposal and treatment of FPW are of increasing concern, because of the potential risk of FPW contamination to the surrounding aquatic environment and drinking water sources when emitted. Among numerous organic substances present in FPW, of particular concern are those that are persistent, mobile and toxic (PMT) and very persistent and very mobile (vPvM). PMT and vPvM substances have the greatest potential to spread in groundwater and are the hardest to remediate. This study presents the outcome of a literature review to identify organic compounds that were previously detected in FPW. The 162 target compounds identified from this review were assessed to see if they can be considered PMT/vPvM substances based on their substance properties. Our results indicated that most FPW substances are "not PMT", accounting for 108 (66.7 %) compouds. In total 22 FPW substances can be considered PMT/vPvM or very likely to meet this criteria if more data were available. Examples of PMT substances in FPW include anthracene, 1,4-dioxane and 1,4-dichlorobenzene. PMT/vPvM compounds identified in FPW should be prioritized for risk management measures and monitoring in order to protect regional water resources.

Produced Water Treatment and Valorization: A Techno-Economical Review

In recent years, environmental concerns have urged companies in the energy sector to modify their industrial activities to facilitate greater environmental stewardship. For example, the practice of unconventional oil and gas extraction has drawn the ire of regulators and various environmental groups due to its reliance on millions of barrels of fresh water—which is generally drawn from natural sources and public water supplies—for hydraulic fracturing well stimulation. Additionally, this process generates two substantial waste streams, which are collectively characterized as flowback and produced water. Whereas flowback water is comprised of various chemical additives that are used during hydraulic fracturing; produced water is a complex mixture of microbiota, inorganic and organic constituents derived from the petroliferous strata. This review will discuss the obstacles of managing and treating flowback and produced waters, concentrating on the hardest constituents to remove by current technologies and their effect on the environment if left untreated. Additionally, this work will address the opportunities associated with repurposing produced water for various applications as an alternative to subsurface injection, which has a number of environmental concerns. This review also uses lithium to evaluate the feasibility of extracting valuable metals from produced water using commercially available technologies.

Detection and treatment of organic matters in hydraulic fracturing wastewater from shale gas extraction: A critical review

Although shale gas has shown promising potential to alleviate energy crisis as a clean energy resource, more attention has been paid to the harmful environmental impacts during exploitation. It is a critical issue for the management of shale gas wastewater (SGW), especially the organic compounds. This review focuses on analytical methods and corresponding treatment technologies targeting organic matters in SGW. Firstly, detailed information about specific shale-derived organics and related organic compounds in SGW were overviewed. Secondly, the state-of-the art analytical methods for detecting organics in SGW were summarized. The gas chromatography paired with mass spectrometry was the most commonly used technique. Thirdly, relevant treatment technologies for SGW organic matters were systematically explored. Forward osmosis and membrane distillation ranked the top two most frequently used treatment processes. Moreover, quantitative analyses on the removal of general and single organic compounds by treatment technologies were conducted. Finally, challenges for the analytical methods and treatment technologies of organic matters in SGW were addressed. The lack of effective trace organic detection techniques and high cost of treatment technologies are the urgent problems to be solved. Advances in the extraction, detection, identification and disposal of trace organic matters are critical to address the issues.

Aerobic biological degradation of organic matter and fracturing fluid additives in high salinity hydraulic fracturing wastewaters

Reuse of hydraulic fracturing wastewaters depends on effective tailored treatment to prepare the water for the intended end use. Aerobic biological treatment of hydraulic fracturing produced water was examined to degrade dissolved organic carbon (DOC) and polyethylene glycols (PEGs). Biological treatment experiments of three produced water samples with DOC concentrations ranging from 22 to 420 mg/L and total dissolved solids (TDS) levels ranging from 26 to 157 g/L were conducted in 48-240 h batches. Samples were not pretreated to remove suspended solids and were inoculated with activated sludge and acclimated over several weeks. Results show that between 50% and 80% of DOC was removed in 12-24 h but a sizeable portion, on a mass basis, remained in the samples with higher DOC concentrations. PEGs were also shown to readily biodegrade into singly- and doubly-carboxylated metabolites, but were not shown to degrade past that point, leading to accumulation of PEG-dicarboxylates (PEG-diCs) in the batch reactors. Possible explanations include residence times that were too long, resulting in starved microbial populations (and thus, a stopping of PEG degradation) or the presence of other ethoxylated additives that degraded into PEGs and PEG-diCs and fed this accumulation. This work demonstrates that a well-acclimated microbial culture is capable of degrading a large portion of DOC in hydraulic fracturing wastewaters across a wide spectrum of TDS concentrations, indicating that biological treatment is a viable option for enabling reuse of produced water.

Sustainable microalgae-based technology for biotransformation of benzalkonium chloride in oil and gas produced water: A laboratory-scale study

Many countries have implemented stringent regulatory standards for discharging produced water (PW) from the oil and gas extraction process. Among the different chemical pollutants occurring in PW, surfactants are widely applied in the oil and gas industry to provide a barrier from metal corrosion. However, the release of these substances from the shale formation can pose serious hazardous impacts on the aquatic environment. In this study, a low-cost and eco-friendly microalgae laboratory-scale technology has been tested for biotransformation of benzalkonium chloride (BAC_C12 and BAC_C14) in seawater and PW during 14-days of treatment (spiked at 5 mg/L). From the eight microalgae strains selected, Tetraselmis suecica showed the highest removal rates of about 100% and 54% in seawater and PW, respectively. Suspect screening analysis using liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) allowed the identification of 12 isomeric intermediates generated coming from biotransformation mechanisms. Among them, the intermediate [OH-BAC_C12] was found as the most intense compound generated from BAC_C12, while the intermediate [2OH-BAC_C14] was found as the most intense compound generated from BAC_C14. The suggested chemical structures demonstrated a high reduction on their amphiphilic properties, and thus, their tendency to be adsorbed into sediments after water discharge. In this study, Tetraselmis suecica was classified as the most successful specie to reduce the surfactant activity of benzalkonium chloride in treated effluents.

Hazardous substances as the dominant non-methane volatile organic compounds with potential emissions from liquid storage tanks during well fracturing: A modeling approach

Chemical additives used in hydraulic fracturing fluids (HFFs) are made up of various organic compounds that are potential human carcinogens. To estimate the emissions from these organic constituents in on-site liquid storage tanks, studies were performed using the AP-42 model on data collected from 72,023 wells put into production using hydraulic fracturing between 2008 and 2014 in the United States. Results show that a total of 8.11 × 10⁵ kg volatile organic compounds (VOCs) were potentially emitted from liquid storage tanks during fracturing operations, which was relatively low compared to other sources/activities in well fracturing. The median well emission roughly increased from 0.110 to 0.786 kg per well in 2008 and 2014, respectively, and was primarily due to the increase in the volume of chemical additives for fracturing one well. Of NMVOC emissions, 95.1% was contributed by 60 compounds listed on the priority list of hazardous substances defined by the Agency for Toxic Substances & Disease Registry (ATSDR), while 16.7% was caused by 15 carcinogenic compounds. Specially, methanol, formaldehyde, 2-propanol, and ethanol accounted for 55.5%, 16.6%, 11.7%, and 8.31% of NMVOC emissions. Our study highlights methanol, formaldehyde, 2-propanol, and ethanol as the targeted compounds for reducing organic emissions and occupational inhalation exposures related to storage tank operations.

Public reporting of hydraulic fracturing chemicals in the USA, 2011-18: a before and after comparison of reporting formats

BACKGROUND

Hydraulic fracturing often involves the injection of millions of gallons of fracturing fluids into underground shales to extract oil and natural gas, raising health concerns over potential water contamination. Many state and federal governmental agencies rely on the third-party FracFocus online registry for disclosure of chemical ingredients in fracturing fluids, but withholding chemicals as trade secrets is common. In 2016, a new format, known as the systems approach was widely encouraged as a method of reducing withholding by decoupling disclosed chemicals from their functions, protecting against reverse-engineering of fracture fluid formulas by competitors. In this study, we assess the extent to which elevated use of the systems approach in FracFocus version 3.0 translated into greater chemical disclosure.

METHODS

We analysed 108 137 disclosure forms submitted to FracFocus between Jan 1, 2011, and Dec 31, 2018, to estimate the effect of expanded use of the systems approach on chemical withholding. We compared the proportion of forms withholding at least one chemical ingredient across time, between approaches, and by state and drilling operator.

FINDINGS

Since the 2016 expansion of the systems approach, 15 677 (82%) of systems approach forms have withheld an ingredient. 13 462 (89%) of 15 062 traditional FracFocus version 3.0 forms withheld an ingredient. In the quarter following the transition (July, to September, 2016), 1211 (93%) of 1304 traditional forms withheld an ingredient, compared with only 958 (76%) of 1262 systems approach forms. However, withholding rates increased throughout 2017 and, by 2018, 6949 (87%) of 8016 systems approach forms were withholding ingredients. At the end of our analysis period in the fourth quarter of 2018, systems approach forms had even greater withholding (903 [88%] of 1025 forms) than did traditional forms (855 [85%] of 1004 forms). We did not find that states or operators that submitted more systems approach forms had lower withholding.

INTERPRETATION

The systems approach has not reduced FracFocus chemical withholding, which continues to occur in around 87% of well fracture disclosures. FracFocus might not be an appropriate substitute for regulatory action, and measures are urgently needed for environmental and public safety.

FUNDING

University of Chicago Argonne National Laboratory Seed Grant.

Adsorption of Ba2+ and Sr2+ on Ti3C2Tx MXene in model fracking wastewater

Wastewater from hydraulic fracking contains both organic and inorganic pollutants; the latter include radioactive nuclides such as Ba²⁺ and Sr²⁺. We explored whether MXene (Ti₃C₂T_x), a novel adsorbent, could remove Ba²⁺ and Sr²⁺ from model wastewater. Zeta potential analysis showed that MXene had a high negative surface charge. MXene adsorbed Ba²⁺ and Sr²⁺ via electrostatic attraction, as confirmed by the adsorption at different solution pH values and in the presence of various concentrations of other ions (NaCl and CaCl₂). MXene exhibited outstanding adsorption of Ba²⁺ and Sr²⁺, to approximately 180 and 225 mg g^-1, respectively, when 1 g L^-1 MXene was admixed with adsorbates at 2 g L^-1. MXene exhibited very rapid adsorption kinetics, attaining equilibrium within 1 h. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy revealed that MXene adsorbed Ba²⁺ and Sr²⁺, respectively, via ion exchange and inner-sphere complex formation. Finally, we performed MXene reusability tests; reusability was excellent over at least four cycles. Thus, MXene removed Ba²⁺ and Sr²⁺ from model fracking wastewater.

The impact of several hydraulic fracking chemicals on Nile tilapia and evaluation of the protective effects of Spirulina platensis

Hydraulic fracturing (fracking) chemicals are used to maximize the extraction of hard-to-reach underground energy resources. Large amounts of fracking fluid could escape to the surrounding environments, including underground and surface water resources, during the chemical mixing stage of the hydraulic fracturing water cycle due to equipment failure or human error. However, the impact of pollution resulting from operational discharges is difficult to assess in aquatic ecosystems. In this study, pathological investigations, chromosomal aberrations, DNA damage, and biochemical and hematological parameters were used to evaluate the effects of such chemicals on Nile tilapia. Chromosomal aberrations are considered very sensitive genetic markers of exposure to genotoxic chemicals and are used as indicators of DNA damage. The appearance of different types of chromosomal aberrations (gaps and breaks) due to chemical exposure was significantly reduced by treatment with spirulina. Various deleterious findings in Nile tilapia, in the current study, could attributed to the presence of fracking chemicals in the aquatic environment. However, the presence of spirulina in the diet reduced the hazards of such chemicals. In addition, cytogenetic studies in the current work revealed the importance of spirulina in ameliorating the genotoxic effects of a mixture of some chemicals used in fracking.

High total dissolved solids in shale gas wastewater inhibit biodegradation of alkyl and nonylphenol ethoxylate surfactants

Hydraulic fracturing fluids are injected into unconventional oil and gas systems to stimulate hydrocarbon production, returning to the surface in flowback and produced waters containing a complex mixture of xenobiotic additives and geogenic compounds. Nonionic polyethoxylates are commonly added surfactants that act as weatherizers, emulsifiers, wetting agents, and corrosion inhibitors in hydraulic fracturing fluid formulations. Understanding the biodegradability of these ubiquitous additives is critical for produced water pre-treatment prior to reuse and for improving treatment trains for external beneficial reuse. The objective of this study was to determine the effect of produced water total dissolved solids (TDS) from an unconventional natural gas well on the aerobic biodegradation of alkyl ethoxylate and nonylphenol ethoxylate surfactants. Changes in surfactant concentrations, speciation and metabolites, as well as microbial community composition and activity were quantified over a 75-day aerobic incubation period. Alkyl ethoxylates (AEOs) were degraded faster than nonylphenol ethoxylates (NPEOs), and both compound classes and bulk organic carbon biodegraded slower in TDS treatments (10 g L^-1, 40 g L^-1) as compared to controls. Short-chain ethoxylates were more rapidly biodegraded than longer-chain ethoxylates, and changes in the relative abundance of metabolites including acetone, alcohols, and carboxylate and aldehyde intermediates of alkyl units indicated metabolic pathways may shift in the presence of higher produced water TDS. Our key finding that polyethoxylated alcohol surfactant additives are less labile at high TDS has important implications for produced water management, as these fluids are increasingly recycled for beneficial reuse in hydraulic fracturing fluids and other purposes.

Flowback verses first-flush: new information on the geochemistry of produced water from mandatory reporting

Unconventional oil and gas development uses the subsurface injection of large amounts of a variety of industrial chemicals, and there are concerns about the return of these chemical to the surface with water produced with oil and gas from stimulated wells. Produced water, including any flowback of injected fluids, must be managed so as to protect human health and the environment, and understanding the chemistry of produced water from stimulated wells is necessary to ensure the safe management of produced water. In 2014, California instituted mandatory reporting for all well stimulations, including sampling produced water two times and comprehensive chemical characterization of fluids injected and fluids recovered from stimulated wells. In this study, we analyzed data from mandatory reporting with the objective of closing previously identified data gaps concerning oil-field chemical practices and the nature of flowback and produced water from stimulated wells. It was found that the plug-flow conceptual model of flowback developed in shale formations, where salinity increases over time as produced water is extracted, was not appropriate for characterizing produced water from unconventional wells in these oil reservoirs, which are predominately diatomite and sandstones. In these formations stimulation caused a "first-flush" phenomena, where salts and metals were initially high and then decreased in concentration over time, as more produced water was extracted. Although widely applied to meet regulatory requirements, total carbohydrate measurement was not found to be a good chemical indicator of hydraulic fracturing flowback. Mandatory reporting closed data-gaps concerning chemical use, provided new information on acid treatments, and allowed more detailed analysis of hydraulic fracturing practices, including comparison of water use by geological formation.

Game-based analysis of energy-water nexus for identifying environmental impacts during Shale gas operations under stochastic input

Environmental issues have become some of the greatest challenges encountered across the life cycle Shale gas operations, and mostly involve the management, disposal, and spill of flowback and produced (FP) waters during the process of hydraulic fracturing. This study evaluates Shale gas resources, addresses water resource management problems, and identifies the corresponding environmental implications of FP waters under uncertainty. Multiple tools, including structural optimization, process design, cost analysis, environmental assessment, and stochastic technology, are integrated into a general modeling framework based on game theory. This mathematic framework corresponds to a dominant-subordinate-interactive problem, where two major participants are identified as the downstream decision maker at the dominant level (e.g., power generation sector) and the upstream decision maker at the subordinate level (e.g., Shale gas producer). The Monte Carlo technique is used for simulating the estimated ultimate recovery (EUR) of a single well. Thereafter, the developed model is applied to a special case study of the Marcellus Shale play in Beaver County, Pennsylvania. Multiple decisions regarding gas production, processing, water management, as well as electricity generation would been examined under different probability levels. Results indicate that the changes in violation levels would lead to distinct environmental and economic performances of the supply chain. A lower probability level of the EUR value would correspond to an increased reliability on fulfilling the system demands, and then to higher economic benefits and freshwater supply; conversely, a higher probability level of the EUR value would result in lower economic benefits and lower freshwater supply, and the risk of violating the EUR value would also increase.

Hazard assessment of hydraulic fracturing chemicals using an indexing method

The rapid expansion of unconventional natural gas production has triggered considerable public concerns, particularly regarding environmental and human health (EHH) risks posed by various chemical additives used in hydraulic fracturing (HF) operations. There is a need to assess the potential EHH hazards of additives used in real-world HF operations. In this study, HF additive and fracturing fluid data was acquired, and EHH hazards were assessed using an indexing approach. The indexing system analyzed chemical toxicological data of different ingredients contained within additives and produced an aggregated EHH safety index for each additive, along with an indicator describing the completeness of the chemical toxicological data. The results show that commonly used additives are generally associated with medium-level EHH hazards. In each additive category, ingredients of high EHH concern were identified, and the high hazard designation was primarily attributed to ingredients' high aquatic toxicity and carcinogenic effects. Among all assessed additive categories, iron control agents were identified as the greatest EHH hazards. Lack of information, such as undisclosed ingredients and chemical toxicological data gaps, has resulted in different levels of assessment uncertainties. In particular, friction reducers show the highest data incompleteness with regards to EHH hazards. This study reveals the potential EHH hazards associated with chemicals used in current HF field operations and can provide decision makers with valuable information to facilitate sustainable and responsible unconventional gas production.