Hydraulic Fracturing Flowback Research Articles

Hydrogeochemistry and indicators of flowback and produced water from wells that are hydraulically fractured with recycled wastewater: A case study of the Changning gas field in the Sichuan Basin

With the increasing number of shale gas wells being hydraulically fractured with recycled flowback and produced water to reduce the consumption of fresh water, geochemical indicators of hydraulic fracturing flowback fluids (HFFFs) from such wells need to be found to evaluate the potential pollutants caused by shale gas development. To fill this knowledge gap, we analysed 64 HFFF samples from 3 Changning wells (fracked with recycled wastewater) to form a time series and compared them to HFFF samples from 3 Weiyuan wells (fracked with fresh water). We also made comparisons of HFFFs from two types of wells in the Appalachian Basin with reported data. The results indicated that regardless of the fracturing fluid being used, the water‒rock reaction caused by the hydraulic fracturing process resulted in the release of exchangeable phase elements, such as lithium, boron, with relatively depleted δ7Li and δ11B, and strontium with relatively enriched 87Sr/86Sr values on the shale surface, into the HFFFs. The composition of the injected fracturing fluid affected the strength of the water‒rock reaction, but the effect is negligible, as the fracturing process can still form the unique Sr, Li, and B isotope ratios of the HFFF. Thus, the elemental signatures (B/Cl and Sr/Cl) and isotopic fingerprints (δ11B, δ7Li, and 87Sr/86Sr) derived from HFFFs can be used to distinguish between HFFFs from wells hydraulically fractured by either fresh water or recycled wastewater and flowback water from conventional oil and gas wells. The results are important for the environmental evaluation of the large number of wells being fracked with recycled wastewater each year.

In vivo exposure to electronic waste (e-waste) leachate and hydraulic fracturing fluid adversely impacts the male reproductive system

Human health effects can arise from unregulated manual disassembly of electronic waste (e-waste) and/or hydraulic fracturing fluid spills. There is limited literature on the effects of e-waste and hydraulic fracturing wastewater exposure on the male reproductive system. Thus, this proof-of-concept study begins to address the question of how wastewater from two potentially hazardous environmental processes could affect sperm quality. Therefore, three groups of eight-week-old adult mice were exposed (5 d/wk for 6 wks) via a mealworm (Tenebrio molitor and Zophabas morio) feeding route to either: (1) e-waste leachate (50% dilution) from the Alaba Market (Lagos, Nigeria); (2) West Virginia hydraulic fracturing flowback (HFF) fluid (50% dilution); or, (3) deionized water (control). At 24-hours (hr), 3 weeks (wk), or 9-wk following the 6-wk exposure period, cohorts of mice were necropsied and adverse effects/persistence on the male reproductive system were examined. Ingestion of e-waste leachate or HFF fluid decreased number and concentration of sperm and increased both chromatin damage and numbers of morphological abnormalities in the sperm when compared to control mice. Levels of serum testosterone were reduced post-exposure (3- and 9-wk) in mice exposed to e-waste leachate and HFF when compared to time-matched controls, indicating the long-term persistence of adverse effects, well after the end of exposure. These data suggest that men living around or working in vicinity of either e-waste or hydraulic fracturing could face harmful effects to their reproductive health. From both a human health and economic standpoint, development of prevention and intervention strategies that are culturally relevant and economically sensitive are critically needed to reduce exposure to e-waste and HFF-associated toxic contaminants.

A multi-stage enhanced flocculation reactor for the treatment of simulated shale gas hydraulic fracturing flowback fluid: Effect of aspect ratios for the intense mixing section

Flocculation is a significant process in treating shale gas hydraulic fracturing flowback fluids. To achieve a high removal rate of pollutant, a range of multi-stage enhanced flocculation reactors that incorporated sequential intense, moderate, and weak mixing sections along the flow direction were devised, in which the aspect ratios (ARs) in the intense mixing section were varied. The results of the computer simulation indicated that the reactor with AR of 3.5 exhibited a gradual decrease in velocity and energy along the flow direction, and the flow field distribution is highly uniform and symmetrical. The generated flow field promoted the formation of small flocs in the intense mixing section and facilitated the collision of small flocs in the moderate mixing section, while preventing the fragmentation of flocs in the weak mixing section, therefore resulting in the generation of large and compact flocs. Moreover, the generated flocs demonstrated a good resistance to shear and oscillation, facilitating their separation from the simulated flowback fluids. The obtained reactor achieved remarkable removal efficiencies of 80.15 % for COD and 89.06 % for turbidity. Furthermore, when treating bentonite suspension, the multi-stage flocculation reactor achieved a turbidity removal rate of 99.34 % with a processing time of only 2.38 min and a settling time of just 20 min. This demonstrated the broad applicability of this reactor to various types of wastewater. This work provides valuable insights into the design of efficient flocculation reactors by integrating multiple mixing intensities within a reactor.

Spatial and temporal variation in toxicity and inorganic composition of hydraulic fracturing flowback and produced water

Hydraulic fracturing for oil and gas extraction produces large volumes of wastewater, termed flowback and produced water (FPW), that are highly saline and contain a variety of organic and inorganic contaminants. In the present study, FPW samples from ten hydraulically fractured wells, across two geologic formations were collected at various timepoints. Samples were analyzed to determine spatial and temporal variation in their inorganic composition. Results indicate that FPW composition varied both between formations and within a single formation, with large compositional changes occurring over short distances. Temporally, all wells showed a time-dependent increase in inorganic elements, with total dissolved solids increasing by up to 200,000 mg/L over time, primarily due to elements associated with salinity (Cl, Na, Ca, Mg, K). Toxicological analysis of a subset of the FPW samples showed median lethal concentrations (LC50) of FPW to the aquatic invertebrate Daphnia magna were highly variable, with the LC50 values ranging from 1.16% to 13.7% FPW. Acute toxicity of FPW significantly correlated with salinity, indicating salinity is a primary driver of FPW toxicity, however organic components also contributed to toxicity. This study provides insight into spatiotemporal variability of FPW composition and illustrates the difficulty in predicting aquatic risk associated with FPW.

Toxicity identification evaluation for hydraulic fracturing flowback and produced water during shale gas exploitation in China: Evidence from tissue residues and gene expression.

Hydraulic fracturing flowback and produced water (HF-FPW) from shale gas extraction processes is a highly complex medium with potential threats to the environment. Current research on ecological risks of FPW in China is limited, and the link between major components of FPW and their toxicological effects on freshwater organisms is largely unknown. By integrating chemical and biological analyses, toxicity identification evaluation (TIE) was used to reveal causality between toxicity and contaminants, potentially disentangling the complex toxicological nature of FPW. Here, FPW from different shale gas wells, treated FPW effluent, and a leachate from HF sludge were collected from southwest China, and TIE was applied to obtain a comprehensive toxicity evaluation in freshwater organisms. Our results showed that FPW from the same geographic zone could cause significantly different toxicity. Salinity, solid phase particulates, and organic contaminants were identified as the main contributors to the toxicity of FPW. In addition to water chemistry, internal alkanes, PAHs, and HF additives (e.g., biocides and surfactants) were quantified in exposed embryonic fish by target and non-target tissue analyses. The treated FPW failed to mitigate the toxicity associated with organic contaminants. Transcriptomic results illustrated that organic compounds induced toxicity pathways in FPW-exposed embryonic zebrafish. Similar zebrafish gene ontologies were affected between treated and untreated FPW, again confirming that sewage treatment did not effectively remove organic chemicals from FPW. Thus, zebrafish transcriptome analyses revealed organic toxicant-induced adverse outcome pathways and served as evidence for TIE confirmation in complex mixtures under data-poor scenarios.

Performance and microbial community analysis of combined bioreactors in treating high–salinity hydraulic fracturing flowback and produced water

The anoxic/oxic systems are a widely used biological strategy for wastewater treatment. However, little is known about the performance and microbial community correlation of different combined bioreactors in the treatment of high-COD and high-salinity hydraulic fracturing flowback and produced water (HF-FPW). In this study, the performance of Up-flow anaerobic sludge bed-bio-contact oxidation reactor (UASB-BCOR) and Fixed-bed baffled reactor (FBR-BCOR) in treating HF-FPW was investigated and compared. The results suggested the FBR-BCOR could efficiently remove COD, SS, NH4+-N, and oil pollutants, and it exhibited better resistance to the negative interference of hydraulic shock load on it. Besides, the correlation analysis first disclosed the key functional genera during the degradation process, including Ignavibacterium, Ellin6067, and Zixibacteria. Moreover, network analysis revealed that the difference of microbial co-occurrence network structure is the main driving factor for the difference of bioreactor processing capacity. This work demonstrates the feasibility and potential of FBR-BCOR in treating HF-FPW.

Improved degradation of petroleum contaminants in hydraulic fracturing flowback and produced water using laccase immobilized on functionalized biochar

Large quantities of hydraulic fracturing flowback and produced water (HF-FPW) represent an important environmental issue owing to their inclusion of toxic petroleum contaminants. Enzymatic degradation is a promising approach for treating these pollutants. However, the low stability and poor reusability of free enzymes greatly inhibit their applications. This study investigated the effect of biochar-immobilized laccases on the biodegradation of petroleum contaminants in HF-FPW. Acid functionalization of corn straw biochar increased its surface area and pore volume, allowing it to adsorb additional laccase on the surface. Biochar-immobilized laccase exhibited a high tolerance to a low pH and high temperatures and retained >81.0% of its relative activity at 4 °C for 20 d. In addition, the immobilized laccase displayed reusability after six reaction cycles, retaining 40.9% of its activity. Supplementation with immobilized laccase substantially improved microbial growth and fluorescein diacetate hydrolase activity in HF-FPW, which were up to 25.5 times and 4.9 times higher than those of the free laccase treatment, respectively. The immobilized laccase also elevated the transcription levels of degradation genes such as rub and xylE, and greatly enhanced the biodegradation of n-alkanes (reduction from 112.4 mg/L to 41.9 mg/L) and polycyclic aromatic hydrocarbons (reduction from 2606.2μg/L to 1526.6μg/L). Full-length 16S rRNA gene sequencing revealed that Pseudomonas stutzeri, Pseudomonas balearica, and Stenotrophomonas maltophilia dominated the microbial community and were potential functional populations. This study represents the first attempt of utilizing biochar-immobilized laccase to treat HF-FPW and has important implications for efforts to develop strategies for HF-FPW remediation.

Spatial and temporal water chemistry variations of hydraulic fracturing flowback and produced waters from the Duvernay Formation

Chemical characterization of hydraulic fracturing (HF) flowback and produced water (FPW) is important to the environmental sustainability of HF operations. In this research, we analyzed and compared HF FPW samples from different well locations as well as FPW samples from a single well at different stages of FPW production in the Duvernay Formation using a suite of analytical techniques and statistical methods. The results provide vital information to assess the reusability of FPW and support the choice of water handling, treatment, or disposal options. Additionally, this work contributes to a more complete understanding of regional FPW chemical composition and has the potential to provide guidance on best practices for future applications of HF fluid additives. While reuse of FPW is desirable, it is not always feasible. In these scenarios, the transportation of FPW offsite for treatment and/or disposal increases the risk of spills to near-surface environments. This work provides data to aid spill clean-up efforts and to determine the environmental fate of FPW contaminants. Overall, the information presented in this work may be used to provide economic benefits to the oil and gas sector by increasing FPW reuse that will directly decrease wastewater disposal costs and reduce environmental impacts of HF operations by decreasing the volume of used surface water and the risk of FPW surface spills.

Shale gas hydraulic fracturing flowback fluid treatment using a modified vortex flocculation reactor: Effects of the axial and tangential inlet angles

Flocculation technology has been widely applied in treating shale gas hydraulic fracturing flowback fluid. To improve flocculation efficiency, we designed a series of vortex flocculation reactors with variable axial and tangential inlet angles. It was found that a flow field beneficial to flocculation would be formed when the axial and tangential inlet angles were 45° and 30°, respectively. Under this condition, the turbulent dissipation rate of the flow field was high near the inlet and decreased step by step from the bottom to the top of the reactor. The flocs were denser and more resistant to shearing and oscillations. Moreover, this reactor exhibited superior chemical oxygen demand and turbidity removal rates of 78.21% and 88.10%, respectively, which increased by 28.08% and 23.69%, when compared with the traditional reactor (both axial and tangential inlet angles were 0°). This study is a reference for developing and optimizing high-performance vortex flocculation reactors.

Sensitivity Assessment of Boron Isotope as Indicator of Contaminated Groundwater for Hydraulic Fracturing Flowback Fluids Produced from the Dameigou Shale of the Northern Qaidam Basin

Hydrogeochemical processes occurring in contaminated groundwater and aquifer systems may reduce the sensitivity of boron isotopes as an indicator of hydraulic fracturing flowback fluids (HFFF) in groundwater. In this paper, based on the Chaiye-1 well (the first continental shale gas well in the northern Qaidam Basin), the hydrogeochemical processes affecting boron isotopes were analyzed in HFFF-contaminated Neogene (NG1 and NG2) and Quaternary (QG1) groundwater around the shale gas field. Then, a model for boron isotopes in HFFF-contaminated groundwater was constructed to assess the sensitivity of boron isotopes as an HFFF indicator. The results show that, limited by the range of pH values and saturation indices (SI) in HFFF-contaminated groundwater, the dissolution of alkali feldspar and precipitation of carbonate have little effect on the boron isotopes in shallow groundwater. For the NG2 aquifer system containing clay minerals, the δ11B of simulated contaminated groundwater (40.0–55.6‰) is always higher than that of the corresponding groundwater mixed conservatively (−6.4–55.6‰) due to preferential adsorption of boron isotopes onto clay minerals, indicating preferential adsorption would reduce the sensitivity of boron isotopes as an indicator of groundwater contamination from HFFF. For the scenario of HFFF contamination, when the mixing ratio of HFFF in contaminated groundwater increases by 5%, boron isotopes in Neogene (NG1 and NG2) and Quaternary (QG1) groundwater have detectable responses to HFFF contamination, suggesting δ11B is a sensitive indicator of HFFF contamination in shallow groundwater from the Dameigou Shale in the northern Qaidam Basin.

Treatment for hydraulic fracturing flowback fluid of shale gas by ceramic membrane-ED-H/L pressure RO process

The ceramic membrane-ED-H/L pressure RO combined process was constructed for the treatment of fracturing flowback fluid, and the mechanism and influencing factors were investigated. The removal efficiency of TDS and COD reached 97.5 % and 31.9 %, respectively, through coagulation-ceramic membrane which was contaminated slightly by TSS due to the “cross-flow” operation. However, according to the analysis of ceramic membrane by FTIR, SEM and EDS, it was indicated the decreasing of membrane flux would be caused by organic and inorganic composite made from PAM, calcium and barium crystals. The removal of organic pollutants was positively correlated with operating voltage in ED. The removal efficiency of and COD reached 79.3 % on 20 V operating voltage. Based on the analysis of organic matter composition by CG-MS and 3D fluorescence spectroscopy, it was showed the removal efficiency of polar substance, such as phenol, was higher than non-polar substance, such as n-butane due to the electromigration. For the removal of the ions, the removal efficiency of Ca2+, Mg2+, Na+, K+, SO42− and Cl− reached 99.7 %, 99.6 %, 95.8 %, 99.2 %, 99.3 % and 96.4 % respectively, indicating ion valence had a significant influence on ion removal by ED. The concentrated water and diluted water produced by ED were treated by the RO in high- and low-pressure operation, respectively, in order to improve membrane flux. The COD and TDS were about 11.6 mg/L and 4.0 mg/L in diluted water treated by the RO in low-pressure operation respectively, showing membrane flux hardly decreased significantly with high stability and flux.

Latent impacts on juvenile rainbow trout (Oncorhynchus mykiss) cardio-respiratory function and swimming performance following embryonic exposures to hydraulic fracturing flowback and produced water

Technologies associated with hydraulic fracturing continue to be prevalent in many regions worldwide. As a result, the production of flowback and produced water (FPW) – a wastewater generated once pressure is released from subterranean wellbores – continues to rise in regions experiencing fracturing activities, while waste management strategies attempt to mitigate compounding burdens of increased FPW production. The heightened production of FPW increases the potential for release to the environment. However, relatively few studies have directly investigated how ecosystems and organisms may be latently affected long after exposures occur. The current study examines rainbow trout exposed in ovo at select critical cardiac developmental time points to differing dilutions and lengths of time (acute versus chronic) to determine how FPW-mediated exposure in ovo may alter later cardiac function and development. After exposure, we allowed fish to grow for ∼ 8 months post-fertilization and measured fish swimming performance, aerobic scope, and cardiac structure of juvenile trout. Acute 48 h embryonic 5% FPW exposure at either 3 days post-fertilization (dpf) or 10 dpf significantly reduced later swimming performance and aerobic scope in juvenile trout. In ovo exposure to 2.5% FPW at 3 dpf yielded significant decreases in these metrics as well, while exposing trout to 2.5% FPW at 10 dpf did not induce as significant effects. Morphometric analyses of heart muscle tissue in all treatments decreased compact myocardium thickness. Chronic 1% FPW in ovo exposure for 28 days induced similar reductions in swimming performance, aerobic scope, and decreased compact myocardium thickness as acute exposures. Overall, our results demonstrate that FPW exposure during egg development ultimately results in persistently impaired heart morphology and resulting physiological (swimming) performance.

Degradation of dibutyl phthalate by ozonation in the ultrasonic cavitation-rotational flow interaction coupled-field: performance and mechanism.

Dibutyl phthalate (DBP) is present in hydraulic fracturing flowback and produced water. Degradation of DBP in aqueous by means of ozonation in ultrasonic cavitation-rotational flow interaction coupled-field (UC-RF coupled-field) was studied. The effect of ozone dosage, ozone intake flow, operating temperature, initial pH, DBP initial concentration, liquid flow rate, and ultrasonic power on the DBP removal was investigated. Results indicated that the DBP degradation rate was strongly influenced by the liquid flow rate and the ultrasonic power over the range investigated. HCO3- and Cl- revealed an inhibitory effect on the DBP removal. SO42- seemed to have no effect on DBP removal. The ozone utilization efficiencies in the UC-RF coupled-field were 2.77 and 1.13 times higher than those in the conventional microporous aeration (CMA) and rotating-flow microbubble aeration (RFMA), respectively. The DBP degradation rate was diminished in the presence of tert-butyl alcohol. Cavitation bubbles are considered as innumerable microreactors. Degradation of DBP by direct ozonation, hydroxyl radical (·OH) oxidation, high pressure, and high-temperature pyrolysis was demonstrated. Finally, a possible degradation pathway of DBP is obtained on the basis of the main reaction intermediates.

Chemical and isotopic evolution of flowback fluids from the Utica Gas Shale Play, Eastern Ohio USA

Hydraulic fracturing flowback fluids were collected from two Utica/Point Pleasant well pads in eastern Ohio. One site was in the wet gas zone (UPPW), while the site ∼50 km south consisted of four wells on the same pad in the dry gas zone (UPPS). Samples of input fluids also were collected before and during hydraulic fracturing. Flowback fluids are Na-Ca-Cl brines with total dissolved salt (TDS) concentrations that increase over several months from ∼100 to 200 g/L. The slightly higher TDS of the dry gas fluids are in part due to recycled flowback used as input fluids, and in part due to lower volume of water used in hydraulic fracturing. Concentrations of most major ions (Ca2+, Mg2+, Na+, Sr2+, Fe, Mn, Cl−, Br−) are similar for the five wells sampled, although small but systematic changes occur in the major element ratios over time.Most notably, an increase in the Sr/Cl ratio corresponds to an increase in the 87Sr/86Sr ratio in the fluids, suggesting interactions with a more radiogenic Sr source in the subsurface. Dissolved Ba concentrations and Ra activities were different between the two sites, reflecting a high SO42− fluid used at the UPPW site, and water-rock reactions occurring during hydraulic fracturing at the UPPS site.Water oxygen (δ18O) and hydrogen (δD) isotopes for input fluids used in the UPPW4 well and fresh water used for the UPPS wells fall on the Global Meteoric waterline (GMWL). Flowback fluids from both sites are relatively enriched in δ18O and δD compared to the input, but do not appear to follow a simple mixing trend, suggesting reaction and isotopic exchange with carbonates and fractionation due to imbibition in the rock. Cl isotopes, δ37Cl in the FP fluids varied from ∼ −0.43 to +0.13‰, the largest variation was observed in the earlier stages of flowback, while in the later stages δ37Cl exhibited a small but systematic increase over time, suggesting diffusion control of isotopic composition.Some of the trace species measured (dissolved Fe, Mn, thiosulfate and organic acids) do not follow the same trends as the major ions, suggesting contributions from input fluids, or microbially mediated reactions are exerting control on their concentrations. Input water chemistry exerts an important control on the Sr and Ba concentrations in flowback water. High SO42− in the input fluids used for hydraulically fracturing the wet gas well leads to precipitation of barite-celestite in flowback fluids.

Geochemical processes during hydraulic fracturing in a tight sandstone reservoir revealed by field and laboratory experiments

The application of hydraulic fracturing has transformed tight sandstone gas into a very important global unconventional resource. The accurate description of geochemical processes during hydraulic fracturing can provide essential information for improving tight gas production. In this study, field fracturing and laboratory water-rock interaction experiments were designed and performed in conjunction with geochemistry, isotope, XRF, XRD and SEM techniques to reveal the prevalent geochemical processes. Sixty-five flowback fluid samples were collected from a hydraulic fracturing well and a tight sandstone sample was drilled from gas reservoir to perform water-rock interaction experiments. The results indicate that hydraulic fracturing flowback fluid is a complex mixture, with high TDS values (0.93–33.04 g/L) and heavy isotopes (e.g., mean δ18O of −5.35‰, mean 87Sr/86Sr of 0.714651). Geochemistry and isotope data reveal that the mixing process between fracturing fluid and formation water exerts an important influence on the flowback fluid chemistry, while water-rock and fluid-fluid interactions are also variably important during the hydraulic fracturing process. Pyrite oxidation process is confirmed during hydraulic fracturing in the tight sandstone reservoir, while the addition of gel breaker makes the process prominent. Due to high clay mineral contents (24%), ion exchange and adsorption/desorption are critical factors affecting the stability of the clay minerals during the entire fracturing and flowback processes. Approximately, 20%-43% of the strontium was removed from the solution by ion exchange between the 8 and 44 h intervals of the flowback process. The fractures derived from fracturing connect different types of high salinity formation water, leading to potential mineral precipitation (e.g., barite and calcite). The analysis of formation water needs to be taken into consideration during hydraulic fracturing operations.

Embryonic cardio-respiratory impairments in rainbow trout (Oncorhynchus mykiss) following exposure to hydraulic fracturing flowback and produced water

During hydraulic fracturing, wastewaters - termed flowback and produced water (FPW) - are created as a by-product during hydrocarbon extraction. Given the large volumes of FPW that a single well can produce, and the history of FPW release to surface water bodies, it is imperative to understand the hazards that hydraulic fracturing and FPW pose to aquatic biota. Using rainbow trout embryos as model organisms, we investigated impacts to cardio-respiratory system development and function following acute (48 h) and sub-chronic (28-day) FPW exposure by examining occurrences of developmental deformities, rates of embryonic respiration (MO2), and changes in expression of critical cardiac-specific genes. FPW-exposed embryos had significantly increased rates of pericardial edema, yolk-sac edema, and tail/trunk curvatures at hatch. Furthermore, when exposed at three days post-fertilization (dpf), acute 5% FPW exposures significantly increased embryonic MO2 through development until 15 dpf, where a switch to significantly reduced MO2 rates was subsequently recorded. A similar trend was observed during sub-chronic 1% FPW exposures. Interestingly, at certain specific developmental timepoints, previous salinity exposure seemed to affect embryonic MO2; a result not previously observed. Following acute FPW exposures, embryonic genes for cardiac development and function were significantly altered, although at termination of sub-chronic exposures, significant changes to these same genes were not found. Together, our evidence of induced developmental deformities, modified embryonic MO2, and altered cardiac transcript expression suggest that cardio-respiratory tissues are toxicologically targeted following FPW exposure in developing rainbow trout. These results may be helpful to regulatory bodies when developing hazard identification and risk management protocols concerning hydraulic fracturing activities.

Identifying strontium sources of flowback fluid and groundwater pollution using 87Sr/86Sr and geochemical model in Sulige gasfield, China

Hydraulic fracturing technology has made unconventional oil and gas development economically viable; however, it can lead to potential environmental issues such as groundwater pollution. Strontium isotope (87Sr/86Sr) is considered as a sensitive tracer to indicate potential groundwater contamination. In this study, strontium (Sr) and 87Sr/86Sr sources of hydraulic fracturing flowback fluid are identified with 87 flowback fluid samples and 5 borehole core samples. High Sr concentrations and 87Sr/86Sr values were found in fracturing flowback fluid. The hydrogeochemistry evidence shows high Sr and 87Sr/86Sr in fracturing flowback fluid mainly comes from formation water with high ion concentrations, while Sr and 87Sr/86Sr of formation water develop in diagenesis and long term water-rock interaction (e.g., feldspar dissolution and clay mineral transformations) under the high temperature and pressure. A complete evaluation system was executed to assess the sensitivity of 87Sr/86Sr indicating potential pollution on groundwater. The mixing curves which 87Sr/86Sr combined with Sr and Cl were also established by mixing models to indicate groundwater pollution. The modeling results show mineral dissolution/precipitation and cation exchange have little impact on 87Sr/86Sr in the mixing process between fracturing flowback fluid and groundwater, which 87Sr/86Sr can identify contamination when only 0.89% of fracturing flowback fluid mixes with groundwater. Finally, the potential contamination pathways are discussed. It is highly unlikely fracturing flowback fluid contaminates groundwater and soil through upward migration, whereas leakage is a more prevalent pollution pathway.

Accelerating mineral carbonation in hydraulic fracturing flowback and produced water using CO2-rich gas

Mineral carbonation is a Carbon Capture Utilization and Storage (CCUS) technique that can be used to remove or divert carbon dioxide (CO2) from the atmosphere and store it in carbonate minerals. Hydraulic fracturing flowback and produced water (FPW) is Ca- and Mg-rich wastewater generated by the petroleum industry that can be used to sequester CO2 in benign minerals. Here, we describe the rate and efficiency of mineral carbonation achieved by sparging 10% CO2/90% N2 gas into pH-adjusted FPW, collected from the Duvernay Formation in the Western Canadian Sedimentary Basin. Our results indicate that calcite (CaCO3) precipitated at the expense of brucite [Mg(OH)2] dissolution following CO2 injection; as such, no Mg-carbonate precipitates were formed. The carbonation reaction reached steady state within 1 h and 14.2% of the aqueous Ca in the FPW was precipitated as calcite, sequestering 1.56 ± 0.33 g CO2 L−1 of FPW. Our dissolved inorganic carbon measurements, geochemical models, and stable carbon isotope results indicate that CO2 mineralization can be maximized by maintaining solution at pH ≥ 10 during CO2 sparging. If all of the Ca and Mg in the FPW could be carbonated, it would offer a greater CO2 sequestration potential of 12.5 ± 0.3 g CO2 L−1.

Unlocking the potential of hydraulic fracturing flowback and produced water for CO2 removal via mineral carbonation

Flowback and produced water (FPW) generated by hydraulic fracturing operations is highly saline and contains elevated concentrations of ions including calcium and magnesium. Here, we investigate the use of FPW as a source of calcium and magnesium for carbon dioxide (CO2) removal and storage in carbonate minerals. We performed pH titration experiments to precipitate calcium and magnesium from three FPW samples from Alberta and Saskatchewan, Canada. Depending on the pH (8.5–12), calcite (CaCO3) and brucite [Mg(OH)2], with occasional aragonite (CaCO3) and portlandite [Ca(OH)2] precipitate from FPW within 24 h of exposure to atmospheric pCO2 at ∼18 °C. Our experiments demonstrate that pH adjustments are an effective means of precipitating calcium and magnesium carbonates and hydroxides from FPW, but that relying solely upon passive removal of CO2 from air is limiting to carbonation. We estimate that carbonation of all calcium and magnesium from brines produced in conventional and hydraulic fracturing operations in Canada could store up to 1,010 Mt CO2 annually. Carbonation rates could be improved by using higher pCO2 gases, such as flue gases from fossil energy generation (via CO2 capture), gas streams produced by Direct Air Capture plants or using novel looping technologies.

Isotopic characteristics of the excess hydraulic fracturing flowback fluid in tight oil reservoir: Implication for source, composition, and flowback stage division

Hydraulic fracturing flow-back fluid (FFF) poses a significant challenge to environmental security, and it also can provide valuable information for geological and engineering applications. In order to reveal the source and composition of excess FFF in Jimsar tight oil reservoir, Junngar Basin, Northwest of China, and determine the stage of the hydraulic fracturing flow-back process, this study systematically collected the samples of surface water (SW), hydraulic fracturing fluid (HFF), and FFF from three horizontal wells in the study area. After measuring and analyzing the thousand deviation values of diplogen (δD) and oxygen (δ18O) isotopes from the collected samples, we obtained the geochemical information and the temporal variation characteristics. By analyzing the influence degree of isotope exchange of Water Rock Interaction (WRI) and nonlinear fitting the field measured data of the FFF, the convergent model of δ18O with flow-back time of the FFF was constructed. Based on the law of mass isotope conservation, we proposed a method to calculate the content of formation water in the FFF. The results showed that the SW (δDSW = −73.35‰, δ18OSW = −11.30‰) and HFF (δDHFF = −73.03‰, δ18OHFF = −11.20‰) samples conform to the isotopic characteristics of atmospheric precipitation in the study area. In contrast, the FFF samples are characterized by a positive drift in δ18O and a negative drift in δD, clearly deviating from the atmospheric waterline distribution. The water composition of FFF has changed. The temporal variation characteristics of the δ18O in FFF indicated that the flow-back process can be divided into three stages: The first stage was about 15 days after the flow-back process. As the formation water began to mix into the flow-back fluid, the δ18O of FFF increased rapidly. The second stage was 15–40 days after the flow-back process, and the increase rate of δ18O was smaller than that in the first stage. The isotopic composition of FFF gradually shifted to formation water dominated. The third stage was 40 days after the flow-back process, and the δ18O tended to be stable. To be specific, as formation water was continuously mixed into the fracturing fluid, the composition of FFF gradually changed from HFF dominated to formation water. It was calculated from the field measured data that the original δ18O of formation water was −6.902‰; on the 60th day of the flow-back process, the content of formation water in FFF was about 84% and 81% in well JHW43 and JHW44, respectively. Conclusively, the FFF is mainly composed of formation water.