Fracturing Fluid Flowback Research Articles

Evaluation of Self-Degradation and Plugging Performance of Temperature-Controlled Degradable Polymer Temporary Plugging Agent.

Temporary plugging diversion fracturing (TPDF) technology has been widely used in various oil fields for repeated reconstruction of high-water-cut old oil wells and horizontal well reservoir reconstruction. Previous studies have carried out in-depth study on the pressure-bearing law and placement morphology of different types of temporary plugging agents (TPAs) in fractures, but there are relatively few studies on TPA accumulation body permeability. To solve this problem, an experimental device for evaluating the TPA performance with adjustable fracture pores is proposed in this paper. Based on the test of fracturing fluid breaking time and residue content, the low damage of fracturing fluid to the reservoir is determined. The TPA degradation performance test determines whether the TPA causes damage to the hydraulic fracture after the temporary plugging fracturing. Finally, by testing the TPA pressure-bearing capacity and the temporary plugging aggregation body permeability, the plugging performance and the aggregation body permeability are determined. The results show the following: (1) Guar gum fracturing fluid shows good gel-breaking performance under the action of breaking agent, and the recommended concentration of breaking agent is 300 ppm. At 90~120 °C, the degradation rate of the three types of TPAs can reach more than 65%, and it can be effectively carried into the wellbore during the fracturing fluid flowback stage to achieve the effect of removing the TPA in the fracture. (2) The results of the pressure-bearing performance of the TPA show that the two kinds of TPAs can quickly achieve the plugging effect after plugging start: the effect of ZD-2 (poly lactic-co-glycolic acid (PLGA)) particle-and-powder combined TPA on forming an effective temporary plugging accumulation body in fractures is better than that of ZD-1 (PLGA) pure powder. There are large pores between the particles, and the fracturing fluid can still flow through the pores, so the ZD-3 (a mixture of lactide and PLGA) granular temporary plugging agent cannot form an effective plugging. (3) The law of length of the temporary plugging accumulation body shows that the ZD-2 combined TPA has stronger plugging ability for medium-aperture simulated fracture pores, while the ZD-1 powder TPA has stronger plugging ability for small aperture simulated fracture pores, and the ZD-3 granular TPA should be avoided alone as far as possible. This study further enriches and improves the understanding of the mechanism of temporary plugging diverting fracturing fluid.

Coordinated development of shale gas benefit exploitation and ecological environmental conservation in China: a mini review

The large-scale development and utilization of shale gas is significant for achieving the “Carbon Peak and Carbon Neutrality” goals. However, addressing the ecological environmental challenges stemming from extensive hydraulic fracturing is imperative. Drawing from the successful exploration and development of shale gas in the Sichuan Basin, this paper employs a bibliometric approach and utilizes the Web of Science database as its data source to review the impact of shale gas development on the ecological environment. Furthermore, effective strategies for achieving coordinated development of shale gas benefit exploitation and ecological environmental conservation in China are identified. The findings highlight that the ecological impact of shale gas development has been a major focus of research over the past decade, primarily involving concerns such as water resources consumption, groundwater pollution, methane emissions, and waste management. These challenges can be addressed by adopting measures such as responsible water usage, maintaining well integrity, proper storage and disposal of fracturing flowback fluids, and appropriate management of drilling solid waste. The key to achieving green and efficient shale gas development in China lies in constructing a solid theoretical framework for benefit exploitation, refining environmental management standards and regulations, and promoting the development of clean production technologies specific to shale gas. Additionally, establishing a distinct exploration and development theory and fostering technical innovation for deep shale gas (buried depth > 3500m) are pivotal for enhancing and stabilizing production in China. Clarifying the theoretical logic of benefit development and improving the environmental protection law of shale gas development are of great significance for realizing the scale benefit development of shale gas and the harmonious development of ecological environment in China.

Research Progress in Treatment and Utilization of Fracturing Flowback Fluid

Research Progress in Treatment and Utilization of Fracturing Flowback Fluid

Efficient electro-Fenton processes on a novel self-supported single-atom Fe electrode: Mechanism and practical application

Electro-Fenton technology is widely applied in the field of water treatment for refractory organic pollutant degradation. Herein, a novel self-supported single-atom Fe electrode was fabricated via simple electrodeposition and pyrolysis approach for the first time. The prepared single-atom electrode showed excellent activity and stability for degradation of aromatic compounds in electro-Fenton (EF) process, in which the 4-hydroxybenzoic acid (4-HBA) pollutant is completely decomposed by the substitution, decarboxylation, hydroxylation, and oxidation reactions. Significantly, the electrode possessed great performance for purification of the shale gas fracturing flowback fluid. The degradation pathways of organics in real matrix were also studied in detail. The characterization analysis proved that the single-atom Fe was in situ grown on electrode surface, confirming to be Fe-N/O construction with coordination number of ∼4.3. Therefore, the EF mechanism was preliminary proposed by analyzing all possible configurations of single-atom Fe (FeN4, FeN3O1, FeN2O2, and FeN1O3). Results implied that the FeN2O2 structure may contribute to improving EF performance by enhancing the O2 adsorption and promoting the breakage of *OOH to form H2O2. Additionally, the good adsorption of FeN2O2 toward organic pollutant was also greatly conducive to the EF degradation. This study provides a feasible strategy for self-supported single-atom Fe electrode and demonstrated its application for efficient EF treatment of real wastewater.

The mechanisms of inhibition and lubrication of clean fracturing flowback fluids in water-based drilling fluids

Abstract This study presents a novel approach for the reuse of uncontaminated fracturing flowback fluids to improve the inhibitory and lubricating properties of water-based drilling fluids (WBFs), curb environmental pollution arising from flowback fluids, and substantially mitigate the expenses associated with WBFs. The experimental design was optimized using orthogonal experiments and range analyses, whereby the modified rubber powder was set at 2.0%, xanthan gum at 0.15%, and a plant phenol to modified complexing agent ratio of 1:0.01. The assessment of the performance evaluation tests indicated that the use of uncontaminated fracturing flowback fluids as the base water can remarkably enhance the inhibitory and lubricating properties of WBFs. Precisely, this approach reduces the linear expansion rate from 62.31% to 21.25%, the reduction rate of extreme pressure lubrication coefficient by 87.98%, and the reduction rate of mud cake sticking factor by 59.86%. This investigation has established the potential environmental and economic benefits of reusing clean fracturing flowback fluids in WBFs.

Experimental study on the effect of tight gas fracturing flowback fluid composition on the performance of modified polyacrylamide viscosity reducing and slippery water system

AbstractTight gas belongs to unconventional gas reservoirs, and to obtain high gas production, it needs to be fractured and reformed. After the construction is completed, a large amount of flowback fluid is produced. In order to reduce the cost of flowback fluid treatment and avoid environmental pollution, a slippery water system with flowback fluid is usually used on the site of hydraulic fracturing. Almost all flowback fluids contain high‐order cations such as calcium ions, magnesium ions, iron ions, and a large amount of suspended solids. Some flowback fluids contain incomplete gel‐breaking micelles and unseparated condensate oil. The performance of the viscosity‐reducing and slippery water system with flowback fluid as the base fluid is poor, usually manifested as low viscosity of the slippery water, low friction reduction rate, and high formation damage. To study the effect of tight gas fracturing flowback fluid on the performance of modified polyacrylamide viscosity‐reducing and slippery water system, this paper found through cryo‐electron microscopy scanning experiments that the flowback fluid made the modified polyacrylamide molecular chain unable to form a complex network structure and showed the phenomenon of reduced strength and aggregation. The effects of mineralization degree, calcium and magnesium ions, divalent and trivalent iron ions, suspended solids, pH value, and oil content on the viscosity, friction reduction performance, and rock damage of the viscosity‐reducing and slippery water system were analyzed experimentally. It was found that the viscosity of the viscosity‐reducing and slippery water system was mainly affected by divalent iron ions, calcium and magnesium ions and other divalent cations; the friction reduction rate was mainly affected by the content of suspended solids and oil content; and the rock damage was mainly affected by the pH value and the content of suspended solids. Based on this, recommended parameters for reusing tight gas fracturing flowback fluid are given to guide the smooth progress of hydraulic fracturing construction on‐site.

Effect of reservoir temperatures on the stabilization and flowback of CO2 foam fracturing fluid containing nano-SiO2 particles: An experimental study

CO2 foam fracturing technology shows promise concerning enhancing coalbed methane (CBM) recovery and realizing CO2 geo-sequestration in deep un-mineable coal seams. However, one of the main challenges for successful CO2 foam fracturing is the foam destabilization and rupture that are caused by reservoir temperatures. The application of nanotechnology can improve foam stability. This paper aims to investigate the mechanism of CO2 foam stabilization by nano-SiO2 particles and the effect on fracturing fluid flowback at different reservoir temperatures. The foaming performance, interfacial rheological properties, and wettability of sodium dodecyl sulfate (SDS) and SDS/SiO2 dispersions in distilled water were examined using the foam scanner and interfacial rheometer. The results show that the foaming capacity of a CO2 foam fracturing fluid is found to increase with increases in temperature while the foam half-life is decreased. With an increase in the 0.2 mass% SDS + 0.3 mass% nano-SiO2 solution temperature from 20 °C to 60 °C, the foaming capacity increases by 24.42%, from 0.86 to 1.07, while the foam half-life decreases by 94.14%, from 7254 s to 425 s. The addition of nano-SiO2 particles reduces the foaming capacity of the SDS solution but substantially increases the foam half-life. When the temperature is 30 °C, the foaming capacity of 0.2 mass% SDS + 0.3 mass% nano-SiO2 solution is 8.33% lower than that of 0.2% SDS solution, but the foam half-life increases by 100.29%. The adsorption of nano-SiO2 particles at the gas-liquid interfaces increases both the viscoelastic and elastic moduli, which in turn enhances the ability of the foam to resist external disturbances. The viscoelastic and elastic moduli of the foam are both observed to decrease with increasing temperature, while both high temperatures and the presence of nano-SiO2 particles increase the capillary resistance of the fluid, which will degrade flowback. This study provides basic theoretical support for the application of CO2 foam fracturing technology to CBM production enhancement.

Evaluation of the fracturing fluid flowback based on perforation clusters for horizontal shale gas wells using data-mining methods

Multi-stage hydraulic fracturing is a crucial technique in the development of horizontal shale gas wells. After fracturing and shut-in for several days, the well would be opened and the fracturing fluid injected into the gas formation would flow back to the ground along with extracted gas. Field experts suggest fracturing fluid flowback plays a key role in the production of shale gas and hope to find the relationship between flowback and production. However, the flowback and production data we collected from 161 wells in one shale gas field in China illustrate that there is no general relationship between flowback and production. The main reason we deduce is that the commonly-used cumulative flowback amount is not a good indicator to represent shale gas wells’ flowback situation. Therefore, we propose a new flowback indicator based on filed data and a shale gas flow model. The proposed indicator is the cumulative flowback ratio per fracturing cluster calculated on production days, where production day is a newly proposed time measurement substituting the calendar day. Further study illustrates that the proposed indicator can be easily predicted using a random forest model with engineering parameters, geological parameters, and well operation parameters. Besides, fracturing scale parameters and brittle mineral proportion are identified as the most important controlling factors of the proposed indicator. With the help of the newly proposed flowback indicator, field experts can have a new way to comprehend each well’s flowback characteristics and make better development plans.

A novel approach to reducing the biological toxicity of shale gas fracturing flowback fluid through recycling of high-value nano-BaSO4

Shale gas fracturing flowback fluid (FFBF) is a hazardous waste with high biological toxicity, which is difficult to recycle and particularly harmful to the environment. The mainstream research aims to reduce the biological toxicity of FFBF. However, innovative methods to reduce FFBF's biological toxicity and simultaneously achieve resource utilization are scarce. In this study, we reduced FFBF's biotoxicity for the first time by removing Ba2+ ion and simultaneously recovering high-value nano-BaSO4 through a liquid-liquid two-phase co-precipitation reaction. The results showed that the removal rate of Ba2+ reached 93%, and the recovery rate of nano-BaSO4 from FFBF reached 91%. The value of the recovered nano-BaSO4 similar to the commercial nano-BaSO4 was confirmed via characterizing the physicochemical properties. The effect of reducing toxicity by analyzing changes in duckweed's physical chemistry, key genes, metabolome, and transcriptome. We found that duckweed mortality in a 100% concentration test solution after nano-BaSO4 recovery was reduced to 66.32% compared to 100% before recovery. The chlorophyll a and b contents were significantly improved, and NH3–N and Tot-P absorption increased after nano-BaSO4 recovery. We also analyzed key genes associated with carbohydrate and fatty acid metabolism by comparing before and after nano-BaSO4 recovery. Results showed significant changes in some key genes after nano-BaSO4 recovery. Additionally, secondary metabolite accumulation were also analyzed. The results showed that the metabolic composition was significantly different after recovering nano-BaSO4. These results indicate that the toxicity of FFBF can be reduced not only by removing Ba2+ ion but also by achieving resource utilization through recycling nano-BaSO4. Therefore, this study provides a potential new method for decreasing FFBF toxicity and a means to generate new value from FFBF.

Research on the Convection-Reaction-Diffusion Model of Contaminants in Fracturing Flowback Fluid in Non-Equidistant Artificial Fractures with Arbitrary Inclination in (3+1)-Dimensional Space-Time.

This paper extends the improved fracture equivalent method and then establishes (3+1)-dimensional convection-reaction-diffusion models of contaminants in fracturing flowback fluid in the i-th artificial fracture with arbitrary inclination by comprehensively analyzing the convection effect of fracturing flowback fluid during the flowback process, the diffusion effect of pollutants in fracturing flowback fluid, and the possible chemical reactions between the fracturing fluid and shale matrix. Next, we use a series of transformations and solving methods to solve the established model and obtain semi-analytical solutions of the (3+1)-dimensional convection-reaction-diffusion models. Finally, this paper takes chloride ions as an example to study the concentration changes of pollutants in fracturing flowback fluid in three-dimensional artificial fractures with arbitrary inclination and analyzes the influence of various main control factors on the chloride ion concentration at the inlet end of the i-th artificial fracture with arbitrary inclination.

Stress Sensitivity of Proppant-Containing Fractures and Its Influence on Gas Well Productivity

Formation pressure gradually decreases with fracturing fluid flowback and gas production. Due to the stress sensitivity of the fractures, the permeability of the artificial fractures after fracturing becomes lower, which significantly affects gas well productivity. This paper focuses on two questions: (1) the stress sensitivity of proppant-containing fractures with different roughness and (2) tight gas well productivity considering stress sensitivity. Two types of artificial fracture samples, smooth and rough, are prepared and filled with different proppant concentrations. Then, the changing confining pressure method is used to quantify sample stress sensitivity. On this basis, the productivity equation for the fractured well with finite conductivity that considers fracture and matrix stress sensitivity is derived, and the influence of stress sensitivity on productivity is discussed. The results show that proppant concentration and fracture surface roughness will significantly affect fracture permeability and stress sensitivity; with increasing proppant concentration, fracture permeability increases, stress sensitivity decreases, and well productivity increases; under the same proppant concentration, the stress sensitivity is lower and the gas production is higher for smooth fracture; and when the artificial fracture changes from no proppant to proppant, the productivity of the fracturing well is improved the most.

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.

Investigation of Fracturing Fluid Flowback in Hydraulically Fractured Formations Based on Microscopic Visualization Experiments

Fracturing fluids are widely applied in the hydraulic fracturing of shale gas reservoirs, but the fracturing fluid flowback efficiency is typically less than 50%, severely limiting the shale gas recovery. Additionally, the mechanism and main influencing factors of fracturing fluid flowback are unclear. In this study, microscopic experiments are conducted to simulate the fracturing fluid flowback progress in shale gas reservoirs. The mechanism and factors affecting fracturing fluid flowback/retention in the fracture zone were analyzed and clarified. Results show that the ultimate flowback efficiency of fracturing fluid is positively correlated with the fracturing fluid concentration and the gas driving pressure difference. There are four kinds of mechanisms responsible for fracturing fluid retention in the pore network: viscous resistance, the Jamin effect, the gas blockage effect and the dead end of the pore. Additionally, the ultimate flowback efficiency of the fracturing fluid increases linearly with increasing capillary number. These insights will advance the fundamental understanding of fracturing fluid flowback in shale gas reservoirs and provide useful guidance for shale gas reservoirs development.

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.

Machine-Learning-Based Hydraulic Fracturing Flowback Forecasting

AbstractHydraulic fracturing is an indispensable procedure to the economic development of shale gas. The flowback of the hydraulic fracturing fluid is one of the most important parameters recorded after shale gas wells are put into production. Generally, the flowback ratio is used as the flowback indicator during hydraulic fracturing. The flowback ratio has a great influence on shale gas production. However, the flowback ratio is subjected to various affecting factors with their correlativity unclear. Based on a large amount of original geological, engineering, and dynamic data acquired from 373 hydraulically fractured horizontal wells, the flowback characteristics were systematically studied based on machine learning. Based on the data analysis and random forest forecasting, a new indicator, single-cluster flowback ratio, was proposed, which can more effectively reflect the inherent relationship between flowback fluid volume and influencing factors. The results of training random forests for big data show that this indicator has better learnability and predictability. A good linear relationship exists between single-cluster flowback ratios in different production stages. Accordingly, the 30-day single-cluster flowback ratio can be used to predict the 90-day and 180-day single-cluster flowback ratios. The main controlling factors of production and flowback ratio were also systematically analyzed. It is found that the main controlling factors of the flowback ratio include the number of fracturing clusters, the total amount of sand, number of fracturing stages, and fluid injection intensity per cluster. This study can provide a fundamental reference for analyzing the hydraulically fracturing fluid flowback for shale gas reservoirs.

A review of advanced oxidation process towards organic pollutants and its potential application in fracturing flowback fluid.

Fracturing flowback fluid (FFF) including various kinds of organic pollutants that do harms to people and new treatments are urgently needed. Advanced oxidation processes (AOPs) are suitable methods in consideration with molecular weight, removal cost and efficiency. Here, we summarize the recent studies about AOP treatments towards organic pollutants and discuss the application prospects in treatment of FFF. Immobilization and loading methods of catalysts, evaluation method of degradation of FFF, and continuous treatment process flow are discussed in this review. In conclusion, further studies are urgently needed in aspects of catalyst loading methods, macromolecule organic evaluation methods, industrial process, and pathways of macromolecule organics' decomposition.

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.

Development of resource treatment technology for fracturing backflow fluids of tight sandstone

Abstract Fracturing is an important means to realize the development value of tight sandstone unconventional reservoirs, which consumes serious water resources and generates high viscosity of backflow fluid with petroleum and suspended matter pollutants. Therefore, it is of great significance to recycle fracturing fluid from tight sandstone with low-carbon and environmental protection. In this study, the fracturing fluid of tight sandstone in a block of a certain oilfield was collected as the research object, and a comprehensive water quality analysis was carried out. The combined process technology for resource treatment of fracturing flowback fluid in tight sandstone were formed by studying on the influence factors of oxidation gel breaking, flocculation sedimentation, ion removal, filtration and process optimization. After treatment, the mass concentration of iron ion in fracturing flowback fluid was less than 5 mg/L, the mass concentration of suspended matter was less than 10 mg/L, and the mass concentration of oil was less than 5 mg/L, which could meet the water quality requirements of fluid distribution and reuse, and avoid the environmental pollution risk of flowback fluid effectively, while the consumption level of water resources in fracturing construction also was greatly reduced. This paper will have positive significance for the resource treatment technology and development of tight sandstone fracturing fluid.

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process.

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H2O2 concentration, Fe2+ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H2O2 concentration of 80mM, the Fe2+ concentration of 5mM, the ultrasonic power of 180W, the ultrasonic frequency of 20-25kHz, the temperature of 39℃, the reaction time of 30min, and the COD removal rate reached 81.15%, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na<BQ<t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21mg/L, and the COD value decreased to 80.83mg/L after 60min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.

Hydrochemistry, Sources and Management of Fracturing Flowback Fluid in Tight Sandstone Gasfield in Sulige Gasfield (China)

Hydraulic fracturing technologies have been frequently utilized in the oil and gas industry as exploration and development efforts have progressed, resulting in a significant increase in the extraction of natural gas and petroleum from low-permeability reservoirs. However, hydraulic fracturing requires a large amount of freshwater, and the process results in the production of large volumes of flowback water along with natural gas. In this study, three tight sandstone gas wells were fractured in the Sulige gasfield (China), and a total of 103 flowback fluid samples were collected. The hydrochemical characteristics, water quality and sources of hydrochemical components in the flowback fluid were discussed. The results show that the flowback fluid is characterized by high salinity (Total dissolved solids (TDS) up to 38,268mg/L, Cl- up to 24,000mg/L), high concentrations of metal ions (e.g., Fe, Sr2+, Ba2+) and high chemical oxygen demand (COD). The flowback fluid is a complex mixture of fracturing fluid and formation water, and its composition is impacted by water-rock interactions that occur during hydraulic fracturing. The major contaminants include COD, Fe, Ba2+, Cl-, Mn and pH, which constitute a high risk of environmental pollution. Meanwhile, chemical elements such as K, Ba and Sr are unusually enriched in the flowback fluid, which has an excellent potential for recycle of chemical elements. The Sulige gasfield's flowback fluid recovery methods and treatment scenarios were discussed, taking into consideration the pollution and resource characteristics of the flowback fluid. Options for dealing with the flowback fluid include deep well reinjection, reuse for making up fracturing fluid, recycling of chemical elements and diverse reuse of flowback water. This research offers guidance for managing the fracturing flowback fluid in unconventional oil and gas fields.