Shale Gas Hydraulic Fracturing Research Articles

Geochemical characteristics of shale gas hydraulic fracturing flowback/produced water in Zheng’an block, northern Guizhou Province, China

Guizhou Province of China is rich in shale gas resources. In recent years, important progress has been made in the exploration and development of shale gas in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Zheng'an block in northern Guizhou, adjacent to Sichuan Basin. Due to the complex geological conditions and fragile ecological environment in the shale gas distribution area, serious environmental pollution risks may exist in shale gas exploitation. Therefore, this paper conducted element, hydrogen and oxygen isotope analyses for shale gas fracturing flowback/produced water of Well AY7-4 in Zheng'an block. The results showed that the contents of K, Na, Ca, Mg and NH4+ in the flowback/produced water of Well AY7-4 were very high, with an average of 118 mg/L, 7616 mg/L, 266 mg/L, 47 mg/L and 76 mg/L, respectively. The content of Na, Ca and Mg is similar to that of shale gas flowback/produced water in Weiyuan, but lower than that in Changning and Fuling. NH4+ content was similar to that in Changning, but much higher than that in Weiyuan. The average Cl content was 11605 mg/L, which was similar to that in Weiyuan, but lower than that in Changning and Fuling. The average Br content is 48 mg/L, slightly lower than that of Weiyuan, and about half of that of Changning and Fuling. Correspondingly, the Br/Cl value of Well AY7-4 is the lowest, reflecting its relatively low Br content. The average content of Li, B and Sr is 17 mg/L, 10 mg/L and 45 mg/L, respectively, which is similar to that of the Weiyuan, Changning and Fuling shale gas fields. The distribution model of Li and Sr is similar to that of Cl, Br and Na, but the B content and B/Cl value of Well AY7-4 are the lowest. The linear relationship between Br and Cl contents and between δD and δ18O of flowback/produced water of Well AY7-4, freshwater used for hydraulic fracturing and hydraulic fracturing injected fluid indicates that flowback/produced water of Well AY7-4 is mainly the mixed product between low salinity injected fracturing fluid and high salinity brine retained in shale formation. The hydrogen and oxygen isotopic compositions gradually become heavier over time, indicating that the proportion of high salt end formation brine in flowback/produced water is increasing. The contents of Cl, Br, Na and NH4+ in the flowback/produced water of Well AY7-4 are far higher than the allowable discharge value, which is a potential environmental pollution risk and cannot be discharged directly.

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.

Environmentally relevant concentrations of chemically complex shale gas wastewater led to reduced fitness of water fleas (Daphnia carinata): Multiple lines of evidence approach

Shale gas hydraulic fracturing generates flowback waters that pose a threat to aquatic organisms if released into the environment. In order to prevent adverse effects on aquatic ecosystems, multiple lines of evidence are needed to guide better decisions and management actions. This study employed a multi-disciplinary approach, combining direct toxicity assessment (DTA) on the water flea Daphnia carinata and LC-MS metabolomics analysis to determine the impact of a major ion salinity control (SC) and a cumulative flowback shale gas wastewater (SGW) from a well in the Beetaloo Sub-basin, Northern Territory, Australia. The exposures included a culture water control, simply further referred to as ‘control’, SC at 1% and 2% (v/v) and SGW at 0.125, 0.25, 0.5, 1% and 2% (v/v). The results showed that reproduction was significantly increased at SGW 0.5%, and significantly decreased when exposed to SC 2%. SGW 2% was found to be acutely toxic for the D. carinata (< 48-h). Second generation (F1) of D. carinata exposed to 0.125–1% SGW generally saw reduced activity in four oxidative biomarkers: glutathione S-transferase, lipid peroxidation, reactive oxygen species, and superoxide dismutase. At the metabolomics level, we observed significant changes in 103 metabolites in Daphnia exposed to both SGW and elevated salinity, in comparison to the control group. These changes indicate a range of metabolic disturbances induced by SGW and salinity, such as lipid metabolism, amino acid metabolism, nucleotide synthesis, energy production, and the biosynthesis of crucial molecules like hormones and pigments. These multiple lines of evidence approach not only highlights the complexities of SGW's impact on aquatic ecosystems but also underscores the importance of informed decision-making and management practices to safeguard the environment and its inhabitants.

Environmental Implications of Shale Gas Hydraulic Fracturing: A Comprehensive Review on Water Contamination and Seismic Activity in the United States

Recent scholarship has highlighted the significant environmental impact of the rapidly expanding hydraulic fracturing industry, which is projected to grow from USD 15.31 billion in 2021 to USD 28.93 billion in 2028 at a Compound Annual Growth Rate (CAGR) of 9.5%. Recognizing the need for comprehensive, national-scale evaluations, this review of the literature investigates contamination and induced seismicity associated with shale gas hydraulic fracturing in the United States. Employing systematic reviews of the literature and federal reports up until July 2023, this study reveals multiple areas of concern, including water and soil contamination, seismic activity, and air pollution. A notable finding is the average use of 2.4 million gallons of water per well in hydraulic fracturing, of which only 15–35% is typically retrieved. However, ongoing studies are actively exploring remediation strategies, including advancements in monitoring and treatment technologies, as well as the potential of reusing wastewater for hydraulic fracturing, as exemplified by the Garfield County region in Colorado; they utilized 100% wastewater to mitigate the impact of contamination. These findings underscore the need for stringent regulations, sustained research, and effective management practices. This work emphasizes the importance of a collaborative approach that leverages field studies, experimental investigations, and computational advancements to ensure the responsible development of shale gas resources.

Study on Fault Activation Evaluation Mechanism and Sensitivity Analysis in Shale Gas Hydraulic Fracturing

Shale gas hydraulic fracturing usually activates nearby faults and makes them slip. In horizontal wells, fault slip can result in serious casing deformation. Casing deformation slows the fracturing process, lowers production, and raises the cost of a shale gas well. It is challenging to obtain underground data on fault activation because of the deep shale reservoirs. As a result, the current study needed to indicate how hydraulic fracturing affects fault activation length. This made it challenging to control casing deformation. The fluid-structure coupled finite element method was used in this study to create a coupled seepage-stress model for heterogeneous shale formation. With microseismic signs and hydraulic fracking for shale gas, this model examined the variation law of pore pressure and ground stress. The fault activation coefficient was created to assess the fault activation duration and the impact of hydraulic fracturing. The model was verified by the microseismic signal. The outcomes of the numerical simulation demonstrate how the rapid rise in formation pore pressure during hydraulic fracturing affected the ground stress at the fault interface. The influence of ground stress variation at the fault interface on fault activation could not be ignored. Increased fault elastic modulus, fracture pressure, fracture time, and the fault Poisson ratio result in longer fault activation lengths. The length of the fault’s activation was decreased by the increase in fracture stage, distance from the fault, friction angle within the fault, and fault angle. Finally, a shale gas horizontal well with casing deformation in block C was analyzed. The results showed that reducing the fracturing duration can reduce the activation length of the fault by 68.25%, resulting in a 9.1 mm fault slide and a 0.86 mm casing deformation, respectively. This study offers theoretical guidelines for preventing fault activation during hydraulic fracturing in horizontal shale gas wells.

Experimental evaluation of the flow resistance of CO2 foam fracturing fluids and simulation prediction for fracture propagation

Shale gas fracturing requires huge amounts of water, but most well pads are located mainly in hilly areas where water is scarce. Water supply issues have limited the industrialization of shale gas development. CO2 foam fracturing fluids can meet the requirements for large-scale hydraulic fracturing of shale gas and relieve pressure on water resources. Friction calculations of CO2 foam fracturing fluids in conduit flow are key to the reliability of overall fracturing procedures, affecting fracture targeting and reservoir stimulation effects. Through the analysis of the experimental data of carbon dioxide foam fracturing fluid flow under the simulated reservoir conditions, the influence of pressure, temperature, shear rate, foam quality and other factors on the friction characteristics of CO2 foam fracturing fluid was obtained, and the mathematical calculation model of the friction coefficient of CO2 foam fracturing fluid was established, and the pipe string friction and bottom hole pressure during the fracturing process were obtained, Thus, the shape and extension behavior of hydraulic fractures in the process of carbon dioxide foam fracturing in shale reservoir are simulated and predicted, which provides a theoretical basis for effective evaluation of fracturing effect.

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.

Water footprint of shale gas development in China in the carbon neutral era

The production of shale gas in China has repercussions for the global energy landscape and carbon neutrality. However, limited and threatened water resources may hinder the expansion of shale-derived natural gas, one of China's most promising development prospects. Coupling historical trends with policy guidance, we project that baseline water stress will intensify in two-thirds of China's provinces in the next decade. By 2035, annual water use for shale gas hydraulic fracturing activities is likely to increase to 16–35 million m3, with 13.8–23.7 million m3 of wastewater produced annually to extract 38–48 billion m3 of gas from ∼4800 shale gas wells. Analysis suggests that this projection is based on previously underestimated geological constraints (e.g., deep continental facies) in shale gas development in China. Nevertheless, forecasts suggest that the water footprint of shale development will become impossible to ignore, particularly in drought-stricken areas, indicating the potential risk of competition for water among shale development, domestic use, food production, and ecological protection. Meanwhile, the annual wastewater management market will increase to $0.2 billion by 2035. Our study suggests a critical need to direct attention to the (shale) energy-water nexus and develop multi-pronged policies to facilitate China's transition to carbon neutrality.

How can casing deformation be prevented during hydraulic fracturing of shale gas?—A case study of the Weiyuan area in Sichuan, China

In the process of hydraulic fracturing of shale gas horizontal wells in the Weiyuan area of Sichuan, China, casing deformation (CD) is a frequent problem that has seriously affected the benefits of shale gas development and remains to be solved for many years. In this paper, based on the analyses of Multi-finger Imaging Tool-24 (MIT-24) data, microseismic data, and the relationship between CD and engineering parameters, we confirm that the wellbore morphology in all CD sections in the Weiyuan area is consistent with shear deformation characteristics and clarify the cause of all CD: hydraulic fracturing leads to increased fluid pressure in well-intersecting faults and large fractures (F-Fs), inducing their shear slip, and eventually leads to asymmetric compression on the casing by strata on both sides of F-Fs, i.e., CD. On this basis, we propose a set of methods to control (or moderate) the shear slip of F-Fs by reducing the additional fluid pressure in target F-Fs during hydraulic fracturing to prevent CD, including multi-cluster perforations, temporary plugging F-Fs and fracturing fluid flowback. We also analyze the theoretical basis, feasibility and workflow of these methods. These methods have been tested in 44 horizontal wells in the Weiyuan area, of which the result is a radical decrease in the CD rate of the single well (from 54% to 9.1%), indicating that the slip of F-Fs and the resulting CD during hydraulic fracturing can be controlled and providing a reference for the prevention of hydraulic fracturing-induced earthquakes.

Optimization of the Water-Energy Nexus in Hydraulic Fracturing Processes Using CO2 and Water as Fracturing Fluids

Hydraulic fracturing has paved the way for the extraction of substantial quantities of shale gas. Traditionally, water (in significant quantities) has been used as the primary fracturing fluid. In addition to the significant water usage in fracturing, large quantities of shale gas wastewater have been generated. Driven by the need for better management of water resources in hydraulic fracturing, the introduction of CO2 (captured from industrial emissions) has been considered an element in the fracturing fluid. This paper proposes a mathematical programming formulation to synthesize the best configuration for the use of water and CO2 associated with shale gas hydraulic fracturing operations while taking into account the fluctuations in water availability, generation of CO2, and the flowback water based on a time horizon. The proposed formulation incorporates a strategic planning that minimizes the total annual cost (TAC) considering water requirements, generation and capture of CO2, as well as the capacity of the equipment for treatment technologies, transportation fees, storage units, and disposal. A case study is presented to demonstrate the usefulness of the proposed methodology. The results show that at a higher percentage of CO2 in the fracturing fluid, the TAC increases but the freshwater required decreases. Furthermore, the trade-offs and impact of freshwater availability have been identified.

Study of the coagulation-flocculation treatment of flowback water from shale gas hydraulic fracturing by using combination of dithiocarbamate compound-polyacrylamide

In this paper, a dithiocarbamate-type flocculant DTC-TETA was prepared by using triethylenetetramine as the material and combination of DTC-TETA and polyacrylamide was used for the coagulation-flocculation of flowback water from shale gas hydraulic fracturing (FWSG). The coagulation-flocculation process was optimized by using turbidity as index and the recommended process was as follows: DTC-TETA dosage 200 mg/L, anionic polyacrylamide AN905 dosage 1 mg/L, flocculation stirring speed 200 rpm, flocculation stirring time 3 min and settlement time 5 min. The turbidity of FWSG can be reduced to be 13 NTU from the initial turbidity of more than 2000 NTU under the recommended process. The performance of DTC-TETA was much better than that of polyaluminum chloride and the Fe2+ in FWSG also can be removed. The function mechanism of DTC-TETA was investigated through the studies of zeta potential change of suspended solids and structural characteristics of flocs. The results confirmed that the flocs were developed by the network formed by the coordination reaction between DTC-TETA and Fe2+, which can filter out suspended solids. This study signifies that both suspended solids and Fe2+ ion can be removed by using DTC-TETA as flocculant, which is a new choice for the FWSG treatment.

Isotopic geochemical characteristics and identification indexes of shale gas hydraulic fracturing flowback/produced water

China is rich in shale gas resources, which are mainly distributed in densely populated southern marine carbonate areas. The geological and surface conditions are complex, the ecological environment is fragile, and water resources are scarce or unevenly distributed. Therefore, large-scale fracturing mining has high pressure of water resources utilization and serious risk of water environment pollution. In this paper, the geochemical characteristics of traditional and non-traditional stable isotopes such as hydrogen, oxygen, boron, lithium, strontium in shale gas hydraulic fracturing flowback/produced water (FP water) were comprehensively analyzed. The results show that, the hydrogen and oxygen isotopic composition of the FP water in Sichuan Basin, China has similar evolution trend with the produced water of conventional wells from Cambrian, Permian and Triassic Xujiahe, Jialingjiang and Leikoupo formations, but different from that of the Sinian conventional produced water. It indicates that the FP water in Sichuan Basin is a mixture of fracturing injected fluid and formation brine retained in Silurian shale. The saline end member is close to the formation water of Cambrian, but with higher δ11B values. The FP water in Sichuan Basin has δ11B values close to that of the Marcellus FP water, and both are derived from the evaporated seawater. The δ11B values of FP water in Sichuan Basin have overlap with that of the conventional produced water from different strata, so it can not be precisely distinguished. However, the δ11B and B/Cl values of the FP water in Sichuan Basin can be clearly distinguished from the river and the FP water from non-marine facies shale in Qaidam Basin. The FP water in Sichuan Basin has slightly higher δ7Li values than that of the Marcellus FP water, but has overlap with that of the Yangtze River. The average value of 87Sr/86Sr of FP water is 0.7197 in Weiyuan and 0.7193 in Changning, which is much higher than that of the produced water from conventional wells in different formations. This is because the Silurian shale is affected by terrestrial siliceous sediments and the underlying Sr-rich fluids. As a result, 87Sr/86Sr values measured in the Silurian strata in southern Sichuan Basin are high, which makes 87Sr/86Sr values become an effective index to distinguish shale gas fracturing FP water from conventional gas well produced water and shallow groundwater in Sichuan Basin.

Hydraulic fracturing flowback chemical composition diversity as a factor determining possibilities of its management

The chemical characteristic of flowback fluid from hydraulic fracturing for shale gas exploration/production in various localizations is presented. The results of statistical analysis have shown that variability in the chemical composition of these fluids is statistically significant and depends on the time difference between fracturing process and flowback sampling as well as sampling spot within the installation for flowback collection. Parameters which depend on sampling schedule (time and spot of sampling) are as follows: electrical conductivity and concentration of ammonia, boron, barium, calcium, lithium, sodium, magnesium, manganese, sodium, strontium, silicate, bromide, and chloride. Independent parameters are pH, total organic carbon (TOC), concentration of potassium, and iron. The ranges of the values of the characteristic parameters were determined, taking into account the representativeness of the samples, supported by statistical tests. The methods for the reuse of flowback fluids in terms of chemical composition are presented.

Integration of coagulation and ozonation with flat-sheet ceramic membrane filtration for shale gas hydraulic fracturing wastewater treatment: A laboratory study.

The performance of the integrated process of coagulation and ozonation with ceramic membrane filtration was evaluated for the treatment of shale gas hydraulic fracturing flowback wastewater (HFFW). The removal efficiencies of carbon oxygen demand (CODCr ), dissolved organic carbon (DOC), petroleum oils, and turbidity in effluent by the combined process were 87.1%, 72.2%, 94.3%, and 99.6%, respectively. Compared with sole membrane filtration, the transmembrane pressure (TMP) of ceramic membrane filtration was reduced by >99% with the integrated process. The coagulation and ozonation can effectively remove the organics with high molecular weights in the cake layer of ceramic membrane. To the best of our knowledge, this work proposed the combined process of coagulation, ozonation, and flat-sheet ceramic membrane filtration for the treatment of HFFW for the first time. The water quality of the effluent met the discharge standard (Comprehensive Wastewater Discharge Standard GB8978-1996). The findings can provide an important technical foundation for the innovation of integrated equipment for HFFW treatment. PRACTITIONER POINTS: An integrated process combining coagulation and ozonation with flat-sheet ceramic membrane ultrafiltration for the treatment of shale gas wastewater. The water quality of this integrated process met the discharge standard. Coagulation and ozonation effectively alleviated the membrane fouling related to organics with high molecular weights. A new avenue for on-site treatment of shale gas wastewater and an alternative of the current centralized wastewater management.

Invited Perspective: Oil and Gas Development and Adverse Birth Outcomes: What More Do We Need to Know?

Invited Perspective: Oil and Gas Development and Adverse Birth Outcomes: What More Do We Need to Know?

Evaluation of anionic and non-ionic surfactant performance for Montney shale gas hydraulic fracturing fluids

Hydraulic fracturing is often used in unconventional shale reservoirs, and 50%–95% of the injected hydraulic fracturing fluid remains in the formation due to the capillary effect. This phenomenon has been observed in the Montney shale formation, Canada, where the flowback water recovery is generally less than 25%. Surfactant is one of the hydraulic fracturing fluid additives for reducing surface tension and capillary forces to facilitate water flowback recovery. Surfactant loss due to adsorption by the reservoir rocks reduces the chemical’s efficiency, and this causes water retention in the formation and reduces water flowback recovery. The compatibility of surfactant with reservoir rock is critical to minimize surfactant adsorption on the rock surface because this diminishes the primary function of the surfactant hydraulic fracturing fluid additive and to ensure cost-effectiveness. This study evaluates surfactant efficiency to improve flowback recovery for the Montney shale formation based on IFT, surface tension, and adsorption. This study evaluates surfactant performance and performs a fluid–fluid interaction experiment and fluid-rock compatibility investigation. Several commercial surfactants are screened for low interfacial tension and surface tension. Further analysis is carried out by evaluating the fluid-rock compatibility using the static soaking test at reservoir pressure and temperature. The pre-soaking and post-soaking test fluids were analyzed for water composition, liquid–liquid interfacial tension, surface tension, and pH. Results showed that the selected surfactant is a critical determiner of the hydraulic fracturing fluid performance. SOLOTERRA 938 is an anionic surfactant that has good compatibility with Montney shale formation. Unlike other non-ionic surfactants, SOLOTERRA 938 retains the interfacial tension and surface tension after seven days of interaction with reservoir rock. The interfacial tension remained unchanged at 0.1 mN/m. The surface tension decreased from 28.4 to 27.5 mN/m with air and from 21.7 to 20.8 mN/m with hydrocarbon because surfactant behavior changes with pH change. The surfactant concentration was measured using high-pressure liquid chromatography, and the loss was 12% after seven days of interaction with the reservoir rock (from 0.1 to 0.088wt%). The adsorption calculated based on the concentration volume showed a low value of between 0.43 and 0.97 mg/g rock.

Enhanced treatment of shale gas fracturing waste fluid through plant-microbial synergism.

Cost-efficient and environmentally friendly treatment of hydraulic fracturing effluents is of great significance for the sustainable development of shale gas exploration. We investigated the synergistic effects of plant-microbial treatment of shale gas fracturing waste fluid. The results showed that illumination wavelength and temperature are direct drivers for microbial treatment effects of CODCr and BOD5, while exhibit little effects on nitrogen compounds, TDS, EC, and SS removals as well as microbial species and composition. Plant-microbial synergism could significantly enhance the removal of pollutants compared with removal efficiency without plant enhancement. Additionally, the relative abundance and structure of microorganisms in the hydraulic fracturing effluents greatly varied with the illumination wavelength and temperature under plant-microbial synergism. 201.24 g water dropwort and 435 mg/L activated sludge with illumination of 450-495 nm (blue) at 25 °C was proved as the best treatment condition for shale gas fracturing waste fluid samples, which showed the highest removal efficiency of pollutants and the lowest algal toxicity in treated hydraulic fracturing effluents. The microbial community composition (36.73%Flavobacteriia, 25.01% Gammaproteobacteria, 18.55%Bacteroidia, 9.3% Alphaproteobacteria, 4.1% Cytophagia, and 2.83% Clostridia) was also significantly different from other treatments. The results provide a potential technical solution for improved treatment of shale gas hydraulic fracturing effluents.

Source Parameters of Three Moderate Size Earthquakes in Weiyuan, China, and Their Relations to Shale Gas Hydraulic Fracturing

AbstractOn 7 September 2019, an ML5.4 earthquake struck the Weiyuan area in southwestern China. This is the largest and most damaging event in the Weiyuan shale gas field. In the next 4 months, two earthquakes with ML4.3 and ML5.2 rattled the same area. In this study, we obtain source parameters of these earthquakes (e.g., centroid location, focal mechanism, and rupture directivity) to investigate whether they are induced by hydraulic fracturing of shale gas production. We first invert for high‐resolution centroid locations and focal mechanisms of two M ~ 3 earthquakes recorded by a temporary dense seismic array. We then adopt the M ~ 3 events as references to obtain reliable centroid locations and rupture directivity of those moderate‐size earthquakes. The results show that all earthquakes have centroid depths of no more than 3 km and are within 2 km to injection wells of shale gas production, which suggest that these earthquakes may be induced by local hydraulic fracturing. The ML5.2 earthquake has the same rupture directivity to NE as the ML5.4 event and is located in the zone of positive Coulomb stress change caused by the latter. However, the long time lapse of the ML5.2 earthquake and the existence of an injection well within 2 km suggest that it is more likely induced by hydraulic fracturing than triggered statically by the ML5.4 earthquake.

Public opposition to shale gas extraction in Algeria: Potential application of France's ‘Duty of Care Act’

Algeria, a former French Colony, gained independence from France in 1962. It can be argued, however, that the legacy of post-colonialism continues, particularly with respect to the extractive industries. Both France and Algeria have large unconventional shale deposits—France has the second largest shale gas deposits in Europe after Poland and Algeria has the third largest in the world. Proposals to extract shale gas have led to widespread public opposition in both France and Algeria. The protests in France arguably led to the 2011 ban on hydraulic fracturing for shale gas, followed by the 2017 decision to ban all hydrocarbon exploration and extraction (unconventional and conventional) in French territory by 2040. Hydrocarbon company Total S.A., headquartered in France, has given up on operating in France but has now focused on potential development in Algeria, arguably an illustration of the continuation of a post-colonial relationship or NIMBY'ism (Not In My Back Yard). This perspective article aims to briefly highlight issues related to unconventional hydrocarbons in Algeria and introduce an emerging regulatory mechanism that could potentially provide a remedy to protect human and environmental rights and provide a model for future legislation in other countries. France's 2017 Duty of Care Act (Devoir de Vigilance) requires companies headquartered in France of a certain size to develop a ‘plan of care’ that mandates corporate responsibility throughout the supply chain and all subsidiaries, including outside French territory, and moreover provides a mechanism for legal recourse in the event of environmental or human rights harm from business activities.

Growing seismicity in the Sichuan Basin and its association with industrial activities.

In the Sichuan Basin, seismic activity has been low historically, but in the past few decades, a series of moderate to strong earthquakes have occurred. Especially since 2015, earthquake activity has seen an unprecedented continuous growth trend, and the magnitude of events is increasing. Following the M5.7 Xingwen earthquake on 18 Dec. 2018, which was suggested to be induced by shale gas hydraulic fracturing, a swarm of earthquakes with a maximum magnitude up to M6.0 struck Changning and the surrounding counties. Questions arose about the possible involvement of industrial actions in these destructive events. In fact, underground fluid injection in salt mine fields has been occurring in the Sichuan Basin for more than 70 years. Disposal of wastewater in natural gas fields has also continued for about 40 years. Since 2008, injection for shale gas development in the southern Sichuan Basin has increased rapidly. The possible link between the increasing seismicity and increasing injection activity is an important issue. Although surrounded by seismically active zones to the southwest and northwest, the Sichuan Basin is a rather stable region with a wide range of geological settings. First, we present a brief review of earthquakes of magnitude 5 or higher since 1600 to obtain the long-term event rate and explore the possible link between the rapidly increasing trend of seismic activity and industrial injection activities in recent decades. Second, based on a review of previous research results, combined with the latest data, we describe a comprehensive analysis of the characteristics and occurrence conditions of natural and injection-induced major seismic clusters in the Sichuan Basin since 1700. Finally, we list some conclusions and insights, which provide a better understanding of why damaging events occur so that they can either be avoided or mitigated, point out scientific questions that need urgent research, and propose a general framework based on geomechanics for assessment and management of earthquake-related risks.Electronic Supplementary MaterialSupplementary material is available for this article at 10.1007/s11430-020-9646-x and is accessible for authorized users.