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A reliable empirical prediction of the height of fracturing (HoF) is significant for mining impact assessment and mine sustainability. However, the prediction accuracy is often limited by the parameter and data coverage involved in empirical models. This paper develops a new predictive model that incorporates mining parameters, as well as the proportion and strength of stiff strata, as predictors for enhanced mining impact assessments. A HoF database has been established by sourcing 80 cases from 50 mines in Australia and China. Statistical interpretation identifies positive correlations of HoF to mining height, panel width, and cover depth. Numerical modelling and sensitivity analysis identify that both the proportion and strength of stiff units negatively correlate to HoF and are more significant than bedding plane frequency. The two critical rock parameters are statistically independent and should be considered for enhanced HoF predictions. A predictive model is established by nonlinear regression over the 80 datasets, with both rock parameters involved by mapping to a dimensionless indicator of strata competency considering dimensional consistency. The model is tested with an R 2 of 0.84 and more accurate predictions than several historical models regarding 24 new cases. Prediction bounds with a confidence level of 95% are developed considering the rock parameter variability, providing conservative HoF predictions for cases where significant natural features should be preserved for sustainable mining practices. This paper assesses the influence of rock parameters that have not been considered in historical models on continuous fracturing and provides an enhanced empirical method for mining impact assessment. Highlights A database is established comprising 80 height of fracturing (HoF) cases collected from 50 mines in Australia and China. Mining height is identified as the most influential parameter of continuous fracturing and is followed by the depth of cover and panel width. Stiff unit proportion and strength are critical rock parameters of HoF, statistically independent and more significant than bedding plane frequency. A new HoF predictive model is developed with mining and critical rock parameters involved and is verified via test datasets and historical models. Prediction bounds are established considering the rock parameter variability, providing conservative predictions for sustainable mining practices.

Assessment of mining impact on groundwater is one of critical considerations for longwall extension and sustainability, however usually constrained by limited data availability, hydrogeological variation, and the complex coupled hydro-mechanical behaviour. This paper aims to determine the factors and mechanism of groundwater depressurisation and identify knowledge gaps and methodological limitations for improving groundwater impact assessment. Analysis of dewatering cases in Australian, Chinese, and US coalfields demonstrates that piezometric drawdown can further lead to surface hydrology degradation, while the hydraulic responses vary with longwall parameters and geological conditions. Statistical interpretation of 422 height of fracturing datasets indicates that the groundwater impact positively correlates to panel geometry and depth of cover, and more pronounced in panel interaction and top coal caving cases. In situ stress, rock competency, clay mineral infillings, fault, valley topography, and surface–subsurface water interaction are geological and hydrogeological factors influencing groundwater hydraulics and long-term recovery. The dewatering mechanism involves permeability enhancement and extensive flow through fracture networks, where interconnected fractures provide steep hydraulic gradients and smooth flow pathways draining the overlying water to goaf of lower heads. Future research should improve fracture network identification and interconnectivity quantification, accompanied by description of fluid flow dynamics in the high fracture frequency and large fracture aperture context. The paper recommends a research framework to address the knowledge gaps with continuous data collection and field-scale numerical modelling as key technical support. The paper consolidates the understanding of longwall mining impacting mine hydrology and provides viewpoints that facilitate an improved assessment of groundwater depressurisation.

To address the issue of low viscosity and poor high-temperature shear resistance of suspension liquid type fracturing fluids commonly used in continuous fracturing operations for high-temperature unconventional oil reservoirs with large displacement mineralized water, A novel titanium crosslinking agent has been prepared, which can significantly enhances the temperature resistance and shear resistance of the gel. In addition, a novel dialysis purification method is proposed, which allows the titanium crosslinker to be pre-mixed with anhydrous suspension, and overcomes the defect of uneven mixing due to high viscosity fluid when add crosslinker, which can’t be solved by boron or zirconium crosslinker. Here, the crosslinking agent was prepared by mixing butyl titanate, lactic acid, triethanolamine and water according to a certain molar ratio. Then, the resulting gel was obtained by pre-mixing with suspension fracturing fluid liquid, and can maintain the viscosity of 63.1mPa·s at a shear rate of 170 s −1 and 150 °C, which is nearly twice that of the gel to bring with added externally crosslinking agents. The fracturing fluid can effectively increase fracturing efficiency, and has excellent application prospects in the context of High temperature deep well and large displacement fracturing.

A numerical analysis model for sand-mudstone interbedded fracturing based on field application in South China is presented in this paper. The proposed model can analyze the influence laws of different longitudinal lithology changes, stress difference changes, different interlayer positions, and fracturing fluid construction parameters on fracture characteristics. Based on the study of fracture characteristics of low-modulus mudstone, a set of layered stress loading experimental devices was independently designed and developed. Experimental analysis shows that the stress difference has a limited limiting effect on the interlayer propagation of hydraulic fracturing fractures in the Weizhou Formation, and the fracture height is prone to interlayer propagation. The injection of high-rate and high-viscosity fracturing fluid has a significant impact on the hydraulic fracture surface penetration. Numerical simulation analysis shows that the smaller the elastic modulus of the mudstone interlayer and the lower the minimum horizontal principal stress compared to the sandstone layer, the more favorable it is for fracture propagation. Field application showed that the highest injection rate of the fracturing pump in well A was 7 m3/min for south-west Weizhou oilfield shale oil. The interpretation results of the acoustic logging after fracturing showed obvious response characteristics of the formation fractures, and the farthest detection fracture response well distance was 12 m, indicating a good fracturing transformation effect and providing technical support for subsequent offshore shale oil fracturing construction.

Hydraulic fracturing has been widely used in low permeability coalbed methane reservoirs to enhance gas production. To better evaluate the hydraulic fracturing curve and its effect on gas productivity, geological and engineering data of 265 development coalbed methane wells and 14 appraisal coalbed methane wells in the Zhengzhuang block were investigated. Based on the regional geologic research and statistical analysis, the microseismic monitoring results, in-situ stress parameters, and gas productivity were synthetically evaluated. The results show that hydraulic fracturing curves can be divided into four types (descending type, stable type, wavy type, and ascending type) according to the fracturing pressure and fracture morphology, and the distributions of different type curves have direct relationship with geological structure. The vertical in-situ stress is greater than the closure stress in the Zhengzhuang block, but there is anomaly in the aggregation areas of the wavy and ascending fracturing curves, which is the main reason for the development of multi-directional propagated fractures. The fracture azimuth is consistent with the regional maximum principle in-situ stress direction (NE–NEE direction). Furthermore, the 265 fracturing curves indicate that the coalbed methane wells owned descending, and stable-type fracturing curves possibly have better fracturing effect considering the propagation pressure gradient (FP) and instantaneous shut-in pressure (PISI). Two fracturing-productivity patterns are summarized according to 61 continuous production wells with different fracturing type and their plane distribution, which indicates that the fracturing effect of different fracturing curve follows the pattern: descending type > stable type > wavy type > ascending type.

In this work, efficient Fenton strategy have been proposed for degradation of shale gas fracturing flow-back wastewater using the spherical Fe/Al 2 O 3 supported catalyst. Prior to actual fracturing fluid treatment, the typical model wastewaters such as p -nitrophenol and polyacrylamide were employed to evaluate the catalytic properties of prepared catalyst, and then Fenton treatment of the shale gas fracturing flow-back wastewater was performed on the self-assembled catalytic degradation reactor for continuous flow purification. Results showed that under the conditions of 0.25 mol L −1 impregnating concentration, pH 4, 50 g L −1 catalyst and 0.75 mL L −1 30% H 2 O 2 , the removal efficiency of p -nitrophenol and polyacrylamide reached 74% and 61%, respectively, while the COD removal of fracturing flow-back fluid was approximately 48% with the residual 88 mg L −1 COD, meeting the emission standards of the integrated wastewater discharge standard (GB 8978-1996, COD < 100 mg L −1 ). This work offers new alternatives for Fenton treatment of real wastewater by efficient and low-cost supported catalysts.

Accurate evaluation of the impact range of hydraulic fracturing (HF) in coal seams is the key to optimizing HF design schemes. In this study, multistage HF processes in Well No. 1 of the Xinji No. 2 coal mine were monitored and analyzed using ground microseismic (MS) monitoring technology. An improved particle swarm optimization algorithm and waveform similarity superposition method were used to locate HF-induced MS events with different signal-to-noise ratios. The results showed that the seismic source location points were distributed horizontally within a 120 m range on both sides of the fracturing well, and vertically distributed from − 615 to − 675 m. The MS events envelope method was used to calculate the stimulated reservoir volume (SRV) of nine fracturing sections, totaling approximately 1,977,000 m3, with the largest SRV in Sections Nos. 2 and 6. Through continuous fracture network (CFN) modeling, the overall fracture extension of the HF was revealed to be rectangular and evenly distributed on both sides of the fracturing well. The main direction of the fracture extended outward along the vertical direction, in line with the direction of the injection hole. By calculating the CFN branch index (BI) and CFN length, the results showed that the fracture networks of Sections Nos. 1, 4, and 6 were more complex, and the CFN lengths of Sections Nos. 1, 2, 6, and 9 were longer. Combining the fracture network size, MS event parameters, and SRV, we determined that Sections Nos. 2 and 6 have longer fracture networks, larger HF ranges, and the best HF effect. This study is important for the evaluation of the effective range of HF in coal seams and for the design and parameter optimization of HF schemes.HighlightsMicroseismic events with different signal-to-noise ratios were accurately located.The stimulated reservoir volume and the number of microseismic events in the fractured area are positively correlated.The fracture extension pattern of hydraulic fracturing was obtained by continuous fracture network modeling.

Mg-6Zn-2X(Fe/Cu/Ni) alloys were prepared through semi-continuous casting, with the aim of identifying a degradable magnesium (Mg) alloy suitable for use in fracturing balls. A comparative analysis was conducted to assess the impacts of adding Cu and Ni, which result in finer grains and the formation of galvanic corrosion sites. Scanner electronic microscopy examination revealed that precipitated phases concentrated at grain boundaries, forming a semi-continuous network structure that facilitated corrosion penetration in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys. Pitting corrosion was observed in Mg-6Zn-2Fe, while galvanic corrosion was identified as the primary mechanism in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys. Among the tests, the Mg-6Zn-2Ni alloy exhibited the highest corrosion rate (approximately 932.9 mm/a) due to its significant potential difference. Mechanical testing showed that Mg-6Zn-2Ni alloy possessed suitable ultimate compressive strength, making it a potential candidate material for degradable fracturing balls, effectively addressing the challenges of balancing strength and degradation rate in fracturing applications.

In this paper, we present a novel adaptive continuous–discontinuous approach for the analysis of phase field fracture. An initial trimmed hexahedral (TH) mesh is created by cutting a hexahedral background grid with the boundary of the solid domain. Octree-based adaptive mesh refinement is performed on the initial TH mesh based on an energy-based criterion to accurately resolve the damage evolution along the phase field crack. Critical damage isosurfaces of the phase field are used to convert fully developed phase field cracks into discontinuous discrete cracks. Mesh coarsening is also performed along the discontinuous discrete cracks to reduce the computational cost. Three-dimensional problems of quasi-brittle fracture are investigated to verify the effectiveness and efficiency of the present adaptive continuous–discontinuous approach for the analysis of phase field fracture.

This paper proposes a hybrid rock discrete fracture analysis (RDFA) method that combines the rock failure process analysis (RFPA) method and discrete element method. Based on the continuum mechanics, statistical damage mechanics, and contact theory, RDFA offers a comprehensive framework to simulate the continuous–discontinuous behaviors encompassing fracture and fragmentation within rocks. Through the newly developed nodal updating scheme, RDFA enables adaptive node adjustments at critical crack tips once the strength criteria is met, effectively capturing the initiation and propagation of zero-thickness cracks. Notably, RDFA accommodates the heterogeneity of rock masses, allowing for the synchronized consideration of localized damage and fine-crack evolution. RDFA was calibrated by modelling the Brazilian splitting tests on rock, aligning closely with the analytical solutions. Subsequently, the rock specimens containing single or double flaws were uniaxially compressed. The results showed that when the flaw inclination angle α increased from 0° to 60°, the distance between the initiation position of cracks and the flaw tip decreased exponentially; the crack initiation stress first decreased and then increased with the growth of α , and when α  = 30°, it reached the minimum value of 15.2 MPa. RDFA can effectively replicate rock fracturing processes, failure modes, and critical strengths across diverse inclinations. Highlights The rock discrete fracture analysis method was proposed by combining the rock failure process analysis method and discrete element method. It enables adaptive node adjustments at the critical crack tips using the newly developed nodal updating scheme. It can effectively capture the initiation and propagation of zero-thickness cracks. It accommodates the heterogeneity of rock masses, allowing for the synchronized consideration of localized damage and fine-crack evolution.