The exploitation pattern of the invertebrate resource (Oratosquilla oratoria) was investigated in the coastal waters of the Shandong Peninsula, along with the seasonal variation in body length ...structure, spatial distribution in abundance, and interannual stock status. Results showed that the model with only catch data suggested both stocks in the north and south were suffering from extreme fishing pressure without explicit recovery (North: B2019/BMSY = 0.468 and F2019/FMSY = 1.88 in CMSY. South: B2019/BMSY = 0.349 and F2019/FMSY = 2.59 in CMSY). However, the other two assessment models indicated that the northern stock began to gradually recover as the fishing pressure dropped to an appropriate level after the original overfished status (North: B2019/BMSY = 0.738 and F2019/FMSY = 0.882 in AMSY, B2019/BMSY = 0.831 and F2019/FMSY = 0.774 in BSM. South: B2019/BMSY = 0.164 and F2019/FMSY = 1.44 in AMSY, B2019/BMSY = 0.384 and F2019/FMSY = 1.76 in BSM). Overall, the stock status in the north was better than that in the south. This study suggested that spatial exploitation pattern and quarterly differences should be considered in fishery management process.
•Difference in body length structure results in the seasonal variation of LBB results.•Oratosquilla oratoria stock status in the Bohai Sea was better than that in the Yellow Sea.•Oratosquilla oratoria stock was generally over-exploited in the coastal waters of the Shandong Peninsula.
•Fault reactivation under CO2 injection was simulated using a two-way coupled model.•Strain-dependent permeability was applied to represent the fault hydrological behaviour.•A close history match of ...bottomhole pressure was achieved over the period modelled.•Fault reactivation results in Coulomb stress changes in near-fault areas.•The variation of computed Coulomb stress changes matches the heightened field recorded seismicity.
Stress transfer caused by injection-induced fault reactivation plays a significant role in triggering induced seismicity. This work aims to investigate to which extent the shear slip stress transfer mechanism might have contributed to a 4-month period of heightened microseismicity around one of the horizontal injection wells (KB-502) at the In Salah CO2 storage site. Building upon previous reservoir modelling and history matching work by the authors, coupled geomechanical and reservoir modelling of CO2 injection at KB-502 was carried out, featuring the explicit simulation of injection-induced fault reactivation and stress transfer, and the implementation of a strain-dependent permeability model to represent the fault hydrological behaviour. This approach allows a much-improved overall match to the field bottomhole pressures at KB-502 over the previous results, where fault zone reactivation and associated dynamic permeability behaviour were not considered, especially over the 4-month period of interest. Based upon the coupled modelling results, Coulomb stress changes were used to evaluate the potential for enhanced microseismicity related to CO2 injection-induced fault reactivation at KB-502. Analyses on the potential for microseismicity have shown that seismic events are likely to take place in both hydraulically connected regions and stress transfer influenced regions. The variation of computed Coulomb stress changes in near-fault areas compares favourably with the heightened field recorded seismicity during the period modelled. The integrated interpretation of microseismic monitoring and coupled geomechanics and reservoir modelling have suggested that the shear slip stress transfer mechanism was active and contributed to the occurrence of induced seismicity at In Salah.
The complex boundary of the elliptical inclusion rendered it difficult to solve the problem of wave scattering. In this study, the steady‐state response was analyzed using the wave function expansion ...method. Subsequently, the Ricker wavelet was employed as the transient disturbance, and Fourier transform was used to determine the distribution of transient dynamic stress concentration around the elliptical inclusion. The effects of wave number, elliptical axial ratio, and difference in material properties on the distribution of the dynamic stress concentration around the elliptical inclusion were evaluated. The numerical results revealed that the dynamic stress concentration always appeared at both ends of the major axis and minor axis of the elliptical inclusion, and the difference in material properties between the inclusion and medium influenced the variations in the dynamic stress concentration factor with the wave number and elliptical axial ratio.
Summary
In actual geotechnical and civil engineering, dynamic stress concentrations around cavities generated by wave sources widely exist. In this study, based on the complex variable theory and ...Fourier transform method, the expression of the dynamic stress concentration factor (DSCF) around a circular cavity in infinite homogeneous media subjected to transient waves with arbitrary waveform is obtained. The relationships between both steady‐state and transient DSCF and their waveform parameters are investigated quantitatively. The results indicate that a relatively large tensile stress is generated with low Poisson's ratio under steady‐state incidence. Under the condition of transient incidence, the position of the wave peak has a minor effect on the DSCF in the case of small wavenumber, but it has a significant effect in the opposite case. It is found that when the wavenumber is high, such as 0.5, the stress response lags behind the stress wave. In addition, the closer the wave peak to the center of the waveform, the greater the potential damage of the transient incidence.
In this research, the damage process and dynamic failure behavior of some sandstone rocks, containing an elliptical hole, were evaluated. For this reason, a series of laboratory tests under both ...static and dynamic loads in 4 different orientations of the elliptical hole was performed. Modified Split Hopkinson Pressure Bar testing machine was employed to apply impact load. Dynamic fracture evolution was recorded by utilizing a high-speed camera to evaluate the macro damage evolution process. Scanning electron microscope analysis and thin section studies were also used to assess mineral's behavior regarding micro-crack evolution. Furthermore, the experimental tests were numerically simulated, and strain energy density and dynamic stress concentration factor were measured to evaluate the effect of elliptical hole inclination on dynamic response. The results indicated that when the largest diameter is perpendicular to core axis, the rock shows the lowest strength in both static and dynamic loading conditions. Also, with increasing hole inclination, both strain energy density and dynamic stress concentration factor decreased. Evaluation of fracture surface indicated that grain-boundary cracks are the dominant type of cracks and iron oxide cement distribution has a vital role in the development of the cracks.
A probabilistic risk assessment framework was developed to mathematically represent the complex engineering phenomena of rock bursts and gas outbursts for a heterogeneous coal seam. An innovative ...object-based non-conditional simulation approach was used to distribute lithological heterogeneity present in the coal seam to respect their geological origin. The changing mining conditions during longwall top coal caving mining (LTCC) were extracted from a coupled numerical model to provide statistically sufficient data for probabilistic analysis. The complex interdependencies among abutment stress, pore pressure, the volume of total gas emission and incremental energy release rate, their stochastic variations and uncertainty were realistically implemented in the GoldSim software, and 100,000 equally likely scenarios were simulated using the Monte Carlo method to determine the probability of rock bursts and gas outbursts. The results obtained from the analysis incorporate the variability in mechanical, elastic and reservoir properties of coal due to lithological heterogeneity and result in the probability of the occurrence of rock bursts, coal and gas outbursts, and safe mining conditions. The framework realistically represents the complex mining environment, is resilient and results are reliable. The framework is generic and can be suitably modified to be used in different underground mining scenarios, overcoming the limitations of earlier empirical indices used.
Highlights
Parameters causing rockbursts and gas outbursts were linked along with their influences and interdependencies into a probabilistic risk assessment framework.
Dynamically updated system feedback from the numerical model was fed into the framework to represent the current stress state in retreating mining and estimate the probability of the occurrence of rockbursts and gas outbursts.
Statistically significant data were used to quantify the probability of rockbursts and gas outbursts using Monte Carlo simulation.
Mining-induced microseismicity is widely considered as a result of slippage of pre-existing critically stressed fractures caused by stress perturbations around an advancing face. An in-depth analysis ...of the recorded microseismicity associated with longwall top coal caving mining at Coal Mine Velenje in Slovenia has been previously carried out and reported by the authors. It has been concluded that while microseismic event rate is affected by mining intensity (longwall face daily advance rate) as well as local abundance of pre-existing fractures, spatial and magnitude characteristics of microseismicity are predominantly influenced by the latter. Based upon this improved understanding of fracture-slip seismic-generation mechanism, the current work aimed at establishing a data-driven yet physics-based probabilistic forecasting methodology for hazardous microseismicity using microseismic monitoring data with concurrent face advance records. Through performing statistical analyses and probability distribution fitting for temporal, magnitude and spatial characteristics of microseismicity within a time window, a short-term forecasting model is developed to estimate the probability of potentially hazardous microseismicity over the next time interval in the form of a joint probability. The real time forecasting of hazardous microseismicity during longwall coal mining is realised through regularly updating the statistical model using the most recent microseismic sequence datasets and face advance records. This forecasting methodology is featured by the physical basis which provides a good explicability of forecasting results, and the probabilistic perspective which accounts for the stochastic nature of mining-induced microseismicity. This model has been employed to make time-varying forecasts of hazardous microseismicity around two longwall panels over a one-year coal production period at Coal Mine Velenje, and satisfactory results at both panels were achieved. In addition, the analysis suggested that the energy magnitude distribution of microseismicity is a dominant factor in contributing to the potential of hazardous microseismicity. This statistical model using microseismic monitoring data has important implications in the evaluation of mining-induced hazards and optimal control of longwall face advance in burst-prone deep-level mining sites.
•A probabilistic model was proposed for evaluation of seismic hazard potential.•Time-varying forecasting of hazardous microseismicity was verified.•Local fracture attributes are reflected in recorded microseismicity.•Segmental stationary of seismicity shows spatial continuity of fracture attributes.
Abstract
Post‐injection seismicity associated with hydraulic stimulation has posed great challenges to hydraulic fracturing operations. This work aims to identify the causal mechanism of the post ...shut‐in
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2.9 earthquake in August 2019 at the Preston New Road, UK, amongst three plausible mechanisms, that is, the post shut‐in pore pressure diffusion, poroelastic stressing on a non‐overpressurized fault, and poroelastic stressing on an overpressurized fault. A 3D fully coupled poroelastic model that considers the poroelastic solid deformation, fluid flow in both porous rocks and fracture structures, and hydrofracturing‐induced pressure perturbations was developed to simulate the hydromechanical response of the shale reservoir formation to hydraulic fracturing operations at the site. Based on the model results, Coulomb stress changes and seismicity rate were further evaluated on the PNR‐2 fault responsible for the earthquake. Model results have shown that increased pore pressure plays a dominant role in triggering the fault slippage, although the poroelastic stress may have acted to promote the slippage. Amongst the three plausible mechanisms, the post shut‐in pore pressure diffusion is the most favored in terms of Coulomb stress change, seismicity rate, timing of fault slippage and rupture area. The coupled modeling results suggested that the occurrence of the post shut‐in
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2.9 earthquake was a three‐staged process, involving first propagation of fracture tips that stimulated surrounding reservoir formations, then hydraulic connection with and subsequent pore pressure diffusion to the conductive PNR‐2 fault, and eventually fault activation primarily under the direct impact of increased pore pressure.
Plain Language Summary
Hydraulic fracturing operations at the Preston New Road, UK caused a sequence of induced seismicity, with the largest magnitude 2.9 earthquake occurring after the fracturing operations stopped. The source of this earthquake was identified as a fault structure well oriented to rupture. However, it is unclear whether the fault slippage was primarily caused by direct fluid pressure increase on the fault, stress perturbations generated by injected fluids, or the combined effects of the two. We used computer modeling to simulate the hydrofracturing‐induced pressure perturbations, fluid pressure diffusion and associated stress changes during and after hydraulic fracturing operations at the site. Based on simulated stress and pressure fields, we evaluated the potential for fault slippage and relative seismicity counts on the fault identified. Model results have shown that the occurrence of the earthquake is predominantly attributed to increased fluid pressure on the fault after fluid injection, although stress perturbations generated by injected fluids may have contributed to fault rupture. Our findings suggest that the fracturing operations drove hydraulic fractures to impinge on the fault, which was conductive and allowed gentle fluid pressure diffusion to the fault after injection stopped, ultimately leading to the occurrence of the magnitude 2.9 earthquake.
Key Points
A coupled poroelastic model considering hydrofracturing‐induced pressure perturbations was developed to evaluate induced seismicity
The post shut‐in
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2.9 earthquake at the Preston New Road, UK was triggered by pore pressure diffusion to a conductive fault
The causal mechanism of induced seismicity highly depends on fault permeability and its connectivity to injection regions
Water content and incident energy are important factors in influencing the mechanical properties and stress field of coal seam, which are closely related to the dynamic disaster intensity. In this ...study, after doing some static compression tests in different water content, comprehension dynamic compressive tests on pre-stressed coal specimens under different water contents and incident energy levels were conducted using a modified Split Hopkinson Pressure Bar test system. The effects of water contents and incident energy levels on dynamic behavior of the studied coal were evaluated by analysis of dynamic stress-strain curves, inspection of the occurred damage and in-situ test on the mine site. For detail analysis, some indices including peak strength, elastic modulus, dissipation energy, impact energy index, and failure characteristics were employed. The results indicated that dynamic strength and elastic modulus are negatively correlated with the water content and positively correlated with the incident energy. Two types of the dynamic failure behavior including incident energy-dominated failure and incident energy-induced failure were analyzed based on dissipation energy and stress-strain curve types. The coal burst occurrence possibility was proposed according to the dissipation energy density. Finally, based on laboratory test results and field engineering practices, the dynamic disaster mechanisms and their respective prevention concepts were further discussed.
Particle gradations significantly affects the dynamic response of water-saturated soft coal. To obtain the dynamic response of soft coal to various particle gradations, static and dynamic mechanical ...properties of water-saturated soft coal with different particle gradations were tested and compared. During these processes, the enhancement coefficient of the dynamic mechanical parameters to the corresponding static mechanical parameters was set as an index to describe the effect of non-uniformity coefficient Cu and median diameter d50. The results demonstrate that both the static and dynamic mechanical parameters of the water-saturated soft coal were affected by particle gradations. The enhancement coefficient was affected by both the d50 and Cu, which was microscopically attributed to effect of the d50 and Cu on the average dynamic liquid bridge force and scale dynamic rupture energy among the particles based on the microstructure and dynamic fracture evolution processes. In addition, the dimensionless scale rupture energy model among the water-bearing particles varied with the d50 and Cu were further established and applied to discuss the effect mechanism of particle gradations on the dynamic response of water-saturated soft coal. On this basis, the support measures of roadways in coal seam with different particle gradations were further discussed.
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