Imperial College London

ProfessorSevketDurucan

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Mining and Environmental Engineering
 
 
 
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Contact

 

+44 (0)20 7594 7354s.durucan

 
 
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Location

 

1.36Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

162 results found

Cao W, Durucan S, Cai W, Shi J-Q, Korre Aet al., 2020, A physics-based probabilistic forecasting methodology for hazardous microseismicity associated with longwall coal mining, International Journal of Coal Geology, ISSN: 0166-5162

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, t

Journal article

Cao W, Yildirim B, Durucan S, Wolf K-H, Cai W, Agrawal H, Korre Aet al., 2020, Fracture behaviour and seismic response of naturally fractured coal subjected to true triaxial stresses and hydraulic fracturing, Fuel: the science and technology of fuel and energy, ISSN: 0016-2361

Hydraulic fracturing of coalbed methane wells has been widely practised as an effective method to increase drainage efficiency in low-permeability, low-pressure and low-saturated coal seams. To investigate hydraulic fracture performance and associated seismic response in coal, hydraulic fracturing experiments were carried out on two cubic coal blocks containing a host of natural fractures using a true triaxial rock testing machine equipped with loading, injection and acoustic systems. The acoustic system uses transducers with active sources to repetitively generate and receive ultrasonic P/S wave pulses for characterising mechanical properties of the coal blocks and revealing fracture growth. Silicon oil was injected into the middle of coal blocks to create hydraulic fractures under deviatoric stress conditions, and the stress and displacement, borehole pressure and volume, and seismic response were recorded over the injection process. X-ray computed tomography (CT) was conducted before and after the experiments to identify the location and geometry of hydraulic and natural fractures. Results have shown that the fracturing behaviour, the drawdown period of borehole pressure and the intrusion of fracturing fluid are dominated by the complexity and insulation offered by internal natural fracture networks of coal blocks. In addition, seismic spectrograms captured both fracture initiation and its subsequent interaction with natural fractures, which indicates that the induced fracture and fracturing fluid interfere with the propagation of seismic waves and influence ultrasonic seismic characteristics. Seismic velocity tomography of ultrasonic acoustic signals recorded also provided the spatial information of fractures, such as approximate locations of pre-existing fractures and injection-disturbed regions.

Journal article

Stork AL, Chalari A, Durucan S, Korre A, Nikolov Set al., 2020, Fibre-optic monitoring for high-temperature Carbon Capture, Utilization and Storage (CCUS) projects at geothermal energy sites, First Break, Vol: 38, Pages: 61-67, ISSN: 0263-5046

It is often assumed that geothermal energy provides a clean source of renewable energy without emissions of carbon dioxide (CO2) or other greenhouse gases. In fact, most geothermal energy plants emit CO2 and small amounts of other gases, typically up to 5% of by weight. Reinjection of produced CO2 back into the geothermal fields has been proposed by several researchers in the past. The EU funded CarbFix and CarbFix2 projects have successfully demonstrated that CO2 reinjection into basaltic rocks can provide a safe and efficient geological storage method. The ACT Programme funded SUCCEED project is focused on understanding the effects of and developing technologies to enable reinjection of produced CO2 at geothermal plants in different geological settings. Monitoring the process is vital to understand the effects, possibilities and limitations of injection but the availability of suitable sensors is limited in high-temperature and harsh environments. This problem can be overcome with the use of distributed fibre-optic sensors which are able to withstand such harsh environments and record temperature, seismic and strain signals. This article describes actual and planned deployments of Distributed Acoustic Sensing (DAS) technology at the Hellisheidi and Kizildere geothermal fields in Iceland and Turkey, respectively, and outlines the practical considerations for such deployments.

Journal article

Cao W, Durucan S, Cai W, Shi J-Q, Korre A, Jamnikar S, Rošer J, Lurka A, Siata Ret al., 2020, The role of mining intensity and pre-existing fracture attributes on spatial, temporal and magnitude characteristics of microseismicity in longwall coal mining, Rock Mechanics and Rock Engineering, Vol: 53, Pages: 4139-4162, ISSN: 0723-2632

Knowledge regarding microseismic characteristics associated with longwall coal mining is crucial in evaluating the potential for underground mining hazards. Although microseismicity is induced by mining activities, it still remains uncertain as to what extent mining activities influence the spatial, temporal, and magnitude characteristics of microseismicity. To establish a thorough understanding of the relationship between microseismic characteristics and mining activities, a 27-month long microseismic monitoring campaign was conducted around a highly stressed coal zone and eight producing longwall panels at Coal Mine Velenje in Slovenia. Each microseismic event was classified to be associated with the producing longwall panel that triggered it, and the microseismic response to multi-panel longwall top coal caving face advance was analysed. Monitoring data have shown that locations of microseismic events coincided with stress concentrated regions. It was established that both seismic count and energy-intensive regions associated with coal mining in different panels are spatially connected, but they do not fully overlap with mined-out or stress concentrated areas. In addition, microseismic event counts frequency was found to be well correlated with mining intensity, while seismic energy magnitude and spatial distribution are poorly correlated with the same. Therefore, microseismic characteristics could not be explained solely by the mining-induced stress transfer and mining intensity, but are believed to be dominated by pre-existing natural fractures throughout the coal seam. Analyses of these observations helped the development of a conceptual seismic-generation model, which provides new insights into the causes of microseismicity in coal mining.

Journal article

Cao W, Shi J-Q, Durucan S, Si G, Korre Aet al., 2020, Gas-driven rapid fracture propagation under unloading conditions in coal and gas outbursts, International Journal of Rock Mechanics and Mining Sciences, Vol: 130, ISSN: 1365-1609

Coal and gas outbursts have long posed a serious risk to safe and efficient production in coal mines. It is recognised that coal and gas outbursts are triggered by excavation unloading followed by gas-driven rapid propagation of a system of pre-existing or mining-induced fractures. Gas-filled fractures parallel to a working face are likely to experience opening first, then expansion and rapid propagation stages under unloading conditions. The fracture opening is driven by the effective stress inside the fracture, while the fracture expansion and rapid propagation is propelled by the pressure build-up of desorbed gas in the vicinity of the fracture. Based upon this understanding, this research aimed to identify the key factors affecting outburst initiation and its temporal evolution during roadway developments. Specifically, the response of pre-set fractures in a thin coal seam sandwiched between rock layers to roadway development is simulated using a geomechanical model coupled with fracture mechanics for fracture opening and propagation. In addition, kinetic gas desorption and its migration into open fractures is considered. During simulations outburst is deemed to occur when the fracture length exceeds the dimension of a host element. The findings of this research suggest that the simulated coal and gas outburst caused by roadway development may be considered as a dynamic gas desorption-driven fracture propagation process. The occurrence of coal and gas outbursts is found to be influenced mainly by the coal properties, fracture attributes, and initial gas pressure and the in situ stress conditions. Furthermore, the model predictions in terms of dome-shaped erupted-zone and layer-by-layer coal breakage are consistent with the field reports. In addition, the model results suggest that delayed occurrence of coal and gas outbursts, especially after sudden exposure of a coal seam or after blasting disturbance, reported in the literature may be related to the gas desorp

Journal article

Agrawal H, Cao W, Durucan S, Korre Aet al., 2020, Development of a probabilistic risk assessment methodology to evaluate the effect of lithological heterogeneity on rock bursts and gas outbursts in longwall coal mining

© 2020 ARMA, American Rock Mechanics Association A coupled geomechanical and gas flow model was developed to analyse rock burst and gas outburst risk associated with retreating longwall coal mining in heterogeneous coal seams. Mechanical, elastic and reservoir properties of a heterogeneous coal seam were attributed consistently for several realisations to analyse their influence on rock burst and gas outburst potential. Several scenarios were developed by varying the degree of lithological heterogeneity caused by xylite within a mostly detritic lignite coal seam in the modelled heterogeneous zone. Model results have shown that, as the longwall face approaches the heterogeneous zone, the changes in vertical stress along the face, as well as ahead of it, are affected strongly by the degree of heterogeneity. The potential for a rapid increase in gas emission rate and outburst risk, which may occur as the face cuts through the heterogeneous zone, was also found to depend largely on the degree of heterogeneity implemented.

Conference paper

Korre A, Durucan S, Nie Z, 2019, Life cycle environmental impact assessment of coupled underground coal gasification and CO2 capture and storage: Alternative end uses for the UCG product gases, International Journal of Greehouse Gas Control, Vol: 91, ISSN: 1750-5836

Underground coal gasification (UCG) has the potential to provide a source of energy or chemical feedstockderived from coal seams, where traditional mining methods are not suitable or are uneconomical. This paperpresents the life cycle inventory models developed for the UCG processes and three alternative syngasutilisation options with and without CO2 capture and storage. The paper compares the life cycle carbonfootprint of two different conventional above ground coal fired power generation options with UCG IntegratedGasification Combined Cycle power generation with/without CCS for two different lignites and onebituminous coal. One of the lignites is then used to compare the life cycle performance of different syngasutilisation options: power generation, ammonia production with power generation, and methanol productionwith power generation. It was found that the life cycle carbon footprint of conventional above ground coalfired power generation is very much dependent on the in-situ methane content of the coal used, and methaneemissions experienced during mining and accompanying upstream processes, whereas the same for UCGIGCC power depends more on the process dependent syngas composition. UCG methanol production withassociated power and CCS is shown to release more life cycle CO2-eq emissions per tonne of lignite consumedthan that of UCG ammonia production with associated power and CCS and UCG CCGT power generationwith CCS. Furthermore, when chemicals production from UCG is considered as the main objective, the mostsubstantial improvements in comparison to conventional methods are associated with UCG ammonia processper tonne of chemical produced.

Journal article

Shi JQ, Durucan S, Korre A, Ringrose P, Mathieson Aet al., 2019, History matching and pressure analysis with stress-dependent permeability using the In Salah CO2 storage case study, International Journal of Greenhouse Gas Control, Vol: 91, ISSN: 1750-5836

Using the In Salah CO2 storage case study, this study demonstrates how reservoir simulation history-matching and pressure analysis can be used to improve conformance assurance. By adopting a holistic approach to reservoir simulation and history matching, in conjunction with the injection pressure analysis and use of microseismic monitoring data, an improved understanding of the injection processes at the In Salah storage site was gained, revealing distinctively different responses to CO2 injection at each of the three injection wells. It has been shown that injection well performance at wells KB-501 and KB-503 was characterised by periods of matrix and fracture flow, the latter being due to shear reactivation of existing fractures in the vicinity of the wellbore. In contrast, the analysis at KB-502 revealed that CO2 injection has resulted in fracture reactivation in both shear and tensile modes with propagation both laterally and vertically.The findings of this study have shown that the injection-induced microseismic events recorded close to the KB-502 well is mainly caused by injecting CO2 into a 4-kilometer long fracture-zone intersecting the borehole. This fracture zone experienced tensile opening of fractures during injection and then subsequent partial closure after the injection was suspended. It is furthermore clear that the rather unique combination of microseismic and InSAR monitoring data and reservoir history matching around the injection well KB-502 provide highly valuable insights into injection-induced seismicity and fracture flow behaviour for CO2 storage projects. Episodes of flow in natural fractures can be separated from flow in induced fractures and the need for a dynamic, stress-dependent, permeability variable have been demonstrated.

Journal article

Cao W, Shi J-Q, Durucan S, Korre A, Jamnikar Set al., 2019, Numerical modelling of anomalous microseismicity influenced by lithological heterogeneity in longwall top coal caving mining, International Journal of Coal Geology, Vol: 216, ISSN: 0166-5162

Mining-induced microseismicity has been extensively used to evaluate the potential for rock bursts and coal and gas outbursts in underground coal mines. In a research project completed a few years ago, it was observed that characteristics of microseismicity around a working longwall panel were fairly consistent over the monitoring period until a lithological heterogeneity zone with a relatively high coal strength was reached. The current research presented in this paper aims at achieving a better understanding of the effect of lithological heterogeneity on microseismic activity in longwall coal mining. The heterogeneous zone inferred from the tomography measurements was first digitalised and implemented into a 3D geomechanical model. A microseismicity modelling approach which combines deterministic stress and failure analysis together with a stochastic fracture slip evaluation was used to simulate the evolution of microseismicity induced by the progressive face advance passing through the heterogeneous zone. The heterogeneity was taken into account by varying the material strength and the fracture attributes of the elements within the high strength zone. Results have shown that both the high rock strength of coal lithotype and low power law scaling exponent of fractures within this zone contribute to the reduction in fitted b values from frequency-magnitude distribution of microseismicity and the increase in fitted Gaussian distribution parameters to the logarithmic event energy. These deviations are believed to result from the combined effects of increased stress drops and slipped fracture sizes when the heterogeneous zone is approached.

Journal article

Cai W, Durucan S, Shi JQ, Cao W, Agrawal H, Korre A, Jamnikar S, Rošer Jet al., 2019, Development of fractal-fuzzy evaluation methodology and its application for seismic hazards assessment using microseismic monitoring in coal mining, 53rd U.S. Rock Mechanics/Geomechanics Symposium, Publisher: American Rock Mechanics Association

Seismic hazards have become one of the common risks in underground coal mining and their assessment is an important component of the safety management. In this study, a methodology, involving nine fractal dimension-based indices and a fuzzy comprehensive evaluation model, has been developed based on the processed real time microseismic data from an underground coal mine, which allows for a better and quantitative evaluation of the likelihood for the seismic hazards. In the fuzzy model, the membership function was built using a Gaussian shape and the weight of each index was determined using the performance metric F score derived from the confusion matrix. The assessment results were initially characterised as a probability belonging to each of four risk levels (none, weak, moderate and strong). The comprehensive result was then evaluated by integrating the maximum membership degree principle (MMDP) and the variable fuzzy pattern recognition (VFPR). The model parameters of this methodology were first calibrated using historical microseismic data over a period of seven months at Coal Mine Velenje in Slovenia, and then applied to analyse more recent microseismic monitoring data. The results indicate that the calibrated model was able to assess seismic hazards in the mine.

Conference paper

Cao W, Durucan S, Cai W, Shi JQ, Korre Aet al., 2019, Multiple-panel longwall top coal caving induced microseismicity: Monitoring and development of a statistical forecasting model for hazardous microseismicity, 53rd U.S. Rock Mechanics/Geomechanics Symposium, Publisher: American Rock Mechanics Association

Continuous microseismic monitoring was carried out around 9 producing longwall top coal caving (LTCC) panels with concurrently recorded daily face advance rates at Coal Mine Velenje in Slovenia over a 27-month monitoring period. The monitoring results suggested that spatial and magnitude characteristics of microseismicity are dominated by those of underlying fractures, while microseismic event rate is under the combined effects of local natural fracture abundance and mining intensity. On this basis, a data-driven yet physics-based forecasting methodology was established for LTCC induced hazardous microseismicity, which is above a given threshold of energy magnitude and within a certain distance to the longwall face. Statistical analyses were first conducted to characterise temporal, magnitude and spatial characteristics of long-term recorded microseismicity, based on which a short-term forecasting model was developed to calculate the probability of hazardous microseismicity considering the three characteristics. The model developed was employed to forecast the likelihood of hazardous microseismicity at one of these LTCC panels, and the forecasted results were supported by the monitoring. This statistical model has important implications in the evaluation of mining-induced hazards, and it can be used to optimise longwall face advance rates to minimise the risk of hazardous microseismicity in burst-prone deep-level mining sites.

Conference paper

Yildirim B, Durucan S, Cao W, Cai W, Shi J, Korre A, Wolf KHet al., 2019, Experimental and numerical investigation into hydraulic fracture and natural fracture interaction in shale formations, 53rd U.S. Rock Mechanics/Geomechanics Symposium, Publisher: American Rock Mechanics Association

Two 0.3 m × 0.3 m × 0.3 m shale blocks, one representing a homogeneous sample while the other representing a naturally fractured sample, are modelled using the lattice based DEM code, XSite. The synthetic rock mass approach (SRM), which assigns the smooth joint contacts (SJM) to the weakness planes, is used to represent the natural fractures in shale block-2. Firstly, the developed models are compared with the findings of previously conducted true-triaxial hydraulic fracturing experiments with acoustic measurements, and their subsequent computed tomography (CT) and seismic velocity tomography results. The 3D model results confirmed the curved shape hydraulic fractures, which propagated perpendicular to the minimum stress directions in both shale blocks. Model results also captured the natural fracture (NF) and hydraulic fracture (HF) interaction, particularly the arrest, the dilation of major NFs, followed by crossing with offset mechanism, in shale block-2. Secondly, the parametric studies are carried out to investigate the role of fluid flow rate (q), and fluid viscosity (µ) on different NF/HF interaction mechanisms. The effects of q and µ are discussed based on the total stimulated area including the tensile and shear microcracks, the pipe apertures, and the pressure evolutions within NFs.

Conference paper

Agrawal H, Durucan S, Cao W, Cai Wet al., 2019, Evaluation of parameters affecting the energy accumulation in longwall mining, 53rd U.S. Rock Mechanics/Geomechanics Symposium, Publisher: American Rock Mechanics Association

The elastic strain energy accumulation in a retreating longwall mining panel is dependent on several parameters which have been identified using elastic theory for beams in an elastic supporting medium. The identified parameters were varied to identify the parameters that have a strong influence on the elastic strain energy accumulation. Upon sensitivity analysis, mining depth, length of cantilever roof in the goaf, coal seam thickness, roof thickness, Young’s modulus of coal seam and roof were identified as the main influencing parameters. The analytical equations were validated by comparing the results with previous studies and a case-specific numerical model. The results obtained from analytical equations were comparable with those obtained from a numerical model. The developed analytical equations will provide a handy tool to make daily, weekly and monthly prediction of areas of high elastic strain energy accumulations inside the solid coal pillar. Hence, the paper finds direct application in improving the safety of people working in coal mines, minimising machine downtime and production delays.

Conference paper

Si G, Durucan S, Shi JQ, Korre A, Cao Wet al., 2019, Parametric analysis of slotting operation induced failure zones to stimulate low permeability coal seams, Rock Mechanics and Rock Engineering, Vol: 52, Pages: 163-182, ISSN: 0723-2632

The main constrain for effective gas drainage in coal mines is the low permeability nature of coal reservoirs. As coal mining activities are extending to deeper subsurface, the ever-increasing in situ stress conditions is anticipated to result in much lower permeability and more challenges for gas emission control in coal mines. In recent years, hydraulic slotting using high-pressure waterjet along underground gas drainage boreholes, as a general solution to stimulate low permeability coal seams, has become increasingly favourable. This paper presents a systematic investigation into the sensitivity of borehole slotting performance to a number of field and operational parameters. A wide range of geomechanical properties, in situ stress conditions, slot geometry and spacing of multiple slots were considered in a series of numerical simulations. The relations between these key parameters and the failure zone size/volume induced by slotting were quantified. The effect of different parameters in improving slotting performance has also been ranked, which provides theoretical base for mine operators to optimise slotting operations.

Journal article

Yildirim B, Durucan S, Cao W, Cai W, Shi J, Korre A, Wolf KHet al., 2019, Experimental and numerical investigation into hydraulic fracture and natural fracture interaction in shale formations

Copyright 2019 ARMA, American Rock Mechanics Association. Two 0.3 m × 0.3 m × 0.3 m shale blocks, one representing a homogeneous sample while the other representing a naturally fractured sample, are modelled using the lattice based DEM code, XSite. The synthetic rock mass approach (SRM), which assigns the smooth joint contacts (SJM) to the weakness planes, is used to represent the natural fractures in shale block-2. Firstly, the developed models are compared with the findings of previously conducted true-triaxial hydraulic fracturing experiments with acoustic measurements, and their subsequent computed tomography (CT) and seismic velocity tomography results. The 3D model results confirmed the curved shape hydraulic fractures, which propagated perpendicular to the minimum stress directions in both shale blocks. Model results also captured the natural fracture (NF) and hydraulic fracture (HF) interaction, particularly the arrest, the dilation of major NFs, followed by crossing with offset mechanism, in shale block-2. Secondly, the parametric studies are carried out to investigate the role of fluid flow rate (q), and fluid viscosity (µ) on different NF/HF interaction mechanisms. The effects of q and µ are discussed based on the total stimulated area including the tensile and shear microcracks, the pipe apertures, and the pressure evolutions within NFs.

Conference paper

Cai W, Durucan S, Shi JQ, Cao W, Agrawal H, Korre A, Jamnikar S, Rošer Jet al., 2019, Development of fractal-fuzzy evaluation methodology and its application for seismic hazards assessment using microseismic monitoring in coal mining

Copyright 2019 ARMA, American Rock Mechanics Association. Seismic hazards have become one of the common risks in underground coal mining and their assessment is an important component of the safety management. In this study, a methodology, involving nine fractal dimension-based indices and a fuzzy comprehensive evaluation model, has been developed based on the processed real time microseismic data from an underground coal mine, which allows for a better and quantitative evaluation of the likelihood for the seismic hazards. In the fuzzy model, the membership function was built using a Gaussian shape and the weight of each index was determined using the performance metric F score derived from the confusion matrix. The assessment results were initially characterised as a probability belonging to each of four risk levels (none, weak, moderate and strong). The comprehensive result was then evaluated by integrating the maximum membership degree principle (MMDP) and the variable fuzzy pattern recognition (VFPR). The model parameters of this methodology were first calibrated using historical microseismic data over a period of seven months at Coal Mine Velenje in Slovenia, and then applied to analyse more recent microseismic monitoring data. The results indicate that the calibrated model was able to assess seismic hazards in the mine.

Conference paper

Agrawal H, Durucan S, Cao W, Cai Wet al., 2019, Evaluation of parameters affecting the energy accumulation in longwall mining

Copyright 2019 ARMA, American Rock Mechanics Association. The elastic strain energy accumulation in a retreating longwall mining panel is dependent on several parameters which have been identified using elastic theory for beams in an elastic supporting medium. The identified parameters were varied to identify the parameters that have a strong influence on the elastic strain energy accumulation. Upon sensitivity analysis, mining depth, length of cantilever roof in the goaf, coal seam thickness, roof thickness, Young’s modulus of coal seam and roof were identified as the main influencing parameters. The analytical equations were validated by comparing the results with previous studies and a case-specific numerical model. The results obtained from analytical equations were comparable with those obtained from a numerical model. The developed analytical equations will provide a handy tool to make daily, weekly and monthly prediction of areas of high elastic strain energy accumulations inside the solid coal pillar. Hence, the paper finds direct application in improving the safety of people working in coal mines, minimising machine downtime and production delays.

Conference paper

Yildirim B, Durucan S, Cao W, Cai W, Shi J, Korre A, Wolf KHet al., 2019, Experimental and numerical investigation into hydraulic fracture and natural fracture interaction in shale formations

Copyright 2019 ARMA, American Rock Mechanics Association. Two 0.3 m × 0.3 m × 0.3 m shale blocks, one representing a homogeneous sample while the other representing a naturally fractured sample, are modelled using the lattice based DEM code, XSite. The synthetic rock mass approach (SRM), which assigns the smooth joint contacts (SJM) to the weakness planes, is used to represent the natural fractures in shale block-2. Firstly, the developed models are compared with the findings of previously conducted true-triaxial hydraulic fracturing experiments with acoustic measurements, and their subsequent computed tomography (CT) and seismic velocity tomography results. The 3D model results confirmed the curved shape hydraulic fractures, which propagated perpendicular to the minimum stress directions in both shale blocks. Model results also captured the natural fracture (NF) and hydraulic fracture (HF) interaction, particularly the arrest, the dilation of major NFs, followed by crossing with offset mechanism, in shale block-2. Secondly, the parametric studies are carried out to investigate the role of fluid flow rate (q), and fluid viscosity (µ) on different NF/HF interaction mechanisms. The effects of q and µ are discussed based on the total stimulated area including the tensile and shear microcracks, the pipe apertures, and the pressure evolutions within NFs.

Conference paper

Agrawal H, Durucan S, Cao W, Cai Wet al., 2019, Evaluation of parameters affecting the energy accumulation in longwall mining

Copyright 2019 ARMA, American Rock Mechanics Association. The elastic strain energy accumulation in a retreating longwall mining panel is dependent on several parameters which have been identified using elastic theory for beams in an elastic supporting medium. The identified parameters were varied to identify the parameters that have a strong influence on the elastic strain energy accumulation. Upon sensitivity analysis, mining depth, length of cantilever roof in the goaf, coal seam thickness, roof thickness, Young’s modulus of coal seam and roof were identified as the main influencing parameters. The analytical equations were validated by comparing the results with previous studies and a case-specific numerical model. The results obtained from analytical equations were comparable with those obtained from a numerical model. The developed analytical equations will provide a handy tool to make daily, weekly and monthly prediction of areas of high elastic strain energy accumulations inside the solid coal pillar. Hence, the paper finds direct application in improving the safety of people working in coal mines, minimising machine downtime and production delays.

Conference paper

Cao W, Durucan S, Cai W, Shi JQ, Korre Aet al., 2019, Multiple-panel longwall top coal caving induced microseismicity: Monitoring and development of a statistical forecasting model for hazardous microseismicity

Copyright 2019 ARMA, American Rock Mechanics Association. Continuous microseismic monitoring was carried out around 9 producing longwall top coal caving (LTCC) panels with concurrently recorded daily face advance rates at Coal Mine Velenje in Slovenia over a 27-month monitoring period. The monitoring results suggested that spatial and magnitude characteristics of microseismicity are dominated by those of underlying fractures, while microseismic event rate is under the combined effects of local natural fracture abundance and mining intensity. On this basis, a data-driven yet physics-based forecasting methodology was established for LTCC induced hazardous microseismicity, which is above a given threshold of energy magnitude and within a certain distance to the longwall face. Statistical analyses were first conducted to characterise temporal, magnitude and spatial characteristics of long-term recorded microseismicity, based on which a short-term forecasting model was developed to calculate the probability of hazardous microseismicity considering the three characteristics. The model developed was employed to forecast the likelihood of hazardous microseismicity at one of these LTCC panels, and the forecasted results were supported by the monitoring. This statistical model has important implications in the evaluation of mining-induced hazards, and it can be used to optimise longwall face advance rates to minimise the risk of hazardous microseismicity in burst-prone deep-level mining sites.

Conference paper

Cai W, Durucan S, Shi JQ, Cao W, Agrawal H, Korre A, Jamnikar S, Rošer Jet al., 2019, Development of fractal-fuzzy evaluation methodology and its application for seismic hazards assessment using microseismic monitoring in coal mining

Copyright 2019 ARMA, American Rock Mechanics Association. Seismic hazards have become one of the common risks in underground coal mining and their assessment is an important component of the safety management. In this study, a methodology, involving nine fractal dimension-based indices and a fuzzy comprehensive evaluation model, has been developed based on the processed real time microseismic data from an underground coal mine, which allows for a better and quantitative evaluation of the likelihood for the seismic hazards. In the fuzzy model, the membership function was built using a Gaussian shape and the weight of each index was determined using the performance metric F score derived from the confusion matrix. The assessment results were initially characterised as a probability belonging to each of four risk levels (none, weak, moderate and strong). The comprehensive result was then evaluated by integrating the maximum membership degree principle (MMDP) and the variable fuzzy pattern recognition (VFPR). The model parameters of this methodology were first calibrated using historical microseismic data over a period of seven months at Coal Mine Velenje in Slovenia, and then applied to analyse more recent microseismic monitoring data. The results indicate that the calibrated model was able to assess seismic hazards in the mine.

Conference paper

Durucan S, Cao W, Cai W, Shi JQ, Korre A, Si G, Jamnikar S, Roser Jet al., 2019, Monitoring, assessment and mitigation of rock burst and gas outburst induced seismicity in longwall top coal caving mining, Pages: 11-20

© 2019 Taylor & Francis Group, London. Underground coal extractions lead to continuous stress and pressure redistribution around mine openings which, in some cases, may lead to coal and gas outburst and rock bursts. This paper presents seismic monitoring research, which aimed at characterising the dynamic behaviour of the coal seam in response to gateroad development and longwall top coal caving mining at Coal Mine Velenje. The early campaigns involved time-lapse active seismic tomography and microseismic monitoring at the two selected longwall panels. Based on the findings of this early work, a more comprehensive microseismic monitoring programme was set up. Seismic monitoring data were processed and used for model development and rock burst/gas outburst risk assessment purposes, which also led to the development of measures to mitigate against seismic hazards.

Conference paper

Santibanez-Borda E, Govindan R, Elahi N, Korre A, Durucan Set al., 2019, Maximising the dynamic CO2 storage capacity through the optimisation of CO2 injection and brine production rates, International Journal of Greenhouse Gas Control, Vol: 80, Pages: 76-95, ISSN: 1750-5836

CO2 storage capacity in saline aquifers can dramatically be reduced by pressure build up due to the CO2 injection process. In this paper, a novel optimisation strategy that maximises the CO2 storage capacity utilisation and net profits before tax is presented in a scenario of simultaneous CO2 injection and brine production to help control pressure build up and increase the effective storage capacity. The strategy is tested at the region surrounding the Forties and Nelson fields, assuming both as pure saline aquifer traps. The optimisation was performed considering constraints such that the CO2 plume distribution does not migrate outside the license boundaries, the fracture pressure is not reached within the reservoir, and the CO2 injection and brine production rates occur within feasible limits. The problem was first formulated analytically with the aid of surrogate models, and then optimised using the SIMPLEX and Generalized Reduced Gradient methods.Results for the Forties and Nelson fields show that by allowing five brine production wells producing up to 2.2 MMtonnes/year, the CO2 storage capacity increased between 112-145% compared to the case where no brine production is practiced.

Journal article

Xue Z, Shi JQ, Yamauchi Y, Durucan Set al., 2018, Fiber optic sensing for geomechanical monitoring: (1)-distributed strain measurements of two sandstones under hydrostatic confining and pore pressure conditions, Applied Sciences (Switzerland), Vol: 8

In this study distributed optic fiber has been used to measure both the Rayleigh and Brillouin frequency shift of two different sandstone core samples under controlled hydrostatic confining and pore pressure in the laboratory. The Berea sandstone core is relatively homogeneous, whereas the Tako sandstone core is visibly heterogeneous with a coarse-grain and a fine-grain region. Rayleigh frequency has been found to have a superior performance over Brillouin frequency in terms of better consistency (less scattering) in the tests carried out. The strain gauge readings reveal considerable anisotropy in the stiffness of the Berea core between perpendicular (vertical) and parallel to the bedding (hoop) directions. The strains converted from Rayleigh frequency shift measurements agree reasonably well with readings by one of the four hoop strain gauge channels under increasing confining/pore pressure. For the Tako sandstone core, the contrast in the grain-size, and thus rock elastic properties, is clearly reflected in the hoop strain measurement by both strain gauges and distributed optic fiber. The outcomes of the test have demonstrated successfully the use of a single optic fiber for measuring rock strain response at different regions of a heterogeneous core sample along a continuous trajectory.

Journal article

Yildirim B, Cao W, Shi JQ, Durucan S, Korre Aet al., 2018, Discrete element modelling of hydraulic fracture interaction with natural fractures in shale formations, 2nd International Discrete Fracture Network Engineering Conference, Publisher: American Rock Mechanics Association

Research presented in this paper aimed at establishing a better understanding of natural fracture (NF)/hydraulic fracture (HF) interaction mechanisms and fracture network development in naturally fractured and nonhomogeneous shale formations through numerical modelling using the two-dimensional particle flow code (PFC2D). Hydraulic fracture propagation was firstly modelled in a 30 m x 30 m model representing intact rock by bonded particle method (BPM), which served as a base case in the research. Then a single, deterministic natural fracture was embedded into the same model by a smooth joint contact model (SJM) to investigate different NF/HF interaction mechanisms under a range of different conditions by varying the angle of approach, differential horizontal stress, and the mechanical properties of a fracture within the model. Based on the parametric research findings, number and diversity of natural fractures in the model were increased both deterministically and stochastically, and the results are compared and discussed.

Conference paper

Yildirim B, Cao W, Durucan S, Korre A, Wolf KH, Bakker R, Barnhoorn Aet al., 2018, The effect of natural fracture heterogeneity on hydraulic fracture performance and seismic response in shale and coal formations, 52nd U.S. Rock Mechanics/Geomechanics Symposium, Publisher: American Rock Mechanics Association.

Two 0.3 m × 0.3 m × 0.3 m cubic blocks of shale and coal were used for hydraulic fracturing experiments under true tri-axial stress conditions. The shale block used was highly homogeneous and without visible fractures, while the coal block contained a host of natural fractures. The mechanical and hydraulic properties of both rocks were characterized through multi-stage triaxial tests, Brazilian disk tests, and porosity and permeability measurements. A true tri-axial rock testing machine equipped with loading, pump and acoustic systems was used in the experiment. The acoustic system uses 48 transducers with active sources to repetitively generate and receive ultrasonic P/S wave pulses to reveal fracture initiation and growth. Before the experiment, initial seismic response of both blocks was recorded under hydrostatic stress conditions to characterize anisotropy and heterogeneity of the blocks as reference. Silicon oil was injected centrally into both blocks to create a hydrofracture under deviatoric stress conditions and the load, displacement, pump pressure and volume, and seismic response during the injection process were recorded. Results from two blocks are being compared in terms of hydrofracture geometry and seismic features.

Conference paper

Cao W, Shi JQ, Durucan S, Si G, Korre Aet al., 2018, Gas-driven rapid fracture propagation and gas outbursts under unloading conditions in coal seams, 52nd U.S. Rock Mechanics/Geomechanics Symposium, Publisher: American Rock Mechanics Association

Coal and gas outbursts have long posed a serious risk to safe and efficient production in coal mines. It is recognised that the coal and gas outbursts are triggered by excavation unloading followed by gas-driven rapid propagation of a system of preexisting or mining-induced fractures. Gas-filled fractures parallel to a working face are likely to experience opening first, then expansion and rapid propagation stages under unloading conditions. This research aimed to identify the key factors affecting outburst initiation and its temporal evolution during roadway developments. Specifically, the response of pre-set fractures in a coal seam sandwiched between rock layers to roadway development is simulated using a geomechanical model coupled with fracture mechanics for fracture opening and propagation. In addition, kinetic gas desorption and its migration into open fractures is considered. During simulations outburst is deemed to occur when the fracture length exceeds the dimension of a host element. The findings of this research suggests that the simulated coal and gas outburst may be considered as a dynamic gas desorption-driven fracture propagation process. The occurrence of coal and gas outbursts is found to be influenced mainly by the coal properties, fracture attributes, and initial gas pressure and the in situ stress conditions.

Conference paper

Cao W, Shi J, Si G, Durucan S, Korre Aet al., 2018, Numerical modelling of microseismicity associated with longwall coal mining, International Journal of Coal Geology, Vol: 193, Pages: 30-45, ISSN: 0166-5162

Microseismicity has long been a precursor for underground mining hazards such as rockbursts and coal and gas outbursts. In this research, a methodology combining deterministic stress and failure analysis and stochastic fracture slip evaluation, based upon the widely accepted fracture slip seismicity-generation mechanism, has been developed to simulate microseismic events induced by longwall mining. Using the built-in DFN facility in FLAC3D, discrete fractures following a power law size distribution are distributed throughout a 3D continuum model in a probabilistic way to account for the stochastic nature of microseismicity. The DFN-based modelling approach developed was adopted to simulate the evolution of microseismicity induced by the progressive face advance in a longwall top coal caving (LTCC) panel at Coal Mine Velenje, Slovenia. At each excavation step, global stress and failure analysis with reference to the strain-softening post-failure behaviour characteristic of coal, and fracture slip evaluation for microseismicity are conducted sequentially. The model findings are compared to the microseismic event data recorded during a long-term field monitoring campaign conducted at the same LTCC panel. It was found that the released energy and frequency-magnitude distribution of microseismicity are associated with the slipped fracture sizes and fracture size distribution. These features for recorded microseismic events were fairly constant until a xylite rich heterogeneous zone ahead of the working face was approached, which indicates that fractures within the extracted coal seam follow the same size distribution. The features obtained from modelled microseismic events were consistent over the production period, and matched well the field observations. Furthermore, the model results indicate that the power law fracture size distribution can be used to model longwall-mining-induced microseismicity. This model provides a unique prospective to understand longwall coal m

Journal article

Shi J-Q, Durucan S, 2018, Variation in horizontal stress with pore pressure depletion in coal under uniaxial strain conditions: An update on the modelling of laboratory data, International Journal of Coal Geology, Vol: 187, Pages: 94-97, ISSN: 0166-5162

Building upon the previous modelling work on coalbed methane reservoirs by the authors, recently reported experimental horizontal stress data for two coal samples tested under uniaxial strain conditions have been analysed. As well as CH₄, non-adsorbing Helium has also been used in the experiments. Deviation between the model and the experimental CH₄ stress data at low pore pressures (< 3 MPa) are observed, which, as in the previous study, may be attributed to the onset of shear failure experienced by the coal samples. In addition, CO₂ was also used on one of the samples after the CH₄ experiment. The post-failure CO₂ stress data could be matched using a combination of a reduced Young's Modulus and an increased Poisson's ratio. The results of this study have provided further evidence for the validity of the equation for computing the changes in the effective horizontal stress in producing coalbed reservoirs, which forms an integral part of the Shi and Durucan permeability model.

Journal article

Korre A, Durucan S, Shi J, 2018, CO2 injection induced microseismicity around well KB-502 at in Salah and insights from reservoir history matching

© 2018 Society of Petroleum Engineers. All rights reserved. In the In Salah CO2 storage project in central Algeria, three long-reach horizontal injection wells (KB-501, KB-502 and KB-503) were used to inject the CO2, removed from the gas production stream, into the down-dip aquifer leg of the Carboniferous C10.2 gas reservoir. Between 2004 and 2011, over 3.8 million tonnes of CO2 have been stored in the c. 1.9km deep Carboniferous sandstone unit (C10.2) at the Krechba field. In a previous study by the authors, history matching of the (estimated) injection bottomhole pressure was carried out for KB-502 over the first injection period between April 2005 and July 2007. In the current work, history matching has been extended to the end of injection period in 2011. The obtained results are correlated with the reported induced microseismicity. The reservoir simulation results obtained have provided useful information which allows us to better interpret the recorded microseimicity induced by CO2 injection into a well.

Conference paper

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