Imperial College London

MrHarshitAgrawal

Faculty of EngineeringDepartment of Earth Science & Engineering

Research Assistant
 
 
 
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Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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17 results found

Jahanbakhsh A, Liu Q, Mosleh MH, Agrawal H, Farooqui NM, Buckman J, Recasens M, Marotovaler M, Korre A, Durucan Set al., 2021, An investigation into co2–brine–cement–reservoir rock interactions for wellbore integrity in co2 geological storage, Energies, Vol: 14, Pages: 1-20, ISSN: 1996-1073

Geological storage of CO2 in saline aquifers and depleted oil and gas reservoirs can help mitigate CO2 emissions. However, CO2 leakage over a long storage period represents a potential concern. Therefore, it is critical to establish a good understanding of the interactions between CO2–brine and cement–caprock/reservoir rock to ascertain the potential for CO2 leakage. Accordingly, in this work, we prepared a unique set of composite samples to resemble the cement–reservoir rock inter-face. A series of experiments simulating deep wellbore environments were performed to investigate changes in chemical, physical, mechanical, and petrophysical properties of the composite samples. Here, we present the characterisation of composite core samples, including porosity, permeability, and mechanical properties, determined before and after long‐term exposure to CO2‐rich brine. Some of the composite samples were further analysed by X‐ray microcomputed tomography (X‐ray μ‐CT), X‐ray diffraction (XRD), and scanning electron microscopy–energy‐dispersive X‐ray (SEM–EDX). Moreover, the variation of ions concentration in brine at different timescales was studied by per-forming inductively coupled plasma (ICP) analysis. Although no significant changes were observed in the porosity, permeability of the treated composite samples increased by an order of magnitude, due mainly to an increase in the permeability of the sandstone component of the composite samples, rather than the cement or the cement/sandstone interface. Mechanical properties, including Young’s modulus and Poisson’s ratio, were also reduced.

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, Vol: 288, Pages: 1-15, 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

Ghosh N, Agrawal H, Singh SK, Banerjee Get al., 2020, Optimum Chain Pillar Design at the Deepest Multi-Seam Longwall Workings in India, MINING METALLURGY & EXPLORATION, Vol: 37, Pages: 651-664, ISSN: 2524-3462

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

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

Agrawal H, Pal BK, Chatterjee S, 2019, Optimization of opencast mines using minimum cut algorithm – a case study from iron mine, Journal of Mines, Metals and Fuels, Vol: 67, Pages: 469-478, ISSN: 0022-2755

The demand and supply gap are on a rising trend in this developing world for all the minerals/ores. There is an acute need for suitable technological advancements in the field of mine planning with an aim for zero mining waste. The advanced technology will not only help in the optimum extraction of ores but will also maximize the profit ensuring safety and productivity. In this paper, an open pit optimization algorithm is proposed using a minimum cut algorithm and heuristic algorithm. The parametric minimum cut algorithm is used to generate pit shells, same as other mining software, and the resource constraints are imposed on the generated pit shells results using the heuristic algorithm to optimize the production plan. A case study is presented in an iron ore deposit from India, and the results were compared to the traditional method.

Journal article

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

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

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

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

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

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

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

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

Satyendra SK, Harshit A, Awanindra SP, 2017, Rib stability: A way forward for safe coal extraction in India, International Journal of Mining Science and Technology, Vol: 27, Pages: 1087-1091, ISSN: 2095-2686

Ensuring rib stability during pillar extraction is of prime importance in bord and pillar (B&P) method of underground coal mining with caving. Rib stability has been assessed here by way of assessing factor of safety (FOS), a ratio of the strength of rib to stress on it. Earlier formulations for rib stability when applied to case studies gave very low FOS value suggesting significant ground control problems, which were contrary to the field observations. This has necessitated the need to revisit the concept of rib stability. The stress coming on the rib is estimated with the use of numerical modeling technique using the FLAC3D software. The methodology of assessing rib-stability with the help of suggested rib-strength formulation has been validated at eight Indian coal mines. The outcome of this study finds relevance and importance in ensuring underground coal liquidation with improved safety and conservation.

Journal article

Singh DR, Mishra AK, Agrawal H, Singh SKet al., 2017, Parametric analysis for underground metal mine working stability, Pages: 3561-3568

Fully grouted rock bolts are considered the most economical support system for exposed unsupported rock in various mining operations. The paper presents parametric study of an underground metal mine with the horizontal cut-and-fill method of mining at the depth of 150 meters from the surface through numerical simulation using Fast Lagrangian Analysis of Continua (FLAC3D). Four different height of extraction i.e. 3m, 5m, 6m & 7m has been excavated numerically to evaluate the induced stress value and its parametric variation with the different height of extraction. Factor of safety was calculated numerically for estimating the stability of different stope height. The performance of the bolts were studied by conducting series of in-situ pullout tests, and parametric analysis of stress along the length of the bolt at different extraction/stope height. The load-deformation curve of bolts indicates the de-bonding nature of bolt with axial deformation of 42-46 mm. From the parametric study, it can be apprehended that with lode width of 8m and average height of extraction/stope (5m) the underground working does not experienced any pronounced ground control problems. At extraction height more than 5m the induced stress values are more and the chances of roof fall and failure of rock bolts are higher.

Conference paper

Singh S, Singh R, Singh AP, Agrawal Het al., 2016, Closing of a running mine and suggesting a new approach of winning of otherwise-left unextracted coal reserves, Journal of Mines, Metals and Fuels, Vol: 64, Pages: 335-340, ISSN: 0022-2755

In the workable Rayatwari seam of CRC colliery, WCL, having thickness of about 17m, 2nd lift depillaring was reportedly completed in the year 2001. Till 2009, no activity was undertaken as the areas were known cases of poor stowing and in some areas 'no stowing' was done due to many technical and some non-Technical reasons. At some worst places, the roof collapses exposed even the sandstone roof The study, with an aim to find a solution and as described briefly in this paper, has assessed the associated risks, overlying roof strata and the general regional stability of the mine and also reasons for those. The low block safety factor contours in simulated models of the mine suggested the expected high rock load to be supported that was found unpractical to execute. Moreover, the re-supporting exercises would call for additional risk to men and machine and might not be feasible technically as well as economically. To provide an alternative to the mine life and also to provide ingress and egress to the dip-side coal reserves, it was recommended to drive at least two sets of galleries in coal, suitably located keeping the sandstone or the competent coal (if weak shale/weathered sandstone is encountered) in roof of these galleries. Subsequently depillaring of the developed coal reserves, but hitherto located inaccessibly at dip-side of main dip at the moment, may then be taken up. The Indian inspectorate supported the recommendations by CSIR-CIMFR and the mine has recently started implementing the same.

Journal article

Singh DR, Mishra AK, Agrawal H, Manna Cet al., 2016, Analysis of un-tensioned fully grouted rock bolt : A case study, International Conference on Recent Advances in Rock Engineering (RARE), Publisher: ATLANTIS PRESS, Pages: 110-117, ISSN: 2352-5401

Conference paper

Satyendra K S, Agrawal H, Singh AP, 2016, Rib geomechanics: Its impacts in coal pillar extraction, Recent Advances in Rock Engineering (RARE 2016), Publisher: Atlantis Press

Conference paper

Agrawal H, Singh SK, Mandal PK, Singh APet al., 2015, 3-Dimensional numerical modelling: An effective enabler for CM deployment in coal seams, Journal of Mines, Metals and Fuels, Vol: 63, Pages: 111-118, ISSN: 0022-2755

Continuous miner (CM) is deployed worldover for both development and depillaring in coal seams. Compared to conventional bord and pillar (B&P) workings, the workings with CM deployment are generically of higher dimensions i.e., of wider gallery (6.0 or more) and, as the case may be, of enhanced (more than 3 m, the statutory) height, may be from very start of the operation. Understandably, the CM deployment is associated with faster rate of development advance and also swifter retreat during depillaring. Roof bolts (resin-grouted primarily) are widely used support system as an effective and economical way with CM deployment. In India, designers have now started considering the option of mobile roof supports. CM deployment has demanded a paradigm shift in understanding and assessing the related ground control problems and the parameters which are dominant here, have not been given due importance while developing empirical norms/formulations, the latter mostly in case of conventional B&P workings. Furthermore, rocks are idiosyncratic in nature. Empirical normsare condemned to be site-specific or limited to the range-specific of considered parameters. In such situation, numerical modelling provides researchers a handy tool to assess the stability of the workings and to design support, linking with suitable support safety factor (SSF). It is possible to establish a methodology to undertake the modelling so that CM deployment, established mainly in Australia, USA and South Africa may take up the gruntlet in underground coal mining. This paper describes, in brief, about the aspects of numerical modelling, calculations of rock loads, estimation of block safety factor contours and finally the execution of design parameters and geometry in a demonstrative case study.

Journal article

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