Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries,although there are critical research gaps that remain unfilled.In this paper,numer...Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries,although there are critical research gaps that remain unfilled.In this paper,numerical simulation is conducted on Gosford sandstone to investigate the borehole breakout and its associated borehole size effect,including temperature influence.The discrete element method(DEM)model shows that the borehole breakout angular span is constant after the initial formation,whereas its depth propagates along the minimum horizontal stress direction.This indicates that the breakout angular span is a reliable parameter for horizontal stress estimation.The borehole size effect simulations illustrated the importance of borehole size on breakout geometries in which smaller borehole size leads to higher breakout initiation stress as well as the stress re-distribution from borehole wall outwards through micro-cracking.This implies that the stress may be averaged over a distance around the borehole and breakout initiation occurs at the borehole wall rather than some distance into the rock.In addition,the numerical simulation incorporated the thermal effect which is widely encountered in deep geothermal wells.Based on the results,the higher temperature led to lower breakout initiation stress with same borehole size,and more proportion of shear cracks was generated under higher temperature.This indicates that the temperature might contribute to the micro-fracturing mode and hence influences the horizontal stress estimation results from borehole breakout geometries.Numerical simulation showed that breakout shape and dimensions changed considerably under high stress and high temperature conditions,suggesting that the temperature may need to be considered for breakout stress analysis in deep locations.展开更多
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...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 fuid 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 ofgroundwaterdepressurisation.展开更多
基金The work reported here is funded by Australian Coal Industry’s Research Program(ACARP)grant no.C26063.
文摘Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries,although there are critical research gaps that remain unfilled.In this paper,numerical simulation is conducted on Gosford sandstone to investigate the borehole breakout and its associated borehole size effect,including temperature influence.The discrete element method(DEM)model shows that the borehole breakout angular span is constant after the initial formation,whereas its depth propagates along the minimum horizontal stress direction.This indicates that the breakout angular span is a reliable parameter for horizontal stress estimation.The borehole size effect simulations illustrated the importance of borehole size on breakout geometries in which smaller borehole size leads to higher breakout initiation stress as well as the stress re-distribution from borehole wall outwards through micro-cracking.This implies that the stress may be averaged over a distance around the borehole and breakout initiation occurs at the borehole wall rather than some distance into the rock.In addition,the numerical simulation incorporated the thermal effect which is widely encountered in deep geothermal wells.Based on the results,the higher temperature led to lower breakout initiation stress with same borehole size,and more proportion of shear cracks was generated under higher temperature.This indicates that the temperature might contribute to the micro-fracturing mode and hence influences the horizontal stress estimation results from borehole breakout geometries.Numerical simulation showed that breakout shape and dimensions changed considerably under high stress and high temperature conditions,suggesting that the temperature may need to be considered for breakout stress analysis in deep locations.
文摘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 fuid 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 ofgroundwaterdepressurisation.
