In shale gas reservoir stimulation,proppants are essential for sustaining fracture conductivity.However,increasing closing stress causes proppants to embed into the rock matrix,leading to a progressive decline in frac...In shale gas reservoir stimulation,proppants are essential for sustaining fracture conductivity.However,increasing closing stress causes proppants to embed into the rock matrix,leading to a progressive decline in fracture permeability and conductivity.Furthermore,rock creep contributes to long-term reductions in fracture performance.To elucidate the combined effects of proppant embedding and rock creep on sustained conductivity,this study conducted controlled experiments examining conductivity decay in propped fractures under varying closing stresses,explicitly accounting for both mechanisms.An embedded discrete fracture model was developed to simulate reservoir production under different conductivity decay scenarios,while evaluating the influence of proppant parameters on fracture performance.The results demonstrate that fracture conductivity diminishes rapidly with increasing stress,yet at 50 MPa,the decline becomes less pronounced.Simulated production profiles show strong agreement with actual gas well data,confirming the model’s accuracy and predictive capability.These findings suggest that employing a high proppant concentration with smaller particle size(5 kg/m^(2),70/140 mesh)is effective for maintaining long-term fracture conductivity and enhancing shale gas recovery.This study provides a rigorous framework for optimizing proppant selection and designing stimulation strategies that maximize reservoir performance over time.展开更多
The characteristics of wintertime volatile organic compounds(VOCs)in the North China Plain(NCP)region are complicated and remain obscure.VOC measurements were conducted by a proton transfer reaction time-of-flight mas...The characteristics of wintertime volatile organic compounds(VOCs)in the North China Plain(NCP)region are complicated and remain obscure.VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer(PTR-ToF-MS)at a rural site in the NCP from November to December 2018.Uncalibrated ions measured by PTRToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector(GC-MS/FID).The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions,the secondary formation of oxygenated VOCs(OVOCs)is non-negligible in the wintertime,i.e.,OVOCs accounts for 42%±7%in the total VOCs(151.3±75.6 ppbV).We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes.The chemical changes of organic carbon in a pollution accumulation period were investigated,which suggests an essential role of fragmentation reactions for large,chemically reduced compounds during the heavy-polluted stage in wintertime pollution.The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of“coal to gas”strategies in curbing air pollutants.The high abundances of some key species(e.g.oxygenated aromatics)indicate the strong emissions of coal combustion in wintertime of NCP.The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52204051,52304046).
文摘In shale gas reservoir stimulation,proppants are essential for sustaining fracture conductivity.However,increasing closing stress causes proppants to embed into the rock matrix,leading to a progressive decline in fracture permeability and conductivity.Furthermore,rock creep contributes to long-term reductions in fracture performance.To elucidate the combined effects of proppant embedding and rock creep on sustained conductivity,this study conducted controlled experiments examining conductivity decay in propped fractures under varying closing stresses,explicitly accounting for both mechanisms.An embedded discrete fracture model was developed to simulate reservoir production under different conductivity decay scenarios,while evaluating the influence of proppant parameters on fracture performance.The results demonstrate that fracture conductivity diminishes rapidly with increasing stress,yet at 50 MPa,the decline becomes less pronounced.Simulated production profiles show strong agreement with actual gas well data,confirming the model’s accuracy and predictive capability.These findings suggest that employing a high proppant concentration with smaller particle size(5 kg/m^(2),70/140 mesh)is effective for maintaining long-term fracture conductivity and enhancing shale gas recovery.This study provides a rigorous framework for optimizing proppant selection and designing stimulation strategies that maximize reservoir performance over time.
基金supported by the National Key R&D Plan of China(No.2019YFE0106300)the National Natural Science Foundation of China(No.41877302)+3 种基金Guangdong Natural Science Funds for Distinguished Young Scholar(No.2018B030306037)Key-Area Research and Development Program of Guangdong Province(No.2019B110206001)Guangdong Innovative and Entrepreneurial Research Team Program(No.2016ZT06N263)supported by Special Fund Project for Science and Technology Innovation Strategy of Guangdong Province(No.2019B121205004)
文摘The characteristics of wintertime volatile organic compounds(VOCs)in the North China Plain(NCP)region are complicated and remain obscure.VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer(PTR-ToF-MS)at a rural site in the NCP from November to December 2018.Uncalibrated ions measured by PTRToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector(GC-MS/FID).The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions,the secondary formation of oxygenated VOCs(OVOCs)is non-negligible in the wintertime,i.e.,OVOCs accounts for 42%±7%in the total VOCs(151.3±75.6 ppbV).We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes.The chemical changes of organic carbon in a pollution accumulation period were investigated,which suggests an essential role of fragmentation reactions for large,chemically reduced compounds during the heavy-polluted stage in wintertime pollution.The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of“coal to gas”strategies in curbing air pollutants.The high abundances of some key species(e.g.oxygenated aromatics)indicate the strong emissions of coal combustion in wintertime of NCP.The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.
