Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter conten...Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter content, bedding planes, natural fractures, porosity and stress regime among others), external factors like wellbore orientation and stimulation design play a role. In this study, we present a series of true triaxial hydraulic fracturing experiments conducted on Lushan shale to investigate the interplay of internal factors (bedding, natural fractures and in situ stress) and external factors (wellbore orientation) on the growth process of fracture networks in cubic specimens of 200 mm in length. We observe relatively low breakdown pressure and fracture propagation pressure as the wellbore orientation and/or the maximum in situ stress is subparallel to the shale bedding plane. The wellbore orientation has a more prominent effect on the breakdown pressure, but its effect is tapered with increasing angle of bedding inclination. The shale breakdown is followed by an abrupt response in sample displacement, which reflects the stimulated fracture volume. Based on fluid tracer analysis, the morphology of hydraulic fractures (HF) is divided into four categories. Among the categories, activation of bedding planes (bedding failure, BF) and natural fractures (NF) significantly increase bifurcation and fractured areas. Under the same stress regime, a horizontal wellbore is more favorable to enhance the complexity of hydraulic fracture networks. This is attributed to the relatively large surface area in contact with the bedding plane for the horizontal borehole compared to the case with a vertical wellbore. These findings provide important references for hydraulic fracturing design in shale reservoirs.展开更多
New natural rubber(NR)/nitrile butadiene rubber(NBR)/hindered phenol(AO-80)composites with high-damping properties were prepared in this study.The morpholo-gical,structural,and mechanical properties were characterized...New natural rubber(NR)/nitrile butadiene rubber(NBR)/hindered phenol(AO-80)composites with high-damping properties were prepared in this study.The morpholo-gical,structural,and mechanical properties were characterized by atomic force micro-scopy(AFM),polarized Fourier transform infrared spectrometer(FTIR),dynamic mechanical thermal analyzer(DMTA),and a tensile tester.Each composite consisted of two phases:the NR phase and the NBR/AO-80 phase.There was partial compat-ibility between the NR phase and the NBR/AO-80 phase,and the NR/NBR/AO-80(50/50/20)composite exhibited a co-continuous morphology.Strain-induced crystal-lization occurred in the NR phase at strains higher than 200%,and strain-induced orientation appeared in the NBR/AO-80 phase with the increase of strain from 100%to 500%.The composites had a special stress–strain behavior and mechanical properties because of the simultaneous strain-induced orientation and strain-induced crystalliza-tion.In the working temperature range of a seismic isolation bearing,the composites(especially the NR/NBR/AO-80(50/50/20)composite)presented a high loss factor,high area of loss peak(TA),and high hysteresis energy.Therefore,the NR/NBR/AO-80 rubber composites are expected to have important application as a high-perfor-mance damping material for rubber bearing.展开更多
A mixture of NaOH and Na2SO3 was used in modification of banana stem fibers (BSF). Unidirectional BSF reinforced natural rubber (NR) lamina composites were made using compression moulding method. The results of the te...A mixture of NaOH and Na2SO3 was used in modification of banana stem fibers (BSF). Unidirectional BSF reinforced natural rubber (NR) lamina composites were made using compression moulding method. The results of the tensile loading in 0°, 45° and 90° to the fiber directions of the composite with fiber mass fraction of 30% were studied. Surface modification of the BSF with a mixture of 4% NaOH and 2% Na2SO3 increased the tensile strength and elastic modulus of the composite to 4.03 MPa and 147.34 MPa respectively from 3.12 MPa and 84.30 MPa of the untreated. Variation in properties due to fiber orintations was observed indicating a higher value of properties in the 0° fiber orientation than in 45° and 90° directions. The result of scanning electron microscope (SEM) micrographs of the surfaces of the fibers indicted an improvement in bonding of the fiber bundles prior to lamination with natural rubber as a result of surface treatment which resulted in its higher tensile strength.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52064006 and 52004072)It was.also supported by the program(Grant No.202006050112)of China Scholarship Council(CSC)for the first author's visit at the Helm-holtz Centre Potsdam,GFZ German Research Centre for Geosciences.
文摘Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter content, bedding planes, natural fractures, porosity and stress regime among others), external factors like wellbore orientation and stimulation design play a role. In this study, we present a series of true triaxial hydraulic fracturing experiments conducted on Lushan shale to investigate the interplay of internal factors (bedding, natural fractures and in situ stress) and external factors (wellbore orientation) on the growth process of fracture networks in cubic specimens of 200 mm in length. We observe relatively low breakdown pressure and fracture propagation pressure as the wellbore orientation and/or the maximum in situ stress is subparallel to the shale bedding plane. The wellbore orientation has a more prominent effect on the breakdown pressure, but its effect is tapered with increasing angle of bedding inclination. The shale breakdown is followed by an abrupt response in sample displacement, which reflects the stimulated fracture volume. Based on fluid tracer analysis, the morphology of hydraulic fractures (HF) is divided into four categories. Among the categories, activation of bedding planes (bedding failure, BF) and natural fractures (NF) significantly increase bifurcation and fractured areas. Under the same stress regime, a horizontal wellbore is more favorable to enhance the complexity of hydraulic fracture networks. This is attributed to the relatively large surface area in contact with the bedding plane for the horizontal borehole compared to the case with a vertical wellbore. These findings provide important references for hydraulic fracturing design in shale reservoirs.
基金This work was supported by the National Natural Science Foundation of China[grant number 51320105012],[grant number 51221002],[grant number 51103006],[grant number 51373010].
文摘New natural rubber(NR)/nitrile butadiene rubber(NBR)/hindered phenol(AO-80)composites with high-damping properties were prepared in this study.The morpholo-gical,structural,and mechanical properties were characterized by atomic force micro-scopy(AFM),polarized Fourier transform infrared spectrometer(FTIR),dynamic mechanical thermal analyzer(DMTA),and a tensile tester.Each composite consisted of two phases:the NR phase and the NBR/AO-80 phase.There was partial compat-ibility between the NR phase and the NBR/AO-80 phase,and the NR/NBR/AO-80(50/50/20)composite exhibited a co-continuous morphology.Strain-induced crystal-lization occurred in the NR phase at strains higher than 200%,and strain-induced orientation appeared in the NBR/AO-80 phase with the increase of strain from 100%to 500%.The composites had a special stress–strain behavior and mechanical properties because of the simultaneous strain-induced orientation and strain-induced crystalliza-tion.In the working temperature range of a seismic isolation bearing,the composites(especially the NR/NBR/AO-80(50/50/20)composite)presented a high loss factor,high area of loss peak(TA),and high hysteresis energy.Therefore,the NR/NBR/AO-80 rubber composites are expected to have important application as a high-perfor-mance damping material for rubber bearing.
文摘A mixture of NaOH and Na2SO3 was used in modification of banana stem fibers (BSF). Unidirectional BSF reinforced natural rubber (NR) lamina composites were made using compression moulding method. The results of the tensile loading in 0°, 45° and 90° to the fiber directions of the composite with fiber mass fraction of 30% were studied. Surface modification of the BSF with a mixture of 4% NaOH and 2% Na2SO3 increased the tensile strength and elastic modulus of the composite to 4.03 MPa and 147.34 MPa respectively from 3.12 MPa and 84.30 MPa of the untreated. Variation in properties due to fiber orintations was observed indicating a higher value of properties in the 0° fiber orientation than in 45° and 90° directions. The result of scanning electron microscope (SEM) micrographs of the surfaces of the fibers indicted an improvement in bonding of the fiber bundles prior to lamination with natural rubber as a result of surface treatment which resulted in its higher tensile strength.
