Compaction and silicon cementation are the dominant processes reducing porosity and permeability in quartzose sandstones during diagenesis. Despite the wealth of information about quartz cementation, there are still u...Compaction and silicon cementation are the dominant processes reducing porosity and permeability in quartzose sandstones during diagenesis. Despite the wealth of information about quartz cementation, there are still unanswered questions related to mechanisms of growth of quartz cement and the diagenesis processes. In this study we present an electron backscatter diffraction （EBSD） analysis, combined with optics and cathodoluminescence （CL） information, for the quartz sandstones from the Upper Triassic Xujiahe Formation of Sichuan Basin, in order to reveal the microstructural and crystallographic features of the silica cementation and detrital grain during the compaction. The EBSD is a crucial technique to provide essential crystallographic data on the quartz grain and its cement. Quartz cement is shown to be syntaxial to its host quartz grain. EBSD data-based orientation maps show dauphin6 twinning and low angle boundary to be common in the host grains and quartz cement of the samples. The dauphin6 twins occurred in grain-grain contacts and in cement-crystal boundaries, and commonly crossed grain cement boundaries. These features indicate that there may be two types of dauphin6 twins, one inherited twins from the source area and the other developed by compaction-induced grain boundary deformation. These investigations suggest that strong mechanical compaction may occur after and/or during quartz cement growth in the later diagenesis of the Xujiahe sandstones. EBSD has a capability of revealing microstructural information and regarding mechanisms of diagenesis crystal growth in quartzose sandstones.展开更多
The amount of inert quartz tailing used in concrete construction is limited due to the low strength development of cementitious materials that may be caused by the quartz tailing. We manage to increase the strength of...The amount of inert quartz tailing used in concrete construction is limited due to the low strength development of cementitious materials that may be caused by the quartz tailing. We manage to increase the strength of blended cement by modifying quartz tailing through solid-phase reaction of quartz tailing with carbide slag at high temperature. The mineral composition and morphology of the modified quartz tailing were examined by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The mechanical properties and microstructure of blended cement mortars containing modified quartz tailing were investigated. Results showed that the strengths of blended cement mortars containing modified quartz tailing were close to those of the corresponding blended cement mortars containing quartz tailing at early age of 3 d, but increased significantly to be similar to that of plain Portland cement mortars at late ages of 90 d. This is attributed to the microstructure densification and the enhancement of interface between quartz tailing and cement paste due to the hydration of b-C_2 S surface layer on modified quartz tailing.展开更多
The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study em...The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.展开更多
Discoveries of deep high-quality carbonate reservoirs challenged the general understanding on the evolution of porosity decreasing with depth.New mechanisms of pore generation and preservation in the deep realm requir...Discoveries of deep high-quality carbonate reservoirs challenged the general understanding on the evolution of porosity decreasing with depth.New mechanisms of pore generation and preservation in the deep realm require to be proposed.Dolostones in the Feixianguan and Dengying Formations experienced maximum depths in excess of 8000 m,but still retained high porosity.Petrographic observation and homogenization temperatures help to identify products of deep fluid-rock interactions,visual and experimental porosity were used to quantify reservoir effects,the distribution of products finally being plotted to unravel the mechanisms.Th data reveal that thermochemical sulfate reduction(TSR),burial dissolution and quartz cementation are typical deep fluid-rock interactions.The SO_(4)^(2-)of residual porewater sourced from the evaporative dolomitizing fluid was supplied for TSR in the hydrocarbon column,the TSR-inducing calcite cements were homogeneously dispersed in the hydrocarbon column.Quartz cementation was caused by the increasing acidity and Si-rich residual porewater in the oil column.Burial dissolution is forced by organic acid and limited in oil-water contact.This study suggests that seal and source rocks not only play important roles in hydrocarbon accumulation,but also have a general control on the deep fluid-rock interactions and porosity evolution in the deep burial realm.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos. 40802050,40872149)China Postdoctoral Science Foundation (Grant No. 20070420065)
文摘Compaction and silicon cementation are the dominant processes reducing porosity and permeability in quartzose sandstones during diagenesis. Despite the wealth of information about quartz cementation, there are still unanswered questions related to mechanisms of growth of quartz cement and the diagenesis processes. In this study we present an electron backscatter diffraction （EBSD） analysis, combined with optics and cathodoluminescence （CL） information, for the quartz sandstones from the Upper Triassic Xujiahe Formation of Sichuan Basin, in order to reveal the microstructural and crystallographic features of the silica cementation and detrital grain during the compaction. The EBSD is a crucial technique to provide essential crystallographic data on the quartz grain and its cement. Quartz cement is shown to be syntaxial to its host quartz grain. EBSD data-based orientation maps show dauphin6 twinning and low angle boundary to be common in the host grains and quartz cement of the samples. The dauphin6 twins occurred in grain-grain contacts and in cement-crystal boundaries, and commonly crossed grain cement boundaries. These features indicate that there may be two types of dauphin6 twins, one inherited twins from the source area and the other developed by compaction-induced grain boundary deformation. These investigations suggest that strong mechanical compaction may occur after and/or during quartz cement growth in the later diagenesis of the Xujiahe sandstones. EBSD has a capability of revealing microstructural information and regarding mechanisms of diagenesis crystal growth in quartzose sandstones.
基金Funded by the Program for Changjiang Scholars and Innovative Research Team in University(PCSIRT)(No.IRT1146)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)+4 种基金Scientific Research Foundation of Education Department of Anhui Province-(No.KJ2013A257)the State Key Laboratory of MaterialsOriented Chemical Engineering(No.KL12-12)National Natural Science Foundation of China(Nos.51608004,51578004)Opening Foundation of State Key Laboratory of High Performance Civil Engineering Materials(No.2014CEM010)Natural Science Foundation of the Anhui Higher Education Institution(No.KJ2016A818)
文摘The amount of inert quartz tailing used in concrete construction is limited due to the low strength development of cementitious materials that may be caused by the quartz tailing. We manage to increase the strength of blended cement by modifying quartz tailing through solid-phase reaction of quartz tailing with carbide slag at high temperature. The mineral composition and morphology of the modified quartz tailing were examined by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The mechanical properties and microstructure of blended cement mortars containing modified quartz tailing were investigated. Results showed that the strengths of blended cement mortars containing modified quartz tailing were close to those of the corresponding blended cement mortars containing quartz tailing at early age of 3 d, but increased significantly to be similar to that of plain Portland cement mortars at late ages of 90 d. This is attributed to the microstructure densification and the enhancement of interface between quartz tailing and cement paste due to the hydration of b-C_2 S surface layer on modified quartz tailing.
基金the Helmholtz association for funding the main parts of the modeling and simulation research work under the program“MTET:38.04.04”。
文摘The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.
基金financially supported by the National Key R&D Program of China(Grant No.2017YFC0603104)the National Natural Science Foundation of China(Grant No.42002170)。
文摘Discoveries of deep high-quality carbonate reservoirs challenged the general understanding on the evolution of porosity decreasing with depth.New mechanisms of pore generation and preservation in the deep realm require to be proposed.Dolostones in the Feixianguan and Dengying Formations experienced maximum depths in excess of 8000 m,but still retained high porosity.Petrographic observation and homogenization temperatures help to identify products of deep fluid-rock interactions,visual and experimental porosity were used to quantify reservoir effects,the distribution of products finally being plotted to unravel the mechanisms.Th data reveal that thermochemical sulfate reduction(TSR),burial dissolution and quartz cementation are typical deep fluid-rock interactions.The SO_(4)^(2-)of residual porewater sourced from the evaporative dolomitizing fluid was supplied for TSR in the hydrocarbon column,the TSR-inducing calcite cements were homogeneously dispersed in the hydrocarbon column.Quartz cementation was caused by the increasing acidity and Si-rich residual porewater in the oil column.Burial dissolution is forced by organic acid and limited in oil-water contact.This study suggests that seal and source rocks not only play important roles in hydrocarbon accumulation,but also have a general control on the deep fluid-rock interactions and porosity evolution in the deep burial realm.
