Brittleness is pivotal in predicting shale reservoir quality and designing hydraulic fracturing strategies.However,intricate diagenetic environment of shale,characterized by distinct bedding structures,challenges the ...Brittleness is pivotal in predicting shale reservoir quality and designing hydraulic fracturing strategies.However,intricate diagenetic environment of shale,characterized by distinct bedding structures,challenges the isotropic-based brittleness assessment methods.This study introduces a new quantitative approach to assess shale brittleness anisotropy,integrating anisotro pic elastic responses and tensile fracturing mechanisms.The proposed model effectively reduces uncertainty in the causal relationship between Young's modulus and brittle failure.Comprehensive experimental validation encompassed 18samples from six groups of Chang 7 terrestrial shale in Ordos Basin.The optimal anisotropic tensile strength criterion(N-Z criterion,error<5%)was identified,enhancing the theoretical accuracy of the proposed model.Comparative experimental results demonstrate that the model adeptly predicts brittleness strength and directional variation characteristics across variations in mineral type,content and microstructure,underscoring its effectiveness.Additionally,theoretical predictions on shale samples with different organic matter reveal that brittleness strength and its anisotropy across varying OM are not monotonously decreasing.The research highlights that brittleness characteristics are influenced by both mineral type/content and microstructural distribution.Notably,the prevalence of isotropic brittle minerals is the primary determinant of brittleness strength,positively correlated.Conversely,ductile mineral conte nt(striped skeletal support-type OM and clay)negatively corre lates with brittlene ss strength,acting as se condary controlling factors.The impact of pore-filled OM on brittleness appears negligible.Rock physical modeling base d on equivalent media theory for shale with pore-filled and/or striped OM further elucidates the mechanisms driving these variations.These findings attach great importance in assessment of terrestrial shale geological and engineering"sweet-spots".展开更多
Microcosmic details of pore structure are the essential factors affecting the elastic properties of tight sandstone reservoirs,while the relationships in between are still incompletely clear due to the fact that quant...Microcosmic details of pore structure are the essential factors affecting the elastic properties of tight sandstone reservoirs,while the relationships in between are still incompletely clear due to the fact that quantitative or semi-quantitative experiments are hard to achieve.Here,three sets of tight sandstone samples from the Junggar Basin are selected elaborately based on casting thin sections,XRD detection,and petro-physical measurement,and each set is characterized by a single varied microcosmic factor(pore connectedness,pore type,and grain size)of the pore structure.An ultrasonic pulse transmission technique is conducted to study the response of elastic properties to the varied microcosmic details of pore structure in the situation of different pore fluid(gas,brine,and oil)saturation and confining pressure.Observations show samples with less connectedness,inter-granular dominant pores,and smaller grain size showed greater velocities in normal conditions.Vpis more sensitive to the variations of pore type,while Vsis more sensitive to the variations of grain size.Samples with better connectedness at fluid saturation(oil or brine)show greater sensitivity to the confining pressure than those with gas saturation with a growth rate of 6.9%-11.9%,and the sensitivity is more likely controlled by connectedness.The pore types(inter-granular or intra-granular)can be distinguished by the sensitivity of velocities to the variation of pore fluid at high confining pressure(>60 MPa).The samples with small grain sizes tend to be more sensitive to the variations of confining pressure.With this knowledge,we can semi-quantitatively distinguish the complex pore structures with different fluids by the variation of elastic properties,which can help improve the precision of seismic reservoir prediction for tight sandstone reservoirs.展开更多
Understanding the quantitative responses of anisotropic dynamic properties in organic-rich shale with different kerogen content(KC)is of great significance in hydrocarbon exploration and development.Conducting control...Understanding the quantitative responses of anisotropic dynamic properties in organic-rich shale with different kerogen content(KC)is of great significance in hydrocarbon exploration and development.Conducting controlled experiments with a single variable is challenging for natural shales due to their high variations in components,diagenesis conditions,or pore fluid.We employed the hot-pressing technique to construct 11 well-controlled artificial shale with varying KC.These artificial shale samples were successive machined into prismatic shape for ultrasonic measurements along different directions.Observations revealed bedding perpendicular P-wave velocities are more sensitive to the increasing KC than bedding paralleling velocities due to the preferential alignments of kerogen.All elastic stiffnesses except C_(13)are generally decreasing with the increasing KC,the variation of C_(1) and C_(33)on kerogen content are more sensitive than those of C_(44)and C_(66).Apparent dynamic mechanical parameters(v and E)were found to have linear correlation with the true ones from complete anisotropic equations independent of KC,which hold value towards the interpretation of well logs consistently across formations,Anisotropic mechanical parameters(ΔE and brittlenessΔB)tend to decrease with the reducing KC,withΔB showing great sensitivity to KC variations.In the range of low KC(<10%),the V_(P)/V_(S) ratio demonstrated a linearly negative correlation with KC,and the V_(P)/V_(S) ratio magnitude of less than 1.75may serve as a significant characterization for highly organic-rich(>10%)shale,compilation of data from natural organic rich-shales globally verified the similar systematic relationships that can be empirically used to predict the fraction of KC in shales.展开更多
基金supported by the National Natural Science Foundation of China(42274175)Sichuan Provincial Joint Fund Project for Science,Technology and Education(2025NSFSC2035)Innovative Experimental Project at Institutions of Higher Education in Sichuan Province(Advanced Quantitative Rock Physics Investigations on the"Acoustic,Electrical,and Mechanical"Characte ristics of Unco nventional Reservoirs Subjected to Extre meHigh Temperature and High Pressure Environments)。
文摘Brittleness is pivotal in predicting shale reservoir quality and designing hydraulic fracturing strategies.However,intricate diagenetic environment of shale,characterized by distinct bedding structures,challenges the isotropic-based brittleness assessment methods.This study introduces a new quantitative approach to assess shale brittleness anisotropy,integrating anisotro pic elastic responses and tensile fracturing mechanisms.The proposed model effectively reduces uncertainty in the causal relationship between Young's modulus and brittle failure.Comprehensive experimental validation encompassed 18samples from six groups of Chang 7 terrestrial shale in Ordos Basin.The optimal anisotropic tensile strength criterion(N-Z criterion,error<5%)was identified,enhancing the theoretical accuracy of the proposed model.Comparative experimental results demonstrate that the model adeptly predicts brittleness strength and directional variation characteristics across variations in mineral type,content and microstructure,underscoring its effectiveness.Additionally,theoretical predictions on shale samples with different organic matter reveal that brittleness strength and its anisotropy across varying OM are not monotonously decreasing.The research highlights that brittleness characteristics are influenced by both mineral type/content and microstructural distribution.Notably,the prevalence of isotropic brittle minerals is the primary determinant of brittleness strength,positively correlated.Conversely,ductile mineral conte nt(striped skeletal support-type OM and clay)negatively corre lates with brittlene ss strength,acting as se condary controlling factors.The impact of pore-filled OM on brittleness appears negligible.Rock physical modeling base d on equivalent media theory for shale with pore-filled and/or striped OM further elucidates the mechanisms driving these variations.These findings attach great importance in assessment of terrestrial shale geological and engineering"sweet-spots".
基金supported by the Open Fund(PLC2020002,PLC20190507)of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Chengdu University of Technology)National Natural Science Foundation of China(42004112,42274175,42030812,41974160)+1 种基金sponsored by Special projects of local science and technology development guided by the central government in Sichuan(2021ZYD0030)Natural Science Foundation of Sichuan Province(23NSFSC5311)
文摘Microcosmic details of pore structure are the essential factors affecting the elastic properties of tight sandstone reservoirs,while the relationships in between are still incompletely clear due to the fact that quantitative or semi-quantitative experiments are hard to achieve.Here,three sets of tight sandstone samples from the Junggar Basin are selected elaborately based on casting thin sections,XRD detection,and petro-physical measurement,and each set is characterized by a single varied microcosmic factor(pore connectedness,pore type,and grain size)of the pore structure.An ultrasonic pulse transmission technique is conducted to study the response of elastic properties to the varied microcosmic details of pore structure in the situation of different pore fluid(gas,brine,and oil)saturation and confining pressure.Observations show samples with less connectedness,inter-granular dominant pores,and smaller grain size showed greater velocities in normal conditions.Vpis more sensitive to the variations of pore type,while Vsis more sensitive to the variations of grain size.Samples with better connectedness at fluid saturation(oil or brine)show greater sensitivity to the confining pressure than those with gas saturation with a growth rate of 6.9%-11.9%,and the sensitivity is more likely controlled by connectedness.The pore types(inter-granular or intra-granular)can be distinguished by the sensitivity of velocities to the variation of pore fluid at high confining pressure(>60 MPa).The samples with small grain sizes tend to be more sensitive to the variations of confining pressure.With this knowledge,we can semi-quantitatively distinguish the complex pore structures with different fluids by the variation of elastic properties,which can help improve the precision of seismic reservoir prediction for tight sandstone reservoirs.
基金supported by the National Natural Science Foundation of China(42004112,42274175,42030812,41974160)Natural Science Foundation of Sichuan Province(2023NSFSC0764)。
文摘Understanding the quantitative responses of anisotropic dynamic properties in organic-rich shale with different kerogen content(KC)is of great significance in hydrocarbon exploration and development.Conducting controlled experiments with a single variable is challenging for natural shales due to their high variations in components,diagenesis conditions,or pore fluid.We employed the hot-pressing technique to construct 11 well-controlled artificial shale with varying KC.These artificial shale samples were successive machined into prismatic shape for ultrasonic measurements along different directions.Observations revealed bedding perpendicular P-wave velocities are more sensitive to the increasing KC than bedding paralleling velocities due to the preferential alignments of kerogen.All elastic stiffnesses except C_(13)are generally decreasing with the increasing KC,the variation of C_(1) and C_(33)on kerogen content are more sensitive than those of C_(44)and C_(66).Apparent dynamic mechanical parameters(v and E)were found to have linear correlation with the true ones from complete anisotropic equations independent of KC,which hold value towards the interpretation of well logs consistently across formations,Anisotropic mechanical parameters(ΔE and brittlenessΔB)tend to decrease with the reducing KC,withΔB showing great sensitivity to KC variations.In the range of low KC(<10%),the V_(P)/V_(S) ratio demonstrated a linearly negative correlation with KC,and the V_(P)/V_(S) ratio magnitude of less than 1.75may serve as a significant characterization for highly organic-rich(>10%)shale,compilation of data from natural organic rich-shales globally verified the similar systematic relationships that can be empirically used to predict the fraction of KC in shales.
