Shale reservoirs contain numerous bedding fractures,making the formation of complex fracture networks during fracturing a persistent technical challenge in evaluating shale fracture morphology.Distributed optical fibe...Shale reservoirs contain numerous bedding fractures,making the formation of complex fracture networks during fracturing a persistent technical challenge in evaluating shale fracture morphology.Distributed optical fiber sensing technology can effectively capture the process of fracture initiation and propagation,yet the evaluation method for the initiation and propagation of bedding fractures remains immature.This study integrates a distributed optical fiber sensing device based on optical frequency domain reflectometry(OFDR)with a large-scale true tri-axial fracturing physical simulation apparatus to conduct real-time monitoring experiments on shale samples from the Lianggaoshan Formation in the Sichuan Basin,where bedding is well-developed.The experimental results demonstrate that two bedding fractures in the shale sample initiated and propagated.The evolution characteristics of fiber-optic strain in a horizontal adjacent well,induced by the initiation and propagation of bedding fractures,are characterized by the appearance of a tensile strain convergence zone in the middle of the optical fiber,flanked by two compressive strain convergence zones.The initiation and propagation of the distal bedding fracture causes the fiber-optic strain in the horizontal adjacent well to superimpose,with the asymmetric propagation of the bedding fracture leading to an asymmetric tensile strain convergence zone in the optical fiber.Utilizing a finite element method coupled with a cohesive element approach,a forward model of fiber-optic strain in the horizontal adjacent well induced by the initiation and propagation of hydraulic fracturing bedding fractures was constructed.Numerical simulation analyses were conducted to evaluate the evolution of fiber-optic strain in the horizontal adjacent well,confirming the correctness of the observed evolution characteristics.The presence of a"wedge-shaped"tensile strain convergence zone in the fiber-optic strain waterfall plot,accompanied by two compressive strain convergence zones,indicates the initiation and propagation of bedding fractures during the fracturing process.These findings provide valuable insights for interpreting distributed fiber-optic data in shale fracturing field applications.展开更多
A self-designed full-diameter core experimental facility was used to evaluate the flow heterogeneity of bedding fractures at four radial directions under different closure pressures and injection rates,using full-diam...A self-designed full-diameter core experimental facility was used to evaluate the flow heterogeneity of bedding fractures at four radial directions under different closure pressures and injection rates,using full-diameter cores retaining original natural bedding fractures.The distribution morphology of bedding surface affects the conductivity of bedding fractures,and the flow capacity of bedding fractures in four radial directions varies greatly with the closure pressure and injection rate.The rougher the fracture surface,the greater the flow capacity varies with the closure pressure.For unsupported bedding fractures,the mean percentage error(MPE)of the conductivity in four radial directions increase gradually with the increase of the closure pressure.This phenomenon is especially prominent in deep rock samples.It is indicated that the flow heterogeneity of bedding fractures tends to increase with the closure pressure.When proppant is placed in the fracture,at a low closure pressure,due to the combined effects of self-support of rough fracture surface,proppant instability and uneven proppant placement,the flow heterogeneity is greater than that when proppant is not placed at the same closure pressure;however,with the increase of the closure pressure,the proppant becomes compact and stable,and the flow heterogeneity is mitigated gradually.展开更多
Bedding fractures are among the key factors affecting the production efficiency of shale oil and gas,but relatively little research has been conducted on the effectiveness of bedding fractures.Based on field outcrops ...Bedding fractures are among the key factors affecting the production efficiency of shale oil and gas,but relatively little research has been conducted on the effectiveness of bedding fractures.Based on field outcrops and drill cores from the Fuling area in the Sichuan Basin,this work discusses the development,filling,and opening characteristics of bedding fractures and their quantitative impact on physical properties.Multiple methods were employed,e.g.,immersion testing,wet illumination,high-power microscanning,imaging logging identification and experimental measurement.The results indicate that the highest density reaches 437 fractures per meter,with apertures less than 0.5µm being the majority.The average permeability of the shale samples with vertical bedding is 44.6 times that of the shale samples with parallel bedding,while the porosity exhibits less anisotropy.Many open bedding fractures with gas outlets in the core are shown by on-site immersion experiments and electron microscopy scanning experiments.Each dark stripe on the imaging logging map corresponds to a bedding fracture,and the thickness of the dark stripes corresponds to the aperture of the bedding fracture.There is no need to consider unfilled bedding fractures,as fractures filled with calcite veins and pyrite crystals can also become effective seepage channels because of the pores within the calcite veins and between the pyrite crystals.The utilization and transformation of bedding fractures during fracturing is one of the key steps in producing shale oil and gas.It is necessary to combine the in situ stress field,bedding fracture characteristics,and fracturability of shales to reasonably utilize bedding fractures to transform oil and gas reservoirs.展开更多
Core,thin section,conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag.Bedding parallel fractures are c...Core,thin section,conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag.Bedding parallel fractures are common in fine grained sedimentary rocks which are characterized by layered structures.Core and thin section analysis reveal that fractures in Lucaogou Formation include tectonic inclined fracture,bedding parallel fracture,and abnormal high pressure fracture.Bedding parallel fractures are abundant,but only minor amounts of them remain open,and most of them are partly to fully sealed by carbonate minerals(calcite)and bitumen.Bedding parallel fractures result in a rapid decrease in resistivity,and they are recognized on image logs to extend along bedding planes and have discontinuous surfaces due to partly-fully filled resistive carbonate minerals as well as late stage dissolution.A comprehensive interpretation of distribution of bedding parallel fractures is performed with green line,red line,yellow line and blue line representing bedding planes,induced fractures,resistive fractures,and open(bedding and inclined)fractures,respectively.The strike of bedding parallel fractures is coinciding with bedding planes.Bedding parallel fractures are closely associated with the amounts of bedding planes,and high density of bedding planes favor the formation of bedding parallel fractures.Alternating dark and bright layers have the most abundant bedding parallel fractures on the image logs,and the bedding parallel fractures are always associated with low resistivity zones.The results above may help optimize sweet spots in fine grained sedimentary rocks,and improve future fracturing design and optimize well spacing.展开更多
Chinaʼs continental shale exhibits favorable geological characteristics and substantial resource potential,yet oil recovery for natural energy extraction remains critically low.Investigating the mechanisms of hydrauli...Chinaʼs continental shale exhibits favorable geological characteristics and substantial resource potential,yet oil recovery for natural energy extraction remains critically low.Investigating the mechanisms of hydraulically induced bedding fracture to generate complex fracture networks in continental shale,and establishing effective flow systems,is of utmost importance.This study employs laboratory experiments and numerical simulations to investigate the flow capacity and percolation behavior of hydraulically induced bedding fractures by different fluids in full-diameter shale cores.Hydraulic stimulation using different fluids generates bedding plane fracture networks,establishing effective flow systems.Eroded and detached shale fragments support localized fractures,thereby increasing their opening and enhancing flow capacity.Cetyltrimethylammonium bromide(CTAB)solution and SiO2 solution reduce the hydration of the shale surface,preventing shale fragments from swelling and disintegrating,leading to more stable percolation behavior.Eroded and spalled shale fragments near the injection point are transported to farther locations,where they help support localized fractures.This process differs from conventional hydraulic fracturing.Under a constant injection rate,the velocity in the smaller flow paths near the closure is significantly higher than that in the main flow paths,leading to pronounced bypass flow behavior.This restricts the percolation of fluid during imbibition in shale cores.The results provide valuable insights into the mechanism of hydraulically induced bedding fracture in continental shale,offering guidance for the effective development of shale reservoirs.展开更多
CO_(2)injection in shale oil reservoirs has emerged as a promising technique for simultaneously achieving CO_(2)geological storage and enhancing shale oil recovery.This study investigates the potential of CO_(2)inject...CO_(2)injection in shale oil reservoirs has emerged as a promising technique for simultaneously achieving CO_(2)geological storage and enhancing shale oil recovery.This study investigates the potential of CO_(2)injection into shale oil reservoirs with natural fractures for carbon storage and enhanced oil recovery through a combination of experimental and numerical simulations.It focuses on the synergistic effects on carbon storage capacity and oil recovery efficiency.A series of CO_(2)injection experiments using online NMR T_(2)and stratified T_(2)technology were conducted to validate the feasibility of carbon storage and oil recovery in shale oil reservoirs.The shale samples consist of three distinct pore space systems:kerogen,inorganic matrix,and shale bedding fractures.A coupled multiscale-multiphase simulation model was developed to facilitate a comprehensive analysis of the underlying mechanisms.In the model,kerogen,inorganic matrix,and shale bedding fractures are defined as triple-continuum media.The model integrates the mechanisms of molecular diffusion,adsorption,and viscous flow to accurately represent the mass transport processes during CO_(2)injection in shale oil reservoirs.Within this framework,a series of mass transport partial differential equations were derived to describe the CO_(2)injection process.The finite element method was used to numerically solve these equations,and the proposed model was validated against experimental results.Sensitivity analyses yielded the following results:(1)The shale bedding fractures are not only key reservoir spaces for shale oil but also the key mass transfer channels for shale oil and CO_(2)during CO_(2)injection.Increasing the permeability of the shale bedding fractures can significantly improve oil recovery efficiency and CO_(2)adsorption amount.(2)The kerogen content and organic porosity have a significant impact on CO_(2)adsorption amount and shale oil recovery factor,respectively.(3)High production pressure is essential for maximizing carbon storage capacity.Simultaneously,increasing injection pressure can effectively enhance carbon storage and shale oil recovery.展开更多
The lithology, lithofacies, reservoir properties and shale oil enrichment model of the fine-grained sedimentary system in a lake basin with terrigenous clastics of large depression are studied taking the organic-rich ...The lithology, lithofacies, reservoir properties and shale oil enrichment model of the fine-grained sedimentary system in a lake basin with terrigenous clastics of large depression are studied taking the organic-rich shale in the first member of Cretaceous Qingshankou Formation(shortened as Qing 1 Member) in the Changling Sag, southern Songliao Basin as an example. A comprehensive analysis of mineralogy, thin section, test, log and drilling geologic data shows that lamellar shale with high TOC content of semi-deep lake to deep lake facies has higher hydrocarbon generation potential than the massive mudstone facies with medium TOC content, and has bedding-parallel fractures acting as effective reservoir space under over pressure. The sedimentary environments changing periodically and the undercurrent transport deposits in the outer delta front give rise to laminated shale area. The laminated shale with medium TOC content has higher hydrocarbon generation potential than the laminated shale with low TOC content, and the generated oil migrates a short distance to the sandy laminae to retain and accumulate in situ. Ultra-low permeability massive mudstone facies as the top and bottom seals, good preservation conditions, high pressure coefficient, and lamellar shale facies with high TOC are the conditions for "lamellation type" shale oil enrichment in some sequences and zones. The sequence and zone with laminated shale of medium TOC content in oil window and with micro-migration of expelled hydrocarbon are the condition for the enrichment of "lamination type" shale oil. The tight oil and "lamination type" shale oil are in contiguous distribution.展开更多
基金the financial support by National Natural Science Foundation of China(No.52334001)。
文摘Shale reservoirs contain numerous bedding fractures,making the formation of complex fracture networks during fracturing a persistent technical challenge in evaluating shale fracture morphology.Distributed optical fiber sensing technology can effectively capture the process of fracture initiation and propagation,yet the evaluation method for the initiation and propagation of bedding fractures remains immature.This study integrates a distributed optical fiber sensing device based on optical frequency domain reflectometry(OFDR)with a large-scale true tri-axial fracturing physical simulation apparatus to conduct real-time monitoring experiments on shale samples from the Lianggaoshan Formation in the Sichuan Basin,where bedding is well-developed.The experimental results demonstrate that two bedding fractures in the shale sample initiated and propagated.The evolution characteristics of fiber-optic strain in a horizontal adjacent well,induced by the initiation and propagation of bedding fractures,are characterized by the appearance of a tensile strain convergence zone in the middle of the optical fiber,flanked by two compressive strain convergence zones.The initiation and propagation of the distal bedding fracture causes the fiber-optic strain in the horizontal adjacent well to superimpose,with the asymmetric propagation of the bedding fracture leading to an asymmetric tensile strain convergence zone in the optical fiber.Utilizing a finite element method coupled with a cohesive element approach,a forward model of fiber-optic strain in the horizontal adjacent well induced by the initiation and propagation of hydraulic fracturing bedding fractures was constructed.Numerical simulation analyses were conducted to evaluate the evolution of fiber-optic strain in the horizontal adjacent well,confirming the correctness of the observed evolution characteristics.The presence of a"wedge-shaped"tensile strain convergence zone in the fiber-optic strain waterfall plot,accompanied by two compressive strain convergence zones,indicates the initiation and propagation of bedding fractures during the fracturing process.These findings provide valuable insights for interpreting distributed fiber-optic data in shale fracturing field applications.
基金Supported by National Natural Science Foundation of China Regional Innovation and Development Joint Fund(U19A2043)Project of PetroChina Chuanqing Drilling Engineering Co.,Ltd.(CQ2021B-39-Z2-4).
文摘A self-designed full-diameter core experimental facility was used to evaluate the flow heterogeneity of bedding fractures at four radial directions under different closure pressures and injection rates,using full-diameter cores retaining original natural bedding fractures.The distribution morphology of bedding surface affects the conductivity of bedding fractures,and the flow capacity of bedding fractures in four radial directions varies greatly with the closure pressure and injection rate.The rougher the fracture surface,the greater the flow capacity varies with the closure pressure.For unsupported bedding fractures,the mean percentage error(MPE)of the conductivity in four radial directions increase gradually with the increase of the closure pressure.This phenomenon is especially prominent in deep rock samples.It is indicated that the flow heterogeneity of bedding fractures tends to increase with the closure pressure.When proppant is placed in the fracture,at a low closure pressure,due to the combined effects of self-support of rough fracture surface,proppant instability and uneven proppant placement,the flow heterogeneity is greater than that when proppant is not placed at the same closure pressure;however,with the increase of the closure pressure,the proppant becomes compact and stable,and the flow heterogeneity is mitigated gradually.
基金sponsored by the China Postdoctoral Science Foundation(No.2021M703000):Formation mechanism of a compressive fracture network constrained by weak surfaces of shale bedding.
文摘Bedding fractures are among the key factors affecting the production efficiency of shale oil and gas,but relatively little research has been conducted on the effectiveness of bedding fractures.Based on field outcrops and drill cores from the Fuling area in the Sichuan Basin,this work discusses the development,filling,and opening characteristics of bedding fractures and their quantitative impact on physical properties.Multiple methods were employed,e.g.,immersion testing,wet illumination,high-power microscanning,imaging logging identification and experimental measurement.The results indicate that the highest density reaches 437 fractures per meter,with apertures less than 0.5µm being the majority.The average permeability of the shale samples with vertical bedding is 44.6 times that of the shale samples with parallel bedding,while the porosity exhibits less anisotropy.Many open bedding fractures with gas outlets in the core are shown by on-site immersion experiments and electron microscopy scanning experiments.Each dark stripe on the imaging logging map corresponds to a bedding fracture,and the thickness of the dark stripes corresponds to the aperture of the bedding fracture.There is no need to consider unfilled bedding fractures,as fractures filled with calcite veins and pyrite crystals can also become effective seepage channels because of the pores within the calcite veins and between the pyrite crystals.The utilization and transformation of bedding fractures during fracturing is one of the key steps in producing shale oil and gas.It is necessary to combine the in situ stress field,bedding fracture characteristics,and fracturability of shales to reasonably utilize bedding fractures to transform oil and gas reservoirs.
基金financially supported by the National Natural Science Foundation of China(No.42002133,42072150)Natural Science Foundation of Beijing(8204069)+1 种基金Strategic Cooperation Project of PetroChina and CUPB(ZLZX2020-01-06-01)Science Foundation of China University of Petroleum,Beijing(No.2462021YXZZ003)
文摘Core,thin section,conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag.Bedding parallel fractures are common in fine grained sedimentary rocks which are characterized by layered structures.Core and thin section analysis reveal that fractures in Lucaogou Formation include tectonic inclined fracture,bedding parallel fracture,and abnormal high pressure fracture.Bedding parallel fractures are abundant,but only minor amounts of them remain open,and most of them are partly to fully sealed by carbonate minerals(calcite)and bitumen.Bedding parallel fractures result in a rapid decrease in resistivity,and they are recognized on image logs to extend along bedding planes and have discontinuous surfaces due to partly-fully filled resistive carbonate minerals as well as late stage dissolution.A comprehensive interpretation of distribution of bedding parallel fractures is performed with green line,red line,yellow line and blue line representing bedding planes,induced fractures,resistive fractures,and open(bedding and inclined)fractures,respectively.The strike of bedding parallel fractures is coinciding with bedding planes.Bedding parallel fractures are closely associated with the amounts of bedding planes,and high density of bedding planes favor the formation of bedding parallel fractures.Alternating dark and bright layers have the most abundant bedding parallel fractures on the image logs,and the bedding parallel fractures are always associated with low resistivity zones.The results above may help optimize sweet spots in fine grained sedimentary rocks,and improve future fracturing design and optimize well spacing.
基金supported by the Frontier and Fundamental Research of Active Nanofluids Flooding for Enhanced Oil Recovery through Discontinuous and Variable-circle Modes in High Temperature and High Salinity Offshore Oilfields(U22B6005)National Natural Science Foundation of China(No.52274037)Study on Key Issues of Enhanced Oil Recovery of Gulong Shale Oil(DQYT-2022-JS-761).
文摘Chinaʼs continental shale exhibits favorable geological characteristics and substantial resource potential,yet oil recovery for natural energy extraction remains critically low.Investigating the mechanisms of hydraulically induced bedding fracture to generate complex fracture networks in continental shale,and establishing effective flow systems,is of utmost importance.This study employs laboratory experiments and numerical simulations to investigate the flow capacity and percolation behavior of hydraulically induced bedding fractures by different fluids in full-diameter shale cores.Hydraulic stimulation using different fluids generates bedding plane fracture networks,establishing effective flow systems.Eroded and detached shale fragments support localized fractures,thereby increasing their opening and enhancing flow capacity.Cetyltrimethylammonium bromide(CTAB)solution and SiO2 solution reduce the hydration of the shale surface,preventing shale fragments from swelling and disintegrating,leading to more stable percolation behavior.Eroded and spalled shale fragments near the injection point are transported to farther locations,where they help support localized fractures.This process differs from conventional hydraulic fracturing.Under a constant injection rate,the velocity in the smaller flow paths near the closure is significantly higher than that in the main flow paths,leading to pronounced bypass flow behavior.This restricts the percolation of fluid during imbibition in shale cores.The results provide valuable insights into the mechanism of hydraulically induced bedding fracture in continental shale,offering guidance for the effective development of shale reservoirs.
基金supported by the Key Project of National Natural Science Foundation of China(U23A20596).
文摘CO_(2)injection in shale oil reservoirs has emerged as a promising technique for simultaneously achieving CO_(2)geological storage and enhancing shale oil recovery.This study investigates the potential of CO_(2)injection into shale oil reservoirs with natural fractures for carbon storage and enhanced oil recovery through a combination of experimental and numerical simulations.It focuses on the synergistic effects on carbon storage capacity and oil recovery efficiency.A series of CO_(2)injection experiments using online NMR T_(2)and stratified T_(2)technology were conducted to validate the feasibility of carbon storage and oil recovery in shale oil reservoirs.The shale samples consist of three distinct pore space systems:kerogen,inorganic matrix,and shale bedding fractures.A coupled multiscale-multiphase simulation model was developed to facilitate a comprehensive analysis of the underlying mechanisms.In the model,kerogen,inorganic matrix,and shale bedding fractures are defined as triple-continuum media.The model integrates the mechanisms of molecular diffusion,adsorption,and viscous flow to accurately represent the mass transport processes during CO_(2)injection in shale oil reservoirs.Within this framework,a series of mass transport partial differential equations were derived to describe the CO_(2)injection process.The finite element method was used to numerically solve these equations,and the proposed model was validated against experimental results.Sensitivity analyses yielded the following results:(1)The shale bedding fractures are not only key reservoir spaces for shale oil but also the key mass transfer channels for shale oil and CO_(2)during CO_(2)injection.Increasing the permeability of the shale bedding fractures can significantly improve oil recovery efficiency and CO_(2)adsorption amount.(2)The kerogen content and organic porosity have a significant impact on CO_(2)adsorption amount and shale oil recovery factor,respectively.(3)High production pressure is essential for maximizing carbon storage capacity.Simultaneously,increasing injection pressure can effectively enhance carbon storage and shale oil recovery.
基金Supported by the National Natural Science Foundation of China(41972156)。
文摘The lithology, lithofacies, reservoir properties and shale oil enrichment model of the fine-grained sedimentary system in a lake basin with terrigenous clastics of large depression are studied taking the organic-rich shale in the first member of Cretaceous Qingshankou Formation(shortened as Qing 1 Member) in the Changling Sag, southern Songliao Basin as an example. A comprehensive analysis of mineralogy, thin section, test, log and drilling geologic data shows that lamellar shale with high TOC content of semi-deep lake to deep lake facies has higher hydrocarbon generation potential than the massive mudstone facies with medium TOC content, and has bedding-parallel fractures acting as effective reservoir space under over pressure. The sedimentary environments changing periodically and the undercurrent transport deposits in the outer delta front give rise to laminated shale area. The laminated shale with medium TOC content has higher hydrocarbon generation potential than the laminated shale with low TOC content, and the generated oil migrates a short distance to the sandy laminae to retain and accumulate in situ. Ultra-low permeability massive mudstone facies as the top and bottom seals, good preservation conditions, high pressure coefficient, and lamellar shale facies with high TOC are the conditions for "lamellation type" shale oil enrichment in some sequences and zones. The sequence and zone with laminated shale of medium TOC content in oil window and with micro-migration of expelled hydrocarbon are the condition for the enrichment of "lamination type" shale oil. The tight oil and "lamination type" shale oil are in contiguous distribution.
