Currently,unconventional reservoirs are characterized by low single well-controlled reserves,high initial production but fast production decline.This paper sorts out the problems of energy dispersion and limited lengt...Currently,unconventional reservoirs are characterized by low single well-controlled reserves,high initial production but fast production decline.This paper sorts out the problems of energy dispersion and limited length and height of main hydraulic fractures induced in staged multi-cluster fracturing,and proposes an innovative concept of“energy-focused fracturing development”.The technical connotation,theoretical model,and core techniques of energy-focused fracturing development are systematically examined,and the implementation path of this technology is determined.The energy-focused fracturing development technology incorporates the techniques such as geology-engineering integrated design,perforation optimization design,fracturing process design,and drainage engineering control.It transforms the numerous,short and dense hydraulic fractures to limited,long and sparse fractures.It focuses on fracturing energy,and aims to improve the fracture length,height and lateral width,and the proppant long-distance transportation capacity,thus enhancing the single well-controlled reserves and development effect.The energy-focused fracturing development technology has been successfully applied in the carbonate reservoirs in buried hill,shallow coalbed methane reservoirs,and coal-rock gas reservoirs in China,demonstrating the technology's promising application.It is concluded that the energy-focused fracturing development technology can significantly increase the single well production and estimated ultimate recovery(EUR),and will be helpful for efficiently developing low-permeability,unconventional and low-grade resources in China.展开更多
The Chang-63 reservoir in the Huaqing area has widely developed tight sandstone ＂thick sand layers, but not reservoirs characterized by rich in oil＂, and it is thus necessary to further study its oil and gas enrichm...The Chang-63 reservoir in the Huaqing area has widely developed tight sandstone ＂thick sand layers, but not reservoirs characterized by rich in oil＂, and it is thus necessary to further study its oil and gas enrichment law. This study builds porosity and fracture development and evolution models in different deposition environments, through core observation, casting thin section, SEM, porosity and permeability analysis, burial history analysis, and ＂four-property-relationships＂ analysis.展开更多
Drilling fluids with complicated compositions are becoming more common as the oil and gas industry develops. The production of hazardous cuttings is increasing, which not only stifles the oil and gas industry’s devel...Drilling fluids with complicated compositions are becoming more common as the oil and gas industry develops. The production of hazardous cuttings is increasing, which not only stifles the oil and gas industry’s development but also poses a severe environmental threat. Deep underground re-injection is a cost-effective and efficient method for dealing with hazardous cuttings. Numerous experiments and numerical studies on cuttings re-injection have been conducted in the past thirty years. However, there is still a divergence of views on the fracture development in the process of cuttings re-injection. A comprehensive review of existing studies is necessary to help researchers advance this technology. This paper provides a review of the fundamental studies on fracture behaviors during the deep underground re-injection of drilling cuttings. The limitations of the existing studies are also discussed to inspire new research endeavors.展开更多
In view of the bottleneck of shale gas development technologies,the latest progresses in such theories on the fields like fracture network fracability evaluation,fracture network propagation mechanism,stimulated reser...In view of the bottleneck of shale gas development technologies,the latest progresses in such theories on the fields like fracture network fracability evaluation,fracture network propagation mechanism,stimulated reservoir volume(SRV)evaluation and fracturing fluid research&development were analyzed comprehensively in reference to the existing achievements and experiences in North American shale gas reservoir development and based on the probes,practices and cognitions of shale gas development technologies in China since 2005.First,the study on the shale brittleness develops from the definition of mineral and mechanical semi-quantitative threshold measurement to a comprehensive evaluation which integrates rock constituents,elastic mechanics and development characteristics of natural fractures together.Second,the study on the fracture network development develops from the directional extension theory to the simulation of fracture network formation in the stochastic distribution pattern of natural fractures.Third,the study on SRV develops from the micro-seismic monitoring based instrument and technology to the mathematical theory evaluation method dependent on the discrete fracture network and extended finite element.And fourth,the study on fracturing fluids develops from the wide application of slick water(drag reducing water)and a linear gel fracturing fluid system to the development and application of novel fracturing fluids with little or no water.Then,the theoretical and technological challenges were pointed out,including the comprehensive fracability evaluation of reservoir fracture networks,the deep seated shale gas fracturing,the operation curve diagnosis of shale gas fracturing,the shale gas refracturing theory,and the research&development and flowback control of novel fracturing fluids.Finally,the development trend of related technologies was predicted so as to provide a theoretical and technical guidance for the efficient shale gas development in China in the future.展开更多
This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof.The caving area of the overburden rock is divided...This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof.The caving area of the overburden rock is divided into three zones:the delamination fracture zone,broken fracture zone,and compaction zone.The caving and fracture zones'heights are approximately 110 m above the coal seam,with a maximum subsidence of 11 m.The delamination fracture zone's porosity range is between 0.2 and 0.3,while the remainder of the roof predominantly exhibits a porosity of less than 0.1.In addition,the numerical model's stress analysis revealed that the overburden rock's displacement zone forms an'arch-beam'structure starting from 160 m,with the maximum and minimum stress values decreasing as the distance of advancement increases.In the stress beam interval of the overburden rock,the maximum value changes periodically as the advancement distance increases.Based on a comparative analysis between observable data from on-site work and numerical simulation results,the stress data from the numerical simulation are essentially consistent with the actual results detected on-site,indicating the validity of the numerical simulation results.展开更多
The principles of fracture development during underwater blasting are examined based on explosion and impact dynamics,fluid dynamics,fracture dynamics,and field testing.The research reveals that the fracturing of the ...The principles of fracture development during underwater blasting are examined based on explosion and impact dynamics,fluid dynamics,fracture dynamics,and field testing.The research reveals that the fracturing of the surrounding rock during underwater blasting is due to the combined action of shock and stress waves for the initial rock breakage and subsequent water expansion.The fracture development model for the surrounding rock of a drilling hole during underwater blasting is established.The rock fracturing range under the combined action of shock and stress waves is developed,as well as the fracture propagation rules after the wedging of the water medium into the fractures.Finally,the results of deep-hole underwater blasting tests on large rocks confirm the efficient utilization of explosive in the hole to improve the safety conditions.Accordingly,safe and static rock breaking under the detonation of high-effect explosive can be achieved.In addition,super-dynamic loading from the explosions and static loading from the water medium in the hole can be adequately combined for rock breaking.展开更多
To investigate the dynamic behavior and energy dissipation of the rock−concrete interface,dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar.The test results reveal t...To investigate the dynamic behavior and energy dissipation of the rock−concrete interface,dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar.The test results reveal that with the change of the interface inclination angles(θ),the influence of interface groove width on the bearing capacity of specimens also varies.Whenθincreases from 0°to 30°,the bearing capacity of the specimen increases first and then decreases with the rise of the interface groove width;the optimal groove width on the rock surface in this range of interface inclination angles is 5 mm.Whenθincreases from 45°to 90°,the bearing capacity of the specimen has no obvious change.Moreover,whenθincreases from 0°to 45°,the dissipated energy of the specimens rises obviously at first and then tends to be stable as the width of the interface groove increases.展开更多
Based on the occurrence features of Group B coal-seams at a coal mine in the Huainan coal mining area, the elasto-plastic mechanical damage constitutive functions and numerical model for the protective layer excavatio...Based on the occurrence features of Group B coal-seams at a coal mine in the Huainan coal mining area, the elasto-plastic mechanical damage constitutive functions and numerical model for the protective layer excavation were established. With the UDEC2D computer program, after the upper protective layer was mined, the stress field change trends, crack development, and expansion deformation trends of underlying coal rock seams in the floor of the working face were simulated and analyzed. The simulation results show the stress changes in coal rock seams, the evolution process of pre-cracks during the process of upper protective layer mining, the caved zone and fractured zone of the underlying coal rock seams. At the same time, the results from the actual investigation and analysis of protected layer deformation match the simulation values, which verifies the validity and accuracy of numerical simulation results. The study results have an important guiding significance for gas management in low permeability and high gas coal seams with similar mining conditions.展开更多
The coalbed methane(CBM)reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures,so cementing slurry(“slurry”for short)can invade...The coalbed methane(CBM)reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures,so cementing slurry(“slurry”for short)can invade into CBM reservoir easily,resulting in reservoir damage and abnormal increase of reservoir transformation fracturing pressure.In order to reveal the damage mechanisms of slurry to this type of coal reservoirs,we analyzed the physical and chemical properties and potential damage modes of coal rocks.Then,the development situations of fractures and pores before and after the coal core samples were internally contaminated and the invasion and plugging situations of slurry in fractures and pores were analyzed intuitively by means of CT scanning and scanning electron microscope(SEM),and the percentage of slurry and fractures in coal core volume was calculated.In this way,a method to quantitatively evaluate the damage of slurry to coal reservoirs was established.And the following research results were obtained.First,under the effect of differential pressure,slurry and its filtrate invade into coal reservoirs along the fractures.The invasion degree varies with the development degree of fractures and pores.The more developed the fractures and pores,the higher the invasion degree.Second,the cement products formed after the slurry in the reservoirs gets cemented and solidified fill the fractures and pores tightly and cover the surface of coal core samples densely,so CBM flowing channels are blocked severely.Consequently,the permeability of coal core samples decreases and the compressive strength of coal rocks increase,leading to the abnormal increase of subsequent fracturing pressure and impacting the fracturing stimulation effects.Third,the effect of slurry filtrate on the alkali sensitivity and velocity sensitivity of coal rocks is much less than the damage degree of slurry invasion to coal rocks.In conclusion,this newly developed quantitative evaluation method for the damage of slurry to coal reservoirs is of guiding significance to improving the cement job quality of coal reservoirs and ensuring the efficient CBM development.展开更多
Effective migration system of coalbed methane(CBM)reservoir,which was controlled by development degree and opening-closing degree of fractures,determines the permeability of coal reservoir and can be characterized by ...Effective migration system of coalbed methane(CBM)reservoir,which was controlled by development degree and opening-closing degree of fractures,determines the permeability of coal reservoir and can be characterized by the pore-fracture system in the extrinsic form.In this paper,based on coal matrix elastic self-regulating effect theory and coal reservoir combined elastic energy theory,the fracture opening-closing degree parameterΔand the fracture development degree parameterξare suggested for the quantitative study of the effective migration system of CBM reservoir in southern Qinshui Basin.Further,the control functions ofξandΔto CBM enrichment and high production are discussed.The results show that in present stage the area with highξvalue is located in Anze and Qinyuan,and then Zhengzhuang and Fangzhuang,where fracture development degree is high.The area with highΔvalue is located in Zhengzhuang and Fanzhuang,and then Anze and Qinyuan,indicating where coal matrix elastic self-regulating positive effect dominates and fractures tend to be open.Through the comprehensive analysis onξandΔ,it can be found that their best match area is located in Zhengzhuang and Fanzhuang,with high values for fracture development degree and opening-closing degree probably bringing about high fluid pressure and good permeability of reservoirs,which are advantageous to an abundant CBM production.展开更多
基金Supported by the PetroChina Scentific and Technological Projects(2023ZZ082023ZZ28)。
文摘Currently,unconventional reservoirs are characterized by low single well-controlled reserves,high initial production but fast production decline.This paper sorts out the problems of energy dispersion and limited length and height of main hydraulic fractures induced in staged multi-cluster fracturing,and proposes an innovative concept of“energy-focused fracturing development”.The technical connotation,theoretical model,and core techniques of energy-focused fracturing development are systematically examined,and the implementation path of this technology is determined.The energy-focused fracturing development technology incorporates the techniques such as geology-engineering integrated design,perforation optimization design,fracturing process design,and drainage engineering control.It transforms the numerous,short and dense hydraulic fractures to limited,long and sparse fractures.It focuses on fracturing energy,and aims to improve the fracture length,height and lateral width,and the proppant long-distance transportation capacity,thus enhancing the single well-controlled reserves and development effect.The energy-focused fracturing development technology has been successfully applied in the carbonate reservoirs in buried hill,shallow coalbed methane reservoirs,and coal-rock gas reservoirs in China,demonstrating the technology's promising application.It is concluded that the energy-focused fracturing development technology can significantly increase the single well production and estimated ultimate recovery(EUR),and will be helpful for efficiently developing low-permeability,unconventional and low-grade resources in China.
文摘The Chang-63 reservoir in the Huaqing area has widely developed tight sandstone ＂thick sand layers, but not reservoirs characterized by rich in oil＂, and it is thus necessary to further study its oil and gas enrichment law. This study builds porosity and fracture development and evolution models in different deposition environments, through core observation, casting thin section, SEM, porosity and permeability analysis, burial history analysis, and ＂four-property-relationships＂ analysis.
基金financially supported by National Natural Science Foundation of China(Grant Nos.52074312 and 52004298)。
文摘Drilling fluids with complicated compositions are becoming more common as the oil and gas industry develops. The production of hazardous cuttings is increasing, which not only stifles the oil and gas industry’s development but also poses a severe environmental threat. Deep underground re-injection is a cost-effective and efficient method for dealing with hazardous cuttings. Numerous experiments and numerical studies on cuttings re-injection have been conducted in the past thirty years. However, there is still a divergence of views on the fracture development in the process of cuttings re-injection. A comprehensive review of existing studies is necessary to help researchers advance this technology. This paper provides a review of the fundamental studies on fracture behaviors during the deep underground re-injection of drilling cuttings. The limitations of the existing studies are also discussed to inspire new research endeavors.
基金supported by National Natural Science Foundation of China“Dynamic fracture control mechanism and water-free fracturing theory for shale formations”(No.51490653).
文摘In view of the bottleneck of shale gas development technologies,the latest progresses in such theories on the fields like fracture network fracability evaluation,fracture network propagation mechanism,stimulated reservoir volume(SRV)evaluation and fracturing fluid research&development were analyzed comprehensively in reference to the existing achievements and experiences in North American shale gas reservoir development and based on the probes,practices and cognitions of shale gas development technologies in China since 2005.First,the study on the shale brittleness develops from the definition of mineral and mechanical semi-quantitative threshold measurement to a comprehensive evaluation which integrates rock constituents,elastic mechanics and development characteristics of natural fractures together.Second,the study on the fracture network development develops from the directional extension theory to the simulation of fracture network formation in the stochastic distribution pattern of natural fractures.Third,the study on SRV develops from the micro-seismic monitoring based instrument and technology to the mathematical theory evaluation method dependent on the discrete fracture network and extended finite element.And fourth,the study on fracturing fluids develops from the wide application of slick water(drag reducing water)and a linear gel fracturing fluid system to the development and application of novel fracturing fluids with little or no water.Then,the theoretical and technological challenges were pointed out,including the comprehensive fracability evaluation of reservoir fracture networks,the deep seated shale gas fracturing,the operation curve diagnosis of shale gas fracturing,the shale gas refracturing theory,and the research&development and flowback control of novel fracturing fluids.Finally,the development trend of related technologies was predicted so as to provide a theoretical and technical guidance for the efficient shale gas development in China in the future.
基金National Key R&D Program of China(2023YFC3009100,2023YFC3009102)National Natural Science Foundation of China(52304198)Open Fund of the National and Local Joint Engineering Research Center for Safe and Accurate Coal Mining(EC2021016).
文摘This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof.The caving area of the overburden rock is divided into three zones:the delamination fracture zone,broken fracture zone,and compaction zone.The caving and fracture zones'heights are approximately 110 m above the coal seam,with a maximum subsidence of 11 m.The delamination fracture zone's porosity range is between 0.2 and 0.3,while the remainder of the roof predominantly exhibits a porosity of less than 0.1.In addition,the numerical model's stress analysis revealed that the overburden rock's displacement zone forms an'arch-beam'structure starting from 160 m,with the maximum and minimum stress values decreasing as the distance of advancement increases.In the stress beam interval of the overburden rock,the maximum value changes periodically as the advancement distance increases.Based on a comparative analysis between observable data from on-site work and numerical simulation results,the stress data from the numerical simulation are essentially consistent with the actual results detected on-site,indicating the validity of the numerical simulation results.
基金National Natural Science Foundation of China(51604262)Foundation Research Project of Jiangsu Province(BK20160256)China Postdoctoral Science Foundation Project(2018M632424).
文摘The principles of fracture development during underwater blasting are examined based on explosion and impact dynamics,fluid dynamics,fracture dynamics,and field testing.The research reveals that the fracturing of the surrounding rock during underwater blasting is due to the combined action of shock and stress waves for the initial rock breakage and subsequent water expansion.The fracture development model for the surrounding rock of a drilling hole during underwater blasting is established.The rock fracturing range under the combined action of shock and stress waves is developed,as well as the fracture propagation rules after the wedging of the water medium into the fractures.Finally,the results of deep-hole underwater blasting tests on large rocks confirm the efficient utilization of explosive in the hole to improve the safety conditions.Accordingly,safe and static rock breaking under the detonation of high-effect explosive can be achieved.In addition,super-dynamic loading from the explosions and static loading from the water medium in the hole can be adequately combined for rock breaking.
基金supported by the National Natural Science Foundation of China (No.41772313)the National Natural Science Foundation for Young Scientists of China (No.52104111)+3 种基金the Hunan Science and Technology Planning Project,China (No.2019RS3001)the Natural Science Foundation of Hunan Province,China (No.2021JJ30819)Key Science and Technology Project of Guangxi Transportation Industry (Research on fine blasting and disaster control technology of mountain expressway tunnel),Chinathe financial contribution and convey their appreciation for supporting this basic research。
文摘To investigate the dynamic behavior and energy dissipation of the rock−concrete interface,dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar.The test results reveal that with the change of the interface inclination angles(θ),the influence of interface groove width on the bearing capacity of specimens also varies.Whenθincreases from 0°to 30°,the bearing capacity of the specimen increases first and then decreases with the rise of the interface groove width;the optimal groove width on the rock surface in this range of interface inclination angles is 5 mm.Whenθincreases from 45°to 90°,the bearing capacity of the specimen has no obvious change.Moreover,whenθincreases from 0°to 45°,the dissipated energy of the specimens rises obviously at first and then tends to be stable as the width of the interface groove increases.
基金Supported by the National Natural Science Foundation of China （51004003） the Natural Science Foundation of Ministry of Education of Anhui Province （K J2010A091 ）
文摘Based on the occurrence features of Group B coal-seams at a coal mine in the Huainan coal mining area, the elasto-plastic mechanical damage constitutive functions and numerical model for the protective layer excavation were established. With the UDEC2D computer program, after the upper protective layer was mined, the stress field change trends, crack development, and expansion deformation trends of underlying coal rock seams in the floor of the working face were simulated and analyzed. The simulation results show the stress changes in coal rock seams, the evolution process of pre-cracks during the process of upper protective layer mining, the caved zone and fractured zone of the underlying coal rock seams. At the same time, the results from the actual investigation and analysis of protected layer deformation match the simulation values, which verifies the validity and accuracy of numerical simulation results. The study results have an important guiding significance for gas management in low permeability and high gas coal seams with similar mining conditions.
基金supported by the National Major Science&Technology Project“Development of large oil/gas fields and CBM”(No.:2016ZX05044)the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China(No.:IRT_14R58)。
文摘The coalbed methane(CBM)reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures,so cementing slurry(“slurry”for short)can invade into CBM reservoir easily,resulting in reservoir damage and abnormal increase of reservoir transformation fracturing pressure.In order to reveal the damage mechanisms of slurry to this type of coal reservoirs,we analyzed the physical and chemical properties and potential damage modes of coal rocks.Then,the development situations of fractures and pores before and after the coal core samples were internally contaminated and the invasion and plugging situations of slurry in fractures and pores were analyzed intuitively by means of CT scanning and scanning electron microscope(SEM),and the percentage of slurry and fractures in coal core volume was calculated.In this way,a method to quantitatively evaluate the damage of slurry to coal reservoirs was established.And the following research results were obtained.First,under the effect of differential pressure,slurry and its filtrate invade into coal reservoirs along the fractures.The invasion degree varies with the development degree of fractures and pores.The more developed the fractures and pores,the higher the invasion degree.Second,the cement products formed after the slurry in the reservoirs gets cemented and solidified fill the fractures and pores tightly and cover the surface of coal core samples densely,so CBM flowing channels are blocked severely.Consequently,the permeability of coal core samples decreases and the compressive strength of coal rocks increase,leading to the abnormal increase of subsequent fracturing pressure and impacting the fracturing stimulation effects.Third,the effect of slurry filtrate on the alkali sensitivity and velocity sensitivity of coal rocks is much less than the damage degree of slurry invasion to coal rocks.In conclusion,this newly developed quantitative evaluation method for the damage of slurry to coal reservoirs is of guiding significance to improving the cement job quality of coal reservoirs and ensuring the efficient CBM development.
基金jointly supported by National Natural Science Foundation of China(Grant No.41272178)the Major Projects of National Science and Technology of China(Grant No.2011ZX05034)+1 种基金National Basic Research Program of China(Grant No.2009CB219605)"Qinglan"Project of Jiangsu Province
文摘Effective migration system of coalbed methane(CBM)reservoir,which was controlled by development degree and opening-closing degree of fractures,determines the permeability of coal reservoir and can be characterized by the pore-fracture system in the extrinsic form.In this paper,based on coal matrix elastic self-regulating effect theory and coal reservoir combined elastic energy theory,the fracture opening-closing degree parameterΔand the fracture development degree parameterξare suggested for the quantitative study of the effective migration system of CBM reservoir in southern Qinshui Basin.Further,the control functions ofξandΔto CBM enrichment and high production are discussed.The results show that in present stage the area with highξvalue is located in Anze and Qinyuan,and then Zhengzhuang and Fangzhuang,where fracture development degree is high.The area with highΔvalue is located in Zhengzhuang and Fanzhuang,and then Anze and Qinyuan,indicating where coal matrix elastic self-regulating positive effect dominates and fractures tend to be open.Through the comprehensive analysis onξandΔ,it can be found that their best match area is located in Zhengzhuang and Fanzhuang,with high values for fracture development degree and opening-closing degree probably bringing about high fluid pressure and good permeability of reservoirs,which are advantageous to an abundant CBM production.
