Hydrogeochemical processes that would occur in polluted groundwater and aquifer system,may reduce the sensitivity of Sr isotope being the indicator of hydraulic fracturing flowback fluids(HFFF)in groundwater.In this p...Hydrogeochemical processes that would occur in polluted groundwater and aquifer system,may reduce the sensitivity of Sr isotope being the indicator of hydraulic fracturing flowback fluids(HFFF)in groundwater.In this paper,the Dameigou shale gas field in the northern Qaidam Basin was taken as the study area,where the hydrogeochemical processes affecting Sr isotope was analysed.Then,the model for Sr isotope in HFFF-polluted groundwater was constructed to assess the sensitivity of Sr isotope as HFFF indicator.The results show that the dissolution can release little Sr to polluted groundwater and cannot affect the εSr(the deviation of the 87Sr/86Sr ratio)of polluted groundwater.In the meantime,cation exchange can considerably affect Sr composition in the polluted groundwater.The Sr with low εSr is constantly released to groundwater from the solid phase of aquifer media by cation exchange with pollution of Quaternary groundwater by the HFFF and it accounts for 4.6% and 11.0% of Sr in polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater,respectively.However,the Sr from cation exchange has limited impact on Sr isotope in polluted groundwater.Addition of Sr from cation exchange would only cause a 0.2%and 1.2% decrease in εSr of the polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater,respectively.These results demonstrate that hydrogeochemical processes have little effect on the sensitivity of Sr isotope being the HFFF indicator in groundwater of the study area.For the scenario of groundwater pollution by HFFF,when the HFFF accounts for 5%(in volume percentage)of the polluted groundwater,the HFFF can result in detectable shifts of εSr(Δ_(εSr)=0.86)in natural groundwater.Therefore,after consideration of hydrogeochemical processes occurred in aquifer with input of the HFFF,Sr isotope is still a sensitive indicator of the Quaternary groundwater pollution by the HFFF produced in the Dameigou shale of Qaidam Basin.展开更多
Centralized and group well deployment and factory-like fracturing techniques are adopted for low-permeability tight sandstone reservoirs in the Sulige Gasfield,Ordos Basin,so as to realize its efficient and economic d...Centralized and group well deployment and factory-like fracturing techniques are adopted for low-permeability tight sandstone reservoirs in the Sulige Gasfield,Ordos Basin,so as to realize its efficient and economic development.However,environmental protection is faced with grim situations because fluid delivery rises abruptly on site in a short time due to centralized fracturing of the well group.Based on the characteristics of gas testing after fracturing in this gas field,a fracturing flowback fluid recovery and treatment method suitable for the Sulige Gasfield has been developed with the landform features of this area taken into account.Firstly,a high-efficiency well-to-well fracturing flowback fluid recovery and reutilization technique was developed with multi-effect surfactant polymer recoverable fracturing fluid system as the core,and in virtue of this technique,the treatment efficiency of conventional guar gum fracturing fluid system is increased.Secondly,for recovering and treating the end fluids on the well sites,a fine fracturing flowback fluid recovery and treatment technique has been worked out with“coagulation and precipitation,filtration and disinfection,and sludge dewatering”as the main part.Owing to the application of this method,the on-site water resource utilization ratio has been increased and environmental protection pressure concerned with fracturing operation has been relieved.In 2014,field tests were performed in 62 wells of 10 well groups,with 32980 m3 cumulative treated flowback fluid,17160 m3 reutilization volume and reutilization ratio over 70%.Obviously,remarkable social and economical benefits are thus realized.展开更多
Previous studies on post-fracturing flowback fluids focus primarily on their cleaning and discharge,high salinity sources,and damage to gas reservoirs.An analysis of the geochemical characteristics of these fluids hel...Previous studies on post-fracturing flowback fluids focus primarily on their cleaning and discharge,high salinity sources,and damage to gas reservoirs.An analysis of the geochemical characteristics of these fluids helps develop an improved understanding of the preservation condition and fracturing performance of shale gas reservoirs.This study analyzed the ion,total dissolved solids(TDS)concentration,and stable isotope characteristics of post-fracturing flowback fluids from five horizontal shale gas wells in the Luzhou area.Among these wells,two were subjected to hydraulic fracturing using fresh water,and three using reused flowback fluids.The results indicate that with increasing flowback time,the post-fracturing flowback fluids from wells subjected to hydraulic fracturing using fresh water showed increased TDS concentration,heavier stable isotopes,and the presence of new ion components.These results indicate the mixing of a large volume of formation water into the fluids.In contrast,postfracturing flowback fluids from wells subjected to hydraulic fracturing using reused flowback fluids exhibited a slow increase in the TDS concentration and stable isotopes.As the flowback time increased,the trends in TDS concentration and stable isotope ratios of post-fracturing flowback fluids from shale gas wells subjected to fracturing using fresh water evolved toward those of post-fracturing flowback fluids from shale gas wells undergoing fracturing using reused flowback fluids.Measurements show that post-fracturing flowback fluids from both well types exhibited roughly the same properties after one year of shale gas production.This result suggests that post-fracturing flowback fluids from wells using reused flowback fluids progressively took on the formation water properties.In particular,postfracturing flowback fluids from well Lu 211—a well subjected to hydraulic fracturing using fresh water—showed a low sodium-chloride coefficient,a low coefficient of variation,high TDS concentration,heavy stable isotopes,and a high nitrate ion concentration.This indicates a formation water source of the fluids and the poor sealing of the formation water,which hinders shale gas enrichment.The quantification of the fracturing fluid and formation water contents in the post-fracturing flowback fluids reveals that higher TDS concentration and heavier stable isotopes in the fluids appear to correspond to higher formation water content and lower fracturing fluid content,as well as higher fracturing performance.A systematic analysis of the geochemical characteristics and flowback pattern of fracturing fluids indirectly provides insights into the flow path of formation water,water body mixing,rock-water interactions,and fluid sources.Besides,the analysis offers a new perspective for understanding the preservation conditions and fracturing performance of shale gas reservoirs.展开更多
Reutilizing flowback fluid and produced water to prepare fracturing fluid is still an urgent problem that needs to be solved and is not well solved.In this work,an anti-salt associative thickener(AAT)was synthesized b...Reutilizing flowback fluid and produced water to prepare fracturing fluid is still an urgent problem that needs to be solved and is not well solved.In this work,an anti-salt associative thickener(AAT)was synthesized by free radical copolymerization,and the molecular structure of AAT was demonstrated by FTIR and 1H-NMR.Furthermore,compared with a common anti-salt thickener(HAT),the comprehensive performances of AAT were systematically investigated under the conditions of fresh water,flowback fluid and produced water in Sulige Gasfield.The results show that under the conditions of an average salinity of 34,428 mg/L and an average high-valent ion content of 4967 mg/L,AAT can present good thickening capacity,temperature and shear resistance,drag reduction efficiency,sand-carrying ability,gel-breaking property and high-effective crosslinking capacity with organic zirconium crosslinker at high salinity,which implicates the great potential and feasibility to prepare fracturing fluid by reutilizing high-salinity f lowbackfluid and produced water without further treatment.Moreover,the possible mechanisms of the associative thickener to achieve high-effective drag reduction and sand-carrying might be the existence of reversible supramolecular structures and the significant increase of viscoelasticity by shear stretching in turbulent state.At the same time,both physical and chemical interaction can make a significant contribution to high-effective crosslinking capacity of associative thickener.All results and findings can provide an important reference for the design of novel fracturing fluid and the reutilization of high salinity water in stimulation applications.展开更多
The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that o...The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.展开更多
In this paper,the Lower Silurian Longmaxi shale samples and the backflow fracturing fluid in the Changning Block of the Sichuan Basin were selected to investigate the damage mechanism of retained fracturing fluid to f...In this paper,the Lower Silurian Longmaxi shale samples and the backflow fracturing fluid in the Changning Block of the Sichuan Basin were selected to investigate the damage mechanism of retained fracturing fluid to fractures in shale gas reservoirs.Thus,experiments were conducted on fracturing fluid backflow and gas-driving fracturing fluids.The changes of liquid permeability of shale samples,solid particle size distribution and turbidity of the backflow fracturing fluid were monitored.The gas permeability before and after fracturing fluid gas drive was compared,and the damage degree and mechanism of the backflow fracturing fluid to the fractures in shale samples were analyzed.And the following research results were obtained.First,the damage rate of shale permeability after the fracturing fluid backflow is between 53.1%and 97.6%,and the range of the solid particle size of the flowback fluid is significantly reduced.The main reservoir damage modes include phase trapping damage caused by liquid phase retention,blockage caused by the solid phase residue,particle migration induced by gas-carrying liquid and salt precipitation.Second,in the stage of gas phase flow,the damage rate of permeability drops to 23.1-80.2%,and the damage caused by liquid phase retention is relieved,but the damage caused by the blockage of solid phase residue and the salt precipitation of flowback on the facture surface is inevitable.Third,based on the damage mechanism of fracturing fluid backflow in shale gas wells to fractures,considering the treatment difficulty of the flowback and its damage to reservoir fractures,it is recommended to give a full play to the fracturing capacity of fracturing fluid and optimize the properties and dosages of fracturing fluid so as to reduce the flowback of fracturing fluid as much as possible.展开更多
CO_(2) dry fracturing is a promising alternative method to water fracturing in tight gas reservoirs,especially in water-scarce areas such as the Loess Plateau.The CO_(2) flowback efficiency is a critical factor that a...CO_(2) dry fracturing is a promising alternative method to water fracturing in tight gas reservoirs,especially in water-scarce areas such as the Loess Plateau.The CO_(2) flowback efficiency is a critical factor that affects the final gas production effect.However,there have been few studies focusing on the flowback characteristics after CO_(2) dry fracturing.In this study,an extensive core-to-field scale study was conducted to investigate CO_(2) flowback characteristics and CH_(4) production behavior.Firstly,to investigate the impact of core properties and production conditions on CO_(2) flowback,a series of laboratory experiments at the core scale were conducted.Then,the key factors affecting the flowback were analyzed using the grey correlation method based on field data.Finally,taking the construction parameters of Well S60 as an example,a dual-permeability model was used to characterize the different seepage fields in the matrix and fracture for tight gas reservoirs.The production parameters after CO_(2) dry fracturing were then optimized.Experimental results demonstrate that CO_(2) dry fracturing is more effective than slickwater fracturing,with a 9.2%increase in CH_(4) recovery.The increase in core permeability plays a positive role in improving CH_(4) production and CO_(2) flowback.The soaking process is mainly affected by CO_(2) diffusion,and the soaking time should be controlled within 12 h.Increasing the flowback pressure gradient results in a significant increase in both CH_(4) recovery and CO_(2) flowback efficiency.While,an increase in CO_(2) injection is not conducive to CH_(4) production and CO_(2) flowback.Based on the experimental and field data,the important factors affecting flowback and production were comprehensively and effectively discussed.The results show that permeability is the most important factor,followed by porosity and effective thickness.Considering flowback efficiency and the influence of proppant reflux,the injection volume should be the minimum volume that meets the requirements for generating fractures.The soaking time should be short which is 1 day in this study,and the optimal bottom hole flowback pressure should be set at 10 MPa.This study aims to improve the understanding of CO_(2) dry fracturing in tight gas reservoirs and provide valuable insights for optimizing the process parameters.展开更多
基金This study was supported by the National Natural Science Foundation of China(No.41302192)Natural Science Foundation of Hebei Province of China(No.D2018504011)+1 种基金China Geological Survey(No.DD20190555)the Ministry of land and resources of the People’s Republic of China(No.201411052).
文摘Hydrogeochemical processes that would occur in polluted groundwater and aquifer system,may reduce the sensitivity of Sr isotope being the indicator of hydraulic fracturing flowback fluids(HFFF)in groundwater.In this paper,the Dameigou shale gas field in the northern Qaidam Basin was taken as the study area,where the hydrogeochemical processes affecting Sr isotope was analysed.Then,the model for Sr isotope in HFFF-polluted groundwater was constructed to assess the sensitivity of Sr isotope as HFFF indicator.The results show that the dissolution can release little Sr to polluted groundwater and cannot affect the εSr(the deviation of the 87Sr/86Sr ratio)of polluted groundwater.In the meantime,cation exchange can considerably affect Sr composition in the polluted groundwater.The Sr with low εSr is constantly released to groundwater from the solid phase of aquifer media by cation exchange with pollution of Quaternary groundwater by the HFFF and it accounts for 4.6% and 11.0% of Sr in polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater,respectively.However,the Sr from cation exchange has limited impact on Sr isotope in polluted groundwater.Addition of Sr from cation exchange would only cause a 0.2%and 1.2% decrease in εSr of the polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater,respectively.These results demonstrate that hydrogeochemical processes have little effect on the sensitivity of Sr isotope being the HFFF indicator in groundwater of the study area.For the scenario of groundwater pollution by HFFF,when the HFFF accounts for 5%(in volume percentage)of the polluted groundwater,the HFFF can result in detectable shifts of εSr(Δ_(εSr)=0.86)in natural groundwater.Therefore,after consideration of hydrogeochemical processes occurred in aquifer with input of the HFFF,Sr isotope is still a sensitive indicator of the Quaternary groundwater pollution by the HFFF produced in the Dameigou shale of Qaidam Basin.
文摘Centralized and group well deployment and factory-like fracturing techniques are adopted for low-permeability tight sandstone reservoirs in the Sulige Gasfield,Ordos Basin,so as to realize its efficient and economic development.However,environmental protection is faced with grim situations because fluid delivery rises abruptly on site in a short time due to centralized fracturing of the well group.Based on the characteristics of gas testing after fracturing in this gas field,a fracturing flowback fluid recovery and treatment method suitable for the Sulige Gasfield has been developed with the landform features of this area taken into account.Firstly,a high-efficiency well-to-well fracturing flowback fluid recovery and reutilization technique was developed with multi-effect surfactant polymer recoverable fracturing fluid system as the core,and in virtue of this technique,the treatment efficiency of conventional guar gum fracturing fluid system is increased.Secondly,for recovering and treating the end fluids on the well sites,a fine fracturing flowback fluid recovery and treatment technique has been worked out with“coagulation and precipitation,filtration and disinfection,and sludge dewatering”as the main part.Owing to the application of this method,the on-site water resource utilization ratio has been increased and environmental protection pressure concerned with fracturing operation has been relieved.In 2014,field tests were performed in 62 wells of 10 well groups,with 32980 m3 cumulative treated flowback fluid,17160 m3 reutilization volume and reutilization ratio over 70%.Obviously,remarkable social and economical benefits are thus realized.
基金supported by China National Petroleum Corporation(NO:2023ZZ21)。
文摘Previous studies on post-fracturing flowback fluids focus primarily on their cleaning and discharge,high salinity sources,and damage to gas reservoirs.An analysis of the geochemical characteristics of these fluids helps develop an improved understanding of the preservation condition and fracturing performance of shale gas reservoirs.This study analyzed the ion,total dissolved solids(TDS)concentration,and stable isotope characteristics of post-fracturing flowback fluids from five horizontal shale gas wells in the Luzhou area.Among these wells,two were subjected to hydraulic fracturing using fresh water,and three using reused flowback fluids.The results indicate that with increasing flowback time,the post-fracturing flowback fluids from wells subjected to hydraulic fracturing using fresh water showed increased TDS concentration,heavier stable isotopes,and the presence of new ion components.These results indicate the mixing of a large volume of formation water into the fluids.In contrast,postfracturing flowback fluids from wells subjected to hydraulic fracturing using reused flowback fluids exhibited a slow increase in the TDS concentration and stable isotopes.As the flowback time increased,the trends in TDS concentration and stable isotope ratios of post-fracturing flowback fluids from shale gas wells subjected to fracturing using fresh water evolved toward those of post-fracturing flowback fluids from shale gas wells undergoing fracturing using reused flowback fluids.Measurements show that post-fracturing flowback fluids from both well types exhibited roughly the same properties after one year of shale gas production.This result suggests that post-fracturing flowback fluids from wells using reused flowback fluids progressively took on the formation water properties.In particular,postfracturing flowback fluids from well Lu 211—a well subjected to hydraulic fracturing using fresh water—showed a low sodium-chloride coefficient,a low coefficient of variation,high TDS concentration,heavy stable isotopes,and a high nitrate ion concentration.This indicates a formation water source of the fluids and the poor sealing of the formation water,which hinders shale gas enrichment.The quantification of the fracturing fluid and formation water contents in the post-fracturing flowback fluids reveals that higher TDS concentration and heavier stable isotopes in the fluids appear to correspond to higher formation water content and lower fracturing fluid content,as well as higher fracturing performance.A systematic analysis of the geochemical characteristics and flowback pattern of fracturing fluids indirectly provides insights into the flow path of formation water,water body mixing,rock-water interactions,and fluid sources.Besides,the analysis offers a new perspective for understanding the preservation conditions and fracturing performance of shale gas reservoirs.
基金supported financially by the Introduction Pro gram of Tianchi Talent on Young Doctor in Xinjiang(grant No.2023TCXZGCY01)the Science and Technology Project of CNPC Western Drilling Engineering Co.,LTD(grant No.2023XZ201).
文摘Reutilizing flowback fluid and produced water to prepare fracturing fluid is still an urgent problem that needs to be solved and is not well solved.In this work,an anti-salt associative thickener(AAT)was synthesized by free radical copolymerization,and the molecular structure of AAT was demonstrated by FTIR and 1H-NMR.Furthermore,compared with a common anti-salt thickener(HAT),the comprehensive performances of AAT were systematically investigated under the conditions of fresh water,flowback fluid and produced water in Sulige Gasfield.The results show that under the conditions of an average salinity of 34,428 mg/L and an average high-valent ion content of 4967 mg/L,AAT can present good thickening capacity,temperature and shear resistance,drag reduction efficiency,sand-carrying ability,gel-breaking property and high-effective crosslinking capacity with organic zirconium crosslinker at high salinity,which implicates the great potential and feasibility to prepare fracturing fluid by reutilizing high-salinity f lowbackfluid and produced water without further treatment.Moreover,the possible mechanisms of the associative thickener to achieve high-effective drag reduction and sand-carrying might be the existence of reversible supramolecular structures and the significant increase of viscoelasticity by shear stretching in turbulent state.At the same time,both physical and chemical interaction can make a significant contribution to high-effective crosslinking capacity of associative thickener.All results and findings can provide an important reference for the design of novel fracturing fluid and the reutilization of high salinity water in stimulation applications.
基金supported by the National Natural Science Foundation of China(Grant No.52022087).
文摘The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.
基金supported by General Program of National Natural Science Foundation of China"Study on the gas transmission mechanism for permeability improvement and acceleration through oxidation-assisted cracking in organic matter-enriched shale"(No.:51674209)Major Breeding Project of Sichuan Provincial Colleges,Universities for Conversion of Scientific&Technological Achievements"Method of improving gas recovery of organic matter-enriched shale gas reservoirs"(No.:17CZ0040)2017 Science&Technology Project of PetroChina Southwest Oil&Gasfield Company"Study on the interaction mechanism of shale and fracturing fluids and flowback rules in the Changning Block"(No.20170302-03).
文摘In this paper,the Lower Silurian Longmaxi shale samples and the backflow fracturing fluid in the Changning Block of the Sichuan Basin were selected to investigate the damage mechanism of retained fracturing fluid to fractures in shale gas reservoirs.Thus,experiments were conducted on fracturing fluid backflow and gas-driving fracturing fluids.The changes of liquid permeability of shale samples,solid particle size distribution and turbidity of the backflow fracturing fluid were monitored.The gas permeability before and after fracturing fluid gas drive was compared,and the damage degree and mechanism of the backflow fracturing fluid to the fractures in shale samples were analyzed.And the following research results were obtained.First,the damage rate of shale permeability after the fracturing fluid backflow is between 53.1%and 97.6%,and the range of the solid particle size of the flowback fluid is significantly reduced.The main reservoir damage modes include phase trapping damage caused by liquid phase retention,blockage caused by the solid phase residue,particle migration induced by gas-carrying liquid and salt precipitation.Second,in the stage of gas phase flow,the damage rate of permeability drops to 23.1-80.2%,and the damage caused by liquid phase retention is relieved,but the damage caused by the blockage of solid phase residue and the salt precipitation of flowback on the facture surface is inevitable.Third,based on the damage mechanism of fracturing fluid backflow in shale gas wells to fractures,considering the treatment difficulty of the flowback and its damage to reservoir fractures,it is recommended to give a full play to the fracturing capacity of fracturing fluid and optimize the properties and dosages of fracturing fluid so as to reduce the flowback of fracturing fluid as much as possible.
基金support from the National Natural Science Foundation of China(No.51904324,No.51974348)the Prospective Basic Major Science and Technology Projects for the 14th Five Year Plan(No.2021DJ2202).
文摘CO_(2) dry fracturing is a promising alternative method to water fracturing in tight gas reservoirs,especially in water-scarce areas such as the Loess Plateau.The CO_(2) flowback efficiency is a critical factor that affects the final gas production effect.However,there have been few studies focusing on the flowback characteristics after CO_(2) dry fracturing.In this study,an extensive core-to-field scale study was conducted to investigate CO_(2) flowback characteristics and CH_(4) production behavior.Firstly,to investigate the impact of core properties and production conditions on CO_(2) flowback,a series of laboratory experiments at the core scale were conducted.Then,the key factors affecting the flowback were analyzed using the grey correlation method based on field data.Finally,taking the construction parameters of Well S60 as an example,a dual-permeability model was used to characterize the different seepage fields in the matrix and fracture for tight gas reservoirs.The production parameters after CO_(2) dry fracturing were then optimized.Experimental results demonstrate that CO_(2) dry fracturing is more effective than slickwater fracturing,with a 9.2%increase in CH_(4) recovery.The increase in core permeability plays a positive role in improving CH_(4) production and CO_(2) flowback.The soaking process is mainly affected by CO_(2) diffusion,and the soaking time should be controlled within 12 h.Increasing the flowback pressure gradient results in a significant increase in both CH_(4) recovery and CO_(2) flowback efficiency.While,an increase in CO_(2) injection is not conducive to CH_(4) production and CO_(2) flowback.Based on the experimental and field data,the important factors affecting flowback and production were comprehensively and effectively discussed.The results show that permeability is the most important factor,followed by porosity and effective thickness.Considering flowback efficiency and the influence of proppant reflux,the injection volume should be the minimum volume that meets the requirements for generating fractures.The soaking time should be short which is 1 day in this study,and the optimal bottom hole flowback pressure should be set at 10 MPa.This study aims to improve the understanding of CO_(2) dry fracturing in tight gas reservoirs and provide valuable insights for optimizing the process parameters.
