To achieve the secondary production in multistage fracturing wells of tight oil,milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later.In thi...To achieve the secondary production in multistage fracturing wells of tight oil,milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later.In this paper,first of all,the working mechanism of milling tools for multistage fracturing ball seats was studied and a mechanical analysis model of single abrasive grain was established.Then,an experimental system for milling tools was developed,and the experimental tests of the flat,the blade,and the slope milling tool were conducted in order.Besides,the morphology of chips and the surface morphology of the workpiece after the experiment were analyzed.Also,the working performance of milling tools was evaluated from the perspectives of working safety,working efficiency,and wear resistance of the milling tool.The results show that the torque of the milling tool increases nonlinearly with the increase in the cutting depth of the abrasive grain and increases linearly with the increase in the cutting width.Also,the chips are irregular particles and the size is mainly from 10 to 50μm.So,the chips should be pumped up with a small pump pressure and a large displacement.Besides this,the cutting depths of the abrasive grains are from 216.20 to 635.47μm and the bottom surface of the milling tool should be eccentric to avoid the zero point of cutting speed.Furthermore,the torque of the slope milling tool is 23.8%larger than that of the flat milling tool,which is also 30.4%smaller than that of the blade milling tool.Compared with the flat milling tool,the working efficiency of the blade milling tool improves by 79.9%and the slope milling tool improves by 111.1%.Also,the wear resistance of the blade milling tool decreases by 102.7%,while the slope milling tool declines by 32.6%when compared with the flat milling tool.Therefore,the slope milling tool has the characteristics of moderate torque,stable working conditions,the highest working efficiency,and fine wear resistance,which is preferably used to mill multistage fracturing ball seats.This study provides a theoretical basis and guidance for milling multistage fracturing ball seats on-site and realizing production with a large diameter in later stages of multistage fracturing wells.展开更多
Ball-drop fracturing is a kind of technology that is commonly used for multistage fracturing of shale gas horizontal wells.At present,the ball injector cannot satisfy the operation demands of large bore and small spac...Ball-drop fracturing is a kind of technology that is commonly used for multistage fracturing of shale gas horizontal wells.At present,the ball injector cannot satisfy the operation demands of large bore and small spacing fracturing of shale gas wells due to its disadvantages,such as a small size of fracturing ball,a limited number of balls,complicated structure and poor applicability.In this paper,a new type of automatic ball injector with rotating plate and large bore was designed.There is a ball storage at the upper part of the ball injector and a ball injecting mechanism inside the pedestal at the lower part.And the ball injecting mechanism is controlled by the drive motor to inject the balls one by one.Then,collision analysis was carried out on its ball injecting process by using finite element method(FEM).Finally,simulation and prototype tests were conducted by using the arbitrary Lagrangian-Eulerian(ALE)mesh adaption method and the coupled smoothed particle hydrodynamics method(FEM-SPH).And the following research results were obtained.First,in the process of ball collision,the maximum equivalent stress,equivalent plastic strain and displacement are generated at the edge of the rotating plate.The maximum stress is about 600 MPa,which is less than the yield strength of 42CrMo(930 MPa),so the strength requirement is satisfied with a certain safety margin.Second,the prototype successfully passes the continuous ball injecting test of 12-stage fracturing process with the ball diameter of 64-108 mm and the ball contrast of 4 mm.In conclusion,this automatic ball injector with rotating plate and large bore is advantageous with simple operation and wide applicability and can effectively address the needs of multistage fracturing of shale gas horizontal wells.展开更多
Multistage fracturing technology has been used to enhance tight hydrocarbon resource recovery.Determining the proper well spacing and fracturing strategy is crucial for generating a complex fracture network that facil...Multistage fracturing technology has been used to enhance tight hydrocarbon resource recovery.Determining the proper well spacing and fracturing strategy is crucial for generating a complex fracture network that facilitates oil and gas flow in reservoirs.The stress-shadow effect that occurs between multiple wells significantly affects the development of fracture networks in reservoirs.However,the quantification of the stress-shadow effect and its influence on fracture networks has not been satisfactorily resolved because of the difficulties in detecting and identifying fracture propagation and reorientation in reservoirs.In this study,based on the geological information from the Shengli oilfield,we applied a hybrid finite element-discrete element method to analyze engineering-scale three-dimensional fracture propagation and reorientation by altering well spacings and fracturing strategies.The results indicate that the fracturing area generated by the synchronous fracturing scheme is much smaller than those generated by the sequential and alternative schemes.An alternative hydrofracturing scheme is optimal with respect to fracturing area.The stress-blind area was defined to quantify the mechanical disturbance between adjacent wells.Our study improves the understanding of the effect of fracturing schemes on fracture networks and the impact of independent factors contributing to stress-shadow effects.展开更多
The “well factory” mode's high-density well placement and multi-stage hydraulic fracturing technology enable efficient development of unconventional oil and gas resources.However,the deployment of platform wells...The “well factory” mode's high-density well placement and multi-stage hydraulic fracturing technology enable efficient development of unconventional oil and gas resources.However,the deployment of platform wells in the “well factory” model results in small wellbore spacing,and the stress disturbances caused by fracturing operations may affect neighboring wells,leading to inter-well interference phenomena that cause casing deformation.This study investigates the issue of inter-well interference causing casing deformation or even failure during multi-stage hydraulic fracturing in the “well factory”model,and predicts high-risk locations for casing failure.A flow-mechanics coupled geomechanical finite element model with retaining geological stratification characteristics was established.Based on the theory of hydraulic fracturing-induced rock fragmentation and fluid action leading to the degradation of rock mechanical properties,the model simulated the four-dimensional evolution of multi-well fracturing areas over time and space,calculating the disturbance in the regional stress field caused by fracturing operations.Subsequently,the stress distribution of multiple well casings at different time points was calculated to predict high-risk locations for casing failure.The research results show that the redistribution of the stress field in the fracturing area increases the stress on the casing.The overlapping fracturing zones between wells cause significant stress interference,greatly increasing the risk of deformation and failure.By analyzing the Mises stress distribution of multi-well casings,high-risk locations for casing failure can be identified.The conclusion is that the key to preventing casing failure in platform wells in the “well factory” model is to optimize the spatial distribution of fracturing zones between wells and reasonably arrange well spacing.The study provides new insights and methods for predicting casing failure in unconventional oil and gas reservoirs and offers references for optimizing drilling and fracturing designs.展开更多
Multistage hydraulic fracturing of horizontal wells(MFHW)is a promising technology for controlling coal burst caused by thick and hard roofs in China.However,challenges remain regarding the MFHW control mechanism of c...Multistage hydraulic fracturing of horizontal wells(MFHW)is a promising technology for controlling coal burst caused by thick and hard roofs in China.However,challenges remain regarding the MFHW control mechanism of coal burst and assessment of the associated fracturing effects.In this study,these challenges were investigated through numerical modelling and field applications,based on the actual operating parameters of MFHW for hard roofs in a Chinese coal mine.A damage parameter(D)is proposed to assess the degree of hydraulic fracturing in the roof.The mechanisms and effects of MFHW for controlling coal burst are analyzed using microseismic(MS)data and front-abutment stress distribution.Results show that the degree of fracturing can be categorized into lightly-fractured(D≤0.3),moderately fractured(0.3<D≤0.6),well-fractured(0.6<D≤0.9),and over-fractured(0.9<D≤0.95).A response stage in the fracturing process,characterized by a slowdown in crack development,indicates the transition to a wellfractured condition.After MFHW,the zone range and peak value of the front-abutment stress decrease.Additionally,MS events shift from near the coal seam to the fractured roof layers,with the number of MS events increases while the average MS energy decreases.The MFHW control mechanisms of coal bursts involve mitigating mining-induced stress and reducing seismic activity during longwall retreat,ensuring stresses remain below the ultimate stress level.These findings provide a reference for evaluating MFHW fracturing effects and controlling coal burst disasters in engineering.展开更多
Multistage multi-cluster hydraulic fracturing has enabled the economic exploitation of shale reservoirs,but the interpretation of hydraulic fracture parameters is challenging.The pressure signals after pump shutdown a...Multistage multi-cluster hydraulic fracturing has enabled the economic exploitation of shale reservoirs,but the interpretation of hydraulic fracture parameters is challenging.The pressure signals after pump shutdown are influenced by hydraulic fractures,which can reflect the geometric features of hydraulic fracture.The shutdown pressure can be used to interpret the hydraulic fracture parameters in a real-time and cost-effective manner.In this paper,a mathematical model for shutdown pressure evolution is developed considering the effects of wellbore friction,perforation friction and fluid loss in fractures.An efficient numerical simulation method is established by using the method of characteristics.Based on this method,the impacts of fracture half-length,fracture height,opened cluster and perforation number,and filtration coefficient on the evolution of shutdown pressure are analyzed.The results indicate that a larger fracture half-length may hasten the decay of shutdown pressure,while a larger fracture height can slow down the decay of shutdown pressure.A smaller number of opened clusters and perforations can significantly increase the perforation friction and decrease the overall level of shutdown pressure.A larger filtration coefficient may accelerate the fluid filtration in the fracture and hasten the drop of the shutdown pressure.The simulation method of shutdown pressure,as well as the analysis results,has important implications for the interpretation of hydraulic fracture parameters.展开更多
The sleeve sealing ball seat is one of the important components in the multistage fracturing process of horizontal wells.The erosion and wear of the surface will decrease the sealing performance of the fracturing ball...The sleeve sealing ball seat is one of the important components in the multistage fracturing process of horizontal wells.The erosion and wear of the surface will decrease the sealing performance of the fracturing ball and the ball seat.This leads to pressure leakage during the fracturing process and fracturing failure.In this paper,combined with the actual ball seat materials and working conditions during the fracturing process,the erosion tests of ductile iron and tungsten carbide materials under different erosion speeds,angles,and mortar concentrations are carried out.Then the erosion test results were analyzed by mathematical fitting,and a set of erosion models suitable for sliding sleeve setting ball seat materials were innovatively established.For the first time,this paper combines the erosion model obtained from the experiment and the computational fluid dynamics(CFD)with Fluent software to simulate the erosion of the ball seat.Based on the simulation results,the morphology of the sliding sleeve seat ball after erosion is predicted.Through analysis of the test and simulation results,it is showed that the erosion rate of tungsten carbide material is lower and the wear resistance is better under the condition of small angle erosion.This research can offer a strong basis for fracturing site selection,surface treatment methods,and prediction of failure time of ball seats.展开更多
Multistage fracturing of horizontal wells is a critical technology for unconventional oil and gas reservoir stimulation. Ball-throwing temporary plugging fracturing is a new method for realizing uniform fracturing alo...Multistage fracturing of horizontal wells is a critical technology for unconventional oil and gas reservoir stimulation. Ball-throwing temporary plugging fracturing is a new method for realizing uniform fracturing along horizontal wells and plays an important role in increasing oil and gas production. However,the transportation and sealing law of temporary plugging balls(TPBs) in the perforation section of horizontal wells is still unclear. Using COMSOL computational fluid dynamics and a particle tracking module, we simulate the transportation process of TPBs in a horizontal wellbore and analyse the effects of the ball density, ball diameter, ball number, fracturing fluid injection rate, and viscosity on the plugging efficiency of TPB transportation. This study reveals that when the density of TPBs is close to that of the fracturing fluid and a moderate diameter of the TPB is used, the plugging efficiency can be substantially enhanced. The plugging efficiency is greater when the TPB number is close to twice the number of perforations and is lower when the number of TPBs is three times the number of perforations.Adjusting the fracturing fluid injection rate from low to high can control the position of the TPBs,improving plugging efficiency. As the viscosity of the fracturing fluid increases, the plugging efficiency of the perforations decreases near the borehole heel and increases near the borehole toe. In contrast, the plugging efficiency of the central perforation is almost unaffected by the fracturing fluid viscosity. This study can serve as a valuable reference for establishing the parameters for temporary plugging and fracturing.展开更多
基金supported by the National Science and Technology Major Project under Grant Nos.2016ZX05042004 and 2017ZX05072the Joint Funds of the National Natural Science Foundation of China under Grant No.U1762104+2 种基金the Postgraduate Innovation Project Foundation under Grant No.YCX2019054the Fundamental Research Funds for the Central Universities under Grant No.20CX02306Athe Opening Fund of National Engineering Laboratory of Offshore Geophysical and Exploration Equipment。
文摘To achieve the secondary production in multistage fracturing wells of tight oil,milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later.In this paper,first of all,the working mechanism of milling tools for multistage fracturing ball seats was studied and a mechanical analysis model of single abrasive grain was established.Then,an experimental system for milling tools was developed,and the experimental tests of the flat,the blade,and the slope milling tool were conducted in order.Besides,the morphology of chips and the surface morphology of the workpiece after the experiment were analyzed.Also,the working performance of milling tools was evaluated from the perspectives of working safety,working efficiency,and wear resistance of the milling tool.The results show that the torque of the milling tool increases nonlinearly with the increase in the cutting depth of the abrasive grain and increases linearly with the increase in the cutting width.Also,the chips are irregular particles and the size is mainly from 10 to 50μm.So,the chips should be pumped up with a small pump pressure and a large displacement.Besides this,the cutting depths of the abrasive grains are from 216.20 to 635.47μm and the bottom surface of the milling tool should be eccentric to avoid the zero point of cutting speed.Furthermore,the torque of the slope milling tool is 23.8%larger than that of the flat milling tool,which is also 30.4%smaller than that of the blade milling tool.Compared with the flat milling tool,the working efficiency of the blade milling tool improves by 79.9%and the slope milling tool improves by 111.1%.Also,the wear resistance of the blade milling tool decreases by 102.7%,while the slope milling tool declines by 32.6%when compared with the flat milling tool.Therefore,the slope milling tool has the characteristics of moderate torque,stable working conditions,the highest working efficiency,and fine wear resistance,which is preferably used to mill multistage fracturing ball seats.This study provides a theoretical basis and guidance for milling multistage fracturing ball seats on-site and realizing production with a large diameter in later stages of multistage fracturing wells.
基金supported by the National Major Science and Technology Project“Study on coalbed methane recovery equipment and technologies”(No.2016ZX05042-004)Graduate Student Innovation Project Funding Project“Study on the design of pneumatic technologies and equipment for unloading liquids and producing gas through a preset pipe string”(No.YCX2018058).
文摘Ball-drop fracturing is a kind of technology that is commonly used for multistage fracturing of shale gas horizontal wells.At present,the ball injector cannot satisfy the operation demands of large bore and small spacing fracturing of shale gas wells due to its disadvantages,such as a small size of fracturing ball,a limited number of balls,complicated structure and poor applicability.In this paper,a new type of automatic ball injector with rotating plate and large bore was designed.There is a ball storage at the upper part of the ball injector and a ball injecting mechanism inside the pedestal at the lower part.And the ball injecting mechanism is controlled by the drive motor to inject the balls one by one.Then,collision analysis was carried out on its ball injecting process by using finite element method(FEM).Finally,simulation and prototype tests were conducted by using the arbitrary Lagrangian-Eulerian(ALE)mesh adaption method and the coupled smoothed particle hydrodynamics method(FEM-SPH).And the following research results were obtained.First,in the process of ball collision,the maximum equivalent stress,equivalent plastic strain and displacement are generated at the edge of the rotating plate.The maximum stress is about 600 MPa,which is less than the yield strength of 42CrMo(930 MPa),so the strength requirement is satisfied with a certain safety margin.Second,the prototype successfully passes the continuous ball injecting test of 12-stage fracturing process with the ball diameter of 64-108 mm and the ball contrast of 4 mm.In conclusion,this automatic ball injector with rotating plate and large bore is advantageous with simple operation and wide applicability and can effectively address the needs of multistage fracturing of shale gas horizontal wells.
基金supported in part by the National Key Research and Development Project of China(No.2022YFC3004602)in part by the National Natural Science Foundation of China(Nos.52121003 and 52342403).
文摘Multistage fracturing technology has been used to enhance tight hydrocarbon resource recovery.Determining the proper well spacing and fracturing strategy is crucial for generating a complex fracture network that facilitates oil and gas flow in reservoirs.The stress-shadow effect that occurs between multiple wells significantly affects the development of fracture networks in reservoirs.However,the quantification of the stress-shadow effect and its influence on fracture networks has not been satisfactorily resolved because of the difficulties in detecting and identifying fracture propagation and reorientation in reservoirs.In this study,based on the geological information from the Shengli oilfield,we applied a hybrid finite element-discrete element method to analyze engineering-scale three-dimensional fracture propagation and reorientation by altering well spacings and fracturing strategies.The results indicate that the fracturing area generated by the synchronous fracturing scheme is much smaller than those generated by the sequential and alternative schemes.An alternative hydrofracturing scheme is optimal with respect to fracturing area.The stress-blind area was defined to quantify the mechanical disturbance between adjacent wells.Our study improves the understanding of the effect of fracturing schemes on fracture networks and the impact of independent factors contributing to stress-shadow effects.
基金supported by the National Natural Science Foundation of China (No.52104008&No.52274042)the Natural Science Foundation of Sichuan,China (No.2024NSFSC0963)。
文摘The “well factory” mode's high-density well placement and multi-stage hydraulic fracturing technology enable efficient development of unconventional oil and gas resources.However,the deployment of platform wells in the “well factory” model results in small wellbore spacing,and the stress disturbances caused by fracturing operations may affect neighboring wells,leading to inter-well interference phenomena that cause casing deformation.This study investigates the issue of inter-well interference causing casing deformation or even failure during multi-stage hydraulic fracturing in the “well factory”model,and predicts high-risk locations for casing failure.A flow-mechanics coupled geomechanical finite element model with retaining geological stratification characteristics was established.Based on the theory of hydraulic fracturing-induced rock fragmentation and fluid action leading to the degradation of rock mechanical properties,the model simulated the four-dimensional evolution of multi-well fracturing areas over time and space,calculating the disturbance in the regional stress field caused by fracturing operations.Subsequently,the stress distribution of multiple well casings at different time points was calculated to predict high-risk locations for casing failure.The research results show that the redistribution of the stress field in the fracturing area increases the stress on the casing.The overlapping fracturing zones between wells cause significant stress interference,greatly increasing the risk of deformation and failure.By analyzing the Mises stress distribution of multi-well casings,high-risk locations for casing failure can be identified.The conclusion is that the key to preventing casing failure in platform wells in the “well factory” model is to optimize the spatial distribution of fracturing zones between wells and reasonably arrange well spacing.The study provides new insights and methods for predicting casing failure in unconventional oil and gas reservoirs and offers references for optimizing drilling and fracturing designs.
基金financial support for this work provided by the National Natural Science Foundation of China(Nos.52274147,52374101,and 32111530138)the Jiangsu Province Basic Research Special Fund-Soft Science Research(No.BZ2024024)the State Key Research Development Program of China(No.2022YFC3004603).
文摘Multistage hydraulic fracturing of horizontal wells(MFHW)is a promising technology for controlling coal burst caused by thick and hard roofs in China.However,challenges remain regarding the MFHW control mechanism of coal burst and assessment of the associated fracturing effects.In this study,these challenges were investigated through numerical modelling and field applications,based on the actual operating parameters of MFHW for hard roofs in a Chinese coal mine.A damage parameter(D)is proposed to assess the degree of hydraulic fracturing in the roof.The mechanisms and effects of MFHW for controlling coal burst are analyzed using microseismic(MS)data and front-abutment stress distribution.Results show that the degree of fracturing can be categorized into lightly-fractured(D≤0.3),moderately fractured(0.3<D≤0.6),well-fractured(0.6<D≤0.9),and over-fractured(0.9<D≤0.95).A response stage in the fracturing process,characterized by a slowdown in crack development,indicates the transition to a wellfractured condition.After MFHW,the zone range and peak value of the front-abutment stress decrease.Additionally,MS events shift from near the coal seam to the fractured roof layers,with the number of MS events increases while the average MS energy decreases.The MFHW control mechanisms of coal bursts involve mitigating mining-induced stress and reducing seismic activity during longwall retreat,ensuring stresses remain below the ultimate stress level.These findings provide a reference for evaluating MFHW fracturing effects and controlling coal burst disasters in engineering.
基金The work is supported by the Sub-Project of“Research on Key Technologies and Equipment of Reservoir Stimulation”of China National Petroleum Corporation Post–14th Five-Year Plan Forward-Looking Major Science and Technology Project“Research on New Technology of Monitoring and Diagnosis of Horizontal Well Hydraulic Fracture Network Distribution Pattern”(2021DJ4502).
文摘Multistage multi-cluster hydraulic fracturing has enabled the economic exploitation of shale reservoirs,but the interpretation of hydraulic fracture parameters is challenging.The pressure signals after pump shutdown are influenced by hydraulic fractures,which can reflect the geometric features of hydraulic fracture.The shutdown pressure can be used to interpret the hydraulic fracture parameters in a real-time and cost-effective manner.In this paper,a mathematical model for shutdown pressure evolution is developed considering the effects of wellbore friction,perforation friction and fluid loss in fractures.An efficient numerical simulation method is established by using the method of characteristics.Based on this method,the impacts of fracture half-length,fracture height,opened cluster and perforation number,and filtration coefficient on the evolution of shutdown pressure are analyzed.The results indicate that a larger fracture half-length may hasten the decay of shutdown pressure,while a larger fracture height can slow down the decay of shutdown pressure.A smaller number of opened clusters and perforations can significantly increase the perforation friction and decrease the overall level of shutdown pressure.A larger filtration coefficient may accelerate the fluid filtration in the fracture and hasten the drop of the shutdown pressure.The simulation method of shutdown pressure,as well as the analysis results,has important implications for the interpretation of hydraulic fracture parameters.
基金This research was funded by the National Natural Science Foundation of China(grant number 51675534).
文摘The sleeve sealing ball seat is one of the important components in the multistage fracturing process of horizontal wells.The erosion and wear of the surface will decrease the sealing performance of the fracturing ball and the ball seat.This leads to pressure leakage during the fracturing process and fracturing failure.In this paper,combined with the actual ball seat materials and working conditions during the fracturing process,the erosion tests of ductile iron and tungsten carbide materials under different erosion speeds,angles,and mortar concentrations are carried out.Then the erosion test results were analyzed by mathematical fitting,and a set of erosion models suitable for sliding sleeve setting ball seat materials were innovatively established.For the first time,this paper combines the erosion model obtained from the experiment and the computational fluid dynamics(CFD)with Fluent software to simulate the erosion of the ball seat.Based on the simulation results,the morphology of the sliding sleeve seat ball after erosion is predicted.Through analysis of the test and simulation results,it is showed that the erosion rate of tungsten carbide material is lower and the wear resistance is better under the condition of small angle erosion.This research can offer a strong basis for fracturing site selection,surface treatment methods,and prediction of failure time of ball seats.
基金supported by the National Natural Science Foundation of China (No. 52074250)。
文摘Multistage fracturing of horizontal wells is a critical technology for unconventional oil and gas reservoir stimulation. Ball-throwing temporary plugging fracturing is a new method for realizing uniform fracturing along horizontal wells and plays an important role in increasing oil and gas production. However,the transportation and sealing law of temporary plugging balls(TPBs) in the perforation section of horizontal wells is still unclear. Using COMSOL computational fluid dynamics and a particle tracking module, we simulate the transportation process of TPBs in a horizontal wellbore and analyse the effects of the ball density, ball diameter, ball number, fracturing fluid injection rate, and viscosity on the plugging efficiency of TPB transportation. This study reveals that when the density of TPBs is close to that of the fracturing fluid and a moderate diameter of the TPB is used, the plugging efficiency can be substantially enhanced. The plugging efficiency is greater when the TPB number is close to twice the number of perforations and is lower when the number of TPBs is three times the number of perforations.Adjusting the fracturing fluid injection rate from low to high can control the position of the TPBs,improving plugging efficiency. As the viscosity of the fracturing fluid increases, the plugging efficiency of the perforations decreases near the borehole heel and increases near the borehole toe. In contrast, the plugging efficiency of the central perforation is almost unaffected by the fracturing fluid viscosity. This study can serve as a valuable reference for establishing the parameters for temporary plugging and fracturing.
