Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Bas...Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Basin of China,we presented an integrated workflow to investigate how(1)proppant placement in induced fracture and(2)non-linear flow in reservoir matrix would affect well productivity and fluid flow in the reservoir.Compared with our research before(Yue et al.,2020),here we extended this study into the development of multi-stage fractured horizontal wells(MFHWs)with large-scale complicated fracture geometry.The integrated workflow is based on the finite element method and consists of simulation models for proppant-laden fluid flow,fracture flow,and non-linear seepage flow,respectively.Simulation results indicate that the distribution of proppant inside the induced cracks significantly affects the productivity of the MFHW.When we assign an idealized proppant distribution instead of the real distribution,there will be an overestimation of 44.98%in daily oil rate and 30.63%in cumulative oil production after continuous development of 1000 days.Besides,threshold pressure gradient(TPG)also significantly affects the well performance in tight oil reservoirs.If we simply apply linear Darcy’s law to the reservoir matrix,the overall cumulative oil production can be overrated by 77%after 1000 days of development.In general,this research provides new insights into the development of tight oil reservoirs with TPG and meanwhile reveals the significance of proppant distribution and non-linear fluid flow in the production scenario design.展开更多
An autonomous altitude adjustment system for a stratospheric satellite(StratoSat)platform is proposed.This platform consists of a helium balloon,a ballonet,and a two-way blower.The helium balloon generates lift to bal...An autonomous altitude adjustment system for a stratospheric satellite(StratoSat)platform is proposed.This platform consists of a helium balloon,a ballonet,and a two-way blower.The helium balloon generates lift to balance the platform gravity.The two-way blower inflates and deflates the ballonet to regulate the buoyancy.Altitude adjustment is achieved by tracking the differential pressure difference(DPD),and a threshold switching strategy is used to achieve blower flow control.The vertical acceleration regulation ability is decided not only by the blower flow rate,but also by the designed margin of pressure difference(MPD).Pressure difference is a slow-varying variable compared with altitude,and it is adopted as the control variable.The response speed of the actuator to disturbance can be delayed,and the overshoot caused by the large inertia of the platform is inhibited.This method can maintain a high tracking accuracy and reduce the complexity of model calculation,thus improving the robustness of controller design.展开更多
Modelling of migration and accumulation of elements Au and Ag in rocks under temperatures of 350–450°C and a confining pressure of 300 MPa and axial pressure of 100–150 MPa is conducted. It is found that the co...Modelling of migration and accumulation of elements Au and Ag in rocks under temperatures of 350–450°C and a confining pressure of 300 MPa and axial pressure of 100–150 MPa is conducted. It is found that the contents of gold and silver get higher in metallic sulphides such as pyrite, chalcopyrite and sphalerite as well as in quartz and muscovite, and get lower in chlorite, biotite, seriate, albite and calcite, showing that tectono-dynamics is one of the important factors for petrogenesis and metallogenesis.展开更多
Since October 2008,China's social consumption of electricity had,for the first time,grown negatively compared to the same period of the previous year,and in November the negative growth range further expanded. The...Since October 2008,China's social consumption of electricity had,for the first time,grown negatively compared to the same period of the previous year,and in November the negative growth range further expanded. The major pressure faced by the electricity industry has now turned from the contradiction between coal and electricity to electricity quantity. This is undoubtedly a true and new test to electricity enterprises which get used to high growth but are now suffering great losses. The reform of electricity system has already been in great difficulties and now is getting into a more serious situation. In order to help readers improve their knowledge and understanding of the current tough situation faced by the electricity industry and discuss how to alleviate and get through the difficulty resulted from the economic crisis "encountered once every one hundred years" by joint efforts of all parties concerned,a Seminar on Crisis and Countermeasures for Electricity Industry was held on November 20,2008. Here are some extracts from the speeches of four experts.展开更多
An opened bottom cylinder is a large-diameter cylinder placed on a rubber base or embedded in a soil foundation. The settlement of such a cylinder differs greatly from that of a closed bottom cylinder and so does the ...An opened bottom cylinder is a large-diameter cylinder placed on a rubber base or embedded in a soil foundation. The settlement of such a cylinder differs greatly from that of a closed bottom cylinder and so does the distribution of inner soil pressure over the opened bottom cylindrical structure. Through investigation of the settlement and the inner soil pressure on the opened bottom cylinder by model experiments, the interactions among the filler inside the cylinder, subsoil and cylinder are analyzed. The adjusting mechanism of friction resistance between the inner filler and the wall of the cylinder during overturning of the cylinder is discussed. Based on the experimental study, a method for calculating the inner soil pressure on the cylindrical structure under axisymmetric loading or non- axisymmetric (with lateral) loading is proposed in this paper. Meanwhile, the effective anti-overturning ratio of the opened bottom cylinder is derived.展开更多
A novel laboratory simulation method for modeling multi-staged fracturing in a horizontal well was established based on a true tri-axial hydraulic fracturing simulation system. Using this method, the influences of net...A novel laboratory simulation method for modeling multi-staged fracturing in a horizontal well was established based on a true tri-axial hydraulic fracturing simulation system. Using this method, the influences of net pressure in hydraulic fracture, stage spacing, perforation parameter, horizontal stress bias and well cementation quality on the propagation geometry of multiple fractures in a tight sandstone formation were studied in detail. The specimen splitting and analogy analysis of fracturing curve patterns reveals: Multiple fractures tend to merge under the condition of high horizontal stress bias and short stage spacing with pre-existing hydraulic fractures under critical closure situation, and the propagation of subsequent fractures is possibly suppressed because of high net pressure in pre-created fractures and asymmetric distribution of fracture width. And the subsequently created fractures are situated in the induced stress decreasing zone due to long stage spacing, leading to weak stress interference, and perforation with intense density and deep penetration facilitates the decrease of initiation fracture pressure. The deflection angle of subsequent fracture and horizontal stress variation tend to be amplified under low horizontal bias with constant net pressure in fractures. The longitudinal fracture is likely to be initiated at the interface of wellbore and concrete sample with poor cementation quality. The initiation fracture pressure of the different stages increases in turn, with the largest increase of 30%. Pressure quickly declines after initiation with low propagation pressure when the transverse hydraulic fracture is formed. The pressure reduces with fluctuation after the initiation of fracture when the fracture deflects, the extension pressure is high, and the fracture formed is tortuous and narrow. There is a violently fluctuant rise of pressure with multiple peak values when longitudinal fracture created, and it is hard to distinguish the features between the initiation stage and propagation stage.展开更多
A oilfield was an oil reservoir with strong bottom water in offshore, the water cut was as high as 96%. In the high water cut stage, the most effective way of increasing oil production was to extract liquid and increa...A oilfield was an oil reservoir with strong bottom water in offshore, the water cut was as high as 96%. In the high water cut stage, the most effective way of increasing oil production was to extract liquid and increase oil. The processing capacity of oilfield fluid was limited by the conditions. By using Petrel-RE-2017 software, combining reservoir engineering and percolation mechanics methods, this paper analyzes the effect of large-scale liquid pumping, expand coverage and shut-in coning in oil reservoirs with bottom water, and formulates the adjustment strategy of single well production structure of the whole oilfield. It was confirmed that large-scale liquid production can expand coverage and shutting down well can reduce water cut. It can provide reference and guidance for oil field with strong bottom water when it encounters bottleneck of liquid treatment capacity.展开更多
Shale gas wells frequently suffer from liquid loading and insufficient formation pressure in the late stage of production.To address this issue,an intelligent production optimization method for low pressure and low pr...Shale gas wells frequently suffer from liquid loading and insufficient formation pressure in the late stage of production.To address this issue,an intelligent production optimization method for low pressure and low productivity shale gas well is proposed.Based on the artificial intelligence algorithms,this method realizes automatic production and monitoring of gas well.The method can forecast the production performance of a single well by using the long short-term memory neural network and then guide gas well production accordingly,to fulfill liquid loading warning and automatic intermittent production.Combined with adjustable nozzle,the method can keep production and pressure of gas wells stable automatically,extend normal production time of shale gas wells,enhance automatic level of well sites,and reach the goal of refined production management by making production regime for each well.Field tests show that wells with production regime optimized by this method increased 15%in estimated ultimate reserve(EUR).Compared with the development mode of drainage after depletion recovery,this method is more economical and can increase and stabilize production effectively,so it has a bright application prospect.展开更多
The response of an adjustable critical-flow Venturi nozzle is investigated through a set indoor experiments aimed to determine the related critical flow rate,critical pressure ratio,and discharge coefficient.The effec...The response of an adjustable critical-flow Venturi nozzle is investigated through a set indoor experiments aimed to determine the related critical flow rate,critical pressure ratio,and discharge coefficient.The effect of a variation in the cone displacement and liquid content on the critical flow characteristics is examined in detail and it is shown that the former can be used to effectively adjust the critical flow rate.The critical pressure ratio of the considered nozzle is above 0.85,and the critical flow control deviation of the gas flow is within±3%.Liquid flow can reduce the gas critical mass flow rate accordingly,especially for the cases with larger liquid volume and lower inlet pressure.The set of results and conclusions provided are intended to support the optimization of steam injection techniques in the context of heavy oil recovery processes.展开更多
基金The authors gratefully acknowledge the financial supports from the National Science Foundation of China under Grant 52274027 as well as the High-end Foreign Experts Recruitment Plan of the Ministry of Science and Technology China under Grant G2022105027L.
文摘Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Basin of China,we presented an integrated workflow to investigate how(1)proppant placement in induced fracture and(2)non-linear flow in reservoir matrix would affect well productivity and fluid flow in the reservoir.Compared with our research before(Yue et al.,2020),here we extended this study into the development of multi-stage fractured horizontal wells(MFHWs)with large-scale complicated fracture geometry.The integrated workflow is based on the finite element method and consists of simulation models for proppant-laden fluid flow,fracture flow,and non-linear seepage flow,respectively.Simulation results indicate that the distribution of proppant inside the induced cracks significantly affects the productivity of the MFHW.When we assign an idealized proppant distribution instead of the real distribution,there will be an overestimation of 44.98%in daily oil rate and 30.63%in cumulative oil production after continuous development of 1000 days.Besides,threshold pressure gradient(TPG)also significantly affects the well performance in tight oil reservoirs.If we simply apply linear Darcy’s law to the reservoir matrix,the overall cumulative oil production can be overrated by 77%after 1000 days of development.In general,this research provides new insights into the development of tight oil reservoirs with TPG and meanwhile reveals the significance of proppant distribution and non-linear fluid flow in the production scenario design.
基金the National Natural Science Foundation of China(No.52175103)。
文摘An autonomous altitude adjustment system for a stratospheric satellite(StratoSat)platform is proposed.This platform consists of a helium balloon,a ballonet,and a two-way blower.The helium balloon generates lift to balance the platform gravity.The two-way blower inflates and deflates the ballonet to regulate the buoyancy.Altitude adjustment is achieved by tracking the differential pressure difference(DPD),and a threshold switching strategy is used to achieve blower flow control.The vertical acceleration regulation ability is decided not only by the blower flow rate,but also by the designed margin of pressure difference(MPD).Pressure difference is a slow-varying variable compared with altitude,and it is adopted as the control variable.The response speed of the actuator to disturbance can be delayed,and the overshoot caused by the large inertia of the platform is inhibited.This method can maintain a high tracking accuracy and reduce the complexity of model calculation,thus improving the robustness of controller design.
文摘Modelling of migration and accumulation of elements Au and Ag in rocks under temperatures of 350–450°C and a confining pressure of 300 MPa and axial pressure of 100–150 MPa is conducted. It is found that the contents of gold and silver get higher in metallic sulphides such as pyrite, chalcopyrite and sphalerite as well as in quartz and muscovite, and get lower in chlorite, biotite, seriate, albite and calcite, showing that tectono-dynamics is one of the important factors for petrogenesis and metallogenesis.
文摘Since October 2008,China's social consumption of electricity had,for the first time,grown negatively compared to the same period of the previous year,and in November the negative growth range further expanded. The major pressure faced by the electricity industry has now turned from the contradiction between coal and electricity to electricity quantity. This is undoubtedly a true and new test to electricity enterprises which get used to high growth but are now suffering great losses. The reform of electricity system has already been in great difficulties and now is getting into a more serious situation. In order to help readers improve their knowledge and understanding of the current tough situation faced by the electricity industry and discuss how to alleviate and get through the difficulty resulted from the economic crisis "encountered once every one hundred years" by joint efforts of all parties concerned,a Seminar on Crisis and Countermeasures for Electricity Industry was held on November 20,2008. Here are some extracts from the speeches of four experts.
文摘An opened bottom cylinder is a large-diameter cylinder placed on a rubber base or embedded in a soil foundation. The settlement of such a cylinder differs greatly from that of a closed bottom cylinder and so does the distribution of inner soil pressure over the opened bottom cylindrical structure. Through investigation of the settlement and the inner soil pressure on the opened bottom cylinder by model experiments, the interactions among the filler inside the cylinder, subsoil and cylinder are analyzed. The adjusting mechanism of friction resistance between the inner filler and the wall of the cylinder during overturning of the cylinder is discussed. Based on the experimental study, a method for calculating the inner soil pressure on the cylindrical structure under axisymmetric loading or non- axisymmetric (with lateral) loading is proposed in this paper. Meanwhile, the effective anti-overturning ratio of the opened bottom cylinder is derived.
文摘A novel laboratory simulation method for modeling multi-staged fracturing in a horizontal well was established based on a true tri-axial hydraulic fracturing simulation system. Using this method, the influences of net pressure in hydraulic fracture, stage spacing, perforation parameter, horizontal stress bias and well cementation quality on the propagation geometry of multiple fractures in a tight sandstone formation were studied in detail. The specimen splitting and analogy analysis of fracturing curve patterns reveals: Multiple fractures tend to merge under the condition of high horizontal stress bias and short stage spacing with pre-existing hydraulic fractures under critical closure situation, and the propagation of subsequent fractures is possibly suppressed because of high net pressure in pre-created fractures and asymmetric distribution of fracture width. And the subsequently created fractures are situated in the induced stress decreasing zone due to long stage spacing, leading to weak stress interference, and perforation with intense density and deep penetration facilitates the decrease of initiation fracture pressure. The deflection angle of subsequent fracture and horizontal stress variation tend to be amplified under low horizontal bias with constant net pressure in fractures. The longitudinal fracture is likely to be initiated at the interface of wellbore and concrete sample with poor cementation quality. The initiation fracture pressure of the different stages increases in turn, with the largest increase of 30%. Pressure quickly declines after initiation with low propagation pressure when the transverse hydraulic fracture is formed. The pressure reduces with fluctuation after the initiation of fracture when the fracture deflects, the extension pressure is high, and the fracture formed is tortuous and narrow. There is a violently fluctuant rise of pressure with multiple peak values when longitudinal fracture created, and it is hard to distinguish the features between the initiation stage and propagation stage.
文摘A oilfield was an oil reservoir with strong bottom water in offshore, the water cut was as high as 96%. In the high water cut stage, the most effective way of increasing oil production was to extract liquid and increase oil. The processing capacity of oilfield fluid was limited by the conditions. By using Petrel-RE-2017 software, combining reservoir engineering and percolation mechanics methods, this paper analyzes the effect of large-scale liquid pumping, expand coverage and shut-in coning in oil reservoirs with bottom water, and formulates the adjustment strategy of single well production structure of the whole oilfield. It was confirmed that large-scale liquid production can expand coverage and shutting down well can reduce water cut. It can provide reference and guidance for oil field with strong bottom water when it encounters bottleneck of liquid treatment capacity.
基金Supported by the China National Science and Technology Major Project(2017ZX05037-004).
文摘Shale gas wells frequently suffer from liquid loading and insufficient formation pressure in the late stage of production.To address this issue,an intelligent production optimization method for low pressure and low productivity shale gas well is proposed.Based on the artificial intelligence algorithms,this method realizes automatic production and monitoring of gas well.The method can forecast the production performance of a single well by using the long short-term memory neural network and then guide gas well production accordingly,to fulfill liquid loading warning and automatic intermittent production.Combined with adjustable nozzle,the method can keep production and pressure of gas wells stable automatically,extend normal production time of shale gas wells,enhance automatic level of well sites,and reach the goal of refined production management by making production regime for each well.Field tests show that wells with production regime optimized by this method increased 15%in estimated ultimate reserve(EUR).Compared with the development mode of drainage after depletion recovery,this method is more economical and can increase and stabilize production effectively,so it has a bright application prospect.
基金The authors would like to acknowledge the support provided by the National Natural Science Foundation of China(No.62173049)the open fund of the Key Laboratory of Exploration Technologies for Oil and Gas Resources(Yangtze University),Ministry of Education(Grant K2021-17).
文摘The response of an adjustable critical-flow Venturi nozzle is investigated through a set indoor experiments aimed to determine the related critical flow rate,critical pressure ratio,and discharge coefficient.The effect of a variation in the cone displacement and liquid content on the critical flow characteristics is examined in detail and it is shown that the former can be used to effectively adjust the critical flow rate.The critical pressure ratio of the considered nozzle is above 0.85,and the critical flow control deviation of the gas flow is within±3%.Liquid flow can reduce the gas critical mass flow rate accordingly,especially for the cases with larger liquid volume and lower inlet pressure.The set of results and conclusions provided are intended to support the optimization of steam injection techniques in the context of heavy oil recovery processes.
