The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading f...The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading frequency, loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments. Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption, fracture surface with high quality, low cycle times, and high efficiency. The appropriate parameters were as follows： loading frequency 3-5 Hz, notch tip radius r = （0.2-0.3） mm, opening angle α = 60°, and notch depth t = （0.14-0.17）D.展开更多
Railway steel bridge belongs to large-scale weld structures suffered with cyclic dynamic stress generated by the train. In recent years, the section of bridge member becomes bigger, plate becomes thicker, connection f...Railway steel bridge belongs to large-scale weld structures suffered with cyclic dynamic stress generated by the train. In recent years, the section of bridge member becomes bigger, plate becomes thicker, connection form becomes more complicated and steel bridge is applied to wider districts even in the lower temperature environment. Thus, fatigue and fracture problems become more serious. On the basis of CTOD （crack tip open displacement） test data of 372 specimens tested in different temperatures, this paper discusses research work about fracture proof design that involves how to determine the criterion of CVN （Charpy V-notch） impact toughness by establishing the relationship between CTOD and CVN, how to prevent from brittle fracture by stress control in railway steel bridge design based on COD （crack open displacement） design curve through the test data and how to do the fatigue design for railway steel bridge at -50 ℃ of design temperature in an easy way. The method of fatigue design at -50 ℃ environment has been used for railway steel bridge structure of Qinghai-Tibet Railway in China.展开更多
Horizontal wells in the anisotropic reservoirs can be stimulated by hydraulic fracturing in order to create multiple finite-conductivity vertical fractures. Several methods for evaluating the productivity of the horiz...Horizontal wells in the anisotropic reservoirs can be stimulated by hydraulic fracturing in order to create multiple finite-conductivity vertical fractures. Several methods for evaluating the productivity of the horizontal wells have been presented in the literature. With such methods, however, it is still difficult to obtain an accurate result. This paper firstly presents the dimensionless conductivity theory of vertical fractures. Then models for calculating the equivalent wellbore radius and the skin factor due to flow convergence to the well bore are proposed after analyzing the steady-state flow in porous reservoirs. By applying the superposition principle to the pressure drop, a new method for evaluating the productivity of horizontal wells intercepted by multiple finite-conductivity fractures is developed. The influence of fracture conductivity and fracture half length on the horizontal well productivity is quantitatively analyzed with a synthetic case. Optimum fracture number and fracture space are further discussed in this study. The results prove that the method outlined here should be useful to design optimum fracturing of horizontal wells.展开更多
In this work, the unified fracture design （UFD） is extended for the first time to the fractured horizontal wells in heterogeneous closed box-shaped tight gas reservoirs. Utilizing the direct boundary element method ...In this work, the unified fracture design （UFD） is extended for the first time to the fractured horizontal wells in heterogeneous closed box-shaped tight gas reservoirs. Utilizing the direct boundary element method and influence function, the dimensionless fracture productivity index is obtained and expressed in the function of proppant volume and fracture geometry at the pseu- do-steady state. With the iterative method, the effectively propped permeability, kfe, is corrected using the i^-situ Reynolds number, NRe. The goal of this paper is to present a new UFD extension to design the proppant volume and the optimal fracture geometry. The results show that there exists an optimal proppant volume for a certain reservoir. The small aspect ratio （yJXe） and high permeability reservoirs need short and wide fractures to diminish the non-Darcy effect. On the contrary, long and narrow fractures are required for the large aspect ratio and low permeability reservoirs. A small proppant volame is prone to creating long fractures, while a relatively large proppant volume creates wide fractures. The new extension can be used to evaluate the previous fracture parameters and design the following fracture parameters of the fractured horizontal well in heterogeneous tight gas reservoirs, with the non-Darcy effect taken into account.展开更多
Maximizing petroleum production while efficiently managing the operational costs is the oil and gas industry's primary goal which requires innovative engineering approaches and production-enhancing treatments such...Maximizing petroleum production while efficiently managing the operational costs is the oil and gas industry's primary goal which requires innovative engineering approaches and production-enhancing treatments such as hydraulic fracturing(HF).During the HF process,the injected fluid mixed with sands or proppants will create permanent fluid channels to drain more of the reservoir volume.The level of complexity and various constraints involved in real field treatments have made HF even more chal-lenging in layered carbonate reservoirs with the water drive mechanism.A prominent concern is the downward fracture growth to the oil/water contact zone that may cause unfavorable water cut levels.This fracture height confinement criterion necessitates optimization of fracture dimension design.Fracture height development is mainly a function of in-situ stress conditions and stress magnitude differences between geologic layers.In cases with a water table at the proximity of the wellbore,fracture height directly affects the operational success.This paper demonstrates a practical step-by-step approach towards the design of hydraulic fracturing treatment in an offshore carbonate oil reservoir.The modeling process involves optimization of the location,number,and conductivity of the proposed fractures.In-jection of high viscosity fluid causes a bi-wing vertical planar fracture to propagate perpendicular to the direction of minimum horizontal stress in the strike-slip faulting regime.Dimensions of the induced hydraulic fractures are also impacted by the amount and type of proppants.However,as with this case study,the magnitude of vertical stress is in the same range as the maximum horizontal stress;the fracture height growth is the limiting factor.The LGR method is used to define fractures in the dynamic reservoir model which has been built based on a complete set of data ranging from the analyses of logs,core samples,and seismic details,to perform production forecasts and economic evaluation.Then a hydraulic fracture software is implemented to provide a timetable for fracturing fluid volume and mixing proppant concentration for the desired fracture dimensions.The results show that,despite the operator's previous perception,five hydraulic fractures per well would be economical,which include a 150 ft long fracture and four shorter fractures with an approximate length of 75 ft designed to manage the risk of penetration into the water-bearing formations.Due to the reservoir pressure drop by time and more flexible fracture dimension constraints at earlier stages of production,executing such stimulations earlier than later would improve the commercial outcomes.展开更多
Unified Fracture Design(UFD)bridges the gap between practices and theory in the hydraulic fracturing industry.It represents a technique to design hydraulic fracturing treatment with a particular amount of proppant.Thi...Unified Fracture Design(UFD)bridges the gap between practices and theory in the hydraulic fracturing industry.It represents a technique to design hydraulic fracturing treatment with a particular amount of proppant.This design could provide the maximum fold-of-increase(FOI)in productivity-index(PI)after hydraulic fracturing treatment.The UFD optimization tool is very effective,but it has assumptions like any other model.One assumption of UFD optimization technique;is a single-layer assumption.This assumption does not align with the limited entry fracturing design concept.In limited entry fracturing,the frictional pressure is employed to offset the stress differences between multi-layers reservoirs to attain fluid injection through these layers,intended to deliver an optimal fracture conductivity in all layers.The drawback of this assumption is the underestimation of the actual value of FOI in PI.This paper aims to recast the original unified fracture design approach to extend the optimal UFD to a multilayer reservoir to predict the FOI in PI after limited entry fracturing treatment.The recasting tool for this problem to find the optimum solution is Artificial Neural Networks(ANN).The architected ANN model is based on actual historical data of limited entry fracturing treatments.A statistical comparison between the proposed ANN model and classical UFD technique demonstrates that ANN model solution has a more reliable estimation of FOI in PI with the actual historical data.展开更多
基金supported by the Ministry of Education of China(No.208152)Gansu Natural Science Foundation(No.3ZS061-A52-47).
文摘The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading frequency, loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments. Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption, fracture surface with high quality, low cycle times, and high efficiency. The appropriate parameters were as follows： loading frequency 3-5 Hz, notch tip radius r = （0.2-0.3） mm, opening angle α = 60°, and notch depth t = （0.14-0.17）D.
文摘Railway steel bridge belongs to large-scale weld structures suffered with cyclic dynamic stress generated by the train. In recent years, the section of bridge member becomes bigger, plate becomes thicker, connection form becomes more complicated and steel bridge is applied to wider districts even in the lower temperature environment. Thus, fatigue and fracture problems become more serious. On the basis of CTOD （crack tip open displacement） test data of 372 specimens tested in different temperatures, this paper discusses research work about fracture proof design that involves how to determine the criterion of CVN （Charpy V-notch） impact toughness by establishing the relationship between CTOD and CVN, how to prevent from brittle fracture by stress control in railway steel bridge design based on COD （crack open displacement） design curve through the test data and how to do the fatigue design for railway steel bridge at -50 ℃ of design temperature in an easy way. The method of fatigue design at -50 ℃ environment has been used for railway steel bridge structure of Qinghai-Tibet Railway in China.
文摘Horizontal wells in the anisotropic reservoirs can be stimulated by hydraulic fracturing in order to create multiple finite-conductivity vertical fractures. Several methods for evaluating the productivity of the horizontal wells have been presented in the literature. With such methods, however, it is still difficult to obtain an accurate result. This paper firstly presents the dimensionless conductivity theory of vertical fractures. Then models for calculating the equivalent wellbore radius and the skin factor due to flow convergence to the well bore are proposed after analyzing the steady-state flow in porous reservoirs. By applying the superposition principle to the pressure drop, a new method for evaluating the productivity of horizontal wells intercepted by multiple finite-conductivity fractures is developed. The influence of fracture conductivity and fracture half length on the horizontal well productivity is quantitatively analyzed with a synthetic case. Optimum fracture number and fracture space are further discussed in this study. The results prove that the method outlined here should be useful to design optimum fracturing of horizontal wells.
基金supported by the National Natural Science Foundation of China(Grant Nos.5152540451504203&51374178)+2 种基金Open Fund(Grant No.PLN1515)of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)a special fund from China’s central government for the development of local colleges and universities-the National First-level Discipline in the Oil and Gas Engineering Project(Grant No.20150727)Scientific Research Starting Project of Southwest Petroleum University(Grant No.2014QHZ004)
文摘In this work, the unified fracture design （UFD） is extended for the first time to the fractured horizontal wells in heterogeneous closed box-shaped tight gas reservoirs. Utilizing the direct boundary element method and influence function, the dimensionless fracture productivity index is obtained and expressed in the function of proppant volume and fracture geometry at the pseu- do-steady state. With the iterative method, the effectively propped permeability, kfe, is corrected using the i^-situ Reynolds number, NRe. The goal of this paper is to present a new UFD extension to design the proppant volume and the optimal fracture geometry. The results show that there exists an optimal proppant volume for a certain reservoir. The small aspect ratio （yJXe） and high permeability reservoirs need short and wide fractures to diminish the non-Darcy effect. On the contrary, long and narrow fractures are required for the large aspect ratio and low permeability reservoirs. A small proppant volame is prone to creating long fractures, while a relatively large proppant volume creates wide fractures. The new extension can be used to evaluate the previous fracture parameters and design the following fracture parameters of the fractured horizontal well in heterogeneous tight gas reservoirs, with the non-Darcy effect taken into account.
文摘Maximizing petroleum production while efficiently managing the operational costs is the oil and gas industry's primary goal which requires innovative engineering approaches and production-enhancing treatments such as hydraulic fracturing(HF).During the HF process,the injected fluid mixed with sands or proppants will create permanent fluid channels to drain more of the reservoir volume.The level of complexity and various constraints involved in real field treatments have made HF even more chal-lenging in layered carbonate reservoirs with the water drive mechanism.A prominent concern is the downward fracture growth to the oil/water contact zone that may cause unfavorable water cut levels.This fracture height confinement criterion necessitates optimization of fracture dimension design.Fracture height development is mainly a function of in-situ stress conditions and stress magnitude differences between geologic layers.In cases with a water table at the proximity of the wellbore,fracture height directly affects the operational success.This paper demonstrates a practical step-by-step approach towards the design of hydraulic fracturing treatment in an offshore carbonate oil reservoir.The modeling process involves optimization of the location,number,and conductivity of the proposed fractures.In-jection of high viscosity fluid causes a bi-wing vertical planar fracture to propagate perpendicular to the direction of minimum horizontal stress in the strike-slip faulting regime.Dimensions of the induced hydraulic fractures are also impacted by the amount and type of proppants.However,as with this case study,the magnitude of vertical stress is in the same range as the maximum horizontal stress;the fracture height growth is the limiting factor.The LGR method is used to define fractures in the dynamic reservoir model which has been built based on a complete set of data ranging from the analyses of logs,core samples,and seismic details,to perform production forecasts and economic evaluation.Then a hydraulic fracture software is implemented to provide a timetable for fracturing fluid volume and mixing proppant concentration for the desired fracture dimensions.The results show that,despite the operator's previous perception,five hydraulic fractures per well would be economical,which include a 150 ft long fracture and four shorter fractures with an approximate length of 75 ft designed to manage the risk of penetration into the water-bearing formations.Due to the reservoir pressure drop by time and more flexible fracture dimension constraints at earlier stages of production,executing such stimulations earlier than later would improve the commercial outcomes.
文摘Unified Fracture Design(UFD)bridges the gap between practices and theory in the hydraulic fracturing industry.It represents a technique to design hydraulic fracturing treatment with a particular amount of proppant.This design could provide the maximum fold-of-increase(FOI)in productivity-index(PI)after hydraulic fracturing treatment.The UFD optimization tool is very effective,but it has assumptions like any other model.One assumption of UFD optimization technique;is a single-layer assumption.This assumption does not align with the limited entry fracturing design concept.In limited entry fracturing,the frictional pressure is employed to offset the stress differences between multi-layers reservoirs to attain fluid injection through these layers,intended to deliver an optimal fracture conductivity in all layers.The drawback of this assumption is the underestimation of the actual value of FOI in PI.This paper aims to recast the original unified fracture design approach to extend the optimal UFD to a multilayer reservoir to predict the FOI in PI after limited entry fracturing treatment.The recasting tool for this problem to find the optimum solution is Artificial Neural Networks(ANN).The architected ANN model is based on actual historical data of limited entry fracturing treatments.A statistical comparison between the proposed ANN model and classical UFD technique demonstrates that ANN model solution has a more reliable estimation of FOI in PI with the actual historical data.
