Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in C...Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in China are generally of strong heterogeneity,which causes different fracture initiation pressures in different positions of lateral,making it difficult to ensure the balanced fracture initiation and propagation between clusters in multi-cluster perforating.It is in urgent need to precisely evaluate the difference in rock strength in lateral and determine the well section with similar rock strength to deploy fractures,so as to reach the goal of balanced stimulation.Based on the drilling and logging data,this paper establishes an unsupervised clustering model of mechanical specific energy of bit at the bottomhole the lateral.Then,the influence of drill string friction,composite drilling and jet-assisted rock breaking on the mechanical specific energy is analyzed,and the distribution and clustering categories of bottomhole mechanical specific energy with decimeter spatial resolution are obtained.Finally,a fracture deployment optimization method for horizontal well volumetric fracturing aiming balanced stimulation is developed by comprehensively considering inter-fracture interference,casing collar position,plug position,and clustering result of bottomhole mechanical specific energy.The following results are obtained.First,compared with brittleness index,Poisson's ratioandstressdifference,perforation erosion area isina strongercorrelationwith themechanical specific energy,andthemechanical specific energy can effectively characterize the difference in the amount of proppant injected into the perforation clusters in the lateral,so it can be served as one of the important indicators for the selection of fracture deployment position.Second,the drilling and logging data cleaning and smoothing and the clustering number selection by the elbow method are the key steps to obtain the clustering results of bottomhole mechanical specific energy,which can tell the difference in the mechanical specific energy with decimeter-level resolution.Third,the interval with mechanical specific energy within 10%of the averagevalue in the section is selected for deploying perforation clusters,and the compiled computer algorithm can automatically determine the optimal position of fracturing section and cluster,so as to realize the differential design of stage spacing and cluster spacing.In conclusion,the research results can further improve the fractures deployment efficiency and balanced stimulation of volumetric fracturing in unconventional oil andgasreservoirs,and this technology is expected to provide ideas andnew methods forthe fracturedeployment optimization of horizontal well volumetric fracturing in unconventional oil and gas reservoirs.展开更多
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
For figuring out the stress interference of multiphase fracture combinations and its effect on the fracture initiation pressure of subsequent hydraulic fracturing,a calculation model for the coupled stress field with ...For figuring out the stress interference of multiphase fracture combinations and its effect on the fracture initiation pressure of subsequent hydraulic fracturing,a calculation model for the coupled stress field with multiple induced fractures preexisted was established based on the calculation model for the stress field with single induced fracture preexisted,and the change laws of circumferential stress field around the wellbore under the effect of induced stress were analyzed.Then,the fracture initiation pressure of subsequent hydraulic fracturing was calculated according to the fracturing mechanics criterion.Finally,the effects of the length,phase,horizontal principal stress difference co-efficient and quantity of preexisting fractures on its initiation pressure were analyzed.And the following research results were obtained.First,the circumferential stress difference in the area near the fractures behind the preexisting fractures increase greatly and even the horizontal principal stress is reversed.Second,as the length of new preexisting fractures increases,the initiation pressure of initial preexisting fractures rises first and then drops.And when the length of new preexisting fractures is equal to that of the initial preexisting fractures,the initiation pressure of initial preexisting fractures drops quickly first and then slowly.Third,the initiation pressure of high phase fractures is lower than that of low phase fractures.Fourth,with the increase of fracture quantity,the initiation pressure of new preexisting fractures drops gradually,but the decline trend of initiation pressure difference is not obvious.Fifth,the stress interference of multiphase fractures influences the fracture initiation pressure,and high-phase long fractures and low-phase short fractures are both favorable for the simultaneous initiation of multiphase fractures.Sixth,syn-chronous propagation of multiple fractures can generate more complicated stress interference and excite the evolution of hydraulic fracture network,so as to realize uniform fracturing stimulation.In conclusion,the research results can provide a theoretical guidance for the design of fracturing operation,e.g.perforation phase of blasting induced fracturing,scale of induced fractures,and pump pressure of subsequent hydraulic fracturing.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
Exploration and development practices have proved that staged volumetric fracturing stimulation in horizontal wells is a key technology for tight sandstone gas development,and reservoir sweet spot is an important basi...Exploration and development practices have proved that staged volumetric fracturing stimulation in horizontal wells is a key technology for tight sandstone gas development,and reservoir sweet spot is an important basis for the perforation position selection and staged fracturing in the process of well location deployment and reservoir stimulation.Tight sandstone reservoirs are usually characterized by sandstone and mudstone interlayers with different thicknesses,and complex natural fracture distribution and geostress state.It is hard to predict“geological-engineering”dual sweet spots,and these two kinds of sweet spots are usually in different zones.As a result,there lacks a basis for the optimization of fracturing parameters to stimulate tight sandstone reservoirs.This paper establishes a geological sweet spot prediction model which takes into account total hydrocarbon content,reservoir porosity and other factors,then puts forward a 3D multi-scale engineering sweet spot evaluation method which takes into account lithology,fracture morphology,fracture mechanical behavior,and dilatation and shear dilation effect,andfinally a“geological-engineering”dual sweet spot evaluation model for tight sandstone reservoirs.Two wells in the tight sandstone gasfield in the Linxing Block of the Ordos Basin were selected as a case,and the dual sweet spot profiles,fracturing pressure and SRV were compared and analyzed.The results show that:1)shear dilation angle influences the distribution of engineering sweet spots at the most in the study area,followed by dissipated energy,elastic modulus and fracture energy;2)the geological sweet spot zone with a high coefficient is not necessarily the pay zone with high shale gas production;3)the engineering sweet spot zone with a high coefficient needs lower fracture pressure and can be stimulated relatively sufficiently;4)high-quality geological sweet spots and high-quality engineering sweet spots are poorly consistent in spatial location.In conclusion,the stimulation of tight sandstone gas reservoirs shall take geological sweet spot as the basis and engineering sweet spot as the guarantee,and the distribution of dual sweep spots should be considered comprehensively.The multi-scale“geological-engineering”dual sweet spot evaluation method proposed in this paper provides important technical support for the prediction of sweet spots of the tight sandstone gas and the optimization of development schemes in the study area.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 Science Fund for Excellent Youth of the National Natural Science Foundation of China"Well hydrodynamics and engineering"(No.52122401).
文摘Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in China are generally of strong heterogeneity,which causes different fracture initiation pressures in different positions of lateral,making it difficult to ensure the balanced fracture initiation and propagation between clusters in multi-cluster perforating.It is in urgent need to precisely evaluate the difference in rock strength in lateral and determine the well section with similar rock strength to deploy fractures,so as to reach the goal of balanced stimulation.Based on the drilling and logging data,this paper establishes an unsupervised clustering model of mechanical specific energy of bit at the bottomhole the lateral.Then,the influence of drill string friction,composite drilling and jet-assisted rock breaking on the mechanical specific energy is analyzed,and the distribution and clustering categories of bottomhole mechanical specific energy with decimeter spatial resolution are obtained.Finally,a fracture deployment optimization method for horizontal well volumetric fracturing aiming balanced stimulation is developed by comprehensively considering inter-fracture interference,casing collar position,plug position,and clustering result of bottomhole mechanical specific energy.The following results are obtained.First,compared with brittleness index,Poisson's ratioandstressdifference,perforation erosion area isina strongercorrelationwith themechanical specific energy,andthemechanical specific energy can effectively characterize the difference in the amount of proppant injected into the perforation clusters in the lateral,so it can be served as one of the important indicators for the selection of fracture deployment position.Second,the drilling and logging data cleaning and smoothing and the clustering number selection by the elbow method are the key steps to obtain the clustering results of bottomhole mechanical specific energy,which can tell the difference in the mechanical specific energy with decimeter-level resolution.Third,the interval with mechanical specific energy within 10%of the averagevalue in the section is selected for deploying perforation clusters,and the compiled computer algorithm can automatically determine the optimal position of fracturing section and cluster,so as to realize the differential design of stage spacing and cluster spacing.In conclusion,the research results can further improve the fractures deployment efficiency and balanced stimulation of volumetric fracturing in unconventional oil andgasreservoirs,and this technology is expected to provide ideas andnew methods forthe fracturedeployment optimization of horizontal well volumetric fracturing in unconventional oil and gas reservoirs.
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.
基金Project supported by the National Natural Science Foundation of China,“Microscopic Damage Mechanism of Saturated Brittle Rock during Blasting Induced Fracturing and Its Control Law on Macroscopic Damage”(No.51874339)the Natural Science Foundation of Shandong Province,“Study on the Coupled Response Mechanism of Crack Propagation and Rock Damage in the fracturing condition of multistage strong pulse”(No.ZR2016EEQ04)the Fundamental Research Funds for the Central Universities,China,“Study on the Mechanical Mechanism of Multistage Blasting Induced SRV in Deep-Seated Tight Reservoirs with High Horizontal Stress Difference”(No.17CX05004).
文摘For figuring out the stress interference of multiphase fracture combinations and its effect on the fracture initiation pressure of subsequent hydraulic fracturing,a calculation model for the coupled stress field with multiple induced fractures preexisted was established based on the calculation model for the stress field with single induced fracture preexisted,and the change laws of circumferential stress field around the wellbore under the effect of induced stress were analyzed.Then,the fracture initiation pressure of subsequent hydraulic fracturing was calculated according to the fracturing mechanics criterion.Finally,the effects of the length,phase,horizontal principal stress difference co-efficient and quantity of preexisting fractures on its initiation pressure were analyzed.And the following research results were obtained.First,the circumferential stress difference in the area near the fractures behind the preexisting fractures increase greatly and even the horizontal principal stress is reversed.Second,as the length of new preexisting fractures increases,the initiation pressure of initial preexisting fractures rises first and then drops.And when the length of new preexisting fractures is equal to that of the initial preexisting fractures,the initiation pressure of initial preexisting fractures drops quickly first and then slowly.Third,the initiation pressure of high phase fractures is lower than that of low phase fractures.Fourth,with the increase of fracture quantity,the initiation pressure of new preexisting fractures drops gradually,but the decline trend of initiation pressure difference is not obvious.Fifth,the stress interference of multiphase fractures influences the fracture initiation pressure,and high-phase long fractures and low-phase short fractures are both favorable for the simultaneous initiation of multiphase fractures.Sixth,syn-chronous propagation of multiple fractures can generate more complicated stress interference and excite the evolution of hydraulic fracture network,so as to realize uniform fracturing stimulation.In conclusion,the research results can provide a theoretical guidance for the design of fracturing operation,e.g.perforation phase of blasting induced fracturing,scale of induced fractures,and pump pressure of subsequent hydraulic fracturing.
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.
文摘Exploration and development practices have proved that staged volumetric fracturing stimulation in horizontal wells is a key technology for tight sandstone gas development,and reservoir sweet spot is an important basis for the perforation position selection and staged fracturing in the process of well location deployment and reservoir stimulation.Tight sandstone reservoirs are usually characterized by sandstone and mudstone interlayers with different thicknesses,and complex natural fracture distribution and geostress state.It is hard to predict“geological-engineering”dual sweet spots,and these two kinds of sweet spots are usually in different zones.As a result,there lacks a basis for the optimization of fracturing parameters to stimulate tight sandstone reservoirs.This paper establishes a geological sweet spot prediction model which takes into account total hydrocarbon content,reservoir porosity and other factors,then puts forward a 3D multi-scale engineering sweet spot evaluation method which takes into account lithology,fracture morphology,fracture mechanical behavior,and dilatation and shear dilation effect,andfinally a“geological-engineering”dual sweet spot evaluation model for tight sandstone reservoirs.Two wells in the tight sandstone gasfield in the Linxing Block of the Ordos Basin were selected as a case,and the dual sweet spot profiles,fracturing pressure and SRV were compared and analyzed.The results show that:1)shear dilation angle influences the distribution of engineering sweet spots at the most in the study area,followed by dissipated energy,elastic modulus and fracture energy;2)the geological sweet spot zone with a high coefficient is not necessarily the pay zone with high shale gas production;3)the engineering sweet spot zone with a high coefficient needs lower fracture pressure and can be stimulated relatively sufficiently;4)high-quality geological sweet spots and high-quality engineering sweet spots are poorly consistent in spatial location.In conclusion,the stimulation of tight sandstone gas reservoirs shall take geological sweet spot as the basis and engineering sweet spot as the guarantee,and the distribution of dual sweep spots should be considered comprehensively.The multi-scale“geological-engineering”dual sweet spot evaluation method proposed in this paper provides important technical support for the prediction of sweet spots of the tight sandstone gas and the optimization of development schemes in the study area.
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.
