Hydraulic fracturing,as a key technology of deep energy exploitation,accelerates the rapid development of the modern petroleum industry.To study the mechanisms of hydraulic fracture propagation and rock failure mode o...Hydraulic fracturing,as a key technology of deep energy exploitation,accelerates the rapid development of the modern petroleum industry.To study the mechanisms of hydraulic fracture propagation and rock failure mode of the vertical well hydraulic fracturing,the true triaxial hydraulic fracturing test and numerical simulation are carried out,and the influence of the principal stress difference,water injection displacement,perforation angle and natural fracture on fracture propagation is analyzed.The results show that the fracture propagation mode of limestone is mainly divided into two types:the single vertical fracture and the transverse-longitudinal crossed complex fracture.Under high displacement,the fracturing pressure is larger,and the secondary fracture is more likely to occur,while variable displacement loading is more likely to induce fracture network.Meanwhile,the amplitude of acoustic emission(AE)waveform of limestone during fracturing is between 0.01 and 0.02 mV,and the main frequency is maintained in the range of 230−300 kHz.When perforation angleθ=45°,it is easy to produce the T-type fracture that connects with the natural fracture,while X-type cracks are generated whenθ=30°.The results can be used as a reference for further study on the mechanism of limestone hydraulic fracturing.展开更多
Hydraulic fracturing is one of the efficient means for the abundant low-permeability CBM （coal-bed methane） reserves in China, however, due to the unique features of coal seams （i.e., low temperature, strong adsorp...Hydraulic fracturing is one of the efficient means for the abundant low-permeability CBM （coal-bed methane） reserves in China, however, due to the unique features of coal seams （i.e., low temperature, strong adsorption and abnormal development of natural fracture systems） as compared with the conventional reservoirs, the fractures propagate is difficult and the risk of damage to coal seam itself and the hydraulic fractures would be extremely high in the course of fracturing. As a result, losses would be suffered on the post-frac production of CBM wells.With the mean of numerical simulation, in this paper, the main factors have impact on the post-frac results as well as the extent to which the impact is brought were researched, and the technical solutions for the improvement of the fracturing performance was put forwards.展开更多
Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger move...Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger movement and the mechanism of pulsating pressure formation using theoretical research, mathematical modeling and field testing. We analyze the effect of pulsating pressure on the formation and growth of fractures in coal by using the pulsating hydraulic theory in hydraulics. The research results show that the amplitude of fluctuating pressure tends to increase in the case where the exit is blocked, caused by pulsating pressure reflection and frictional resistance superposition, and it contributes to the growth of fractures in coal. The crack initiation pressure of pulsating hydraulic fracturing is 8 MPa, which is half than that of normal hydraulic fracturing; the pulsating hydraulic fracturing influence radius reaches 8 m. The total amount of gas extraction is increased by 3.6 times, and reaches 50 LJmin at the highest point. The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2 times larger than that of normal hydraulic fracturing. The technology provides a technical measure for gas drainage of high gas content and low permeability in the single coal bed.展开更多
Hydraulic fracture （HF） in porous rocks is a complex multi-physics coupling process which involves fluid flow, diffusion and solid deformation. In this paper, the extended finite element method （XFEM） coupling wit...Hydraulic fracture （HF） in porous rocks is a complex multi-physics coupling process which involves fluid flow, diffusion and solid deformation. In this paper, the extended finite element method （XFEM） coupling with Biot theory is developed to study the HF in permeable rocks with natural fractures （NFs）. In the recent XFEM based computational HF models, the fluid flow in fractures and interstitials of the porous media are mostly solved separately, which brings difficulties in dealing with complex fracture morphology. In our new model the fluid flow is solved in a unified framework by considering the fractures as a kind of special porous media and introducing Poiseuille-type flow inside them instead of Darcy-type flow. The most advantage is that it is very convenient to deal with fluid flow inside the complex frac^xre network, which is important in shale gas extraction. The weak formulation for the new coupled model is derived based on virtual work principle, which includes the XFEM formulation for multiple fractures and fractures intersection in porous media and finite element formulation for the unified fluid flow. Then the plane strain Kristianovic-Geertsma-de Klerk （KGD） model and the fluid flow inside the fracture network are simulated to validate the accuracy and applicability of this method. The numerical results show that large injection rate, low rock permeability and isotropic in-situ stresses tend to lead to a more uniform and productive fracture network.展开更多
In shale gas fracking, the stimulated natural fracture system is often critical to the gas production. In this paper, we present the results of state-of-the-art modeling of a detailed parametric evolution of the shear...In shale gas fracking, the stimulated natural fracture system is often critical to the gas production. In this paper, we present the results of state-of-the-art modeling of a detailed parametric evolution of the shear stimulation effect in discrete fracture network(DFN) formations. Two-dimensional computational modeling studies have been used in an attempt towards understanding how naturally fractured reservoirs response in hydraulic fracturing. Simulations were conducted as a function of:(1) the in-situ stress ratio;(2) internal friction angle of DFN;(3) DFN orientation with the stress field; and(4) operational vari- ables such as injection rate. A sensitivity study reveals a number of interesting observations resulting from these parameters on the shear stimulation in natural fracture system. This work strongly links the production technology, geomechanical evaluation and aids in the understanding and optimization of hydraulic fracturing simulations in naturally fractured reservoirs.展开更多
Fracking is one of the kernel technologies in the remarkable shale gas revolution. The extended finite element method is used in this paper to numerically investigate the interaction between hydraulic and natural frac...Fracking is one of the kernel technologies in the remarkable shale gas revolution. The extended finite element method is used in this paper to numerically investigate the interaction between hydraulic and natural fractures, which is an important issue of the enigmatic fracture network formation in fracking. The criteria which control the opening of natural fracture and crossing of hydraulic fracture are tentatively presented. Influence factors on the interaction process are systematically analyzed, which include the approach angle, anisotropy of in-situ stress and fluid pressure profile.展开更多
基金Projects(51879148,51709159,51911530214)supported by the National Natural Science Foundation of ChinaProject(2019GSF111030)supported by Shandong Provincial Key R&D Program of ChinaProject(KT201804)supported by the Project of Special Fund for Science and Technology of Water Resources Department of Guizhou Province,China。
文摘Hydraulic fracturing,as a key technology of deep energy exploitation,accelerates the rapid development of the modern petroleum industry.To study the mechanisms of hydraulic fracture propagation and rock failure mode of the vertical well hydraulic fracturing,the true triaxial hydraulic fracturing test and numerical simulation are carried out,and the influence of the principal stress difference,water injection displacement,perforation angle and natural fracture on fracture propagation is analyzed.The results show that the fracture propagation mode of limestone is mainly divided into two types:the single vertical fracture and the transverse-longitudinal crossed complex fracture.Under high displacement,the fracturing pressure is larger,and the secondary fracture is more likely to occur,while variable displacement loading is more likely to induce fracture network.Meanwhile,the amplitude of acoustic emission(AE)waveform of limestone during fracturing is between 0.01 and 0.02 mV,and the main frequency is maintained in the range of 230−300 kHz.When perforation angleθ=45°,it is easy to produce the T-type fracture that connects with the natural fracture,while X-type cracks are generated whenθ=30°.The results can be used as a reference for further study on the mechanism of limestone hydraulic fracturing.
文摘Hydraulic fracturing is one of the efficient means for the abundant low-permeability CBM （coal-bed methane） reserves in China, however, due to the unique features of coal seams （i.e., low temperature, strong adsorption and abnormal development of natural fracture systems） as compared with the conventional reservoirs, the fractures propagate is difficult and the risk of damage to coal seam itself and the hydraulic fractures would be extremely high in the course of fracturing. As a result, losses would be suffered on the post-frac production of CBM wells.With the mean of numerical simulation, in this paper, the main factors have impact on the post-frac results as well as the extent to which the impact is brought were researched, and the technical solutions for the improvement of the fracturing performance was put forwards.
基金the National Natural Science Foundation of China(No.51274195)the National Basic Research Program of China(No.2011CB201205)+1 种基金the Ph.D.Foundation of Henan Polytechnic University(No.60207005)the Education Department of Hennan Province(No.14B440007)
文摘Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger movement and the mechanism of pulsating pressure formation using theoretical research, mathematical modeling and field testing. We analyze the effect of pulsating pressure on the formation and growth of fractures in coal by using the pulsating hydraulic theory in hydraulics. The research results show that the amplitude of fluctuating pressure tends to increase in the case where the exit is blocked, caused by pulsating pressure reflection and frictional resistance superposition, and it contributes to the growth of fractures in coal. The crack initiation pressure of pulsating hydraulic fracturing is 8 MPa, which is half than that of normal hydraulic fracturing; the pulsating hydraulic fracturing influence radius reaches 8 m. The total amount of gas extraction is increased by 3.6 times, and reaches 50 LJmin at the highest point. The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2 times larger than that of normal hydraulic fracturing. The technology provides a technical measure for gas drainage of high gas content and low permeability in the single coal bed.
基金supported by the National Natural Science Foundation of China(Grant Nos.11532008,and 11372157)
文摘Hydraulic fracture （HF） in porous rocks is a complex multi-physics coupling process which involves fluid flow, diffusion and solid deformation. In this paper, the extended finite element method （XFEM） coupling with Biot theory is developed to study the HF in permeable rocks with natural fractures （NFs）. In the recent XFEM based computational HF models, the fluid flow in fractures and interstitials of the porous media are mostly solved separately, which brings difficulties in dealing with complex fracture morphology. In our new model the fluid flow is solved in a unified framework by considering the fractures as a kind of special porous media and introducing Poiseuille-type flow inside them instead of Darcy-type flow. The most advantage is that it is very convenient to deal with fluid flow inside the complex frac^xre network, which is important in shale gas extraction. The weak formulation for the new coupled model is derived based on virtual work principle, which includes the XFEM formulation for multiple fractures and fractures intersection in porous media and finite element formulation for the unified fluid flow. Then the plane strain Kristianovic-Geertsma-de Klerk （KGD） model and the fluid flow inside the fracture network are simulated to validate the accuracy and applicability of this method. The numerical results show that large injection rate, low rock permeability and isotropic in-situ stresses tend to lead to a more uniform and productive fracture network.
基金supported by the National Natural Science Foundation of China(Grant Nos.4122790141330643&41502294)+2 种基金China Postdoctoral Science Foundation Funded Project(Grant No.2015M571118)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB10030000XDB10030300&XDB10050400)
文摘In shale gas fracking, the stimulated natural fracture system is often critical to the gas production. In this paper, we present the results of state-of-the-art modeling of a detailed parametric evolution of the shear stimulation effect in discrete fracture network(DFN) formations. Two-dimensional computational modeling studies have been used in an attempt towards understanding how naturally fractured reservoirs response in hydraulic fracturing. Simulations were conducted as a function of:(1) the in-situ stress ratio;(2) internal friction angle of DFN;(3) DFN orientation with the stress field; and(4) operational vari- ables such as injection rate. A sensitivity study reveals a number of interesting observations resulting from these parameters on the shear stimulation in natural fracture system. This work strongly links the production technology, geomechanical evaluation and aids in the understanding and optimization of hydraulic fracturing simulations in naturally fractured reservoirs.
基金supported by the National Natural Science Foundation of China (Grant No. 11372157)the Special Research Grant for Doctor Discipline by Ministry of Education of China (Grant No. 20120002110075)the Foundation for the Author of National Excellent Doctoral Dissertation of China (FANEDD) (Grant No. 201326)
文摘Fracking is one of the kernel technologies in the remarkable shale gas revolution. The extended finite element method is used in this paper to numerically investigate the interaction between hydraulic and natural fractures, which is an important issue of the enigmatic fracture network formation in fracking. The criteria which control the opening of natural fracture and crossing of hydraulic fracture are tentatively presented. Influence factors on the interaction process are systematically analyzed, which include the approach angle, anisotropy of in-situ stress and fluid pressure profile.
