Shale gas reservoirs are different from conventional ones in terms of their bedding architectures,so their hydraulic fracturing rules are somewhat different.In this paper,shale hydraulic fracturing tests were carried ...Shale gas reservoirs are different from conventional ones in terms of their bedding architectures,so their hydraulic fracturing rules are somewhat different.In this paper,shale hydraulic fracturing tests were carried out by using the triaxial hydraulic fracturing test system to identify the effects of natural bedding directions on the crack propagation in the process of hydraulic fracturing.Then,the fracture initiation criterion of hydraulic fracturing was prepared using the extended finite element method.On this basis,a 3D hydraulic fracturing computation model was established for shale gas reservoirs.And finally,a series of studies were performed about the effects of bedding directions on the crack propagation created by hydraulic fracturing in shale reservoirs.It is shown that the propagation rules of hydraulically induced fractures in shale gas reservoirs are jointly controlled by the in-situ stress and the bedding plane architecture and strength,with the bedding direction as the main factor controlling the crack propagation directions.If the normal tensile stress of bedding surface reaches its tensile strength after the fracturing,cracks will propagate along the bedding direction,and otherwise vertical to the minimum in-situ stress direction.With the propagating of cracks along bedding surfaces,the included angle between the bedding normal direction and the minimum in-situ stress direction increases,the fracture initiation and propagation pressures increase and the crack areas decrease.Generally,cracks propagate in the form of nonplane ellipsoids.With the injection of fracturing fluids,crack areas and total formation filtration increase and crack propagation velocity decreases.The test results agree well with the calculated crack propagation rules,which demonstrate the validity of the above-mentioned model.展开更多
By revisiting the three stage theory for the progress of science proposed by Taketani in 1942, the footmarks of fluidization research are examined. The bubbling and fast fluidization issues were emphasized so that the...By revisiting the three stage theory for the progress of science proposed by Taketani in 1942, the footmarks of fluidization research are examined. The bubbling and fast fluidization issues were emphasized so that the future offluidization research can be discussed among scientists and engineers in a wider perspective. The first cycle of fluidization research was started in the early 1940s by an initial stage of phenomenology. The second stage of structural studies was kicked off in the early 1950s with the introduction of the two phase theory. The third stage of essential studies occurred in the early 1960s in the form of bubble hydrodynamics. The second cycle, which confirmed the aforementioned three stages closed at the turn of the century, established a general understanding of suspension structures including agglomerating fluidization, bubbling, turbulent and fast fluidizations and pneumatic transport; also established powerful measurement and numerical simulation tools.After a general remark on science, technology and society issues the interactions between fluidization technology and science are revisited. Our future directions are discussed including the tasks in the third cycle, particularly in its phenomenology stage where strong motivation and intention are always necessary, in relation also to the green reforming of the present technology. A generalized definition of ＇fluidization＇ is proposed to extend fluidization principle into much wider scientific fields, which would be effective also for wider collaborations.展开更多
基金Project supported by the National Natural Science Foundation of China“Stimulation to gas recovery from super-critical CO_(2) multi-pulse gas-blasting low-permeability coals”(Grant No.51574137).
文摘Shale gas reservoirs are different from conventional ones in terms of their bedding architectures,so their hydraulic fracturing rules are somewhat different.In this paper,shale hydraulic fracturing tests were carried out by using the triaxial hydraulic fracturing test system to identify the effects of natural bedding directions on the crack propagation in the process of hydraulic fracturing.Then,the fracture initiation criterion of hydraulic fracturing was prepared using the extended finite element method.On this basis,a 3D hydraulic fracturing computation model was established for shale gas reservoirs.And finally,a series of studies were performed about the effects of bedding directions on the crack propagation created by hydraulic fracturing in shale reservoirs.It is shown that the propagation rules of hydraulically induced fractures in shale gas reservoirs are jointly controlled by the in-situ stress and the bedding plane architecture and strength,with the bedding direction as the main factor controlling the crack propagation directions.If the normal tensile stress of bedding surface reaches its tensile strength after the fracturing,cracks will propagate along the bedding direction,and otherwise vertical to the minimum in-situ stress direction.With the propagating of cracks along bedding surfaces,the included angle between the bedding normal direction and the minimum in-situ stress direction increases,the fracture initiation and propagation pressures increase and the crack areas decrease.Generally,cracks propagate in the form of nonplane ellipsoids.With the injection of fracturing fluids,crack areas and total formation filtration increase and crack propagation velocity decreases.The test results agree well with the calculated crack propagation rules,which demonstrate the validity of the above-mentioned model.
文摘By revisiting the three stage theory for the progress of science proposed by Taketani in 1942, the footmarks of fluidization research are examined. The bubbling and fast fluidization issues were emphasized so that the future offluidization research can be discussed among scientists and engineers in a wider perspective. The first cycle of fluidization research was started in the early 1940s by an initial stage of phenomenology. The second stage of structural studies was kicked off in the early 1950s with the introduction of the two phase theory. The third stage of essential studies occurred in the early 1960s in the form of bubble hydrodynamics. The second cycle, which confirmed the aforementioned three stages closed at the turn of the century, established a general understanding of suspension structures including agglomerating fluidization, bubbling, turbulent and fast fluidizations and pneumatic transport; also established powerful measurement and numerical simulation tools.After a general remark on science, technology and society issues the interactions between fluidization technology and science are revisited. Our future directions are discussed including the tasks in the third cycle, particularly in its phenomenology stage where strong motivation and intention are always necessary, in relation also to the green reforming of the present technology. A generalized definition of ＇fluidization＇ is proposed to extend fluidization principle into much wider scientific fields, which would be effective also for wider collaborations.
