Proppant transport within fractures is one of the most critical tasks in oil,gas and geothermal reservoir stimulation,as it largely determines the ultimate performance of the operating well.Proppant transport in rough...Proppant transport within fractures is one of the most critical tasks in oil,gas and geothermal reservoir stimulation,as it largely determines the ultimate performance of the operating well.Proppant transport in rough fracture networks is still a relatively new area of research and the associated transport mechanisms are still unclear.In this study,representative parameters of rough fracture surfaces formed by supercritical CO_(2) fracturing were used to generate a rough fracture network model based on a spectral synthesis method.Computational fluid dynamics(CFD)coupled with the discrete element method(DEM)was used to study proppant transport in this rough fracture network.To reveal the turning transport mechanism of proppants into branching fractures at the intersections of rough fracture networks,a comparison was made with the behavior within smooth fracture networks,and the effect of key pumping parameters on the proppant placement in a secondary fracture was analyzed.The results show that the transport behavior of proppant in rough fracture networks is very different from that of the one in the smooth fracture networks.The turning transport mechanisms of proppant into secondary fractures in rough fracture networks are gravity-driven sliding,high velocity fluid suspension,and fracture structure induction.Under the same injection conditions,supercritical CO_(2)with high flow Reynolds number still has a weaker ability to transport proppant into secondary fractures than water.Thickening of the supercritical CO_(2)needs to be increased beyond a certain value to have a significant effect on proppant carrying,and under the temperature and pressure conditions of this paper,it needs to be increased more than 20 times(about 0.94 m Pa s).Increasing the injection velocity and decreasing the proppant concentration facilitates the entry of proppant into the branching fractures,which in turn results in a larger stimulated reservoir volume.The results help to understand the proppant transport and placement process in rough fracture networks formed by reservoir stimulation,and provide a theoretical reference for the optimization of proppant pumping parameters in hydraulic fracturing.展开更多
Under the fact that considerable explo ration and production of unconventional re sources and wo rsening global climate,reducing carbon emission and rationally utilizing carbon resources have been drawn increasing att...Under the fact that considerable explo ration and production of unconventional re sources and wo rsening global climate,reducing carbon emission and rationally utilizing carbon resources have been drawn increasing attention.Supercritical CO_(2)(SC-CO_(2)) has been proposed as anhydrous fracturing fluid to develop unconventional reservoirs,since its advantages of reducing water consumption,reservoir contamination etc.Well understanding of SC-CO_(2)fracturing mechanism and key influencing factors will exert significant impact on the application of this technology in the field.In this paper,the fundamental studies on SC-CO_(2)fracturing from the aspects of laboratory experiment and simulation are reviewed.The fracturing experimental setups,fracture monitoring and characterizing methods,unconventional formation categories,numerical simulation approaches,fracturing mechanism and field application etc.,are analyzed.The fundamental study results indicate that compared with conventional hydraulic fracturing,SC-CO_(2)fracturing can reduce fracture initiation pressure and easily induce complex fracture networks with multiple branches.The field test further verifies the application prospect and the possibility of carbon storage.However,due to the limitation of reservoir complexity and attributes of SC-CO_(2),massive challenges will be encountered in SC-CO_(2)fracturing.According to the current research status,the limitations in basic research and field application are summarized,and the future development direction of this technology and relevant suggestions are proposed.展开更多
Supercritical CO_(2)fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage,improving shale gas recovery and storing CO_(2)underground.Deep insight into the pr...Supercritical CO_(2)fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage,improving shale gas recovery and storing CO_(2)underground.Deep insight into the proppant-transport behavior of CO_(2)is required to better apply this technique in the engineering field.In the present paper,we adopted a coupled Computational Fluid Dynamics and Discrete Element Method(CFD-DEM)approach to simulate the proppant transport in a fracking fracture with multiple perforation tunnels.Previous experiments were first simulated to benchmark the CFD-EDM approach,and then various pumping schedules and injection parameters(injection location,multi-concentration injection order,multi-density injection order and injection temperature)were investigated to determine the placement characteristics of proppant.Results indicate that the swirling vortex below the injection tunnels dominates the proppant diffusion in the fracture.The velocity of fluid flow across the proppant bank surface in multi-concentration injection shows a positive correlation with the proppant concentration.Injecting high-density proppant first can promote the transportation of low-density proppant injected later in the fracture to a certain extent.Decreasing the initial injection temperature of supercritical CO_(2)slurry helps enhance the particle-driving effect of fluid and improve the performance of supercritical CO_(2)in carrying proppant.展开更多
基金the support from the National Key Research and Development Program of China(Grant No.2022YFE0137200)the Natural Science Basic Research Program of Shaanxi Province,China(Program No.2024JC-YBQN-0381,2023JC-QN-0403)+2 种基金the Natural Science Basic Research Program of Shaanxi Province,China(Program No.2022JC-37)the Innovation Capability Support Program of Shaanxi(Program No.2023-CX-TD31)the Funded by Open Foundation of Shaanxi Key Laboratory of Carbon Dioxide Sequestration and Enhanced Oil Recovery,and the Youth Innovation Team of Shaanxi Universities。
文摘Proppant transport within fractures is one of the most critical tasks in oil,gas and geothermal reservoir stimulation,as it largely determines the ultimate performance of the operating well.Proppant transport in rough fracture networks is still a relatively new area of research and the associated transport mechanisms are still unclear.In this study,representative parameters of rough fracture surfaces formed by supercritical CO_(2) fracturing were used to generate a rough fracture network model based on a spectral synthesis method.Computational fluid dynamics(CFD)coupled with the discrete element method(DEM)was used to study proppant transport in this rough fracture network.To reveal the turning transport mechanism of proppants into branching fractures at the intersections of rough fracture networks,a comparison was made with the behavior within smooth fracture networks,and the effect of key pumping parameters on the proppant placement in a secondary fracture was analyzed.The results show that the transport behavior of proppant in rough fracture networks is very different from that of the one in the smooth fracture networks.The turning transport mechanisms of proppant into secondary fractures in rough fracture networks are gravity-driven sliding,high velocity fluid suspension,and fracture structure induction.Under the same injection conditions,supercritical CO_(2)with high flow Reynolds number still has a weaker ability to transport proppant into secondary fractures than water.Thickening of the supercritical CO_(2)needs to be increased beyond a certain value to have a significant effect on proppant carrying,and under the temperature and pressure conditions of this paper,it needs to be increased more than 20 times(about 0.94 m Pa s).Increasing the injection velocity and decreasing the proppant concentration facilitates the entry of proppant into the branching fractures,which in turn results in a larger stimulated reservoir volume.The results help to understand the proppant transport and placement process in rough fracture networks formed by reservoir stimulation,and provide a theoretical reference for the optimization of proppant pumping parameters in hydraulic fracturing.
基金supported by the Natural Science Foundation of China(Grant Nos.51922107,51874318,51827804and 41961144026)
文摘Under the fact that considerable explo ration and production of unconventional re sources and wo rsening global climate,reducing carbon emission and rationally utilizing carbon resources have been drawn increasing attention.Supercritical CO_(2)(SC-CO_(2)) has been proposed as anhydrous fracturing fluid to develop unconventional reservoirs,since its advantages of reducing water consumption,reservoir contamination etc.Well understanding of SC-CO_(2)fracturing mechanism and key influencing factors will exert significant impact on the application of this technology in the field.In this paper,the fundamental studies on SC-CO_(2)fracturing from the aspects of laboratory experiment and simulation are reviewed.The fracturing experimental setups,fracture monitoring and characterizing methods,unconventional formation categories,numerical simulation approaches,fracturing mechanism and field application etc.,are analyzed.The fundamental study results indicate that compared with conventional hydraulic fracturing,SC-CO_(2)fracturing can reduce fracture initiation pressure and easily induce complex fracture networks with multiple branches.The field test further verifies the application prospect and the possibility of carbon storage.However,due to the limitation of reservoir complexity and attributes of SC-CO_(2),massive challenges will be encountered in SC-CO_(2)fracturing.According to the current research status,the limitations in basic research and field application are summarized,and the future development direction of this technology and relevant suggestions are proposed.
基金National Natural Science Foundation of China(Grant No.51874318,51922107,and41961144026)support from the National Key Scientific Research Instrument Research Project of NSFC(Grant No.51827804)
文摘Supercritical CO_(2)fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage,improving shale gas recovery and storing CO_(2)underground.Deep insight into the proppant-transport behavior of CO_(2)is required to better apply this technique in the engineering field.In the present paper,we adopted a coupled Computational Fluid Dynamics and Discrete Element Method(CFD-DEM)approach to simulate the proppant transport in a fracking fracture with multiple perforation tunnels.Previous experiments were first simulated to benchmark the CFD-EDM approach,and then various pumping schedules and injection parameters(injection location,multi-concentration injection order,multi-density injection order and injection temperature)were investigated to determine the placement characteristics of proppant.Results indicate that the swirling vortex below the injection tunnels dominates the proppant diffusion in the fracture.The velocity of fluid flow across the proppant bank surface in multi-concentration injection shows a positive correlation with the proppant concentration.Injecting high-density proppant first can promote the transportation of low-density proppant injected later in the fracture to a certain extent.Decreasing the initial injection temperature of supercritical CO_(2)slurry helps enhance the particle-driving effect of fluid and improve the performance of supercritical CO_(2)in carrying proppant.
