| The pores of tight oil reserviors are mostly nano or micro sized,the structure is complex,flow resistance is high,thus the tight oil is difficult to exploite.Experimental tests and empirical hypothesis models are commonly used to study the fluid transport characteristics in tight oil substrates,but rarely the basic theories from microcosmic perspective are used.Therefore,this paper analyzed the effects of the nano-and micro-sized pores percolation from the unique liquid character and the micro inteaction between liquid and solid of the nano-and micro-sized tube,and the pores structures combined the the pore network simulation.First,the Lifshitz–van der Waals interaction between the liquid and the wall in circular tube was derevied,the flow of compressible liquid under Lifshitz–van der Waals interaction,the Bingham liquid under electroviscous force were studied respectively,the dynamic equations were established,vorticity-stream functions and regular perturbation method were adopted,the approximate analytical solutions were obtained.The results indicates that the wall-liquid Lifishitz-van der Waals interaction not affect the flow rate as acting alone,while it will reduce the flow rate and increase the resistance coefficient as considered the compressibility of the liquid.The coupling effect of electroviscous force and Bingham plasticity of liquid will cause the decrease of velocity,which is mainly reflected in the increase of the flow core width and the decrease of electric field intensity.Furthermore,the nonlinear velocity model of nano-and micro-sized tube considered the Lifshitz-van der Waals force,electroviscous force,compressibility and Bingham characteristics was established,and the effects of various factors on the speed curve and micro-scale effect were analyzed.The velocity-pressure curve has the nonlinear characteristic with threshold pressure gradient(TPG),and the lower limit of movable fluid(R_m)appears,the nonlinear and TPG is caused by the Bingham plastic of the liquid,the Lifishitz-van der Waals force and compressibility increase TPG,and the electroviscous force will aggravate the nonlinear degree.R_m is produced by Bingham plasticity and Lifishitz-van der Waals force under compressibility,when displacement pressure gradient is greater than 20 MPa/m,it is mainly affected by the latter.Based on this,a new nonlinear flow velocity model and a calculation model of R_m and TPG for nano-and micro-sized circular tubes were proposed.The theoretical value of R_m is 10-30 nm,which is approximately consistent with the experimental results.Last,the 3-D pore network simulation program was developed by Matlab software,the velocity model of nano-and micro-sized tube with Lifishitz-van der Waals force,electroviscosity force and compressibility was introduced,the seepage characteristics of liquid single-phase and water-driven oil two-phase in nano-and micro-sized porous media were analyzed.The flow of single-phase liquid seepage decreased obviously considering liquid-solid interaction and compressibility,the smaller the average throat radius is,the more significant the influence is,and the water breakthrough point will be delayed for the two-phase liquid seepage of water drive oil flows,which is the embodiment of the combined resistance action of liquid-solid force and compressibility.This indicates that the influence of liquid-solid force,fluid properties and pore structure on the liquid flow should be carefully considered in the actual nano-and micro-sized porous media,and provide a theoretical guidance for tight oil exploitation. |
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