Study On The Dynamic Mechanism Of Liquid Flow In Elastic Saturated Porous Media Under Low-frequency Vibration Oil Extraction Technology

Low-frequency vibration oil extraction technology is a physical,environmental,and simple method applied in the process of oil and gas field development.It uses the downhole artificial source to strike the formation.It has great potential for the complex reservoirs to improve the injection and output,because of its advantages of low cost,high effectivity,and low damage to the formation and environment.However,bad effects of this technology such as instability or decrease output are found in some wells in the trial,which restrict the application of this technology.To improve the field effect stability and optimize decision-making,the key lies in the explanation for dynamic seepage mechanism in the reservoir under elastic waves.Because the existing qualitative and half quantitative methods have not considered the coupling effect between the seepage field with a certain initial flow rate and the low-frequency elastic wave field,a dynamic method consider above coupling effect is necessary.Based on the Biot poroelastic theory used in seismic exploration engineering as well as the known experimental mechanisms of low-frequency vibration oil extraction technology,the dynamic model of liquid flow in elastic porous media saturated with single-phase fluid of a certain initial flow rate under low-frequency vibration is established.Through analysis on the wave propagation influenced by the initial flow in the porous media and simulation on the seepage change influenced by the low-frequency vibration,a theoretical guidance for deep cognition to the inner function mechanism of above technology can be achieved.Firstly,combining the known experimental mechanisms of low-frequency vibration oil extraction technology,the general Darcy flow theory,Biot poroelastic theory,the mathematic model for flow in elastic porous media saturated with single-phase fluid of a certain initial flow rate under low-frequency vibration is given.The mathematic model contains the constitutive equation of elastic,homogeneous,and isotropic porous media,the generalized Darcy motion equation considering threshold pressure gradient of low-permeability layer,an improved equation about the effective porosity variation under vibration considering compressibility of matrix and liquid,proportion of seepage interconnected pores,and change of adhesive layer in capillary tube,an equation about the decreased viscosity with vibration parameter,and the definition conditions with constant-pressure in boundaries.Secondly,through Helmholtz decomposition of solid/fluid displacement and introduction of potential function for macro-flow,the wave number in porous media with a certain initial flow rate as well as its sensitivity of P1,P2,and S wave on vibration parameter and physical properties are derived.Then,The approximate solution about solid and fluid displacements in one dimension or radial dimension of the governing equation are obtained,after Laplace transformation,Durbin discretization,and Matlab programming.Finally,numerical simulations on the seepage change under a single elastic wave in one ideal dimension,plane radial dimension,and three dimension physical models are carried successively with COMSOL system.The experimental results about permeability increase and vibration frequency are compared with those from one ideal dimension physical model.The influence of low-frequency vibration oil extraction technology on the relative flow rate,pore pressure,and porosity are analyzed.Sensitivity about above influence under different vibration parameter(frequency,amplitude,and incident angle)and physical properties(initial porosity,permeability,and viscosity)are done as well.The results show that: the initial flow has mainly decreased the velocity of P1 wave and increased its attenuation;little influence is impacted on the P2 and S wave;the relative flow rate and porosity are enhanced by the single low-frequency elastic wave,and periodically fluctuation is found with the pore pressure versus vibration time;better seepage capacity increase is achieved when closer to the vibration source;there exist an optimal vibration frequency and local optimal amplitude,20 Hz and 100?m with the basic parameters in the paper;the function mechanisms of the low-frequency vibration oil extraction technology are reflected to a certain extent.