Study On The Influence Of Viscous Pore Fluid Stress On Body Waves In Porous Media And Borehole Waves

Acoustic wave is widely used in oil and gas resource exploration and earth science exploration.The acoustic response of formation contains abundant geological information,so scholars pay much attention to the study of formation acoustic field.At present,most studies use the elastic wave mechanics theory of fluid-saturated porous media proposed by Biot,which is referred to as Biot theory for short.The constitutive equation of Biot theory does not consider the visc ous stress of the fluid in the porous media,but the fluid in the pore formation actually has the viscous stress.In view of this situation,this paper considers the fluid viscous stress,deduces the governing equation of porous media on the basis of Biot theory,analyzes the influence of fluid viscous stress on the mass wave of porous media,and deduces and calculates the borehole acoustic field under this condition.The results show that the slow shear wave exists in the pore formation saturated with visc ous fluid,and the slow shear wave has the characteristics of high attenuation and low velocity.In the case of high frequency and high viscosity,the phase velocity is higher and easier to be recognized.The main contents of this paper include:The relevant calculations of the waves(fast longitudinal wave,slow longitudinal wave and fast shear wave)propagating in pore formation under Biot model are carried out,and the characteristics of seepage movement when these three waves propagating in pore formation are illustrated.At the same time,the constitutive equation in Biot model is discussed.Based on Biot theory,considering the shear viscosity of Newtonian fluids in actual formation,a viscosimetric modified Biot model is derived,and the body waves in pore formation are calculated.Based on Fortran language,the effects of frequency and fluid viscosity on the velocity and inverse quality factors of four body waves were studied and compared with Biot model.The borehole acoustic field model is established.The boundary conditions of borehole acoustic field are extended,the integral expression of field quantity is derived and the analytical solution of corresponding borehole acoustic field is calculated.Based on Fortran language,the full waveform of borehole acoustic field corresponding to Biot model and viscosity modified Biot model is calculated.