Study On The Seismic Wave Field Excited By A Point Source In A Fluid-Porous Medium Model

It is a hot issue to explore the new method of oil and gas exploration based on seismic effect,and its progress has attracted much attention from geophysical exploration.In order to better explain the law of excitation and propagation of the epicard wave field and the influence of various formation parameters on the seismic wave field,In this paper,we use the offshore oil and gas exploration as the background to study the seismoelectric wave field excited by different point sources in horizontal stratified geology containing seawater layers.Firstly,it is pointed out that the existence of double electric layer at the solid-liquid interface is the main cause of the seismoelectric effect,and the Pride theory of the porous medium and the important results of the elastic wave Biot theory are summarized.Secondly,for the fluid-porosity medium half-space model,we present the analytical expressions for calculating the seismic electric wave field excited by different point sources,Through the numerical simulation,the full-wave waveforms of the acoustic wave induced electromagnetic field under different formation conditions(Water/stiffporous medium configuration,Water/softporous medium configuration),and the understanding of the interface electromagnetic wave and the coseismic electromagnetic field accompanying the seismic body wave and surface wave were obtained.The results show that the velocity of the seismic P wave in the velocity field and the pressure field is the fastest,followed by the shear wave and Leaky Rayleigh wave,and finally the fluidsound wave and Stoneley wave are reached;in the recording of the electric field and the magnetic field,the electromagnetic waves with acoustic waves are first received.Studies have found that a receiver arranged in a porous medium can receive an electromagnetic field accompanying P,S,Leaky Rayleigh waves,and Scholte waves,and that an electromagnetic field synchronized with each wave contains the contributions of multiple waves.The study also found that Stoneley waves in the velocity field are sensitive to the distance from the source to the receiving point.In the sound pressure field,although the transverse wave does not directly produce sound pressure,the reflected P wave and the slow longitudinal wave generated by the shear wave at the interface will be causes changes in the sound pressure field.The simulation results also show that the vertical electric field is mainly contributed by the converted Ps wave,and its intensity is two orders of magnitude higher than the horizontal electric field component.At the same time,the electric field is more sensitive to the depth of the receiving point than the magnetic field.Finally,on this basis,the seismic-electrical responses at the interface between air-fluid and two-layer porous media are simulated.The theory of radiation and propagation of different point sources in the horizontal layered structure is analyzed in detail,and further snapshots are made through the wave field.The propagation of the elastic wave in the medium under the explosion point is shown.The results show that although no electric field signal accompanying the transmitted P wave is observed in the fluid,the accompanying slow longitudinal wave,S wave and electromagnetic wave appear at the interface of the fluid-porosity medium;Although there is a double electric layer in the porous medium,there is no electric field and magnetic field accompanying the slow longitudinal wave in the porous layer.The influence of the change of pore fluid medium parameters on the seismic wave field is also investigated.The results show that the electric fields accompanied by P,Leaky Rayleigh waves,sound wave and Scholte waves are very sensitive to the degree of mineralization,and the electric field accompanying the S wave is not very sensitive to the degree of mineralization.under low-frequency conditions,the permeability changes have little effect on the accompanying electric field and accompanying magnetic field.The higher the formation permeability,the faster the electromagnetic wave decays,the faster the attenuation of the formation electromagnetic wave,The electric field accompanied by Stoneleystrength is relatively sensitive to the permeability.