| The complex conductivity and electrokinetic effects,which are related to the electrical double layer in water-filled porous media,have important application value in many fields of earth science.However,the mechanism of complex conductivity and its correlation with pore parameters of underground rocks are not clear.In addition,the existing electrokinetic model of water saturated porous media cannot explain the electrokinetic phenomena in water partially saturated rocks,such as oil and gas reservoirs.In response to the above questions,the thesis establishes a new complex conductivity model and gives a new permeability prediction from complex conductivity effect.The electrokinetic coupling coefficient with wider applicable conditions is derived,and an electrokinetic model of partially saturated porous media is established.Then,the effect of saturation on the properties of seismoelectric waves is analyzed.The main research results are as follows:Based on the Stern layer polarization theory,a new complex conductivity model is established,in which the effects of grain shape,surface roughness,inter-grain contact and grain size distribution on the relaxation time and chargeability are introduced.By fitting the experimental data of complex conductivity,it shows that the model in this paper ha s higher fitting accuracy.A permeability prediction expressed with relaxation time is derived by a new relationship between relaxation time and pore size.The permeability model is verified by predicting the permeability of various rock samples.The result shows that he model can efficiently predict porosity permeability within 7orders of magnitude(from 0.1 m Darcy to 100 Darcy).Based on capillary model,the electrokinetic coupling coefficient is extended to the case of arbitrary pore size with boundary slip.The influences of pore size and boundary slip on the electrokinetic coupling coefficient are analyzed.It is concluded that the stenghth of electrokinetic effect increases with the pore size when the assumption of thin electric al double layer is inapplicable.The boundary slip can obviously enhance the electrokinetic effects of the porous media.The influence of Debye-Huckel approximation on the accuracy of the electrokinetic coupling coefficient is investigated.The result shows that for most porous media,the Debye-Hückel approximation can be used to accurately describe the electrokinetic effect as long as the pore size is greater than 7 times of the Debye length.By comparing the permeability model of porous media with that based on capillary bundle,the equivalence of the two models is verified.By comparing with the experimental data,it is verified that the capillary tube bundle model can effectively describe the seepage and electrokinetic effect of pore fluid.On this basis,the distribution of two-phase fluid in porous media,and the seepage and electrokinetic properties of partially saturated porous media are described by regarding the pore of porous media as capillary bundles with different sizes.Based on the capillary bundles model,an electrokinetic model of water partially saturated porous media is established.The model is verified by comparing the wave velocity of fast longitudinal and its coseismic conversion calculated by this model with the experimental results.Then,the influence of saturation on the velocity and coseismic conversion of seismoelectric wave is analysed with the model.The application of seismoelectric wave s in the explorations of vadose zone depth and oil reservoir is investigated theoretically.The seismoelectric wave field in horizontal layered formation is simulated with the electrokinetic model of partially saturated porous media.The displacement and electric field signal s received by receivers are compared,and the influence of reservoir saturation on seismoelectric wave field is investigated.The simulation results show that the seismoelectric wave has obvious advantages in the vadose zone and reservoir exploration. |
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