| Seismoelectric effects induced by the coupling of seismic wave fields and electromagnetic fields are closely related to reservoir parameters.The study of seismoelectric effects in fluid-filled porous media can contribute to a better description of reservoir characteristics.Aiming at the generation mechanism of seismoelectric effects and the difficulty of acquiring seismoelectric signals,the seismoelectric effects in saturated sandstone samples are studied experimentaly,and the measurement of seismoelectric effects is analyzed to find a better measuring method.Also,the seismoelectric interface responses of sandstone models with different geometries are studied by using the seismoelectric physical modelling experiments.The amplitude characteristics and the polarity reversal of the seismoelectric interface responses of the incident and reflected waves at multiple interfaces of the porous rock samples are studied.The seismoelectric measuring method present the key points of seismoelectrics measurements,which can significantly improve the reliability of seismoelectric measurement.It is confirmed that two kinds of seismoelectric effects can be induced when seismic waves propagate in fluid-filled porous media.The response of the wedge model verifies that thin layers can enhance seismoelectric conversions.The intensity differences of seismoelectric signals induced by incident waves and reflected waves of multi-interface may affect the judgement of the depth of underground interface.The characteristics of polarity reversal of seismoelectric interface response can contribute to the correction of the polarity change in seismoelectric records caused by the change of electrode position.The relationship between seismoelectric coupling coefficients and the reservoir porosity-permeability characteristics in frequency domain are investigated through experiments and theoretical simulation.The experimental values of seismoelectric coupling coefficients in sandstone samples are obtained by seismoelectric measurement.Based on the seismoelectric coupling model of reservoir described by micro-capillary model,the variations of seismoelectric coupling coefficients with permeability and porosity are analyzed.The numerical and experimental results show that the seismoelectric coupling coefficient increases with the increase of porosity,but the effects of permeability on seismoelectric coupling are complex and can be divided into two permeability regions where 4.05 m D is the permeability demarcation point,below this permeability value,the seismoelectric coupling enhances with the increase of permeability in the frequency range of seismic exploration;and over this value,the seismioelectric coupling increases first and then decreases with the increase of permeability in the seismic frequency range.Both theoretical and experimental results show that the seismoelectric conversion is more sensitive to permeability changes in the low permeability range,suggesting that seismoelectric conversion may have advantages in detecting low permeability reservoirs.Based on the relationship between seismoelectric conversion and permeability proposed in this study,the permeability of reservoir can be inferred when the results of seismoelectric conversion of reservoir are known.Based on Pride's theory of and seismoelectric experiments,the characteristics of seismoelectronic conversion in shale and the causes of strong seismoelectric conversion in low porosity and low permeability shale are figured out.The influence factors of frequency-dependent seismoelectric coupling coefficients and the influencing degree of each parameter are studied.The results show that the tortuosity increase can decrease the seismoelectric effects in shale,and porosity and zeta potential can enhance the seismoelectric conversion in shale,while permeability has little effect on the seismoelectric coupling of shale.The relationship between zeta potential and seismoelectric signal indicates that the enhancement of seismoelectric conversion is closely related to the increase of zeta,while zeta potential is related to rock minerals,this means that the seismoelectric conversion has a close link with minerals.The results show that compared with seismic exploration for shale reservoirs,seismic-electric effect can directly detect the mineral characteristics of shale.An electroseismic experimental device is set up to measure the electroseismic signals of saturated rock samples.The travel time,polarity and spectrum characteristics of the electroseismic signals are obtained.Also,the relationships between porosity,permeability,fluid concentration and electroseismic coupling coefficients are studied by numerical modeling.The results indicate that the relationships between porosity,permeability and electroseismic coupling are similar to that of seismoelectric conversion,but the effects of fluid concentration on electroseismic coupling is completely opposite to that on seismoelectric coupling.The feasibility of electroseismic detection for reservoir parameters is confirmed by the study of electroseismic conversion. |
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