油水两相饱和储层中平面震电波场响应特性

Response characteristics of the plane seismoelectric waves in the oil-bearing reservoir

现有的孔隙介质震电理论缺乏针对含油储层震电耦合的数学模型及定量模拟,制约了该方法在含油储层中的推广应用.本文将非饱和孔隙介质中弹性波动理论与含油储层中动电耦合理论及麦克斯韦电磁理论相结合,建立了描述油水两相饱和储层中震电耦合波的数学方法,定量模拟了含油储层中平面震电波场响应特性,并探讨了储层参数对震电波场响应的影响.研究结果表明:油水两相饱和储层中震电耦合产生四种震电耦合波,震电横波、震电纵波P1、P2和P3波;震电波场响应具有频散特性,频率增大,震电纵波P2和P3波传播速度显著增大,震电波衰减常数均增大;相同频率下,震电纵波P2波电场强度及电流密度与固相速度比值的模值相比其它三种震电波的均较大,说明其激发电场和电流能力较强;震电波场响应受到宏观储渗参数的影响,储层孔隙度增大,震电波的传播速度均减小,三种震电纵波的衰减常数均增大,且震电横波和震电纵波P1波的电场强度与固相速度比值的模值均增大,震电纵波P2和P3波的均减小;储层渗透率增大,震电波的传播速度均增大,震电横波的衰减常数、电场强度与固相速度比值的模值亦增大,而三种震电纵波的则相反;含水饱和度增大,震电横波、震电纵波P1(低频时)和P2波的传播速度均减小,衰减常数、电场强度及电流密度与固相速度比值的模值均增大,震电纵波P3波的则相反;震电波响应电场强度及电流密度与固相速度比值的相位在高频时出现频散现象,同样受到储层参数的影响.

Mathematical model and quantitative simulation of the seismoelectric coupling in oil-bearing reservoirs are presently needed, for promoting the popularization and application of the seismoelectric method.Therefore this article combines the elastic wave theory in the unsaturated porous media and Maxwell＇s electromagnetic theory, using the electrokinetic coupling theory in oil-bearing reservoirs,in order to establish the mathematical method of describing the seismoelectric coupling waves in the oil-bearing reservoirs.Then the responses of the seismoelectric coupling waves are quantitatively simulated, and the influence of reservoir parameters on the seismoelectric wave responses are analyzed in the oil-bearing reservoirs. The results show that the seismoelectric coupling in the oil-bearing reservoirs induces four kinds of seismoelectric coupling waves, including the seismoelectric shear wave,seismoelectric longitudinal waves P1,P2 and P3.And the responses of the seismoelectric waves have the dispersion character.As the frequency increases,the velocities of the seismoelectric longitudinal waves P2 and P3 both increase, as well as the attenuations of the four seismoelectric waves;At the same frequency,the electric field intensity and the current density generated by the solid velocity of the seismoelectric longitudinal wave P2 have the bigger modulus values than those of the other three waves.Responses of the seismoelectric waves are influenced by the reservoir parameters such as porosity, permeability and water saturation.When the porosity increases,the velocities of the four kinds of seismoelectric waves all decrease, while the attenuations of the three kinds of seismoelectric longitudinal waves increase.The modulus value of the electric field intensity or current density generated by the solid velocity of the seismoelectric shear wave or seismoelectric longitudinal waves P1 increases with the porosity increasing,but that of the electric field intensity induced by the solid velocity of seismoelectric longitudinal waves P2 or P3 decreases;As the permeability increases, velocities of the four kinds of seismoelectric waves all increase,and the attenuation of the seismoelectric shear wave increase,as well as the modulus value of the electric field intensity induced by the solid velocity of the seismoelectric shear wave,but these of the three kinds of the seismoelectric longitudinal waves decrease;When the water saturation increases,the velocities of the seismoelectric shear wave and seismoelectric longitudinal waves P1 and P2 all decrease,while the attenuations and the modulus values of the electric field intensities or current densities generated by the solid velocities of them increase,but those of the seismoelectric longitudinal wave P3 all change conversely.The phases of the electric field intensities or current densities generated by the solid velocities responded by the seismoelectric waves show the dispersion phenomena at high frequencies,also affected by thereservoir parameters.