基于Dias新模型的大地电磁激发极化特性

Magnetotelluric induced polarization characteristics based on new Dias model

在大地电磁测深法(magnetotelluric method,MT)中,通常不考虑岩矿石产生的激发极化(induced polarization,IP)效应,电阻率被认为是一个与频率无关的电性实数,但实际上,地下介质会因为电化学的作用而产生IP效应,含IP效应的地层的电阻率不再是一个与频率无关的实数,而是一个与频率有关的复数。如果在正演模拟时用实电阻率表示地层电阻率,则计算的视电阻率和相位与实际情况不符,不符程度取决于极化程度。基于岩矿石IP效应的Dias新模型,研究了IP效应对MT视电阻率和相位的影响,分别计算了不含IP效应和含IP效应的一维层状大地(均匀半空间、盖层、基底和中间层4种模型)的电磁响应,并对比分析了其差异。结果表明,利用MT进行勘探时,若工区内存在极化地层,则实测的视电阻率和相位包含了IP效应的贡献,因此从MT资料中提取激电谱参数是可行的。

Resistivity has been considered as an electrical real parameter independent of frequency in the magnetotelluric method(MT),generally without considering the induced polarization(IP)effect produced by rock and ore,but in fact,the underground media will generate IP effect due to electrochemical action,and the resistivity of the stratum containing IP effect is no longer a real number independent of frequency,but a complex number related to frequency.If the formation resistivity is expressed by real resistivity in forward modeling,the calculated apparent resistivity and phase do not correspond to the actual situation,and the degree of discrepancy depends on the degree of polarization.Based on the new Dias model of rock and ore IP response,the effect of IP effect on the apparent resistivity and phase of MT was studied.The electromagnetic responses of one-dimensional layered earth models(homogeneous half space model,cap layer model,basement model and interlayer model)without and with IP effect were calculated respectively,and the differences were compared and analyzed.The results show that when MT is used for exploration,if there are polarized strata in the work area,the measured apparent resistivity and phase include the contribution of IP effect,so it is feasible to extract IP parameters from MT data.