Numerical Simulation And Analysis Of Direct Current Resistivity Method For Marine Anisotropic Medium

By the influence of sedimentary environment and rock crystal structure,seabed strata bedding and geological breakage is serious.So electric anisotropy is obvious,and marine geological environment anisotropic model is more suitable to describe the real.The electromagnetic sounding technology is widely used in exploration of marine geology resources for high efficiency,low cost and good physical discrimination.The DC resistivity method can easily avoid the influence of air wave.The marine anisotropic geo-electric model use DC resistivity method,which is easy to identify submarine anisotropic characteristics and can be more accurate seabed mineral exploration.According to the passivity of electromagnetic field,we introduce scalar potential.Based on the boundary conditions of electromagnetic fields in the interface,we derive the upper and lower extension equations respectively.Solving the Green function of emission source,we extend the continuation equations to the source,and we obtain the coupling equation of each scalar potential.By means of Euler rotation,we calculate the resistivity tensor of arbitrary anisotropy and use log interval sampling Fast Hanker Transform to solve integral kernel function.Finally,the numerical simulation of the direct current resistivity method for ocean anisotropic media is presented.Based on the electromagnetic field continuation formula,we develop a numerical calculation program and perform precision verification to ensure the reliability of this study.We investigate the anisotropic characteristics of the direct current resistivity method in marine anisotropic formation by using the homogeneous half space model.By calculating the variation characteristics of marine anisotropic homogeneous half space resistivity with the dipole moment,we found that the apparent resistivity is greatly affected by a high conductivity of seawater at small electrode distance.Comparison of the apparent resistivity polarity maps by different ocean electromagnetic sounding methods,we can see that the anisotropic anomalies are obvious.It is found that the apparent resistivity is different in different directions,and the results are similar to the distribution characteristics of apparent resistivity of land resistivity method.When the direction of the current changed,the apparent resistivity changed.Therefore,we suggested that the actual exploration should be carried out along the axis of measurement or vertical measurement.Finally,we calculate the electromagnetic field distribution in the cross section,longitudinal section and three-dimensional space.Due to the influence of the channel effect,the electromagnetic field has a tendency to extend to small resistance.At the same time,Different electromagnetic field components have different sensitivity to the recognition of seabed anisotropy.Summarizing the anisotropic characteristics caused by the direct current resistivity method,we further investigate the anomalies of the mineral deposits in the marine anisotropic background.By setting up the model of the carbohydrate and the reservoir model,we calculate the electromagnetic field response and apparent resistivity of different models.When changing the depth of sea water or the thickness of overburden layer,we can calculate the apparent resistivity ratio or normalized electromagnetic field.We know that the depth of sea water and the thickness of coating will affect the detection effect of DC resistivity method.Shallower the sea water is,shallower the mineral deposits are.When the dip angle of the anisotropic formation is changed,the measured apparent resistivity and electromagnetic field response are also different.The reason for this phenomenon is that the channel effect will lead strong electromagnetic response.Therefore,the mineral anomaly in vertical anisotropy stratum is the largest one.This paper discusses the influence of air wave on the controlled source electromagnetic sounding,and proves that the DC resistivity method is an inevitable choice for the electromagnetic prospecting in shallow sea mineral resources.By comparing the electromagnetic response of the oil reservoir with different electrical parameters,it is found that the oil reservoir is assumed to isotropic and high resistivity layer is reasonable.The anisotropy of formation has great influence on the DC resistivity method.Taking into account the anisotropic development of marine strata and the resistivity method is not affected by air wave,we believe that the DC resistivity method is particularly suitable for exploration and detection of the mineral deposits in shallow water area.