Research On Occam Inversion Technology Of Cone Field Source Transient Electromagnetic

The layered half-space transient electromagnetic forward calculation formula is introd uced,and the 140-point Hankel transform method of D.Guptasarma and B.Singh is used t o calculate the frequency domain vertical magnetic field response,and use the cosine transf orm formula to convert the frequency domain response to the time domain.The effects of d evice coefficients and changing geoelectric model parameters on the forward response are discussed respectively.The results show that the larger the radius of the top-bottom coil,th e slower the response decays,the longer the time to reach the late stage,and the smaller the early induction intensity.The forward modeling of the typical geoelectric model reveals th at the transient electromagnetic method is more sensitive to the reflection of low-resistance anomalies.In the inversion part,the typical 2-layer(D-type,G-type),3-layer(A-type,H-type,Ktype,Q-type),4-layer(KH-type)and 5-layer(KHK-type)geoelectric models are firstly cal culated and compared with the results of the smoke ring inversion method;Secondly,carry out the inversion of conical field source transient electromagnetic quasi-two-dimensional f orward model and one-dimensional profile.The research results show that the Occam inver sion method is suitable for conical source transient electromagnetic,and the inversion effec t is better than the "smoke ring" inversion,the resolution of the layer interface is better,and it is more consistent with the model formation resistivity,the apparent resistivity curve obt ained by forward modeling the inversion resistivity has a smaller error.Then the optimizati on analysis of Occam parameters was carried out.1.The Lagrange multiplier search metho d is improved,and the binary search method is combined with the logarithmic search meth od to avoid the randomness of the value.2.Select different initial input models for inversio n.It is found that the inversion results are basically consistent,that is,the method has little dependence on the initial model.3.Add 5%,10%,20% random noise for inversion.The re sults show that when the noise does not exceed 10%,the inversion results have little differe nce;when the noise exceeds 10%,the deviation of the inversion results is obvious.It show s that the method has certain anti-noise ability.4.Inversion is carried out after adding restri ctive prior conditions to make it more in line with the actual stratigraphic conditions and pr ovide new methods and techniques for comprehensive geophysical interpretation.The inve rsion and comparison results of the measured data show that the inversion effect of the Occ am method is obvious.It is feasible to apply the inversion method to the processing of mea sured data,which provides new ideas and technical methods for the processing and interpre tation of actual data.