Full-time Transient Electromagnetic OCCAM Constrained Inversion Method

Transient Electromagnetic Method(TEM)has the advantages of high detection accuracy,arge depth,high construction efficiency and sensitivity to low-resistance anomalous bodies.It s often used as the preferred method for water-rich detection of coal-measure formations.However,the accuracy of transient electromagnetic inversion still has certain problems and needs to be improved.This paper proposes a full-time transient electromagnetic OCCAM inversion with logging constraints,which aims to improve the ambiguity and non-uniqueness problems in conventional inversion methods.First,the thesis analyzes the transient electromagnetic field in a uniform half-space,and then studies the transient electromagnetic response characteristics under complex conditions.The transient electromagnetic response characteristics of vertical step and oblique step are compared and analyzed.Based on this,the one-dimensional full-time forward modeling of transient electromagnetic is studied.By establishing different target depths and different targets in a uniform layered half space Models such as layer electrical properties and different target layer thicknesses analyze the transient electromagnetic response characteristics of different geoelectric models,which provide theoretical support for the inversion and interpretation work.Secondly,based on conventional one-dimensional OCCAM inversion and quasi-two-dimensional inversion with lateral constraints,by modifying the model roughness matrix in the objective function,adding model constraints,the iterative format of the modified objective function is deduced,and then the The rock resistivity parameter is used as a priori information for the transient electromagnetic constrained inversion algorithm.A four-layer geoelectric model was established,and full-time one-dimensional OCCAM inversion,full-time quasi-two-dimensional OCCAM inversion with lateral constraints,and full-time lithology constrained OCCAM inversion were performed respectively,and full-time lithology constraints were found The accuracy of OCCAM inversion is better than that of full-time quasi-two-dimensional OCCAM inversion with lateral constraints,and the accuracy of full-time quasi-two-dimensional OCCAM inversion with lateral constraints is better than that of full-time one-dimensional OCCAM inversion.Finally,perform full-time one-dimensional OCCAM inversion of the measured transient electromagnetic data,full-time pseudo-two-dimensional OCCAM inversion with lateral constraints,and full-time lithology constrained OCCAM inversion,combining known data to perform three inversions The resistivity profile of the results of the analysis was analyzed,and it was found that the addition of prior rock resistivity information in the lithology constrained inversion can greatly improve the resolution of anomalous bodies.It is a very effective inversion method;it will be based on lithology.The results of the constrained full-time transient electromagnetic lateral confinement inversion are compared with the results of the conventional transient electromagnetic confinement inversion and the commercial software INTERPEX inversion.The full-time transient electromagnetic lateral confinement inversion method based on lithological constraints can Significantly improve the resolution of anomalous bodies,reflecting more geological information.