Study About 2.5 Forward And Inversion Of Centrl Loop Transient Electromagnetic Method

The transient electromagnetic method as electromagnetic method developed rapidly in recent years, because of its advantages of high resolution, wide exploration depth, is widely used in engineering, environment, hydrology, energy exploration etc.. However, the transient electromagnetic method of data interpretation level is still relatively low, in the field, basically in a one-dimensional stage, at this stage of 2D and 3D inversion technique cannot be used in practical production. But with the rapid development of computer technology, and the emergence of transient electromagnetic advanced intelligent instrument, the transient electromagnetic data interpretation is also proposed new requirements. In this paper the problem, based on transient electromagnetic 2.5 dimensional as the research object. 2.5 dimensional transient electromagnetic inversion problem, namely the three-dimensional source, twodimensional geoelectric section, compared with the 3D model, which requires only the section instead of the entire volume of discrete processing, reduces the computation; compared with the one-dimensional, two-dimensional model, which can better approximate the geological conditions. Not many studies now 2.5 dimensional transient electromagnetic problems, and there are many shortcomings, mainly in the calculation precision and speed, the degree of the 2.5 dimensional transient electromagnetic inversion is still not applied in actual production, so for the 2.5 dimensional simulation of further research is very meaningful and this value, otherwise a written is of no significance. The central loop transient electromagnetic method is one of the most commonly used, but not much in the present research, this paper chose the transient electromagnetic loop 2.5 dimensional inversion problem as the research object.This paper from the one-dimensional transient electromagnetic forward modeling of derivation of Maxwell equation, the numerical filtering and numerical Hankel cosine filter, get the transient electromagnetic response of one dimensional type, the one-dimensional transient electromagnetic forward. Based on the emission parameters to understand the different emission parameters of the transient electromagnetic response, the transmitting line box length is longer, the transient electromagnetic response attenuation is slower, the early time is longer, with the increase of the emission current, the amplitude of transient electromagnetic response is linear increase. Through the establishment of various geoelectric model, so as to understand the transient electromagnetic response, including D type, G type and H type.In 2.5 dimensional transient electromagnetic forward, starting from the Maxwell equation, solutions of the transient electromagnetic anomalies in 2.5 dimensional problem of partial differential equations, variational problem, boundary problem is derived in detail. In this one focuses on the analysis of several key problems: Laplasse transform, Fu Liye transform, to the calculation of non component. The use of unstructured grid of this tool, the abnormal area in the grid and measuring points near the encrypted local, greatly reduces the number of grid cells and the number of nodes, thereby reducing unnecessary computing nodes. Can be achieved on the division of complex models by the unstructured mesh generation method, the application scope of the 2.5 dimensional transient electromagnetic forward extended well. The establishment of K and H two models, and the transient electromagnetic forward 2.5 dimensional finite element calculation, the analytical results and also the solution of the model were compared, we can know the finite element solution and analytic solution, the error is very small, illustrate the feasibility and effectiveness of the 2.5 dimensional Co. element solution. The transient electromagnetic forward 2.5 dimensional finite element method of vertical low baffle shaped body and a low resistance cylinder, two cylinder and low resistance of the three models were simulated, low vertical board shaped body, the maximum value in the plate plate on both sides, at present the minimum low resistance cylinder; the body in the simulation, when the cylinder, each measuring road appeared obvious symmetry, and the emergence of the cylinder top unimodal anomaly; two low resistance cylinder exist at the same time, when the spread to two cylinders at the time, appeared in two symmetrical maxima, maxima in the middle at minimum.In the inversion, the first is the use of one-dimensional inversion, two equal resistivity algorithm "fast inversion smoke rings", and set a variety of models of inversion, summed up the inversion method with fast inversion, inversion of resistivity profile can be roughly described by the geological characteristics of distribution. For the 2.5 dimensional inversion of transient electromagnetic method, this paper proposes to the smoke ring inversion and measurement of geological information as the initial model, namely the use of smoke ring inversion as the 2.5 inversion reference, and through the artificial to inversion result and 2.5 dimension forward model are compared, namely human joint inversion, achieve instant 2.5 transient electromagnetic inversion. This method has certain feasibility.