The Study Of Central-loop Transient Electromagnetic Pseudo-seismic Interpretation Imaging Technology

As an important electromagnetic prospecting method, transient electromagnetic method (TEM) is widely used in resource prospecting and engineering exploration with its unique excellence. Along with the increasement of difficulty to prospect resource and the enhancement of precision requirement for engineering exploration, improving the transient electromagnetic interpretation level and the method resolving power is shown more and more important. By virtue of some mature imaging techniques which have been developed in seismic exploration to explain the physical property or geometrical property parameter for the purpose of advancing the method interpretation precision is the urgent problem to be resolved in transient electromagnetic data interpretation.Transient electromagnetic pseudo-seismic interpretation method is the method of absorbing the valid means used in seismic exploration to the electromagnetism explanation, according to similar principle of electromag- netic wave and flexible wave in mathematics expression and physics meanings. This method can efficiently divide the reflect interface and electrical property stratum under the condition of 1D plain symmetrical layered medium, and has its own characteristic compared with normal interpretation methods.In order to improve the vertical resolution of the transient electromagnetic method, considering the situation that central-loop equipment is now widely used in resource prospecting and engineering exploration in China, we make a study of the principle of central-loop TEMimaging technology and a numerical calculation method. The law of propagation of electromagnetic wave and seismic wave in media is analyzed. According to the similarity between the propagation of magnetic dipole source TEM field and reflected seismic wave, method is discussed to explain TEM data with the pseudo-seismic interpretation. Two vital equations are analyzed among the imaging process, the one is transient electromagnetic response expression to the layered medium, the other is linear equations which contain unknown reflection coefficients. Transient electromagnetic response to the layered earth is discussed in the frequency domain, then a double integral in which the kernel is unknown is obtained. The solution of the electromagnetic field in the medium of layered earth is separated into the forms of upper and down traveling waves, then a set of linear equations contain reflection coefficients are obtained. In order to enhance the data quality and imaging precision, wavelet analysis is applied to eliminate noise from the transient electromagnetic signal. The numerical solution of wave-impedance and reflection coefficients is given as follows: Transforming the magnetic field data from time into frequency domain, replacing the kernel of equation with the equivalent wave-impedance of homogeneous half-space, getting the equivalent wave-impedance in the frequency domain after digital filtering, then returning the equivalent wave-impedance into the time domain, constructing equations with it, getting reflection coefficients from the equation with the method of linear programming in the time domain, imaging the profile diagrams according to the parameter of reflection coefficients. By processing the data from models, the TEM pseudo-seismic interpretation method is validated correct and feasible. At the same time the imaging precision is discussed, getting the conclusion that the selection of equationsparameters, division of isochronous layer and the selection of better arithmetic to solve linear equations have influence on the imaging precision.At last the processed results of the field data are shown that the arithmetic is credible, the profile diagrams are distinct, and the method has reached anticipated effection. The study in this paper can provide the reference for the research in the interpretation of seismic data simulated by transient electromagnetic method and in imaging to earth.