Comparative study of 3D joint inversion based on multi-section resistivity data

Abstract

A 3D joint inversion of 2D electrical prospecting data can effectively solve the shortcomings of the 2D electrical method in detecting the spatial forms of anomalous bodies. However, the direction and interval between 2D electrical prospecting survey lines can affect the workload of field prospectors and the accuracy of the subsequent 3D inversion. This study established a physical model of an indoor water tank. Multiple sections of 2D electrical survey lines were laid and survey line data was acquired. The intersection angles between 2D electrical survey lines and anomalous bodies as well as the relations between the 3D inversion characteristics and 2D electrical prospecting data for different line intervals were studied. The results of this study indicate that the electrical response of cylindrical anomalous bodies tends to become weaker, first slowly and then faster, with a decrease in the angle. When the intersection angle is between 60° and 90°, the inverted forms of the anomalous bodies are unchanged. When the interaction angle is less than 60°, there is a significant twisting of the bodies and the electrical response is obviously weaker. The 3D joint inversion imaging using multi-section resistivity data can effectively improve the recognition on the spatial forms of objects. However, the joint inversion obtained with different survey line intervals varies in how precisely the objects are depicted. The increase in the interval between survey lines can be divided into four main stages in terms of the 3D joint inversion. To maintain the efficiency of practical prospecting and because survey data forming shallow strata are affected by external interference, it was found experimentally that the optimum interval for the effective depiction of the locations and forms of objects ranges from 8 cm to 12 cm. Specifically, the least number of 2D survey lines can be deployed while ensuring the overall accuracy and reliability of the survey result when the survey line interval/2D electrical prospecting inversion depth ranges from 8/17 to 12/17. The study results may help us to guide the arrangement of electrical survey lines in field prospecting and improve construction efficiency and the accuracy of joint inversion.