Analysis of electrical resistivity and acoustic wave velocity characteristics in fault structures and their combined application in the detection process

Abstract

Finding out the specific location of the fault structure is of great significance for the engineering site selection and stability evaluation. Electrical resistivity tomography and acoustic logging are geophysical methods widely used in detecting fracture structures. Although electrical resistivity tomography is sensitive to low resistance bodies and has a large detection range, it is difficult to accurately delineate the boundary position of geological bodies because of its limited resolution. Acoustic logging can identify strata accurately, but its lateral detection range is limited. This study combined the advantages of the two methods in fault structure detection to improve the precision of geological body delineation. Firstly, the correlation between the resistivity of rock before and after fracture and the change of acoustic wave velocity was proved by physical property experiments. Then the case analysis of the resistivity and acoustic wave velocity characteristics of the fault structure and their combined application in the detection process was conducted. Finally, the depth correction of the inversion result of the electrical resistivity tomography was carried out using the acoustic logging data; and the three-dimensional distribution position of the fault structure in the underground space was obtained. Theresults show that the resistivity and acoustic wave velocity of the rock after fracture are lower than those before fracture. The fracture zone of the fault structure exists in the inversion section of the electrical resistivity tomography with a low resistivity anomaly region. On the wave velocity curve, the wave velocity value in the fracture zone decreases significantly. The combined detection mode of the two methods could provide a guidance for the delineation of the specific location of the fracture structure. The drilling results also verified that the inversion results of the electrical resistivity tomography corrected by acoustic logging data are more consistent with the actual geological conditions than those without correction.

Keywords

• fault gouge zone
• depth correction
• physical parameters
• electrical resistivity tomography
• acoustic logging