Geophysical electrical potential inversion for grouting remote monitoring of coal mine double-layered wellbores

Abstract

This work aims to remotely monitor the grouting process of double-layered wellbores in deep coal mining area by proposing a new geophysical electrical potential inversion imaging method. The proposed geophysical method is able to evaluate the grouting quality between the inner and outer walls of the wellbores by inverting the geologic electrical potential. Th challenge lies here in the potential inversion is that the thickness of the grouting space is extremely narrow when comparing with the wellbore diameter. To solve this problem, a constrained inversion model is developed to precisely generate the three-dimensional (3D) resistivity distributions of the double-layered wellbore based on the measured geologic electrical potential. A special designed test platform is constructed and experimental tests have been conducted to examine the performance of the proposed geophysical inversion imaging method. The geologic electrical potential of the grouting space is measured and remotely transmitted to the ground processing center; and the constrained inversion model is applied to the geologic signals to calculate the resistivity distributions at different grouting stages and produce the 3D geophysical images. The analysis results suggest that the present geophysical monitoring method can effectively visualize the grouting to evaluate the construction quality of the wellbore.

Keywords

• Structural health monitoring
• Double-layer wellbore
• Direct current resistivity
• Constrained inversion method