Research And Application Of Time-lapse Electrical Resistivity Tomography

As a new technique for monitoring the dynamic process of shallow subsurface,the time-lapse resistivity tomography has been used more and more widely,but it is rare to see examples applied to the roadway.In this paper,the time-lapse resistivity method is studied systematically by means of numerical simulation,physical simulation and underground actual experiment.The main achievements and innovations of this paper are as follows:(1)In order to cope with the dual pressure of narrow space and dynamic mining,a new Underground time-lapse ERT observation system was developed by transforming the traditional two-dimensional observation system into a three-dimensional observation system and redesigning the borehole sampling electrode.By comparing and analyzing the various device forms of the time-lapse ERT,the form of the device suitable for the environment of the mine is clarified.(2)Through the cut-in of the forward calculation of the single-latitude time-lapse ERT,the calculation process of solving the forward problem of three-dimensional resistivity by using the finite element method with tetrahedral element is derived from the basic mathematical principle of ERT tomography.The solution of Poisson equation in discrete form is obtained.By introducing the multi-algebraic grid-conjugate gradient preprocessing algorithm,the computation time of the Jacobian matrix time is reduced,the requirement of coal mine dynamic monitoring and short-term analysis is met,and it is highly robust against the jump of conductivity coefficient.For the three-dimensional complex mesh of the well environment,it also has better adaptability.The filtering algorithm of dynamic process is constructed through the model state process equation and observation model.The state estimation of the time-lapse model is obtained by calculating the data set of time-lapse observation.(3)Based on the geoelectric section characteristics of coal formation stratification distribution,this paper proposes a new time-lapse 3d fine inversion and fast inversion algorithm to image the change of resistivity with time.By pre-estimating the geological body change region and allocating the appropriate time Lagrangian value,the recorded data are preliminarily analyzed by differential imaging,and then the 4D-ATC inversion method is applied to the entire data set recorded in all monitoring steps.The imaging results are more focused on the area of expected change for imaging changes in resistivity over time.The fast algorithm of the well lane time-lapse ERT through the introduction of the clustering strategy greatly reduces the number of inversions while maintaining the stability of the imaging,effectively satisfying the requirements of qualitative,semi-quantitative and quantitative algorithms of coal mine safety monitoring for fast inversion and highlighting dynamic change.This is especially important for monitoring complex,highly variable targets,because anomalies in these regions change over time and are mistakenly assumed to be artifacts.