Exploration practice of ground transient electromagnetic method for groundwater resources in Northern Shaanxi Coal  Mining Area

Large-scale exploitation of coal resources in the upper and middle reaches of the Yellow River basin has caused continuous deterioration of ecological environment. It is helpful to realize the coordinated development of coal resources exploitation and ecological environment protection to master the influence law of coal exploitation on groundwater environment. Using the transient electromagnetic method to study groundwater occurrence characteristics is one of the key contents. Take groundwater resources occurs in Zhiluo Group and Yanan Group strata at Northern Shaanxi Coal Mining Area as two research objects,based on the drilling geological columnar and apparent resistivity logging curves,the normal and abnormal geoelectric models were constructed by the strata overlying the main coal seams in the study area. Through forward-modeling of the ground transient electromagnetic one-dimensional program,the induced voltage and all-time apparent resistivity curves were obtained by different geoelectric models,and the differences of data of transient electromagnetic field responded by different geoelectric models were analyzed. The results show that,the response characteristics of transient electromagnetic field changes with the water-rich conditions of the target aquifers and the effective observation time for the transient electromagnetic field to distinguish different target aquifers is 0.000 1 s to 0.01 s. The feasibility to detect the water content of the target aquifers using the transient electro 〖LM〗magnetic method can be determined in theory. The field detection test further gives the transient electromagnetic observation parameters applicable to the study area,and obtains the distribution characteristics of the electrical parameters of the target aquifer. Based on the principle of statistics,the identification threshold of the electrical anomaly of zhiluo and Yanan aquifers is determined to be 34 Ω·m and 48 Ω·m,respectively.According to this,the groundwater occurrence characteristics of zhiluo and Yanan strata are revealed respectively. In which,the former has strong water enrichment with relatively developed fissures of rock,and the latter has weak water enrichment with relatively integrality of rock. Finally,in view of the influence law of coal mining on groundwater environment,the subsequent focus of transient electromagnetic detection and related influencing factors are pointed out.