Mine water inflow pattern in the distribution area of paleochannel sand bodies of the Zhiluo Formation in the northern part of the Ordos Basin

In the past ten years, the coal mining operation in the northern part of the Ordos Basin has been frequently threatened by the groundwater of the Zhiluo Formation, and even some water inrush accidents have occurred. In the area, the mines with the groundwater of the Zhiluo Formation as water source are distributed continuously, and are closely related to the paleochannel sand bodies of the Zhiluo Formation. In order to explain the mine water inflow model in the distribution area of the paleochannel sand bodies of the Zhiluo Formation in the southern area of Shenfu, on the basis of the study of the spatial distribution of paleochannel sand bodies in the Zhiluo Formation and their control effect on groundwater occurrence, the relationship between the paleochannel sand bodies and the mine water inflow in the Zhiluo Formation was analyzed from the scale of the study area, the scale of the well field and the scale of the working face, and the mine water inflow model under the paleochannel sand bodies of the Zhiluo Formation was proposed. The results show that the paleochannel scouring zone of the Zhiluo Formation in the southern area of Shenfu is developed along the line of Hongyannao-Erlintu-Jinjie, and the fifth member of the Yan’an Formation in the erosion zone is almost completely eroded, and the fourth member of the Yan’an Formation is also scoured in some areas. According to the analysis of the sand dispersion system and the development characteristics of the aquifer rock group, the paleochannel sand bodies filled and deposited in the scouring zone are divided into three grades. The water-richness of the paleochannel sand bodies of the Zhiluo Formation is mainly controlled by the scale, physical characteristics and weathering of the sand body, and the water-richness of the first-order sand body (main channel) is stronger than that of the second-class sand body (branch channel) and the third-order sand body (delta bay and tributary bay), and its water richness will be further enhanced when the sand body is weathered. Based on the analysis of the relationship between sand body classification, weathered sand body thickness and mine water inflow at different scales, three water inflow modes of production mines under paleochannel sand bodies in the eastern part of the study area were proposed. The strong water inrush mode is mainly located in the distribution area of the first-class sand body, and the thickness of the weathered sand body is generally ≥ 30 m. Medium water inrush mode is mainly located at the edge of the primary sand body or secondary sand body area, the thickness of the weathered sand body is generally 10−30 m. The weak water inrush mode is mainly located in the tertiary sand body area, and the thickness of the weathered sand body is generally < 10 m.