Study On The Control Of Mantle Branch Structure On The Development Of Collapse Column In North China Basin

Karst collapse column is a special geological phenomenon in North China coal field geology.Water inrush of water guide column frequently causes flood wells and death disasters.With the gradual development of coal mines in China,the karst collapse column becomes more and more easy to guide the confined aquifer,which is a major threat to the production safety of the mining area.It is found that the distribution of collapse plumes is consistent with the third-order structure of mantle plume mantle branch structure.This paper is based on the hydrogeological conditions of the mantle plume in North China,discusses the material and energy effects associated with mantle upwelling forming mantle branch structure,designs and completes the supercritical water karst experiment under the condition of high CO2 partial pressure,carries out the numerical simulation calculation of karst water convection under different conditions,and verifies the theory of "mantle branch controlling pillar" in typical mining areas.The following conclusions are drawn:1.Associated thermal effects and CO2 effect in mantle branch structures:The mantle branch often appears at the edge of the North China Basin.As a evidence and channel for magmatic activity,it brings deep matter and energy to the earth's crust:(1)The thinning of crust and intrusion of magmatite have changed the original geothermal field.The results are as follows: the modern magmatic activity makes the regional geothermal energy abundant and the earth heat flow value increase;the longer time magmatic activity caused the regional coal metamorphism to be higher,and the middle to high metamorphic range coal.(2)Mantle fluid carries deep carbon dioxide to the lithosphere,and its quantity is enormous.CO2 gas reservoirs have been found in some mantle branches.In addition to direct carrying,magma intrusion associated metasomatism is also an important way to produce carbon dioxide.2.The data of supercritical water karst test show that the quality of the samples before and after the reaction,the blurring of artificial marks and the appearance of microscopic caverns can be judged: the supercritical water environment under high CO2 condition is conducive to the development of karst.In addition,the strength of the sample decreases obviously and is easily broken,so the supercritical area can be regarded as the dominant position of karst collapse,and its quantitative description needs further mechanical experiments.3.The local thermal effect of mantle branch will lead to the phenomenon of karst water convection in limestone and promote the effect of groundwater runoff,especially for vertical runoff.When the flow field is located in a large permeability structural belt(such as fault),the structural belt is the optimal channel for vertical runoff.The thermal convection in the presence of various heat sources is simulated and calculated.The supercritical area near the heat source is the dominant position of karst space and karst collapse.4.The theory of mantle branch controlling column can be used to judge the hydraulic conductivity of collapse column.The development area of subsided column is high,and the degree of coal metamorphism is not high.Often collapse pillars collapse and compacted,and have strong water conductivity;otherwise,poor conductivity or no water diversion.According to the two typical coalfield geological data of Qinshui coalfield mining area(over-metamorph and palaeogethermal area)in Hebei Fengfeng mining area(Modern geothermal area),the application of the theory of mantle branch control column is better than that of Shanxi.