Law and model of Jurassic sedimentary water control in Northern Shaanxi Province

There is uneven water-enrichment in Jurassic sandstone aquifers in northern Shaanxi Province,and a great difference between actual mine water inflow and the predicted value at exploration stage.In order to improve the prediction accuracy of mine water inflow,scientifically and efficiently guide mine water prevention and control,this paper respectively studied the relationship between sedimentary micro-facies,lithology and its assemblage,microscopic pore structure and water-enrichment using sedimentary micro-facies division,qualitative statistics of geological information and grey correlation quantitative analysis,laboratory test of microscopic pore structure from the angle of sedimentary water control.The mechanism of sedimentary water control was revealed and the law of sedimentary water control was summarized,then,the sedimentary water control mode was put forward.The results show that:① the thicker the coarse clastic rocks such as coarse sandstone and middle sandstone is,the stronger the water-enrichment it is,and the thicker the fine clastic rocks such as mudstone and sandy mudstone is,the weaker the water-enrichment it is.② When the degrees of weathering are the same,the lower the classification level of sandstone microscopic pore structure (The microscopic pore structure include type Ⅰ for large pore and coarse throat,type Ⅱ for mesopore and middle-fine throat,type Ⅲ for keyhole and fine throat,type Ⅳ for small-microporous and micro-fine throat) and the coarser the grain size are,the stronger the water-enrichment aquifer is,while the degrees of weathering are different and the stratigraphic age is the same,the lower the classification level of sandstone microscopic pore structure and the coarser the grain size are,the stronger the water-enrichment aquifer is.③ The Zhiluo Formation aquifer is dominated by fluvial sedimentary system,and the sedimentary facies are meandering river and braided river,sedimentary microfacies are channel and floodplain.When the sedimentary facies are the same in Zhiluo Formation aquifer,the water-enrichment of channel sedimentary microfacies are stronger than that of the floodplain sedimentary microfacies,and the lithology of channel sedimentary is mainly conglomerate,coarse sandstone and middle sandstone.The upper strata of Yan’an formation aquifer is dominated by delta sedimentary system,delta plain sedimentary facies,distributary channel and distributary bay sedimentary microfacies,and the water-enrichment of distributary channel are stronger than that of the distributary bay sedimentary microfacies,and the distributary channel is mainly composed of middle sandstone,occasionally siltstone.④ The sedimentary water control model in the study area has been divided into four types,which are braided river sedimentary and strongly water-enrichment type,meandering river sedimentary and medium water-enrichment type,delta plain distributary channel sedimentary and weak water-enrichment type,delta plain distributary interbay sedimentary and extremely weak water-enrichment type.The research results can provide scientific basis for aquifer water-enrichment prediction and mine water disaster prevention.