陕北侏罗系砂岩宏观−微观特征及其富水性响应机制

Responding mechanism of macro-micro characteristics and water abundance on Jurassic sandstone in Northern Shaanxi Province

砂岩含水层富水性是矿井防治水的基础,随着陕北侏罗纪煤田煤炭资源逐步开发,侏罗系砂岩含水层富水性研究对保障矿井安全高效开采意义重大,但其非均质性如何影响富水性,即影响机制尚不明确。以大海则煤矿为研究区,通过沉积相划分与38块典型岩样铸体薄片图像分析、压汞、核磁共振等实验室测试,结合钻孔抽水试验成果,研究侏罗系直罗组、延安组沉积相、微观孔隙结构及其与富水性之间的关系,揭示了砂岩微观孔隙结构与富水性的响应机制。研究结果表明:大海则煤矿直罗组下段主要发育河流沉积体系河流砂坝和河漫滩沉积微相,延安组三段主要发育三角洲沉积体系分流河道和分流间湾沉积微相,河流沉积体系普遍较三角洲沉积体系含水层富水性强,以粗砂岩、中砂岩为主的河道砂坝富水性相较以中砂岩、细砂岩为主的河漫滩富水性强,砂岩厚度、砂地比较大的分流河道较砂岩厚度、砂地比较小的分流间湾富水性大;根据砂岩物性、孔隙分布、连通性等将侏罗系砂岩微观孔隙结构划分为大孔粗喉型(Ⅰ类)、中孔−中−细喉型(Ⅱ类)、小孔细喉型(Ⅲ类)、小−微孔−微细喉型(Ⅳ类)4种类型,孔隙结构由Ⅰ类到Ⅳ类依次变差,富水性依次变弱;砂岩宏观沉积相与微观孔隙结构共同表征含水层富水程度。研究结果为砂岩含水层特征研究及其富水性科学预测提供了一种新思路,为矿井防治水提供了理论依据。

The water abundance of sandstone aquifer is the basis of mine water prevention and control.With the gradual development of the Jurassic coal resources in northern Shaanxi areas,the study of water abundance of Jurassic sandstone aquifer is of great significance to ensure safe and efficient mining.However,how its heterogeneity affects water abundance,that is the influence mechanism is still unclear.Taking Dahaize Coal Mine as the research area,through the division of sedimentary facies and 38 typical sandstone samples casting thin section image analysis,mercury injection,nuclear magnetic resonance and so on laboratory tests,combined with the results of borehole pumping test,the sedimentary facies,micro pore structure and its relationship with water abundance of Jurassic Zhiluo Formation and Yan’an Formation were studied.The response mechanism of sandstone microscopic pore structure on water abundance is revealed.The results show that the lower Zhiluo Formation in Dahaize Coal Mine mainly develops river sand dam and flood plain sedimentary microfacies of river sedimentary system;The third section of Yan’an Formation mainly develops distributary channel and interdistributary bay sedimentary microfacies of delta sedimentary system.The river sedimentary system is generally more water abundance than the aquifer of delta sedimentary system.The water abundance of channel sand dam dominated by coarse sandstone and medium sandstone is stronger than that of flood plain dominated by medium sandstone and fine sandstone.The water abundance of distributary channel with large sandstone thickness and sand ratio is larger than that of interdistributary bay with small sandstone thickness and sand ratio.The microscopic pore structure could be divided into four types by physical properties,lithology,pore distribution,connectivity,which are typeⅠfor large pore and coarse throat,typeⅡfor mesopore and middle-fine throat,typeⅢfor keyhole and fine throat,typeⅣfor small-microporous and mi-cro-fine throat,and the pore structure becomes worse and the water abundance becomes weaker from I to IV.The macroscopic sediment-ary facies and microscopic pore structure of the sandstone jointly characterize the water abundance of aquifer.It provides a new idea for the characteristics and scientific prediction of water abundance of sandstone aquifer,and provides theoretical basis for mine water control.