锦界煤矿侏罗系砂岩微观孔隙结构类型及富水性研究

Study on microscopic pore structure types of Jurassic sandstone and water abundance in Jinjie Coal Mine

砂岩富水性是顶板突水危险性评价的重要指标之一,研究砂岩的微观孔隙结构,对于认识其与含水层富水性的关系具有重要的意义,以锦界煤矿3-1煤顶板侏罗系砂岩为例,通过薄片鉴定和压汞实验对所采集到的砂岩样品的微观孔隙结构进行研究,最终对比钻孔单位涌水量,分析该区砂岩微观孔隙结构与富水性的关系。研究结果表明:侏罗系延安组砂岩中泥质的含量(平均25.5%)大于直罗组砂岩中泥质的含量(平均4%)。将砂岩的孔隙结构按照毛管压力曲线形态和排驱压力大小划分为Ⅰ类低排驱压力型、Ⅱ类中排驱压力型和Ⅲ类高排驱压力型。Ⅰ类低排驱压力型砂岩以大于10μm的粒间和晶间孔隙为主,将该区大于10μm的孔隙定为有效孔隙,则其有效孔隙占比达61.68%,且该含水层承压水头在66.30 m左右,具有一定的压力水头,大量赋存在孔隙中的重力水在一定的压力水头下自由移动,是其中等富水性的重要原因。Ⅱ类中排驱压力型砂岩以0.1~10.0μm的颗粒内和粒间孔隙为主,该类孔隙体积占51.44%。Ⅲ类高排驱压力型砂岩以小于0.1μm的晶粒内孔隙为主,该类孔隙体积占45.32%。Ⅱ类中排驱压力型砂岩和Ⅲ类高排驱压力型砂岩的有效孔隙仅占21.92%,此类砂岩为弱富水性。

The water abundance of sandstone is one of the important indexes for the risk assessment of roof water inrush.It is of great significance to study the microscopic pore structure of sandstone for understanding its relationship with the water abundance of aquifer.In this paper,taking the Jurassic sandstone of 3-1 coal roof in Jinjie Coal Mine as an example.The microscopic pore structure of sandstone was studied by thin section identification and mercury porosimeter method.Finally,the relationship between the microscopic pore structure and water abundance of sandstone in the study area was analyzed by comparing the unit water inflow of borehole.The results show that the clay content(25.5%on average)in Yan’an formation of Jurassic is much higher than that in Zhiluo formation(4%on average).According to the shape of capillary pressure curve and displacement pressure,the pore structure of sandstone can be divided into three types:low displacement pressure type Ⅰ,medium displacement pressure type Ⅱ and high displacement pressure typeⅢ.The low displacement pressure type Ⅰ sandstone is mainly composed of intergranular and intercrystal pores which is larger than 10μm.If the pores in the study area larger than 10 meters were regarded as effective pores,the ratio of effective pore volume would reach 61.68%.The confined water head of the aquifer is about 66.30 m,with a certain pressure head,and a large number of gravity water in the pores moves freely under a certain confined water head,which is an important reasons of mediumwater abundance.In the medium displacement pressure type Ⅱ sandstone are dominated by intragranular and intergranular pores between 0.1μm and 10.0μm,The pore volume of this type accounts for 51.44%.In the high displacement pressure type Ⅲ sandstone,the intergranular pores are mainly less than 0.1μm,The pore volume of this class accounts for 45.32%.In the medium displacement pressure typeⅡand in the high displacement pressure type Ⅲ,the effective pore volume are only 21.92%,which are weak water abundance.