兖州煤田奥陶系灰岩地下水水化学特征及其形成机理

鲁西南兖州煤田的奥陶系灰岩地下水对煤田深部煤炭开采具有潜在的水害威胁,且为研究区的主要供水水源之一,其水化学特征及形成机理分析,可为该区深部煤炭开采水害防治和地下水资源利用提供依据。经过目的层水样的采集与测试可知,地下水水化学类型以SO_4-Ca-Mg型为主,SO_4~(2-)含量为537~2 296 mg/L,Ca~(2+)和Mg~(2+)的平均含量分别为455.7 mg/L和116.6 mg/L,TDS的范围为961~3 555 mg/L,pH值为6.9~8.0。Ca~(2+)和SO_4~(2-)随TDS的增加而增加,呈良好线性关系,推断TDS的增加主要来自Ca~(2+)和SO_4~(2-)的贡献。由饱和指数(SI)可知,地下水中的白云石和方解石均处于过饱和状态,而绝大部分的水样的石膏饱和指数均小于0,处于不饱和状态。石膏的饱和指数与地下水中TDS呈正相关关系。这些结果表明,在该含水层中地下水运移过程中不断发生水岩相互作用,主要包括石膏溶解、白云石和方解石沉淀或溶解、离子交换等反应。

Hydrochemical Characteristics and Formation Mechanism of Ordovician Limestone Groundwater in the Yanzhou Coalfield

The Ordovician limestone aquifer of the Yanzhou coalfield in southwest Shandong Province is the main source of mine filling water and one of the main water supply sources, and hence the chemical characteristics and formation mechanism of the Ordovician limestone water can provide the basis for groundwater resource utilization and deep coal mining risk assessment. After sampling and analyzing of the groundwater, the authors found that the major chemical type of groundwater is SO4-Ca-Mg type. The SO2- 4 values are from 537 mg/L to 2 296 mg/L, and the average concentrations of Ca2+ and Mg2+ are 455.7 mg/L and 116.6 mg/L respectively. The pH values range from 6.9 to 8.0. The TDS (total dissolved solids) values vary from 961 mg/L to 3 555 mg/L, increasing linearly with the increase of concentrations of Ca2+ and SO2- 4. These data indicate that the increase of TDS mainly comes from Ca2+ and SO2- 4. The saturation index (SI) data show that groundwater is oversaturated with dolomite and calcite, and undersaturated (SI<0) with gypsum for most of the samples. In addition, the saturation index of gypsum is positively correlated with TDS of groundwater. These results suggest that the interaction between water and rock occurs during the transition of groundwater in limestone aquifer, mainly including dissolution of gypsum, precipitation or dissolution of dolomite and calcite, and ion exchange.