| 地球化学模拟方法确定黏性土孔隙水化学组分 |
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| 引用本文： | 李静,梁杏,陈乃嘉,张亚年,杨吉龙.地球化学模拟方法确定黏性土孔隙水化学组分[J].水文地质工程地质,2017,0(1):1-8. |
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| 作者姓名： | 李静 梁杏 陈乃嘉 张亚年 杨吉龙 |
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| 基金项目： | 国家自然科学基金（41272258，41502231）；中央高校基本科研业务费专项基金（CUGL1500824）；湖北省自然科学基金（KZ15K380）；博士后基金（1231536） |
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| 摘 要： | 黏性土孔隙水的地球化学行为对于弱透水层水质水量研究、污染物在黏性土中的迁移、核废物储存场址评价及油气储层的盖层评价等均具有重要作用。受低渗透性限制，传统方法提取黏性土孔隙水非常困难。通过实验测定黏性土的物化特性，利用PHREEQC软件模拟计算了孔隙水组成。通过浸提实验，利用阴离子可通过孔隙度（50%总孔隙度）确定模型中孔隙水的Cl-和SO2-4含量；根据岩土的阳离子交换量及各离子的交换选择系数，矿物沉淀 溶解平衡，确定了孔隙水的主要化学组分。结果显示，模拟的孔隙水化学组分与压榨液（相当于原位孔隙水）相近，不同于浸提液。传统的浸提方法不可直接换算为孔隙水，受矿物可交换点阳离子的释出与矿物溶解影响，各离子含量被明显高估。模拟所得天津滨海区黏性土阳离子交换量为13.4~37.8 meq/100g土，可交换离子以Na、Mg、Ca为主。所得孔隙水为还原环境，且随着深度增加，还原性增强。模型中所选矿物均为平衡状态，溶液中可能存在的矿物大部分为未饱和或平衡状态，仅部分含Fe、Al矿物过饱和。由结果可知Fe含量偏高，对控制Fe元素的矿物需进一步精确测定。本方法在低渗透，超固结，低含水量介质的孔隙水相关研究中将发挥重要作用。
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| 关 键 词： | 黏性土 孔隙水 化学组分 模拟 天津滨海 |
| 收稿时间： | 2016-04-15 |
| 修稿时间： | 2016-06-12 |
Determination of chemical compositions of pore water in clay rich formations using geochemical modeling |
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| LI Jing,LIANG Xing,CHEN Naijia,ZHANG Yanian,YANG Jilong.Determination of chemical compositions of pore water in clay rich formations using geochemical modeling[J].Hydrogeology and Engineering Geology,2017,0(1):1-8. |
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| Authors: | LI Jing LIANG Xing CHEN Naijia ZHANG Yanian YANG Jilong |
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| Abstract: | Chemical behavior of pore water in clay-rich aquitards plays an important role in the quality and quantity studies of aquitard pore water. It is also of great significance in transport of contaminant in clay formations, in evaluation of a host rock for radioactive waste storage and in cap evaluation of oil and gas reservoirs. However, the traditional methods to extract pore water are quite difficult due to the low permeability of clay. This paper presents an approach for calculating pore water compositions in the aquitards, using the PHREEQC software, based on the laboratory-measured properties of core samples. The Cl- and SO2-4 contents are calculated through leaching experiment by anion-access porosity (50% of the total porosity). Based on the cation exchange capacity and exchange selectivity coefficient, the mineral phase equilibrium is included in the model, and the major ion contents are constrained. The results show that the modeled pore water compositions reclose to the squeeze water (basically in-situ pore water) other than the leaching water. The obvious over-estimate of the pore water compositions is calculated by the leaching water due to the dissolution of minerals and desorption of clay minerals. The cation exchange capacity is between 13.4 and 37.8 meq/100g soil in the Tianjin coastal clay formation, with the major exchangeable ions of Na, Mg and Ca. The pore water is reductive, and becomes much stronger with depth. The mineral phases we choose in the model is shown to be in equilibrium with the contacting pore water. There are also some exceptions that Fe (hydr) oxides and Al-bearing minerals oversaturated are observed, indicating that more accurate Fe-mineral measurement is needed to constrain the Fe content. This method has a great potential in low permeability, consolidated, and low water content clay pore water studies. |
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