摘要
以河南省新近系明化镇组热储层细砂为多孔介质,在15~60℃的低温地热范围内,以硝酸盐为示踪剂开展室内土柱试验,并采用CXTFIT 2.1软件进行数据拟合来研究其运移机制。首先在40℃,达西流速2.62 cm/h、6.18 cm/h时研究了硝酸盐的运移机制及其时空变化规律,然后探讨了运移参数随温度的变化规律。结果表明,溶质的运移主要集中在可动区,不可动区的运移及质量传递可忽略,一维对流-弥散模型可以很好地表征其运移机制,并能有效预测硝酸盐质量浓度的时空变化情况。硝酸盐的纵向弥散系数、分子扩散系数、机械弥散系数及多孔介质的弥散度值均随温度升高而增加,但Peclet数相反,由弥散引起的溶质运移作用随温度升高而逐渐增强。
This paper is engaged in a study of the migration mechanism of NO-3in the porous medium under the geothermal environment,Henan. For our research purpose,we have carried out column experiments of nitrate in a temperature range between15 ℃ and 60 ℃ in the loose-pore geothermal reservoir matrix,which is believed having been formulated in the Neolithic Period in Minghuazhen Formation. In our work,we have adopted the computer code CXTFIT to fit the experimental data and made the exploration of the migration mechanism of the nitrate and spacetime distribution of the nitrate concentration at 40 ℃ at Darcy＇s fluxes of 2. 62 cm / h and 6. 18 cm / h. At the same time,we have also traced the effect of the temperature on the migration parameters of nitrate at 7 different temperatures. The results of our exploration have shown that the nitrate migration has mainly been going on in the mobile water region,though it would be possible for the migration and mass transfer from the mobile soil-water region to the immobile region to be neglected. Due to the low organic carbon content in the matrix（ 0. 745 mg / g）,we have also neglected the denitrification of nitrate during the short test duration of our experiments and the background values of the nitrite,ammonium and Fe2 ＋in the eluted samples in our study. The convection-dispersion equation（ CDE） proves to be well fit for the experimental data in a range of R2 variation from 0. 98 to 0. 99 though it would be impossible to improve R2 when simulated with the the physical non-equilibrium model. Therefore,it makes us believe that it is possible for the CDE model to be used for describing the nitrate migration process and forecast the distribution of the nitrate concentration with time and depth. In addition,with the increase of temperature,such key indexes as the longitudinal dispersion coefficient of the solution,the molecular diffusion coefficient,the mechanical dispersion coefficient and the dispersity of the used porous media may all be expected to increase too. What is more,the increase in temperature may suggest that either the role of advection,or the role of dispersion may all be supposed to increase from 15 ℃ to 60 ℃ with the decrease of the Peclet number. However,in spite of the above situation,the nitrate migration in the porous medium proves to remain still dominated by the advection even at 60 ℃ because of the great Peclet number（ P =87. 5845）.
出处
《安全与环境学报》
CAS
CSCD
北大核心
2015年第5期320-324,共5页
Journal of Safety and Environment
基金
国家自然科学基金项目(41402216)
河南省教育厅科学技术研究重点项目(13B610039)
河南理工大学博士基金项目
河南省高校科技创新团队支持计划项目(15IRTSTHN027)
关键词
环境学
地球化学
多孔介质
地热环境
运移机制
硝酸盐
environmentalology
geochemistry
porous media
geothermal environment
migration mechanism
nitrate
