Van Meir Nathalie, Lebbe Luc
Ghent University, Department of Geology and Soil Science Krijgslaan, 281 (S8)B-9000 Ghent, Belgium.
Ground Water. 2003 Jan-Feb;41(1):33-40. doi: 10.1111/j.1745-6584.2003.tb02565.x.
This paper presents an empirical relationship of quantitatively linked electromagnetic (EM) borehole recordings of the total dissolved solids (TDS) in pore water in the Quaternary deposits of the Belgian coastal plain. First, the long normal (LN) logs are linked to EM logs, then the already developed relationships between LN resistivity measurements and the TDS values are rewritten for EM recordings. The main parameter in these equations is the formation factor, which is derived from ground water analyses and LN logs through Archie's law. The EM recording has several advantages compared to the LN logs. The EM analysis allows measuring in PVC-cased wells and is not hindered by the invasion zone around the well. Furthermore, it has a high vertical resolution. LN logs can be measured only once, after drilling a well; EM recordings can be repeated several times in monitoring wells, which allows the gathering of time-dependent data over a complete vertical cross section. Such data could be obtained with LN logs only in wells with screens over the full-depth interval, which causes a hydraulic short circuit. This short circuit can result in a large artificial flow through the well between different levels, resulting in a salinity profile, which is no longer representative for the studied site. Remediation against short circuiting is a reduction of the screened interval, which strongly reduces the gathered information. The application of the derived equations is one of setting up a monitoring network along the Belgian coast to monitor the trend in salinity levels and comparing present salinity levels with older LN recordings to investigate the salinity changes in the last 30 years. Deep wells already present in the Belgiancoastal plain can then be used to monitor both the fresh water head changes and the salt water evolution. The technique has also been used for parameter identification for which real concentration measurements were needed.
本文介绍了比利时沿海平原第四纪沉积物孔隙水中总溶解固体（TDS）的定量关联电磁（EM）钻孔记录的经验关系。首先，将长电位（LN）测井与电磁测井相关联，然后针对电磁记录重新建立已有的LN电阻率测量值与TDS值之间的关系。这些方程中的主要参数是地层因数，它是通过阿尔奇定律从地下水分析和LN测井中推导出来的。与LN测井相比，电磁记录有几个优点。电磁分析允许在PVC套管井中进行测量，并且不受井周围侵入带的影响。此外，它具有较高的垂直分辨率。LN测井在完井后只能测量一次；电磁记录可以在监测井中重复多次，这使得能够在完整的垂直剖面上收集随时间变化的数据。只有在全深度间隔都有筛管的井中，才能用LN测井获得这样的数据，这会导致水力短路。这种短路会导致不同层位之间通过井的大量人为流动，从而产生一个盐度剖面，该剖面不再代表所研究的场地。防止短路的补救措施是减小筛管间隔，这会大大减少所收集的信息。所推导方程的应用之一是在比利时海岸沿线建立一个监测网络，以监测盐度水平的趋势，并将当前盐度水平与较旧的LN记录进行比较，以研究过去30年中的盐度变化。比利时沿海平原现有的深井随后可用于监测淡水水头变化和盐水演化。该技术还被用于需要实际浓度测量的参数识别。
