Radar frequency dielectric dispersion in sandstone: Implications for determination of moisture and clay content
Radar frequency dielectric dispersion in sandstone: Implications for determination of moisture and clay content
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DOI：
10.1029/2001wr000923
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发表时间：
2003-02
影响因子：
5.4
通讯作者：
L. West;K. Handley;Yi Huang;M. Pokar
中科院分区：
文献类型：
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作者：
L. West;K. Handley;Yi Huang;M. Pokar
介电常数之间的关系，水饱和度，和粘土含量的舍伍德砂岩从英格兰东北部的特点是作为一个更广泛的研究的包气带水分动态和污染脆弱性的含水层的一部分。使用特殊构造的电介质电池，测量了从清洁的中粒砂岩到含有高达5%粘土的细粒砂岩的各种岩性在整个饱和度范围内的介电常数。介电常数Kr在350 MHz和1000 MHz之间很大程度上与频率无关。在350 MHz以下，细粒、富含粘土的砂岩的Kr显示出频率分散。对由细级渥太华砂和蒙脱石粘土组成的砂岩的物理模型的测试表明，砂岩中的粘土矿物是其频散行为的原因。这些测试还表明，增加孔隙流体盐度会增加频率范围低端的介电色散，这表明这是由与片状粘土颗粒相关的界面麦克斯韦-瓦格纳机制引起的。水饱和的砂：粘土混合物在高频（超过650 MHz）下表现出非常低的介电常数。这种效应与盐度无关，可能是由于膨胀粘土中固体、束缚水和自由水的分层几何排列所致。矿物介电常数约为5的复折射率法（CRIM）在350和1000 MHz之间的频率下与所有舍伍德砂岩岩性的水饱和度与介电常数数据以及在较低频率下与粘土贫乏砂岩的水饱和度与介电常数数据良好匹配。低于350 MHz时，某些舍伍德砂岩岩性中存在百分之几的粘土，会大幅提高其CRIM最佳拟合矿物介电常数。
The relationship between dielectric permittivity, water saturation, and clay content for the Sherwood Sandstone from NE England was characterized as part of a wider study of the vadose zone moisture dynamics and pollution vulnerability of this aquifer. Dielectric permittivity was measured over the full range of saturation levels, for various lithologies ranging from clean medium‐grained sandstone to fine‐grained sandstone containing up to 5% clay, using a specially constructed dielectric cell. Dielectric constant, Kr, is largely independent of frequency between 350 MHz and 1000 MHz. Below 350 MHz, Kr of fine‐grained, clay‐rich sandstone shows frequency dispersion. Tests on physical models of the sandstone consisting of a fine fraction of Ottawa Sand and montmorillonite clay indicate that the clay minerals within the sandstone are responsible for its frequency dispersive behavior. These tests also show that increasing pore fluid salinity increases dielectric dispersion at the lower end of the frequency range, which indicates that this arises from the interfacial Maxwell‐Wagner mechanism associated with platy clay particles. Water saturated sand:clay mixtures show very low dielectric constants at high frequencies (over 650 MHz). This effect is independent of salinity and probably results from the layered geometric arrangement of solids, bound and free water within the swelling clay. The complex refractive index method (CRIM) with a mineral dielectric constant of about 5 provides a good match to the water saturation versus dielectric constant data for all Sherwood Sandstone lithologies at frequencies between 350 and 1000 MHz and for clay‐poor sandstone at lower frequencies. Below 350 MHz the presence of a few percent of clay in some Sherwood Sandstone lithologies raises their CRIM best fit mineral dielectric constant substantially.