Dielectric Measurement for Solid Cylindrical Samples

In this paper we describe a coaxial-circular cell for wide band dielectric measurements on solid cylindrical samples. Combined with existing data-processing algorithms, the technique can be applied to a variety of materials including oilfield rocks. The simple cylindrical sample geometry is a distinctive feature of this method and is a significant advantage of the technique. Commonly used coaxial cells require cylindrical samples modified with a central hole to accommodate the inner electrode of the coaxial line. Although this configuration presents no problem for liquid samples, for solid samples, precise machining is required to insure good measurements. For rock materials, which must be ground into shape using circular diamond cutters, creating good coaxial samples for coaxial cells is an art; it can be difficult, or impossible, in case of weakly consolidated rocks. In addition, in a coaxial sample it is difficult to achieve homogeneous partial saturation. In contrast partial saturation of solid cylindrical samples can be achieved relatively easy. Hence the capability to measure simple cylindrical samples that this new cell provides not only simplifies the sample preparation but also allows for the partial saturation experiments. We discuss the experimental set up, forward model and the inversion methodology, which are required for this geometry. We also assess the uncertainty associated with the measurement. The forward model was validated by the numerical modeling of the cell response. We obtained a good fit between measured and expected results for several materials with known permittivity and conductivity including brines and glycerol. Permittivity and conductivity of brines were calculated from the measurements of DC conductivity and temperature using the Klein-Swift model [3]. Glycerol permittivity was taken from Buckley and Maryott [4]. Measurements of carbonate rocks at partial saturations are presented. INTRODUCTION The knowledge of the permittivity and its frequency behavior is important in both basic and applied research. Dielectric measurements are a particularly informative technique for geophysical applications [1]. In the laboratory dielectric properties can be measured by different methods employing various sample sizes and shapes [5]. Until now coaxial cells were commonly utilized [5-8]. The knowledge of both reflection and transmission coefficients allows for closed form expression derivation and simplifies the computation