Error quantification of a plug scale lab dielectric spectroscopy setup and its application in material characterization

Wide band Dielectric Spectroscopy has been newly introduced in oil industry.Dielectrics measurement is acting on water molecules and sensitive to pore water content and distribution in all the salinity range.In this case,application of Dielectric Spectroscopy is important in difficult environment such as fresh water or heavy oil.With the introduction of downhole logging device to measure multi-frequency dielectrics,the requirement of an adequate lab measurement device on similar petrophysical parameters with similar measurement physics becomes important and with high priority.There are non-destructive dielectric measurement devices available in the literature.However the major limitation of those devices is the sample measurement volume.Those devices either work on powder samples,mm-range thin discs or 1 cm range small cylindrical plugs.In carbonate heterogeneity can act in a wide range of scale and modify petrophysical parameters greatly.In this case,the small-sized sample measured properties may not be representative enough for the 1.5-in diameter rock plug,which is the oil industry standard plug size. In this paper we will present the frequency response pattern and error quantification on a non-destructive device that is able to measure Dielectric Spectroscopy on the standard 1.5-in or even larger diameter rock plugs.The detailed characterization of the device presented in this paper shows that the repeatability of this device is within 2% of the material dielectric constant value for dry rock plugs and 3% of material value for wet rock plugs.Error bar can also be given on dielectric dispersion curves as a quality control.Application of this device reveals that frequency response of dry,low loss material is not the same as brine saturated high loss material.The algorithm used in the inversion and its error analysis is presented in detail in the paper. Different types of materials are measured with this large probe.The measurement on fused quartz,Teflon,ceramics and silicon materials matches the value of literature,which gives confidence of our setup.The measured value of calcite,dolomite and anhydrite provides good estimation end points for calcium carbonate rocks with complex lithology.In the literature the values of these minerals are in a variation range and difficult to use for oil industry.The measurements on two artificial mono-crystalline Silicon plugs,one with annealing and one without,reveals the pissibq sensitivity of dielectric spectroscopy on molecular structure variation.The measured dielectric constant on calcite crystal has larger value than literature which is usually measured on powders also agrees with the assumption that crystal size may have effect on dielectric constant value. Although the device is large-bore that can overcome horizontal heterogeneity effect imposed by carbonate sample size,manipulating the lab measurement and interpretation still allow us to identify vertical heterogeneity existed on the core plug.The heterogeneity can be caused by lithology distribution,pore system distribution,temperature etc… The case study result on carbonate outcrops presented in this paper shows that porosity heterogeneity existed in the upper part of the rock plug compared to the lower part of the same plug is captured by Dielectric Spectroscopy measurement and confirmed by NMR 1D profiling porosity distribution and CT-scan image.