Study of Dielectric Tools and Dielectric Property of Rocks
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Dielectric tools have mainly been used for identifying freshwater zones in oil- or gas-bearing formations. New-generation dielectric tools are also used for detecting shale reservoirs, heavy oil, and residue oil in invasion zones. However, currently commercialized tools either lack information on frequency dispersive behavior or offer redundant logging curves. This dissertation investigates both the design and simulation of novel array dielectric tools; meanwhile, it throws light on the dielectric properties of rocks through lab measurements. A multi-component, multi-spacing array dielectric tool working at 5 different frequencies in the range of 10 MHz to 1 GHz was studied. It covered the frequency gap between propagation tools and conventional dielectric tools. Tool sensitivity was carefully investigated to demonstrate tool capability in exploring formation properties, including permittivity, conductivity, dipping, and anisotropy. Meanwhile, tool simulations with COMSOL provided comprehensive evaluations of tool performance. From the simulation results, it was found that the size of the tool pad has an influence on tool response, especially when lower frequency channels are fired. However, the impact from borehole mud can be negligible since the tool is pushed against the borehole wall. Moreover, the existence of mud cakes and invasions affect the measurements and depth of investigation of the tool as well. In addition, vertical resolution was studied for different formation conditions. The designed tool was proven to be able to detect thin conductive beds or beds with high dielectric constants. In the past few decades, dielectric dispersion has been observed from core data. Practical core measurements for dielectric constant and conductivity were also conducted in this dissertation to study the dielectric properties of sediment rocks. A parallel plate system was used for the study. The relative dielectric constant and conductivity were measured in a frequency range from 10 KHz to 1GHz. Measured data agreed well with the resistivity log inversion results, and large dielectric enhancement at the induction frequencies was observed. Dielectric and conductivity corrections were applied to the original log to correct the errors caused by dielectric dispersions. The results lead to the conclusion that dielectric correction should be added to the resistivity inversion routine to avoid misinterpretation.