The use of RFID technology to measure dielectric coefficients of diethyl ether-oil-brine mixtures for enhanced imbibition experiments.

Abstract

Characterization of fluid properties is significant in the petroleum engineering practice, especially in solvent-based enhanced oil recovery (SEOR) where the use of injected chemicals should ideally be reduced to the bare minimum in order to minimize the costs and environmental impact of SEOR. However, current techniques for measurement inside cores, pipes and other enclosed spaces are inconvenient as the measurement devices must be connected from the inside to the outside, causing leakage problems. A possible solution to this problem is the usage of a Radio Frequency Identification (RFID) communication system. RFID is the use of wireless electromagnetic fields to transfer data. This research examines the feasibility of using UHF RFID technology for wireless laboratory measurement of the dielectric coefficients of diethyl ether-oil-brine mixtures in enhanced imbibition experiments. A typical enhanced imbibition experimental setup consists of an oil saturated core placed in brine containing a solvent (Amott-cell). By means of measurements with the RFID system we aim to determine the concentration of diethyl ether in the oleic and aqueous phase of the mixture according to the corresponding dielectric coefficients. As a precursor to the RFID measurements, we first determine the concentration dependent partition coefficient, i.e. the ratio of the diethyl ether concentrations in the oleic and aqueous phase, using the Anton Paar density meter DMA-4100M. The density-meter measurements are followed by experiments to determine the real part of the dielectric coefficients of the pure components as a function of frequency, at 23 degrees Celsius. With the dielectric coefficients of the pure components identified, we use the Böttcher equation to calculate the effective dielectric coefficient of mixtures with a known composition. Subsequently, the relation between RFID response and diethyl ether fractions in the oleic and aqueous phase is investigated, starting with simulations of three RFID models using COMSOL Multiphysics software. The aim of these simulations is to examine the relation between the dielectric coefficient in relation to frequency and scattering parameter (S-parameter) response, and create an understanding of the influence of the tag’s encasement and the thickness of media blocks covering the tag. With the state-of-the-art physical setup (CISC RFID Xplorer-2000) we then measure the dependence of the Xplorer-2000 response as a function of the dielectric coefficient. In terms of response we focus on the following parameters: the S-parameter (S21), the minimum power at tag position (Pmin), the scalar difference between the radar cross-sections of the tag (RCS) and the backscattered power. From the graphs where we plotted RFID response versus the dielectric coefficient we observe that some frequencies show a larger dependence in the domain of interest than others. However, when applying this most optimal frequency in a graph where we plot the RFID response as a function of diethyl ether volume fractions in the oleic or aqueous phase, in some cases the relation results in a curve containing one or several maxima. In this situation more frequencies must be used to attain unique and accurate response values. From the RFID response parameters, the power at tag position (Pmin) is the advisable response parameter when determining ether fractions in a diethyl ether-oil-water system. In order to investigate the full potential of the RFID CISC Xplorer-2000 system for the determination of dielectric coefficients in an imbibition experiment, more measurements are required of media with dielectric coefficients ranging from 4.43 to 79.08 for the aqueous phase mixtures and dielectric coefficients ranging from 2.05 to 4.43 for the oleic phase mixtures. Nevertheless, based on this research we can conclude that it is possible to use RFID technology to determine the diethyl ether concentration in the oleic and the aqueous phase with a few percent (0.02).