Dielectric Property Measurements in Frequency Domain of Water Saturated Clean and Oil Sands at Elevated Thermobaric Conditions

Abstract

Electromagnetic (EM) irradiation is a relatively nascent, but promising oil recovery method. It is well-positioned to enable carbon-free oil production from heavy oil- and bitumen-rich formations. Unfortunately, this method has not been widely adopted yet due to a lack of understanding of the dielectric properties of oil-bearing rocks at elevated thermobaric conditions. The present work aims to bridge this gap by conducting dielectric property frequency spectra measurements of heated and pressurized "native" core samples. A patented system was commissioned and a series of dielectric measurements of saturated oil sand core samples were performed in two successive heating-cooling cycles within the 20°C to 220°C range. The pore pressure was kept constant above steam saturation point for the first cycle and was purged by the second cycle’s end to induce evaporation. Moreover, every measured sample was compacted by a load of 1000 psi (6.89 MPa). In addition, a comprehensive database management system was designed to facilitate automatic data acquisition of the time- and temperature-series of the relative dielectric constant and conductivity frequency responses. The relative dielectric constant and the conductivity frequency spectra were found to be directly proportionate to temperature with some level of hysteresis between the heating and cooling cycle trends. To better visualize and interpret this behavior, three-dimensional maps of the dielectric properties in frequency-temperature domain were constructed. Singularities were observed in the results for the saturated clean and oil sand samples at certain resonant frequencies. Those frequencies signify extremums in the EM energy transfer to the formation. Increased values in the relative dielectric constant and decreased values in the conductivity at frequencies smaller than 1 MHz were attributed to the electrode polarization effect, which becomes more prominent at higher temperatures and concentration of dissolved solids. In all heating experiments of water saturated clean sands a full evaporation of the pore fluid was achieved, and the dielectric properties would approach the properties of air. However, no steam desiccated zones were observed in the oil sand samples. As a result, the local concentration of ions, minerals and other solids present in the pore fluid increased, which was further confirmed by the increase in the measured dielectric properties. To the best of the authors’ knowledge this was the first time the dielectric measurements of "native" oil sand sample cores that make up most heavy oil- and bitumen-bearing formations in Athabasca region, were performed in variable temperature-pressure-steam quality environments. These measurements should provide better means to modelling of electromagnetic energy dissipation in different parts of the formation and forecasting oil production by relevant EM heating methods.