Rock Wetting Condition Inferred from Dielectric Response
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Rock Wetting Condition Inferred From Dielectric Response Yani Carolina Araujo, Mariela Araujo and Hernán Guzmán Reservoir Department, PDVSA Intevep, Caracas, Venezuela. ABSTRACT Wettability is a manifestation of rock-fluid interactions associated with fluid distribution in porous media. Conventional wettability evaluation is performed by a sequence of spontaneous and forced displacements of different fluids into a porous sample, a method which is costly and time consuming. A new attractive approach is to estimate this quantity from dielectric measurements, since they can be done rapidly and economically. The dielectric frequency response of several rock samples of known wettability condition was studied in the range from 10 Hz to 100 MHz. Samples were saturated with brine and oil. The results confirm the strong influence of wetting condition on dielectric response. Water wet samples have significantly higher values of ε’ and ε’’ (real and imaginary parts of generalized complex permitivity) than oil wet samples. In particular, the high frequency behavior of ε’’ is most affected. Different regimes are identified as a function of frequency. They correspond to zones where different polarization effects are manifested. We quantify this effect and find a correlation with the modified Amott wettability index. Based on these findings, we propose an experimental protocol for the indirect measurement of wettability at laboratory scale. INTRODUCTION The oil industry is devoted to the recovery of the highest possible amount of hydrocarbons from reservoirs, which typically are at deep locations in the ground, under variable temperature and pressure conditions. For this objective, an interesting and useful information about the reservoir is the knowledge of the spatial distribution of fluids, and their affinity for the mineral surface, a quantity described by the wettability condition [1]. Several direct and indirect methods have been used in the industry to learn about the behavior of multiphase flow in porous reservoirs, which is a challenging task due to the opaque nature of natural porous media. Among those we find the use of a variety of tracers, including radioactive materials, high magnetic susceptibility materials, x-ray absorbing tracers, neutron diffraction techniques and nuclear magnetic resonance which has been used to get saturation on cores [2,3]. Dielectric measurements have been used in oil industry to characterize and investigate physical properties of rock samples by non destructive, rapid, economic and accurate techniques. Dielectric properties of reservoir rocks depend on the permittivity and conductivity, density of the fluids and their saturation, and how they are distributed inside the porous structure. In the literature, it has been reported that the dielectric constant is a very useful parameter to measure the level of water saturation in rocks [4,5]. For saturated samples this parameter depends strongly on frequency. Wettability is one of the petrophysical properties that most affects the dielectric resp
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