Crude Oil Electrical Conductivity Measurements at High Temperatures: Introduction of Apparatus and Methodology

Abstract

In this paper, the electrical conductivity measurements of four types of crude oils at reservoir conditions were carried out using an in-house-developed pressurized cell. The newly introduced apparatus has the capability of performing electrical conductivity measurements of various reservoir fluids at high-pressure, high-temperature (HPHT) conditions. The cell can be pressurized with an inert gas to be far enough above the bubble points (P b ) of crude oils. The alternate voltage (AV) cycle methodology was applied to perform the experiments. In this method, the subtraction of electrical currents when the voltage alternated between two specified values (0 and 2 V in this work) was used to calculate the conductivity. The reliability of the methodology and equipment in making conductivity tests has been verified by comparing the conductivity results to the "rest conductivity" values measured via a standard method. Variation of crude oil electrical conductivity showed a strong relation to the physical and chemical properties of the reservoir fluids, including the electrical nature of compounds in oils and viscosity of fluids. The experimental data were fitted well to the Arrhenius model with a clear break point at a certain temperature for each oil, which can be linked to the structural change of the fluids at the mentioned temperatures.

Review of Asphaltenes in an Electric Field

“…In general, the relationship between crude oil electrical conductivity and temperature was exponential. 80 Similar results were reported by Rocha et al ( 2019), who employed an impedance spectroscopy method to measure the electrical conductivity of heavy and medium crude oils, and water in oil (W/O) emulsions at 30 °C and 50 °C. 81 The results revealed that an increase in temperature results in an increase in electrical conductivity.…”

“…Increased oil viscosity contributes to lower conductivity at low temperatures. In general, the relationship between crude oil electrical conductivity and temperature was exponential . Similar results were reported by Rocha et al (2019), who employed an impedance spectroscopy method to measure the electrical conductivity of heavy and medium crude oils, and water in oil (W/O) emulsions at 30 °C and 50 °C .…”

“…78,80−86 It has been shown that the crude oils rich with asphaltenes had a higher conductivity than other oils. 80 The conductivity of crude oil solution was suggested to be governed not only by the amount of asphaltenes in the crude oil but also by their aggregation state and mobility. The crude oil diluted with heptane showed a lower conductivity than those same oils diluted with the same amount of toluene.…”

“…Electrical conductivity (EC) represents the ability of material to conduct an electric current. EC measurements have been utilized to understand behavior of asphaltenes alone and their interactions with other crude oil components in different solvents. ,− It has been shown that the crude oils rich with asphaltenes had a higher conductivity than other oils . The conductivity of crude oil solution was suggested to be governed not only by the amount of asphaltenes in the crude oil but also by their aggregation state and mobility.…”

Influence of Wax Precipitation on the Impedance Spectroscopy of Waxy Oils

“…The relationship between conductivity and temperature in many nonaqueous systems can be described by the Arrheniustype equation, 31−33 and some previous research 59,60 suggest that an Arrhenius-type conductivity−temperature dependence, shown in eq 5, can be observed with crude oils as well…”