Development and Application of Electrical-Joule-Heating Simulator for Heavy-Oil Reservoirs

Abstract

Summary In the electrical-Joule-heating process, the reservoirs are heated in situ by dissipation of electrical energy to reduce the viscosity of oil. In principle, electrical current passes through the reservoir fluids mostly because of the electrical conductivity of saturated fluids such as saline water. The flow of electrical current through the reservoir raises the heat in the reservoir and thereby dramatically reduces the oil viscosity. In this process, electrical current can flow between electrical-potential sources (electrodes) in wells, and then electrical energy is dissipated to generate the heat. Therefore, the regions around the electrodes in (or around) the wells are extremely heated. Because the wells act as line sources for the electrical potential, greater heating takes place near the wellbore, causing possible vaporization of water in that region. Because steam has very-low electrical conductivity, it can reduce the efficiency of this process significantly. In this process electrical conductivity plays a very important role. To increase efficiency of this type of heating process, the presence of optimum saline-water saturation is an essential factor. To model the electrical Joule heating in the presence of multiphase-fluid flow, we use three Maxwell classical electromagnetism equations. These equations are simplified and assumed for low frequency to obtain the conservation of the electrical-current equation and Ohm's law. The conservation of electrical current and Ohm's law are implemented by use of a finite-difference method in a four-phase chemical-flooding reservoir simulator (UTCHEM 2011.7). The Joule-heating rate caused by dissipation of electrical energy is calculated and added to the energy equation as a source term. The formulation and implementation of electrical heating are validated against a reference analytical solution and verified with a reservoir simulator. A typical-reservoir model is built, and constant electrical potential with alternating current is applied to the model to study the efficiency of the electrical-heating process properly. The efficiency of this process is evaluated in the presence of water-saturated fractures and evaporation effect. Results illustrate that water saturation in the presence of fractures and electrical conductivity of saturated rock have an important effect on the Joule-heating process. The importance of the fractures saturated by saline water and operation of such processes below the boiling point are key findings in this paper to obtain high recovery in comparison with other conventional-thermal-recovery methods.