Low Frequency Electrical Heating for High Viscous or Heavy Oil Reservoirs

The electrical low frequency heating is a thermal recovery process that has been proposed for high viscous and heavy oil reservoirs. In this process, the high viscous or heavy oil is heated by electrical energy to lower the viscosity; then production wells are opened or injection of chemical, hot water, or steam is started. In this thermal process, electrical current passes through reservoir fluids due to electrical conductivity of fluids. The flow of electrical current through reservoir leads to heating the reservoir and thereby reducing oil viscosity.

>Reservoir rock and existing fluids are used as electrical resistance elements. In order for the electrical current to be able to flow through porous media and generate heat, one of the liquid phases should be continues and conductible. In this study, three basic equations of classical electricity and magnetism, developed by Maxwell in 1863, are simplified and assumed for low frequency to obtain conservation of electrical current equation and Ohm's law. Consequently, conservation of electrical current equation and Ohm's law are solved for the electric potential using numerical finite difference method in the UTCHEM simulator. The heating rate due to electrical current is calculated and then added to energy equation as source term for each grid block at each time step.

The conducting path for electrical current is through the continuous brine phase. Therefore, the water saturation and electrical conductivity of this phase have an important effect on the heating process. The reason is that the electrical conductivity of water phase is relatively high compared to rock, oil, and gas phases and this leads the electrical current density in water phase to be much more than other phases. Electrical conductivity of water phase can also be easily increased by injecting high saline water into the reservoir and increase heating substantially. This is highly beneficial and the main advantage of electrical heating mechanism is to obtain high recovery in comparison to other thermal recovery methods.

The efficiency of this ­­process depends on heterogeneity, geological connectivity, solution gas and gas cap, bottom water zone or aquifer, initial water saturation and residual oil saturation during operation. It also depends on the amount of heat lost in overburden and upper burden as well as inside the reservoir, productivity, and thermal and electrical properties of fluids and rock.