Electromagnetic Heating Methods for Heavy Oil Reservoirs

Abstract

Abstract The most widely used method of thermal oil recovery is by injecting steam into the reservoir. A well-designed steam injection project is very efficient in recovering oil, however its applicability is limited in many situations. Simulation studies and field experience has shown that low injectivity reservoirs and small thickness of the oil-bearing zone limit the performance of steam injection. This paper discusses alternative methods of transferring heat to heavy oil reservoirs, based on electromagnetic energy. We present a detailed analysis of low frequency electric resistive (ohmic) heating and higher frequency electromagnetic heating (microwave frequency). We show the applicability of electromagnetic heating in two example reservoirs. The first reservoir has thin sand zones separated by impermeable shale layers and viscous oil (9541 cp at initial reservoir conditions). We model preheating the reservoir with low frequency current using two horizontal electrodes, before injecting steam. The second reservoir has low permeability and oil viscosity of 33 cp at initial reservoir conditions. In this case we use a high frequency microwave antenna located 30 ft from the producing well as the heat source. Simulation results presented in this paper suggest that electromagnetic heating may be a good stimulation technique for heavy oil reservoirs with low injectivity or with thin payzones. We identify the parameters which are critical for electromagnetic heating. We also discuss past field applications of electromagnetic heating as well as technical challenges and limitations. Introduction Steam injection is the most effective method for improving heavy oil production. However, there are certain situations where it may not work very well. These could be for:Very deep formations, where heat losses in the wellbore are significant and the quality of steam reaching the formation is very low.Thin pay-zones, where heat losses to adjacent (non oil-bearing) formations may be significant.Situations where generating and injecting steam may be environmentally unacceptable (example: through permafrost) or commercially uneconomical (in space limited offshore platforms).Low permeability formations, where the injected fluid may have difficulty penetrating deep into the reservoir.Reservoir heterogeneity, where high permeability streaks or fractures may cause early injected fluid breakthrough and reduce sweep. In this paper we discuss alternative methods for heating heavy oil reservoirs, which may be economically viable alternatives to steam in certain situations. We describe two electromagnetic heating methods—low frequency electric resistive (ohmic) heating and high frequency microwave heating. We demonstrate the applicability of electromagnetic heating with two example reservoirs—one which has thin sand zones separated by impermeable shale layers and another which has low permeability. For tar-sands or extremely high viscosity reservoirs, where the temperature effect on viscosity is significant, electromagnetic heating could be used as a pre-heating tool to create preferential pathways for steam injection. This would minimize the heat losses[1] during steam injection, and improve steam injection performance.