Opportunities of Downhole Dielectric Heating in Venezuela: Three Case Studies Involving Medium, Heavy and Extra-Heavy Crude Oil Reservoirs

Abstract

Abstract The use of electromagnetic radiation, radiofrequency (RF) and microwaves(MW), for downhole dielectric heating has potential applications inenhanced/improved oil recovery processes (EOR). The Lambert's equation wascoupled to a commercial simulator in order to model reservoir dielectricheating. Using a MW heated (2.45 GHz) one-dimensional reactor, thismathematical model was validated in the presence of crude oil/sand cores. Threedifferent conceptual reservoirs were evaluated which involved a medium crudeoil (24°API), a shallow (1100 ft) Lake Maracaibo heavy oil (11°API) and a thinpayzone (20 ft) Orinoco Basin extra-heavy crude (7.7°API). For all the casesevaluated, numerical simulation results showed an important acceleration in theoil production due to RF and MW heating which was attributed to reduction ofcrude viscosity coupled with favorable relative water-to-oil permeabilities.For example, in the shallow heavy oil case, RF heating led to an increase of86% of the cumulative oil production in comparison with the cold productioncase, using 140 MHz at 50 kW over a ten-year period. Furthermore, calculatedenergy gains (measured as the ratio between the energy extracted as crude oilequivalent to energy added to the reservoir as electricity) were in the 8 to 20range, indicating that the process is favorable from the thermodynamic point ofview. These conceptual numerical simulation results indicate the high potentialof dielectric heating technology for medium, heavy and extra-heavy EOR withpossible field applications. Introduction The use of electromagnetic radiation, radiofrequency and microwaves, fordownhole dielectric heating has potential applications in enhanced/improved oilrecovery processes (EOR)1–3. In general, radiations whosefrequencies range from 10 to 100 MHz are referred to as radio frequencies (RF)and in the range 300 MHz to 300 GHz to microwaves (MW)1–3.Specifically, the heating of formation fluids and porous media can lead toimproved mobility of the oleic phase, relative to the aqueous and gas phases, with the concomitant increase in oil production. Four different approaches to take the electric energy downhole have beenreported in the literature1. These are single and inter-wellelectromagnetic heating, resistive tubing heating and RF or MW dielectricheating. In this artilce, only the latter concept will be studied mainly forits advantages of higher penetration into the reservoir and its compatibilityto shallow and thin payzone reservoirs (directionality)1–3. As found in laboratory measurements, hydrocarbon-containing sands can absorbRF and MW to reach very high temperatures (300–400°C) veryrapidly4–6. Wan et al. studied the thermal decomposition ofCanadian Tar Sands using short-time microwave pulses (3–5 s) and one atmosphereof pressure4. Several light hydrocarbons were detected (C2-C8) andtheir molar distribution did not change in the presence of water4.Milan studied the MW absorption of petroleum containing sands using MW of 2450MHz 5 and proposed an empirical model in which the electromagnetic energy has amaximum penetration of 15 meters5. Cambon et al. carried outthe extraction of crude oil from Canadian Tar Sand at different times (3–20min)and powers (from 0 to 2.5 kW at 2.45 GHz) 6. The authors reported upto 86% yield in distillable products with similar quality as those obtained byconventional methods6. All these results demonstrate at laboratoryscale, the feasibility of using RF and MW radiation for dielectric heating ofoil containing sands4–6.