Feasibility of Reservoir Heating by Electromagnetic Irradiation

Abstract

Introduction Conventional thermal EOR methods, such as fireflooding and steamflooding, are commercially viable when properly applied. Every conventional method has one or more limitations. If the reservoir is shallow, the reservoir pressure may be too low to maintain a steam drive. If a reservoir is too deep, wellbore heat losses become excessive. Fireflooding does not have the same depth constraints as steamflooding, but fireflood success depends on crude composition. Each of the conventional thermal methods requires sufficient reservoir transmissibility to achieve fluid injection. EMH has the potential for overcoming some of the limitations of conventional thermal methods. Reviews of EMH techniques have been presented by Baker-Jarvis and Inguva, and Kim. Especially noteworthy as background for derivations presented in later sections of this paper was the work by Abernethy. Abernethy coupled paper was the work by Abernethy. Abernethy coupled electromagnetic absorption and fluid flow in a one dimensional radial model of wellbore behavior. He made the simplifying assumption that heat losses to adjacent formations could be neglected at his level of approximation. Later work by McPherson, et al., Hiebert, et al., and Kim accounts for more physical effects, but has a corresponding increase incomplexity. Our goal is to present a simple algorithm for estimating the temperature profile of an irradiated reservoir. The algorithm includes heat losses to adjacent formations, and is designed to be a tool for determining the feasibility of heating a reservoir with electromagnetic energy. The EMH process relies on preferential absorption of electromagnetic energy as the means for increasing the temperature of a material. Different materials have different electromagnetic absorption properties. The ability of an electromagnetic wave to transfer energy to a medium depends on the molecular composition of the medium. Suppose a medium contains mobile molecules with a molecular dipole moment (such as water). The passing electromagnetic wave will exert a torque on the polar molecules as their dipole moments try to align with the oscillating electric field of the electromagnetic wave. Interaction of an oscillating polar molecule with its neighbors generates frictional heat and raises the temperature of the medium. The magnitude of temperature increase of a material depends on the amount of electromagnetic energy absorbed by the irradiated material. Electromagnetic Power attenuation in a porous medium is discussed in Section II. A simple algorithm for estimating the temperature increase associated with reservoir irradiation is given in Section III. Applications of the algorithm in Section IV illustrate typical sources of input data and algorithm results. Some hardware considerations are provided in Section V, and near-wellbore applications arc discussed in Section Vi. Conclusions are presented in Section VII.