Abstract

Electromagnetic near-wellbore heating concept can be used to increase the recovery of reservoirs contends viscous oil. This method is based on the transformation of the electromagnetic energy in thermal. Normally, the existent commercial thermal simulators don't still contemplate the option of this technique. An adaptation of the simulator STARS from CMG was made, emulating the external electromagnetic source of energy, here idealized as injecting energy in a certain volume around the well, with the same intensity of a conventional thermal energy source. The cells of the wells and the simulation mesh are chosen so that the phenomenon of transfer of energy to the formation represents the electromagnetic heating phenomenon. The model proposed in this study includes the peculiarities of the reservoir (geology variations, reservoir heterogeneity of different scales, permeability, fluid characteristics, etc) with the means of treatment of these parameters in the STARS simulator. This study was accomplished with the use of a central producing well four other ones, only electrically heated and especially perforated and completed, and two others for injecting water. The obtained results subsidize the use of this alternative thermal method and the use of this technique in conjunction with injection of water in the reservoir. The tool of analysis proposal still aids the interpretations of the main parameters involved in the process of electromagnetic heating, besides allowing an evaluation of its advantages and limitations.

Introduction

In the petroleum industry the main methods for heavy oils recovery are the thermal ones. They seek, by increasing the medium temperature of the reservoir, reduce the viscosity of the fluids and, consequently, increase the mobility of the phase oil. The principal method is steam injection.

Alternatively to the classic thermal methods, the electromagnetic heating is based on the transformation of the electromagnetic energy in thermal [Abernathy (1976), Burger et al (1985), Pizarro et al (1990), Spencer et al (1985), Sresty et al (1981), Todd et al (1978)]. This method bases on the direct interaction among the electromagnetic field and the particles electrically sensitive of the reservoir that can be ions or dipolar molecules of the fluids. The electromagnetic nearwellbore heating concept can be used for this purpose from a single well. This heating process appears to be technically attractive, due to the volumetric reservoir heating by radio frequency energy as a result of dielectric losses in the zones containing water. It doesn't depend on the thermal diffusion of the medium, but it depends directly on the antenna design.

By the action of the electromagnetic field excited from electrodes placed in the reservoir, electric currents of conduction, rotation and displacement are created transforming great part of the electromagnetic energy in thermal.

The distribution of these currents depends on the electric characteristics of the medium (conductivity and electric permitivity) and of the frequency employed. The current is responsible for the heating process and the propagation of the electromagnetic wave in the dissipative medium. For practical reasons the applicator must radiate in all directions of the hydrocarbon medium surrounding the wellbore.

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