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Journal of Porous Media

Impact factor: 1.035

ISSN Print: 1091-028X
ISSN Online: 1934-0508

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Journal of Porous Media

DOI: 10.1615/JPorMedia.v17.i11.10
pages 937-952

COMPOSITIONAL EFFECTS IN LIGHT/MEDIUM OIL RECOVERY BY AIR INJECTION: VAPORIZATION VS. COMBUSTION

Negar Khoshnevis Gargar
Delft University of Technology, Civil Engineering and Geosciences, Stevinweg 1, 2628 CE Delft, The Netherlands
Alexei A. Mailybaev
Instituto Nacional de Matematica Pura e Aplicada (IMPA), Estrada Dona Castorina 110, Rio de Janeiro 22460-320, Brazil
Dan Marchesin
Instituto Nacional de Matematica Pura e Aplicada (IMPA), Estrada Dona Castorina 110, Rio de Janeiro 22460-320, Brazil
Hans Bruining
Delft University of Technology, Civil Engineering and Geosciences, Stevinweg 1, 2628 CE Delft, The Netherlands

ABSTRACT

Combustion can be used to enhance recovery of heavy, medium, or light oil in highly heterogeneous reservoirs. Such broad range of applicability is attained because not only do the high temperatures increase the mobility of viscous oils but also the high thermal diffusion spreads the heat evenly and reduces heterogeneity effects. For the latter reason, combustion is also used for the recovery of light oils. The reaction mechanisms are different for light oils, where vaporization is dominant, whereas for medium nonvolatile oils combustion is dominant. We will only consider combustion of medium and light oils. Therefore we ignore coke formation and coke combustion. It is our goal to investigate the relative importance of vaporization and combustion in a two-component mixture of volatile and nonvolatile oils in a low air injection rate regime. By changing the composition we can continuously change the character of the combustion process. We derive a simplified model for the vaporization/combustion process, and implement it in a finite element package, COMSOL. For light oil mixtures, the solution consists of a thermal wave upstream, a combined vaporization/combustion wave in the middle (with vaporization upstream of combustion) and a saturation wave downstream. For medium mixtures the vaporization/condensation sequence is reversed and vaporization moves ahead of the combustion. Due to its low viscosity, the light oil is displaced by the gases to a region outside the reach of oxygen and therefore less oil remains behind to reach the combustion zone. This leads to a high combustion front velocity. For oil with more nonvolatile components, vaporization occurs downstream of the combustion zone. As more oil stays behind to feed the combustion zone, the velocity of the combustion zone is slower, albeit the temperatures are much higher. The relative importance of vaporization/combustion depends also on the injection rate, pressure, initial temperature, and oil viscosity. Numerical calculations allow to estimate the bifurcation points where the character of the combustion changes from a vaporization-dominated to a combustion-dominated process.