Combined Experimental and Numerical Investigation into Combustion Characteristics of Crude Oil under Different Permeability Ranges: Thermal EOR Implication

Abstract

In situ combustion (ISC) has drawn much attention in the exploitation of heavy oil reservoirs because of its small surface footprint and high recovery efficiency relative to steam injection. As for now, the combustion characteristics of heavy crude oil under different permeability ranges have not been well-understood, particularly in low-permeability conditions. In this work, we systematically conducted the combustion tube (CT) experiments under permeabilities of roughly 650 and 480 mD. Following that, a reaction kinetics model that could simulate the CT results well was established. Finally, the corrected reservoir simulation approach was used to study the ISC characteristics of one heavy oil in the permeability range of 50–1000 mD. The combustion characteristics under different permeability ranges could be classified into four main types on the basis of the experimental studies and numerical predictions. (1) The consecutive combustion front failed to be formed from 50 to 180 mD. (2) The consecutive combustion front was formed and the coking zone appeared from 180 to 250 mD, which was accompanied by weak heat release and serious plugging effect of the oil bank and coking zone. (3) The stable combustion front was formed with obvious heat release from 250 to 500 mD, and there was a weak plugging effect of the oil bank and coking zone at the initial stage of combustion. (4) In the permeability range of 500–1000 mD, the stable combustion front featured with a peak temperature higher than 500 °C was formed with a negligible plugging effect of the oil bank and coking zone. For heavy oil reservoirs with permeabilities lower than 250 mD, much attention should be put on the variations into combustion front temperature and displacement pressure difference at the initial period of combustion. If the temperature continued to decrease and/or the displacement pressure difference continued to rise, some measures should be actively adjusted to increase heat release yielded by combustion, including the increase of the air injection rate and ignition temperature, the injection of catalysts, and so forth. This work could add new insights into the differences and connections of combustion characteristics of heavy oil under different permeability ranges, which should be of great significance for thermal enhanced oil recovery.

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