Simulation of stability or failure of a combustion front during in-situ combustion in a Post-SAGD process

The highly viscous nature of heavy oil/bitumen in the Lloydminster area leads to difficulty for oil recovery and production. In-situ combustion (ISC) is an attractive candidate as a post-SAGD (steam assisted gravity drainage) operation to improve oil mobilization and maximize oil production. The objective of the study was to demonstrate that the stability or failure of a combustion front when in-situ combustion is implemented in a post-SAGD reservoir can be realistically simulated on the basis of a sound understanding of the underlying chemical reactions, whose rates and stoichiometry have been determined from laboratory measurements. This accomplishment represents a significant step towards an improved application of the in-situ combustion processes. The simulations were performed with the Computer Modelling Group's (CMG) commercial simulator STARS. Four dominant ISC chemical reactions (i.e., pyrolysis of non-volatile oil, low-temperature oxidation, pyrolysis of partially oxidized oil, and combustion) were developed on the basis of available experimental data. Material and energy balances were applied. A representative fluid properties package was obtained by tuning components' parameters to match with available vapor-liquid equilibrium data. ISC was initiated after the steam-assisted gravity drainage stage had been simulated. By successively reducing the simulated initial (pre-SAGD) oil saturation in steps, it was shown that the combustion front changed from stable propagation to being extinguished at a low initial oil saturation around 0.06, for which a combustion-front temperature of 400 °C was maintained. The residual oil saturation approached zero after combustion. •A new, experimentally supported model is presented for the simulation of in-situ combustion.•A high-temperature combustion front can be plausibly predicted.•Three indicators demonstrate whether a combustion front had been successfully developed.•The minimum required oil saturation needed to maintain a stable combustion front was predicted to be 0.06.•The cumulative enthalpy of the produced fluid was 67.50% of the injected enthalpy.•The solid coke component is smoothly distributed along the combustion front.