The performance and probability of success of in-situ combustion (ISC) is highly dependent on a multitude of parameters that define the reservoir conditions. The presence of reservoir heterogeneities makes it, therefore, practically impossible to predict a set of operational parameters that would provide efficient ISC performance. Dynamic control, whereby operational parameters are adjusted based on the reservoir conditions at the predicted combustion-front position, has the potential to significantly improve ISC performance. One-dimensional combustion tube experiments are the quickest method to determine the potential candidates for ISC. However, experiments conducted at average reservoir initial conditions do not provide data on the range of required operational parameters in a heterogeneous setting. Therefore, lab-scale experiments should be extended to screening tests by evaluating the ISC performance at the upper and lower limits of the reservoir initial conditions. To pave the way for dynamic control of ISC, this study investigates the effect of varying initial water saturation and initial oil saturation with one-dimensional combustion tube experiments on a bitumen sample (1.018 g/cm3) with high asphaltene content (∼35 wt%).
ISC performance change with varying initial oil and water saturations are discussed in terms of effluent gas composition, temperature profiles, total experiment time, oil recovery, behavior of fluid (oil, water, steam, and gas) front movements, X-Ray cross sectional images on postmortem samples, and the level of oil upgrading at different initial fluid saturations.
Our results indicate that the presence of initial water assists the combustion process and around 30% initial water enhances the ISC performance which can be maintained by steam injection prior to ISC if reservoir initial saturation is less than 30%. Moreover, initial oil saturation has been found to be the most critical parameter which defines the amount of fuel formed, and as a consequence, the heat generated.
The findings provide a significant improvement in our understanding of optimum operational conditions for a range of initial fluid saturations, bringing us one step closer to dynamic control of field-scale ISC.