Abstract
Potential candidates for in-situ combustion (ISC) are screened in the laboratory by one-dimensional combustion tube runs or reaction kinetics experiments, or, ideally, a combination of both. While one-dimensional experiments are conducted at average reservoir conditions, reservoir heterogeneities may have an impact on the amount of fuel formed and, consequently, the amount of heat generated. Therefore, prior to field applications of any potential candidates, it is essential to understand the upper and lower limits of the reservoir rock and fluid properties, and how ISC functions within those limits. In this study, the effect of varying connate water saturation, initial oil saturation, clay content, permeability, and porosity are investigated with one-dimensional combustion tube experiments on different heavy crudes (8-20 °API) with asphaltene content ranging from 10 to 18 wt% for different reservoir rocks including carbonates and sandstone. Process dynamics for good and poor ISC candidates are discussed in terms of effluent gas composition, temperature profiles and histories, total experiment time, oil recovery, behavior of fluid (oil, water, steam, and gas) front movements, and the level of oil upgrading at different reservoir conditions. Fuel consumption along with air requirements are analyzed for each experiment analytically. For good ISC candidates as identified by laboratory screening, the reservoir conditions that may lead to poor ISC field performance are estimated. It is observed that the reactivity of reservoir rocks at elevated temperatures (in the presence of oxygen) and the initial oil saturation are two important parameters that influence the fate of ISC. The findings considerably advance our understanding of field-scale ISC through the evaluation and interpretation of experimental data for different reservoir conditions.
