Research on the Variation Laws of In Situ Combustion in Heavy Oil Reservoirs with Different Oil Saturations

This study investigates the behavior of heavy oil reservoirs under varying oil saturation conditions through laboratory-scale in situ combustion (ISC) physical simulation experiments. The research focuses on the propagation stability of the combustion front and key parameters influencing the in situ combustion process, with a systematic examination of crude oil composition changes and upgrading mechanisms during ISC. By employing gas chromatography (GC) and infrared spectroscopy (IR) analyses, this study evaluates the transformation of saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes in the produced oil before and after ISC. The results demonstrate that oil saturation plays a critical role in determining combustion efficiency, cracking dynamics, and upgrading performance. At high oil saturation (65%), combustion reactions are vigorous, yielding enhanced cracking efficiency, a significant increase in light hydrocarbon content, and effective conversion of heavy components, achieving optimal upgrading outcomes. Conversely, at low oil saturation (30%), cracking efficiency is reduced, light hydrocarbons are lost, and heavy components, including asphaltenes and polycyclic aromatic hydrocarbons, accumulate, resulting in less effective upgrading. Nonetheless, ignition and stable combustion are achievable even at low oil saturation levels. This study offers strategies to optimize ISC operations tailored to different oil saturation conditions, providing valuable insights for improving combustion efficiency and enhancing the quality of produced oil in heavy oil reservoirs.