Evolution of Hydrocarbons and Carboxylic Acids in Heavy Oil during In Situ Combustion in Xinjiang Oilfield

Abstract

In situ combustion (ISC) has attracted extensive attention in the development of heavy oil reservoirs because of its high recovery efficiency and low energy consumption. The ISC has been successfully implemented in the PetroChina Xinjiang oilfield. However, due to the complexity in the composition of heavy oil and the ISC process itself, the molecular composition changes have not been well characterized in field samples. In this study, we used gas chromatography–mass spectrometry (GC–MS) and high-resolution Fourier transform ion cyclotron resonance mass spectrometry analysis to evaluate the molecular composition of heavy oil samples obtained from the ISC field of the Xinjiang oilfield, both before and after ISC. Small-molecule hydrocarbons were identified by GC–MS, including n-alkanes, benzenes, and naphthalenes, which have an important contribution to reducing the viscosity and improving the quality of ISC oil. Although trace amounts of fatty acids were generated in the process, the contribution of the generated fatty acids to TAN can be ignored compared with the inherent naphthenic acids. The results indicate that the ISC has a positive effect on in situ upgrading of heavy oil.

In-Situ Combustion for Heavy Oil and Oil Sands Recovery: Recent Progress, Field Applications, and Future Perspectives

“…When the reservoir was converted to an ISC, the estimated OOIP was around 40%. The pilot ISC process was operated, and the process was monitored by temperature and produced oil properties. ,,− Dynamic strategies were applied to improve the combustion front sweep efficiency. A pattern drive was operated at the first stage, and a line drive was followed as a second stage to obtain better control of combustion front propagation.…”