Numerical investigation of the mechanisms in co-injection of steam and enriched air process using combustion tube tests

Abstract

Co-injection of steam and enriched air process has great potential to recover oil sands especially when the oil sands are sufficiently preheated by SAGD. Before applying such a process in the field, it is important to understand the involved reaction kinetics and displacement mechanisms. In this work, numerical modelling has been performed to investigate the performance of co-injection processes, in which enriched air (95% oxygen) was introduced after a period of hot water and steam flooding. A group of combustion tube tests were conducted to measure combustion front velocity, temperature profiles along the tube, oil production, and produced gas compositions. A three-dimensional radial numerical model was developed using CMG STARS to reproduce the combustion tube test results. A reaction kinetic model derived from Ramped Temperature Oxidation (RTO) tests was incorporated and further tuned to match dynamic experimental measurements. The close agreement between the measured and simulated combustion characteristics, including combustion front velocity, temperature profiles, and gas production, confirms that the key chemical reactions have been captured. Also, there is a great match between the measured and simulated liquid production, indicating that the drive mechanisms have been adequately understood. It is found co-injection of steam and enriched air has the potential to improve oil recovery because ISC is able to recover a portion of the residual oil left behind by the steam flooding. Steam still plays a dominant role in displacement of bitumen. The ultimate recovery factor was about 90% of OOIP for the aforementioned combustion tube tests. Using enriched air concentration of 12 to 35 vol.%, the steam front propagated faster than the combustion front, the velocity of which is controlled by the fuel consumption rate and oxygen injection rate. Even at low oxygen injection rates, high temperature oxidation (HTO) was observed. It is suggested that high initial temperature for co-injection of steam and enriched air helps reduce the amount of low temperature oxidation (LTO) and therefore decreased coke deposition, leading to higher combustion front velocity and stable high temperature combustion. The reaction model is able to reproduce all measured results and represent all of the aforementioned phenomena.