Steam injection is a widely used thermal technology to recover heavy oil and oil sands resources, while high operating costs have made it vulnerable to low crude oil prices. In-Situ Combustion (ISC) provides an alternative to steam injection with the advantage of low operating costs and high energy efficiency. Hybrid steam and ISC has great potential in oil sands recovery because it combines the advantages of both steam injection and ISC. Before design of this hybrid process, it is important to understand the displacement mechanisms during this hybrid process.

In this study, numerical simulation has been performed to investigate the performance of co-injection of an air and steam process at the experimental scale. A three-dimensional radial numerical model has been developed using CMG STARS to simulate a steam flood test and a combustion tube test. The co-injection of enriched air and steam was performed after a period of hot water flooding in the combustion tube test. Simulated temperature profiles and combustion front velocities were matched with experimental measured results, indicating that the high temeprautre oxidation (HTO) reactions were captured in the simulation. In order to understand displacement mechnisms, simulation results obtained from both tests have been compared and analyzed, including temperature profiles, a steam front velocity, residual oil saturation, and oil recovery.

It is found that co-injection of steam and enriched air has the potential to improve oil recovery. An ultimate recovery factor of around 90% is achieved for the co-injection of the steam and enriched air process, while the recovery factor is around 60% for the steam flooding test. This is because ISC is able to recover residual oil left behind by the steam flooding. However, steam still plays a dominant role in displacement of bitumen. The steam front propagates faster than the combustion front. Also, the steam front travels faster with the presence of the combustion front, indicating that the combustion front behaves as a heat source for steam front propagation. This work greatly increases the understanding of displacement mechanisms in a hybrid steam and combustion process.

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