Feasibility of spontaneous ignition during air injection in light oil reservoirs

Air injection in light oil reservoirs is a complicated EOR (enhanced oil recovery) technique. Till now, the mechanisms of HPAI (high pressure air injection) are still under controversy. Some researchers state that the heat generation is not important for the recovery of light oil during HPAI, and consider the LTO (low temperature oxidation) is only to remove the oxygen but not to establish the combustion front, while others claim that the spontaneous ignition and sustainable combustion front are the key aspects for a success HPAI project. The experimental trials on spontaneous ignition of HPAI to light oil are reviewed and discussed in this paper. This paper also investigates the spontaneous ignition feasibility through both analytical method and numerical method. The review shows that the combustion tube test is used to study combustion sustainability but not suitable to study the spontaneous ignition, and the thermal experiments can only be applied as screening tool to select favorable oil for HPAI in terms of feasibility of spontaneous ignition while further core flooding tests are still required. This paper also proposes an approach which associates thermal experiments with numerical simulation method to investigate the spontaneous ignition of a light oil. A case study is performed with a Wolfcamp light oil, the simulation study shows that the LTO of this light oil cannot induce spontaneous ignition during air injection in both core flooding experiment and field application. The analytical approach is very sensitive to the kinetic data which is used to estimate the ignition delay time. As a result, the analytical method may be misleading in terms of the feasibility of spontaneous ignition, if inappropriate data are selected.