An analytical model to estimate the oxidation time required to reach spontaneous ignition with heat loss being considered

Abstract

During air injection into an oil reservoir, an oxidation reaction generates heat to raise the reservoir temperature. When the reservoir temperature reaches an ignition temperature, spontaneous ignition occurs. There is a time delay from the injection to ignition. There are mixed results regarding the feasibility of spontaneous ignition in real-field projects and laboratory experiments. No analytical model is available in the literature to estimate the oxidation time required to reach spontaneous ignition with heat loss. This paper proposes an analytical model considering heat loss. The feasibility of spontaneous ignition from theoretical points, and experimental and field project observations are discussed. Using analytical models with and without heat loss, the factors that affect spontaneous ignition are investigated. Based on the discussions and investigations, we find that it is more difficult for spontaneous ignition to occur in laboratory experiments than in oil reservoirs; spontaneous ignition is strongly affected by the initial reservoir temperature, oil activity, and heat loss; spontaneous ignition is only possible when the initial reservoir temperature is high, the oil oxidation rate is high, and the heat loss is low.