Detailed analysis of Toe-to-Heel Air Injection for heavy oil production

The Toe-To-Heel Air Injection (THAI) operation at Kerrobert, Saskatchewan proved that commercial oil rate is possible together with production of partially upgraded heavy oil. Despite physical model experimentation and simulation investigations of THAI, no detailed analysis has been conducted on a THAI field operation to resolve recovery mechanisms and the strengths and limitations of the process. Here, we present, for the first time, a detailed evaluation of the Kerrobert THAI field operation to find causal relationships between injectants and production rates, gas composition, and temperature rise within the reservoir and which downhole reactions are key in the process i.e. low temperature oxidation, high temperature oxidation, thermal cracking/thermolysis, coke gasification and aquathermolysis. The results demonstrate that there is a competition between oxygen injection for heat generation via oxidation reactions versus air injection leading to cooling of the system which limits the peak oil rate. General comparisons are made to a neighboring Steam-Assisted Gravity Drainage (SAGD) operation in the same formation. A comparison of THAI and SAGD in the formation indicates that although THAI yields significantly lower normalized oil rates than SAGD, it is more energy efficient than SAGD.