Field performance and numerical simulation study on the toe to heel air injection (THAI) process in a heavy oil reservoir with bottom water

Abstract

Extra-heavy oil and bitumen (EHOB) comprise 30 percent of the remaining recoverable fossil fuel resources on Earth. This means EHOB could play an important role in a secure transition towards net zero emissions (NZE) by 2050. Technological developments, such as toe to heel air injection (THAI), have been shown to efficiently recover heavy oil with reduced environmental footprint. The Kerrobert project was the first to utilise the THAI technology in presence of bottom water (BW) in the reservoir. The project demonstrated a good performance (with average oil rate of 10 m3/day per well) compared to the conventional ISC operations in a BW situation. Lessons taken from the Kerrobert operational experience can assist the forthcoming THAI operations explicitly in the presence of BW. Dynamic field data for one of the best performing THAI pilot well pairs (K2), were analysed in this work. It was found that the K2 pilot must have experienced interference from K5, which is the closest neighbouring THAI well pair to the K2. Previously developed THAI models have not been validated against actual field data. A new field-scale THAI model in the presence of BW was constructed and, for the first time, validated against the field data from the Kerrobert project in this work. In addition, the quasi-staggered line drive well arrangement, as used for the K2 pilot, was studied. The daily and cumulative oil production rates were predicted well (the final agreement with field data was within 3 percent). The history matched model was then used to investigate the effect of the variation in air injection rates on THAI performance in presence of BW. Major developed zones during the propagation of the combustion front were numerically examined. It was demonstrated that extra air ingress from the neighbouring THAI well pair has caused a reduction in oxygen utilisation throughout the process. As a result, the simulated temperature profile declined with the increasing combustion time. The oxygen profile around the horizontal producer (HP) well was studied via the new history-matched model. An inversely proportional relationship was detected between the coke concentration and the oxygen profile around the HP well. It was found that the size of the steam zone, ahead of the combustion front, differs with variation in air injection rates. It was observed that some of the mobilised oil sank into the BW, leaving a significant amount of oil trapped in the reservoir. To prevent such an event, the location of the HP well was altered as a potential strategy to optimise the THAI efficiency. Consequently, the oxygen utilisation was improved by 13%, resulting in 73% higher cumulative oil production in comparison with the history-matched model.