The oil/steam ratio for both Cyclic Steam Stimulation (CSS) and Steam Flooding (SF) has almost reached economic limits in Liaohe, China's largest heavy oilfield. Complex displacement of CSS and SF assisted with foaming agents and CO2 has been applied at commercial scale to increase the oil production. In this paper, we will present a field case study of the complex displacement operation. We will discuss the details from the foaming agent selection, completion design, operation management and performance data analysis.

To improve production rates for the low producing CSS and SF wells, a recovery method of complex displacement has been implemented at commercial scale in Liaohe oilfield. The application of the method depends on the reservoir condition, well completion design, injection time, types of foaming agents and so on. After a complicated optimization and careful field implementation, a satisfactory result was achieved. A complete field case will be studied in detail and comprehensive field performance data will be presented and analyzed.

For both CSS and SF operations, the type of foaming agent and especially its injection rates for each of these operations is the key to the success of the project. Different types of foaming agents and injection rates have been trialed. The injection rates of CO2,and steam to form the agent have been optimized. Relatively mature complex displacement development technology has been developed for both CSS and SF and will be presented in the paper. As of today, more than 480 CSS wells have been operated with the assistance of CO2. The oil/steam ratio in those application well groups has increased by 7%, while the operating cost has decreased by 7.9%. Three SF well groups assisted with hot air foam have been tested. The incremental oil production was more than 60%. The goals of cost reduction and oil production increase have been achieved with the complex displacement method in both CSS and SF.

As far as we know, this is the first paper to comprehensively introduce this type of complex displacement recovery method for CSS and SF in heavy oil operations.

This complex displacement recovery method has been proved to be an effective method to improve the heavy oil recovery in Liaohe. It is believed the learning and experience can be beneficial for the other heavy oilfields around the world. In the meantime, it could also facilitate the utilization and storage of CO2.

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