Comparing CSS and SAGD vs.THAI

A short discussion on the merits of steam vs. in-situ combustion techniques...

I was recently asked about the pros and cons of steam injection technologies such as cyclic steam injection (CSS) or steam assisted gravity drainage (SAGD) over a process known as Toe Heel Air Injection or THAI™ which is an in-situ combustion method for producing heavy oil. In this technique, fire-flooding starts from a vertical well, while the oil is produced from a horizontal well having its toe in close proximity to the vertical air-injection well.

In short, the answer to which is preferred is "it all depends" and further the processes could be potentially complementary --that is in-situ combustion methods, such as THAI, could be used following steam injection methods such as CSS and SAGD.  But the main difference is that CSS, Steam Flood and SAGD are proven production methods which will allow economic recovery of 30-80% but require favorable reservoir conditions such as good vertical and horizontal permeability, relatively thick pay zones (typically of more than 10 meters), absence of shale barriers that might impede steam distribution in the pay zone, or the presence of top or bottom gas or water zones which can act as thief zones thus lowering the efficiency of the thermal energy.  In addition, steam injection methods are currently uneconomical in offshore or deep reservoir conditions (these limits might one day be mitigated with new technologies such as down-hole steam generation).

THAI on the other hand is just at an experimental phase (see news release from Petrobank). Being a  new technique, it does have a number of challenges to overcome such as the proper control of the combustion front, effects of produced coke and thermal effects on the producing wells, but it has the potential to operate in a wider range of reservoir conditions than current steam injection processes.  Furthermore, it has the potential to operate at a much higher energy efficiency and not be limited by fresh water needs as steam injection methods. 

Additional insight on the various recovery techniques can be found in our recent article Highlighting Heavy Oil and with our Interview with Dr. Ali Suat Bagci.

Jorge.