THAI (Toe to Heel Air Injection) and Beyond
by Franklin L. Foster, Ph.D.
As mentioned elsewhere on this site, in the early days of the Lloydminster patch, heavy oil was excruciatingly frustrating. Small productions of conventional oil giving way to increasingly viscous and, therefore, unproduceable oil. Innovation was always, by necessity, a part of the local patch. In the early days unconventional production methods were called "how do we get the damned stuff out" but are now referred to as IOR (improved oil recovery) or EOR (enhanced oil recovery). Not surprisingly one of the early ideas was to apply heat. As early as 1951, tests were being done on what is now called ISC (In-Situ Combustion). Almost 60 years later, descendents of this technique are promising to make major contributions to the recovery of heavy oil.
Conventional ISC uses an injection well to ignite and maintain combustion through air injection and drive oil toward the producing well. This process is fraught with several problems, not least of which is that the producing well is always in the cold region away from the combustion. What has revolutionized the process is the advent of horizontal wells. Now, the horizontal well "toe" can be drilled to be in close proximity to the combustion zone, resulting in startling increases in recovery rates (to as high as 80%, whereas, in the old days 20% might be considered good).
Above is a diagram showing how the "toe" of the horizontal well penetrates the optimum oil production regions and drives the oil toward the producing well's "heel". Even more exciting, adding an annular sheath of catalytic material along the length of the horizontal well can effectively upgrade the oil prior to production.
In recent field tests, improvements in viscosity from the range of 10° API to the range of 16° API have been achieved. Such innovations which may lead to significantly enhanced oil recoveries from such "mature" fields as the North Sea.
These comments based on a presentation was made to the Petroleum Society of CIM, Lloydminster (Heavy Oil) Section in September 2007 by Dr. Malcolm Greaves, of the University of Bath, Department of Chemical Engineering.