Halfin -

Interesting article. At least on a basic concept level, the THAI process looks like a major improvement over the conventional schemes, as it actually uses part of the bitumen as fuel rather than more valuable fossil fuels. Furthermore, the more in situ you can make the process, the better.

A major consideration that may not be sufficienly appreciated at this time is the composition and disposition of the combustion gases. Unless these are just allowed to migrate to the surface through the porous overburned, then they would probably have to be collected via some sort of a network of exhaust wells.

The disposition of these gases will not be a trivial matter.The article cites a combustion gas generation rate of 255,000 cubic meters per day for a system producing 660 bpd of bitumen liquid. That is a LOT of gas for a relatively small amount of production.

 Being that the combustion is underground and proceeds from a highly oxidizing state to an oxygen-starved state (i.e, near the face of the liquifying bitumen), it is a certainty that the combustion gases will contain a high fraction of unburned hydrocarbons, possible mixed with carbon monoxide and sulfur dioxide. For a full-scale system I very much doubt that it will be acceptable to release a huge volume of such highly contaminated gases to the atmosphere without some sort of emission controls. A network of exhaust wells connected to a vapor incinerator would handle the unburned hydrocarbons and the CO, but additional controls would be needed to remove the SO2. I'm not saying that air pollution control is going to be a project killer, but it is something that will add to the complexity and cost of a full-scale system.  It is not obvious from the short blurb that I read that this requirement has been fully appreciated.

Don't forget that they're flooding with air, and the off-gases are going to contain a lot of nitrogen.

Flooding with oxygen and steam (and recycled CO2?) might improve energy recovery; it would certainly reduce gas volumes.

Engineer Poet -

I'm not sure I see the significance of the fact that the off-gases will contain a lot of nitrogen, other than that it increases the volume of the off-gases.  Certainly, it will not result in any significant NOx emissions, because you need very high reaction temperatures for that to happen. As such, the nitrogen is largly just going along for the ride.

True, using oxygen plus steam would reduce the volume of the off-gases several fold, but then you would need to build a very large oxygen plant on site. Depending on how the economics look, that might be a good way to go.

I know the whole reason for doing tar sands is to obtain liquid fuel, but I can't help wondering whether in some cases it might be a whole hell of a lot easier to just do in situ gasification of the tar sands and use the product gases (probably much like coal gas) as a substitute for our increasingly tight natural gas supplies. What do you think?

I think the people in the business probably know what their most profitable product is.