Steam injection has a pretty remarkable ability to drive out almost all of the heavy oil from highly permeable reservoirs but it is costly to generate and there is a lot to be gained if you could improve the overall efficiency of the process.
The inventor of the SAGD process, Roger Butler, also invented another process which uses solvents instead of steam to mobilise the heavy oil. That process is called VAPEX and involves the injection of a hydrocarbon solvent, such as propane, butane or naphtha, alongside hot water to heat the reservoir to between 40ºC and 80ºC, while relying on the solvent to mobilise the oil. It hasn't gained the same popularity as the SAGD process although recent trials in Canada seem to be promising. I am waiting for the final report on the JIVE (Joint Industry Vapour Extraction) project from the Petroleum Research Technology Centre in Saskatchewan with bated breath.
However, a number of companies, Imperial Energy – Roger Butler's former employer – among them, have been trialling a combination of steam and solvent injection. The results are promising, Imperial note 15% to 25% reductions in Steam-Oil Ratio (SOR) and improvements in the oil production rate at their experimental Solvent Assisted SAGD project at Cold Lake. They also succeeded in recovering about 75% of the injected solvent. The latest report on their operations at Cold Lake is from 2012, once again, I keep checking for updates on how this project has progressed since then.
Cenovus has also been testing SAP (Solvent Aided Process) at Christina Lake, once again with some success. The results are buried from page 146 onwards in this presentation to the Alberta Energy Regulator; on one SAGD well pair, addition of solvent to the steam drove the steam oil ratio down to 1.6 from 2.4, and they recovered over 60% of the solvent, which in this case was butane. Connacher has also been trying out co-injection of solvent; in their trials they used a condensate made up of C4 to C8 hydrocarbons. This solvent is a bit denser than used in the other trials, but was compatible with the diluent they add to their bitumen before it is exported, so it made operational sense. They also recorded significant improvements in bitumen production and Steam Oil Ratio, of the order of 30% in each, when about 6% solvent was injected. Recoveries of solvent were very high at nearly 90%, which Connacher attribute to using denser solvent.
There are lots of simulation studies showing significant improvements in SOR, injectivity, oil production and recovery factor compared with pure steam injection. There are also some very interesting laboratory trials on beds packed with sand and oil into which steam, or steam and solvents have been injected. They too support the notion that co-injection of about 5% solvent is helpful. But it is what happens in practice that really matters, and we should thank the Alberta Energy Regulator for making the companies publish the results of their trials.
Of course as with all oilfield processes whether this gets adopted will all come down to the economics, the cost of injecting propane or butane is not trivial. However, with the growth in production of Light Tight Oil (LTO) in the US the price of propane in relation to the price of oil has slumped as excess propane has flooded the market in the Gulf Coast.
Fortunately moving LPG across the ocean is not so difficult and, as from every perspective this seems like a process which could transform a good reservoir depletion strategy (steam flooding) into a great one, it is certainly a technique which we will be looking at very seriously for the Pilot project. Indeed at a 30% to 40% discount to Brent on an energy equivalent basis, propane might make a very good fuel for the steam generators as well.