True. There are a lot of high viscosity deposits or deposits where the formation pressure is insufficient to force the hydrocarbons into the well. There are any number of ways we currently deal with this problem if the deposit is large enough to justify the expense. Water-flood is kind of an entry-level approach. You drill multiple wells in your field. Some you use to produce. Others, you inject water into the formation. The water forces the oil / gas / whatever to come into the producing wells.
Another trick is CO2 flood. That apparently works on some formations, but I'm not really sure what its advantage is over water-flood. My personal favorite is fire-flood. Same basic set-up, but now you are injecting oxygen. The key in this is to make dadgum certain your injector wells are dry. NO WATER must be present or the corrosion will eat your casing alive. But the oxygen will basically ignite downhole. You keep on pumping O2. The flame front moves into the formation, heating everything up ungodly hot and forcing any fluids out ahead of it; towards your producing well(s) if you designed your field right. You can handle very high viscosity fields in this manner. Refining what you produce from a fire-flood field is usually quite painful because it is essentially tar, and the extreme heat will drive the mineral solubility way up until it gets to the surface, cools off, and everything gets all sticky again.
Huff-and-puff steam injectors are another flavor. But all this is really to say, yes, there are methods and procedures we can and do employ to get at difficult-to-recover oil. But it is difficult and very expensive. It is also much less effective on relatively small or diffuse deposits. There is also a difficult-to-quantify ecological cost to consider.
