What about our water? No matter how much we drink, I don't see the ocean level going down.
As far as igneous rocks, it is unlikely that the liquid state of oil would be found in them. Now, if you take oil, and subject it to enough heat and pressure, you get a diamond. So... even though it might be very difficult to get it out, even something as solid as a diamond may be made of the very molecules that were oil. If oil were anywhere near a volcano, the oil would be turned into something else. Since igneous rocks are the results of this type of uprising from the surface, and explosions, and oil is usually found deep underground, that may be why the two aren't found together.
The hydrologic cycle is just that: cyclical. We probably get a very small increase from meteorite infalls.
As far as igneous rocks, it is unlikely that the liquid state of oil would be found in them.
Why? Certain igneous units contain more than enough pore space to accommodate kerogen/crude. There seems no reason that if reservoirs are filled from the bottom-up there should be intrusion into both igneous and metamorphic structures. Yet this is not observed except as the reverse situation where prior hydrocarbons within meta-sediments have, under intense heat and pressure, metamorphosed into graphite.
...oil is usually found deep underground,
Oil is found at all depths within the crust depending on location. Fields in Iraq for example, are ¨low-lift¨ where the deposits are very close to the surface...and just a few dozen blocks from where I am at Park La Brea in Los Angeles are the famous ¨tar pits¨ where crude has broached the surface, much to the demise of thousands of animals over tens of thousands of years.
The Russians have drilled some deep wells thru some very hard ferrous-silicates, into strata that the Geologist said couldn't contain oil. Guess what not only did they get oil, the ferrous-silicates they drilled thru, altered their drill bits making them better than anything you can make topside.
They studied this and have developed an additive for internal combustion engines, drivetrains, and bearings that makes them impervious to Hydrogen enbrittlement, increases fuel efficiency, and decreases friction. Link