an oil field is the result of plenty of cash and time, spent on hardware and staff roaming hostile parts of the planet in search for oil.
That's covered by capital, machinery and labor inputs. Ultimately, you still need the actualg geological structure, and that one is not going to be an output in a timeframe that makes sense for a purposes. Just define "oil field" in a narrow sense, and you bump against that problem again. In the long run, we're all dead. John Maynard Keynes
Of course, we are not in a pure Leontieff model since the coefficient of oil discovery will vary over time. The oil itself will change also, making refining less efficient, etc...
But this was to be expected: we are modeling a depletion process, which is irreversible just like entropic decay. The pure leontieff model is reversible if you keep all coefficients constants, it is always conceivable to return to a previous state of equilibrium. Which will not be possible with oil: once it's all CO2 in the stratosphere we won't be able to drive so many hummers... Pierre
